SIP C. Jennings Internet-Draft Cisco Systems Expires: January 13, 2006 N. Modadugu Stanford University July 12, 2005 Using DTLS as a Transport for SIP draft-jennings-sip-dtls-01 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 January 13, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This draft specifies how to use Datagram Transport Layer Security (DTLS) as a transport for SIP. DTLS is a new protocol for providing TLS security over a datagram protocol. This draft is being discussed on the sip@ietf.org mailing list. Jennings & Modadugu Expires January 13, 2006 [Page 1] Internet-Draft DTLS Transport for SIP July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Transport Parameters . . . . . . . . . . . . . . . . . . . . . 3 4. DTLS Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Locating DTLS SIP Servers . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9.1 Normative References . . . . . . . . . . . . . . . . . . . 5 9.2 Informational References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . 7 Jennings & Modadugu Expires January 13, 2006 [Page 2] Internet-Draft DTLS Transport for SIP July 2005 1. Introduction Datagram Transport Layer Security (DTLS) [7] provides communication privacy similar to TLS for datagram packets. SIP can run over both stream and datagram transports, including UDP and TCP. SIP already defines how to use TLS with stream oriented transports. This specification extends SIP to use DTLS with datagram oriented transports. There has been considerable discussion of why SIP needs DTLS when we have TLS. This is the wrong question. The right question is why SIP has UDP and TCP (not to mention SCTP). There are two reasons for believing that UDP is likely to be an important protocol in SIP for the foreseeable future. o In theory, there is no problem building systems that terminate a million TCP connections on a single host. In practice, the common operating systems used for building SIP aggregation devices make this impossible. To date, no one has demonstrated terminating over 100k SIP TCP connections to a single host. Doing that many connections with UDP has not been difficult. o If we want to talk about "running code" for SIP, it's UDP. Unless UDP is deprecated for SIP, it is important to provide a reasonable level of security for it. The dominant technique for providing security for SIP/TCP is DTLS. Although in principle S/MIME can be used to provide security for both SIP/UDP and SIP/TCP, deployment has been minimal. Given that SIP/UDP is not likely to disappear any time soon, this leaves us with two options: 1. Leave UDP users without a channel-level security mechanism; or 2. Provide SIP/UDP users with an alternate security mechanism. We don't consider the first option to be acceptable. The obvious approach to the second option is to use DTLS, which provides UDP with a level of channel security equivalent to that which TLS provides for TCP. 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. Transport Parameters SIP URIs can carry a transport parameter indicating the transport Jennings & Modadugu Expires January 13, 2006 [Page 3] Internet-Draft DTLS Transport for SIP July 2005 protocol to be used. This specification defines two new values for the transport parameter: "dtls-udp" for the SIP URI transport parameter to be used for messages sent using DTLS over UDP, and "dtls-dccp" for messages sent using DTLS over DCCP. The update to the ABNF in RFC 3261 for this parameter is the following: transport-param = "transport=" ( "udp" / "tcp" / "sctp" / "tls" / "tls-sctp" "dtls-dccp" / "dtls-udp" / other-transport) The following is an example of SIP URIs using "dtls-udp": sip:alice@example.com;transport=dtls-udp Via header fields also carry a transport protocol identifier. This specification extends RFC 3261 to define the value "DTLS-UDP" for DTLS over UDP and "DTLS-DCCP" for DTLS over DCCP. The update to the ABNF in RFC 3261 for this parameter is the following: transport = "UDP" / "TCP" / "TLS" / "SCTP" / "TLS-SCTP" "DTLS-DCCP" / "DTLS-UDP" / other-transport The following is an example Via header field: Via: SIP/2.0/DTLS-UDP atlanta.example.com:5060 4. DTLS Usage The normal rules for sending a request over UDP in RFC 3261 apply to sending over DTLS. Note that the congestion safety rules for UDP do not apply to DCCP. In addition, the normal rules for validating a TLS connection in RFC 3261 apply to DTLS connections. Requests with a SIPS URI can be sent over DTLS as well as TLS. 5. Locating DTLS SIP Servers The normal rules from RFC 3263 [4] apply when locating a SIP server that supports DTLS. The following new NAPTR[5] service values are defined: "SIPS+D2U" for UDP, and "SIPS+D2D" for DCCP. In addition, the service value "SIP+D2D" should be used for SIP without DTLS over DCCP. The default port for DTLS over UDP is 5061. Jennings & Modadugu Expires January 13, 2006 [Page 4] Internet-Draft DTLS Transport for SIP July 2005 6. Security Considerations The security issues with SIP using DTLS are equivalent to the issues of using SIP with TLS. All the security considerations in RFC 3261 relevant to TLS apply to DTLS. 7. IANA Considerations The IANA is requested to update the following entry to the "SIP/SIPS URI Parameters" registry. The reference to this RFC should appear in double-brackets and be appended to the list of references already listed on for the transport parameter, as indicated in RFC 3969 [6]. The result is shown below: Parameter Name Predefined Values Reference -------------- ----------------- --------- transport Yes [RFC3261] [[RFCXXXX]] This document also defines new NAPTR service field values. The IANA is requested to register these values under the "Registry for the SIP SRV Resource Record Services Field". The resulting entries should be: Services Field Protocol Reference -------------------- -------- --------- SIPS+D2U UDP [RFCXXXX] SIPS+D2D DCCP [RFCXXXX] SIP+D2D DCCP [RFCXXXX] [Note to IANA: Please replace XXXX with the RFC number of this specification.] 8. Acknowledgments Much of text and outline for this specification came from [8] authored by Jonathan Rosenberg, Henning Schulzrinne, and Gonzalo Camarillo. Eric Rescorla provided helpful comments and text. 9. References 9.1 Normative References [1] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", draft-rescorla-dtls-05 (work in progress), June 2005. [2] 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. Jennings & Modadugu Expires January 13, 2006 [Page 5] Internet-Draft DTLS Transport for SIP July 2005 [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, June 2002. [5] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002. 9.2 Informational References [6] Camarillo, G., "The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP)", BCP 99, RFC 3969, December 2004. [7] Kohler, E., "Datagram Congestion Control Protocol (DCCP)", draft-ietf-dccp-spec-09 (work in progress), November 2004. [8] Rosenberg, J., "The Stream Control Transmission Protocol (SCTP) as a Transport for the Session Initiation Protocol (SIP)", draft-ietf-sip-sctp-06 (work in progress), February 2005. Authors' Addresses Cullen Jennings Cisco Systems 170 West Tasman Drive MS: SJC-21/2 San Jose, CA 95134 USA Phone: +1 408 902-3341 Email: fluffy@cisco.com Nagendra Modadugu Stanford University 353 Serra Mall Stanford, CA 94305 USA Email: Nagendra@cs.stanford.edu Jennings & Modadugu Expires January 13, 2006 [Page 6] Internet-Draft DTLS Transport for SIP July 2005 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. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Jennings & Modadugu Expires January 13, 2006 [Page 7]