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Versions: (draft-fischl-mmusic-sdp-dtls) 00

Network Working Group                                          J. Fischl
Internet-Draft                               CounterPath Solutions, Inc.
Intended status: Standards Track                           H. Tschofenig
Expires: July 26, 2008                            Nokia Siemens Networks
                                                        January 23, 2008


  Session Description Protocol (SDP) Indicators for Datagram Transport
                         Layer Security (DTLS)
                   draft-ietf-mmusic-sdp-dtls-00.txt

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   This Internet-Draft will expire on July 26, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This specification defines how to use the Session Description
   Protocol (SDP) to signal that media will be transported over Datagram
   Transport Layer Security (DTLS) or where the SRTP security context is
   established using DTLS and.  It reuses the syntax and semantics for
   an SDP 'fingerprint' attribute that identifies the certificate which
   will be presented during the DTLS handshake.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  DTLS Certificates . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  SDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Session Description for RTP/SAVP over DTLS  . . . . . . . . . . 4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     9.2.  Informational References  . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8




































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1.  Introduction

   Session Description Protocol (SDP) RFC 2327 [7] has been used to set
   up the transport of various types of media with RTP [9] over UDP
   [10], TCP [14], and TLS [2].  DTLS [12] is a protocol for applying
   TLS security to datagram protocols such as UDP and DCCP [1].  This
   specification defines new SDP protocol syntax that allow SDP to
   indicate that DTLS should be used to transport the media when TLS is
   used.

   The handling of TLS sessions in SDP is defined in [2] that discusses
   only TLS over TCP.  This document extends that specification to also
   deal with TLS over datagram protocols such as UDP and DCCP and when
   (D)TLS is used to establish keys for SRTP as in [5]


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [6].


3.  DTLS Certificates

   The two endpoints in the exchange present their identities as part of
   the DTLS handshake procedure using certificates.  This document uses
   certificates in the same style as described in Comedia over TLS in
   SDP [2].

   If self-signed certificates are used, the content of the
   subjectAltName attribute inside the certificate MAY use the uniform
   resource identifier (URI) of the user.  This is useful for debugging
   purposes only and is not required to bind the certificate to one of
   the communication endpoints.  The integrity of the certificate is
   ensured through the fingerprint attribute in the SDP.  The
   subjectAltName is not an important component of the certificate
   verification.

   If the endpoint is also able to make anonymous sessions, a distinct,
   unique, self-signed certificate SHOULD be provided for this purpose.

   The generation of public/private key pairs is relatively expensive.
   Endpoints are not required to generate certificates for each session.

   The endpoints MAY cache their certificates and reuse them across
   multiple sessions.




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   [Editor's Note: Certificate lifetime issues will be discussed in a
   future draft version.]


4.  SDP

   In addition to the usual contents of an SDP [13] message, each 'm'
   line will also contain several attributes as specified in RFC 4145
   [11] and [2].

   The endpoint MUST use the setup and connection attributes defined in
   "TCP-Based Media Transport in the SDP" [11].  For the purposes of
   this specification, a setup:active endpoint will act as a DTLS client
   and a setup:passive endpoint will act as a DTLS server.  The
   connection attribute indicates whether or not to reuse an existing
   DTLS association.

   A certificate fingerprint is the output of a one-way hash function
   computed over the distinguished encoding rules (DER) form of the
   certificate.  The endpoint MUST use the certificate fingerprint
   attribute as specified in [2].

   TODO: The MMUSIC working group is currently studying the problem of
   signalling in SDP the ability/desire to initiate a secure channel
   rather than an insecure one [3][4].  We need to use those techniques
   when they are finalized.


5.  Session Description for RTP/SAVP over DTLS

   This specification defines new tokens to describe the protocol used
   in SDP "m=" lines.  The new values defined for the proto field are:

   o  When a RTP/SAVP stream is transported over DTLS with DCCP, then
      the token SHALL be DCCP/TLS/RTP/SAVP.
   o  When a RTP/SAVP stream is transported over DTLS with UDP, the
      token SHALL be UDP/TLS/RTP/SAVP.
   o  When a RTP/SAVP stream is transported over TLS with TCP, the token
      SHALL be TCP/TLS/RTP/SAVP.
   o  When media is transported over DTLS with UDP, the token SHALL be
      UDP/TLS.
   o  When media is transported over DTLS with DCCP, the token SHALL be
      DCCP/TLS.

   For RTP profiles other than AVP, a new token should be defined in the
   form of DCCP/TLS/RTP/xyz, UDP/TLS/RTP/xyz and TCP/TLS/RTP/xyz where
   xyz is replaced with an appropriate token for that profile.




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6.  IANA Considerations

   This specification updates the "Session Description Protocol (SDP)
   Parameters" registry as defined in Appendix B of RFC 2327 [7].
   Specifically it adds the following values to the table for the
   "proto" field.

   Type            SDP Name                     Reference
   ----            ------------------           ---------
   proto           TCP/TLS/RTP/SAVP              [RFC-XXXX]
                   UDP/TLS/RTP/SAVP              [RFC-XXXX]
                   DCCP/TLS/RTP/SAVP             [RFC-XXXX]
                   UDP/TLS                      [RFC-XXXX]
                   DCCP/TLS                     [RFC-XXXX]

   Note to RFC Editor: Please replace RFC-XXXX with the RFC number of
   this specification.


7.  Security Considerations

   When using self signed certificates, the signalling protocol used to
   transport the SDP MUST ensure the integrity of the SDP so that the
   fingerprint attribute can not be altered.  Failure to do this would
   allow a attacker to insert themselves in the media channel as a man-
   in-the-middle.  A method of ensuring the integrity of the SDP when
   transporting over the SIP RFC 3261 [8] signalling protocol is
   described in [15]


8.  Acknowledgments

   Cullen Jennings contributed substantial text and comments to this
   document.  This document benefitted from discussions with Francois
   Audet, Nagendra Modadugu, Eric Rescorla, and Dan Wing.  Thanks also
   for useful comments by Flemming Andreasen, Rohan Mahy, David McGrew,
   and David Oran.


9.  References

9.1.  Normative References

   [1]   Kohler, E., "Datagram Congestion Control Protocol (DCCP)",
         draft-ietf-dccp-spec-13 (work in progress), December 2005.

   [2]   Lennox, J., "Connection-Oriented Media Transport over the
         Transport Layer Security (TLS) Protocol in the Session



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         Description Protocol (SDP)", RFC 4572, July 2006.

   [3]   Andreasen, F., "SDP Capability Negotiation",
         draft-ietf-mmusic-sdp-capability-negotiation-08 (work in
         progress), December 2007.

   [4]   Andreasen, F., "SDP Capability Negotiation: Requirements and
         Review of Existing Work",
         draft-ietf-mmusic-sdp-capability-negotiation-reqts-01 (work in
         progress), March 2007.

   [5]   McGrew, D. and E. Rescorla, "Datagram Transport Layer Security
         (DTLS) Extension to Establish Keys for  Secure Real-time
         Transport Protocol (SRTP)", draft-ietf-avt-dtls-srtp-01 (work
         in progress), November 2007.

   [6]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [7]   Handley, M. and V. Jacobson, "SDP: Session Description
         Protocol", RFC 2327, April 1998.

   [8]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
         Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
         Session Initiation Protocol", RFC 3261, June 2002.

   [9]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
         "RTP: A Transport Protocol for Real-Time Applications", STD 64,
         RFC 3550, July 2003.

   [10]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
         Conferences with Minimal Control", STD 65, RFC 3551, July 2003.

   [11]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
         Session Description Protocol (SDP)", RFC 4145, September 2005.

   [12]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
         Security", RFC 4347, April 2006.

9.2.  Informational References

   [13]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
         Description Protocol", RFC 4566, July 2006.

   [14]  Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and
         RTP Control Protocol (RTCP) Packets over Connection-Oriented
         Transport", RFC 4571, July 2006.




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   [15]  Fischl, J., Tschofenig, H., and E. Rescorla, "Framework for
         Establishing an SRTP Security Context using DTLS",
         draft-ietf-sip-dtls-srtp-framework-00 (work in progress),
         November 2007.


Authors' Addresses

   Jason Fischl
   CounterPath Solutions, Inc.
   Suite 300, One Bentall Centre, 505 Burrard Street
   Vancouver, BC  V7X 1M3
   Canada

   Phone: +1 604 320-3340
   Email: jason@counterpath.com


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@nsn.com
   URI:   http://www.tschofenig.com
























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