



More Instant Messaging Interoperability                          R. Mahy
Internet-Draft                                             19 April 2026
Intended status: Informational                                          
Expires: 21 October 2026


  Conveying the More Instant Messaging Interoperability Message ID in
         Messaging Layer Security Additional Authenticated Data
                      draft-mahy-mimi-msgid-aad-02

Abstract

   The More Instant Messaging Interoperability (MIMI) content format
   defines a MIMI Message ID, communicated only to members of the
   Messaging Layer Security (MLS) group in which the message was sent.
   This document defines a way to share a Message ID in the MLS
   Additional Authenticated Data (AAD) so it is visible to MIMI
   providers.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://rohanmahy.github.io/mimi-msgid-aad/draft-mahy-mimi-msgid-
   aad.html.  Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-mahy-mimi-msgid-aad/.

   Discussion of this document takes place on the More Instant Messaging
   Interoperability mailing list (mailto:mimi@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/mimi/.
   Subscribe at https://www.ietf.org/mailman/listinfo/mimi/.

   Source for this draft and an issue tracker can be found at
   https://github.com/rohanmahy/mimi-msgid-aad.

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 https://datatracker.ietf.org/drafts/current/.






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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 21 October 2026.

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   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     5.1.  message_id MLS Component Type . . . . . . . . . . . . . .   3
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Many messaging protocols and formats have a Message ID.  The MIMI
   content format defines how to calculate a MIMI Message ID (See
   Section 3.3 of [I-D.ietf-mimi-content]) for an application/mimi-
   content application message.  A MIMI Message ID is currently only
   shared end-to-end encrypted with members of the MLS [RFC9420] group
   in which the message was sent.  This document defines an optional
   mechanism to share a Message ID in the MLS AAD, so it is visible to
   intermediary providers.  This greatly facilitates debugging and
   troubleshooting, but causes a modest reduction in privacy.







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2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Mechanism

   This document defines a new Safe AAD message_id component as
   described in Section 4.9 of [I-D.ietf-mls-extensions].

   When the content of an MLS application message is a MIMI content
   message (media type application/mimi-content), if the message_id
   component is present inside SafeAAD.aad_items, it MUST contain the
   MIMI content Message ID calculated as described in Section 3.3 of
   [I-D.ietf-mimi-content].

      To the extent that other application formats or media types have a
      Message ID, the Message ID for an application message of that type
      or format MAY be conveyed in this extension, using a message ID
      appropriate to the media type of the content.

4.  Security Considerations

   An attacker or provider with access to a fragment of message history,
   and the message logs of a MIMI provider in the path of a message
   could potentially learn more about the participants of a particular
   MIMI room or the room's corresponding MLS group if it can see message
   IDs.

5.  IANA Considerations

5.1.  message_id MLS Component Type

   This document registers a new MLS Component Type in the Specification
   Required range with the following template:

   *  Value: TBD (suggested value 0x0040)

   *  Name: message_id

   *  Where: AD

   *  Recommended: Y

   *  Reference: RFC XXXX



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6.  Normative References

   [I-D.ietf-mimi-content]
              Mahy, R., "More Instant Messaging Interoperability (MIMI)
              message content", Work in Progress, Internet-Draft, draft-
              ietf-mimi-content-08, 2 March 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mimi-
              content-08>.

   [I-D.ietf-mls-extensions]
              Robert, R., "The Messaging Layer Security (MLS)
              Extensions", Work in Progress, Internet-Draft, draft-ietf-
              mls-extensions-09, 2 March 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mls-
              extensions-09>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC9420]  Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
              Omara, E., and K. Cohn-Gordon, "The Messaging Layer
              Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
              July 2023, <https://www.rfc-editor.org/rfc/rfc9420>.

Acknowledgments

   TODO acknowledge.

Author's Address

   Rohan Mahy
   Email: rohan.mahy@gmail.com













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