datatracker.ietf.org
Sign in
Version 5.3.0, 2014-04-12
Report a bug

The Secure Real-time Transport Protocol (SRTP)
RFC 3711

Document type: RFC - Proposed Standard (March 2004; Errata)
Updated by RFC 6904, RFC 5506
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 3711 (Proposed Standard)
Responsible AD: Allison Mankin
Send notices to: <csp@csperkins.org>, <magnus.westerlund@ericsson.com>

Network Working Group                                         M. Baugher
Request for Comments: 3711                                     D. McGrew
Category: Standards Track                            Cisco Systems, Inc.
                                                              M. Naslund
                                                              E. Carrara
                                                              K. Norrman
                                                       Ericsson Research
                                                              March 2004

             The Secure Real-time Transport Protocol (SRTP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document describes the Secure Real-time Transport Protocol
   (SRTP), a profile of the Real-time Transport Protocol (RTP), which
   can provide confidentiality, message authentication, and replay
   protection to the RTP traffic and to the control traffic for RTP, the
   Real-time Transport Control Protocol (RTCP).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.  Notational Conventions . . . . . . . . . . . . . . . . .  3
   2.  Goals and Features . . . . . . . . . . . . . . . . . . . . . .  4
       2.1.  Features . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  SRTP Framework . . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.  Secure RTP . . . . . . . . . . . . . . . . . . . . . . .  6
       3.2.  SRTP Cryptographic Contexts. . . . . . . . . . . . . . .  7
             3.2.1.  Transform-independent parameters . . . . . . . .  8
             3.2.2.  Transform-dependent parameters . . . . . . . . . 10
             3.2.3.  Mapping SRTP Packets to Cryptographic Contexts . 10
       3.3.  SRTP Packet Processing . . . . . . . . . . . . . . . . . 11
             3.3.1.  Packet Index Determination, and ROC, s_l Update. 13
             3.3.2.  Replay Protection. . . . . . . . . . . . . . . . 15
      3.4.  Secure RTCP . . . . . . . . . . . . . . . . . . . . . . . 15

Baugher, et al.             Standards Track                     [Page 1]
RFC 3711                          SRTP                        March 2004

   4.  Pre-Defined Cryptographic Transforms . . . . . . . . . . . . . 19
       4.1.  Encryption . . . . . . . . . . . . . . . . . . . . . . . 19
             4.1.1.  AES in Counter Mode. . . . . . . . . . . . . . . 21
             4.1.2.  AES in f8-mode . . . . . . . . . . . . . . . . . 22
             4.1.3.  NULL Cipher. . . . . . . . . . . . . . . . . . . 25
       4.2.  Message Authentication and Integrity . . . . . . . . . . 25
             4.2.1.  HMAC-SHA1. . . . . . . . . . . . . . . . . . . . 25
       4.3.  Key Derivation . . . . . . . . . . . . . . . . . . . . . 26
             4.3.1.  Key Derivation Algorithm . . . . . . . . . . . . 26
             4.3.2.  SRTCP Key Derivation . . . . . . . . . . . . . . 28
             4.3.3.  AES-CM PRF . . . . . . . . . . . . . . . . . . . 28
   5.  Default and mandatory-to-implement Transforms. . . . . . . . . 28
       5.1.  Encryption: AES-CM and NULL. . . . . . . . . . . . . . . 29
       5.2.  Message Authentication/Integrity: HMAC-SHA1. . . . . . . 29
       5.3.  Key Derivation: AES-CM PRF . . . . . . . . . . . . . . . 29
   6.  Adding SRTP Transforms . . . . . . . . . . . . . . . . . . . . 29
   7.  Rationale. . . . . . . . . . . . . . . . . . . . . . . . . . . 30
       7.1.  Key derivation . . . . . . . . . . . . . . . . . . . . . 30
       7.2.  Salting key. . . . . . . . . . . . . . . . . . . . . . . 30
       7.3.  Message Integrity from Universal Hashing . . . . . . . . 31
       7.4.  Data Origin Authentication Considerations. . . . . . . . 31
       7.5.  Short and Zero-length Message Authentication . . . . . . 32
   8.  Key Management Considerations. . . . . . . . . . . . . . . . . 33
       8.1.  Re-keying  . . . . . . . . . . . . . . . . . . . . . . . 34
             8.1.1.  Use of the <From, To> for re-keying. . . . . . . 34
       8.2.  Key Management parameters. . . . . . . . . . . . . . . . 35
   9.  Security Considerations. . . . . . . . . . . . . . . . . . . . 37
       9.1.  SSRC collision and two-time pad. . . . . . . . . . . . . 37
       9.2.  Key Usage. . . . . . . . . . . . . . . . . . . . . . . . 38
       9.3.  Confidentiality of the RTP Payload . . . . . . . . . . . 39
       9.4.  Confidentiality of the RTP Header. . . . . . . . . . . . 40

[include full document text]