MLS R. Mahy Internet-Draft Wire Intended status: Informational 10 July 2023 Expires: 11 January 2024 A Messaging Layer Security (MLS) extension for More Instant Messaging Interoperability (MIMI) room policies draft-mahy-mls-room-policy-ext-latest Abstract This document describes a Message Layer Security (MLS) GroupContext extension to include More Instant Messaging Interoperability (MIMI) group chat (room) policy inside an MLS group. This allows all users in a group to agree on the current policy and make authorization decisions accordingly. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-mahy-mls-room-policy-ext/. Discussion of this document takes place on the MLS Working Group mailing list (mailto:mls@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/mls/. Subscribe at https://www.ietf.org/mailman/listinfo/mls/. Source for this draft and an issue tracker can be found at https://github.com/rohan-wire/mls-room-policy-ext/. 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 11 January 2024. Copyright Notice Copyright (c) 2023 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 (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. Conventions and Definitions 3. Extension Description 4. Security Considerations 5. IANA Considerations 5.1. room_policy MLS Extension Type 6. Normative References Author's Address 1. Introduction The More Instant Messaging Interoperability (MIMI) group chat framework [I-D.mahy-mimi-group-chat] defines a room policy format. This document describes a Message Layer Security (MLS) [I-D.ietf-mls-protocol] GroupContext extension that allows all users in a group to agree on the current policy and make authorization decisions accordingly. 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. The terms MLS client, MLS group, GroupContext, Commit, Proposal, GroupContextExtensions Proposal, andrequired_capabilities have the same meanings as in the MLS protocol [@!I-D.ietf-mls-protocol]. 3. Extension Description This document specifies a GroupContext MLS extension room_policy of type RoomPolicy (defined in Section 8 of [I-D.mahy-mimi-group-chat]). The syntax is described using the TLS Presentation Language [@!RFC8446]. RoomPolicy room_policy; An MLS client which implements this specification SHOULD include the room_policy extension in the extensions field in the GroupContext of groups it creates which have an associated room policy. It includes a machine readable description of the room policy sufficient for all clients in the group to authorize MLS primitives (like a Commit with an Add Proposal). As new members of the group are added or removed, the member which Commits these membership changes is expected to maintain the room_policy up-to-date, and consistent with the membership of the group by also including an appropriate GroupContextExtensions Proposal any time the policy changes. It also allows a client to inspect the room_policy before joining to determine if the policies are consistent with its own. 4. Security Considerations The Security Considerations of MLS apply. The authorization rules for the RoomPolicy object are described in detail in [I-D.mahy-mimi-group-chat]. Improper use of the extension in this document could allow the creator of an MLS group or the sender of a GroupContextExtensions Proposal to maliciously modify or subvert the policies of a group chat which could result in viewing private information about the participants of the room, loss of confidentiality of the contents of the room (after subverting the policies and until the policies are corrected), and injecting potentially unwanted messages into the room (spam, abuse, phishing, and attempted impersonation). 5. IANA Considerations This document proposes registration of a new MLS Extension Type. RFC EDITOR: Please replace XXXX throughout with the RFC number assigned to this document 5.1. room_policy MLS Extension Type The room_policy MLS Extension Type is used inside GroupContext objects. It contains a RoomPolicy object as defined in Section 8 of [I-D.mahy-mimi-group-chat], representing the room policy for the MLS group corresponding with the room. Template: Value: 0x000B Name: room_policy Message(s): This extension may appear in GroupContext objects Recommended: Y Reference: RFC XXXX 6. Normative References [I-D.ietf-mls-protocol] Barnes, R., Beurdouche, B., Robert, R., Millican, J., Omara, E., and K. Cohn-Gordon, "The Messaging Layer Security (MLS) Protocol", Work in Progress, Internet- Draft, draft-ietf-mls-protocol-20, 27 March 2023, . [I-D.mahy-mimi-group-chat] Mahy, R., "Group Chat Framework for More Instant Messaging Interoperability (MIMI)", Work in Progress, Internet- Draft, draft-mahy-mimi-group-chat-00, 10 July 2023, . [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, . Author's Address Rohan Mahy Wire Email: rohan.mahy@wire.com