draft-ietf-avt-srtp-not-mandatory-04.txt   draft-ietf-avt-srtp-not-mandatory-05.txt 
Network Working Group C. Perkins Network Working Group C. Perkins
Internet-Draft University of Glasgow Internet-Draft University of Glasgow
Intended status: Informational M. Westerlund Intended status: Informational M. Westerlund
Expires: June 25, 2010 Ericsson Expires: July 26, 2010 Ericsson
December 22, 2009 January 22, 2010
Why RTP Does Not Mandate a Single Security Mechanism Why RTP Does Not Mandate a Single Security Mechanism
draft-ietf-avt-srtp-not-mandatory-04.txt draft-ietf-avt-srtp-not-mandatory-05.txt
Abstract
This memo discusses the problem of securing real-time multimedia
sessions, and explains why the Real-time Transport Protocol (RTP),
and the associated RTP control protocol (RTCP), do not mandate a
single media security mechanism.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 25, 2010. This Internet-Draft will expire on July 26, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of Provisions Relating to IETF Documents
publication of this document (http://trustee.ietf.org/license-info). (http://trustee.ietf.org/license-info) in effect on the date of
Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
and restrictions with respect to this document. carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Abstract include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
This memo discusses the problem of securing real-time multimedia described in the Simplified BSD License.
sessions, and explains why the Real-time Transport Protocol (RTP),
and the associated RTP control protocol (RTCP), do not mandate a
single media security mechanism.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. RTP Applications and Deployment Scenarios . . . . . . . . . . 3 2. RTP Applications and Deployment Scenarios . . . . . . . . . . 3
3. Implications for RTP Security . . . . . . . . . . . . . . . . 4 3. Implications for RTP Security . . . . . . . . . . . . . . . . 4
4. Implications for Key Management . . . . . . . . . . . . . . . 5 4. Implications for Key Management . . . . . . . . . . . . . . . 5
5. On the Requirement for Strong Security in IETF protocols . . . 6 5. On the Requirement for Strong Security in IETF protocols . . . 6
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
skipping to change at page 3, line 21 skipping to change at page 3, line 21
security, and defines no standard key exchange mechanism. Rather, a security, and defines no standard key exchange mechanism. Rather, a
number of extensions are defined to provide confidentiality and number of extensions are defined to provide confidentiality and
authentication of RTP media streams and RTCP control messages, and to authentication of RTP media streams and RTCP control messages, and to
exchange security keys. This memo outlines why it is appropriate exchange security keys. This memo outlines why it is appropriate
that multiple extension mechanisms are defined, rather than mandating that multiple extension mechanisms are defined, rather than mandating
a single security and keying mechanism. a single security and keying mechanism.
This memo provides information for the community; it does not specify This memo provides information for the community; it does not specify
a standard of any kind. a standard of any kind.
The structure of this memo is as follows: we begin, in Section 2 by The structure of this memo is as follows. Section 2 describes the
describing the scenarios in which RTP is deployed. Following this, scenarios in which RTP is deployed. Following this, Section 3
Section 3 outlines the implications of this range of scenarios for outlines the implications of this range of scenarios for media
media confidentially and authentication, and Section 4 outlines the confidentially and authentication, and Section 4 outlines the
implications for key exchange. Section 5 outlines how the RTP implications for key exchange. Section 5 outlines how the RTP
framework meets the requirement of BCP 61. Section 6 then concludes framework meets the requirement of BCP 61. Section 6 then concludes
and gives some recommendations. Finally, Section 7 outlines the and gives some recommendations.
security considerations, and Section 8 outlines IANA considerations.
2. RTP Applications and Deployment Scenarios 2. RTP Applications and Deployment Scenarios
The range of application and deployment scenarios where RTP has been The range of application and deployment scenarios where RTP has been
used includes, but is not limited to, the following: used includes, but is not limited to, the following:
o Point-to-point voice telephony (fixed and wireless networks) o Point-to-point voice telephony (fixed and wireless networks)
o Point-to-point video conferencing o Point-to-point video conferencing
skipping to change at page 5, line 22 skipping to change at page 5, line 22
[ETSI.TS.102.474], where one mode of operation uses ISMAcryp [ETSI.TS.102.474], where one mode of operation uses ISMAcryp
(http://www.isma.tv/specs/ISMA_E&Aspec2.0.pdf) to encrypt the RTP (http://www.isma.tv/specs/ISMA_E&Aspec2.0.pdf) to encrypt the RTP
payload data only. payload data only.
Finally, the link layer may be secure, and it may be known that the Finally, the link layer may be secure, and it may be known that the
RTP media data is constrained to that single link (for example, when RTP media data is constrained to that single link (for example, when
operating in a studio environment, with physical link security). An operating in a studio environment, with physical link security). An
environment like this is inherently constrained, but might avoid the environment like this is inherently constrained, but might avoid the
need for application, transport, or network layer media security. need for application, transport, or network layer media security.
All these are application scenarios where RTP has seen commerical All these are application scenarios where RTP has seen commercial
deployment. Other use case also exist, with additional requirements. deployment. Other use case also exist, with additional requirements.
There is no media security protocol that is appropriate for all these There is no media security protocol that is appropriate for all these
environments. Accordingly, multiple RTP media security protocols can environments. Accordingly, multiple RTP media security protocols can
be expected to remain in wide use. be expected to remain in wide use.
4. Implications for Key Management 4. Implications for Key Management
With such a diverse range of use case come a range of different With such a diverse range of use cases come a range of different
protocols for RTP session establishment. Mechanisms used to provide protocols for RTP session establishment. Mechanisms used to provide
security keying for these different session establishment protocols security keying for these different session establishment protocols
can basically be put into two categories: inband and out-of-band in can basically be put into two categories: inband and out-of-band in
relation to the session establishment mechanism. The requirements relation to the session establishment mechanism. The requirements
for these solutions are highly varying. Thus a wide range of for these solutions are highly varying. Thus a wide range of
solutions have been developed in this space: solutions have been developed in this space:
o The most common use case for RTP is probably point-to-point voice o The most common use case for RTP is probably point-to-point voice
calls or centralised group conferences, negotiated using SIP calls or centralised group conferences, negotiated using SIP
[RFC3261] with the SDP offer/answer model [RFC3264], operating on [RFC3261] with the SDP offer/answer model [RFC3264], operating on
skipping to change at page 6, line 12 skipping to change at page 6, line 12
infrastructure. In such environments, the key management protocol infrastructure. In such environments, the key management protocol
is run on the media path, bypassing the untrusted infrastructure. is run on the media path, bypassing the untrusted infrastructure.
Protocols such as DTLS [I-D.ietf-avt-dtls-srtp] or ZRTP Protocols such as DTLS [I-D.ietf-avt-dtls-srtp] or ZRTP
[I-D.zimmermann-avt-zrtp] are useful here. [I-D.zimmermann-avt-zrtp] are useful here.
o For point-to-point client-server streaming of RTP over RTSP, a TLS o For point-to-point client-server streaming of RTP over RTSP, a TLS
association is appropriate to manage keying material, in much the association is appropriate to manage keying material, in much the
same manner as would be used to secure an HTTP session. same manner as would be used to secure an HTTP session.
o A session description may be sent by email, secured using X.500 or o A session description may be sent by email, secured using S/MIME
PGP, or retrieved from a web page, using HTTP with TLS. or PGP, or retrieved from a web page, using HTTP with TLS.
o A session description may be distributed to a multicast group o A session description may be distributed to a multicast group
using SAP or FLUTE secured with S/MIME. using SAP or FLUTE secured with S/MIME.
o A session description may be distributed using the Open Mobile o A session description may be distributed using the Open Mobile
Alliance DRM key management specification [OMA-DRM] when using a Alliance DRM key management specification [OMA-DRM] when using a
point-to-point streaming session setup with RTSP in the 3GPP PSS point-to-point streaming session setup with RTSP in the 3GPP PSS
environment [PSS]. environment [PSS].
o In the 3GPP Multimedia Broadcast Multicast Service (MBMS) system, o In the 3GPP Multimedia Broadcast Multicast Service (MBMS) system,
skipping to change at page 8, line 31 skipping to change at page 8, line 31
[I-D.ietf-avt-dtls-srtp] [I-D.ietf-avt-dtls-srtp]
McGrew, D. and E. Rescorla, "Datagram Transport Layer McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for Secure Security (DTLS) Extension to Establish Keys for Secure
Real-time Transport Protocol (SRTP)", Real-time Transport Protocol (SRTP)",
draft-ietf-avt-dtls-srtp-07 (work in progress), draft-ietf-avt-dtls-srtp-07 (work in progress),
February 2009. February 2009.
[I-D.ietf-mmusic-rfc2326bis] [I-D.ietf-mmusic-rfc2326bis]
Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, "Real Time Streaming Protocol 2.0 and M. Stiemerling, "Real Time Streaming Protocol 2.0
(RTSP)", draft-ietf-mmusic-rfc2326bis-21 (work in (RTSP)", draft-ietf-mmusic-rfc2326bis-22 (work in
progress), June 2009. progress), July 2009.
[I-D.ietf-sip-media-security-requirements] [I-D.ietf-sip-media-security-requirements]
Wing, D., Fries, S., Tschofenig, H., and F. Audet, Wing, D., Fries, S., Tschofenig, H., and F. Audet,
"Requirements and Analysis of Media Security Management "Requirements and Analysis of Media Security Management
Protocols", draft-ietf-sip-media-security-requirements-09 Protocols", draft-ietf-sip-media-security-requirements-09
(work in progress), January 2009. (work in progress), January 2009.
[I-D.zimmermann-avt-zrtp] [I-D.zimmermann-avt-zrtp]
Zimmermann, P., Johnston, A., and J. Callas, "ZRTP: Media Zimmermann, P., Johnston, A., and J. Callas, "ZRTP: Media
Path Key Agreement for Secure RTP", Path Key Agreement for Secure RTP",
draft-zimmermann-avt-zrtp-15 (work in progress), draft-zimmermann-avt-zrtp-17 (work in progress),
March 2009. January 2010.
[MBMS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS); [MBMS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS);
Protocols and codecs TS 26.346". Protocols and codecs TS 26.346".
[MBMS-SEC] [MBMS-SEC]
3GPP, "Security of Multimedia Broadcast/Multicast Service 3GPP, "Security of Multimedia Broadcast/Multicast Service
(MBMS) TS 33.246". (MBMS) TS 33.246".
[OMA-DRM] Open Mobile Alliance, "DRM Specification 2.0". [OMA-DRM] Open Mobile Alliance, "DRM Specification 2.0".
 End of changes. 13 change blocks. 
31 lines changed or deleted 34 lines changed or added

This html diff was produced by rfcdiff 1.33. The latest version is available from http://tools.ietf.org/tools/rfcdiff/