The Messaging Layer Security (MLS) Protocol
draft-ietf-mls-protocol-02

Document Type Active Internet-Draft (mls WG)
Last updated 2018-10-22
Replaces draft-barnes-mls-protocol
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Network Working Group                                          R. Barnes
Internet-Draft                                                     Cisco
Intended status: Informational                               J. Millican
Expires: April 25, 2019                                         Facebook
                                                                E. Omara
                                                                  Google
                                                          K. Cohn-Gordon
                                                    University of Oxford
                                                               R. Robert
                                                                    Wire
                                                        October 22, 2018

              The Messaging Layer Security (MLS) Protocol
                       draft-ietf-mls-protocol-02

Abstract

   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
   participants 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.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   This Internet-Draft will expire on April 25, 2019.

Barnes, et al.           Expires April 25, 2019                 [Page 1]
Internet-Draft                     MLS                      October 2018

Copyright Notice

   Copyright (c) 2018 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Change Log  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Basic Assumptions . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Ratchet Trees . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Tree Computation Terminology  . . . . . . . . . . . . . .   9
     5.2.  Ratchet Tree Nodes  . . . . . . . . . . . . . . . . . . .  12
     5.3.  Blank Nodes and Resolution  . . . . . . . . . . . . . . .  13
     5.4.  Ratchet Tree Updates  . . . . . . . . . . . . . . . . . .  13
     5.5.  Cryptographic Objects . . . . . . . . . . . . . . . . . .  15
       5.5.1.  Curve25519, SHA-256, and AES-128-GCM  . . . . . . . .  15
       5.5.2.  P-256, SHA-256, and AES-128-GCM . . . . . . . . . . .  16
     5.6.  Credentials . . . . . . . . . . . . . . . . . . . . . . .  17
     5.7.  Group State . . . . . . . . . . . . . . . . . . . . . . .  17
     5.8.  Direct Paths  . . . . . . . . . . . . . . . . . . . . . .  19
     5.9.  Key Schedule  . . . . . . . . . . . . . . . . . . . . . .  20
   6.  Initialization Keys . . . . . . . . . . . . . . . . . . . . .  22
   7.  Handshake Messages  . . . . . . . . . . . . . . . . . . . . .  22
     7.1.  Init  . . . . . . . . . . . . . . . . . . . . . . . . . .  24
     7.2.  Add . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     7.3.  Update  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     7.4.  Remove  . . . . . . . . . . . . . . . . . . . . . . . . .  27
   8.  Sequencing of State Changes . . . . . . . . . . . . . . . . .  28
     8.1.  Server-Enforced Ordering  . . . . . . . . . . . . . . . .  29
     8.2.  Client-Enforced Ordering  . . . . . . . . . . . . . . . .  29
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