<?xml version="1.0" encoding="UTF-8"?><?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> <!-- generated by https://github.com/cabo/kramdown-rfc2629 version 1.4.11 --><!DOCTYPE rfcSYSTEM "rfc2629.dtd"[ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]><?rfc toc="yes"?> <?rfc sortrefs="yes"?> <?rfc symrefs="yes"?><rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-trans-rfc6962-bis-42" number="9162" obsoletes="6962" updates="" submissionType="IETF" category="exp"obsoletes="6962">consensus="true" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3"> <!-- xml2rfc v2v3 conversion 3.9.1 --> <front> <title>Certificate Transparency Version 2.0</title> <seriesInfo name="RFC" value="9162"/> <author initials="B." surname="Laurie" fullname="Ben Laurie"> <organization abbrev="Google">Google UK Ltd.</organization> <address> <email>benl@google.com</email> </address> </author> <authorinitials="A." surname="Langley" fullname="Adam Langley"> <organization abbrev="Google">Google Inc.</organization> <address> <email>agl@google.com</email> </address> </author> <author initials="E." surname="Kasper" fullname="Emilia Kasper"> <organization abbrev="Google">Google Switzerland GmbH</organization> <address> <email>ekasper@google.com</email> </address> </author> <authorinitials="E." surname="Messeri" fullname="Eran Messeri"> <organization abbrev="Google">Google UK Ltd.</organization> <address> <email>eranm@google.com</email> </address> </author> <author initials="R." surname="Stradling" fullname="Rob Stradling"> <organization abbrev="Sectigo">Sectigo Ltd.</organization> <address> <email>rob@sectigo.com</email> </address> </author> <date year="2021"month="August" day="31"/>month="November"/> <area>Security</area> <workgroup>TRANS (Public Notary Transparency)</workgroup> <keyword>certificates</keyword> <keyword>pkix</keyword> <keyword>tls</keyword> <keyword>website</keyword> <keyword>webpki</keyword> <keyword>browsers</keyword> <abstract> <t>This document describes version 2.0 of the Certificate Transparency (CT) protocol for publicly logging the existence of Transport Layer Security (TLS) server certificates as they are issued or observed, in a manner that allows anyone to audit certification authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs.</t> <t>This document obsoletes RFC 6962. It also specifies a new TLS extension that is used to send various CT log artifacts.</t> <t>Logs are network services that implement the protocol operations for submissions and queries that are defined in this document.</t><t>[RFC Editor: please update 'RFCXXXX' to refer to this document, once its RFC number is known, through the document. Also, the OID assigned below must also appear in the appendix as indicated. ]</t></abstract> </front> <middle> <section anchor="introduction"title="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>Certificate Transparency aims to mitigate the problem of misissued certificates by providing append-only logs of issued certificates. The logs do not themselves prevent misissuance, but they ensure that interested parties (particularly those named in certificates) can detect such misissuance. Note that this is a general mechanism that could be used for transparently logging any form of binary data, subject to some kind of inclusion criteria. In this document, we only describe its use for public TLS server certificates (i.e., where the inclusion criteria is a valid certificate issued by a public certification authority (CA)). A typical definition of "public" can be found in <xreftarget="CABBR"></xref>.</t>target="CABBR" format="default"/>.</t> <t>Each log contains certificate chains, which can be submitted by anyone. It is expected that public CAs will contribute all their newly issued certificates to one or more logs; however, certificate holders can also contribute their own certificate chains, as can third parties. In order to avoid logs being rendered useless by the submission of large numbers of spurious certificates, it is required that each chain ends with a trust anchor that is accepted by the log. A log may also limit the length of the chain it is willing to accept; such chains must also end with an acceptable trust anchor. When a chain is accepted by a log, a signed timestamp is returned, which can later be used to provide evidence to TLS clients that the chain has been submitted. TLS clients can thus require that all certificates they accept as valid are accompanied by signed timestamps.</t> <t>Those who are concerned about misissuance can monitor the logs, asking them regularly for all new entries, and can thus check whether domains for which they are responsible have had certificates issued that they did not expect. What they do with this information, particularly when they find that a misissuance has happened, is beyond the scope of this document. However, broadly speaking, they can invoke existing business mechanisms for dealing with misissued certificates, such as working with the CA to get the certificaterevoked,revoked or with maintainers of trust anchor lists to get the CA removed. Of course, anyone who wants can monitor the logs and, if they believe a certificate is incorrectly issued, take action as they see fit.</t> <t>Similarly, those who have seen signed timestamps from a particular log can later demand a proof of inclusion from that log. If the log is unable to provide this (or, indeed, if the corresponding certificate is absent from monitors' copies of that log), that is evidence of the incorrect operation of the log. The checking operation is asynchronous to allow clients to proceed without delay, despite possibleissuesissues, such as network connectivity and the vagaries of firewalls.</t> <t>The append-only property of each log is achieved using Merkle Trees, which can be used to efficiently prove that any particular instance of the log is a superset of any particular previous instance and to efficiently detect various misbehaviors of the log (e.g., issuing a signed timestamp for a certificate that is not subsequently logged).</t><t>It is necessary to treat each log as a trusted third party, because the<t>The log auditing mechanisms described in this document can be circumvented by a misbehaving log that shows different, inconsistent views of itself to different clients. Therefore, it is necessary to treat each log as a trusted third party. While mechanisms are being developed to address these shortcomings and thereby avoid the need to blindly trust logs, such mechanisms are outside the scope of this document.</t> <section anchor="requirements-language"title="Requirements Language"> <t>Thenumbered="true" toc="default"> <name>Requirements Language</name> <t> The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described inBCP 14BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</t>here. </t> </section> <section anchor="data_structures"title="Data Structures">numbered="true" toc="default"> <name>Data Structures</name> <t>Data structures are defined and encoded according to the conventions laid out inSection 3 of<xreftarget="RFC8446"></xref>.</t>target="RFC8446" sectionFormat="of" section="3"/>.</t> <t>This document uses object identifiers (OIDs) to identify Log IDs (see <xreftarget="log_id"/>),target="log_id" format="default"/>), the precertificateCMS <spanx style="verb">eContentType</spanx>Cryptographic Message Syntax (CMS) <tt>eContentType</tt> (see <xreftarget="precertificates"/>), andtarget="precertificates" format="default"/>), X.509v3 extensions in certificates (see <xreftarget="cert_transinfo_extension"/>)target="cert_transinfo_extension" format="default"/>), andOCSPOnline Certificate Status Protocol (OCSP) responses (see <xreftarget="ocsp_transinfo_extension"/>).target="ocsp_transinfo_extension" format="default"/>). The OIDs are defined in an arc that was selected due to its short encoding.</t> </section> <section anchor="major-differences-from-ct-10"title="Majornumbered="true" toc="default"> <name>Major Differences from CT1.0">1.0</name> <t>This document revises and obsoletes the CT 1.0 protocol <xreftarget="RFC6962"></xref> protocol,target="RFC6962" format="default"/>, drawing on insights gained from CT 1.0 deployments and on feedback from the community. The major changes are:</t><t><list style="symbols"> <t>Hash<ul spacing="normal"> <li>Hash and signature algorithm agility:permittedPermitted algorithms are now specified in IANAregistries.</t> <t>Precertificateregistries.</li> <li>Precertificate format:precertificatesPrecertificates are now CMS objects rather than X.509 certificates, which avoids violating the certificate serial number uniqueness requirement inSection 4.1.2.2 of<xreftarget="RFC5280"></xref>.</t> <t>Removedtarget="RFC5280" sectionFormat="of" section="4.1.2.2"/>.</li> <li>Removal of precertificate signing certificates and the precertificate poison extension:theThe change of precertificate format means that these are no longerneeded.</t> <t>Logsneeded.</li> <li>Logs IDs:eachEach log is now identified by an OID rather than by the hash of its public key. OID allocations aremanaged byavailable from an IANAregistry.</t> <t><spanx style="verb">TransItem</spanx>registry.</li> <li><tt>TransItem</tt> structure:thisThis new data structure is used to encapsulate most types of CT data. A<spanx style="verb">TransItemList</spanx>,<tt>TransItemList</tt>, consisting of one or more<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structures, can be used anywhere that<spanx style="verb">SignedCertificateTimestampList</spanx><tt>SignedCertificateTimestampList</tt> was used in <xreftarget="RFC6962"></xref>.</t> <t>Merkle treetarget="RFC6962" format="default"/>.</li> <li>Merkle Tree leaves:the <spanx style="verb">MerkleTreeLeaf</spanx>The <tt>MerkleTreeLeaf</tt> structure has been replaced by the<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure, which eases extensibility and simplifies the leaf structure by removing one layer ofabstraction.</t> <t>Unifiedabstraction.</li> <li>Unified leaf format:theThe structure for both certificate and precertificate entries now includes only the TBSCertificate (whereas certificate entries in <xreftarget="RFC6962"></xref>target="RFC6962" format="default"/> included the entirecertificate).</t> <t>Log Artifact Extensions: thesecertificate).</li> <li>Log artifact extensions: These are now typed and managed by an IANA registry, and they can now appear not only inSCTsSigned Certificate Timestamps (SCTs) but also inSTHs.</t> <t>APISigned Tree Heads (STHs).</li> <li>API outputs:complete <spanx style="verb">TransItem</spanx>Complete <tt>TransItem</tt> structures arereturned,returned rather than the constituent parts of eachstructure.</t> <t>get-all-by-hash:structure.</li> <li><tt>get-all-by-hash</tt>: This is a new client API for obtaining an inclusion proof and the corresponding consistency proof at the sametime.</t> <t>submit-entry:time.</li> <li><tt>submit-entry</tt>: This is a new client API, replacingadd-chain<tt>add-chain</tt> andadd-pre-chain.</t> <t>Presenting<tt>add-pre-chain</tt>.</li> <li>Presenting SCTs with proofs: TLS servers may present SCTs together with the corresponding inclusionproofsproofs, using any of the mechanisms that <xreftarget="RFC6962"></xref>target="RFC6962" format="default"/> defined for presenting SCTs only. (Presenting SCTs only is stillsupported).</t> <t>CTsupported).</li> <li>CT TLS extension:the <spanx style="verb">signed_certificate_timestamp</spanx>The <tt>signed_certificate_timestamp</tt> TLS extension has been replaced by the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> TLSextension.</t> <t>Verificationextension.</li> <li>Verification algorithms:added detailedDetailed algorithms for verifying inclusion proofs, for verifying consistency between two STHs, and for verifying a root hash given a complete list of the relevant leaf inputentries.</t> <t>Extensiveentries have been added.</li> <li>Extensive clarifications and editorialwork.</t> </list></t>work.</li> </ul> </section> </section> <section anchor="cryptographic-components"title="Cryptographic Components">numbered="true" toc="default"> <name>Cryptographic Components</name> <section anchor="mht"title="Merkle Hash Trees">numbered="true" toc="default"> <name>Merkle Trees</name> <t>A full description of the MerkleHashTree is beyond the scope of this document. Briefly, it is a binary tree where each non-leaf node is a hash of its children. For CT, the number of children is at most two. Additional information can be found in the Introduction and Referencesectionsections of <xreftarget="RFC8391"/>.</t>target="RFC8391" format="default"/>.</t> <section anchor="mht_definition"title="Definitionnumbered="true" toc="default"> <name>Definition of the MerkleTree">Tree</name> <t>The log uses a binary MerkleHashTree for efficient auditing. The hash algorithm used is one of the log's parameters (see <xreftarget="log_parameters"/>).target="log_parameters" format="default"/>). This document establishes a registry of acceptable hash algorithms (see <xreftarget="hash_algorithms"/>).target="hash_algorithms" format="default"/>). Throughout this document, the hash algorithm in use is referred to as HASH and the size of its output in bytes is referred to as HASH_SIZE. The input to the Merkle Tree Hash is a list of data entries; these entries will be hashed to form the leaves of the MerkleHashTree. The output is a single HASH_SIZE Merkle Tree Hash. Given an ordered list of n inputs, D_n = {d[0], d[1],…,..., d[n-1]}, the Merkle Tree Hash (MTH) is thus defined as follows:</t> <t>The hash of an empty list is the hash of an empty string:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ MTH({}) = HASH().]]></artwork></figure>]]></artwork> <t>The hash of a list with one entry (also known as a leaf hash) is:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ MTH({d[0]}) = HASH(0x00 || d[0]).]]></artwork></figure>]]></artwork> <t>For n > 1, let k be the largest power of two smaller than n (i.e., k < n <= 2k). The Merkle Tree Hash of an n-element list D_n is then defined recursivelyas</t> <figure><artwork><![CDATA[as:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ MTH(D_n) = HASH(0x01 || MTH(D[0:k]) || MTH(D[k:n])),]]></artwork></figure>]]></artwork> <t>where:</t><t><list style="symbols"> <t>||<ul spacing="normal"> <li>|| denotesconcatenation</t> <t>:concatenation</li> <li>: denotes concatenation oflists</t> <t>D[k1:k2]lists</li> <li>D[k1:k2] = D'_(k2-k1) denotes the list {d'[0] = d[k1], d'[1] = d[k1+1],…,..., d'[k2-k1-1] = d[k2-1]} of length (k2 -k1).</t> </list></t>k1).</li> </ul> <t>Note that the hash calculations for leaves and nodes differ; this domain separation is required to give second preimage resistance.</t> <t>Note that we do not require the length of the input list to be a power of two. The resulting Merkle Tree may thus not be balanced; however, its shape is uniquely determined by the number of leaves. (Note: This Merkle Tree is essentially the same as the history tree proposed by <xreftarget="CrosbyWallach"></xref> proposal,target="CrosbyWallach" format="default"/>, except our definition handles non-full treesdifferently).</t>differently.)</t> </section> <section anchor="verify_hash"title="Verifyingnumbered="true" toc="default"> <name>Verifying a Tree Head GivenEntries">Entries</name> <t>When a client has a complete list of<spanx style="verb">entries</spanx><tt>entries</tt> from<spanx style="verb">0</spanx><tt>0</tt> up to<spanx style="verb">tree_size<tt>tree_size -1</spanx>1</tt> and wishes to verify this list against a tree head<spanx style="verb">root_hash</spanx><tt>root_hash</tt> returned by the log for the same<spanx style="verb">tree_size</spanx>,<tt>tree_size</tt>, the following algorithm may be used:</t><t><list style="numbers"> <t>Set <spanx style="verb">stack</spanx><ol spacing="normal" type="1"> <li>Set <tt>stack</tt> to an emptystack.</t>stack.</li> <li> <t>For each<spanx style="verb">i</spanx><tt>i</tt> from<spanx style="verb">0</spanx><tt>0</tt> up to<spanx style="verb">tree_size<tt>tree_size -1</spanx>: <list style="numbers"> <t>Push <spanx style="verb">HASH(0x001</tt>:</t> <ol spacing="normal" type="a"> <li>Push <tt>HASH(0x00 ||entries[i])</spanx>entries[i])</tt> to<spanx style="verb">stack</spanx>.</t> <t>Set <spanx style="verb">merge_count</spanx><tt>stack</tt>.</li> <li>Set <tt>merge_count</tt> to the lowest value(<spanx style="verb">0</spanx>(<tt>0</tt> included) such that<spanx style="verb">LSB(i<tt>LSB(i >>merge_count)</spanx>merge_count)</tt> is not set, where<spanx style="verb">LSB</spanx><tt>LSB</tt> means the least significant bit. In other words, set<spanx style="verb">merge_count</spanx><tt>merge_count</tt> to the number of consecutive<spanx style="verb">1</spanx>s<tt>1</tt>s found starting at the least significant bit of<spanx style="verb">i</spanx>.</t><tt>i</tt>.</li> <li> <t>Repeat<spanx style="verb">merge_count</spanx> times: <list style="numbers"> <t>Pop <spanx style="verb">right</spanx><tt>merge_count</tt> times:</t> <ol spacing="normal" type="i"> <li>Pop <tt>right</tt> from<spanx style="verb">stack</spanx>.</t> <t>Pop <spanx style="verb">left</spanx><tt>stack</tt>.</li> <li>Pop <tt>left</tt> from<spanx style="verb">stack</spanx>.</t> <t>Push <spanx style="verb">HASH(0x01<tt>stack</tt>.</li> <li>Push <tt>HASH(0x01 || left ||right)</spanx>right)</tt> to<spanx style="verb">stack</spanx>.</t> </list></t> </list></t> <t>If<tt>stack</tt>.</li> </ol> </li> </ol> </li> <li>If there is more than one element in the<spanx style="verb">stack</spanx>,<tt>stack</tt>, repeat the same merge procedure (the sub-items of Step2.32(c) above) until only a single elementremains.</t> <t>Theremains.</li> <li>The remaining element in<spanx style="verb">stack</spanx><tt>stack</tt> is the Merkle TreehashHash for the given<spanx style="verb">tree_size</spanx><tt>tree_size</tt> and should be compared by equality against the supplied<spanx style="verb">root_hash</spanx>.</t> </list></t><tt>root_hash</tt>.</li> </ol> </section> <section anchor="merkle_inclusion_proof"title="Merklenumbered="true" toc="default"> <name>Merkle InclusionProofs">Proofs</name> <t>A Merkle inclusion proof for a leaf in a MerkleHashTree is the shortest list of additional nodes in the Merkle Tree required to compute the Merkle Tree Hash for that tree. Each node in the tree is either a leaf node or is computed from the two nodes immediately below it (i.e., towards the leaves). At each step up the tree (towards the root), a node from the inclusion proof is combined with the node computed so far. In other words, the inclusion proof consists of the list of missing nodes required to compute the nodes leading from a leaf to the root of the tree. If the root computed from the inclusion proof matches the true root, then the inclusion proof proves that the leaf exists in the tree.</t> <section anchor="generating-an-inclusion-proof"title="Generatingnumbered="true" toc="default"> <name>Generating an InclusionProof">Proof</name> <t>Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],…,..., d[n-1]}, the Merkle inclusion proof PATH(m, D_n) for the (m+1)th input d[m], 0 <= m < n, is defined as follows:</t> <t>The proof for the single leaf in a tree with a one-element input list D[1] = {d[0]} is empty:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ PATH(0, {d[0]}) = {}]]></artwork></figure>]]></artwork> <t>For n > 1, let k be the largest power of two smaller than n. The proof for the (m+1)th element d[m] in a list of n > m elements is then defined recursivelyas</t> <figure><artwork><![CDATA[as:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ PATH(m, D_n) = PATH(m, D[0:k]) : MTH(D[k:n]) for m < k; and PATH(m, D_n) = PATH(m - k, D[k:n]) : MTH(D[0:k]) for m >= k,]]></artwork></figure>]]></artwork> <t>The : operator and D[k1:k2] are defined the same as in <xreftarget="mht_definition"/>.</t>target="mht_definition" format="default"/>.</t> </section> <section anchor="verify_inclusion"title="Verifyingnumbered="true" toc="default"> <name>Verifying an InclusionProof">Proof</name> <t>When a client has received an inclusion proof (e.g., in a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> of type<spanx style="verb">inclusion_proof_v2</spanx>)<tt>inclusion_proof_v2</tt>) and wishes to verify inclusion of an input<spanx style="verb">hash</spanx><tt>hash</tt> for a given<spanx style="verb">tree_size</spanx><tt>tree_size</tt> and<spanx style="verb">root_hash</spanx>,<tt>root_hash</tt>, the following algorithm may be used to prove the<spanx style="verb">hash</spanx><tt>hash</tt> was included in the<spanx style="verb">root_hash</spanx>:</t> <t><list style="numbers"> <t>Compare <spanx style="verb">leaf_index</spanx><tt>root_hash</tt>:</t> <ol spacing="normal" type="1"> <li>Compare <tt>leaf_index</tt> from the<spanx style="verb">inclusion_proof_v2</spanx><tt>inclusion_proof_v2</tt> structure against<spanx style="verb">tree_size</spanx>.<tt>tree_size</tt>. If<spanx style="verb">leaf_index</spanx><tt>leaf_index</tt> is greater than or equal to<spanx style="verb">tree_size</spanx><tt>tree_size</tt>, then fail the proofverification.</t> <t>Set <spanx style="verb">fn</spanx>verification.</li> <li>Set <tt>fn</tt> to<spanx style="verb">leaf_index</spanx><tt>leaf_index</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> to<spanx style="verb">tree_size<tt>tree_size -1</spanx>.</t> <t>Set <spanx style="verb">r</spanx>1</tt>.</li> <li>Set <tt>r</tt> to<spanx style="verb">hash</spanx>.</t><tt>hash</tt>.</li> <li> <t>For each value<spanx style="verb">p</spanx><tt>p</tt> in the<spanx style="verb">inclusion_path</spanx> array: <vspace blankLines='1'/> If <spanx style="verb">sn</spanx><tt>inclusion_path</tt> array:</t> <ol spacing="normal" type="a"> <li>If <tt>sn</tt> is 0, then stop the iteration and fail the proofverification. <vspace blankLines='1'/> If <spanx style="verb">LSB(fn)</spanx>verification.</li> <li> <t>If <tt>LSB(fn)</tt> is set, or if<spanx style="verb">fn</spanx><tt>fn</tt> is equal to<spanx style="verb">sn</spanx>, then: <list style="numbers"> <t>Set <spanx style="verb">r</spanx><tt>sn</tt>, then:</t> <ol spacing="normal" type="i"> <li>Set <tt>r</tt> to<spanx style="verb">HASH(0x01<tt>HASH(0x01 || p ||r)</spanx></t> <t>If <spanx style="verb">LSB(fn)</spanx>r)</tt>.</li> <li>If <tt>LSB(fn)</tt> is not set, then right-shift both<spanx style="verb">fn</spanx><tt>fn</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> equally until either<spanx style="verb">LSB(fn)</spanx><tt>LSB(fn)</tt> is set or<spanx style="verb">fn</spanx><tt>fn</tt> is<spanx style="verb">0</spanx>.</t> </list> Otherwise: <list style="numbers"> <t>Set <spanx style="verb">r</spanx><tt>0</tt>.</li> </ol> <t>Otherwise:</t> <ol spacing="normal" type="i"> <li>Set <tt>r</tt> to<spanx style="verb">HASH(0x01<tt>HASH(0x01 || r ||p)</spanx></t> </list> Finally,p)</tt>.</li> </ol> </li> <li>Finally, right-shift both<spanx style="verb">fn</spanx><tt>fn</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> onetime.</t> <t>Compare <spanx style="verb">sn</spanx>time.</li> </ol> </li> <li>Compare <tt>sn</tt> to 0. Compare<spanx style="verb">r</spanx><tt>r</tt> against the<spanx style="verb">root_hash</spanx>.<tt>root_hash</tt>. If<spanx style="verb">sn</spanx><tt>sn</tt> is equal to0,0 and<spanx style="verb">r</spanx><tt>r</tt> and the<spanx style="verb">root_hash</spanx><tt>root_hash</tt> are equal, then the log has proven the inclusion of<spanx style="verb">hash</spanx>.<tt>hash</tt>. Otherwise, fail the proofverification.</t> </list></t>verification.</li> </ol> </section> </section> <section anchor="consistency"title="Merklenumbered="true" toc="default"> <name>Merkle ConsistencyProofs">Proofs</name> <t>Merkle consistency proofs prove the append-only property of the tree. A Merkle consistency proof for a Merkle Tree Hash MTH(D_n) and a previously advertised hash MTH(D[0:m]) of the first m leaves, m <= n, is the list of nodes in the Merkle Tree required to verify that the first m inputs D[0:m] are equal in both trees. Thus, a consistency proof must contain a set of intermediate nodes (i.e., commitments to inputs) sufficient to verify MTH(D_n), such that (a subset of) the same nodes can be used to verify MTH(D[0:m]). We define an algorithm that outputs the (unique) minimal consistency proof.</t> <section anchor="generating-a-consistency-proof"title="Generatingnumbered="true" toc="default"> <name>Generating a ConsistencyProof">Proof</name> <t>Given an ordered list of n inputs to the tree, D_n = {d[0], d[1],…,..., d[n-1]}, the Merkle consistency proof PROOF(m, D_n) for a previous Merkle Tree Hash MTH(D[0:m]), 0 < m < n, is defined as:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ PROOF(m, D_n) = SUBPROOF(m, D_n, true)]]></artwork></figure>]]></artwork> <t>In SUBPROOF, the boolean value represents whether the subtree created from D[0:m] is a complete subtree of the Merkle Tree created fromD_n,D_n and, consequently, whether the subtree Merkle Tree Hash MTH(D[0:m]) is known. The initial call to SUBPROOF sets this to be true, and SUBPROOF is then defined as follows:</t> <t>The subproof for m = n is empty if m is the value for which PROOF was originally requested (meaning that the subtree created from D[0:m] is a complete subtree of the Merkle Tree created from the original D_n for which PROOF wasrequested,requested and the subtree Merkle Tree Hash MTH(D[0:m]) is known):</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ SUBPROOF(m, D_m, true) = {}]]></artwork></figure>]]></artwork> <t>Otherwise, the subproof for m = n is the Merkle Tree Hash committing inputs D[0:m]:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ SUBPROOF(m, D_m, false) = {MTH(D_m)}]]></artwork></figure>]]></artwork> <t>For m < n, let k be the largest power of two smaller than n. The subproof is then defined recursively, using the appropriate step below:</t> <t>If m <= k, the right subtree entries D[k:n] only exist in the current tree. We prove that the left subtree entries D[0:k] are consistent and add a commitment to D[k:n]:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ SUBPROOF(m, D_n, b) = SUBPROOF(m, D[0:k], b) : MTH(D[k:n])]]></artwork></figure>]]></artwork> <t>If m > k, the left subtree entries D[0:k] are identical in both trees. We prove that the right subtree entries D[k:n] are consistent and add a commitment toD[0:k].</t> <figure><artwork><![CDATA[D[0:k]:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ SUBPROOF(m, D_n, b) = SUBPROOF(m - k, D[k:n], false) : MTH(D[0:k])]]></artwork></figure>]]></artwork> <t>The number of nodes in the resulting proof is bounded above by ceil(log2(n)) + 1.</t> <t>The : operator and D[k1:k2] are defined the same as in <xreftarget="mht_definition"/>.</t>target="mht_definition" format="default"/>.</t> </section> <section anchor="verify_consistency"title="Verifyingnumbered="true" toc="default"> <name>Verifying Consistency between Two TreeHeads">Heads</name> <t>When a client has a tree head<spanx style="verb">first_hash</spanx><tt>first_hash</tt> for tree size<spanx style="verb">first</spanx>,<tt>first</tt>, has a tree head<spanx style="verb">second_hash</spanx><tt>second_hash</tt> for tree size<spanx style="verb">second</spanx><tt>second</tt> where<spanx style="verb">0<tt>0 < first <second</spanx>,second</tt>, and has received a consistency proof between the two (e.g., in a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> of type<spanx style="verb">consistency_proof_v2</spanx>),<tt>consistency_proof_v2</tt>), the following algorithm may be used to verify the consistency proof:</t><t><list style="numbers"> <t>If <spanx style="verb">consistency_path</spanx><ol spacing="normal" type="1"> <li>If <tt>consistency_path</tt> is an empty array, stop and fail the proofverification.</t> <t>If <spanx style="verb">first</spanx>verification.</li> <li>If <tt>first</tt> is an exact power of 2, then prepend<spanx style="verb">first_hash</spanx><tt>first_hash</tt> to the<spanx style="verb">consistency_path</spanx> array.</t> <t>Set <spanx style="verb">fn</spanx><tt>consistency_path</tt> array.</li> <li>Set <tt>fn</tt> to<spanx style="verb">first<tt>first -1</spanx>1</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> to<spanx style="verb">second<tt>second -1</spanx>.</t> <t>If <spanx style="verb">LSB(fn)</spanx>1</tt>.</li> <li>If <tt>LSB(fn)</tt> is set, then right-shift both<spanx style="verb">fn</spanx><tt>fn</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> equally until<spanx style="verb">LSB(fn)</spanx><tt>LSB(fn)</tt> is notset.</t> <t>Setset.</li> <li>Set both<spanx style="verb">fr</spanx><tt>fr</tt> and<spanx style="verb">sr</spanx><tt>sr</tt> to the first value in the<spanx style="verb">consistency_path</spanx> array.</t><tt>consistency_path</tt> array.</li> <li> <t>For each subsequent value<spanx style="verb">c</spanx><tt>c</tt> in the<spanx style="verb">consistency_path</spanx> array: <vspace blankLines='1'/> If <spanx style="verb">sn</spanx><tt>consistency_path</tt> array:</t> <ol spacing="normal" type="a"> <li>If <tt>sn</tt> is 0, then stop the iteration and fail the proofverification. <vspace blankLines='1'/> If <spanx style="verb">LSB(fn)</spanx>verification.</li> <li> <t>If <tt>LSB(fn)</tt> is set, or if<spanx style="verb">fn</spanx><tt>fn</tt> is equal to<spanx style="verb">sn</spanx>, then: <list style="numbers"> <t>Set <spanx style="verb">fr</spanx><tt>sn</tt>, then:</t> <ol spacing="normal" type="i"> <li>Set <tt>fr</tt> to<spanx style="verb">HASH(0x01<tt>HASH(0x01 || c ||fr)</spanx><vspace /> Set <spanx style="verb">sr</spanx>fr)</tt>.</li> <li>Set <tt>sr</tt> to<spanx style="verb">HASH(0x01<tt>HASH(0x01 || c ||sr)</spanx></t> <t>If <spanx style="verb">LSB(fn)</spanx>sr)</tt>.</li> <li>If <tt>LSB(fn)</tt> is not set, then right-shift both<spanx style="verb">fn</spanx><tt>fn</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> equally until either<spanx style="verb">LSB(fn)</spanx><tt>LSB(fn)</tt> is set or<spanx style="verb">fn</spanx><tt>fn</tt> is<spanx style="verb">0</spanx>.</t> </list> Otherwise: <list style="numbers"> <t>Set <spanx style="verb">sr</spanx><tt>0</tt>.</li> </ol> <t>Otherwise:</t> <ol spacing="normal" type="i"> <li>Set <tt>sr</tt> to<spanx style="verb">HASH(0x01<tt>HASH(0x01 || sr ||c)</spanx></t> </list> Finally,c)</tt>.</li> </ol> </li> <li>Finally, right-shift both<spanx style="verb">fn</spanx><tt>fn</tt> and<spanx style="verb">sn</spanx><tt>sn</tt> onetime.</t> <t>Aftertime.</li> </ol> </li> <li>After completing iterating through the<spanx style="verb">consistency_path</spanx><tt>consistency_path</tt> array as described above, verify that the<spanx style="verb">fr</spanx><tt>fr</tt> calculated is equal to the<spanx style="verb">first_hash</spanx><tt>first_hash</tt> supplied, that the<spanx style="verb">sr</spanx><tt>sr</tt> calculated is equal to the<spanx style="verb">second_hash</spanx> supplied<tt>second_hash</tt> supplied, and that<spanx style="verb">sn</spanx><tt>sn</tt> is0.</t> </list></t>0.</li> </ol> </section> </section> <section anchor="example"title="Example">numbered="true" toc="default"> <name>Example</name> <t>The following is a binary Merkle Tree with 7 leaves:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ hash / \ / \ / \ / \ / \ k l / \ / \ / \ / \ / \ / \ g h i j / \ / \ / \ | a b c d e f d6 | | | | | | d0 d1 d2 d3 d4 d5]]></artwork></figure>]]></artwork> <t>The inclusion proof ford0<tt>d0</tt> is[b, h, l].</t>[<tt>b</tt>, <tt>h</tt>, <tt>l</tt>].</t> <t>The inclusion proof ford3<tt>d3</tt> is[c, g, l].</t>[<tt>c</tt>, <tt>g</tt>, <tt>l</tt>].</t> <t>The inclusion proof ford4<tt>d4</tt> is[f, j, k].</t>[<tt>f</tt>, <tt>j</tt>, <tt>k</tt>].</t> <t>The inclusion proof ford6<tt>d6</tt> is[i, k].</t>[<tt>i</tt>, <tt>k</tt>].</t> <t>The same tree, built incrementally in four steps:</t><figure><artwork><![CDATA[<artwork name="" type="" align="left" alt=""><![CDATA[ hash0 hash1=k / \ / \ / \ / \ / \ / \ g c g h / \ | / \ / \ a b d2 a b c d | | | | | | d0 d1 d0 d1 d2 d3 hash2 hash / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ k i k l / \ / \ / \ / \ / \ e f / \ / \ / \ | | / \ / \ g h d4 d5 g h i j / \ / \ / \ / \ / \ | a b c d a b c d e f d6 | | | | | | | | | | d0 d1 d2 d3 d0 d1 d2 d3 d4 d5]]></artwork></figure>]]></artwork> <t>The consistency proof betweenhash0<tt>hash0</tt> andhash<tt>hash</tt> is PROOF(3, D[7]) =[c, d, g, l]. c, g[<tt>c</tt>, <tt>d</tt>, <tt>g</tt>, <tt>l</tt>]. Non-leaf nodes <tt>c</tt>, <tt>g</tt> are used to verifyhash0,<tt>hash0</tt>, andd, lnon-leaf nodes <tt>d</tt>, <tt>l</tt> are additionally used to showhash<tt>hash</tt> is consistent withhash0.</t><tt>hash0</tt>.</t> <t>The consistency proof betweenhash1<tt>hash1</tt> andhash<tt>hash</tt> is PROOF(4, D[7]) =[l]. hash[<tt>l</tt>]. <tt>hash</tt> can be verified usinghash1=k<tt>hash1</tt>=<tt>k</tt> andl.</t><tt>l</tt>.</t> <t>The consistency proof betweenhash2<tt>hash2</tt> andhash<tt>hash</tt> is PROOF(6, D[7]) =[i, j, k]. k, i[<tt>i</tt>, <tt>j</tt>, <tt>k</tt>]. Non-leaf nodes <tt>k</tt>, <tt>i</tt> are used to verifyhash2,<tt>hash2</tt>, andjnon-leaf node <tt>j</tt> is additionally used to showhash<tt>hash</tt> is consistent withhash2.</t><tt>hash2</tt>.</t> </section> </section> <section anchor="signatures"title="Signatures">numbered="true" toc="default"> <name>Signatures</name> <t>When signing data structures, a logMUST<bcp14>MUST</bcp14> use one of the signature algorithms from the IANACT Signature Algorithms"Signature Algorithms" registry, described in <xreftarget="signature_algorithms"/>.</t>target="signature_algorithms" format="default"/>.</t> </section> </section> <section anchor="submitters"title="Submitters">numbered="true" toc="default"> <name>Submitters</name> <t>Submitters submit certificates or preannouncements of certificates prior to issuance (precertificates) to logs for public auditing, as described below. In order to enable attribution of each logged certificate or precertificate to its issuer, each submissionMUST<bcp14>MUST</bcp14> be accompanied by all additional certificates required to verify the chain up to an accepted trust anchor (<xreftarget="get-anchors"/>).target="get-anchors" format="default"/>). The trust anchor (a root or intermediate CA certificate)MAY<bcp14>MAY</bcp14> be omitted from the submission.</t> <t>If a log accepts a submission, it will return a Signed Certificate Timestamp (SCT) (see <xreftarget="sct"/>).target="sct" format="default"/>). The submitterSHOULD<bcp14>SHOULD</bcp14> validate the returnedSCTSCT, as described in <xreftarget="tls_clients"/>target="tls_clients" format="default"/>, if they understand its format and they intend to use it directly in a TLS handshake or to construct a certificate. If the submitter does not need the SCT (for example, the certificate is being submitted simply to make it available in the log), itMAY<bcp14>MAY</bcp14> validate the SCT.</t> <section anchor="certificates"title="Certificates">numbered="true" toc="default"> <name>Certificates</name> <t>Any entity can submit a certificate (<xreftarget="submit-entry"/>)target="submit-entry" format="default"/>) to a log. Since it is anticipated that TLS clients will reject certificates that are not logged, it is expected that certificate issuers and subjects will be strongly motivated to submit them.</t> </section> <section anchor="precertificates"title="Precertificates">numbered="true" toc="default"> <name>Precertificates</name> <t>CAs may preannounce a certificate prior to issuance by submitting a precertificate (<xreftarget="submit-entry"/>)target="submit-entry" format="default"/>) that the log can use to create an entry that will be valid against the issued certificate. The CAMAY<bcp14>MAY</bcp14> incorporate the returned SCT in the issued certificate. One example of where the returned SCT is not incorporated in the issued certificate is when a CA sends the precertificate to multiplelogs,logs but only incorporates the SCTs that are returned first.</t> <t>A precertificate is a CMS <xreftarget="RFC5652"></xref> <spanx style="verb">signed-data</spanx>target="RFC5652" format="default"/> <tt>signed-data</tt> object that conforms to the following profile:</t><t><list style="symbols"> <t>It MUST<ul spacing="normal"> <li>It <bcp14>MUST</bcp14> be DERencodedencoded, as described in <xreftarget="X690"></xref>.</t> <t><spanx style="verb">SignedData.version</spanx> MUST be v3(3).</t> <t><spanx style="verb">SignedData.digestAlgorithms</spanx> MUSTtarget="X690" format="default"/>.</li> <li><tt>SignedData.version</tt> <bcp14>MUST</bcp14> be v3(3).</li> <li><tt>SignedData.digestAlgorithms</tt> <bcp14>MUST</bcp14> be the same as the<spanx style="verb">SignerInfo.digestAlgorithm</spanx><tt>SignerInfo.digestAlgorithm</tt> OID value (seebelow).</t> <t><spanx style="verb">SignedData.encapContentInfo</spanx>: <list style="symbols"> <t><spanx style="verb">eContentType</spanx> MUSTbelow).</li> <li> <t><tt>SignedData.encapContentInfo</tt>:</t> <ul spacing="normal"> <li><tt>eContentType</tt> <bcp14>MUST</bcp14> be the OID1.3.101.78.</t> <t><spanx style="verb">eContent</spanx> MUST1.3.101.78.</li> <li><tt>eContent</tt> <bcp14>MUST</bcp14> contain a TBSCertificate <xreftarget="RFC5280"></xref>target="RFC5280" format="default"/> that will be identical to the TBSCertificate in the issued certificate, except that the Transparency Information (<xreftarget="x509v3_transinfo_extension"/>)target="x509v3_transinfo_extension" format="default"/>) extensionMUST<bcp14>MUST</bcp14> beomitted.</t> </list></t> <t><spanx style="verb">SignedData.certificates</spanx> MUST be omitted.</t> <t><spanx style="verb">SignedData.crls</spanx> MUST be omitted.</t> <t><spanx style="verb">SignedData.signerInfos</spanx> MUSTomitted.</li> </ul> </li> <li><tt>SignedData.certificates</tt> <bcp14>MUST</bcp14> be omitted.</li> <li><tt>SignedData.crls</tt> <bcp14>MUST</bcp14> be omitted.</li> <li><t><tt>SignedData.signerInfos</tt> <bcp14>MUST</bcp14> contain one<spanx style="verb">SignerInfo</spanx>: <list style="symbols"> <t><spanx style="verb">version</spanx> MUST be v3(3).</t> <t><spanx style="verb">sid</spanx> MUST<tt>SignerInfo</tt>:</t> <ul spacing="normal"> <li><tt>version</tt> <bcp14>MUST</bcp14> be v3(3).</li> <li><tt>sid</tt> <bcp14>MUST</bcp14> use the<spanx style="verb">subjectKeyIdentifier</spanx> option.</t> <t><spanx style="verb">digestAlgorithm</spanx> MUST<tt>subjectKeyIdentifier</tt> option.</li> <li><tt>digestAlgorithm</tt> <bcp14>MUST</bcp14> be one of the hash algorithm OIDs listed in the IANACT Hash Algorithms Registry,"Hash Algorithms" registry, described in <xreftarget="hash_algorithms"/>.</t> <t><spanx style="verb">signedAttrs</spanx> MUSTtarget="hash_algorithms" format="default"/>.</li> <li> <t><tt>signedAttrs</tt> <bcp14>MUST</bcp14> be present andMUST<bcp14>MUST</bcp14> contain twoattributes: <list style="symbols"> <t>Aattributes:</t> <ul spacing="normal"> <li>a content-type attribute whose value is the same as<spanx style="verb">SignedData.encapContentInfo.eContentType</spanx>.</t> <t>A<tt>SignedData.encapContentInfo.eContentType</tt> and</li> <li>a message-digest attribute whose value is the message digest of<spanx style="verb">SignedData.encapContentInfo.eContent</spanx>.</t> </list></t> <t><spanx style="verb">signatureAlgorithm</spanx> MUST<tt>SignedData.encapContentInfo.eContent</tt>.</li> </ul> </li> <li><tt>signatureAlgorithm</tt> <bcp14>MUST</bcp14> be the same OID as<spanx style="verb">TBSCertificate.signature</spanx>.</t> <t><spanx style="verb">signature</spanx> MUST<tt>TBSCertificate.signature</tt>.</li> <li><tt>signature</tt> <bcp14>MUST</bcp14> be from the same (root or intermediate) CA that intends to issue the corresponding certificate (see <xreftarget="binding_intent_to_issue"/>).</t> <t><spanx style="verb">unsignedAttrs</spanx> MUST be omitted.</t> </list></t> </list></t> <t><spanx style="verb">SignerInfo.signedAttrs</spanx>target="binding_intent_to_issue" format="default"/>).</li> <li><tt>unsignedAttrs</tt> <bcp14>MUST</bcp14> be omitted.</li> </ul> </li> </ul> <t><tt>SignerInfo.signedAttrs</tt> is included in the message digest calculation process (seeSection 5.4 of<xreftarget="RFC5652"></xref>),target="RFC5652" sectionFormat="of" section="5.4"/>), which ensures that the<spanx style="verb">SignerInfo.signature</spanx><tt>SignerInfo.signature</tt> value will not be a valid X.509v3 signature that could be used in conjunction with the TBSCertificate (from<spanx style="verb">SignedData.encapContentInfo.eContent</spanx>)<tt>SignedData.encapContentInfo.eContent</tt>) to construct a valid certificate.</t> <section anchor="binding_intent_to_issue"title="Bindingnumbered="true" toc="default"> <name>Binding Intent toIssue">Issue</name> <t>Under normal circumstances, there will be a short delay between precertificate submission and issuance of the corresponding certificate. Longer delays are to be expected occasionally (e.g., due to log serverdowntime), anddowntime); in somecasescases, the CA might not actually issue the corresponding certificate. Nevertheless, a precertificate's<spanx style="verb">signature</spanx><tt>signature</tt> indicates the CA's binding intent to issue the corresponding certificate, which means that:</t><t><list style="symbols"> <t>Misissuance<ul spacing="normal"> <li>Misissuance of a precertificate is considered equivalent to misissuance of the corresponding certificate. The CA should expect to be heldto account,accountable, even if the corresponding certificate has not actually beenissued.</t> <t>Uponissued.</li> <li>Upon observing a precertificate, a client can reasonably presume that the corresponding certificate has been issued. A client may wish to obtain status information (e.g., by using the Online Certificate Status Protocol <xreftarget="RFC6960"></xref>target="RFC6960" format="default"/> or by checking a Certificate Revocation List <xreftarget="RFC5280"></xref>)target="RFC5280" format="default"/>) about a certificate that is presumed to exist, especially if there is evidence or suspicion that the corresponding precertificate wasmisissued.</t> <t>TLSmisissued.</li> <li>TLS clients may have policies that require CAs to be able torevoke,revoke and to provide certificate status servicesfor,for each certificate that is presumed to exist based on the existence of a correspondingprecertificate.</t> </list></t>precertificate.</li> </ul> </section> </section> </section> <section anchor="log-format-and-operation"title="Lognumbered="true" toc="default"> <name>Log Format andOperation">Operation</name> <t>A log is a single, append-only Merkle Tree of submitted certificate and precertificate entries.</t> <t>When it receives and accepts a valid submission, the logMUST<bcp14>MUST</bcp14> return an SCT that corresponds to the submitted certificate or precertificate. If the log has previously seen this valid submission, itSHOULD<bcp14>SHOULD</bcp14> return the same SCT as it returned before, as discussed in <xreftarget="misbehaving_logs"/>.target="misbehaving_logs" format="default"/>. If different SCTs are produced for the same submission, multiple log entries will have to be created, one for each SCT (as the timestamp is a part of the leaf structure). Note that if a certificate was previously logged as a precertificate, then the precertificate's SCT of type<spanx style="verb">precert_sct_v2</spanx><tt>precert_sct_v2</tt> would not be appropriate; instead, a fresh SCT of type<spanx style="verb">x509_sct_v2</spanx><tt>x509_sct_v2</tt> should be generated.</t> <t>An SCT is the log's promise to append to its Merkle Tree an entry for the accepted submission. Upon producing an SCT, the logMUST fulfil<bcp14>MUST</bcp14> fulfill this promise by performing the following actions within a fixed amount of time known as the Maximum Merge Delay (MMD), which is one of the log's parameters (see <xreftarget="log_parameters"/>):</t> <t><list style="symbols"> <t>Allocatetarget="log_parameters" format="default"/>):</t> <ul spacing="normal"> <li>Allocate a tree index to the entry representing the acceptedsubmission.</t> <t>Calculatesubmission.</li> <li>Calculate the root of thetree.</t> <t>Signtree.</li> <li>Sign the root of the tree (see <xreftarget="sth"/>).</t> </list></t>target="sth" format="default"/>).</li> </ul> <t>The log may append multiple entries before signing the root of the tree.</t> <t>Log operatorsSHOULD NOT<bcp14>SHOULD NOT</bcp14> impose any conditions on retrieving or sharing data from the log.</t> <section anchor="log_parameters"title="Log Parameters">numbered="true" toc="default"> <name>Log Parameters</name> <t>A log is defined by a collection of immutable parameters, which are used by clients to communicate with the log and to verify log artifacts. Except for the FinalSigned Tree Head (STH),STH, each of these parametersMUST<bcp14>MUST</bcp14> be established before the log operator begins to operate the log.</t><t><list style="hanging"> <t hangText="Base URL:"> The<dl newline="false" spacing="normal"> <dt>Base URL:</dt> <dd>The prefix used to construct URLs(<xref target="RFC3986"></xref>)<xref target="RFC3986" format="default"/> for client messages (see <xreftarget="client_messages"/>).target="client_messages" format="default"/>). The base URLMUST<bcp14>MUST</bcp14> be an "https" URL,MAY<bcp14>MAY</bcp14> contain a port,MAYand <bcp14>MAY</bcp14> contain a path with any number of pathsegments,segments butMUST NOT<bcp14>MUST NOT</bcp14> contain a query string, fragment, or trailing "/". Example:https://ct.example.org/blue</t> <t hangText="Hash Algorithm:"> Thehttps://ct.example.org/blue.</dd> <dt>Hash Algorithm:</dt> <dd>The hash algorithm used for the Merkle Tree (see <xreftarget="hash_algorithms"/>).</t> <t hangText="Signature Algorithm:"> Thetarget="hash_algorithms" format="default"/>).</dd> <dt>Signature Algorithm:</dt> <dd>The signature algorithm used (see <xreftarget="signatures"/>).</t> <t hangText="Public Key:"> Thetarget="signatures" format="default"/>).</dd> <dt>Public Key:</dt> <dd>The public key used to verify signatures generated by the log. A logMUST NOT<bcp14>MUST NOT</bcp14> use the same keypair as any otherlog.</t> <t hangText="Log ID:"> Thelog.</dd> <dt>Log ID:</dt> <dd>The OID that uniquely identifies thelog.</t> <t hangText="Maximumlog.</dd> <dt>Maximum MergeDelay:"> TheDelay:</dt> <dd>The MMD the log has committed to. This document deliberately does not specify any limits on thevalue,value to allow forexperimentation.</t> <t hangText="Version:"> Theexperimentation.</dd> <dt>Version:</dt> <dd>The version of the protocol supported by the log (currently 1 or2).</t> <t hangText="Maximum2).</dd> <dt>Maximum ChainLength:"> TheLength:</dt> <dd>The longest certificate chain submission the log is willing to accept, if the log imposes anylimit.</t> <t hangText="STHlimit.</dd> <dt>STH FrequencyCount:"> TheCount:</dt> <dd>The maximum number of STHs the log may produce in any period equal to the<spanx style="verb">Maximum<tt>Maximum MergeDelay</spanx>Delay</tt> (see <xreftarget="sth"/>).</t> <t hangText="Final STH:"> Iftarget="sth" format="default"/>).</dd> <dt>Final STH:</dt> <dd>If a log has been closed down (i.e., no longer accepts new entries), existing entries may still be valid. In this case, the client should know the final valid STH in the log to ensure no new entries can be added without detection. This valueMUST<bcp14>MUST</bcp14> be provided in the form of aTransItem<tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>.<tt>signed_tree_head_v2</tt>. If a log is still accepting entries, this value should not beprovided.</t> </list></t>provided.</dd> </dl> <t><xreftarget="JSON.Metadata"></xref>target="JSON.Metadata" format="default"/> is an example of a metadata formatwhichthat includes the above elements.</t> </section> <section anchor="evaluating-submissions"title="Evaluating Submissions">numbered="true" toc="default"> <name>Evaluating Submissions</name> <t>A log determines whether to accept or reject a submission by evaluating it against the minimum acceptance criteria (see <xreftarget="minimum_criteria"/>)target="minimum_criteria" format="default"/>) and against the log's discretionary acceptance criteria (see <xreftarget="discretionary_criteria"/>).</t>target="discretionary_criteria" format="default"/>).</t> <t>If the acceptance criteria are met, the logSHOULD<bcp14>SHOULD</bcp14> accept the submission. (A log may decide, for example, to temporarily reject acceptable submissions to protect itself against denial-of-serviceattacks).</t>attacks.)</t> <t>The logSHALL<bcp14>SHALL</bcp14> allow retrieval of its list of accepted trust anchors (see <xreftarget="get-anchors"/>),target="get-anchors" format="default"/>), each of which is a root or intermediate CA certificate. This list might usefully be the union of root certificates trusted by major browser vendors.</t> <section anchor="minimum_criteria"title="Minimumnumbered="true" toc="default"> <name>Minimum AcceptanceCriteria">Criteria</name> <t>To ensure that logged certificates and precertificates are attributable to an accepted trust anchor, to set clear expectations for what monitors would find in the log, and to avoid being overloaded by invalid submissions, the logMUST<bcp14>MUST</bcp14> reject a submission if any of the following conditions are not met:</t><t><list style="symbols"> <t>The <spanx style="verb">submission</spanx>, <spanx style="verb">type</spanx><ul spacing="normal"> <li>The <tt>submission</tt>, <tt>type</tt>, and<spanx style="verb">chain</spanx><tt>chain</tt> inputsMUST<bcp14>MUST</bcp14> be set as described in <xreftarget="submit-entry"/>.target="submit-entry" format="default"/>. The logMUST NOT<bcp14>MUST NOT</bcp14> accommodate misordered CA certificates or use any other source of intermediate CA certificates to attempt certification pathconstruction.</t>construction.</li> <li> <t>Each of the zero or more intermediate CA certificates in the chainMUST<bcp14>MUST</bcp14> have one or both of the followingfeatures: <list style="symbols"> <t>Thefeatures:</t> <ul spacing="normal"> <li>The Basic Constraints extension with the cA booleanasserted.</t> <t>Theasserted.</li> <li>The Key Usage extension with the keyCertSign bitasserted.</t> </list></t> <t>Eachasserted.</li> </ul> </li> <li>Each certificate in the chainMUST<bcp14>MUST</bcp14> fall within the limits imposed by the zero or more Basic Constraints pathLenConstraint values found higher up thechain.</t> <t>Precertificatechain.</li> <li>Precertificate submissionsMUST<bcp14>MUST</bcp14> conform to all of the requirements in <xreftarget="precertificates"/>.</t> </list></t>target="precertificates" format="default"/>.</li> </ul> </section> <section anchor="discretionary_criteria"title="Discretionarynumbered="true" toc="default"> <name>Discretionary AcceptanceCriteria">Criteria</name> <t>If the minimum acceptance criteria are met but the submission is not fully valid according to <xreftarget="RFC5280"></xref>target="RFC5280" format="default"/> verification rules (e.g., the certificate or precertificate has expired, is not yet valid, has been revoked, exhibits ASN.1 DER encoding errors but the log can still parse it,etc),etc.), then the acceptability of the submission is left to the log's discretion. It is useful for logs to accept such submissions in order to accommodate quirks of CA certificate-issuing software and to facilitate monitoring of CA compliance with applicable policies and technical standards. However, it is impractical for this document to enumerate, and for logs to consider, all of the ways that a submission might fail to comply with <xreftarget="RFC5280"></xref>.</t>target="RFC5280" format="default"/>.</t> <t>LogsSHOULD<bcp14>SHOULD</bcp14> limit the length of chain they will accept. The maximum chain length is one of the log's parameters (see <xreftarget="log_parameters"/>).</t>target="log_parameters" format="default"/>).</t> </section> </section> <section anchor="log_entries"title="Log Entries">numbered="true" toc="default"> <name>Log Entries</name> <t>If a submission is accepted and an SCT is issued, the accepting logMUST<bcp14>MUST</bcp14> store the entire chain used for verification. This chainMUST<bcp14>MUST</bcp14> include the certificate or precertificate itself, the zero or more intermediate CA certificates provided by the submitter, and the trust anchor used to verify the chain (even if it was omitted from the submission). The logMUST<bcp14>MUST</bcp14> provide this chain for auditing upon request (see <xreftarget="get-entries"/>)target="get-entries" format="default"/>) so that the CA cannot avoid blame by logging a partial or empty chain. Each log entry is a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">x509_entry_v2</spanx><tt>x509_entry_v2</tt> or<spanx style="verb">precert_entry_v2</spanx>.<tt>precert_entry_v2</tt>. However, a log may store its entries in any format. If a log does not store this<spanx style="verb">TransItem</spanx><tt>TransItem</tt> in full, it must store the<spanx style="verb">timestamp</spanx><tt>timestamp</tt> and<spanx style="verb">sct_extensions</spanx><tt>sct_extensions</tt> of the corresponding<spanx style="verb">TimestampedCertificateEntryDataV2</spanx><tt>TimestampedCertificateEntryDataV2</tt> structure. The<spanx style="verb">TransItem</spanx><tt>TransItem</tt> can be reconstructed from these fields and the entire chain that the log used to verify the submission.</t> </section> <section anchor="log_id"title="Log ID">numbered="true" toc="default"> <name>Log ID</name> <t>Each log is identified by an OID, which is one of the log's parameters (see <xreftarget="log_parameters"/>)target="log_parameters" format="default"/>) and whichMUST NOT<bcp14>MUST NOT</bcp14> be used to identify any other log. A log's operatorMUST<bcp14>MUST</bcp14> either allocate the OID themselves or request an OID from the Log ID registry (see <xreftarget="log_id_registry"/>).target="log_id_registry" format="default"/>). One way to get an OID arc, from which OIDs can be allocated, is to request a Private Enterprise Number fromIANA,IANA by completing the <eref target="https://pen.iana.org/pen/PenApplication.page">registration form</eref>. The only advantage of the registry is that the DER encoding can be small. (Recall that OID allocations do not require a central registration, although logs will most likely want to make themselves known to potential clients throughout of bandout-of-band means.) Various data structures include the DER encoding of this OID, excluding the ASN.1 tag and length bytes, in an opaque vector:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ opaque LogID<2..127>;]]></artwork></figure>]]></sourcecode> <t>Note that the ASN.1 length and the opaque vector length are identical in size (1 byte) and value, so the full DER encoding (including the tag and length) of the OID can be reproduced simply by prepending an OBJECT IDENTIFIER tag (0x06) to the opaque vector length and contents.</t> <t>The OID used to identify a log is limited such that the DER encoding of its value, excluding the tag and length,MUST<bcp14>MUST</bcp14> be no longer than 127 octets.</t> </section> <section anchor="transitem-structure"title="TransItem Structure">numbered="true" toc="default"> <name>TransItem Structure</name> <t>Various data structures are encapsulated in the<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure to ensure that the type and version of each one is identified in a common fashion:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ enum { x509_entry_v2(0x0100), precert_entry_v2(0x0101), x509_sct_v2(0x0102), precert_sct_v2(0x0103), signed_tree_head_v2(0x0104), consistency_proof_v2(0x0105), inclusion_proof_v2(0x0106), /* Reserved Code Points */ reserved_rfc6962(0x0000..0x00FF), reserved_experimentaluse(0xE000..0xEFFF), reserved_privateuse(0xF000..0xFFFF), (0xFFFF) } VersionedTransType; struct { VersionedTransType versioned_type; select (versioned_type) { case x509_entry_v2: TimestampedCertificateEntryDataV2; case precert_entry_v2: TimestampedCertificateEntryDataV2; case x509_sct_v2: SignedCertificateTimestampDataV2; case precert_sct_v2: SignedCertificateTimestampDataV2; case signed_tree_head_v2: SignedTreeHeadDataV2; case consistency_proof_v2: ConsistencyProofDataV2; case inclusion_proof_v2: InclusionProofDataV2; } data; } TransItem;]]></artwork></figure> <t><spanx style="verb">versioned_type</spanx>]]></sourcecode> <t><tt>versioned_type</tt> is a value from the IANA registry in <xreftarget="versioned_trans_types"/>target="versioned_trans_types" format="default"/> that identifies the type of the encapsulated data structure and the earliest version of this protocol to which it conforms. This document is v2.</t><t><spanx style="verb">data</spanx><t><tt>data</tt> is the encapsulated data structure. The various structures named with the<spanx style="verb">DataV2</spanx><tt>DataV2</tt> suffix are defined in later sections of this document.</t> <t>Note that<spanx style="verb">VersionedTransType</spanx><tt>VersionedTransType</tt> combines the v1<xref target="RFC6962"></xref>type enumerations<spanx style="verb">Version</spanx>, <spanx style="verb">LogEntryType</spanx>, <spanx style="verb">SignatureType</spanx><tt>Version</tt>, <tt>LogEntryType</tt>, <tt>SignatureType</tt>, and<spanx style="verb">MerkleLeafType</spanx>.<tt>MerkleLeafType</tt> <xref target="RFC6962" format="default"/>. Note also that v1 did not define<spanx style="verb">TransItem</spanx>,<tt>TransItem</tt>, but this document provides guidelines (see <xreftarget="v1_coexistence"/>)target="v1_coexistence" format="default"/>) on how v2 implementations canco-existcoexist with v1 implementations.</t> <t>Future versions of this protocol may reuse<spanx style="verb">VersionedTransType</spanx><tt>VersionedTransType</tt> values defined in this document as long as the corresponding data structures are notmodified,modified and may add new<spanx style="verb">VersionedTransType</spanx><tt>VersionedTransType</tt> values for new or modified data structures.</t> </section> <section anchor="log-artifact-extensions"title="Lognumbered="true" toc="default"> <name>Log ArtifactExtensions"> <figure><artwork><![CDATA[Extensions</name> <sourcecode type="tls-presentation"><![CDATA[ enum { reserved(65535) } ExtensionType; struct { ExtensionType extension_type; opaque extension_data<0..2^16-1>; } Extension;]]></artwork></figure>]]></sourcecode> <t>The<spanx style="verb">Extension</spanx><tt>Extension</tt> structure provides a generic extensibility for log artifacts, including SCTs (<xreftarget="sct"/>)target="sct" format="default"/>) and STHs (<xreftarget="sth"/>).target="sth" format="default"/>). The interpretation of the<spanx style="verb">extension_data</spanx><tt>extension_data</tt> field is determined solely by the value of the<spanx style="verb">extension_type</spanx><tt>extension_type</tt> field.</t> <t>This document does not define any extensions, but it does establish a registry for future<spanx style="verb">ExtensionType</spanx><tt>ExtensionType</tt> values (see <xreftarget="log_artifact_extension_registry"/>).target="log_artifact_extension_registry" format="default"/>). Each document that registers a new<spanx style="verb">ExtensionType</spanx><tt>ExtensionType</tt> must specify the context in which it may be used (e.g., SCT, STH, or both) and describe how to interpret the corresponding<spanx style="verb">extension_data</spanx>.</t><tt>extension_data</tt>.</t> </section> <section anchor="tree_leaves"title="Merklenumbered="true" toc="default"> <name>Merkle TreeLeaves">Leaves</name> <t>The leaves of a log's Merkle Tree correspond to the log's entries (see <xreftarget="log_entries"/>).target="log_entries" format="default"/>). Each leaf is the leaf hash (<xreftarget="mht"/>)target="mht" format="default"/>) of a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">x509_entry_v2</spanx><tt>x509_entry_v2</tt> or<spanx style="verb">precert_entry_v2</spanx>,<tt>precert_entry_v2</tt>, which encapsulates a<spanx style="verb">TimestampedCertificateEntryDataV2</spanx><tt>TimestampedCertificateEntryDataV2</tt> structure. Note that leaf hashes are calculated asHASH(0x00<tt>HASH(0x00 ||TransItem),TransItem)</tt>, where the hash algorithm is one of the log's parameters.</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ opaque TBSCertificate<1..2^24-1>; struct { uint64 timestamp; opaque issuer_key_hash<32..2^8-1>; TBSCertificate tbs_certificate; Extension sct_extensions<0..2^16-1>; } TimestampedCertificateEntryDataV2;]]></artwork></figure> <t><spanx style="verb">timestamp</spanx>]]></sourcecode> <t><tt>timestamp</tt> is the date and time at which the certificate or precertificate was accepted by the log, in the form of a 64-bit unsigned number of milliseconds elapsed since the Unix Epoch (1 January 1970 00:00:00 UTC--- see <xreftarget="UNIXTIME"></xref>),target="UNIXTIME" format="default"/>), ignoring leap seconds, in network byte order. Note that the leaves of a log's Merkle Tree are not required to be in strict chronological order.</t><t><spanx style="verb">issuer_key_hash</spanx><t><tt>issuer_key_hash</tt> is the HASH of the public key of the CA that issued the certificate or precertificate, calculated over the DER encoding of the key represented as SubjectPublicKeyInfo <xreftarget="RFC5280"></xref>.target="RFC5280" format="default"/>. This is needed to bind the CA to the certificate or precertificate, making it impossible for the corresponding SCT to be valid for any other certificate or precertificate whose TBSCertificate matches<spanx style="verb">tbs_certificate</spanx>.<tt>tbs_certificate</tt>. The length of the<spanx style="verb">issuer_key_hash</spanx> MUST<tt>issuer_key_hash</tt> <bcp14>MUST</bcp14> match HASH_SIZE.</t><t><spanx style="verb">tbs_certificate</spanx><t><tt>tbs_certificate</tt> is theDER encodedDER-encoded TBSCertificate from the submission. (Note that a precertificate's TBSCertificate can be reconstructed from the correspondingcertificatecertificate, as described in <xreftarget="reconstructing_tbscertificate"/>).</t> <t><spanx style="verb">sct_extensions</spanx>target="reconstructing_tbscertificate" format="default"/>).</t> <t><tt>sct_extensions</tt> is byte-for-byte identical to the SCT extensions of the corresponding SCT.</t> <t>The type of the<spanx style="verb">TransItem</spanx><tt>TransItem</tt> corresponds to the value of the<spanx style="verb">type</spanx><tt>type</tt> parameter supplied in the <xreftarget="submit-entry"/>target="submit-entry" format="default"/> call.</t> </section> <section anchor="sct"title="Signednumbered="true" toc="default"> <name>Signed Certificate Timestamp(SCT)">(SCT)</name> <t>An SCT is a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">x509_sct_v2</spanx><tt>x509_sct_v2</tt> or<spanx style="verb">precert_sct_v2</spanx>,<tt>precert_sct_v2</tt>, which encapsulates a<spanx style="verb">SignedCertificateTimestampDataV2</spanx><tt>SignedCertificateTimestampDataV2</tt> structure:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ struct { LogID log_id; uint64 timestamp; Extension sct_extensions<0..2^16-1>; opaque signature<1..2^16-1>; } SignedCertificateTimestampDataV2;]]></artwork></figure> <t><spanx style="verb">log_id</spanx>]]></sourcecode> <t><tt>log_id</tt> is this log's unique ID, encoded in an opaquevectorvector, as described in <xreftarget="log_id"/>.</t> <t><spanx style="verb">timestamp</spanx>target="log_id" format="default"/>.</t> <t><tt>timestamp</tt> is equal to the timestamp from the corresponding<spanx style="verb">TimestampedCertificateEntryDataV2</spanx><tt>TimestampedCertificateEntryDataV2</tt> structure.</t><t><spanx style="verb">sct_extensions</spanx><t><tt>sct_extensions</tt> is a vector of 0 or more SCT extensions. This vectorMUST NOT<bcp14>MUST NOT</bcp14> include more than one extension with the same<spanx style="verb">extension_type</spanx>.<tt>extension_type</tt>. The extensions in the vectorMUST<bcp14>MUST</bcp14> be ordered by the value of the<spanx style="verb">extension_type</spanx><tt>extension_type</tt> field, smallest value first. All SCT extensions are similar tonon-criticalnoncritical X.509v3 extensions (i.e., the<spanx style="verb">mustUnderstand</spanx><tt>mustUnderstand</tt> field is not set), and a recipientSHOULD<bcp14>SHOULD</bcp14> ignore any extension it does not understand. Furthermore, an implementationMAY<bcp14>MAY</bcp14> choose to ignore any extension(s) that it does understand.</t><t><spanx style="verb">signature</spanx><t><tt>signature</tt> is computed over a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">x509_entry_v2</spanx><tt>x509_entry_v2</tt> or<spanx style="verb">precert_entry_v2</spanx><tt>precert_entry_v2</tt> (see <xreftarget="tree_leaves"/>)target="tree_leaves" format="default"/>) using the signature algorithm declared in the log's parameters (see <xreftarget="log_parameters"/>).</t>target="log_parameters" format="default"/>).</t> </section> <section anchor="tree_head"title="Merklenumbered="true" toc="default"> <name>Merkle TreeHead">Head</name> <t>The log stores information about its Merkle Tree in a<spanx style="verb">TreeHeadDataV2</spanx>:</t> <figure><artwork><![CDATA[<tt>TreeHeadDataV2</tt>:</t> <sourcecode type="tls-presentation"><![CDATA[ opaque NodeHash<32..2^8-1>; struct { uint64 timestamp; uint64 tree_size; NodeHash root_hash; Extension sth_extensions<0..2^16-1>; } TreeHeadDataV2;]]></artwork></figure>]]></sourcecode> <t>The length of NodeHashMUST<bcp14>MUST</bcp14> match HASH_SIZE of the log.</t><t><spanx style="verb">timestamp</spanx><t><tt>timestamp</tt> is the current date and time, using the format defined in <xreftarget="tree_leaves"/>.</t> <t><spanx style="verb">tree_size</spanx>target="tree_leaves" format="default"/>.</t> <t><tt>tree_size</tt> is the number of entries currently in the log's Merkle Tree.</t><t><spanx style="verb">root_hash</spanx><t><tt>root_hash</tt> is the root of the MerkleHashTree.</t><t><spanx style="verb">sth_extensions</spanx><t><tt>sth_extensions</tt> is a vector of 0 or more STH extensions. This vectorMUST NOT<bcp14>MUST NOT</bcp14> include more than one extension with the same<spanx style="verb">extension_type</spanx>.<tt>extension_type</tt>. The extensions in the vectorMUST<bcp14>MUST</bcp14> be ordered by the value of the<spanx style="verb">extension_type</spanx><tt>extension_type</tt> field, smallest value first. If an implementation sees an extension that it does not understand, itSHOULD<bcp14>SHOULD</bcp14> ignore that extension. Furthermore, an implementationMAY<bcp14>MAY</bcp14> choose to ignore any extension(s) that it does understand.</t> </section> <section anchor="sth"title="Signednumbered="true" toc="default"> <name>Signed Tree Head(STH)"> <t>Periodically(STH)</name> <t>Periodically, each logSHOULD<bcp14>SHOULD</bcp14> sign its current tree head information (see <xreftarget="tree_head"/>)target="tree_head" format="default"/>) to produce an STH. When a client requests a log's latest STH (see <xreftarget="get-sth"/>),target="get-sth" format="default"/>), the logMUST<bcp14>MUST</bcp14> return an STH that is no older than the log's MMD. However, since STHs could be used to mark individual clients (by producing a new STH for each query), a logMUST NOT<bcp14>MUST NOT</bcp14> produce STHs more frequently than its parameters declare (see <xreftarget="log_parameters"/>).target="log_parameters" format="default"/>). In general, there is no need to produce a new STH unless there are new entries in the log; however, in the event that a log does not accept any submissions during an MMD period, the logMUST<bcp14>MUST</bcp14> sign the same Merkle Tree Hash with a fresh timestamp.</t> <t>An STH is a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt>, which encapsulates a<spanx style="verb">SignedTreeHeadDataV2</spanx><tt>SignedTreeHeadDataV2</tt> structure:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ struct { LogID log_id; TreeHeadDataV2 tree_head; opaque signature<1..2^16-1>; } SignedTreeHeadDataV2;]]></artwork></figure> <t><spanx style="verb">log_id</spanx>]]></sourcecode> <t><tt>log_id</tt> is this log's uniqueID,ID encoded in an opaquevectorvector, as described in <xreftarget="log_id"/>.</t>target="log_id" format="default"/>.</t> <t>The<spanx style="verb">timestamp</spanx><tt>timestamp</tt> in<spanx style="verb">tree_head</spanx> MUST<tt>tree_head</tt> <bcp14>MUST</bcp14> be at least as recent as the most recent SCT timestamp in the tree. Each subsequent timestampMUST<bcp14>MUST</bcp14> be more recent than the timestamp of the previous update.</t><t><spanx style="verb">tree_head</spanx><t><tt>tree_head</tt> contains the latest tree head information (see <xreftarget="tree_head"/>).</t> <t><spanx style="verb">signature</spanx>target="tree_head" format="default"/>).</t> <t><tt>signature</tt> is computed over the<spanx style="verb">tree_head</spanx><tt>tree_head</tt> field using the signature algorithm declared in the log's parameters (see <xreftarget="log_parameters"/>).</t>target="log_parameters" format="default"/>).</t> </section> <section anchor="merkle-consistency-proofs"title="Merklenumbered="true" toc="default"> <name>Merkle ConsistencyProofs">Proofs</name> <t>To prepare a MerkleConsistency Proofconsistency proof for distribution to clients, the log produces a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">consistency_proof_v2</spanx>,<tt>consistency_proof_v2</tt>, which encapsulates a<spanx style="verb">ConsistencyProofDataV2</spanx><tt>ConsistencyProofDataV2</tt> structure:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ struct { LogID log_id; uint64 tree_size_1; uint64 tree_size_2; NodeHash consistency_path<0..2^16-1>; } ConsistencyProofDataV2;]]></artwork></figure> <t><spanx style="verb">log_id</spanx>]]></sourcecode> <t><tt>log_id</tt> is this log's uniqueID,ID encoded in an opaquevectorvector, as described in <xreftarget="log_id"/>.</t> <t><spanx style="verb">tree_size_1</spanx>target="log_id" format="default"/>.</t> <t><tt>tree_size_1</tt> is the size of the older tree.</t><t><spanx style="verb">tree_size_2</spanx><t><tt>tree_size_2</tt> is the size of the newer tree.</t><t><spanx style="verb">consistency_path</spanx><t><tt>consistency_path</tt> is a vector of Merkle Tree nodes proving the consistency of twoSTHsSTHs, as described in <xreftarget="consistency"/>.</t>target="consistency" format="default"/>.</t> </section> <section anchor="merkle-inclusion-proofs"title="Merklenumbered="true" toc="default"> <name>Merkle InclusionProofs">Proofs</name> <t>To prepare a MerkleInclusion Proofinclusion proof for distribution to clients, the log produces a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">inclusion_proof_v2</spanx>,<tt>inclusion_proof_v2</tt>, which encapsulates an<spanx style="verb">InclusionProofDataV2</spanx><tt>InclusionProofDataV2</tt> structure:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ struct { LogID log_id; uint64 tree_size; uint64 leaf_index; NodeHash inclusion_path<0..2^16-1>; } InclusionProofDataV2;]]></artwork></figure> <t><spanx style="verb">log_id</spanx>]]></sourcecode> <t><tt>log_id</tt> is this log's uniqueID,ID encoded in an opaquevectorvector, as described in <xreftarget="log_id"/>.</t> <t><spanx style="verb">tree_size</spanx>target="log_id" format="default"/>.</t> <t><tt>tree_size</tt> is the size of the tree on which this inclusion proof is based.</t><t><spanx style="verb">leaf_index</spanx><t><tt>leaf_index</tt> is the 0-based index of the log entry corresponding to this inclusion proof.</t><t><spanx style="verb">inclusion_path</spanx><t><tt>inclusion_path</tt> is a vector of Merkle Tree nodes proving the inclusion of the chosen certificate orprecertificateprecertificate, as described in <xreftarget="merkle_inclusion_proof"/>.</t>target="merkle_inclusion_proof" format="default"/>.</t> </section> <section anchor="log_shutdown"title="Shutting downnumbered="true" toc="default"> <name>Shutting Down alog">Log</name> <t>Log operators may decide to shut down a log for various reasons, such as deprecation of the signature algorithm. If there are entries in the log for certificates that have not yet expired, simply making TLS clients stop recognizing that log will have the effect of invalidating SCTs from that log. In order to avoid that, the following actionsSHOULD<bcp14>SHOULD</bcp14> be taken:</t><t><list style="symbols"> <t>Make<ul spacing="normal"> <li>Make it known to clients and monitors that the log will be frozen. This is not part of the API, so it will have to be done via a relevant out-of-bandmechanism.</t> <t>Stopmechanism.</li> <li>Stop accepting new submissions (the error code "shutdown" should be returned for suchrequests).</t> <t>Oncerequests).</li> <li>Once MMD from the last accepted submission has passed and all pending submissions are incorporated, issue a final STH and publish it as one of the log's parameters. Having an STH with a timestamp that is after the MMD has passed from the last SCT issuance allows clients to audit this log regularly without special handling for the final STH. At thispointpoint, the log's private key is no longer needed and can bedestroyed.</t> <t>Keepdestroyed.</li> <li>Keep the log running until the certificates in all of its entries have expired or exist in other logs (this can be determined by scanning other logs or connecting to domains mentioned in the certificates and inspecting the SCTsserved).</t> </list></t>served).</li> </ul> </section> </section> <section anchor="client_messages"title="Lognumbered="true" toc="default"> <name>Log ClientMessages">Messages</name> <t>Messages are sent as HTTPS GET or POST requests. Parameters for POSTs and all responses are encoded as JavaScript Object Notation (JSON) objects <xreftarget="RFC8259"></xref>.target="RFC8259" format="default"/>. Parameters for GETs are encoded as order-independent key/value URL parameters, using the "application/x-www-form-urlencoded" format described in the "HTML 4.01 Specification" <xreftarget="HTML401"></xref>.target="HTML401" format="default"/>. Binary data is base64 encoded according tosection 4 of<xreftarget="RFC4648"></xref>target="RFC4648" sectionFormat="of" section="4"/>, as specified in the individual messages.</t> <t>Clients are configured with a log's base URL, which is one of the log's parameters. Clients construct URLs for requests by appending suffixes to this base URL. This structure places some degree of restriction on how log operators can deploy these services, as noted in <xreftarget="RFC8820"></xref>.target="RFC8820" format="default"/>. However, operational experience with version 1 of this protocol has not indicated that these restrictions are a problem in practice.</t> <t>Note that JSON objects and URL parameters may contain fields not specifiedhere,here to allow for experimentation. Any fields that are not understoodSHOULD<bcp14>SHOULD</bcp14> be ignored.</t> <t>In practice, log servers may include multiple front-end machines. Since it is impractical to keep these machines in perfect sync, errorsmay occurthat are caused by skew between themachines.machines may occur. Where such errors are possible, thefront-endfront end will return additional information (as specifiedbelow)below), making it possible for clients to make progress, if progress is possible.Front-ends MUSTFront ends <bcp14>MUST</bcp14> only serve data that is free of gaps (that is, for example, nofront-endfront end will respond with an STH unless it is also able to prove consistency from all log entries logged within that STH).</t> <t>For example, when a consistency proof between two STHs is requested, thefront-endfront end reached may not yet be aware of one or both STHs. In the case where it is unaware of both, it will return the latest STH it is aware of. Where it is aware of the first but not the second, it will return the latest STH it is aware of and a consistency proof from the first STH to the returned STH. The case where it knows the second but not the first should not arise (see the "no gaps" requirement above).</t> <t>If the log is unable to process a client's request, itMUST<bcp14>MUST</bcp14> return an HTTP response code of 4xx/5xx (see <xreftarget="RFC7231"></xref>),target="RFC7231" format="default"/>), and, in place of the responses outlined in the subsections below, the bodySHOULD<bcp14>SHOULD</bcp14> be a JSONProblem Details Objectproblem details object (see <xreftarget="RFC7807"></xref> Section 3),target="RFC7807" sectionFormat="of" section="3"/>) containing:</t><t><list style="hanging"> <t hangText="type:"> A<dl newline="false" spacing="normal"> <dt>type:</dt> <dd>A URN reference identifying the problem. To facilitate automated response to errors, this document defines a set of standard tokens for use in the<spanx style="verb">type</spanx> field,<tt>type</tt> field within the URN namespace of:"urn:ietf:params:trans:error:".</t> <t hangText="detail:"> A"urn:ietf:params:trans:error:".</dd> <dt>detail:</dt> <dd>A human-readable string describing the error that prevented the log from processing the request, ideally with sufficient detail to enable the error to berectified.</t> </list></t> <t>e.g., Inrectified.</dd> </dl> <t>For example, in response to a request of<spanx style="verb"><Base URL>/ct/v2/get-entries?start=100&end=99</spanx>,<tt><Base URL>/ct/v2/get-entries?start=100&end=99</tt>, the log would return a<spanx style="verb">400<tt>400 BadRequest</spanx>Request</tt> response code with a body similar to the following:</t><figure><artwork><![CDATA[<sourcecode type="json"><![CDATA[ { "type": "urn:ietf:params:trans:error:endBeforeStart", "detail": "'start' cannot be greater than 'end'" }]]></artwork></figure>]]></sourcecode> <t>Most error types are specific to the type of request and are defined in the respective subsections below. The one exception is the "malformed" error type, which indicates that the log server could not parse the client's request because it did not comply with this document:</t><texttable> <ttcol align='left'>type</ttcol> <ttcol align='left'>detail</ttcol> <c>malformed</c> <c>The<table align="center"> <thead> <tr> <th align="left">type</th> <th align="left">detail</th> </tr> </thead> <tbody> <tr> <td align="left">malformed</td> <td align="left">The request could not beparsed.</c> </texttable>parsed.</td> </tr> </tbody> </table> <t>ClientsSHOULD<bcp14>SHOULD</bcp14> treat<spanx style="verb">500<tt>500 Internal ServerError</spanx>Error</tt> and<spanx style="verb">503<tt>503 ServiceUnavailable</spanx>Unavailable</tt> responses as transient failures andMAY<bcp14>MAY</bcp14> retry the same request without modification at a later date. Note thatas per <xref target="RFC7231"></xref>,in the case of a 503responseresponse, the logMAY<bcp14>MAY</bcp14> include a<spanx style="verb">Retry-After:</spanx><tt>Retry-After</tt> header field per <xref target="RFC7231" format="default"/> in order to request a minimum time for the client to wait before retrying the request. In the absence of this header field, this document does not specify a minimum.</t> <t>ClientsSHOULD<bcp14>SHOULD</bcp14> treat any 4xx error as a problem with the request and not attempt to resubmit without some modification to the request. The full status codeMAY<bcp14>MAY</bcp14> provide additional details.</t> <t>This document deliberately does not provide more specific guidance on the use of HTTP status codes.</t> <section anchor="submit-entry"title="Submitnumbered="true" toc="default"> <name>Submit Entry toLog">Log</name> <t>POST <Base URL>/ct/v2/submit-entry</t><t><list style="hanging"> <t hangText="Inputs:"> <list style="hanging"> <t hangText="submission:"> The base64 encoded<dl newline="true" spacing="normal"> <dt>Inputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>submission:</dt> <dd>The base64-encoded certificate orprecertificate.</t> <t hangText="type:"> The <spanx style="verb">VersionedTransType</spanx>precertificate.</dd> <dt>type:</dt> <dd>The <tt>VersionedTransType</tt> integer value that indicates the type of the<spanx style="verb">submission</spanx>:<tt>submission</tt>: 1 for<spanx style="verb">x509_entry_v2</spanx>,<tt>x509_entry_v2</tt> or 2 for<spanx style="verb">precert_entry_v2</spanx>.</t> <t hangText="chain:"> An<tt>precert_entry_v2</tt>.</dd> <dt>chain:</dt> <dd>An array of zero or more JSON strings, each of which is abase64 encodedbase64-encoded CA certificate. The first element is the certifier of the<spanx style="verb">submission</spanx>;<tt>submission</tt>, the second certifies thefirst;first, etc. The last element of<spanx style="verb">chain</spanx><tt>chain</tt> (or, if<spanx style="verb">chain</spanx><tt>chain</tt> is an empty array, the<spanx style="verb">submission</spanx>)<tt>submission</tt>) is certified by an accepted trustanchor.</t> </list> </t> <t hangText="Outputs:"> <list style="hanging"> <t hangText="sct:"> A base64 encoded <spanx style="verb">TransItem</spanx>anchor.</dd> </dl> </dd> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>sct:</dt> <dd><t>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">x509_sct_v2</spanx><tt>x509_sct_v2</tt> or<spanx style="verb">precert_sct_v2</spanx>,<tt>precert_sct_v2</tt>, signed by this log, that corresponds to the<spanx style="verb">submission</spanx>.</t> </list> If<tt>submission</tt>.</t></dd> </dl> <t>If the submitted entry is immediately appended to (or already exists in) this log's tree, then the logSHOULD<bcp14>SHOULD</bcp14> alsooutput: <list style="hanging"> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx>output:</t> <dl newline="false" spacing="normal" indent="3"> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt> signed by thislog.</t> <t hangText="inclusion:"> A base64 encoded <spanx style="verb">TransItem</spanx>log.</dd> <dt>inclusion:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">inclusion_proof_v2</spanx><tt>inclusion_proof_v2</tt> whose<spanx style="verb">inclusion_path</spanx><tt>inclusion_path</tt> array of Merkle Tree nodes proves the inclusion of the<spanx style="verb">submission</spanx><tt>submission</tt> in the returned<spanx style="verb">sth</spanx>.</t> </list> </t> </list></t><tt>sth</tt>.</dd> </dl> </dd> </dl> <t>Error codes:</t><texttable> <ttcol align='left'>type</ttcol> <ttcol align='left'>detail</ttcol> <c>badSubmission</c> <c><spanx style="verb">submission</spanx><table align="center"> <thead> <tr> <th align="left">type</th> <th align="left">detail</th> </tr> </thead> <tbody> <tr> <td align="left">badSubmission</td> <td align="left"> <tt>submission</tt> is neither a valid certificate nor a validprecertificate.</c> <c>badType</c> <c><spanx style="verb">type</spanx>precertificate.</td> </tr> <tr> <td align="left">badType</td> <td align="left"> <tt>type</tt> is neither 1 nor2.</c> <c>badChain</c> <c>The2.</td> </tr> <tr> <td align="left">badChain</td> <td align="left">The first element of<spanx style="verb">chain</spanx><tt>chain</tt> is not the certifier of the<spanx style="verb">submission</spanx>,<tt>submission</tt>, or the second element does not certify the first,etc.</c> <c>badCertificate</c> <c>Oneetc.</td> </tr> <tr> <td align="left">badCertificate</td> <td align="left">One or more certificates inthe <spanx style="verb">chain</spanx><tt>chain</tt> are not valid (e.g., not properlyencoded).</c> <c>unknownAnchor</c> <c>Theencoded).</td> </tr> <tr> <td align="left">unknownAnchor</td> <td align="left">The last element of<spanx style="verb">chain</spanx><tt>chain</tt> (or, if<spanx style="verb">chain</spanx><tt>chain</tt> is an empty array, the<spanx style="verb">submission</spanx>) both<tt>submission</tt>) is not,andnor isnotit certified by, an accepted trustanchor.</c> <c>shutdown</c> <c>Theanchor.</td> </tr> <tr> <td align="left">shutdown</td> <td align="left">The log is no longer acceptingsubmissions.</c> </texttable>submissions.</td> </tr> </tbody> </table> <t>If the version of<spanx style="verb">sct</spanx><tt>sct</tt> is not v2, then a v2 client may be unable to verify the signature. ItMUST NOT<bcp14>MUST NOT</bcp14> construe this as an error. This is to avoid forcing an upgrade of compliant v2 clients that do not use the returned SCTs.</t> <t>If a log detects bad encoding in a chain that otherwise verifiescorrectlycorrectly, then the logMUST<bcp14>MUST</bcp14> either log the certificate or return the"bad certificate""badCertificate" error. If the certificate is logged, an SCTMUST<bcp14>MUST</bcp14> be issued. Logging the certificate is useful, because monitors (<xreftarget="monitor"/>)target="monitor" format="default"/>) can then detect these encoding errors, which may be accepted by some TLS clients.</t> <t>If<spanx style="verb">submission</spanx><tt>submission</tt> is an accepted trust anchor whose certifier is neither an accepted trust anchor nor the first element of<spanx style="verb">chain</spanx>,<tt>chain</tt>, then the logMUST<bcp14>MUST</bcp14> return the"unknown anchor""unknownAnchor" error. A log is not able to generate an SCT for a submission if it does not have access to the issuer's public key.</t> <t>If the returned<spanx style="verb">sct</spanx><tt>sct</tt> is intended to be provided to TLS clients, then<spanx style="verb">sth</spanx><tt>sth</tt> and<spanx style="verb">inclusion</spanx><tt>inclusion</tt> (if returned)SHOULD<bcp14>SHOULD</bcp14> also be provided to TLS clients. For example, if<spanx style="verb">type</spanx><tt>type</tt> was 2 (indicating<spanx style="verb">precert_sct_v2</spanx>)<tt>precert_sct_v2</tt>), then all three<spanx style="verb">TransItem</spanx>s<tt>TransItem</tt>s could be embedded in the certificate.</t> </section> <section anchor="get-sth"title="Retrievenumbered="true" toc="default"> <name>Retrieve LatestSTH">STH</name> <t>GET <Base URL>/ct/v2/get-sth</t> <t>No inputs.</t><t><list style="hanging"> <t hangText="Outputs:"> <list style="hanging"> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx><dl newline="true" spacing="normal"> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt> signed by thislog,log that is no older than the log'sMMD.</t> </list> </t> </list></t>MMD.</dd> </dl> </dd> </dl> </section> <section anchor="get-sth-consistency"title="Retrievenumbered="true" toc="default"> <name>Retrieve Merkle Consistency Proof between TwoSTHs">STHs</name> <t>GET <Base URL>/ct/v2/get-sth-consistency</t><t><list style="hanging"> <t hangText="Inputs:"> <list style="hanging"> <t hangText="first:"> The tree_size<dl newline="true" spacing="normal"> <dt>Inputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>first:</dt> <dd>The <tt>tree_size</tt> of the older tree, indecimal.</t> <t hangText="second:"> The tree_sizedecimal.</dd> <dt>second:</dt> <dd>The <tt>tree_size</tt> of the newer tree, in decimal(optional).</t> </list> </t> </list></t> <t><list style='empty'>(optional).</dd> </dl> <t>Both tree sizes must be from existing v2 STHs. However, because of skew, the receivingfront-endfront end may not know one or both of the existing STHs. If both are known, then only the<spanx style="verb">consistency</spanx><tt>consistency</tt> output is returned. If the first is known but the second is not (or has been omitted), then the latest known STH is returned, along with a consistency proof between the first STH and the latest. If neither are known, then the latest known STH is returned without a consistency proof.</t></list></t> <t><list style="hanging"> <t hangText="Outputs:"> <list style="hanging"> <t hangText="consistency:"> A base64 encoded <spanx style="verb">TransItem</spanx></dd> </dl> <dl newline="true" spacing="normal"> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>consistency:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">consistency_proof_v2</spanx>,<tt>consistency_proof_v2</tt> whose<spanx style="verb">tree_size_1</spanx> MUST<tt>tree_size_1</tt> <bcp14>MUST</bcp14> match the<spanx style="verb">first</spanx><tt>first</tt> input. If the<spanx style="verb">sth</spanx><tt>sth</tt> output is omitted, then<spanx style="verb">tree_size_2</spanx> MUST<tt>tree_size_2</tt> <bcp14>MUST</bcp14> match the<spanx style="verb">second</spanx><tt>second</tt> input. If<spanx style="verb">first</spanx><tt>first</tt> and<spanx style="verb">second</spanx><tt>second</tt> are equal and correspond to a known STH, the returned consistency proofMUST<bcp14>MUST</bcp14> be empty (a<spanx style="verb">consistency_path</spanx><tt>consistency_path</tt> array with zeroelements).</t> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx>elements).</dd> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt>, signed by thislog.</t> </list> </t> </list></t> <t><list style='empty'>log.</dd> </dl> <t>Note that no signature is required for the<spanx style="verb">consistency</spanx> output<tt>consistency</tt> output, as it is used to verify the consistency between twoSTHs, which are signed.</t> </list></t>signed STHs.</t> </dd> </dl> <t>Error codes:</t><texttable> <ttcol align='left'>type</ttcol> <ttcol align='left'>detail</ttcol> <c>firstUnknown</c> <c><spanx style="verb">first</spanx><table align="center"> <thead> <tr> <th align="left">type</th> <th align="left">detail</th> </tr> </thead> <tbody> <tr> <td align="left">firstUnknown</td> <td align="left"><tt>first</tt> is before the latest known STH but is not from an existingSTH.</c> <c>secondUnknown</c> <c><spanx style="verb">second</spanx>STH.</td> </tr> <tr> <td align="left">secondUnknown</td> <td align="left"><tt>second</tt> is before the latest known STH but is not from an existingSTH.</c> <c>secondBeforeFirst</c> <c><spanx style="verb">second</spanx>STH.</td> </tr> <tr> <td align="left">secondBeforeFirst</td> <td align="left"><tt>second</tt> is smaller than<spanx style="verb">first</spanx>.</c> </texttable><tt>first</tt>.</td> </tr> </tbody> </table> <t>See <xreftarget="verify_consistency"/>target="verify_consistency" format="default"/> for an outline of how to use the<spanx style="verb">consistency</spanx><tt>consistency</tt> output.</t> </section> <section anchor="get-proof-by-hash"title="Retrievenumbered="true" toc="default"> <name>Retrieve Merkle Inclusion Proof from Log by LeafHash">Hash</name> <t>GET <Base URL>/ct/v2/get-proof-by-hash</t><t><list style="hanging"> <t hangText="Inputs:"> <list style="hanging"> <t hangText="hash:"> A base64 encoded<dl newline="true" spacing="normal"> <dt>Inputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>hash:</dt> <dd>A base64-encoded v2 leafhash.</t> <t hangText="tree_size:"> The tree_sizehash.</dd> <dt>tree_size:</dt> <dd>The <tt>tree_size</tt> of the tree on which to base the proof, indecimal.</t> </list> </t> </list></t> <t><list style='empty'>decimal.</dd> </dl> <t>The<spanx style="verb">hash</spanx><tt>hash</tt> must be calculated as defined in <xreftarget="tree_leaves"/>.target="tree_leaves" format="default"/>. A v2 STH must exist for the<spanx style="verb">tree_size</spanx>.<tt>tree_size</tt>. Because of skew, thefront-endfront end may not know the requested tree head. In that case, it will return the latest STH it knows, along with an inclusion proof to that STH. If thefront-endfront end knows the requested treeheadhead, then only<spanx style="verb">inclusion</spanx><tt>inclusion</tt> is returned.</t></list></t> <t><list style="hanging"> <t hangText="Outputs:"> <list style="hanging"> <t hangText="inclusion:"> A base64 encoded <spanx style="verb">TransItem</spanx></dd> </dl> <dl newline="true" spacing="normal"> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>inclusion:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">inclusion_proof_v2</spanx><tt>inclusion_proof_v2</tt> whose<spanx style="verb">inclusion_path</spanx><tt>inclusion_path</tt> array of Merkle Tree nodes proves the inclusion of the certificate (as specified by the<spanx style="verb">hash</spanx><tt>hash</tt> parameter) in the selectedSTH.</t> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx>STH.</dd> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt>, signed by thislog.</t> </list> </t> </list></t> <t><list style='empty'>log.</dd> </dl> <t>Note that no signature is required for the<spanx style="verb">inclusion</spanx> output<tt>inclusion</tt> output, as it is used to verify inclusion in the selected STH, which is signed.</t></list></t></dd> </dl> <t>Error codes:</t><texttable> <ttcol align='left'>type</ttcol> <ttcol align='left'>detail</ttcol> <c>hashUnknown</c> <c><spanx style="verb">hash</spanx><table align="center"> <thead> <tr> <th align="left">type</th> <th align="left">detail</th> </tr> </thead> <tbody> <tr> <td align="left">hashUnknown</td> <td align="left"> <tt>hash</tt> is not the hash of a known leaf (may be caused by skew or by a known certificate not yetmerged).</c> <c>treeSizeUnknown</c> <c><spanx style="verb">hash</spanx>merged).</td> </tr> <tr> <td align="left">treeSizeUnknown</td> <td align="left"> <tt>hash</tt> is before the latest known STH but is not from an existingSTH.</c> </texttable>STH.</td> </tr> </tbody> </table> <t>See <xreftarget="verify_inclusion"/>target="verify_inclusion" format="default"/> for an outline of how to use the<spanx style="verb">inclusion</spanx><tt>inclusion</tt> output.</t> </section> <section anchor="get-all-by-hash"title="Retrievenumbered="true" toc="default"> <name>Retrieve Merkle Inclusion Proof,STHSTH, and Consistency Proof by LeafHash">Hash</name> <t>GET <Base URL>/ct/v2/get-all-by-hash</t><t><list style="hanging"> <t hangText="Inputs:"> <list style="hanging"> <t hangText="hash:"> A base64 encoded<dl newline="true" spacing="normal"> <dt>Inputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>hash:</dt> <dd>A base64-encoded v2 leafhash.</t> <t hangText="tree_size:"> The tree_sizehash.</dd> <dt>tree_size:</dt> <dd>The <tt>tree_size</tt> of the tree on which to base the proofs, indecimal.</t> </list> </t> </list></t> <t><list style='empty'>decimal.</dd> </dl> <t>The<spanx style="verb">hash</spanx><tt>hash</tt> must be calculated as defined in <xreftarget="tree_leaves"/>.target="tree_leaves" format="default"/>. A v2 STH must exist for the<spanx style="verb">tree_size</spanx>.</t> </list></t><tt>tree_size</tt>.</t> </dd> </dl> <t>Because of skew, thefront-endfront end may not know the requested tree head or the requested hash, which leads to a number of cases:</t><texttable> <ttcol align='left'>Case</ttcol> <ttcol align='left'>Response</ttcol> <c>latest<table align="center"> <thead> <tr> <th align="left">Case</th> <th align="left">Response</th> </tr> </thead> <tbody> <tr> <td align="left">latest STH < requested treehead</c> <c>Returnhead</td> <td align="left">Return latestSTH</c> <c>latestSTH.</td> </tr> <tr> <td align="left">latest STH > requested treehead</c> <c>Returnhead</td> <td align="left">Return latest STH and a consistency proof between it and the requested tree head (see <xreftarget="get-sth-consistency"/>)</c> <c>indextarget="get-sth-consistency" format="default"/>).</td> </tr> <tr> <td align="left">index of requested hash < latestSTH</c> <c>Return <spanx style="verb">inclusion</spanx></c> </texttable>STH</td> <td align="left">Return <tt>inclusion</tt>.</td> </tr> </tbody> </table> <t>Note that more than one case can betrue,true; in whichcasecase, the returned data is their union. It is also possible for none to betrue,true; in whichcasecase, thefront-end MUSTfront end <bcp14>MUST</bcp14> return an empty response.</t><t><list style="hanging"> <t hangText="Outputs:"> <list style="hanging"> <t hangText="inclusion:"> A base64 encoded <spanx style="verb">TransItem</spanx><dl newline="true" spacing="normal"> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>inclusion:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">inclusion_proof_v2</spanx><tt>inclusion_proof_v2</tt> whose<spanx style="verb">inclusion_path</spanx><tt>inclusion_path</tt> array of Merkle Tree nodes proves the inclusion of the certificate (as specified by the<spanx style="verb">hash</spanx><tt>hash</tt> parameter) in the selectedSTH.</t> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx>STH.</dd> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt>, signed by thislog.</t> <t hangText="consistency:"> A base64 encoded <spanx style="verb">TransItem</spanx>log.</dd> <dt>consistency:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">consistency_proof_v2</spanx><tt>consistency_proof_v2</tt> that proves the consistency of the requested tree head and the returnedSTH.</t> </list> </t> </list></t> <t><list style='empty'>STH.</dd> </dl> <t>Note that no signature is required for the<spanx style="verb">inclusion</spanx><tt>inclusion</tt> or<spanx style="verb">consistency</spanx> outputs<tt>consistency</tt> outputs, as they are used to verify inclusion in and consistency ofSTHs, which are signed.</t> </list></t>signed STHs.</t> </dd> </dl> <t>Errors are the same as in <xreftarget="get-proof-by-hash"/>.</t>target="get-proof-by-hash" format="default"/>.</t> <t>See <xreftarget="verify_inclusion"/>target="verify_inclusion" format="default"/> for an outline of how to use the<spanx style="verb">inclusion</spanx><tt>inclusion</tt> output, and see <xreftarget="verify_consistency"/>target="verify_consistency" format="default"/> for an outline of how to use the<spanx style="verb">consistency</spanx><tt>consistency</tt> output.</t> </section> <section anchor="get-entries"title="Retrievenumbered="true" toc="default"> <name>Retrieve Entries and STH fromLog">Log</name> <t>GET <Base URL>/ct/v2/get-entries</t><t><list style="hanging"> <t hangText="Inputs:"> <list style="hanging"> <t hangText="start:"> 0-based<dl newline="true" spacing="normal"> <dt>Inputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>start:</dt> <dd>0-based index of first entry to retrieve, indecimal.</t> <t hangText="end:"> 0-baseddecimal.</dd> <dt>end:</dt> <dd>0-based index of last entry to retrieve, indecimal.</t> </list> </t> <t hangText="Outputs:"> <list style="hanging"> <t hangText="entries:"> Andecimal.</dd> </dl> </dd> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>entries:</dt> <dd> <t>An array of objects, each consistingof <list style="hanging"> <t hangText="log_entry:"> The base64 encoded <spanx style="verb">TransItem</spanx>of:</t> <dl newline="false" spacing="normal"> <dt>log_entry:</dt> <dd>The base64-encoded <tt>TransItem</tt> structure of type<spanx style="verb">x509_entry_v2</spanx><tt>x509_entry_v2</tt> or<spanx style="verb">precert_entry_v2</spanx><tt>precert_entry_v2</tt> (see <xreftarget="log_entries"/>).</t> <t hangText="submitted_entry:"> JSONtarget="log_entries" format="default"/>).</dd> <dt>submitted_entry:</dt> <dd>JSON object equivalent to inputs that were submitted to<spanx style="verb">submit-entry</spanx>,<tt>submit-entry</tt>, with the addition of the trust anchor to the<spanx style="verb">chain</spanx><tt>chain</tt> field if the submission did not includeit.</t> <t hangText="sct:"> The base64 encoded <spanx style="verb">TransItem</spanx>it.</dd> <dt>sct:</dt> <dd>The base64-encoded <tt>TransItem</tt> of type<spanx style="verb">x509_sct_v2</spanx><tt>x509_sct_v2</tt> or<spanx style="verb">precert_sct_v2</spanx><tt>precert_sct_v2</tt>, corresponding to this logentry.</t> </list> </t> <t hangText="sth:"> A base64 encoded <spanx style="verb">TransItem</spanx>entry.</dd> <dt>sth:</dt> <dd>A base64-encoded <tt>TransItem</tt> of type<spanx style="verb">signed_tree_head_v2</spanx>,<tt>signed_tree_head_v2</tt>, signed by thislog.</t> </list> </t> </list></t>log.</dd> </dl> </dd> </dl> </dd> </dl> <t>Note that this message is not signed -- the<spanx style="verb">entries</spanx><tt>entries</tt> data can be verified by constructing the Merkle Tree Hash corresponding to a retrieved STH. All leavesMUST<bcp14>MUST</bcp14> be v2. However, a compliant v2 clientMUST NOT<bcp14>MUST NOT</bcp14> construe an unrecognizedTransItem<tt>TransItem</tt> type as an error. This means it may be unable to parse some entries, but note that each client can inspect the entries it does recognize as well as verify the integrity of the data by treating unrecognized leaves as opaque input to the tree.</t> <t>The<spanx style="verb">start</spanx><tt>start</tt> and<spanx style="verb">end</spanx><tt>end</tt> parametersSHOULD<bcp14>SHOULD</bcp14> be within the range 0 <= x <<spanx style="verb">tree_size</spanx><tt>tree_size</tt>, as returned by<spanx style="verb">get-sth</spanx><tt>get-sth</tt> in <xreftarget="get-sth"/>.</t>target="get-sth" format="default"/>.</t> <t>The<spanx style="verb">start</spanx><tt>start</tt> parameterMUST<bcp14>MUST</bcp14> be less than or equal to the<spanx style="verb">end</spanx><tt>end</tt> parameter.</t> <t>Each<spanx style="verb">submitted_entry</spanx><tt>submitted_entry</tt> output parameterMUST<bcp14>MUST</bcp14> include the trust anchor that the log used to verify the<spanx style="verb">submission</spanx>,<tt>submission</tt>, even if that trust anchor was not provided to<spanx style="verb">submit-entry</spanx><tt>submit-entry</tt> (see <xreftarget="submit-entry"/>).target="submit-entry" format="default"/>). If the<spanx style="verb">submission</spanx><tt>submission</tt> does not certify itself, then the first element of<spanx style="verb">chain</spanx> MUST<tt>chain</tt> <bcp14>MUST</bcp14> be present andMUST<bcp14>MUST</bcp14> certify the<spanx style="verb">submission</spanx>.</t><tt>submission</tt>.</t> <t>Log serversMUST<bcp14>MUST</bcp14> honor requests where 0 <=<spanx style="verb">start</spanx><tt>start</tt> <<spanx style="verb">tree_size</spanx><tt>tree_size</tt> and<spanx style="verb">end</spanx><tt>end</tt> >=<spanx style="verb">tree_size</spanx><tt>tree_size</tt> by returning a partial response covering only the valid entries in the specified range.<spanx style="verb">end</spanx><tt>end</tt> >=<spanx style="verb">tree_size</spanx><tt>tree_size</tt> could be caused by skew. Note that the following restriction may also apply:</t> <t>LogsMAY<bcp14>MAY</bcp14> restrict the number of entries that can be retrieved per<spanx style="verb">get-entries</spanx><tt>get-entries</tt> request. If a client requests more than the permitted number of entries, the logSHALL<bcp14>SHALL</bcp14> return the maximum number of entries permissible. These entriesSHALL<bcp14>SHALL</bcp14> be sequential beginning with the entry specified by<spanx style="verb">start</spanx>.<tt>start</tt>. Note that a limit on the number of entries is notimmutableimmutable, and therefore the restriction may be changed or lifted at any time and is not listed with the other Log Parameters in <xreftarget="log_parameters"/>.</t>target="log_parameters" format="default"/>.</t> <t>Because of skew, it is possible the log server will not have any entries between<spanx style="verb">start</spanx><tt>start</tt> and<spanx style="verb">end</spanx>.<tt>end</tt>. In thiscasecase, itMUST<bcp14>MUST</bcp14> return an empty<spanx style="verb">entries</spanx><tt>entries</tt> array.</t> <t>In any case, the log serverMUST<bcp14>MUST</bcp14> return the latest STH it knows about.</t> <t>See <xreftarget="verify_hash"/>target="verify_hash" format="default"/> for an outline of how to use a complete list of<spanx style="verb">log_entry</spanx><tt>log_entry</tt> entries to verify the<spanx style="verb">root_hash</spanx>.</t><tt>root_hash</tt>.</t> <t>Error codes:</t><texttable> <ttcol align='left'>type</ttcol> <ttcol align='left'>detail</ttcol> <c>startUnknown</c> <c><spanx style="verb">start</spanx><table align="center"> <thead> <tr> <th align="left">type</th> <th align="left">detail</th> </tr> </thead> <tbody> <tr> <td align="left">startUnknown</td> <td align="left"> <tt>start</tt> is greater than the number of entries in the Merkletree.</c> <c>endBeforeStart</c> <c><spanx style="verb">start</spanx>Tree.</td> </tr> <tr> <td align="left">endBeforeStart</td> <td align="left"> <tt>start</tt> cannot be greater than<spanx style="verb">end</spanx>.</c> </texttable><tt>end</tt>.</td> </tr> </tbody> </table> </section> <section anchor="get-anchors"title="Retrievenumbered="true" toc="default"> <name>Retrieve Accepted TrustAnchors">Anchors</name> <t>GET <Base URL>/ct/v2/get-anchors</t> <t>No inputs.</t><t><list style="hanging"> <t hangText="Outputs:"> <list style="hanging"> <t hangText="certificates:"> An<dl newline="true" spacing="normal"> <dt>Outputs:</dt> <dd> <dl newline="false" spacing="normal"> <dt>certificates:</dt> <dd>An array of JSON strings, each of which is abase64 encodedbase64-encoded CA certificate that is acceptable to thelog.</t> <t hangText="max_chain_length:"> Iflog.</dd> <dt>max_chain_length:</dt> <dd>If the server has chosen to limit the length of chains it accepts, this is the maximum number of certificates in the chain, in decimal. If there is no limit, this isomitted.</t> </list> </t> </list></t> <t><list style='empty'>omitted.</dd> </dl> <t>This data is notsignedsigned, and the protocol depends on the security guarantees of TLS to ensure correctness.</t></list></t></dd> </dl> </section> </section> <section anchor="tls_servers"title="TLS Servers">numbered="true" toc="default"> <name>TLS Servers</name> <t>CT-using TLS serversMUST<bcp14>MUST</bcp14> use at least one of the mechanisms described below to present one or more SCTs from one or more logs to each TLS client during full TLS handshakes, when requested by the client, where each SCT corresponds to the server certificate. (Of course, a server can only send a TLS extension if the client has specified it first.) ServersSHOULD<bcp14>SHOULD</bcp14> also present corresponding inclusion proofs and STHs.</t> <t>A server can provide SCTs using a TLS 1.3 extension(Section 4.2 of <xref target="RFC8446"></xref>)(<xref target="RFC8446" sectionFormat="of" section="4.2"/>) with type<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> (see <xreftarget="tls_transinfo_extension"/>).target="tls_transinfo_extension" format="default"/>). This mechanism allows TLS servers to participate in CT without the cooperation of CAs, unlike the other two mechanisms. It also allows SCTs and inclusion proofs to be updated on the fly.</t> <t>The server may also use an Online Certificate Status Protocol (OCSP) <xreftarget="RFC6960"></xref>target="RFC6960" format="default"/> response extension (see <xreftarget="ocsp_transinfo_extension"/>),target="ocsp_transinfo_extension" format="default"/>), providing the OCSP response as part of the TLS handshake. Providing a response during a TLS handshake is popularly known as "OCSPstapling."stapling". For TLS 1.3, the information is encoded as an extension in the<spanx style="verb">status_request</spanx><tt>status_request</tt> extension data; seeSection 4.4.2.1 of<xreftarget="RFC8446"></xref>.target="RFC8446" sectionFormat="of" section="4.4.2.1"/>. For TLS 1.2(<xref target="RFC5246"></xref>),<xref target="RFC5246" format="default"/>, the information is encoded in the<spanx style="verb">CertificateStatus</spanx><tt>CertificateStatus</tt> message; seeSection 8 of<xreftarget="RFC6066"></xref>.target="RFC6066" sectionFormat="of" section="8"/>. Using stapling also allows SCTs and inclusion proofs to be updated on the fly.</t> <t>CT information can also be encoded as an extension in the X.509v3 certificate (see <xreftarget="cert_transinfo_extension"/>).target="cert_transinfo_extension" format="default"/>). This mechanism allows the use of unmodified TLS servers, but the SCTs and inclusion proofs cannot be updated on the fly. Since the logs from which the SCTs and inclusion proofs originated won't necessarily be accepted by TLS clients for the full lifetime of the certificate, there is a risk that TLS clients may subsequently consider the certificate to benon-compliant and in need of re-issuance or the use ofnoncompliant. In such an event, one of the other twomethods for deliveringmechanisms will need to be used to deliver CTinformation.</t>information, or, if this is not possible, the certificate will need to be reissued.</t> <section anchor="tls-client-authentication"title="TLSnumbered="true" toc="default"> <name>TLS ClientAuthentication">Authentication</name> <t>This specification includes no description of how a TLS server can use CT for TLS client certificates. While this may be useful, it is not documented here for the following reasons:</t><t><list style="symbols"> <t>The<ul spacing="normal"> <li>The greater security exposure is for clients to end up interacting with an illegitimateserver.</t> <t>Inserver.</li> <li>In general, TLS client certificates are not expected to be submitted to CT logs, particularly those intended for general publicuse.</t> </list></t>use.</li> </ul> <t>A future version could include such information.</t> </section> <section anchor="multiple-scts"title="Multiple SCTs">numbered="true" toc="default"> <name>Multiple SCTs</name> <t>CT-using TLS serversSHOULD<bcp14>SHOULD</bcp14> send SCTs from multiplelogs,logs because:</t><t><list style="symbols"> <t>One or more<ul spacing="normal"> <li>The set of logs trusted by TLS clients is neither unified nor static; each client vendor may maintain an independent list of trusted logs, and, over time, new logs maynot havebecomeacceptable to all CT-using TLS clients.trusted and current logs may become distrusted. Note that client discovery, trust, and distrust of logsisare expected to be handledout-of-bandout of band andisare out of scope of thisdocument.</t> <t>Ifdocument.</li> <li>If a CA and a log collude, it is possible to temporarily hide misissuance from clients. When a TLS client requires SCTs from multiple logs to be provided, it is more difficult to mount thisattack.</t> <t>Ifattack.</li> <li>If a log misbehaves or suffers a key compromise, a consequence may be that clients cease to trust it. Since the time an SCT may be in use can be considerable (several years is common in current practice when embedded in a certificate), including SCTs from multiple logs reduces the probability of the certificate being rejected by TLSclients.</t> <t>TLSclients.</li> <li>TLS clients may have policies related to the above risks requiring TLS servers to present multiple SCTs. For example, at the time of writing, Chromium <xreftarget="Chromium.Log.Policy"></xref>target="Chromium.Log.Policy" format="default"/> requires multiple SCTs to be presented withEVExtended Validation (EV) certificates in order for the EV indicator to beshown.</t> </list></t>shown.</li> </ul> <t>To select the logs from which to obtain SCTs, a TLS server can, for example, examine the set of logs popular TLS clients accept and recognize.</t> </section> <section anchor="transitemlist-structure"title="TransItemList Structure">numbered="true" toc="default"> <name>TransItemList Structure</name> <t>Multiple SCTs, inclusion proofs, and indeed<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structures of anytype,type are combined into a list as follows:</t><figure><artwork><![CDATA[<sourcecode type="tls-presentation"><![CDATA[ opaque SerializedTransItem<1..2^16-1>; struct { SerializedTransItem trans_item_list<1..2^16-1>; } TransItemList;]]></artwork></figure>]]></sourcecode> <t>Here,<spanx style="verb">SerializedTransItem</spanx><tt>SerializedTransItem</tt> is an opaque byte string that contains the serialized<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure. This encoding ensures that TLS clients can decode each<spanx style="verb">TransItem</spanx><tt>TransItem</tt> individually (so, for example, if there is a version upgrade, out-of-date clients can still parse old<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structures while skipping over new<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structures whose versions they don't understand).</t> </section> <section anchor="presenting_transitems"title="Presentingnumbered="true" toc="default"> <name>Presenting SCTs,inclusions proofsInclusions Proofs, andSTHs">STHs</name> <t>In each<spanx style="verb">TransItemList</spanx><tt>TransItemList</tt> that is sent during a TLS handshake, the TLS serverMUST<bcp14>MUST</bcp14> include a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structure of type<spanx style="verb">x509_sct_v2</spanx><tt>x509_sct_v2</tt> or<spanx style="verb">precert_sct_v2</spanx>.</t><tt>precert_sct_v2</tt>.</t> <t>Presenting inclusion proofs and STHs in the TLS handshake helps to protect the client's privacy (see <xreftarget="fetching_inclusion_proofs"/>)target="fetching_inclusion_proofs" format="default"/>) and reduces load on log servers. Therefore, if the TLS server can obtain them, itSHOULD<bcp14>SHOULD</bcp14> also include<spanx style="verb">TransItem</spanx>s<tt>TransItem</tt>s of type<spanx style="verb">inclusion_proof_v2</spanx><tt>inclusion_proof_v2</tt> and<spanx style="verb">signed_tree_head_v2</spanx><tt>signed_tree_head_v2</tt> in the<spanx style="verb">TransItemList</spanx>.</t><tt>TransItemList</tt>.</t> </section> <section anchor="tls_transinfo_extension"title="transparency_infonumbered="true" toc="default"> <name>transparency_info TLSExtension">Extension</name> <t>Provided that a TLS client includes the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> extension type in the ClientHello and the TLS server supports the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> extension:</t><t><list style="symbols"> <t>The<ul spacing="normal"> <li>The TLS serverMUST<bcp14>MUST</bcp14> verify that the received<spanx style="verb">extension_data</spanx><tt>extension_data</tt> isempty.</t> <t>Theempty.</li> <li>The TLS serverMUST<bcp14>MUST</bcp14> construct a<spanx style="verb">TransItemList</spanx><tt>TransItemList</tt> of relevant<spanx style="verb">TransItem</spanx>s<tt>TransItem</tt>s (see <xreftarget="presenting_transitems"/>),target="presenting_transitems" format="default"/>), whichSHOULD<bcp14>SHOULD</bcp14> omit any<spanx style="verb">TransItem</spanx>s<tt>TransItem</tt>s that are already embedded in the server certificate or the stapled OCSP response (see <xreftarget="x509v3_transinfo_extension"/>).target="x509v3_transinfo_extension" format="default"/>). If the constructed<spanx style="verb">TransItemList</spanx><tt>TransItemList</tt> is not empty, then the TLS serverMUST<bcp14>MUST</bcp14> include the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> extension with the<spanx style="verb">extension_data</spanx><tt>extension_data</tt> set to this<spanx style="verb">TransItemList</spanx>.<tt>TransItemList</tt>. If the list isemptyempty, then the serverSHOULD<bcp14>SHOULD</bcp14> omit the<spanx style="verb">extension_data</spanx> element,<tt>extension_data</tt> element butMAY<bcp14>MAY</bcp14> send it with an emptyarray.</t> </list></t>array.</li> </ul> <t>TLS serversMUST<bcp14>MUST</bcp14> only include this extension in the following messages:</t><t><list style="symbols"> <t>the<ul spacing="normal"> <li>the ServerHello message (for TLS 1.2 orearlier).</t> <t>theearlier)</li> <li>the Certificate or CertificateRequest message (for TLS1.3).</t> </list></t>1.3)</li> </ul> <t>TLS serversMUST NOT<bcp14>MUST NOT</bcp14> process or include this extension when a TLS session is resumed, since session resumption uses the original session information.</t> </section> </section> <section anchor="certification-authorities"title="Certification Authorities">numbered="true" toc="default"> <name>Certification Authorities</name> <section anchor="x509v3_transinfo_extension"title="Transparencynumbered="true" toc="default"> <name>Transparency Information X.509v3Extension">Extension</name> <t>The Transparency Information X.509v3 extension, which has OID 1.3.101.75 andSHOULD<bcp14>SHOULD</bcp14> benon-critical,noncritical, contains one or more<spanx style="verb">TransItem</spanx><tt>TransItem</tt> structures in a<spanx style="verb">TransItemList</spanx>.<tt>TransItemList</tt>. This extensionMAY<bcp14>MAY</bcp14> be included in OCSP responses (see <xreftarget="ocsp_transinfo_extension"/>)target="ocsp_transinfo_extension" format="default"/>) and certificates (see <xreftarget="cert_transinfo_extension"/>).target="cert_transinfo_extension" format="default"/>). SinceRFC5280<xref target="RFC5280" format="default"/> requires the<spanx style="verb">extnValue</spanx><tt>extnValue</tt> field (an OCTET STRING) of each X.509v3 extension to include the DER encoding of an ASN.1 value, a<spanx style="verb">TransItemList</spanx> MUST NOT<tt>TransItemList</tt> <bcp14>MUST NOT</bcp14> be included directly. Instead, itMUST<bcp14>MUST</bcp14> be wrapped inside an additional OCTET STRING, which is then put into the<spanx style="verb">extnValue</spanx><tt>extnValue</tt> field:</t><figure><artwork><![CDATA[<sourcecode type="asn.1"><![CDATA[ TransparencyInformationSyntax ::= OCTET STRING]]></artwork></figure> <t><spanx style="verb">TransparencyInformationSyntax</spanx>]]></sourcecode> <t><tt>TransparencyInformationSyntax</tt> contains a<spanx style="verb">TransItemList</spanx>.</t><tt>TransItemList</tt>.</t> <section anchor="ocsp_transinfo_extension"title="OCSPnumbered="true" toc="default"> <name>OCSP ResponseExtension">Extension</name> <t>A certification authorityMAY<bcp14>MAY</bcp14> include a Transparency Information X.509v3 extension in the<spanx style="verb">singleExtensions</spanx><tt>singleExtensions</tt> of a<spanx style="verb">SingleResponse</spanx><tt>SingleResponse</tt> in an OCSP response. All included SCTs and inclusion proofsMUST<bcp14>MUST</bcp14> be for the certificate identified by the<spanx style="verb">certID</spanx><tt>certID</tt> of that<spanx style="verb">SingleResponse</spanx>,<tt>SingleResponse</tt> or for a precertificate that corresponds to that certificate.</t> </section> <section anchor="cert_transinfo_extension"title="Certificate Extension">numbered="true" toc="default"> <name>Certificate Extension</name> <t>A certification authorityMAY<bcp14>MAY</bcp14> include a Transparency Information X.509v3 extension in a certificate. All included SCTs and inclusion proofsMUST<bcp14>MUST</bcp14> be for a precertificate that corresponds to this certificate.</t> </section> </section> <section anchor="tls-feature-x509v3-extension"title="TLSnumbered="true" toc="default"> <name>TLS Feature X.509v3Extension">Extension</name> <t>A certification authoritySHOULD NOT<bcp14>SHOULD NOT</bcp14> issue any certificate that identifies the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> TLS extension in a TLS feature extension <xreftarget="RFC7633"></xref>,target="RFC7633" format="default"/>, because TLS servers are not required to support the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> TLS extension in order to participate in CT (see <xreftarget="tls_servers"/>).</t>target="tls_servers" format="default"/>).</t> </section> </section> <section anchor="clients"title="Clients">numbered="true" toc="default"> <name>Clients</name> <t>There are various different functions clients of logs might perform. We describe here some typical clients and how they should function. Any inconsistency may be used as evidence that a log has not behaved correctly, and the signatures on the data structures prevent the log from denying that misbehavior.</t> <t>All clients need various parameters in order to communicate with logs and verify their responses. These parameters are described in <xreftarget="log_parameters"/>,target="log_parameters" format="default"/>, but note that this document does not describe how the parameters are obtained, which isimplementation-dependent (see, forimplementation dependent (for example, see <xreftarget="Chromium.Policy"></xref>).</t>target="Chromium.Policy" format="default"/>).</t> <section anchor="tls_clients"title="TLS Client">numbered="true" toc="default"> <name>TLS Client</name> <section anchor="receiving_transitems"title="Receivingnumbered="true" toc="default"> <name>Receiving SCTs andinclusion proofs">Inclusion Proofs</name> <t>TLS clients receive SCTs and inclusion proofs alongside or in certificates. CT-using TLS clientsMUST<bcp14>MUST</bcp14> implement all of the three mechanisms by which TLS servers may present SCTs (see <xreftarget="tls_servers"/>).</t>target="tls_servers" format="default"/>).</t> <t>TLS clients that support the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> TLS extension (see <xreftarget="tls_transinfo_extension"/>) SHOULDtarget="tls_transinfo_extension" format="default"/>) <bcp14>SHOULD</bcp14> include it in ClientHello messages, with empty<spanx style="verb">extension_data</spanx>.<tt>extension_data</tt>. If a TLS server includes the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> TLS extension when resuming a TLS session, the TLS clientMUST<bcp14>MUST</bcp14> abort the handshake.</t> </section> <section anchor="reconstructing_tbscertificate"title="Reconstructingnumbered="true" toc="default"> <name>Reconstructing theTBSCertificate">TBSCertificate</name> <t>Validation of an SCT for a certificate (where the<spanx style="verb">type</spanx><tt>type</tt> of the<spanx style="verb">TransItem</spanx><tt>TransItem</tt> is<spanx style="verb">x509_sct_v2</spanx>)<tt>x509_sct_v2</tt>) uses the unmodified TBSCertificate component of the certificate.</t> <t>Before an SCT for a precertificate (where the<spanx style="verb">type</spanx><tt>type</tt> of the<spanx style="verb">TransItem</spanx><tt>TransItem</tt> is<spanx style="verb">precert_sct_v2</spanx>)<tt>precert_sct_v2</tt>) can be validated, the TBSCertificate component of the precertificate needs to be reconstructed from the TBSCertificate component of the certificate as follows:</t><t><list style="symbols"> <t>Remove<ul spacing="normal"> <li>Remove the Transparency Information extension (see <xreftarget="x509v3_transinfo_extension"/>).</t> <t>Removetarget="x509v3_transinfo_extension" format="default"/>).</li> <li>Remove embedded v1 SCTs, identified by OID 1.3.6.1.4.1.11129.2.4.2 (seesection 3.3 of<xreftarget="RFC6962"></xref>).target="RFC6962" sectionFormat="of" section="3.3"/>). This allows embedded v1 and v2 SCTs to co-exist in a certificate (see <xreftarget="v1_coexistence"/>).</t> </list></t>target="v1_coexistence" format="default"/>).</li> </ul> </section> <section anchor="validating-scts"title="Validating SCTs">numbered="true" toc="default"> <name>Validating SCTs</name> <t>In order to make use of a received SCT, the TLS clientMUST<bcp14>MUST</bcp14> first validate it as follows:</t><t><list style="symbols"><ul spacing="normal"> <li> <t>Compute the signature input by constructing a<spanx style="verb">TransItem</spanx><tt>TransItem</tt> of type<spanx style="verb">x509_entry_v2</spanx><tt>x509_entry_v2</tt> or<spanx style="verb">precert_entry_v2</spanx>,<tt>precert_entry_v2</tt>, depending on the SCT's<spanx style="verb">TransItem</spanx><tt>TransItem</tt> type. The<spanx style="verb">TimestampedCertificateEntryDataV2</spanx><tt>TimestampedCertificateEntryDataV2</tt> structure is constructed in the following manner:<list style="symbols"> <t><spanx style="verb">timestamp</spanx></t> <ul spacing="normal"> <li><tt>timestamp</tt> is copied from theSCT.</t> <t><spanx style="verb">tbs_certificate</spanx>SCT.</li> <li><tt>tbs_certificate</tt> is the reconstructed TBSCertificate portion of the server certificate, as described in <xreftarget="reconstructing_tbscertificate"/>.</t> <t><spanx style="verb">issuer_key_hash</spanx>target="reconstructing_tbscertificate" format="default"/>.</li> <li><tt>issuer_key_hash</tt> is computed as described in <xreftarget="tree_leaves"/>.</t> <t><spanx style="verb">sct_extensions</spanx>target="tree_leaves" format="default"/>.</li> <li><tt>sct_extensions</tt> is copied from theSCT.</t> </list></t> <t>VerifySCT.</li> </ul> </li> <li>Verify the SCT's<spanx style="verb">signature</spanx><tt>signature</tt> against the computed signature input using the public key of the corresponding log, which is identified by the<spanx style="verb">log_id</spanx>.<tt>log_id</tt>. The required signature algorithm is one of the log'sparameters.</t> </list></t>parameters.</li> </ul> <t>If the TLS client does not have the corresponding log's parameters, it cannot attempt to validate the SCT. When evaluating compliance (see <xreftarget="evaluating_compliance"/>),target="evaluating_compliance" format="default"/>), the TLS client will consider only those SCTs that it was able to validate.</t> <t>Note that SCT validation is not a substitute for the normal validation of the server certificate and its chain.</t> </section> <section anchor="fetching_inclusion_proofs"title="Fetching inclusion proofs">numbered="true" toc="default"> <name>Fetching Inclusion Proofs</name> <t>When a TLS client has validated a received SCT but does not yet possess a corresponding inclusion proof, the TLS clientMAY<bcp14>MAY</bcp14> request the inclusion proof directly from a log using<spanx style="verb">get-proof-by-hash</spanx><tt>get-proof-by-hash</tt> (<xreftarget="get-proof-by-hash"/>)target="get-proof-by-hash" format="default"/>) or<spanx style="verb">get-all-by-hash</spanx><tt>get-all-by-hash</tt> (<xreftarget="get-all-by-hash"/>).</t>target="get-all-by-hash" format="default"/>).</t> <t>Note that fetching inclusion proofs directly from a log will disclose to the log which TLS server the client has been communicating with. This may be regarded as a significant privacy concern, and so it is preferable for the TLS server to send the inclusion proofs (see <xreftarget="presenting_transitems"/>).</t>target="presenting_transitems" format="default"/>).</t> </section> <section anchor="validating_inclusion_proofs"title="Validating inclusion proofs">numbered="true" toc="default"> <name>Validating Inclusion Proofs</name> <t>When a TLS client has received, or fetched, an inclusion proof (and an STH), itSHOULD<bcp14>SHOULD</bcp14> proceed toverifyingverify the inclusion proof to the provided STH. The TLS clientSHOULD<bcp14>SHOULD</bcp14> also verify consistency between the provided STH and an STH it knows about.</t> <t>If the TLS client holds an STH that predates the SCT, itMAY,<bcp14>MAY</bcp14>, in the process of auditing, request a new STH from the log (<xreftarget="get-sth"/>),target="get-sth" format="default"/>) and then verify it by requesting a consistency proof (<xreftarget="get-sth-consistency"/>).target="get-sth-consistency" format="default"/>). Note that if the TLS client uses<spanx style="verb">get-all-by-hash</spanx>,<tt>get-all-by-hash</tt>, then it will already have the new STH.</t> </section> <section anchor="evaluating_compliance"title="Evaluating compliance">numbered="true" toc="default"> <name>Evaluating Compliance</name> <t>It is up to a client's local policy to specify the quantity and form of evidence (SCTs, inclusionproofsproofs, or a combination) needed to achieve compliance and how to handlenon-compliance.</t>noncompliance.</t> <t>A TLS client can only evaluate compliance if it has given the TLS server the opportunity to send SCTs and inclusion proofs by any of the three mechanisms that are mandatory to implement for CT-using TLS clients (see <xreftarget="receiving_transitems"/>).target="receiving_transitems" format="default"/>). Therefore, a TLS clientMUST NOT<bcp14>MUST NOT</bcp14> evaluate compliance if it did not include both the<spanx style="verb">transparency_info</spanx><tt>transparency_info</tt> and<spanx style="verb">status_request</spanx><tt>status_request</tt> TLS extensions in the ClientHello.</t> </section> </section> <section anchor="monitor"title="Monitor">numbered="true" toc="default"> <name>Monitor</name> <t>Monitors watch logs to checkthat they behave correctly,for correct behavior, for certificates of interest, or for both. For example, a monitor may be configured to report on all certificates that apply to a specific domain name when fetching new entries for consistency validation.</t> <t>A monitorMUST<bcp14>MUST</bcp14> at least inspect every new entry in every log it watches, and itMAY<bcp14>MAY</bcp14> also choose to keep copies of entire logs.</t> <t>To inspect all of the existing entries, the monitorSHOULD<bcp14>SHOULD</bcp14> follow these steps once for each log:</t><t><list style="numbers"> <t>Fetch<ol spacing="normal" type="1"> <li>Fetch the current STH (<xreftarget="get-sth"/>).</t> <t>Verifytarget="get-sth" format="default"/>).</li> <li>Verify the STHsignature.</t> <t>Fetchsignature.</li> <li>Fetch all the entries in the tree corresponding to the STH (<xreftarget="get-entries"/>).</t> <t>Iftarget="get-entries" format="default"/>).</li> <li>If applicable, check each entry to see if it's a certificate ofinterest.</t> <t>Confirminterest.</li> <li>Confirm that the tree made from the fetched entries produces the same hash as that in theSTH.</t> </list></t>STH.</li> </ol> <t>To inspect new entries, the monitorSHOULD<bcp14>SHOULD</bcp14> follow these steps repeatedly for each log:</t><t><list style="numbers"> <t>Fetch<ol spacing="normal" type="1"> <li>Fetch the current STH (<xreftarget="get-sth"/>).target="get-sth" format="default"/>). Repeat until the STH changes.ThisTo allow for experimentation, this document does not specify the pollingfrequency, to allow for experimentation.</t> <t>Verifyfrequency.</li> <li>Verify the STHsignature.</t> <t>Fetchsignature.</li> <li>Fetch all the new entries in the tree corresponding to the STH (<xreftarget="get-entries"/>).target="get-entries" format="default"/>). If they remain unavailable for an extended period, then this should be viewed as misbehavior on the part of thelog.</t> <t>Iflog.</li> <li>If applicable, check each entry to see if it's a certificate ofinterest.</t> <t>Either: <list style="numbers"> <t>Verifyinterest.</li> <li> <t>Either:</t> <ol spacing="normal" type="a"> <li>Verify that the updated list of all entries generates a tree with the same hash as the newSTH.</t> </list> Or,STH.</li> </ol> <t>Or, if it is not keeping all logentries: <list style="numbers"> <t>Fetchentries:</t> <ol spacing="normal" type="a"> <li>Fetch a consistency proof for the new STH with the previous STH (<xreftarget="get-sth-consistency"/>).</t> <t>Verifytarget="get-sth-consistency" format="default"/>).</li> <li>Verify the consistencyproof.</t> <t>Verifyproof.</li> <li>Verify that the new entries generate the corresponding elements in the consistencyproof.</t> </list></t> <t>Repeatproof.</li> </ol> </li> <li>Repeat fromstep 1.</t> </list></t>Step 1.</li> </ol> </section> <section anchor="auditing"title="Auditing">numbered="true" toc="default"> <name>Auditing</name> <t>Auditing ensures that the current published state of a log is reachable from previously published states that are known to begood,good and that the promises made by theloglog, in the form ofSCTsSCTs, have been kept. Audits are performed by monitors or TLS clients.</t> <t>In particular, there are four properties of log behaviorpropertiesthat should be checked:</t><t><list style="symbols"> <t>The<ul spacing="normal"> <li>the Maximum Merge Delay(MMD).</t> <t>The(MMD)</li> <li>the STH FrequencyCount.</t> <t>TheCount</li> <li>the append-onlyproperty.</t> <t>Theproperty</li> <li>the consistency of the log view presented to all querysources.</t> </list></t>sources</li> </ul> <t>A benign, conformant log publishes a series of STHs over time, each derived from the previous STH and the submitted entries incorporated into the log since publication of the previous STH. This can be proven through auditing of STHs. SCTs returned to TLS clients can be audited by verifying against the accompanyingcertificate,certificate and using MerkleInclusion Proofs,inclusion proofs against the log's Merkletree.</t>Tree.</t> <t>The action taken by theauditorauditor, if an auditfailsfails, is not specified, but note that ingeneralgeneral, if an audit fails, the auditor is in possession of signed proof of the log's misbehavior.</t> <t>A monitor (<xreftarget="monitor"/>)target="monitor" format="default"/>) can audit by verifying the consistency of STHs it receives,ensureensuring that each entry can be fetched and that the STH is indeed the result of making a tree from all fetched entries.</t> <t>A TLS client (<xreftarget="tls_clients"/>)target="tls_clients" format="default"/>) can audit by verifying an SCT against any STH dated after the SCT timestamp + the Maximum Merge Delay by requesting a Merkle inclusion proof (<xreftarget="get-proof-by-hash"/>).target="get-proof-by-hash" format="default"/>). It can also verify that the SCT corresponds to the server certificate it arrived with (i.e., the log entry is thatcertificate,certificate or is a precertificate corresponding to that certificate).</t> <t>Checking of the consistency of the log view presented to all entities is more difficult to perform because it requires a way to share log responses among a set of CT-usingentities,entities and is discussed in <xreftarget="misbehaving_logs"/>.</t>target="misbehaving_logs" format="default"/>.</t> </section> </section> <section anchor="algorithm-agility"title="Algorithm Agility">numbered="true" toc="default"> <name>Algorithm Agility</name> <t>It is not possible for a log to changeanyeither of its algorithms part way through its lifetime:</t><t><list style="hanging"> <t hangText="Signature algorithm:"> SCT<dl newline="false" spacing="normal"> <dt>Signature algorithm:</dt> <dd>SCT signatures must remain valid so signature algorithms can only be added, notremoved.</t> <t hangText="Hash algorithm:"> Aremoved.</dd> <dt>Hash algorithm:</dt> <dd>A log would have to support the old and new hash algorithms to allowbackwards-compatibilitybackwards compatibility with clients that are not aware of a hash algorithmchange.</t> </list></t>change.</dd> </dl> <t>Allowing multiple signature or hash algorithms for a log would require that all data structures support it and would significantly complicate client implementation, which is why it is not supported by this document.</t> <t>If it should become necessary to deprecate an algorithm used by a live log, then the logMUST<bcp14>MUST</bcp14> befrozenfrozen, as specified in <xreftarget="log_shutdown"/>target="log_shutdown" format="default"/>, and a new logSHOULD<bcp14>SHOULD</bcp14> be started. Certificates in the frozen log that have not yet expired and require new SCTsSHOULD<bcp14>SHOULD</bcp14> be submitted to the new log and the SCTs from that log used instead.</t> </section> <section anchor="iana-considerations"title="IANA Considerations">numbered="true" toc="default"> <name>IANA Considerations</name> <t>The assignment policy criteria mentioned in this section refer to the policies outlined in <xreftarget="RFC8126"></xref>.</t>target="RFC8126" format="default"/>.</t> <section anchor="additions-to-existing-registries"title="Additionsnumbered="true" toc="default"> <name>Additions toexisting registries">Existing Registries</name> <t>Thissub-sectionsubsection defines additions to existing registries.</t> <section anchor="new-entry-to-the-tls-extensiontype-registry"title="Newnumbered="true" toc="default"> <name>New Entry to the TLS ExtensionTypeRegistry">Registry</name> <t>IANAis asked to addhas added the following entry to the "TLS ExtensionType Values" registry defined in <xreftarget="RFC8446"></xref>,target="RFC8446" format="default"/>, with an assigned Value:</t><texttable> <ttcol align='left'>Value</ttcol> <ttcol align='left'>Extension Name</ttcol> <ttcol align='left'>TLS 1.3</ttcol> <ttcol align='left'>Recommended</ttcol> <ttcol align='left'>Reference</ttcol> <c>TBD</c> <c>transparency_info</c> <c>CH,<table align="center"> <thead> <tr> <th align="left">Value</th> <th align="left">Extension Name</th> <th align="left">TLS 1.3</th> <th align="left">DTLS-Only</th> <th align="left">Recommended</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">52</td> <td align="left">transparency_info</td> <td align="left">CH, CR,CT</c> <c>Y</c> <c>RFCXXXX</c> </texttable>CT</td> <td align="left">N</td> <td align="left">Y</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> </section> <section anchor="urn-sub-namespace-for-trans-urnietfparamstrans"title="URNnumbered="true" toc="default"> <name>URN Sub-namespace for TRANS(urn:ietf:params:trans)">(urn:ietf:params:trans)</name> <t>IANAis requested to addhas added a new entry in the "IETF URN Sub-namespace for Registered Protocol Parameter Identifiers" registry, following the template in <xreftarget="RFC3553"/>:</t> <t>Registry name: trans</t> <t>Specification: RFCXXXX</t> <t>Repository: https://www.iana.org/assignments/trans</t> <t>Index value: Notarget="RFC3553" format="default"/>:</t> <dl newline="false" spacing="compact"> <dt>Registry name:</dt> <dd>trans</dd> <dt>Specification:</dt> <dd>RFC 9162</dd> <dt>Repository:</dt> <dd><eref brackets="angle" target="https://www.iana.org/assignments/trans"/></dd> <dt>Index value:</dt> <dd>No transformationneeded.</t>needed.</dd> </dl> </section> </section> <section anchor="new-ct-related-registries"title="Newnumbered="true" toc="default"> <name>New CT-Relatedregistries">Registries</name> <t>IANAis requested to addhas added a new protocol registry, "Public Notary Transparency", to the list that appears athttps://www.iana.org/assignments/</t><eref brackets="angle" target="https://www.iana.org/assignments/"/></t> <t>The rest of this section definessub-registries to bethe subregistries that have been created within the newPublic"Public NotaryTransparencyTransparency" registry.</t> <section anchor="hash_algorithms"title="Hash Algorithms">numbered="true" toc="default"> <name>Hash Algorithms</name> <t>IANAis asked to establishhas established a registry of hash algorithm values, named "Hash Algorithms",thatwith the following registration procedures:</t> <table align="center"> <thead> <tr> <th align="left">Range</th> <th align="left">Registration Procedures</th> </tr> </thead> <tbody> <tr> <td>0x00-0xDF</td> <td>Specification Required</td> </tr> <tr> <td>0xE0-0xEF</td> <td>Experimental Use</td> </tr> <tr> <td>0xF0-0xFF</td> <td>Private Use</td> </tr> </tbody> </table> <t>The "Hash Algorithms" registry initially consists of:</t><texttable> <ttcol align='left'>Value</ttcol> <ttcol align='left'>Hash Algorithm</ttcol> <ttcol align='left'>OID</ttcol> <ttcol align='left'>Reference / Assignment Policy</ttcol> <c>0x00</c> <c>SHA-256</c> <c>2.16.840.1.101.3.4.2.1</c> <c><xref target="RFC6234"></xref></c> <c>0x01<table align="center"> <thead> <tr> <th align="left">Value</th> <th align="left">Hash Algorithm</th> <th align="left">OID</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">0x00</td> <td align="left">SHA-256</td> <td align="left">2.16.840.1.101.3.4.2.1</td> <td align="left"> <xref target="RFC6234" format="default"/></td> </tr> <tr> <td align="left">0x01 -0xDF</c> <c>Unassigned</c> <c> </c> <c>Specification Required</c> <c>0xE00xDF</td> <td align="left">Unassigned</td> <td align="left"> </td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0xE0 -0xEF</c> <c>Reserved</c> <c> </c> <c>Experimental Use</c> <c>0xF00xEF</td> <td align="left">Reserved for Experimental Use</td> <td align="left"> </td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0xF0 -0xFF</c> <c>Reserved</c> <c> </c> <c>Private Use</c> </texttable>0xFF</td> <td align="left">Reserved for Private Use</td> <td align="left"> </td> <td align="left">RFC 9162</td> </tr> </tbody> </table> <t>TheDesignated Expert(s)designated expert(s) should ensure that the proposed algorithm has a public specification and is suitable for use as a cryptographic hash algorithm with no known preimage or collision attacks. These attacks can damage the integrity of the log.</t> </section> <section anchor="signature_algorithms"title="Signature Algorithms">numbered="true" toc="default"> <name>Signature Algorithms</name> <t>IANAis asked to establishhas established a registry of signature algorithm values, named "Signature Algorithms".</t> <t>The following notesshould be added:</t> <t><list style="symbols"> <t>Thishave been added to the registry:</t> <blockquote> <dl newline="true"> <dt><strong>Note:</strong></dt> <dd>This is a subset of theTLS SignatureScheme Registry,"TLS SignatureScheme" registry, limited to those algorithms that are appropriate for CT. A major advantage of this is leveraging the expertise of the TLSworking groupWorking Group and itsDesignated Expert(s).</t> <t>Thedesignated expert(s).</dd> </dl> </blockquote> <blockquote> <dl newline="true"> <dt><strong>Note:</strong></dt> <dd>The value<spanx style="verb">0x0403</spanx><tt>0x0403</tt> appears twice. While this may be confusing, it is okay because the verification process is the same for both algorithms, and the choice of which to use when generating a signature is purely internal to the logserver.</t> </list></t>server.</dd> </dl> </blockquote> <t>The "Signature Algorithms" registry has the following registration procedures:</t> <table align="center"> <thead> <tr> <th align="left">Range</th> <th align="left">Registration Procedures</th> </tr> </thead> <tbody> <tr> <td>0x0000-0x0807</td> <td>Specification Required</td> </tr> <tr> <td>0x0808-0xFDFF</td> <td>Expert Review</td> </tr> <tr> <td>0xFE00-0xFEFF</td> <td>Experimental Use</td> </tr> <tr> <td>0xFF00-0xFFFF</td> <td>Private Use</td> </tr> </tbody> </table> <t>The "Signature Algorithms" registryshouldinitiallyconsistconsists of:</t><texttable> <ttcol align='left'>SignatureScheme Value</ttcol> <ttcol align='left'>Signature Algorithm</ttcol> <ttcol align='left'>Reference / Assignment Policy</ttcol> <c>0x0000<table align="center"> <thead> <tr> <th align="left">SignatureScheme Value</th> <th align="left">Signature Algorithm</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">0x0000 -0x0402</c> <c>Unassigned</c> <c>Specification Required</c> <c>ecdsa_secp256r1_sha256(0x0403)</c> <c>ECDSA0x0402</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> <tr> <td align="left">ecdsa_secp256r1_sha256 (0x0403)</td> <td align="left">ECDSA (NIST P-256) withSHA-256</c> <c><xref target="FIPS186-4"></xref></c> <c>ecdsa_secp256r1_sha256(0x0403)</c> <c>DeterministicSHA-256</td> <td align="left"> <xref target="FIPS186-4" format="default"/></td> </tr> <tr> <td align="left">ecdsa_secp256r1_sha256 (0x0403)</td> <td align="left">Deterministic ECDSA (NIST P-256) withHMAC-SHA256</c> <c><xref target="RFC6979"></xref></c> <c>0x0404HMAC-SHA256</td> <td align="left"> <xref target="RFC6979" format="default"/></td> </tr> <tr> <td align="left">0x0404 -0x0806</c> <c>Unassigned</c> <c>Specification Required</c> <c>ed25519(0x0807)</c> <c>Ed255190x0806</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> <tr> <td align="left">ed25519 (0x0807)</td> <td align="left">Ed25519 (PureEdDSA with the edwards25519curve)</c> <c><xref target="RFC8032"></xref></c> <c>0x0808curve)</td> <td align="left"> <xref target="RFC8032" format="default"/></td> </tr> <tr> <td align="left">0x0808 -0xFDFF</c> <c>Unassigned</c> <c>Expert Review</c> <c>0xFE000xFDFF</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> <tr> <td align="left">0xFE00 -0xFEFF</c> <c>Reserved</c> <c>Experimental Use</c> <c>0xFF000xFEFF</td> <td align="left">Reserved for Experimental Use</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0xFF00 -0xFFFF</c> <c>Reserved</c> <c>Private Use</c> </texttable>0xFFFF</td> <td align="left">Reserved for Private Use</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> <t>TheDesignated Expert(s)designated expert(s) should ensure that the proposed algorithm has a public specification, has a value assigned to it in theTLS SignatureScheme Registry (that IANA"TLS SignatureScheme" registry (which wasasked to establish inestablished by <xreftarget="RFC8446"></xref>),target="RFC8446" format="default"/>), and is suitable for use as a cryptographic signature algorithm.</t> </section> <section anchor="versioned_trans_types"title="VersionedTransTypes">numbered="true" toc="default"> <name>VersionedTransTypes</name> <t>IANAis asked to establishhas established a registry of<spanx style="verb">VersionedTransType</spanx><tt>VersionedTransType</tt> values, named "VersionedTransTypes".</t> <t>The following noteshould behas been added:</t><t><list style="symbols"> <t>The<blockquote> <dl newline="true"> <dt><strong>Note:</strong></dt> <dd>The range 0x0000..0x00FF is reserved so that v1 SCTs are distinguishable from v2 SCTs and other<spanx style="verb">TransItem</spanx> structures.</t> </list></t><tt>TransItem</tt> structures.</dd> </dl> </blockquote> <t>The registration procedures for the "VersionedTransTypes" registry are the following:</t> <table align="center"> <thead> <tr> <th align="left">Range</th> <th align="left">Registration Procedures</th> </tr> </thead> <tbody> <tr> <td>0x0100-0xDFFF</td> <td>Specification Required</td> </tr> <tr> <td>0xE000-0xEFFF</td> <td>Experimental Use</td> </tr> <tr> <td>0xF000-0xFFFF</td> <td>Private Use</td> </tr> </tbody> </table> <t>The "VersionedTransTypes" registryshouldinitiallyconsistconsists of:</t><texttable> <ttcol align='left'>Value</ttcol> <ttcol align='left'>Type and Version</ttcol> <ttcol align='left'>Reference / Assignment Policy</ttcol> <c>0x0000<table align="center"> <thead> <tr> <th align="left">Value</th> <th align="left">Type and Version</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">0x0000 -0x00FF</c> <c>Reserved</c> <c><xref target="RFC6962"></xref></c> <c>0x0100</c> <c>x509_entry_v2</c> <c>RFCXXXX</c> <c>0x0101</c> <c>precert_entry_v2</c> <c>RFCXXXX</c> <c>0x0102</c> <c>x509_sct_v2</c> <c>RFCXXXX</c> <c>0x0103</c> <c>precert_sct_v2</c> <c>RFCXXXX</c> <c>0x0104</c> <c>signed_tree_head_v2</c> <c>RFCXXXX</c> <c>0x0105</c> <c>consistency_proof_v2</c> <c>RFCXXXX</c> <c>0x0106</c> <c>inclusion_proof_v2</c> <c>RFCXXXX</c> <c>0x01070x00FF</td> <td align="left">Reserved</td> <td align="left"> <xref target="RFC6962" format="default"/></td> </tr> <tr> <td align="left">0x0100</td> <td align="left">x509_entry_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0101</td> <td align="left">precert_entry_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0102</td> <td align="left">x509_sct_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0103</td> <td align="left">precert_sct_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0104</td> <td align="left">signed_tree_head_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0105</td> <td align="left">consistency_proof_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0106</td> <td align="left">inclusion_proof_v2</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0x0107 -0xDFFF</c> <c>Unassigned</c> <c>Specification Required</c> <c>0xE0000xDFFF</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> <tr> <td align="left">0xE000 -0xEFFF</c> <c>Reserved</c> <c>Experimental Use</c> <c>0xF0000xEFFF</td> <td align="left">Reserved for Experimental Use</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0xF000 -0xFFFF</c> <c>Reserved</c> <c>Private Use</c> </texttable>0xFFFF</td> <td align="left">Reserved for Private Use</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> <t>TheDesignated Expert(s)designated expert(s) should review the public specification to ensure that it is detailed enough to ensure implementation interoperability.</t> </section> <section anchor="log_artifact_extension_registry"title="Lognumbered="true" toc="default"> <name>Log ArtifactExtension Registry">Extensions</name> <t>IANAis asked to establishhas established a registry of<spanx style="verb">ExtensionType</spanx><tt>ExtensionType</tt> values, named "Log ArtifactExtensions", thatExtensions".</t> <t>The registration procedures for the "Log Artifact Extensions" registry are the following:</t> <table align="center"> <thead> <tr> <th align="left">Range</th> <th align="left">Registration Procedures</th> </tr> </thead> <tbody> <tr> <td>0x0000-0xDFFF</td> <td>Specification Required</td> </tr> <tr> <td>0xE000-0xEFFF</td> <td>Experimental Use</td> </tr> <tr> <td>0xF000-0xFFFF</td> <td>Private Use</td> </tr> </tbody> </table> <t>The "Log Artifact Extensions" registry initially consists of:</t><texttable> <ttcol align='left'>ExtensionType</ttcol> <ttcol align='left'>Status</ttcol> <ttcol align='left'>Use</ttcol> <ttcol align='left'>Reference / Assignment Policy</ttcol> <c>0x0000<table align="center"> <thead> <tr> <th align="left">ExtensionType</th> <th align="left">Status</th> <th align="left">Use</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">0x0000 -0xDFFF</c> <c>Unassigned</c> <c>n/a</c> <c>Specification Required</c> <c>0xE0000xDFFF</td> <td align="left">Unassigned</td> <td align="left">n/a</td> <td align="left"> </td> </tr> <tr> <td align="left">0xE000 -0xEFFF</c> <c>Reserved</c> <c>n/a</c> <c>Experimental Use</c> <c>0xF0000xEFFF</td> <td align="left">Reserved for Experimental Use</td> <td align="left">n/a</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">0xF000 -0xFFFF</c> <c>Reserved</c> <c>n/a</c> <c>Private Use</c> </texttable>0xFFFF</td> <td align="left">Reserved for Private Use</td> <td align="left">n/a</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> <t>The "Use" column should contain one or both of the following values:</t><t><list style="symbols"> <t>"SCT",<ul spacing="normal"> <li>"SCT", for extensions specified for use in Signed CertificateTimestamps.</t> <t>"STH",Timestamps.</li> <li>"STH", for extensions specified for use in Signed TreeHeads.</t> </list></t>Heads.</li> </ul> <t>TheDesignated Expert(s)designated expert(s) should review the public specification to ensure that it is detailed enough to ensure implementation interoperability. They should also verify that the extension is appropriate to the contexts in which it is specified to be used (SCT, STH, or both).</t> </section> <section anchor="log_id_registry"title="Log IDs Registry">numbered="true" toc="default"> <name>Log IDs</name> <t>IANAis asked to establishhas established a registry of Log IDs, named "LogIDs", thatIDs".</t> <t>The registry's registration procedure is First Come First Served.</t> <t>The "Log IDs" registry initially consists of:</t><texttable> <ttcol align='left'>Log ID</ttcol> <ttcol align='left'>Log<table align="center"> <thead> <tr> <th align="left">Log ID</th> <th align="left">Log BaseURL</ttcol> <ttcol align='left'>Log Operator</ttcol> <ttcol align='left'>Reference / Assignment Policy</ttcol> <c>1.3.101.8192URL</th> <th align="left">Log Operator</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">1.3.101.8192 -1.3.101.16383</c> <c>Unassigned</c> <c>Unassigned</c> <c>First Come First Served</c> <c>1.3.101.80.01.3.101.16383</td> <td align="left">Unassigned</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> <tr> <td align="left">1.3.101.80.0 -1.3.101.80.*</c> <c>Unassigned</c> <c>Unassigned</c> <c>First Come First Served</c> </texttable> <t>All1.3.101.80.*</td> <td align="left">Unassigned</td> <td align="left">Unassigned</td> <td align="left"> </td> </tr> </tbody> </table> <t>The following notes have been added to the registry:</t> <blockquote> <dl newline="true"> <dt><strong>Note:</strong></dt> <dd>All OIDs in the range from 1.3.101.8192 to 1.3.101.16383 have been set aside for Log IDs. This is a limited resource of 8,192 OIDs, each of which has an encoded length of 4octets.</t> <t>Theoctets.</dd> </dl> </blockquote> <blockquote> <dl newline="true"> <dt><strong>Note:</strong></dt> <dd>The 1.3.101.80 arc has also been set aside for Log IDs. This is an unlimited resource, but only the 128 OIDs from 1.3.101.80.0 to 1.3.101.80.127 have an encoded length of only 4octets.</t>octets.</dd> </dl> </blockquote> <t>Each application for the allocation of a Log IDMUST<bcp14>MUST</bcp14> be accompanied by:</t><t><list style="symbols"> <t>the<ul spacing="normal"> <li>the Log's Base URL (see <xreftarget="log_parameters"/>).</t> <t>thetarget="log_parameters" format="default"/>) and</li> <li>the Log Operator's contactdetails.</t> </list></t>details.</li> </ul> <t>IANA is asked to reject any request to update a Log ID or Log Base URL in thisregistry,registry because these fields are immutable (see <xreftarget="log_parameters"/>).</t>target="log_parameters" format="default"/>).</t> <t>IANA is asked to accept requests from log operators to update their contact details in this registry.</t> <t>Since log operators can choose to not use this registry (see <xreftarget="log_id"/>),target="log_id" format="default"/>), it is not expected to be a global directory of all logs.</t> </section> <section anchor="error-types-registry"title="Error Types Registry">numbered="true" toc="default"> <name>Error Types</name> <t>IANAis requested to createhas created a new registry for errors, the "Error Types" registry.</t><t>Requirements<t>The registration procedure for this registryareis Specification Required.</t> <t>This registryshould havehas the following three fields:</t><texttable> <ttcol align='left'>Field Name</ttcol> <ttcol align='left'>Type</ttcol> <ttcol align='left'>Reference</ttcol> <c>identifier</c> <c>string</c> <c>RFCXXXX</c> <c>meaning</c> <c>string</c> <c>RFCXXXX</c> <c>reference</c> <c>string</c> <c>RFCXXXX</c> </texttable><table align="center"> <thead> <tr> <th align="left">Field Name</th> <th align="left">Type</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">Identifier</td> <td align="left">string</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">Meaning</td> <td align="left">string</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">Reference</td> <td align="left">string</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> <t>The initial values of the "Error Types" registry, which areas follows,taken from the textabove:</t> <texttable> <ttcol align='left'>Identifier</ttcol> <ttcol align='left'>Meaning</ttcol> <ttcol align='left'>Reference</ttcol> <c>malformed</c> <c>Thein <xref target="client_messages" format="default"/>, are as follows:</t> <table align="center"> <thead> <tr> <th align="left">Identifier</th> <th align="left">Meaning</th> <th align="left">Reference</th> </tr> </thead> <tbody> <tr> <td align="left">malformed</td> <td align="left">The request could not beparsed.</c> <c>RFCXXXX</c> <c>badSubmission</c> <c><spanx style="verb">submission</spanx>parsed.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">badSubmission</td> <td align="left"><tt>submission</tt> is neither a valid certificate nor a validprecertificate</c> <c>RFCXXXX</c> <c>badType</c> <c><spanx style="verb">type</spanx>precertificate.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">badType</td> <td align="left"><tt>type</tt> is neither 1 nor2</c> <c>RFCXXXX</c> <c>badChain</c> <c>The2.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">badChain</td> <td align="left">The first element of<spanx style="verb">chain</spanx><tt>chain</tt> is not the certifier of the<spanx style="verb">submission</spanx>,<tt>submission</tt>, or the second element does not certify the first,etc.</c> <c>RFCXXXX</c> <c>badCertificate</c> <c>Oneetc.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">badCertificate</td> <td align="left">One or more certificates inthe <spanx style="verb">chain</spanx><tt>chain</tt> are not valid (e.g., not properlyencoded)</c> <c>RFCXXXX</c> <c>unknownAnchor</c> <c>Theencoded).</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">unknownAnchor</td> <td align="left">The last element of<spanx style="verb">chain</spanx><tt>chain</tt> (or, if<spanx style="verb">chain</spanx><tt>chain</tt> is an empty array, the<spanx style="verb">submission</spanx>) both<tt>submission</tt>) is not,andnor isnotit certified by, an accepted trustanchor</c> <c>RFCXXXX</c> <c>shutdown</c> <c>Theanchor.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">shutdown</td> <td align="left">The log is no longer acceptingsubmissions</c> <c>RFCXXXX</c> <c>firstUnknown</c> <c><spanx style="verb">first</spanx>submissions.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">firstUnknown</td> <td align="left"><tt>first</tt> is before the latest known STH but is not from an existingSTH.</c> <c>RFCXXXX</c> <c>secondUnknown</c> <c><spanx style="verb">second</spanx>STH.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">secondUnknown</td> <td align="left"><tt>second</tt> is before the latest known STH but is not from an existingSTH.</c> <c>RFCXXXX</c> <c>secondBeforeFirst</c> <c><spanx style="verb">second</spanx>STH.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">secondBeforeFirst</td> <td align="left"><tt>second</tt> is smaller than<spanx style="verb">first</spanx>.</c> <c>RFCXXXX</c> <c>hashUnknown</c> <c><spanx style="verb">hash</spanx><tt>first</tt>.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">hashUnknown</td> <td align="left"><tt>hash</tt> is not the hash of a known leaf (may be caused by skew or by a known certificate not yetmerged).</c> <c>RFCXXXX</c> <c>treeSizeUnknown</c> <c><spanx style="verb">hash</spanx>merged).</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">treeSizeUnknown</td> <td align="left"><tt>hash</tt> is before the latest known STH but is not from an existingSTH.</c> <c>RFCXXXX</c> <c>startUnknown</c> <c><spanx style="verb">start</spanx>STH.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">startUnknown</td> <td align="left"><tt>start</tt> is greater than the number of entries in the Merkletree.</c> <c>RFCXXXX</c> <c>endBeforeStart</c> <c><spanx style="verb">start</spanx>Tree.</td> <td align="left">RFC 9162</td> </tr> <tr> <td align="left">endBeforeStart</td> <td align="left"><tt>start</tt> cannot be greater than<spanx style="verb">end</spanx>.</c> <c>RFCXXXX</c> </texttable><tt>end</tt>.</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> </section> </section> <section anchor="oid-assignment"title="OID Assignment">numbered="true" toc="default"> <name>OID Assignment</name> <t>IANAis asked to assign onehas assigned an object identifier from the "SMI Security for PKIX Module Identifier" registry to identify the ASN.1 module in <xreftarget="asn1_module"/>target="asn1_module" format="default"/> of thisdocument with an assigned Decimal value.</t> <texttable> <ttcol align='left'>Decimal</ttcol> <ttcol align='left'>Description</ttcol> <ttcol align='left'>References</ttcol> <c>TBD</c> <c>id-mod-public-notary-v2</c> <c>RFCXXXX</c> </texttable>document.</t> <table align="center"> <thead> <tr> <th align="left">Decimal</th> <th align="left">Description</th> <th align="left">References</th> </tr> </thead> <tbody> <tr> <td align="left">102</td> <td align="left">id-mod-public-notary-v2</td> <td align="left">RFC 9162</td> </tr> </tbody> </table> </section> </section> <section anchor="security-considerations"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>With CAs, logs, and servers performing the actions described here, TLS clients can use logs and signed timestamps to reduce the likelihood that they will accept misissued certificates. If a server presents a valid signed timestamp for a certificate, then the client knows that a log has committed to publishing the certificate. From this, the client knows that monitors acting for the subject of the certificate have had some time to notice the misissuance and take some action, such as asking a CA to revoke a misissued certificate. A signed timestamp does not guaranteethisthis, though, since appropriate monitors might not have checked the logs or the CA might have refused to revoke the certificate.</t> <t>In addition, if TLS clients will not accept unlogged certificates, then site owners will have a greater incentive to submit certificates to logs, possibly with the assistance of their CA, increasing the overall transparency of the system.</t> <section anchor="misissued-certificates"title="Misissued Certificates">numbered="true" toc="default"> <name>Misissued Certificates</name> <t>Misissued certificates that have not been publicly logged, and thus do not have a valid SCT, are not considered compliant. Misissued certificates that do have an SCT from a log will appear in that public log within the Maximum Merge Delay, assuming the log is operating correctly. Since a log is allowed to serve an STH of any age up to the MMD, the maximum period of time during which a misissued certificate can be used without being available for audit is twice the MMD.</t> </section> <section anchor="detection-of-misissue"title="Detectionnumbered="true" toc="default"> <name>Detection ofMisissue">Misissue</name> <t>The logs do not themselves detect misissued certificates; they rely instead on interested parties, such as domain owners, to monitor them and take corrective action when a misissue is detected.</t> </section> <section anchor="misbehaving_logs"title="Misbehaving Logs">numbered="true" toc="default"> <name>Misbehaving Logs</name> <t>A log can misbehave in several ways. Examplesinclude:include the following: failing to incorporate a certificate with an SCT in the Merkle Tree within the MMD; presenting different, conflicting views of the Merkle Tree at different times and/or to different parties; issuing STHs too frequently; mutating the signature of a logged certificate; and failing to present a chain containing the certifier of a logged certificate.</t> <t>Violation of the MMD contract is detected by log clients requesting a Merkle inclusion proof (<xreftarget="get-proof-by-hash"/>)target="get-proof-by-hash" format="default"/>) for each observed SCT. These checks can be asynchronous and need only be done once per certificate. However, note that there may be privacy concerns (see <xreftarget="fetching_inclusion_proofs"/>).</t>target="fetching_inclusion_proofs" format="default"/>).</t> <t>Violation of the append-only property or the STH issuance rate limit can be detected by multiple clients comparing their instances of the STHs. This technique, known as"gossip,""gossip", is an active area of research and not defined here. Proof of misbehavior in such cases wouldbe:be either a series of STHs that were issued too closely together, proving violation of the STH issuance ratelimit;limit, or an STH with a root hash that does not match the one calculated from a copy of the log, proving violation of the append-only property.</t> <t>Clients that report back SCTs can be tracked or traced if a log produces multiple STHs or SCTs with the same timestamp and data but different signatures. LogsSHOULD<bcp14>SHOULD</bcp14> mitigate this risk by either:</t><t><list style="symbols"> <t>Using<ul spacing="normal"> <li>using deterministic signatureschemes, or</t> <t>Producingschemes or</li> <li>producing no more than one SCT for each distinct submission and no more than one STH for each distincttree_size.<tt>tree_size</tt>. Each of these SCTs and STHs can be stored by the log and served to other clients that submit the same certificate or request the sameSTH.</t> </list></t>STH.</li> </ul> </section> <section anchor="requiring_multiple_scts"title="Multiple SCTs">numbered="true" toc="default"> <name>Multiple SCTs</name> <t>By requiring TLS servers to offer multiple SCTs, each from a different log, TLS clients reduce the effectiveness of an attack where a CA and a log collude (see <xreftarget="multiple-scts"/>).</t>target="multiple-scts" format="default"/>).</t> </section> <section anchor="leakage-of-dns-information"title="Leakagenumbered="true" toc="default"> <name>Leakage of DNSInformation">Information</name> <t>Malicious monitors can use logs to learn about the existence of domain names that might not otherwise be easy to discover. Some subdomain labels may reveal information about the service and software for which the subdomain is used, which in turn might facilitate targeted attacks.</t> </section> </section><section anchor="acknowledgements" title="Acknowledgements"> <t>The authors would like to thank Erwann Abelea, Robin Alden, Andrew Ayer, Richard Barnes, Al Cutter, David Drysdale, Francis Dupont, Adam Eijdenberg, Stephen Farrell, Daniel Kahn Gillmor, Paul Hadfield, Brad Hill, Jeff Hodges, Paul Hoffman, Jeffrey Hutzelman, Kat Joyce, Stephen Kent, SM, Alexey Melnikov, Linus Nordberg, Chris Palmer, Trevor Perrin, Pierre Phaneuf, Eric Rescorla, Rich Salz, Melinda Shore, Ryan Sleevi, Martin Smith, Carl Wallace and Paul Wouters for their valuable contributions.</t> <t>A big thank you to Symantec for kindly donating the OIDs from the 1.3.101 arc that are used in this document.</t> </section></middle> <back><references title='Normative References'> <reference anchor='RFC2119' target='https://www.rfc-editor.org/info/rfc2119'> <front> <title>Key words for use in RFCs to Indicate Requirement Levels</title> <author fullname='S. Bradner' initials='S.' surname='Bradner'><organization/></author> <date month='March' year='1997'/> <abstract><t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract> </front> <seriesInfo name='BCP' value='14'/> <seriesInfo name='RFC' value='2119'/> <seriesInfo name='DOI' value='10.17487/RFC2119'/> </reference> <reference anchor='RFC3986' target='https://www.rfc-editor.org/info/rfc3986'> <front> <title>Uniform Resource Identifier (URI): Generic Syntax</title> <author fullname='T. Berners-Lee' initials='T.' surname='Berners-Lee'><organization/></author> <author fullname='R. Fielding' initials='R.' surname='Fielding'><organization/></author> <author fullname='L. Masinter' initials='L.' surname='Masinter'><organization/></author> <date month='January' year='2005'/> <abstract><t>A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='STD' value='66'/> <seriesInfo name='RFC' value='3986'/> <seriesInfo name='DOI' value='10.17487/RFC3986'/> </reference> <reference anchor='RFC4648' target='https://www.rfc-editor.org/info/rfc4648'> <front> <title>The Base16, Base32, and Base64 Data Encodings</title> <author fullname='S. Josefsson' initials='S.' surname='Josefsson'><organization/></author> <date month='October' year='2006'/> <abstract><t>This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='RFC' value='4648'/> <seriesInfo name='DOI' value='10.17487/RFC4648'/> </reference> <reference anchor='RFC5246' target='https://www.rfc-editor.org/info/rfc5246'> <front> <title>The Transport Layer Security (TLS) Protocol Version 1.2</title> <author fullname='T. Dierks' initials='T.' surname='Dierks'><organization/></author> <author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author> <date month='August' year='2008'/> <abstract><t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='RFC' value='5246'/> <seriesInfo name='DOI' value='10.17487/RFC5246'/> </reference> <reference anchor='RFC5280' target='https://www.rfc-editor.org/info/rfc5280'> <front> <title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title> <author fullname='D. Cooper' initials='D.' surname='Cooper'><organization/></author> <author fullname='S. Santesson' initials='S.' surname='Santesson'><organization/></author> <author fullname='S. Farrell' initials='S.' surname='Farrell'><organization/></author> <author fullname='S. Boeyen' initials='S.' surname='Boeyen'><organization/></author> <author fullname='R. Housley' initials='R.' surname='Housley'><organization/></author> <author fullname='W. Polk' initials='W.' surname='Polk'><organization/></author> <date month='May' year='2008'/> <abstract><t>This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='RFC' value='5280'/> <seriesInfo name='DOI' value='10.17487/RFC5280'/> </reference> <reference anchor='RFC5652' target='https://www.rfc-editor.org/info/rfc5652'> <front> <title>Cryptographic Message Syntax (CMS)</title> <author fullname='R. Housley' initials='R.' surname='Housley'><organization/></author> <date month='September' year='2009'/> <abstract><t>This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='STD' value='70'/> <seriesInfo name='RFC' value='5652'/> <seriesInfo name='DOI' value='10.17487/RFC5652'/> </reference> <reference anchor='RFC6066' target='https://www.rfc-editor.org/info/rfc6066'> <front> <title>Transport Layer Security (TLS) Extensions: Extension Definitions</title> <author fullname='D. Eastlake 3rd' initials='D.' surname='Eastlake 3rd'><organization/></author> <date month='January' year='2011'/> <abstract><t>This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK]</t></abstract> </front> <seriesInfo name='RFC' value='6066'/> <seriesInfo name='DOI' value='10.17487/RFC6066'/> </reference> <reference anchor='RFC6234' target='https://www.rfc-editor.org/info/rfc6234'> <front> <title>US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)</title> <author fullname='D. Eastlake 3rd' initials='D.' surname='Eastlake 3rd'><organization/></author> <author fullname='T. Hansen' initials='T.' surname='Hansen'><organization/></author> <date month='May' year='2011'/> <abstract><t>Federal Information Processing Standard, FIPS</t></abstract> </front> <seriesInfo name='RFC' value='6234'/> <seriesInfo name='DOI' value='10.17487/RFC6234'/> </reference> <reference anchor='RFC6960' target='https://www.rfc-editor.org/info/rfc6960'> <front> <title>X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP</title> <author fullname='S. Santesson' initials='S.' surname='Santesson'><organization/></author> <author fullname='M. Myers' initials='M.' surname='Myers'><organization/></author> <author fullname='R. Ankney' initials='R.' surname='Ankney'><organization/></author> <author fullname='A. Malpani' initials='A.' surname='Malpani'><organization/></author> <author fullname='S. Galperin' initials='S.' surname='Galperin'><organization/></author> <author fullname='C. Adams' initials='C.' surname='Adams'><organization/></author> <date month='June' year='2013'/> <abstract><t>This document specifies a protocol useful in determining the current status of a digital certificate without requiring Certificate Revocation Lists (CRLs). Additional mechanisms addressing PKIX operational requirements are specified in separate documents. This document obsoletes RFCs 2560 and 6277. It also updates RFC 5912.</t></abstract> </front> <seriesInfo name='RFC' value='6960'/> <seriesInfo name='DOI' value='10.17487/RFC6960'/> </reference> <reference anchor='RFC6979' target='https://www.rfc-editor.org/info/rfc6979'> <front> <title>Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA)</title> <author fullname='T. Pornin' initials='T.' surname='Pornin'><organization/></author> <date month='August' year='2013'/> <abstract><t>This document defines a deterministic digital signature generation procedure. Such signatures are compatible with standard Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) digital signatures and can be processed with unmodified verifiers, which need not be aware of the procedure described therein. Deterministic signatures retain the cryptographic security features associated with digital signatures but can be more easily implemented in various environments, since they do not need access to a source of high-quality randomness.</t></abstract> </front> <seriesInfo name='RFC' value='6979'/> <seriesInfo name='DOI' value='10.17487/RFC6979'/> </reference> <reference anchor='RFC7231' target='https://www.rfc-editor.org/info/rfc7231'> <front> <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title> <author fullname='R. Fielding' initials='R.' role='editor' surname='Fielding'><organization/></author> <author fullname='J. Reschke' initials='J.' role='editor' surname='Reschke'><organization/></author> <date month='June' year='2014'/> <abstract><t>The Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.</t></abstract> </front> <seriesInfo name='RFC' value='7231'/> <seriesInfo name='DOI' value='10.17487/RFC7231'/> </reference> <reference anchor='RFC7633' target='https://www.rfc-editor.org/info/rfc7633'> <front> <title>X.509v3 Transport Layer Security (TLS) Feature Extension</title> <author fullname='P. Hallam-Baker' initials='P.' surname='Hallam-Baker'><organization/></author> <date month='October' year='2015'/> <abstract><t>The purpose of the TLS feature extension is to prevent downgrade attacks that are not otherwise prevented by the TLS protocol. In particular, the TLS feature extension may be used to mandate support for revocation checking features in the TLS protocol such as Online Certificate Status Protocol (OCSP) stapling. Informing clients that an OCSP status response will always be stapled permits an immediate failure in the case that the response is not stapled. This in turn prevents a denial-of-service attack that might otherwise be possible.</t></abstract> </front> <seriesInfo name='RFC' value='7633'/> <seriesInfo name='DOI' value='10.17487/RFC7633'/> </reference> <reference anchor='RFC7807' target='https://www.rfc-editor.org/info/rfc7807'> <front> <title>Problem Details for HTTP APIs</title> <author fullname='M. Nottingham' initials='M.' surname='Nottingham'><organization/></author> <author fullname='E. Wilde' initials='E.' surname='Wilde'><organization/></author> <date month='March' year='2016'/> <abstract><t>This document defines a "problem detail" as a way to carry machine- readable details of errors in a HTTP response to avoid the need to define new error response formats for HTTP APIs.</t></abstract> </front> <seriesInfo name='RFC' value='7807'/> <seriesInfo name='DOI' value='10.17487/RFC7807'/> </reference> <reference anchor='RFC8032' target='https://www.rfc-editor.org/info/rfc8032'> <front> <title>Edwards-Curve Digital Signature Algorithm (EdDSA)</title> <author fullname='S. Josefsson' initials='S.' surname='Josefsson'><organization/></author> <author fullname='I. Liusvaara' initials='I.' surname='Liusvaara'><organization/></author> <date month='January' year='2017'/> <abstract><t>This document describes elliptic curve signature scheme Edwards-curve Digital Signature Algorithm (EdDSA). The algorithm is instantiated with recommended parameters for the edwards25519 and edwards448 curves. An example implementation and test vectors are provided.</t></abstract> </front> <seriesInfo name='RFC' value='8032'/> <seriesInfo name='DOI' value='10.17487/RFC8032'/> </reference> <reference anchor='RFC8174' target='https://www.rfc-editor.org/info/rfc8174'> <front> <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title> <author fullname='B. Leiba' initials='B.' surname='Leiba'><organization/></author> <date month='May' year='2017'/> <abstract><t>RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t></abstract> </front> <seriesInfo name='BCP' value='14'/> <seriesInfo name='RFC' value='8174'/> <seriesInfo name='DOI' value='10.17487/RFC8174'/> </reference> <reference anchor='RFC8259' target='https://www.rfc-editor.org/info/rfc8259'> <front> <title>The JavaScript Object Notation (JSON) Data Interchange Format</title> <author fullname='T. Bray' initials='T.' role='editor' surname='Bray'><organization/></author> <date month='December' year='2017'/> <abstract><t>JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.</t><t>This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.</t></abstract> </front> <seriesInfo name='STD' value='90'/> <seriesInfo name='RFC' value='8259'/> <seriesInfo name='DOI' value='10.17487/RFC8259'/> </reference> <reference anchor='RFC8391' target='https://www.rfc-editor.org/info/rfc8391'> <front> <title>XMSS: eXtended Merkle Signature Scheme</title> <author fullname='A. Huelsing' initials='A.' surname='Huelsing'><organization/></author> <author fullname='D. Butin' initials='D.' surname='Butin'><organization/></author> <author fullname='S. Gazdag' initials='S.' surname='Gazdag'><organization/></author> <author fullname='J. Rijneveld' initials='J.' surname='Rijneveld'><organization/></author> <author fullname='A. Mohaisen' initials='A.' surname='Mohaisen'><organization/></author> <date month='May' year='2018'/> <abstract><t>This note describes the eXtended Merkle Signature Scheme (XMSS), a hash-based digital signature system that is based on existing descriptions in scientific literature. This note specifies Winternitz One-Time Signature Plus (WOTS+), a one-time signature scheme; XMSS, a single-tree scheme; and XMSS^MT, a multi-tree variant of XMSS. Both XMSS and XMSS^MT use WOTS+ as a main building block. XMSS provides cryptographic digital signatures without relying on the conjectured hardness of mathematical problems. Instead, it is proven that it only relies on the properties of cryptographic hash functions. XMSS provides strong security guarantees and is even secure when the collision resistance of the underlying hash function is broken. It is suitable for compact implementations, is relatively simple to implement, and naturally resists side-channel attacks. Unlike most other signature systems, hash-based signatures can so far withstand known attacks using quantum computers.</t></abstract> </front> <seriesInfo name='RFC' value='8391'/> <seriesInfo name='DOI' value='10.17487/RFC8391'/> </reference> <reference anchor='RFC8446' target='https://www.rfc-editor.org/info/rfc8446'> <front> <title>The Transport Layer Security (TLS) Protocol Version 1.3</title> <author fullname='E. Rescorla' initials='E.' surname='Rescorla'><organization/></author> <date month='August' year='2018'/> <abstract><t>This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t><t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.</t></abstract> </front> <seriesInfo name='RFC' value='8446'/> <seriesInfo name='DOI' value='10.17487/RFC8446'/> </reference><references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3986.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4648.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5246.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5280.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5652.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6066.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6234.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6960.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6979.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7231.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7633.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7807.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8032.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8259.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8391.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/> <reference anchor="HTML401"target="http://www.w3.org/TR/1999/REC-html401-19991224">target="https://www.w3.org/TR/2018/SPSD-html401-20180327"> <front> <title>HTML 4.01 Specification</title> <author initials="D." surname="Raggett" fullname="David Raggett"><organization></organization><organization/> </author> <author initials="A." surname="Le Hors" fullname="Arnaud Le Hors"><organization></organization><organization/> </author> <author initials="I." surname="Jacobs" fullname="Ian Jacobs"><organization></organization><organization/> </author> <dateyear="1999" month="December" day="24"/>year="2018" month="March"/> </front> <seriesInfoname="World Wide Web Consortiumname="W3C Recommendation"value="REC-html401-19991224"/>value="SPSD-html401-20180327"/> </reference> <reference anchor="FIPS186-4" target="http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf"> <front><title>FIPS PUB 186-4</title> <author > <organization>NIST</organization><title>Digital Signature Standard (DSS)</title> <author> <organization>National Institute of Standards and Technology</organization> </author> <date year="2013"month="July" day="01"/>month="July"/> </front> <seriesInfo name="FIPS PUB" value="186-4"/> </reference> <reference anchor="UNIXTIME" target="http://pubs.opengroup.org/onlinepubs/9699919799.2016edition/basedefs/V1_chap04.html#tag_04_16"> <front> <title>The Open Group Base Specifications Issue7 IEEE Std 1003.1-2008, 2016 Edition</title> <author >7</title> <author> <organization>IEEE</organization> </author> <dateyear="n.d."/>year="2016"/> </front> <seriesInfo name="IEEE Std" value="1003.1-2008"/> <refcontent>Section 4.16 Seconds Since the Epoch</refcontent> </reference> <referenceanchor="X690" >anchor="X690"> <front> <title>Information technology - ASN.1 encodingRules:rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)</title><author ><author> <organization>ITU-T</organization> </author> <dateyear="2015" month="November"/> </front> <seriesInfo name="ISO/IEC" value="8825-1:2002"/> </reference> <reference anchor='RFC3553' target='https://www.rfc-editor.org/info/rfc3553'> <front> <title>An IETF URN Sub-namespace for Registered Protocol Parameters</title> <author fullname='M. Mealling' initials='M.' surname='Mealling'><organization/></author> <author fullname='L. Masinter' initials='L.' surname='Masinter'><organization/></author> <author fullname='T. Hardie' initials='T.' surname='Hardie'><organization/></author> <author fullname='G. Klyne' initials='G.' surname='Klyne'><organization/></author> <date month='June' year='2003'/> <abstract><t>This document describes a new sub-delegation for the 'ietf' URN namespace for registered protocol items. The 'ietf' URN namespace is defined in RFC 2648 as a root for persistent URIs that refer to IETF- defined resources. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>year="2021" month="February"/> </front> <seriesInfoname='BCP' value='73'/> <seriesInfo name='RFC' value='3553'/>name="ITU-T Recommendation" value="X.690"/> <seriesInfoname='DOI' value='10.17487/RFC3553'/>name="ISO/IEC" value="8825-1"/> </reference> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3553.xml"/> </references><references title='Informative References'> <reference anchor='RFC6962' target='https://www.rfc-editor.org/info/rfc6962'> <front> <title>Certificate Transparency</title> <author fullname='B. Laurie' initials='B.' surname='Laurie'><organization/></author> <author fullname='A. Langley' initials='A.' surname='Langley'><organization/></author> <author fullname='E. Kasper' initials='E.' surname='Kasper'><organization/></author> <date month='June' year='2013'/> <abstract><t>This document describes an experimental protocol for publicly logging the existence of Transport Layer Security (TLS) certificates as they are issued or observed, in a manner that allows anyone to audit certificate authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs.</t><t>Logs are network services that implement the protocol operations for submissions and queries that are defined in this document.</t></abstract> </front> <seriesInfo name='RFC' value='6962'/> <seriesInfo name='DOI' value='10.17487/RFC6962'/> </reference> <reference anchor='RFC8126' target='https://www.rfc-editor.org/info/rfc8126'> <front> <title>Guidelines for Writing an IANA Considerations Section in RFCs</title> <author fullname='M. Cotton' initials='M.' surname='Cotton'><organization/></author> <author fullname='B. Leiba' initials='B.' surname='Leiba'><organization/></author> <author fullname='T. Narten' initials='T.' surname='Narten'><organization/></author> <date month='June' year='2017'/> <abstract><t>Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).</t><t>To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.</t><t>This is the third edition of this document; it obsoletes RFC 5226.</t></abstract> </front> <seriesInfo name='BCP' value='26'/> <seriesInfo name='RFC' value='8126'/> <seriesInfo name='DOI' value='10.17487/RFC8126'/> </reference> <reference anchor='RFC8820' target='https://www.rfc-editor.org/info/rfc8820'> <front> <title>URI Design and Ownership</title> <author fullname='M. Nottingham' initials='M.' surname='Nottingham'><organization/></author> <date month='June' year='2020'/> <abstract><t>Section 1.1.1 of RFC 3986 defines URI syntax as "a federated and extensible naming system wherein each scheme's specification may further restrict the syntax and semantics of identifiers using that scheme." In other words, the structure of a URI is defined by its scheme. While it is common for schemes to further delegate their substructure to the URI's owner, publishing independent standards that mandate particular forms of substructure in URIs is often problematic.</t><t>This document provides guidance on the specification of URI substructure in standards.</t><t>This document obsoletes RFC 7320 and updates RFC 3986.</t></abstract> </front> <seriesInfo name='BCP' value='190'/> <seriesInfo name='RFC' value='8820'/> <seriesInfo name='DOI' value='10.17487/RFC8820'/> </reference><references> <name>Informative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6962.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8820.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5912.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6268.xml"/> <reference anchor="CrosbyWallach" target="http://static.usenix.org/event/sec09/tech/full_papers/crosby.pdf"> <front> <title>Efficient Data Structures for Tamper-Evident Logging</title> <author initials="S." surname="Crosby" fullname="Scott A. Crosby"><organization></organization><organization/> </author> <author initials="D." surname="Wallach" fullname="Dan S. Wallach"><organization></organization><organization/> </author> <date year="2009" month="August"/> </front><seriesInfo name="Proceedings<refcontent>Proceedings of the 18th USENIX SecuritySymposium," value="Montreal"/>Symposium, Montreal</refcontent> </reference> <reference anchor="Chromium.Policy"target="http://www.chromium.org/Home/chromium-security/certificate-transparency">target="https://googlechrome.github.io/CertificateTransparency/ct_policy.html"> <front> <title>Chromium CertificateTransparency</title> <author >Transparency Policy</title> <author> <organization>The Chromium Projects</organization> </author><date year="2014"/></front> </reference> <reference anchor="JSON.Metadata" target="https://www.gstatic.com/ct/log_list/log_list_schema.json"> <front> <title>Chromium Log Metadata JSON Schema</title><author ><author> <organization>The Chromium Projects</organization> </author><date year="2014"/></front> </reference> <reference anchor="Chromium.Log.Policy"target="http://www.chromium.org/Home/chromium-security/certificate-transparency/log-policy">target="https://googlechrome.github.io/CertificateTransparency/log_policy.html"> <front> <title>Chromium Certificate Transparency Log Policy</title><author ><author> <organization>The Chromium Projects</organization> </author><date year="2014"/></front> </reference> <reference anchor="CABBR" target="https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.7.3.pdf"> <front> <title>Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates</title><author ><author> <organization>CA/Browser Forum</organization> </author> <date month="October" year="2020"/> </front><format type="PDF" target="https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.7.3.pdf"/><seriesInfo name="Version" value="1.7.3"/> </reference> <reference anchor="X.680"> <front> <title>Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation</title> <author> <organization>ITU-T</organization> </author> <date year="2021" month="February"/> </front> <seriesInfo name="ITU-T Recommendation" value="X.680"/> </reference> </references> </references> <section anchor="v1_coexistence"title="Supportingnumbered="true" toc="default"> <name>Supporting v1 and v2simultaneously (Informative)">Simultaneously (Informative)</name> <t>Certificate Transparency logs have to be either v1 (conforming to <xreftarget="RFC6962"></xref>)target="RFC6962" format="default"/>) or v2 (conforming to this document), as the data structures areincompatibleincompatible, and so a v2 log could not issue a valid v1 SCT.</t> <t>CT clients, however, can support v1 and v2SCTs,SCTs for the samecertificate,certificate simultaneously, as v1 SCTs are delivered in different TLS,X.509X.509, and OCSP extensions than v2 SCTs.</t> <t>v1 and v2 SCTs for X.509 certificates can be validated independently. For precertificates, v2 SCTs should be embedded in the TBSCertificate before submission of the TBSCertificate (inside a v1 precertificate, as described inSection 3.1. of<xreftarget="RFC6962"></xref>)target="RFC6962" sectionFormat="of" section="3.1"/>) to a v1 log so that TLS clients conforming to <xreftarget="RFC6962"></xref>target="RFC6962" format="default"/> but not this document are oblivious to the embedded v2 SCTs. An issuer can follow these steps to produce an X.509 certificate with embedded v1 and v2 SCTs:</t><t><list style="symbols"> <t>Create<ul spacing="normal"> <li>Create a CMSprecertificateprecertificate, as described in <xreftarget="precertificates"/>target="precertificates" format="default"/>, and submit it to v2logs.</t> <t>Embedlogs.</li> <li>Embed the obtained v2 SCTs in the TBSCertificate, as described in <xreftarget="cert_transinfo_extension"/>.</t> <t>Usetarget="cert_transinfo_extension" format="default"/>.</li> <li>Use that TBSCertificate to create a v1 precertificate, as described inSection 3.1. of<xreftarget="RFC6962"></xref>target="RFC6962" sectionFormat="of" section="3.1"/>, and submit it to v1logs.</t> <t>Embedlogs.</li> <li>Embed the v1 SCTs in the TBSCertificate, as described inSection 3.3 of<xreftarget="RFC6962"></xref>.</t> <t>Signtarget="RFC6962" sectionFormat="of" section="3.3"/>.</li> <li>Sign that TBSCertificate (which now contains v1 and v2 SCTs) to issue the final X.509certificate.</t> </list></t>certificate.</li> </ul> </section> <section anchor="asn1_module"title="Annumbered="true" toc="default"> <name>An ASN.1 Module(Informative)">(Informative)</name> <t>The following ASN.1 <xref target="X.680" format="default"/> module may be useful toimplementors.</t> <figure><artwork><![CDATA[implementors. This module references <xref target="RFC5912" format="default"/> and <xref target="RFC6268" format="default"/>.</t> <sourcecode type="asn.1"><![CDATA[ CertificateTransparencyV2Module-2021 -- { id-mod-public-notary-v2 from above, in iso(1) identified-organization(3) ... form } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS EXTENSION FROM PKIX-CommonTypes-2009 -- RFC 5912 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) } CONTENT-TYPE FROM CryptographicMessageSyntax-2010 -- RFC 6268 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) } TBSCertificate FROM PKIX1Explicit-2009 -- RFC 5912 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; -- -- Section 3.2. Precertificates -- ct-tbsCertificate CONTENT-TYPE ::= { TYPE TBSCertificate IDENTIFIED BY id-ct-tbsCertificate } id-ct-tbsCertificate OBJECT IDENTIFIER ::= { 1 3 101 78 } -- -- Section 7.1. Transparency Information X.509v3 Extension -- ext-transparencyInfo EXTENSION ::= { SYNTAX TransparencyInformationSyntax IDENTIFIED BY id-ce-transparencyInfo CRITICALITY { FALSE } } id-ce-transparencyInfo OBJECT IDENTIFIER ::= { 1 3 101 75 } TransparencyInformationSyntax ::= OCTET STRING -- -- Section 7.1.1. OCSP Response Extension -- ext-ocsp-transparencyInfo EXTENSION ::= { SYNTAX TransparencyInformationSyntax IDENTIFIED BY id-pkix-ocsp-transparencyInfo CRITICALITY { FALSE } } id-pkix-ocsp-transparencyInfo OBJECT IDENTIFIER ::= id-ce-transparencyInfo -- -- Section 8.1.2. Reconstructing the TBSCertificate -- ext-embeddedSCT-CTv1 EXTENSION ::= { SYNTAX SignedCertificateTimestampList IDENTIFIED BY id-ce-embeddedSCT-CTv1 CRITICALITY { FALSE } } id-ce-embeddedSCT-CTv1 OBJECT IDENTIFIER ::= { 1 3 6 1 4 1 11129 2 4 2 } SignedCertificateTimestampList ::= OCTET STRING END]]></artwork></figure>]]></sourcecode> </section> <section anchor="acknowledgements" numbered="false" toc="default"> <name>Acknowledgements</name> <t>The authors would like to thank <contact fullname="Erwann Abelea"/>, <contact fullname="Robin Alden"/>, <contact fullname="Andrew Ayer"/>, <contact fullname="Richard Barnes"/>, <contact fullname="Al Cutter"/>, <contact fullname="David Drysdale"/>, <contact fullname="Francis Dupont"/>, <contact fullname="Adam Eijdenberg"/>, <contact fullname="Stephen Farrell"/>, <contact fullname="Daniel Kahn Gillmor"/>, <contact fullname="Paul Hadfield"/>, <contact fullname="Brad Hill"/>, <contact fullname="Jeff Hodges"/>, <contact fullname="Paul Hoffman"/>, <contact fullname="Jeffrey Hutzelman"/>, <contact fullname="Kat Joyce"/>, <contact fullname="Emilia Kasper"/>, <contact fullname="Stephen Kent"/>, <contact fullname="Adam Langley"/>, <contact fullname="SM"/>, <contact fullname="Alexey Melnikov"/>, <contact fullname="Linus Nordberg"/>, <contact fullname="Chris Palmer"/>, <contact fullname="Trevor Perrin"/>, <contact fullname="Pierre Phaneuf"/>, <contact fullname="Eric Rescorla"/>, <contact fullname="Rich Salz"/>, <contact fullname="Melinda Shore"/>, <contact fullname="Ryan Sleevi"/>, <contact fullname="Martin Smith"/>, <contact fullname="Carl Wallace"/>, and <contact fullname="Paul Wouters"/> for their valuable contributions.</t> <t>A big thank you to Symantec for kindly donating the OIDs from the 1.3.101 arc that are used in this document.</t> </section> </back><!-- ##markdown-source: H4sIALh5LmEAA+y9aVsbWbYu+D1+RVzyeTqhSpIBD2mTWdmXxLjMKU9tcFad znSjQAogCkmhowiBKdv3t/d617CHiBDgnE7dfppzKg1SxJ73mte7+v1+Uhf1 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