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. 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/. 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 22 January 2027. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Mahy Expires 22 January 2027 [Page 1] Internet-Draft MLS Out-Of-Band AAD July 2026 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. 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 Mahy Expires 22 January 2027 [Page 2] Internet-Draft MLS Out-Of-Band AAD July 2026 struct { opaque group_id; uint64 epoch; ContentType content_type; SafeAADItem oob_aad; /* <== this is new */ opaque authenticated_data; /* usually just SafeAAD */ } PrivateContentAAD; struct { ProtocolVersion version = mls10; WireFormat wire_format; FramedContent content; /* can contain SafeAAD */ SafeAADItem oob_aad; /* <== 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. Mahy Expires 22 January 2027 [Page 3] Internet-Draft MLS Out-Of-Band AAD July 2026 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 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, . Acknowledgments TODO acknowledge. Author's Address Rohan Mahy Email: rohan.ietf@gmail.com Mahy Expires 22 January 2027 [Page 4]