Internet DRAFT - draft-melnikov-authentication-results-smime
draft-melnikov-authentication-results-smime
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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
to this document. Code Components extracted from this document must
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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------=_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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