The Messaging Layer Security (MLS) Architecture
draft-ietf-mls-architecture-04

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Network Working Group                                           E. Omara
Internet-Draft                                                    Google
Intended status: Informational                             B. Beurdouche
Expires: July 29, 2020                                             INRIA
                                                             E. Rescorla
                                                                 Mozilla
                                                               S. Inguva
                                                                 Twitter
                                                                 A. Kwon
                                                                     MIT
                                                                A. Duric
                                                                    Wire
                                                        January 26, 2020

            The Messaging Layer Security (MLS) Architecture
                     draft-ietf-mls-architecture-04

Abstract

   This document describes the reference architecture, functional and
   security requirements for the Messaging Layer Security (MLS)
   protocol.  MLS provides a security layer for group messaging
   applications with from two to a large number of clients.  It is meant
   to protect against eavesdropping, tampering, and message forgery.

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 July 29, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Omara, et al.             Expires July 29, 2020                 [Page 1]
Internet-Draft              MLS Architecture                January 2020

   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  General Setting . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Group, Members and Clients  . . . . . . . . . . . . . . .   5
     2.2.  Authentication Service  . . . . . . . . . . . . . . . . .   6
     2.3.  Delivery Service  . . . . . . . . . . . . . . . . . . . .   7
       2.3.1.  Key Storage . . . . . . . . . . . . . . . . . . . . .   8
       2.3.2.  Key Retrieval . . . . . . . . . . . . . . . . . . . .   8
       2.3.3.  Delivery of messages and attachments  . . . . . . . .   8
       2.3.4.  Membership knowledge  . . . . . . . . . . . . . . . .   9
       2.3.5.  Membership and offline members  . . . . . . . . . . .  10
   3.  System Requirements . . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Functional Requirements . . . . . . . . . . . . . . . . .  10
       3.1.1.  Asynchronous Usage  . . . . . . . . . . . . . . . . .  10
       3.1.2.  Recovery After State Loss . . . . . . . . . . . . . .  10
       3.1.3.  Support for Multiple Devices  . . . . . . . . . . . .  11
       3.1.4.  Extensibility / Pluggability  . . . . . . . . . . . .  11
       3.1.5.  Privacy . . . . . . . . . . . . . . . . . . . . . . .  11
       3.1.6.  Federation  . . . . . . . . . . . . . . . . . . . . .  11
       3.1.7.  Compatibility with future versions of MLS . . . . . .  12
     3.2.  Security Requirements . . . . . . . . . . . . . . . . . .  12
       3.2.1.  Connections between Clients and Servers (one-to-one)   12
       3.2.2.  Message Secrecy and Authentication  . . . . . . . . .  12
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     4.1.  Transport Security Links  . . . . . . . . . . . . . . . .  15
     4.2.  Delivery Service Compromise . . . . . . . . . . . . . . .  15
     4.3.  Authentication Service Compromise . . . . . . . . . . . .  16
     4.4.  Client Compromise . . . . . . . . . . . . . . . . . . . .  16
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16