Network Working Group J. Fischl Internet-Draft CounterPath Solutions, Inc. Expires: August 30, 2006 H. Tschofenig Siemens February 26, 2006 Session Description Protocol (SDP) Indicators for Datagram Transport Layer Security (DTLS) draft-fischl-mmusic-sdp-dtls-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 30, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This specification defines how to use Session Description Protocol (SDP) to signal that media will be transported over Datagram Transport Layer Security (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 for the DTLS handshake. This allows the security provided Fischl & Tschofenig Expires August 30, 2006 [Page 1] Internet-Draft SDP for DTLS February 2006 by the existing TCP/TLS specifications for stream transported media to also be applicable to media 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 Fischl & Tschofenig Expires August 30, 2006 [Page 2] Internet-Draft SDP for DTLS February 2006 1. Introduction Session Description Protocol (SDP)[1] has been used to set up the transport of various types of media with RTP[7] over UDP[3], TCP[14], and TLS[9]. DTLS[10] is a protocol for applying TLS security to datagram protocols such as UDP and DCCP[2]. This specification defines new SDP protocol identifiers that allow SDP to indicate that DTLS should be used to transport the media. The handling of TLS session in SDP is defined in [9] which discusses only TLS over TCP. This document only 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 [4]. 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 [9]. 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 session, 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. [Editor's Note: Certificate lifetime issues will be discussed in a future draft version.] The endpoints MAY cache their certificates and reuse them across multiple sessions. Fischl & Tschofenig Expires August 30, 2006 [Page 3] Internet-Draft SDP for DTLS February 2006 4. SDP In addition to the usual contents of an SDP [8] message, each 'm' line will also contain several attributes as specified in [6] and [9]. The endpoint MUST use the setup and connection attributes defined in "TCP-Based Media Transport in the SDP" [6]. 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 [9]. 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/DTLS/RTP/xyz where xyz is replaced with an appropriate token for that profile. 6. IANA Considerations This specification updates the "Session Description Protocol (SDP) Parameters" registry at http://www.iana.org/assignments/sdp-parameters as defined in Appendix B of RFC 2327 [1]. Specifically it adds the following values to the Fischl & Tschofenig Expires August 30, 2006 [Page 4] Internet-Draft SDP for DTLS February 2006 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[5] signalling protocol is described in [16] 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] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [2] Kohler, E., "Datagram Congestion Control Protocol (DCCP)", draft-ietf-dccp-spec-13 (work in progress), December 2005. [3] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Fischl & Tschofenig Expires August 30, 2006 [Page 5] Internet-Draft SDP for DTLS February 2006 [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] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005. [7] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [8] Handley, M., "SDP: Session Description Protocol", draft-ietf-mmusic-sdp-new-26 (work in progress), January 2006. [9] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", draft-ietf-mmusic-comedia-tls-05 (work in progress), September 2005. [10] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", draft-rescorla-dtls-05 (work in progress), June 2005. 9.2. Informational References [11] Yon, D., "Connection-Oriented Media Transport in the Session Description Protocol (SDP)", draft-ietf-mmusic-sdp-comedia-10 (work in progress), November 2004. [12] Andreasen, F., "Session Description Protocol Security Descriptions for Media Streams", draft-ietf-mmusic-sdescriptions-12 (work in progress), September 2005. [13] Arkko, J., "Key Management Extensions for Session Description Protocol (SDP) and Real Time Streaming Protocol (RTSP)", draft-ietf-mmusic-kmgmt-ext-15 (work in progress), June 2005. [14] Lazzaro, J., "Framing RTP and RTCP Packets over Connection- Oriented Transport", draft-ietf-avt-rtp-framing-contrans-06 (work in progress), September 2005. [15] Rescorla, E., "TLS Partial Encryption Mode", draft-rescorla-tls-partial-00 (work in progress), January 2006. [16] Fischl, J., Tschofenig, H., and E. Rescorla, "Session Initiation Protocol (SIP) for Media Over Transport Layer Security (TLS)", February 2006. Fischl & Tschofenig Expires August 30, 2006 [Page 6] Internet-Draft SDP for DTLS February 2006 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 Siemens Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Email: Hannes.Tschofenig@siemens.com Fischl & Tschofenig Expires August 30, 2006 [Page 7] Internet-Draft SDP for DTLS February 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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