ZRTP: Media Path Key Agreement for Unicast Secure RTP
RFC 6189

 
Document Type RFC - Informational (April 2011; No errata)
Was draft-zimmermann-avt-zrtp (individual in rai area)
Last updated 2013-03-02
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IESG IESG state RFC 6189 (Informational)
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Responsible AD Robert Sparks
Send notices to prz@mit.edu, alan.b.johnston@gmail.com, jon@callas.org, draft-zimmermann-avt-zrtp@ietf.org

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Internet Engineering Task Force (IETF)                     P. Zimmermann
Request for Comments: 6189                                 Zfone Project
Category: Informational                                 A. Johnston, Ed.
ISSN: 2070-1721                                                    Avaya
                                                               J. Callas
                                                             Apple, Inc.
                                                              April 2011

         ZRTP: Media Path Key Agreement for Unicast Secure RTP

Abstract

   This document defines ZRTP, a protocol for media path Diffie-Hellman
   exchange to agree on a session key and parameters for establishing
   unicast Secure Real-time Transport Protocol (SRTP) sessions for Voice
   over IP (VoIP) applications.  The ZRTP protocol is media path keying
   because it is multiplexed on the same port as RTP and does not
   require support in the signaling protocol.  ZRTP does not assume a
   Public Key Infrastructure (PKI) or require the complexity of
   certificates in end devices.  For the media session, ZRTP provides
   confidentiality, protection against man-in-the-middle (MiTM) attacks,
   and, in cases where the signaling protocol provides end-to-end
   integrity protection, authentication.  ZRTP can utilize a Session
   Description Protocol (SDP) attribute to provide discovery and
   authentication through the signaling channel.  To provide best effort
   SRTP, ZRTP utilizes normal RTP/AVP (Audio-Visual Profile) profiles.
   ZRTP secures media sessions that include a voice media stream and can
   also secure media sessions that do not include voice by using an
   optional digital signature.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6189.

Zimmermann, et al.            Informational                     [Page 1]
RFC 6189                          ZRTP                        April 2011

Copyright Notice

   Copyright (c) 2011 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
   (http://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 ....................................................4
   2. Terminology .....................................................5
   3. Overview ........................................................6
      3.1. Key Agreement Modes ........................................7
           3.1.1. Diffie-Hellman Mode Overview ........................7
           3.1.2. Preshared Mode Overview .............................9
           3.1.3. Multistream Mode Overview ...........................9
   4. Protocol Description ...........................................10
      4.1. Discovery .................................................10
           4.1.1. Protocol Version Negotiation .......................11
           4.1.2. Algorithm Negotiation ..............................13
      4.2. Commit Contention .........................................14
      4.3. Matching Shared Secret Determination ......................15
           4.3.1. Calculation and Comparison of Hashes of
                  Shared Secrets .....................................17
           4.3.2. Handling a Shared Secret Cache Mismatch ............18
      4.4. DH and Non-DH Key Agreements ..............................19
           4.4.1. Diffie-Hellman Mode ................................19
                  4.4.1.1. Hash Commitment in Diffie-Hellman Mode ....20
                  4.4.1.2. Responder Behavior in
                           Diffie-Hellman Mode .......................21
                  4.4.1.3. Initiator Behavior in
                           Diffie-Hellman Mode .......................22
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