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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 7281

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                            March 23, 2014
Expires: September 24, 2014


 Authentication-Results Registration for S/MIME signature verification
             draft-melnikov-authentication-results-smime-09

Abstract

   RFC 7001 specifies the Authentication-Results header field for
   conveying results of message authentication checks.  This document
   defines a new authentication method to be used in the Authentication-
   Results header field for S/MIME related signature checks.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 24, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  "smime" Authentication Method . . . . . . . . . . . . . . . .   2
     3.1.  S/MIME Results  . . . . . . . . . . . . . . . . . . . . .   2
     3.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  body.smime-part . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   [RFC7001] specifies the Authentication-Results header field for
   conveying results of message authentication checks.  As S/MIME
   signature verification (and alteration) is sometimes implemented in
   border message transfer agents, guards and gateways (for example see
   [RFC3183]), there is a need to convey signature verification status
   to Mail User Agents (MUA) and downstream filters.  This document
   defines a new authentication method to be used in the Authentication-
   Results header field for S/MIME related signature checks.

2.  Conventions Used in This Document

   The formal syntax uses the Augmented Backus-Naur Form (ABNF)
   [RFC5234] notation including the core rules defined in Appendix B of
   RFC 5234 [RFC5234].

3.  "smime" Authentication Method

   S/MIME signature and countersignature verification is represented by
   the "smime" method and is defined in [RFC5751].

3.1.  S/MIME Results

   The result values used by S/MIME [RFC5751] are as follows:











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   +-----------+-------------------------------------------------------+
   | Result    | Meaning                                               |
   | code      |                                                       |
   +-----------+-------------------------------------------------------+
   | none      | The message was not signed.                           |
   |           |                                                       |
   | pass      | The message was signed, the signature or signatures   |
   |           | were acceptable to the verifier, and the signature(s) |
   |           | passed verification tests.                            |
   |           |                                                       |
   | fail      | The message was signed and the signature or           |
   |           | signatures were acceptable to the verifier, but they  |
   |           | failed the verification test(s).                      |
   |           |                                                       |
   | policy    | The message was signed, signature(s) passed           |
   |           | verification tests, but the signature or signatures   |
   |           | were not acceptable to the verifier.                  |
   |           |                                                       |
   | neutral   | The message was signed but the signature or           |
   |           | signatures contained syntax errors or were not        |
   |           | otherwise able to be processed.  This result is also  |
   |           | be used for other failures not covered elsewhere in   |
   |           | this list.                                            |
   |           |                                                       |
   | temperror | The message could not be verified due to some error   |
   |           | that is likely transient in nature, such as a         |
   |           | temporary inability to retrieve a certificate or CRL. |
   |           | A later attempt may produce a final result.           |
   |           |                                                       |
   | permerror | The message could not be verified due to some error   |
   |           | that is unrecoverable, such as a required header      |
   |           | field being absent or the signer's certificate not    |
   |           | being available.  A later attempt is unlikely to      |
   |           | produce a final result.                               |
   +-----------+-------------------------------------------------------+

   A signature is "acceptable to the verifier" if it passes local policy
   checks (or there are no specific local policy checks).  For example,
   a verifier might require that the domain in the rfc822Name
   subjectAltName in the signing certificate matches the domain in the
   address of the sender of the message (value of the Sender header
   field, if present.  Value of the From header field otherwise), thus
   making third-party signatures unacceptable.  [RFC5751] advises that
   if a message fails verification, it should be treated as an unsigned
   message.  A report of "fail" here permits the receiver of the report
   to decide how to handle the failure.  A report of "neutral" or "none"
   preempts that choice, ensuring the message will be treated as if it
   had not been signed.



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3.2.  Examples


















































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 Return-Path: <aliceDss@example.com>
 Authentication-Results: example.net;
  smime=fail (certificate is revoked by CRL)
  body.smime-identifier=aliceDss@example.com
  body.smime-part=2
 Received: from ietfa.example.com (localhost [IPv6:::1])
     by ietfa.example.com (Postfix) with ESMTP id 2875111E81A0;
     Fri, 06 Sep 2002 00:35:14 -0700 (PDT)
 MIME-Version: 1.0
 To: User2@example.com
 From: aliceDss@example.com
 Subject: Example 4.8
 Message-Id: <020906002550300.249@example.com>
 Date: Fri, 06 Sep 2002 00:25:21 -0700
 Content-Type: multipart/signed;
     micalg=SHA1;
     boundary="----=_NextBoundry____Fri,_06_Sep_2002_00:25:21";
     protocol="application/pkcs7-signature"

 This is a multi-part message in MIME format.

 ------=_NextBoundry____Fri,_06_Sep_2002_00:25:21

 This is some sample content.
 ------=_NextBoundry____Fri,_06_Sep_2002_00:25:21
 Content-Type: application/pkcs7-signature; name=smime.p7s
 Content-Transfer-Encoding: base64
 Content-Disposition: attachment; filename=smime.p7s

 MIIDdwYJKoZIhvcNAQcCoIIDaDCCA2QCAQExCTAHBgUrDgMCGjALBgkqhkiG9w0BBwGgggL
 gMIIC3DCCApugAwIBAgICAMgwCQYHKoZIzjgEAzASMRAwDgYDVQQDEwdDYXJsRFNTMB4XDT
 k5MDgxNzAxMTA0OVoXDTM5MTIzMTIzNTk1OVowEzERMA8GA1UEAxMIQWxpY2VEU1MwggG2M
 IIBKwYHKoZIzjgEATCCAR4CgYEAgY3N7YPqCp45PsJIKKPkR5PdDteoDuxTxauECE//lOFz
 SH4M1vNESNH+n6+koYkv4dkwyDbeP5u/t0zcX2mK5HXQNwyRCJWb3qde+fz0ny/dQ6iLVPE
 /sAcIR01diMPDtbPjVQh11Tl2EMR4vf+dsISXN/LkURu15AmWXPN+W9sCFQDiR6YaRWa4E8
 baj7g3IStii/eTzQKBgCY40BSJMqo5+z5t2UtZakx2IzkEAjVc8ssaMMMeUF3dm1nizaoFP
 VjAe6I2uG4Hr32KQiWn9HXPSgheSz6Q+G3qnMkhijt2FOnOLl2jB80jhbgvMAF8bUmJEYk2
 RL34yJVKU1a14vlz7BphNh8Rf8K97dFQ/5h0wtGBSmA5ujY5A4GEAAKBgFzjuVp1FJYLqXr
 d4z+p7Kxe3L23ExE0phaJKBEj2TSGZ3V1ExI9Q1tv5VG/+onyohs+JH09B41bY8i7RaWgSu
 OF1s4GgD/oI34a8iSrUxq4Jw0e7wi/ZhSAXGKsZfoVi/G7NNTSljf2YUeyxDKE8H5BQP1Gp
 2NOM/Kl4vTyg+W4o4GBMH8wDAYDVR0TAQH/BAIwADAOBgNVHQ8BAf8EBAMCBsAwHwYDVR0j
 BBgwFoAUcEQ+gi5vh95K03XjPSC8QyuT8R8wHQYDVR0OBBYEFL5sobPjwfftQ3CkzhMB4v3
 jl/7NMB8GA1UdEQQYMBaBFEFsaWNlRFNTQGV4YW1wbGUuY29tMAkGByqGSM44BAMDMAAwLQ
 IUVQykGR9CK4lxIjONg2q1PWdrv0UCFQCfYVNSVAtcst3a53Yd4hBSW0NevTFjMGECAQEwG
 DASMRAwDgYDVQQDEwdDYXJsRFNTAgIAyDAHBgUrDgMCGjAJBgcqhkjOOAQDBC4wLAIUM/mG
 f6gkgp9Z0XtRdGimJeB/BxUCFGFFJqwYRt1WYcIOQoGiaowqGzVI

 ------=_NextBoundry____Fri,_06_Sep_2002_00:25:21--



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4.  IANA Considerations

   IANA is requested to add the the following entries to the "Email
   Authentication Methods" subregistry of the "Email Authentication
   Parameters" registry:














































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   +-------+----------+-------+------------------+---------------------+
   | Metho | Defined  | ptype | property         | value               |
   | d     |          |       |                  |                     |
   +-------+----------+-------+------------------+---------------------+
   | smime | [RFC5751 | body  | smime-part       | A reference to the  |
   |       | ]        |       |                  | MIME body part that |
   |       |          |       |                  | contains the        |
   |       |          |       |                  | signature, as       |
   |       |          |       |                  | defined in Section  |
   |       |          |       |                  | 4.1.                |
   |       |          |       |                  |                     |
   | smime | [RFC5751 | body  | smime-identifier | The email address   |
   |       | ]        |       |                  | [RFC5322]           |
   |       |          |       |                  | associated with the |
   |       |          |       |                  | S/MIME signature.   |
   |       |          |       |                  | The email address   |
   |       |          |       |                  | can be specified    |
   |       |          |       |                  | explicitly or       |
   |       |          |       |                  | derived from the    |
   |       |          |       |                  | identity of the     |
   |       |          |       |                  | signer.  Note that  |
   |       |          |       |                  | this email address  |
   |       |          |       |                  | can correspond to a |
   |       |          |       |                  | counter signature.  |
   |       |          |       |                  |                     |
   | smime | [RFC5751 | body  | smime-serial     | serialNumber of the |
   |       | ]        |       |                  | certificate         |
   |       |          |       |                  | associated with the |
   |       |          |       |                  | S/MIME signature    |
   |       |          |       |                  | (see section        |
   |       |          |       |                  | 4.1.2.2 of          |
   |       |          |       |                  | [RFC5280].          |
   |       |          |       |                  |                     |
   | smime | [RFC5751 | body  | smime-issuer     | Issuer name DN      |
   |       | ]        |       |                  | (e.g. "CN=CA1,ST=BC |
   |       |          |       |                  | ,c=CA") of the      |
   |       |          |       |                  | certificate         |
   |       |          |       |                  | associated with the |
   |       |          |       |                  | S/MIME signature    |
   |       |          |       |                  | (see section        |
   |       |          |       |                  | 4.1.2.4 of          |
   |       |          |       |                  | [RFC5280].          |
   +-------+----------+-------+------------------+---------------------+

   Either both or neither of body.smime-serial and body. smime-issuer
   should be present in an Authentication-Results header field.  body
   .smime-serial and body.smime-issuer are used for cases when body
   .smime-identifier (email address) can't be derived by the entity



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   adding the corresponding Authentication-Results header field.  For
   example this can be used when gatewaying from X.400.

   IANA is requested to add the the following entries to the "Email
   Authentication Result Names" subregistry of the "Email Authentication
   Parameters" registry:

   +-----------+-------------+-----------+--------------------+--------+
   | Code      | Defined     | Auth      | Meaning            | Status |
   |           |             | Method    |                    |        |
   +-----------+-------------+-----------+--------------------+--------+
   | none      | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | pass      | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | fail      | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | policy    | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | neutral   | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | temperror | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   |           |             |           |                    |        |
   | permerror | this        | smime     | [this memo]        | active |
   |           | document    |           | Section 3.1        |        |
   +-----------+-------------+-----------+--------------------+--------+

4.1.  body.smime-part

   body.smime-part contains the MIME body part reference which contains
   the S/MIME signature.  Syntax of this property is described by the
   smime-part ABNF production below.  application/pkcs7-signature or
   application/pkcs7-mime (containing SignedData) media type body parts
   are references using the <section> syntax (see Section 6.4.5 of
   [RFC3501]).  If the signature being verified is encapsulated by
   another CMS content type (e.g. application/pkcs7-mime containing
   EnvelopedData, which contains SignedData), such inner signature body
   part can be references using "section[/section..." syntax.







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       smime-part = section ["/" smime-subpart]
       smime-subpart = smime-part
       section = <Defined in Section 6.4.5 of [RFC3501]>

5.  Security Considerations

   This document doesn't add new security considerations not already
   covered by [RFC7001] and [RFC5751].  In particular security
   considerations related to use of weak cryptography over plaintext,
   weakening and breaking of cryptographic algorithms over time, as well
   as changing the behavior of message processing based on presence of a
   signature specified in [RFC5751] are relevant to this document.
   Similarly, the following security considerations specified in
   [RFC7001] are particularly relevant to this document: Forged Header
   Fields, Misleading Results, Internal MTA Lists and Compromised
   Internal Hosts.

   To repeat something already mentioned in RFC 7001, Section 7.1:

      An MUA or filter that accesses a mailbox whose messages are
      handled by a non-conformant MTA, and understands Authentication-
      Results header fields, could potentially make false conclusions
      based on forged header fields.  A malicious user or agent could
      forge a header field using the DNS domain of a receiving ADMD as
      the authserv-id token in the value of the header field and, with
      the rest of the value, claim that the message was properly
      authenticated.  The non- conformant MTA would fail to strip the
      forged header field, and the MUA could inappropriately trust it.

      For this reason, it is best not to have processing of the
      Authentication-Results header field enabled by default; instead,
      it should be ignored, at least for the purposes of enacting
      filtering decisions, unless specifically enabled by the user or
      administrator after verifying that the border MTA is compliant.
      It is acceptable to have an MUA aware of this specification but
      have an explicit list of hostnames whose Authentication-Results
      header fields are trustworthy; however, this list should initially
      be empty.

   So to emphasize this point: whenever possible, MUAs should implement
   their own S/MIME signature verification instead of implementing this
   specification.

   Note that agents adding Authentication-Results header fields
   containing S/MIME Authentication Method might be unable to verify
   S/MIME signatures inside encrypted CMS content types such as
   EnvelopedData [RFC5652].  So agents processing Authentication-Results
   header fields can't treat lack of an Authentication-Results header



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   field with S/MIME Authentication Method as an indication that the
   corresponding S/MIME signature is missing, invalid or valid.

6.  References

6.1.  Normative References

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

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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

   [RFC7001]  Kucherawy, M., "Message Header Field for Indicating
              Message Authentication Status", RFC 7001, September 2013.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

6.2.  Informative References

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

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

   [RFC5083]  Housley, R., "Cryptographic Message Syntax (CMS)
              Authenticated-Enveloped-Data Content Type", RFC 5083,
              November 2007.












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Appendix A.  Acknowledgements

   Thank you to Murray S. Kucherawy, David Wilson, Jim Schaad, SM and
   Steve Kille for comments and corrections on this document.

Author's Address

   Alexey Melnikov
   Isode Ltd
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com




































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