MLS Extension for Out-Of-Band Additional Authenticated Data
draft-mahy-oob-aad-00

Network Working Group                                            R. Mahy
Internet-Draft                                              21 July 2026
Intended status: Informational                                          
Expires: 22 January 2027

      MLS Extension for Out-Of-Band Additional Authenticated Data
                         draft-mahy-oob-aad-00

Abstract

   This document specifies an explicit way to signal that the Additional
   Authenticated Data does include or should include data elements that
   are conveyed out-of-band (ex: are not in the MLS message).

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/mls-oob-aad/draft-mahy-oob-aad.html.
   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-mahy-oob-aad/.

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

Status of This Memo

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

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   This Internet-Draft will expire on 22 January 2027.

Copyright Notice

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

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   2
   3.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The Messaging Layer Security (MLS) protocol includes message types
   with Additional Authenticated Data.

   [I-D.pham-mls-additional-wire-formats] defined new MLS Wire Formats
   for a similar purpose, however the Wire Format should be orthogonal
   to out-of-band AAD functionality.

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.

   Out-Of-Band AAD and In-Band AAD.

3.  Mechanism

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   struct {
       opaque group_id<V>;
       uint64 epoch;
       ContentType content_type;
       SafeAADItem oob_aad<V>;        /*  <== this is new     */
       opaque authenticated_data<V>;  /* usually just SafeAAD */
   } PrivateContentAAD;

   struct {
       ProtocolVersion version = mls10;
       WireFormat wire_format;
       FramedContent content;         /* can contain SafeAAD  */
       SafeAADItem oob_aad<V>;        /*  <== this is new     */
       select (FramedContentTBS.content.sender.sender_type) {
           case member:
           case new_member_commit:
               GroupContext context;
           case external:
           case new_member_proposal:
               struct{};
       };
   } FramedContentTBS;

   Consists of:

   *  a oob-aad extension type.  This specification cannot be a "safe"
      extension according to [I-D.ietf-mls-extensions] since it requires
      the MLS stack to modify its behavior outside of the concept of the
      specific components it also defines.  The presence of the oob-aad
      extension type in the GroupContext means that all members of the
      group support the extensions and that if an out-of-band AAD
      component is signaled, the members of the room will include its
      actual value in Out-Of-Band AAD, without communicating it in the
      authenticated_data.

   *  an default-oob-aad-component component type.  When present in the
      app_data_dictionary in the GroupContext, the out-of-band value of
      each signaled as-needed component is also included in the Out-Of-
      Band AAD.

   *  an as-needed-oob-aad-component component type.

      -  When present in the app_data_dictionary in the GroupContext it
         enumerates OOB AAD that can be signaled on a per-message basis.

      -  When present as a SafeAadItem in the aad_items list in the
         authenticated_content, the out-of-band value of each signaled
         as-needed component is also included in the Out-Of-Band AAD.

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4.  Security Considerations

   TODO Security

5.  IANA Considerations

   This document has no IANA actions.

6.  References

6.1.  Normative References

   [I-D.ietf-mls-extensions]
              Robert, R., "The Messaging Layer Security (MLS)
              Extensions", Work in Progress, Internet-Draft, draft-ietf-
              mls-extensions-10, 6 July 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mls-
              extensions-10>.

   [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>.

6.2.  Informative References

   [I-D.pham-mls-additional-wire-formats]
              Pham, A., Mularczyk, M., Robert, R., and P. Slatala, "MLS
              Wire Formats for PublicMessage and PrivateMessage without
              authenticated_data", Work in Progress, Internet-Draft,
              draft-pham-mls-additional-wire-formats-00, 21 October
              2024, <https://datatracker.ietf.org/doc/html/draft-pham-
              mls-additional-wire-formats-00>.

Acknowledgments

   TODO acknowledge.

Author's Address

   Rohan Mahy
   Email: rohan.ietf@gmail.com

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