A Messaging Layer Security (MLS) extension for More Instant Messaging Interoperability (MIMI) room policies

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

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¶

  Template:
  Value: 0x000B
  Name: room_policy
  Message(s): This extension may appear in GroupContext objects
  Recommended: Y
  Reference: RFC XXXX

Author's Address