<?xmlversion="1.0" encoding="US-ASCII"?>version='1.0' encoding='UTF-8'?> <!DOCTYPE rfc SYSTEM"rfc2629.dtd" [ <!ENTITY RFC2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"> <!ENTITY RFC5246 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5246.xml"> <!ENTITY RFC6347 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6347.xml"> <!ENTITY RFC7301 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7301.xml"> <!ENTITY RFC8174 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.8174.xml"> <!ENTITY RFC8446 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.8446.xml"> ]> <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> <?rfc strict="yes" ?> <?rfc toc="yes"?> <?rfc tocdepth="4"?> <?rfc symrefs="yes"?> <?rfc sortrefs="yes" ?> <?rfc compact="yes" ?> <?rfc subcompact="no" ?>"rfc2629-xhtml.ent"> <rfc number="8701" xmlns:xi="http://www.w3.org/2001/XInclude" category="info" consensus="true" docName="draft-ietf-tls-grease-04"ipr="trust200902">ipr="trust200902" obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="4" symRefs="true" sortRefs="true" version="3"> <front> <title>ApplyingGREASEGenerate Random Extensions And Sustain Extensibility (GREASE) to TLS Extensibility</title> <seriesInfo name="RFC" value="8701"/> <author fullname="David Benjamin" initials="D." surname="Benjamin"> <organization>Google LLC</organization> <address> <email>davidben@google.com</email> </address> </author> <dateyear="2019" />year="2020" month="January"/> <area>General</area> <keyword>TLS, GREASE</keyword> <abstract> <t>This document describes GREASE (Generate Random Extensions And Sustain Extensibility), a mechanism to prevent extensibility failures in the TLS ecosystem. It reserves a set of TLS protocol values that may be advertised to ensure peers correctly handle unknown values.</t> </abstract> </front> <middle> <sectiontitle="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>The TLS protocol <xref target="RFC8446"/>format="default"/> includes several points of extensibility, including the list of cipher suites and several lists of extensions. The values transmitted in these lists identify implementation capabilities. TLS follows a model where one side, usually the client, advertisescapabilitiescapabilities, and the peer, usually the server, selects them. The responding side must ignore unknown values so that new capabilities may be introduced to the ecosystem while maintaining interoperability.</t> <t>However, bugs may cause an implementation to reject unknown values. It will interoperate with existing peers, so the mistake may spread through the ecosystem unnoticed. Later, when new values are defined, updated peers will discover that the metaphorical joint in the protocol has rusted shut andthatthe new values cannot be deployed without interoperability failures.</t> <t>To avoid this problem, this document reserves some currently unused values for TLS implementations to advertise at random. Correctly implemented peers will ignore these values and interoperate. Peers that do not tolerate unknown values will fail to interoperate, revealing the mistake before it is widespread.</t> <t>In keeping with the rusted joint metaphor, this technique isnamed GREASEcalled "GREASE" (Generate Random Extensions And Sustain Extensibility).</t> <sectiontitle="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 <xreftarget="RFC2119">RFC 2119</xref>[RFC2119]target="RFC2119"/> <xreftarget="RFC8174">RFC 8174</xref>target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</t>here. </t> </section> </section> <sectiontitle="GREASE Values">numbered="true" toc="default"> <name>GREASE Values</name> <t>This document reserves a number of TLS protocol values, referred to as GREASE values. These values were allocated sparsely to discourage server implementations from conditioning on them. For convenience, they were also chosen so all types share a number scheme with a consistent pattern while avoiding collisions with any existing applicable registries in TLS.</t><t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH. The values prefaced with {TBD} are suggested values and subject to change prior to final allocation by IANA.</t><t>The following values are reserved as GREASE values for cipher suites andALPNApplication-Layer Protocol Negotiation (ALPN) <xref target="RFC7301"/>format="default"/> identifiers:</t><?rfc subcompact="yes" ?> <t><list> <t>{TBD} {0x0A,0x0A}</t> <t>{TBD} {0x1A,0x1A}</t> <t>{TBD} {0x2A,0x2A}</t> <t>{TBD} {0x3A,0x3A}</t> <t>{TBD} {0x4A,0x4A}</t> <t>{TBD} {0x5A,0x5A}</t> <t>{TBD} {0x6A,0x6A}</t> <t>{TBD} {0x7A,0x7A}</t> <t>{TBD} {0x8A,0x8A}</t> <t>{TBD} {0x9A,0x9A}</t> <t>{TBD} {0xAA,0xAA}</t> <t>{TBD} {0xBA,0xBA}</t> <t>{TBD} {0xCA,0xCA}</t> <t>{TBD} {0xDA,0xDA}</t> <t>{TBD} {0xEA,0xEA}</t> <t>{TBD} {0xFA,0xFA}</t> </list></t> <?rfc subcompact="no" ?><ul empty="true"> <li>{0x0A,0x0A} </li> <li>{0x1A,0x1A} </li> <li>{0x2A,0x2A} </li> <li>{0x3A,0x3A} </li> <li>{0x4A,0x4A} </li> <li>{0x5A,0x5A} </li> <li>{0x6A,0x6A} </li> <li>{0x7A,0x7A} </li> <li>{0x8A,0x8A} </li> <li>{0x9A,0x9A} </li> <li>{0xAA,0xAA} </li> <li>{0xBA,0xBA} </li> <li>{0xCA,0xCA} </li> <li>{0xDA,0xDA} </li> <li>{0xEA,0xEA} </li> <li>{0xFA,0xFA} </li> </ul> <t>The following values are reserved as GREASE values for extensions, named groups, signature algorithms, and versions:</t><?rfc subcompact="yes" ?> <t><list> <t>{TBD} 0x0A0A</t> <t>{TBD} 0x1A1A</t> <t>{TBD} 0x2A2A</t> <t>{TBD} 0x3A3A</t> <t>{TBD} 0x4A4A</t> <t>{TBD} 0x5A5A</t> <t>{TBD} 0x6A6A</t> <t>{TBD} 0x7A7A</t> <t>{TBD} 0x8A8A</t> <t>{TBD} 0x9A9A</t> <t>{TBD} 0xAAAA</t> <t>{TBD} 0xBABA</t> <t>{TBD} 0xCACA</t> <t>{TBD} 0xDADA</t> <t>{TBD} 0xEAEA</t> <t>{TBD} 0xFAFA</t> </list></t> <?rfc subcompact="no" ?><ul empty="true"> <li>0x0A0A </li> <li>0x1A1A </li> <li>0x2A2A </li> <li>0x3A3A </li> <li>0x4A4A </li> <li>0x5A5A </li> <li>0x6A6A </li> <li>0x7A7A </li> <li>0x8A8A </li> <li>0x9A9A </li> <li>0xAAAA </li> <li>0xBABA </li> <li>0xCACA </li> <li>0xDADA </li> <li>0xEAEA </li> <li>0xFAFA </li> </ul> <t>The values allocated above are thus no longer available for use as TLS or DTLS <xref target="RFC6347"/>format="default"/> version numbers.</t> <t>The following values are reserved as GREASE values forPskKeyExchangeModes.</t> <?rfc subcompact="yes" ?> <t><list> <t>{TBD} 0x0B</t> <t>{TBD} 0x2A</t> <t>{TBD} 0x49</t> <t>{TBD} 0x68</t> <t>{TBD} 0x87</t> <t>{TBD} 0xA6</t> <t>{TBD} 0xC5</t> <t>{TBD} 0xE4</t> </list></t> <?rfc subcompact="no" ?>PskKeyExchangeModes:</t> <ul empty="true"> <li>0x0B </li> <li>0x2A </li> <li>0x49 </li> <li>0x68 </li> <li>0x87 </li> <li>0xA6 </li> <li>0xC5 </li> <li>0xE4 </li> </ul> </section> <sectiontitle="Client-Initiatednumbered="true" toc="default"> <name>Client-Initiated ExtensionPoints">Points</name> <t>Most extension points in TLS are offered by the client and selected by the server. This section details client and server behavior around GREASE values for these.</t> <sectiontitle="Client Behavior">numbered="true" toc="default"> <name>Client Behavior</name> <t>When sending a ClientHello, a clientMAY<bcp14>MAY</bcp14> behave as follows:</t><t><list style="symbols"> <t>A<ul spacing="normal"> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE cipher suite values and advertise them in the "cipher_suites"field.</t> <t>Afield.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE extension values and advertise them as extensions with varying length andcontents.</t> <t>Acontents.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE named group values and advertise them in the "supported_groups" extension, if sent. ItMAY<bcp14>MAY</bcp14> also send KeyShareEntry values for a subset of those selected in the "key_share" extension. For each of these, the "key_exchange" fieldMAY<bcp14>MAY</bcp14> be anyvalue.</t> <t>Avalue.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE signature algorithm values and advertise them in the "signature_algorithms" or "signature_algorithms_cert" extensions, ifsent.</t> <t>Asent.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE version values and advertise them in the "supported_versions" extension, ifsent.</t> <t>Asent.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE PskKeyExchangeMode values and advertise them in the "psk_key_exchange_modes" extension, ifsent.</t> <t>Asent.</li> <li>A clientMAY<bcp14>MAY</bcp14> select one or more GREASE ALPN identifiers and advertise them in the "application_layer_protocol_negotiation" extension, ifsent.</t> </list></t>sent.</li> </ul> <t>ClientsMUST<bcp14>MUST</bcp14> reject GREASE values when negotiated by the server. In particular, the clientMUST<bcp14>MUST</bcp14> fail the connection if a GREASE value appearsanyin any of the following:</t><t><list style="symbols"> <t>The<ul spacing="normal"> <li>The "version" value in a ServerHello orHelloRetryRequest</t> <t>TheHelloRetryRequest</li> <li>The "cipher_suite" value in aServerHello</t> <t>AnyServerHello</li> <li>Any ServerHelloextension</t> <t>Anyextension</li> <li>Any HelloRetryRequest, EncryptedExtensions, or Certificate extension in TLS1.3</t> <t>The1.3</li> <li>The "namedcurve" value in a ServerKeyExchange for anECDHEEphemeral Elliptic Curve Diffie-Hellman (ECDHE) cipher in TLS 1.2 <xref target="RFC5246"/>format="default"/> orearlier</t> <t>Theearlier</li> <li>The signature algorithm in a ServerKeyExchange signature in TLS 1.2 orearlier</t> <t>Theearlier</li> <li>The signature algorithm in a server CertificateVerify signature in TLS1.3</t> </list></t>1.3</li> </ul> <t>Note that this can be implemented without special processing on the client. The client is already required to reject unknown server-selected values, so it may leave GREASE values as unknown and reuse the existing logic.</t> </section> <sectiontitle="Server Behavior">numbered="true" toc="default"> <name>Server Behavior</name> <t> When processing a ClientHello, serversMUST NOT<bcp14>MUST NOT</bcp14> treat GREASE values differently from any unknown value. ServersMUST NOT<bcp14>MUST NOT</bcp14> negotiate any GREASE value when offered in a ClientHello. ServersMUST<bcp14>MUST</bcp14> correctly ignore unknown values in a ClientHello and attempt to negotiate with one of the remaining parameters. (There may not be any known parameters remaining, in which case parameter negotiation will fail.) </t> <t>Note that these requirements are restatements or corollaries of existing server requirements in TLS.</t> </section> </section> <sectiontitle="Server-Initiatednumbered="true" toc="default"> <name>Server-Initiated ExtensionPoints">Points</name> <t>Some extension points are offered by the server and selected by the client. This section details client and server behavior around GREASE values for these.</t> <sectiontitle="Server Behavior">numbered="true" toc="default"> <name>Server Behavior</name> <t>When sending a CertificateRequest in TLS 1.3, a serverMAY<bcp14>MAY</bcp14> behave as follows:</t><t><list style="symbols"> <t>A<ul spacing="normal"> <li>A serverMAY<bcp14>MAY</bcp14> select one or more GREASE extension values and advertise them as extensions with varying length andcontents.</t> <t>Acontents.</li> <li>A serverMAY<bcp14>MAY</bcp14> select one or more GREASE signature algorithm values and advertise them in the "signature_algorithms" or "signature_algorithms_cert" extensions, ifpresent.</t> </list></t>present.</li> </ul> <t>When sending a NewSessionTicket message in TLS 1.3, a serverMAY<bcp14>MAY</bcp14> select one or more GREASE extension values and advertise them as extensions with varying length and contents.</t> <t>ServersMUST<bcp14>MUST</bcp14> reject GREASE values when negotiated by the client. In particular, the serverMUST<bcp14>MUST</bcp14> fail the connection if a GREASE value appearsanyin any of the following:</t><t><list style="symbols"> <t>Any<ul spacing="normal"> <li>Any Certificate extension in TLS1.3</t> <t>The1.3</li> <li>The signature algorithm in a client CertificateVerifysignature</t> </list></t>signature</li> </ul> <t>Note that this can be implemented without special processing on the server. The server is already required to reject unknown client-selected values, so it may leave GREASE values as unknown and reuse the existing logic.</t> </section> <sectiontitle="Client Behavior">numbered="true" toc="default"> <name>Client Behavior</name> <t> When processing a CertificateRequest or NewSessionTicket, clientsMUST NOT<bcp14>MUST NOT</bcp14> treat GREASE values differently from any unknown value. ClientsMUST NOT<bcp14>MUST NOT</bcp14> negotiate any GREASE value when offered by the server. ClientsMUST<bcp14>MUST</bcp14> correctly ignore unknown values offered by the server and attempt to negotiate with one of the remaining parameters. (There may not be any known parameters remaining, in which case parameter negotiation will fail.) </t> <t>Note that these requirements are restatements or corollaries of existing client requirements in TLS.</t> </section> </section> <sectiontitle="Sendingnumbered="true" toc="default"> <name>Sending GREASEValues">Values</name> <t>Implementations advertising GREASE valuesSHOULD<bcp14>SHOULD</bcp14> select them at random. This is intended to encourage implementations to ignore all unknown values rather than any individual value. ImplementationsMUST<bcp14>MUST</bcp14> honor protocol specifications when sending GREASE values. For instance,section 4.2 of<xref target="RFC8446"/>sectionFormat="of" section="4.2"/> forbids duplicate extension types within a single extension block. Implementations sending multiple GREASE extensions in a single blockthusmust therefore ensure the same value is not selected twice.</t> <t>ImplementationsSHOULD<bcp14>SHOULD</bcp14> balance diversity in GREASE advertisements with determinism. For example, a clientwhichthat randomly varies GREASE value positions for each connection may only fail against a broken server with some probability. This risks the failure being masked by automatic retries. A clientwhichthat positions GREASE values deterministically over a period of time (such as a single software release) stresses fewer cases but is more likely to detect bugs from those cases.</t> </section> <section anchor="IANA"title="IANA Considerations">numbered="true" toc="default"> <name>IANA Considerations</name> <t>This document updates theTLS"TLS CipherSuite Registry,Suites" registry, availablefromat <ereftarget="https://www.iana.org/assignments/tls-parameters"/>:</t> <texttable title="Additionstarget="https://www.iana.org/assignments/tls-parameters" brackets="angle"/>:</t> <table align="center"> <name>Additions to the TLS CipherSuite Registry"> <ttcol align='center'>Value</ttcol> <ttcol align='center'>Description</ttcol> <ttcol align='center'>DTLS-OK</ttcol> <ttcol align='center'>Recommended</ttcol> <ttcol align='center'>Reference</ttcol> <c>{TBD} {0x0A,0x0A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x1A,0x1A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x2A,0x2A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x3A,0x3A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x4A,0x4A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x5A,0x5A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x6A,0x6A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x7A,0x7A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x8A,0x8A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0x9A,0x9A}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xAA,0xAA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xBA,0xBA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xCA,0xCA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xDA,0xDA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xEA,0xEA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} {0xFA,0xFA}</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> </texttable> <t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH. The cipher suite numbers listed in the first column are numbers used for interoperability testing and it's suggested that IANA use these values for assignment.</t>Suites Registry</name> <thead > <tr > <th align="center">Value</th> <th align="center">Description</th> <th align="center">DTLS-OK</th> <th align="center">Recommended</th> <th align="center">Reference</th> </tr> </thead> <tbody> <tr> <td align="center">{0x0A,0x0A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x1A,0x1A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x2A,0x2A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x3A,0x3A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x4A,0x4A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x5A,0x5A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x6A,0x6A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x7A,0x7A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x8A,0x8A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0x9A,0x9A}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xAA,0xAA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xBA,0xBA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xCA,0xCA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xDA,0xDA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xEA,0xEA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">{0xFA,0xFA}</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> </tbody> </table> <t>This document updates the "TLS SupportedGroups Registry,Groups" registry, availablefromat <ereftarget="https://www.iana.org/assignments/tls-parameters"/>:</t> <texttable title="Additionstarget="https://www.iana.org/assignments/tls-parameters" brackets="angle"/>:</t> <table align="center"> <name>Additions to the TLS Supported GroupsRegistry"> <ttcol align='center'>Value</ttcol> <ttcol align='center'>Description</ttcol> <ttcol align='center'>DTLS-OK</ttcol> <ttcol align='center'>Recommended</ttcol> <ttcol align='center'>Reference</ttcol> <c>{TBD} 2570</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 6682</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 10794</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 14906</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 19018</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 23130</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 27242</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 31354</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 35466</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 39578</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 43690</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 47802</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 51914</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 56026</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 60138</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> <c>{TBD} 64250</c> <c>Reserved</c> <c>Y</c> <c>N</c> <c>(this document)</c> </texttable> <t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH. The named group numbers listed in the first column are numbers used for interoperability testing and it's suggested that IANA use these values for assignment.</t>Registry</name> <thead> <tr> <th align="center">Value</th> <th align="center">Description</th> <th align="center">DTLS-OK</th> <th align="center">Recommended</th> <th align="center">Reference</th> </tr> </thead> <tbody> <tr> <td align="center">2570</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">6682</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">10794</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">14906</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">19018</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">23130</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">27242</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">31354</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">35466</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">39578</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">43690</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">47802</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">51914</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">56026</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">60138</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">64250</td> <td align="center">Reserved</td> <td align="center">Y</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> </tbody> </table> <t>This document updates the "TLS ExtensionTypeValuesValues" registry, availablefromat <ereftarget="https://www.iana.org/assignments/tls-extensiontype-values"/>:</t> <texttable title="Additionstarget="https://www.iana.org/assignments/tls-extensiontype-values" brackets="angle"/>:</t> <table align="center"> <name>Additions to the TLS ExtensionType Valuesregistry"> <ttcol align='center'>Value</ttcol> <ttcol align='center'>Extension name</ttcol> <ttcol align='center'>TLS 1.3</ttcol> <ttcol align='center'>Recommended</ttcol> <ttcol align='center'>Reference</ttcol> <c>{TBD} 2570</c> <c>Reserved</c> <c>CH,Registry</name> <thead> <tr> <th align="center">Value</th> <th align="center">Extension Name</th> <th align="center">TLS 1.3</th> <th align="center">Recommended</th> <th align="center">Reference</th> </tr> </thead> <tbody> <tr> <td align="center">2570</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 6682</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">6682</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 10794</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">10794</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 14906</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">14906</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 19018</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">19018</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 23130</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">23130</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 27242</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">27242</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 31354</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">31354</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 35466</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">35466</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 39578</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">39578</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 43690</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">43690</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 47802</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">47802</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 51914</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">51914</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 56026</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">56026</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 60138</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">60138</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> <c>{TBD} 64250</c> <c>Reserved</c> <c>CH,NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">64250</td> <td align="center">Reserved</td> <td align="center">CH, CR,NST</c> <c>N</c> <c>(this document)</c> </texttable> <t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH. The extension numbers listed in the first column are numbers used for interoperability testing and it's suggested that IANA use these values for assignment.</t>NST</td> <td align="center">N</td> <td align="center">[RFC8701]</td> </tr> </tbody> </table> <t>This document updates theTLS"TLS Application-Layer Protocol Negotiation (ALPN) ProtocolIDsIDs" registry, availablefromat <ereftarget="https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values"/>:</t> <texttable title="Additionstarget="https://www.iana.org/assignments/tls-extensiontype-values" brackets="angle"/>:</t> <table align="center"> <name>Additions to theALPNTLS Application-Layer Protocol Negotiation (ALPN) Protocol IDsregistry"> <ttcol align='center'>Protocol</ttcol> <ttcol align='center'>Identification Sequence</ttcol> <ttcol align='center'>Reference</ttcol> <c>Reserved</c> <c>{TBD} 0x0A 0x0A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x1A 0x1A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x2A 0x2A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x3A 0x3A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x4A 0x4A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x5A 0x5A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x6A 0x6A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x7A 0x7A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x8A 0x8A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0x9A 0x9A</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xAA 0xAA</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xBA 0xBA</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xCA 0xCA</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xDA 0xDA</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xEA 0xEA</c> <c>(this document)</c> <c>Reserved</c> <c>{TBD} 0xFA 0xFA</c> <c>(this document)</c> </texttable>Registry</name> <thead> <tr> <th align="center">Protocol</th> <th align="center">Identification Sequence</th> <th align="center">Reference</th> </tr> </thead> <tbody> <tr> <td align="center">Reserved</td> <td align="center">0x0A 0x0A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x1A 0x1A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x2A 0x2A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x3A 0x3A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x4A 0x4A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x5A 0x5A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x6A 0x6A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x7A 0x7A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x8A 0x8A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0x9A 0x9A</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xAA 0xAA</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xBA 0xBA</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xCA 0xCA</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xDA 0xDA</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xEA 0xEA</td> <td align="center">[RFC8701]</td> </tr> <tr> <td align="center">Reserved</td> <td align="center">0xFA 0xFA</td> <td align="center">[RFC8701]</td> </tr> </tbody> </table> </section> <section anchor="Security"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>GREASE values cannot be negotiated, so they do not directly impact the security of TLS connections.</t> <t>Historically, when interoperability problems arise in deploying new TLS features, implementations have used a fallback retry on error with the feature disabled. This allows an active attacker to silently disable the new feature. By preventing a class of such interoperability problems, GREASE reduces the need for this kind of fallback. ImplementationsSHOULD NOT<bcp14>SHOULD NOT</bcp14> retry with GREASE disabled on connection failure. While allowing an attacker to disable GREASE is unlikely to have immediate security consequences, such a fallback would prevent GREASE from defending against extensibility failures.</t> <t>If an implementation does not select GREASE values atrandomrandom, it is possible it will allow for fingerprinting of the implementation or perhaps even of individual users. This can result in a negative impact to a user's privacy.</t> </section> </middle> <back> <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.5246.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6347.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7301.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.8446.xml"/> </references> <section anchor="Acknowledgments"title="Acknowledgments">numbered="false" toc="default"> <name>Acknowledgments</name> <t> The author would like to thankAdam Langley, Nick Harper, and Steven Valdez<contact fullname="Adam Langley"/>, <contact fullname="Nick Harper"/>, and <contact fullname="Steven Valdez"/> for their feedback and suggestions. In addition, the rusted joint metaphor is originally due toAdam Langley.<contact fullname="Adam Langley"/>. </t> </section></middle> <back> <references title="Normative References"> &RFC2119; &RFC5246; &RFC6347; &RFC7301; &RFC8174; &RFC8446; </references></back> </rfc>