DTLS-SRTP Handling in SIP Back-to-Back User Agents
RFC 7879

Document Type RFC - Proposed Standard (May 2016; No errata)
Last updated 2016-05-31
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Internet Engineering Task Force (IETF)                   R. Ravindranath
Request for Comments: 7879                                      T. Reddy
Category: Standards Track                                   G. Salgueiro
ISSN: 2070-1721                                                    Cisco
                                                              V. Pascual
                                                                  Oracle
                                                            P. Ravindran
                                                          Nokia Networks
                                                                May 2016

           DTLS-SRTP Handling in SIP Back-to-Back User Agents

Abstract

   Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs)
   exist on the signaling and media paths between the endpoints.  This
   document describes the behavior of B2BUAs when Secure Real-time
   Transport (SRTP) security context is set up with the Datagram
   Transport Layer Security (DTLS) protocol.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   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/rfc7879.

Ravindranath, et al.         Standards Track                    [Page 1]
RFC 7879             DTLS-SRTP Handling in SIP B2BUA            May 2016

Copyright Notice

   Copyright (c) 2016 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Goals and Scope of this Document  . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  B2BUAs Procedures to Allow End-to-End DTLS-SRTP . . . . . . .   5
   4.  Signaling-Plane B2BUA Handling of DTLS-SRTP . . . . . . . . .   5
     4.1.  Proxy-B2BUAs  . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Signaling-Only and SDP-Modifying Signaling-Only B2BUAs  .   6
   5.  Media-Plane B2BUA Handling of DTLS-SRTP . . . . . . . . . . .   6
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
       5.1.1.  Media Relay . . . . . . . . . . . . . . . . . . . . .   6
       5.1.2.  RTP- and RTCP-Aware Media-Aware B2BUA . . . . . . . .   8
   6.  Forking Considerations  . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

Ravindranath, et al.         Standards Track                    [Page 2]
RFC 7879             DTLS-SRTP Handling in SIP B2BUA            May 2016

1.  Introduction

1.1.  Overview

   [RFC5763] describes how the Session Initiation Protocol (SIP)
   [RFC3261] can be used to establish a Secure Real-time Transport
   Protocol (SRTP) [RFC3711] security context with the Datagram
   Transport Layer Security (DTLS) protocol [RFC6347].  It describes a
   mechanism for transporting a certificate fingerprint using the
   Session Description Protocol (SDP) [RFC4566].  The fingerprint
   identifies the certificate that will be presented during the DTLS
   handshake.  DTLS-SRTP is currently defined for point-to-point media
   sessions, in which there are exactly two participants.  Each DTLS-
   SRTP session (described in Section 3 of [RFC5764]) contains a single
   DTLS connection (if RTP and RTP Control Protocol (RTCP) are
   multiplexed) or two DTLS connections (if RTP and RTCP are not
   multiplexed), and either two SRTP contexts (if media traffic is
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