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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 7912

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                          October 14, 2013
Expires: April 17, 2014


                         MMHS Draft and Release
                draft-melnikov-mmhs-authorizing-users-01

Abstract

   This document describes a procedure for when an Military Message
   Handling System (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 April 17, 2014.

Copyright Notice

   Copyright (c) 2013 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



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   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
     7.1.  Forged Header Fields  . . . . . . . . . . . . . . . . . .   5
     7.2.  Intentionally Malformed Header Fields . . . . . . . . . .   6
   8.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   7

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]
   [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

   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].





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   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 Message
   Submission Agent (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.

   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.





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   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] mailbox-list [FWS] CRLF

       mailbox-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].

   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.



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   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 Names",
   defined by Registration Procedures for Message Header Fields
   [RFC3864].  The registration template is as follows:

   Header field name: MMHS-Authorizing-Users

   Applicable protocol: mail ([RFC5322])

   Status: Standard

   Author/Change controller: IETF

   Specification document(s): [[RFC XXXX]]

   Related information:

7.  Security Considerations

7.1.  Forged Header Fields

   A malicious sender may add/change an MMHS-Authorizing-Users header
   field to bypass or alter message authorization procedure invoked for



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   messages with no MMHS-Authorizing-Users header field.  For that
   reason it is important for agents and clients that rely on validity
   of MMHS-Authorizing-Users header field to also verify
   countersignature (or a similar protection mechanism), that confirms
   that a particular person or entity authorized release of a message.

7.2.  Intentionally Malformed Header Fields

   It is possible for an attacker to add an MMHS-Authorizing-Users
   header field that is extraordinarily large or otherwise malformed in
   an attempt to discover or exploit weaknesses in header field parsing
   code.  Implementers must thoroughly verify all such header fields
   received from MTAs and be robust against intentionally as well as
   unintentionally malformed header fields.

8.  Open Issues

   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?

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.



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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

   Many thanks for reviews and text provided by Steve Kille and David
   Wilson.

   Some text in this document was copied from RFC 7001.

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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