The Messaging Layer Security (MLS) Protocol
draft-barnes-mls-protocol-00
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Network Working Group R. Barnes
Internet-Draft Cisco
Intended status: Informational J. Millican
Expires: August 6, 2018 Facebook
E. Omara
Google
K. Cohn-Gordon
University of Oxford
R. Robert
Wire
February 02, 2018
The Messaging Layer Security (MLS) Protocol
draft-barnes-mls-protocol-00
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
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 August 6, 2018.
Barnes, et al. Expires August 6, 2018 [Page 1]
Internet-Draft MLS February 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
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Basic Assumptions . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
5. Binary Trees . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Merkle Trees . . . . . . . . . . . . . . . . . . . . . . 11
5.2.1. Merkle Proofs . . . . . . . . . . . . . . . . . . . . 12
5.3. Ratchet Trees . . . . . . . . . . . . . . . . . . . . . . 12
5.3.1. Blank Ratchet Tree Nodes . . . . . . . . . . . . . . 13
6. Group State . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Cryptographic Objects . . . . . . . . . . . . . . . . . . 15
6.1.1. Curve25519 with SHA-256 . . . . . . . . . . . . . . . 15
6.1.2. P-256 with SHA-256 . . . . . . . . . . . . . . . . . 16
6.2. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 17
7. Initialization Keys . . . . . . . . . . . . . . . . . . . . . 18
7.1. UserInitKey . . . . . . . . . . . . . . . . . . . . . . . 18
7.2. GroupInitKey . . . . . . . . . . . . . . . . . . . . . . 19
8. Handshake Messages . . . . . . . . . . . . . . . . . . . . . 20
8.1. Init . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.2. GroupAdd . . . . . . . . . . . . . . . . . . . . . . . . 22
8.3. UserAdd . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.4. Update . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.5. Delete . . . . . . . . . . . . . . . . . . . . . . . . . 24
9. Sequencing of State Changes . . . . . . . . . . . . . . . . . 25
9.1. Server-side enforced ordering . . . . . . . . . . . . . . 26
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