]> Wire

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sec MLS room policy MIMI room_policy group chat 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 Status information for this document may be found at . Discussion of this document takes place on the MLS Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction The More Instant Messaging Interoperability (MIMI) group chat framework defines a room policy format. This document describes a Message Layer Security (MLS) GroupContext extension that allows all users in a group to agree on the current policy and make authorization decisions accordingly.

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 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].

Extension Description This document specifies a GroupContext MLS extension room_policy of type RoomPolicy (defined in Section 8 of ). The syntax is described using the TLS Presentation Language [@!RFC8446]. 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.

Security Considerations The Security Considerations of MLS apply. The authorization rules for the RoomPolicy object are described in detail in . 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).

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

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 , representing the room policy for the MLS group corresponding with the room.

Normative References Wire This document describes a group instant messaging ("group chat") semantic framework for the More Instant Messaging Interoperability (MIMI) Working Group. It describes several properties and policy options which can be combined to model a wide range of chat and multimedia conference types. It also describes how to build these options as an overlay to Messaging Layer Security (MLS) groups and to authorize MLS primitives. Cisco Inria & Mozilla Phoenix R&D Meta Platforms Google University of Oxford Messaging applications are increasingly making use of end-to-end security mechanisms to ensure that messages are only accessible to the communicating endpoints, and not to any servers involved in delivering messages. Establishing keys to provide such protections is challenging for group chat settings, in which more than two clients need to agree on a key but may not be online at the same time. In this document, we specify a key establishment protocol that provides efficient asynchronous group key establishment with forward secrecy and post-compromise security for groups in size ranging from two to thousands. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.