Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure Real-time Transport Protocol (SRTP)
RFC 5764

Internet Engineering Task Force (IETF)                         D. McGrew
Request for Comments: 5764                                 Cisco Systems
Category: Standards Track                                    E. Rescorla
ISSN: 2070-1721                                               RTFM, Inc.
                                                                May 2010

  Datagram Transport Layer Security (DTLS) Extension to Establish Keys
           for the Secure Real-time Transport Protocol (SRTP)

Abstract

   This document describes a Datagram Transport Layer Security (DTLS)
   extension to establish keys for Secure RTP (SRTP) and Secure RTP
   Control Protocol (SRTCP) flows.  DTLS keying happens on the media
   path, independent of any out-of-band signalling channel present.

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 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/rfc5764.

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McGrew & Rescorla            Standards Track                    [Page 1]
RFC 5764                 SRTP Extension for DTLS                May 2010

   This document may contain material from IETF Documents or IETF
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   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
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   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used In This Document  . . . . . . . . . . . . . .  3
   3.  Overview of DTLS-SRTP Operation  . . . . . . . . . . . . . . .  4
   4.  DTLS Extensions for SRTP Key Establishment . . . . . . . . . .  5
     4.1.  The use_srtp Extension . . . . . . . . . . . . . . . . . .  5
       4.1.1.  use_srtp Extension Definition  . . . . . . . . . . . .  7
       4.1.2.  SRTP Protection Profiles . . . . . . . . . . . . . . .  8
       4.1.3.  srtp_mki value . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Key Derivation . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Key Scope  . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.4.  Key Usage Limitations  . . . . . . . . . . . . . . . . . . 12
   5.  Use of RTP and RTCP over a DTLS-SRTP Channel . . . . . . . . . 13
     5.1.  Data Protection  . . . . . . . . . . . . . . . . . . . . . 13
       5.1.1.  Transmission . . . . . . . . . . . . . . . . . . . . . 13
       5.1.2.  Reception  . . . . . . . . . . . . . . . . . . . . . . 13
     5.2.  Rehandshake and Rekey  . . . . . . . . . . . . . . . . . . 16
   6.  Multi-Party RTP Sessions . . . . . . . . . . . . . . . . . . . 17
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
     7.1.  Security of Negotiation  . . . . . . . . . . . . . . . . . 17
     7.2.  Framing Confusion  . . . . . . . . . . . . . . . . . . . . 17
     7.3.  Sequence Number Interactions . . . . . . . . . . . . . . . 18
       7.3.1.  Alerts . . . . . . . . . . . . . . . . . . . . . . . . 18
       7.3.2.  Renegotiation  . . . . . . . . . . . . . . . . . . . . 18
     7.4.  Decryption Cost  . . . . . . . . . . . . . . . . . . . . . 19
   8.  Session Description for RTP/SAVP over DTLS . . . . . . . . . . 19
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20