One document matched: draft-fischl-mmusic-sdp-dtls-01.txt
Differences from draft-fischl-mmusic-sdp-dtls-00.txt
Network Working Group J. Fischl
Internet-Draft CounterPath Solutions, Inc.
Expires: December 27, 2006 H. Tschofenig
June 25, 2006
Session Description Protocol (SDP) Indicators for Datagram Transport
Layer Security (DTLS)
draft-fischl-mmusic-sdp-dtls-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
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 defines new SDP protocol identifiers.
It reuses the syntax and semantics for an SDP 'fingerprint' attribute
that identifies the certificate which will be presented during the
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DTLS handshake. This allows security provided by the existing DTLS
specification to also be applicable to data that is transported over
a datagram oriented transport.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DTLS Certificates . . . . . . . . . . . . . . . . . . . . . . . 3
4. SDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Session Description for RTP/AVP over DTLS . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
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 [4] has been used to set
up the transport of various types of media with RTP [6] over UDP [7],
TCP [11], and TLS [2]. DTLS [9] is a protocol for applying TLS
security to datagram protocols such as UDP and DCCP [1]. This
specification defines new SDP protocol identifiers 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.
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 [3].
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.
[Editor's Note: Certificate lifetime issues will be discussed in a
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future draft version.]
4. SDP
In addition to the usual contents of an SDP [10] message, each 'm'
line will also contain several attributes as specified in RFC 4145
[8] and [2].
The endpoint MUST use the setup and connection attributes defined in
"TCP-Based Media Transport in the SDP" [8]. 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].
The proto field of the "m=" line MUST be set to the appropriate
transport protocol as defined in this specification.
5. Session Description for RTP/AVP 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/AVP stream is transported over DTLS with DCCP, then the
token SHALL be DCCP/TLS/RTP/AVP.
o When a RTP/AVP stream is transported over DTLS with UDP, the token
SHALL be UDP/TLS/RTP/AVP.
o When a RTP/AVP stream is transported over TLS with TCP, the token
SHALL be TCP/TLS/RTP/AVP.
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.
6. IANA Considerations
This specification updates the "Session Description Protocol (SDP)
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Parameters" registry as defined in Appendix B of RFC 2327 [4].
Specifically it adds the following values to the table for the
"proto" field.
Type SDP Name Reference
---- ------------------ ---------
proto TCP/TLS/RTP/AVP [RFC-XXXX]
UDP/TLS/RTP/AVP [RFC-XXXX]
DCCP/TLS/RTP/AVP [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 [5] signalling protocol is
described in [12]
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
Description Protocol (SDP)", draft-ietf-mmusic-comedia-tls-06
(work in progress), March 2006.
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[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[5] 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.
[6] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[7] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
[8] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
Session Description Protocol (SDP)", RFC 4145, September 2005.
[9] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
9.2. Informational References
[10] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006.
[11] Lazzaro, J., "Framing RTP and RTCP Packets over Connection-
Oriented Transport", draft-ietf-avt-rtp-framing-contrans-06
(work in progress), September 2005.
[12] Fischl, J., Tschofenig, H., and E. Rescorla, "Session
Initiation Protocol (SIP) for Media Over Transport Layer
Security (TLS)", June 2006.
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Authors' Addresses
Jason Fischl
CounterPath Solutions, Inc.
8th Floor, 100 West Pender Street
Vancouver, BC V6B 1R8
Canada
Phone: +1 604 320-3340
Email: jason@counterpath.com
Hannes Tschofenig
Email: Hannes.Tschofenig@gmx.net
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