Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Informational July 03, 2013
Expires: January 04, 2014
MMHS Draft and Release using S/MIME
draft-melnikov-mmhs-authorizing-users-00
Abstract
This document describes a procedure for when an MMHS message is
composed by one user and is only released to the mail transfer system
when one or more authorizing users authorize release of the message
by adding the MMHS-Authorizing-Users header field. The resulting
message can be optionally countersigned, allowing recipients to
verify both the original signature (if any) and countersignatures.
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 January 04, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
Melnikov Expires January 04, 2014 [Page 1]
Internet-Draft Draft and Release using S/MIME July 2013
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Draft and Release procedure . . . . . . . . . . . . . . . . . 3
4. MMHS-Authorizing-Users header field . . . . . . . . . . . . . 4
5. Updated MIXER mapping . . . . . . . . . . . . . . . . . . . . 4
5.1. Mapping from RFC 5322/MIME to X.400 . . . . . . . . . . . 4
5.2. Mapping from X.400 to RFC 5322/MIME . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
1. Introduction
In some secure environments email messages can't be released to the
MTS (Mail Transfer System) and, thus delivered to recipients, unless
they are authorized by one or more Releasing Officers. This document
describes how this mechanism can be realized by an additional
[RFC5322] header field and optionally using S/MIME [RFC5750] and
[RFC5751].
This document describes a procedure for how an email message composed
by one user can be released to the MTS when one or more authorizing
users authorize and optionally countersign the message. The header
communicates which users authorized the message. If signed, the
resulting message allows recipients to verify both the original (if
any) and counter S/MIME signatures. The list of authorizing users is
specified in the MMHS-Authorizing-Users header field Section 4. The
original S/MIME signature generated by the sender (if any) should be
unaffected by additional S/MIME countersignatures.
2. Conventions Used in This Document
Melnikov Expires January 04, 2014 [Page 2]
Internet-Draft Draft and Release using S/MIME July 2013
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 [RFC2119].
The formal syntax uses the Augmented Backus-Naur Form (ABNF)
[RFC5234] notation including the core rules defined in Appendix B of
RFC 5234 [RFC5234]. Terms not defined in this document are taken
from [RFC5322].
3. Draft and Release procedure
The original email message to be sent may or may not include sender's
S/MIME signature. It doesn't include the MMHS-Authorizing-Users
header field. [[Is this true? Is there any use for specifying a
value for the MMHS-Authorizing-Users header field before the message
is countersigned?]]
The document to be sent is first submitted over SMTP [RFC5322]. The
specific mechanism for how it arrives to authorizing user(s) is not
specified in this document. One possibility is for the Submission
MSA to redirect all email messages without the MMHS-Authorizing-Users
header field and/or corresponding S/MIME countersignatures to a
preconfigured mailbox that can be accessed by authorizing user(s).
Each user agent that is used by an authorized user has to perform the
following steps:
1. Verify authenticity of the message. The exact mechanism to do
that is out of scope for this document, but one example is by
verifying the S/MIME signature and making sure that it matches
the sender of the message, as described in [RFC5750] [RFC5751].
2. Check if the message already contains the MMHS-Authorizing-Users
header field with the email address of the authorizing user. If
yes, verify validity of the header field (for example by checking
for S/MIME countersignature). If the validity of the MMHS-
Authorizing-Users header field containing the email address of
the authorizing user can be verified, go to step 5 below.
Otherwise strip the MMHS-Authorizing-Users header field.
Melnikov Expires January 04, 2014 [Page 3]
Internet-Draft Draft and Release using S/MIME July 2013
3. Allow the authorizing user to review content of the message.
Some of the checks can be automated (for example search for
keywords). If based on the check the authorizing user is happy
to release the message to MTS (or to the next authorizing user,
if multiple authorizations are required), the UA should
optionally enable the authorizing user to add S/MIME
countersignature. If the authorizing user wants to block the
message, it can be discarded or returned to sender, and no
further steps from this list should take place.
4. If there is an existing MMHS-Authorizing-Users header field
containing the email address of the authorizing user, skip this
step. Othrwise insert a new MMHS-Authorizing-Users header field
(if absent) containing the email address of the authorizing user
or append the email address of the authorizing user to the end of
the existing MMHS-Authorizing-Users header field.
5. The (possibly) updated email message is either released to the
MTS, or to the next authorizing user, as per email system
configuration.
4. MMHS-Authorizing-Users header field
The MMHS-Authorizing-Users header field specifies the list of
authorizing users that countersigned this email message (using S/
MIME) before it was authorized for release to MTS. Each user is
described by her/his email address.
The MMHS-Authorizing-Users header field specified in this document
MUST NOT appear more than once in message headers.
MMHS-Authorizing-Users = "MMHS-Authorizing-Users:"
[FWS] address-list [FWS] CRLF
address-list = <Defined in RFC 5322>
5. Updated MIXER mapping
This section updates MIXER mapping specified in [RFC2156].
5.1. Mapping from RFC 5322/MIME to X.400
In the absence of the MMHS-Authorizing-Users header field, From and
Sender header fields are mapped to their X.400 equivalents as
specified in [RFC2156].
Melnikov Expires January 04, 2014 [Page 4]
Internet-Draft Draft and Release using S/MIME July 2013
If MMHS-Authorizing-Users header field is present:
1. The first From header field address is mapped to
IPMS.Heading.originator if there is no Sender header field and
the remaining From header field addresses + the MMHS-Authorizing-
Users header field address(es) are mapped to IPMS.Heading
.authorizing-users. If a Sender header field is present, the
From header field address(es) and the MMHS-Authorizing-Users
header field address(es) are mapped to IPMS.Heading.authorizing-
users.
2. The Sender header field (if present) is mapped to
IPMS.Heading.originator.
5.2. Mapping from X.400 to RFC 5322/MIME
Mapping from X.400 to Internet is controlled by whether or not a
particular message is considered to be a military message. A message
is considered to be a military message (as defined by ACP 123
[ACP123] and also specified in STANAG 4406 [STANAG-4406]) if there
are any MMHS heading extensions present. Alternatively, this MAY be
done by configuration (i.e. all messages can be considered to be
military messages).
For non military messages, mapping from X.400 as specified in
[RFC2156] is used.
For military messages, the following mapping is used:
1. IPMS.Heading.originator is mapped to From header field.
2. The IPMS.Heading.authorizing-users is mapped to MMHS-Authorizing-
Users header field.
6. IANA Considerations
IANA is requested to add the MMHS-Authorizing-Users header field
specified in Section 4 to the "Permanent Message Header Field
Registry", defined by Registration Procedures for Message Header
Fields [RFC3864].
7. Security Considerations
TBD
8. Open Issues
Melnikov Expires January 04, 2014 [Page 5]
Internet-Draft Draft and Release using S/MIME July 2013
Netnews Approved header field has the same syntax and semantics as
the one described here. Should it be used (and be formally
registered for email) instead?
Allow use of MMHS-Authorized-Users/Approved for specifying who should
authorize release of the message (as opposed to just for recording of
who authorized release so far)?
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2156] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay):
Mapping between X.400 and RFC 822/MIME", RFC 2156, January
1998.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5750] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, January 2010.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[ACP123] CCEB, ., "Common Messaging strategy and procedures", ACP
123, May 2009.
9.2. Informative References
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[STANAG-4406]
NATO, ., "STANAG 4406 Edition 2: Military Message Handling
System", STANAG 4406, March 2005.
Appendix A. Acknowledgements
Melnikov Expires January 04, 2014 [Page 6]
Internet-Draft Draft and Release using S/MIME July 2013
Many thanks for reviews and text provided by Steve Kille and David
Wilson.
Author's Address
Alexey Melnikov
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
EMail: Alexey.Melnikov@isode.com
Melnikov Expires January 04, 2014 [Page 7]