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Versions: 00 01 02 03 04 05                                             
Network Working Group                                        C. Jennings
Internet-Draft                                             Cisco Systems
Expires: September 26, 2006                                  N. Modadugu
                                                     Stanford University
                                                          March 25, 2006


Session Initiation Protocol (SIP) over Datagram Transport Layer Security
                                 (DTLS)
                       draft-jennings-sip-dtls-02

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   This Internet-Draft will expire on September 26, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This specification defines how to use Datagram Transport Layer
   Security (DTLS) as a transport for Session Initiation Protocol (SIP).
   DTLS is a protocol for providing Transport Layer Security (TLS)
   security over a datagram protocol.  This specification also specifies
   the IANA registrations for using SIP with Datagram Congestion Control
   Protocol (DCCP).



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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 . . . . . . . . . . . . . . . . . . . . 4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   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

   Datagram Transport Layer Security (DTLS) [2] provides communication
   privacy similar to TLS [1] for datagram packets.  SIP can run over
   both stream and datagram transports, including UDP and TCP.  SIP [4]
   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 how
   does SIP secure UDP.  The dominant technique for providing security
   for SIP/TCP is TLS.  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.

   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 [5].


3.  Transport Parameters

   SIP URIs can carry a transport parameter indicating the transport
   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[3] 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




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   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 [6] apply when locating a SIP server
   that supports DTLS.  The following new NAPTR[7] service values are
   defined: "SIPS+D2U" for UDP, and "SIPS+D2D" for DCCP[9].  In
   addition, the service value "SIP+D2D" should be used for SIP without
   DTLS over DCCP.

   The default port for DTLS over UDP or DCCP is 5061.


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 [8].
   The result is shown below:



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   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 [10]
   authored by Jonathan Rosenberg, Henning Schulzrinne, and Gonzalo
   Camarillo.  Jakob Schlyter caught several typos.  Eric Rescorla
   provided helpful comments and text.


9.  References

9.1.  Normative References

   [1]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
        RFC 2246, January 1999.

   [2]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
        Security", draft-rescorla-dtls-05 (work in progress), June 2005.

   [3]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 4234, October 2005.

   [4]  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.

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

   [6]  Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol



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        (SIP): Locating SIP Servers", RFC 3263, June 2002.

   [7]  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
        Three: The Domain Name System (DNS) Database", RFC 3403,
        October 2002.

9.2.  Informational References

   [8]   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.

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

   [10]  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.
































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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































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