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Versions: (draft-hutton-mmusic-opportunistic-negotiation) 00 01

Network Working Group                                          A. Hutton
Internet-Draft                                                     Unify
Updates: 4568,4585 (if approved)                               R. Jesske
Intended status: Standards Track                        Deutsche Telekom
Expires: December 7, 2017                                    A. Johnston
                                                            G. Salgueiro
                                                                B. Aboba
                                                            June 5, 2017

      Negotiating SRTP and RTCP Feedback using the RTP/AVP Profile


   This document describes how the use of the Secure Real-time transport
   protocol (SRTP) [RFC3711]. can be negotiated using the AVP (Audio
   Video Profile) defined in [RFC3551].  Such a mechanism is used to
   provide a means for encrypted media to be used in environments where
   support for encryption is not known in advance, and not required.
   The same mechanism is also applied to negotiation of the Extended RTP
   Profile for Real-time Transport Control Protocol Based Feedback (RTP/
   AVPF) [RFC4585].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on December 7, 2017.

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Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Normative Language  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Use of RTP/AVP profile with SRTP  . . . . . . . . . . . . . .   3
   5.  Use of RTP/AVP profile with RTCP Feedback . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Opportunistic Security [RFC7435] is an approach to security that
   defines a third mode for security between "cleartext" and
   "comprehensive protection" that allows encryption and authentication
   to be used if supported but will not result in failures if it is not
   supported.  In terms of secure media, cleartext is RTP [RFC3550]
   media which is negotiated with the AVP (Audio Video Profile) profile
   defined [RFC3551].  Comprehensive protection is Secure RTP [RFC3711],
   negotiated with a secure profile, such as SAVP or SAVPF [RFC5124].

   [I-D.ietf-sipbrandy-osrtp] describes how Secure Real-time transport
   protocol (SRTP) can be negotiated opportunistically.

   [RFC4568] however requires that SRTP is only negotiated using the
   RTP/SAVP profile [RFC3711] or the RTP/SAVPF profile [RFC5124].  This
   document relaxes this rule by allowing SRTP to be used with the RTP/
   AVP profile when negotiated opportunistically.

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   Similarly [RFC4585] requires that the RTCP extended reports are only
   used in media sessions for which the "AVPF" profile is specified.
   This document therefore also relaxes this rule allowing RTCP based
   feedback to be used with the RTP/AVP profile.

2.  Normative Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119

3.  Motivation

   In theory SDP [RFC4566] allows different RTP profiles such as SAVP,
   AVPF, and AVP to be offered as separate m-lines, and allows the
   answerer to reject profiles it does not support or does not wish to
   use.  However the use of multiple m-lines for such a negotiation is
   not well defined and implementations receiving such an offer are
   likely to reject the SDP Offer rather than use the profile they
   support.  This negotiation failure has been observed when negotiating
   the secure profile (SAVP) and also when negotiating RTCP based
   feedback messages [RFC4585] (RTP/AVPF) or both (RTP/SAVPF).

   To avoid using multiple m-lines to negotiate RTP profiles this draft
   recognized that existing implementation of SRTP, and RTCP feedback,
   make use of the relevant SDP attributes to indicate such
   capabilities.  The approach therefore taken in this draft uses the
   "a=" lines in SDP to negotiate these capabilities in a single offer/
   answer exchange, by offering the AVP profile but indicating the
   supported functionality in a=lines.

4.  Use of RTP/AVP profile with SRTP

   To negotiate SRTP in an opportunistic way such as that described in
   [I-D.ietf-sipbrandy-osrtp] requires a fallback to unencrypted media
   to occur if the remote endpoint does not support SRTP.

   Therefore when negotiating SRTP opportunistically the SDP offerer
   MUST use the AVP profile [RFC3551].  This is independent of the key
   exchange mechanism used.

   The SDP answerer MUST use the AVP profile if it does not encrypt the
   media and MAY use the AVP if it encrypts the media.  The exact
   negotiation mechanism is however outside the scope of this document,
   an example mechanism can be found in [I-D.ietf-sipbrandy-osrtp].

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5.  Use of RTP/AVP profile with RTCP Feedback

   Negotiating the use of the Extended RTP Profile for RTCP Based
   Feedback (RTP/AVPF) [RFC4585] opportunistically also requires the
   offerer to use the AVP profile otherwise the offer is likely to be
   rejected by an answerer who does not support AVPF.

   Therefore when negotiating RTCP Based Feedback opportunistically the
   SDP offerer MUST use the AVP profile [RFC3551] and include the
   "a=rtcp-fb" SDP attribute as described in [RFC4585].

   The SDP answerer indicates support for RTCP Based Feedback by
   including the "a=rtcp-fb" SDP attribute in the SDP Answer.  The RTP
   profile in the SDP answer MAY be set to AVP (SAVP) or AVPF (SAVPF).

   This is an update to [RFC4585] which requires that the "a=rtcp-fb"
   attribute is only used with the AVPF profile.  All other [RFC4585]
   procedures remain unchanged.

6.  IANA Considerations


7.  Security Considerations

   The security considerations of [RFC7435] apply to any opportunistic
   approach to SRTP.

   It is important to note that negotiating SRTP in an opportunistic way
   makes no changes, and has no effect on media sessions in which the
   offer contains a secure profile of RTP, such as SAVP or SAVPF.  As
   discussed in [RFC7435] this is the "comprehensive protection" for
   media mode.

8.  Acknowledgements

   This document is dedicated to our friend and colleague Francois Audet
   who is greatly missed in our community.  His work on improving
   security in SIP and RTP provided the foundation for this work.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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9.2.  Informative References

              Johnston, A., Aboba, B., Hutton, A., Jesske, R., and T.
              Stach, "An Opportunistic Approach for Secure Real-time
              Transport Protocol (OSRTP)", draft-ietf-sipbrandy-osrtp-02
              (work in progress), May 2017.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <http://www.rfc-editor.org/info/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC4568]  Andreasen, F., Baugher, M., and D. Wing, "Session
              Description Protocol (SDP) Security Descriptions for Media
              Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              DOI 10.17487/RFC4585, July 2006,

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
              2008, <http://www.rfc-editor.org/info/rfc5124>.

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <http://www.rfc-editor.org/info/rfc7435>.

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Authors' Addresses

   Andrew Hutton
   Brickhill Street
   Milton Keynes  MK15 0DJ

   Email: andrew.hutton@unify.com

   Roland Jesske
   Deutsche Telekom
   Heinrich-Hertz-Strasse 3-7
   Darmstadt  64295

   Email: R.Jesske@telekom.de

   Alan Johnston
   Bellevue, WA

   Email: alan.b.johnston@gmail.com

   Gonzalo Salgueiro
   7200-12 Kit Creek Road
   RTP, NC  27709

   Email: gsalguei@cisco.com

   Bernard Aboba
   One Microsoft Way
   Redmond, WA  98052

   Email: bernard.aboba@gmail.com

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