wdiff rfc7508.original rfc7508.txt

Network Working Group
Independent Submission L. Cailleux
Internet-Draft
Request for Comments: 7508 DGA MI
Intended status:
Category: Experimental C. Bonatti
Expires: 22 July 2015
ISSN: 2070-1721 IECA
22 January
April 2015

Securing Header Fields with S/MIME
draft-cailleux-secure-headers-08

Abstract

This document describes how the S/MIME protocol can be extended in
order to secure message header fields. fields defined in RFC 5322. This
technology provides security services such as data integrity,
non-repudiation non-
repudiation, and confidentiality. This extension is referred to as
'Secure Headers'.

Status of this This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

Internet-Drafts are working documents of
evaluation.

This document defines an Experimental Protocol for the Internet
Engineering Task Force (IETF). Note that
community. This is a contribution to the RFC Series, independently
of any other groups may
also distribute working documents as Internet-Drafts. RFC stream. The
list of current Internet-Drafts is RFC Editor has chosen to publish this
document at
http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a maximum candidate for any level of six
months Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other
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"work in progress."

This Internet-Draft will expire on 22 July 2015.
http://www.rfc-editor.org/info/rfc7508.

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Table of Contents

1. Introduction..............................................3 Introduction ....................................................2
2. Terminology and conventions used Conventions Used in this document.........3 This Document ...............3
3. Context...................................................5 Context .........................................................4
4. Mechanisms to secure message header fields................7 Secure Message Header Fields ......................6
4.1. ASN.1 syntax Syntax of secure header fields.................9 Secure Header Fields .......................7
4.2. Secure header fields length Header Fields Length and format..............10 Format .....................8
4.3. Canonization algorithm..............................10 Canonicalization Algorithm .................................8
4.4. Header fields statuses..............................10 Field Statuses ......................................8
4.5. Signature Process...................................11 Process ..........................................9
4.5.1. Signature Generation Process...................11 Process ........................9
4.5.2. Signature verification process.................12 Verification Process .....................10
4.6. Encryption and Decryption Processes.................14 Processes .......................11
4.6.1. Encryption Process.............................14 Process .................................11
4.6.2. Decryption Process.............................15 Process .................................12
5. Case of triple wrapping..................................16 Triple Wrapping ........................................13
6. Security Gateways........................................16 Gateways ..............................................13
7. Security Considerations..................................17 Considerations ........................................13
8. IANA Considerations......................................18 Considerations ............................................14
9. References...............................................18 References .....................................................14
9.1. Normative References................................18 References ......................................14
9.2. Informative References..............................19 References ....................................15
Appendix A. Formal syntax Syntax of Secure Header..................20 Header ........................16
Appendix B. Example of Secure Header Fields example....................22
Appendix C. Acknowledgements................................24 .......................18
Acknowledgements ..................................................19
Authors' Addresses ................................................19

1. Introduction

The S/MIME [RFC 5751] [RFC5751] standard defines a data encapsulation format for
the achievement of end to end end-to-end security services such as integrity,
authentication, non-repudiation non-repudiation, and confidentiality. By default,
S/MIME secures message body parts, at the exclusion of the message
header fields.

S/MIME provides an alternative solution to secure header
fields. "The fields: "the
sending client MAY wrap a full MIME [RFC 2045] message in a message/rfc822
wrapper in order to apply S/MIME security services to header fields".
However, the S/MIME solution doesn't provide any guidance regarding
what subset of message header fields to secure, procedures for
clients to reconcile the "inner" and "outer" headers, or procedures
for client interpretation or display of any failures.

Several other security standards specifications supplement S/MIME features, features but
fail to address the target requirement set of this draft. document. Such
other security standards specifications include DKIM [RFC 6376], DomainKeys Identified Mail
(DKIM) [RFC6376], STARTTLS [RFC 3207], [RFC3207], TLS with IMAP [RFC 2595], [RFC2595], and an internet
draft
Internet-Draft referred to as PROTECTED HEADERS. "Protected Headers" [PRHDRS]. An
explanation of what these services accomplish and why they do not
solve this problem can be found in subsequent sections.

The goal of this document is to define end to end end-to-end secure header fields field
mechanisms compliant with S/MIME standard. This technique is based
on the signed attribute fields of a Cryptographic Message Syntax
(CMS) [RFC 5652] [RFC5652] signature.

2. Terminology and conventions used Conventions Used in this document This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119]. [RFC2119].

The terms Message User Agent (MUA), Message Submission Agent
(MSA) (MSA),
and Message Transfer Agent (MTA) terms are defined in
Email the email
architecture document [RFC 5598]. [RFC5598].

The term Domain Confidentiality Authority (DCA) is defined in the
S/MIME Domain Security specification [RFC 3183]. [RFC3183].

End-to-end Internet Mail exchanges are performed between message
originators and recipients.

The term "message message header fields" fields is described in [RFC 5322]. [RFC5322]. A header
field is composed of a name and a value.

Secure Headers technology uses header fields field statuses required to
provide a confidentiality service toward message headers. The
following three terms are used to describe the field statuses:

- Duplicated duplicated (the default status). When this status is present or
if no status is specified, the signature process embeds the header
field value in the digital signature, but the value is will also be
present in the message header fields.

- Deleted. deleted. When this status is present, the signature process
embeds the header field value in the digital signature, and the
encryption process deletes this field from the message to preserve
its confidentiality.

- Modified. modified. When this status is present, the signature process
embeds the header field value in the digital signature, and the
encryption process modifies the value of the header field in the
message. This preserves confidentiality and informs a receiver's non-compliant
noncompliant MUA that secure headers are being used. New values
for each field might be configured by the sender (i.e., "This
header is secured, secured; use a compliant client"). client.").

The term "non-repudiation" non-repudiation is used throughout this document in
deference to the usage in the S/MIME Message Specification
[RFC 5751]. [RFC5751].
It is recognized that this term carries with it much baggage, and
that there is some disagreement as to it's its proper meaning and usage.
However, in the context of this
document document, the term merely refers to
one of a set of possible security services that a conforming
implementation might be able to provide. This document specifies no
normative requirements for non-repudiation.

3. Context

Over the Internet, email usage use has grown and today represents a
fundamental service. Meanwhile, continually increasing threat levels
are motivating the implementation of security services.

Historically, SMTP [RFC 5321] [RFC5321] and IMF [RFC 5322] the Internet Message Format (IMF)
[RFC5322] don't provide, by default, security services. The S/MIME
standard
[RFC 5751] [RFC5751] was published in order to encompass address these needs.
S/MIME defines a data encapsulation format for the provision of end to end end-
to-end security services such as integrity, authentication, non-repudiation non-
repudiation, and confidentiality. By default, S/MIME secures message
body parts, at the exclusion of the message header fields. In order
to protect message header fields (for instance, the "Subject", "To", "From"
"From", or customized fields), several solutions exist.

In Section 3.1 of [RFC5751], S/MIME defines an encapsulation mechanism, chapter 3.1: "The
mechanism:

[...] the sending client may MAY wrap a full MIME message in a
message/rfc822 wrapper in order to apply S/MIME security services
to these header fields. It is up to the receiving client to
decide how to present this inner "inner" header along with the
unprotected outer header". "outer" header.

However, some use cases are not addressed, especially in the case of
message encryption. What happens when header fields are encrypted?
How does the receiving client display these header fields? How can a
subset of header fields be secured? S/MIME doesn't address these
issues.

Some partial header protection is provided by the S/MIME Certificate
Handling specification [RFC 5750]. "Receiving [RFC5750]:

Receiving agents MUST check that the address in the From or Sender
header of a mail message matches an Internet mail address, if
present, in the signer's certificate, if mail addresses are
present in the certificate". certificate.

In some cases cases, this may provide assurance of the integrity of the
From or Sender header values. However, the solution in RFC 5750 solution only
provides a matching mechanism between email addresses, addresses and provides no
protection to other header fields.

Other security standards specifications (introduced below) exist such as DKIM,
STARTTLS and TLS with IMAP IMAP, but they meet other needs (signing
domain, secure channels...). channels, etc.).

STARTTLS and TLS with IMAP provide secure channels between components
of the email system (MUA, MSA, MTA...) MTA, etc.), but end to end end-to-end integrity
cannot be guaranteed.

DKIM defines a domain-level authentication framework for email.
While this permits integrity and origination checks on message header
fields and the message body, it does this for a domain actor (usually
the SMTP service or equivalent) and not for the entity that is
sending, and thus signing signing, the message. (Extensions to DKIM might be
able to solve this issue by authenticating the sender and making a
statement of this fact as part of the signed message headers of this fact.) headers.) DKIM
is also deficient for our purposes purposes, as it does not provide a
confidentially service.

An internet draft Internet-Draft referred to as Protected Headers (PRHDRS) "Protected Headers" [PRHDRS] has
been proposed. Mechanisms described in this draft that document are the
following. "A
following:

[...] a digest value is computed over the canonicalized version of
some selected header fields. This technique resembles header
protection in DKIM. [RFC4871]. Then the digest value is included in a
signed attribute field of a CMS signature". This signature.

(Note that RFC 4871 has been obsoleted by RFC 6376.)

That specification doesn't address all conceivable requirements as
noted below. If the protected header field has been altered, the
original value cannot be determined by the recipient. In addition,
the encryption service cannot provide confidentiality for fields that
must remain present in the message header during transport.

This document proposes a technology for securing message header
fields. It's referred to as Secure Headers. "Secure Headers". It is based on S/MIME
and CMS standards. It provides security services such as data
integrity, confidentiality confidentiality, and non-repudiation of the sender.
Secure Headers is backward compatible with other S/MIME clients.
S/MIME clients who have not implemented Secure Headers technology
need merely ignore specific signed attributes fields in a CMS
signature (which is the default behavior).

4. Mechanisms to secure message header fields Secure Message Header Fields

Secure Headers technology involves the description of a security
policy. This policy MUST describe a secure message profile and list
the header fields to secure. How this security policy is agreed upon
or communicated is beyond the scope of this document.

Secure headers are based on the signed attributes field as defined in
CMS. The details are as follows. The message header fields to be
secured are integrated in a structure (secure
header (SecureHeaderFields structure) which
that is encapsulated in the signed attributes structure of the
SignerInfo object. There is only one value of HeaderFields encoded
into a single SignedAttribute in a signature. See Appendix A for an
example. For each header field present in the secure signature, a
status can be set. Then, as described in chapter Section 5.4 of CMS, CMS
[RFC5652], the message digest calculation process computes a message
digest on the content together with the signed attributes. Details
of the signature generation process are
described in chapter Section 4.5.1 of this
document.

Verification of secure header fields is based on the signature
verification process described in CMS. At the end of this process, a
comparison between the secure header fields and the corresponding
message header fields is performed. If they match, the signature is
valid. Otherwise, the signature is invalid. Details of the
signature verification process are
described in chapter Section 4.5.2 of this document.

Non-conforming S/MIME clients will ignore the signed attribute
containing the secure headers SecureHeaderFields structure, and only perform the
verification process described in CMS. This guarantees backward
compatibility.

Secure headers provide security services such as data integrity, non-repudiation non-
repudiation, and confidentiality.

For different reasons (e.g., usability, limits of IMAP [RFC
3501]), [RFC3501]),
encryption and decryption processes are performed by a third party.
The third party that performs these processes is referred to in the
Domain Security specification as a "Domain Domain Confidentiality Authority" Authority
(DCA). Details of the encryption and decryption processes are described in chapters
Sections 4.6.1 and 4.6.2 of this document.

The architecture of Secure Headers is presented below. The MUA
performs the signature generation process (C) and signature
verification process (F). The DCA performs the message encryption
process (D) and message decryption process (E). The encryption and
decryption processes are optional.

A Domain B Domain
+----------------------+ +----------------------+

+-----+ +-----+ +-----+ +-----+
| MUA | -------> | DCA | ----------> | DCA |--------> | MUA |
| C | | D | | E | | F |
+-----+ +-----+ +-----+ +-----+
SignedMsg EncryptedMsg SignedMsg

Figure 1: Architecture of Secure Headers

4.1. ASN.1 syntax Syntax of secure header fields Secure Header Fields

The ASN.1 notation syntax [ASN1-88] of secure header the SecureHeaderFields structure is the
follow: as
follows:

SecureHeaderFields ::= SET {
canonAlgorithm Algorithm,
secHeaderFields HeaderFields }

id-aa-secureHeaderFieldsIdentifier OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) id-aa(2) secure-headers (to be
defined) secureHeaderFieldsIdentifier(55) }

Algorithm ::= ENUMERATED {
canonAlgorithmSimple(0),
canonAlgorithmRelaxed(1) }

HeaderFields ::= SEQUENCE SIZE (1..MAX) OF HeaderField

HeaderField ::= SEQUENCE {
field-Name HeaderFieldName,
field-Value HeaderFieldValue,
field-Status HeaderFieldStatus DEFAULT duplicated }
HeaderFieldName ::= VisibleString (FROM (ALL EXCEPT (":")))
-- This description matches with the description of
-- field name in the chapters Sections 2.2 and 3.6.8 of RFC 5322

HeaderFieldValue ::= UTF8String
-- This description matches with the description of
-- field body in the chapter Section 2.2 of RFC 5322 as
-- extended by chapter Section 3.1 of RFC 6532.

HeaderFieldStatus ::= INTEGER {
duplicated(0), deleted(1), modified(2) }

4.2. Secure header fields length Header Fields Length and format Format

This specification requires MUA security capabilities in order to
process well formed well-formed headers, as specified in IMF. Notice that it
includes long header fields and folded header fields.

4.3. Canonization algorithm Canonicalization Algorithm

During a message transfer through a messaging system, some components
might modify headers (i.e., space adding or
deletion, lowercase/uppercase rewriting...). deleting space, changing or
lowercase or uppercase). This might lead to header fields a comparison mismatch. mismatch of
header fields. This emphasizes the need of a conversion process in
order to transform data to their canonical form. This process is
named canonization the canonicalization process.

Two canonization canonicalization algorithms are considered here, according to
Section 3.4 of the DKIM specification [RFC 6376], chapter 3.4. [RFC6376]. The simple "simple"
algorithm doesn't allow any modification modification, whereas the relaxed "relaxed"
algorithm accepts slight modifications like spaces space replacement or line
reformatting. Given the scope of this document,
canonization canonicalization
mechanisms only involve header fields.

Implementations SHOULD use the relaxed "relaxed" algorithm to promote
interoperability with non-conforming SMTP products.

4.4. Header fields statuses Field Statuses

Header fields field statuses are necessary to provide a confidentiality
service toward for message headers. In this specification, the
confidentiality of header fields is provided by the DCA. This point
is described in chapter Section 4. The DCA performs the message encryption
process and message decryption process and process; these processes are described
in
details detail in the chapters Sections 4.6.1 and 4.6.2. Although header
fields field
statuses are embedded in the signature, the signature processes
(generation and verification) ignore them. The header field status
defaults to duplicated. "duplicated". If the header field is confidential, the
header field status MUST be either
deleted "deleted" or modified. "modified".

4.5. Signature Process

4.5.1. Signature Generation Process

During the signature generation process, the sender's MUA MUST embed
the SecureHeaderFields structure in the signed attributes, as
described in CMS. The SecureHeaderFields structure MUST include a canonization
canonicalization algorithm.

The sender's MUA MUST have a list of header fields to secure,
statuses
statuses, and a canonization canonicalization algorithm, as defined by the
security policy.

Header fields (names and values) embedded in signed attributes MUST
be the same as the ones those included in the initial message.

If different headers share the same name, all instances MUST be
included in the SecureHeaderFields structure.

If multiple signatures are used, as explained in the CMS and
MULTISIGN [RFC 4853] Multiple
Signer [RFC4853] specifications, the SecureHeaderFields structure
MUST be the same in each SignerInfos object.

If a header field is present and its value is empty, HeaderFieldValue
MUST have a zero-length field-value. field-Value.

Considering secure headers header mechanisms, the signature generation
process MUST perform the following steps:

1) Select the relevant header fields to secure. This subset of
headers is defined according the security policy.

2) Apply the canonization canonicalization algorithm for each selected header
field.

3) Complete the following fields in the SecureHeaderFields
structure according to the initial message: HeaderFieldName,
HeaderFieldValue, and HeaderFieldStatus.

4) Complete the algorithm field according to the
canonization canonicalization
algorithm configured.

5) Embed the SecureHeaderFields structure in the signed attributes
of the SignerInfos object.

6) Compute the signature generation process as described in
CMS, chapter
Section 5.5 of CMS [RFC5652].

4.5.2. Signature verification process Verification Process

During the signature verification process, the receiver's MUA
compares header fields embedded in the SecureHeaderFields structure
with those present in the message. For this purpose, it uses the canonization
canonicalization algorithm identified in the signed attributes. If a
mismatch appears during the comparison process, the receiver's MUA
MUST invalidate the signature. The MUA MUST display information on
the validity of each header field. It MUST also display the values
embedded in the signature.

The receiver's MUA MUST know the list of mandatory header fields in
order to verify their presence in the message. If a header field
defined in a message is in the secure header list, it MUST be
included in the SecureHeaderFields structure. Otherwise, the
receiver's MUA MUST warn the user that a non-
secure non-secure header is
present.

Considering secure headers header mechanisms, the signature verification
process MUST perform the following steps:

1) Execute the signature verification process as described
in CMS, chapter 5.6. Section
5.6 of CMS [RFC5652]. If the signature appears to be invalid,
the process ends. Otherwise, the process continues.

2) Read the type of canonization canonicalization algorithm specified in the
SecureHeaderFields structure.

3) For each field present in the signature, find the matching
header in the message. If there is no matching header, the
verification process MUST warn the user, specifying the missing
header name. The signature is tagged as invalid. Note that
any headers header fields encrypted as per
section Section 4.6 (i.e., status of
"deleted" or "modified") have been are already restored by the
DCA when the signature verification process is performed by the
MUA.

4) Compute the canonization canonicalization algorithm for each header field
value in the message. If the simple "simple" algorithm is used, the
steps described in DKIM, chapter 3.4.1, Section 3.4.1 of DKIM [RFC6376] are
performed. If the relaxed algorithm is used, the steps
described in DKIM,
chapter 3.4.2, Section 3.4.2 of DKIM [RFC6376] are performed.

5) For each field, compare the value stored in the
SecureHeaderFields structure with the value returned by the
canonization
canonicalization algorithm. If the values don't match, the
verification process MUST warn the user. This warning MUST
mention mismatching fields. The signature is tagged as
invalid. If all the comparisons succeed, the verification
process MUST also notify the user (i.e., using an appropriate
icon).

6) Verify that no secure header has been added to the message
header, given the initial fields. If an extra header field has
been added, the verification process MUST warn the user. This
warning MUST mention extra fields. The signature is tagged as
invalid. This step is only performed if the sender and the
recipient share the same security policy.

7) Verify that every each mandatory headers header in the security policy and
present in the message are is also embedded in the
SecureHeaderFields structure. If such headers are missing, the
verification process MUST warn the user and indicate the names
of the missing headers.

The MUA MUST display features for the properties of each secure header field
(name, value value, and status) and canonization the canonicalization algorithm used.

4.6. Encryption and Decryption Processes

Encryption and decryption operations are not performed by MUAs. This
is mainly justified by limitations of existing email delivery
protocols, for example example, IMAP. The solution developed here relies on
concepts explained in Section 4 of the Domain Security
specification, chapter 4. specification
[RFC3183]. A fundamental component of the architecture is the Domain
Confidentiality Authority (DCA). Its purpose is to encrypt and
decrypt messages instead of
(respectively) that being performed by senders and receivers.
receivers (respectively).

4.6.1. Encryption Process

All the computations presented in this chapter section MUST be performed only
if the following conditions are verified:

- The content to be encrypted MUST consist of a signed message
(application/pkcs7-mime with SignedData SignedData, or multipart/signed)
as shown in Section 3.4 of the S/MIME specification, chapter
3.4. specification [RFC5751].

- A SecureHeaderFields structure MUST be included in the
signedAttrs field of the SignerInfo object of the signature.

All the mechanisms described below MUST start at the beginning of the
encryption process, as explained in CMS. They are performed by the
sender's DCA. The For extraction of the field status, the following
steps MUST be performed for each field included in the
SecureHeaderFields structure:

1. Extraction of the field status;

1.1 If the status is Duplicated, "duplicated", the field is left at its
existing value.

1.2

2. If the status is Deleted, "deleted", the header field (name and value)
is removed from the message. Mandatory header fields specified
in [RFC 5322] [RFC5322] MUST be kept.

1.3

3. If the status is Modified, "modified", the header value is replaced by a
new value, as configured in the DCA.

4.6.2. Decryption Process

All the computations presented in this chapter section MUST be performed only
if the following conditions are verified:

- The decrypted content MUST consist of a signature object or a
multipart object, where one part is a detached signature, as
shown in Section 3.4 of the S/MIME specification, chapter 3.4. specification [RFC5751].

- A SecureHeaderFields structure MUST be included in the
SignerInfo object of the signature.

All the mechanisms described below MUST start at the end of the
decryption process, as explained in CMS. They are executed by the
receiver's DCA. The following steps MUST be performed for each field
included in the SecureHeaderFields structure:

1. If the status is Duplicated, "duplicated", the field is left at its
existing value.

2. If the status is Deleted, "deleted", the DCA MUST write a header field
(name and value) in the message. This header MUST be compliant
with the information embedded in the signature.

3. If the status is Modified, "modified", the DCA MUST rewrite a header
field in the message. This header MUST be compliant with the
SecureHeaderFields structure.

5. Case of triple wrapping Triple Wrapping

Secure Headers mechanisms MAY be used with triple wrapping, as
described in ESS [RFC 2634]. Enhanced Security Services (ESS) [RFC2634]. In this
case, a SecureHeaderFields structure MAY be present in the inner
signature, in the outer signature, or both. In the last case, the two structure
SecureHeaderFields structures MAY differ. One MAY consider the
encapsulation of a header field in the inner signature in order to
satisfy confidentiality needs. On the contrary, an outer signature
encapsulation MAY help for delivery purpose. Sender's purposes. The sender's MUA and
receiver's MUA must have a security policy for triple wrapping. This
security policy MUST be composed of two parts. One part dedicated parts -- one for the inner
signature and one part dedicated the other for the outer signature.

6. Security Gateways

Some security gateways sign or verify messages that pass through
them. Compliant gateways MUST apply the process described in chapter Section
4.5.

For non-compliant noncompliant gateways, the presence of a SecureHeaderFields
structure do does not change their behavior.

In some case, gateways MUST generate a new signature or insert
signerInfos into the signedData block. The format of signatures
generated by gateways is outside the scope of this document.

7. Security Considerations

This specification describes an extension of the S/MIME standard. It
provides message headers header integrity, non-
repudiation non-repudiation, and
confidentiality. The signature and encryption processes are
complementary. However, according to the security policy, only the
signature mechanism is applicable. In this case, the signature
process is implemented between MUAs. The encryption process requires
signed messages with the Secure Headers extension. If required, the
encryption process is implemented by DCAs.

This specification doesn't address end-to-end confidentiality for
message header fields. Messages sent and received by MUAs could be
transmitted as plaintext. In order to avoid interception, the use of
TLS is recommended between MUAs and DCAs (uplink and downlink).
Another solution might be the use of S/MIME between MUAs and DCAs in
the same domain.

For the header field confidentiality mechanism to be effective effective, all
DCAs supporting confidentiality must support SH Secure Headers
processing. Otherwise, there is a risk in the case where that headers are not obscured
upon encryption, encryption or not restored upon
decryption process. decryption. In the former case case,
confidentiality of the header fields is compromised. In the latter case
case, the integrity of the headers will appear to be compromised.

8. IANA Considerations

IANA must register a suitable Object Identifier (OID) has registered value 65, mod-sMimeSecureHeadersV1, in the "SMI
Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0)"
registry.

IANA has also registered value 55, id-aa-
secureHeaderFieldsIdentifier, in the identifier id-aa-secureHeaderFieldsIdentifier. "SMI Security for S/MIME
Attributes (1.2.840.113549.1.9.16.2)" registry. This value will be
used to identify an authenticated attribute carried within a CMS [RFC 5652] wrapper.
wrapper [RFC5652]. This attribute OID appears in Section 4.1, 4.1 and
again in the reference definition in Appendix A. An appropriate registry arc is suggested in
those instances of the draft text.

9. References

9.1. Normative References

[RFC 2045] Borenstein, N., "Multipurpose Internet Mail
Extensions Part One", RFC 2045, November 1996.

[RFC 2119]

[RFC2119] Bradner, S., "Key words for use in RFCs to
indicate requirement levels", Indicate
Requirement Levels", BCP 14, RFC 2119, March
1997.

[RFC 2634] 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2634] Hoffman, P., Ed., "Enhanced Security Services for S/MIME",
RFC 2634, June 1999.

[RFC 4853] 1999,
<http://www.rfc-editor.org/info/rfc2634>.

[RFC4853] Housley, R., "Cryptographic Message Syntax (CMS), (CMS) Multiple
Signer Clarification", RFC 4853, April
2007.

[RFC 5322] 2007,
<http://www.rfc-editor.org/info/rfc4853>.

[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.

[RFC 5652] 2008, <http://www.rfc-editor.org/info/rfc5322>.

[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.

[RFC 6376] 2009,
<http://www.rfc-editor.org/info/rfc5652>.

[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, M., DomainKeys Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, September 2011. 2011,
<http://www.rfc-editor.org/info/rfc6376>.

[ASN1-88] CCITT. CCITT, Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.

9.2. Informative References

[RFC 2595]

[PRHDRS] Liao, L. and J. Schwenk, "Header Protection for S/MIME",
draft-liao-smimeheaderprotect-05, Work in Progress, June
2009.

[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, June 1999.

[RFC 3183] 1999, <http://www.rfc-editor.org/info/rfc2595>.

[RFC3183] Dean, T., T. and W. Ottaway, W., "Domain security services Security Services using
S/MIME", RFC 3183, October 2001.

[RFC 3207] 2001,
<http://www.rfc-editor.org/info/rfc3183>.

[RFC3207] Hoffman, P., "SMTP Service Extension for secure Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.

[RFC 3501] 2002,
<http://www.rfc-editor.org/info/rfc3207>.

[RFC3501] Crispin, M., "Internet Message Access Protocol,
version "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.

[RFC 5321] 2003,
<http://www.rfc-editor.org/info/rfc3501>.

[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.

[RFC 5598] 2008, <http://www.rfc-editor.org/info/rfc5321>.

[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, July 2009.

[RFC 5750]
2009, <http://www.rfc-editor.org/info/rfc5598>.

[RFC5750] Ramsdell, B., B. and S. Turner, S., "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, January 2010.

[RFC 5751] 2010,
<http://www.rfc-editor.org/info/rfc5750>.

[RFC5751] Ramsdell, B., B. and S. Turner, S., "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2, 3.2 Message
Specification", RFC 5751, January 2010. 2010,
<http://www.rfc-editor.org/info/rfc5751>.

Appendix A. Formal syntax Syntax of Secure Header

Note: The ASN.1 module contained herein uses the 1988 version of
ASN.1 notation [ASN1-88] for the purposes of alignment with
th the
existing S/MIME specifications. The secure header SecureHeaderFields structure is
defined as follows:

SMimeSecureHeadersV1

mod-SMimeSecureHeadersV1
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0) secure-headers-v1(to be
defined) secure-headers-v1(65) }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

IMPORTS

id-aa
FROM SecureMimeMessageV3dot1
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0)
msg-v3dot1(21) };

-- id-aa is the arc with all new authenticated and
-- unauthenticated attributes produced by the S/MIME
-- Working Group

id-aa-secureHeaderFieldsIdentifier OBJECT IDENTIFIER ::= {
id-aa secure-headers (to be defined) secure-headers(55) }

SecureHeaderFields ::= SET {
canonAlgorithm Algorithm,
secHeaderFields HeaderFields }

Algorithm ::= ENUMERATED {
canonAlgorithmSimple(0),
canonAlgorithmRelaxed(1) }

HeaderFields ::= SEQUENCE SIZE (1..MAX) OF HeaderField

HeaderField ::= SEQUENCE {
field-Name HeaderFieldName,
field-Value HeaderFieldValue,
field-Status HeaderFieldStatus DEFAULT duplicated }

HeaderFieldName ::= VisibleString (FROM (ALL EXCEPT (":")))
-- This description matches with the description of
-- field name in the chapters Sections 2.2 and 3.6.8 of RFC 5322
HeaderFieldValue ::= UTF8String
-- This description matches with the description of
-- field body in the chapter Section 2.2 of RFC 5322 as
-- extended by chapter Section 3.1 of RFC 6532.

HeaderFieldStatus ::= INTEGER {
duplicated(0), deleted(1), modified(2) }

END

Appendix B. Example of Secure Header Fields example

In the following example, the header fields subject, x-ximf-
primary-precedence
x-ximf-primary-precedence, and x-ximf-correspondance-type are secured
and integrated in a SecureHeaders SecureHeaderFields structure. This example
should produce a valid signature.

Extract of from the message header fields fields:

From: John Doe <jdoe@example.com>
To: Mary Smith <mary@example.com>
subject: This is a test of Ext.
x-ximf-primary-precedence: priority
x-ximf-correspondance-type: official

SecureHeaders

The SecureHeaderFields structure extracted from the signature:

2286 150: SEQUENCE {
2289 11: OBJECT IDENTIFIER '1 2 840 113549 1 9 16 2 80'
2302 134: SET {
2305 131: SET {
2308 4: ENUMERATED 1
2314 123: SEQUENCE {
2316 40: SEQUENCE {
2318 25: VisibleString 'x-ximf-primary-precedence'
2345 8: UTF8String 'priority'
2355 1: INTEGER 0
: }
2358 41: SEQUENCE {
2360 26: VisibleString 'x-ximf-correspondance-type'
2388 8: UTF8String 'official'
2398 1: INTEGER 0
: }
2401 36: SEQUENCE {
2403 7: VisibleString 'subject'
2412 22: UTF8String 'This is a test of Ext.'
2436 1: INTEGER 0
: }
: }
: }
: }
: }

Example

The example is displayed as an output of Peter Gutmann's "dumpasn1"
program.

OID used in this example is non-official.

Appendix C. nonofficial.

Acknowledgements

The authors would like to thank Jim Schaad, Alexey Melnikov, Damien
Roque, Thibault Cassan, William Ottaway, and Sean Turner who kindly
provided reviews of the document and/or suggestions for improvement.
As always, all errors and omissions are the responsibility of the
authors.

Authors' Addresses

Laurent CAILLEUX
DGA MI
BP 7
35998 RENNES CEDEX 9
France
Email:

EMail: laurent.cailleux@intradef.gouv.fr

Chris Bonatti
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
Email:
United States

EMail: bonatti252@ieca.com