Network Working Group A. Hutton
Internet-Draft Unify / Atos
Updates: 4568,4585 (if approved) R. Jesske
Intended status: Standards Track Deutsche Telekom
Expires: March 18, 2018 A. Johnston
Rowan University
G. Salgueiro
Cisco
B. Aboba
Microsoft
September 14, 2017
Negotiating SRTP and RTCP Feedback using the RTP/AVP Profile
draft-ietf-mmusic-opportunistic-negotiation-01
Abstract
This document describes how the use of the Secure Real-time transport
protocol (SRTP) [RFC3711]. can be negotiated using the RTP/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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 18, 2018.
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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
(https://trustee.ietf.org/license-info) in effect on the date of
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
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 RTP/AVP (Audio Video Profile)
profile defined [RFC3551]. Comprehensive protection is Secure RTP
[RFC3711], negotiated with a secure profile, such as RTP/SAVP or RTP/
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
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document relaxes this rule by allowing SRTP to be used with the RTP/
AVP profile when negotiated opportunistically.
Similarly [RFC4585] requires that the RTCP extended reports are only
used in media sessions for which the RTP/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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
3. Motivation
In theory SDP [RFC4566] allows different RTP profiles such as RTP/
SAVP, RTP/AVPF, and RTP/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 (RTP/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 RTP/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 RTP/AVP profile [RFC3551]. This is independent of the
key exchange mechanism used.
The SDP answerer MUST use the RTP/AVP profile if it does not encrypt
the media and MAY use the RTP/AVP if it encrypts the media. The
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exact negotiation mechanism is however outside the scope of this
document, an example mechanism can be found in
[I-D.ietf-sipbrandy-osrtp].
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 RTP/AVP profile otherwise the offer is likely to
be rejected by an answerer who does not support RTP/AVPF.
Therefore when negotiating RTCP Based Feedback opportunistically the
SDP offerer MUST use the RTP/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 RTP/AVP (SAVP) or RTP/AVPF
(SAVPF).
This is an update to [RFC4585] which requires that the "a=rtcp-fb"
attribute is only used with the RTP/AVPF profile. All other
[RFC4585] procedures remain unchanged.
6. IANA Considerations
None
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 RTP/SAVP or RTP/
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.
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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,
<https://www.rfc-editor.org/info/rfc2119>.
9.2. Informative References
[I-D.ietf-sipbrandy-osrtp]
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, <https://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,
<https://www.rfc-editor.org/info/rfc3551>.
[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,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://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,
<https://www.rfc-editor.org/info/rfc4568>.
[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,
<https://www.rfc-editor.org/info/rfc4585>.
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[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, <https://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, <https://www.rfc-editor.org/info/rfc7435>.
Authors' Addresses
Andrew Hutton
Unify / Atos
4 Triton Square
London NW1 3HG
UK
Email: andrew.hutton@atos.net
Roland Jesske
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt 64295
Germany
Email: R.Jesske@telekom.de
Alan Johnston
Rowan University
Glassboro, NJ
USA
Email: alan.b.johnston@gmail.com
Gonzalo Salgueiro
Cisco
7200-12 Kit Creek Road
RTP, NC 27709
USA
Email: gsalguei@cisco.com
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Bernard Aboba
Microsoft
One Microsoft Way
Redmond, WA 98052
USA
Email: bernard.aboba@gmail.com
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