One document matched: draft-andreasen-mmusic-securityprecondition-01.txt
Differences from draft-andreasen-mmusic-securityprecondition-00.txt
Internet Engineering Task Force Flemming Andreasen
MMUSIC Working Group Mark Baugher
INTERNET-DRAFT Dan Wing
EXPIRES: August 2004 Cisco Systems
February, 2004
Security Preconditions for
Session Description Protocol Media Streams
<draft-andreasen-mmusic-securityprecondition-01.txt>
Status of this memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines a new security precondition for the Session
Description Protocol precondition framework described in RFC 3312.
A security precondition can be used to delay session establishment
or modification until media stream security has been negotiated
successfully.
INTERNET-DRAFT Security Preconditions February, 2004
1. Notational Conventions..........................................2
2. Introduction....................................................2
3. Security Precondition Definition................................3
4. Examples........................................................3
5. Security Considerations.........................................5
6. IANA Considerations.............................................5
7. Acknowledgements................................................5
8. Authors' Addresses..............................................5
9. Normative References............................................6
10. Informative References..........................................6
Intellectual Property Statement......................................6
Acknowledgement......................................................7
1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
RFC 3312 defines the concept of a Session Description Protocol (SDP)
[SDP] precondition, which is a condition that has to be satisfied
for a given media stream in order for session establishment or
modification to proceed. When the precondition is not met, session
progress is delayed until the precondition is satisfied, or the
session establishment fails. For example, RFC 3312 defines the
Quality of Service precondition, which is used to ensure
availability of network resources prior to establishing (i.e.
alerting) a call.
Media streams can either be provided in cleartext and with no
integrity checks, or some kind of media security can be applied,
e.g. encryption. For example, the Audio/Video profile of the Real-
Time Transfer protocol (RTP) [RFC3551] is normally used without any
security services whereas the Secure Real-time Transport Protocol
(SRTP) [SRTP] is always used with security services. When media
stream security is being negotiated, e.g. using the mechanism
defined in SDP Security Descriptions [SDESC], both the offerer and
the answerer need to know the cryptographic parameters being used
for the media stream. If the offerer offers multiple choices for
the cryptographic parameters, or the cryptographic parameters
selected by the answerer may differ from those of the offerer (e.g.
the key used in one direction versus the other). In such cases, to
avoid clipping, the offerer must receive the answer prior to
receiving any media packets from the answerer. This can be achieved
by using a security precondition, which is used to ensure the
successful negotiation of media stream security prior to session
establishment or modification.
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3. Security Precondition Definition
The security precondition type is defined by the string "sec" and
hence we modify the grammar found in RFC 3312 as follows:
precondition-type = "sec" | "qos" | token
RFC 3312 defines support for two kinds of status types, namely
segmented and end-to-end. The security precondition-type defined
here MUST be used with the end-to-end status type; use of the
segmented status type is undefined.
An entity that wishes to delay session establishment or modification
until media stream security has been established uses this
precondition-type in an offer. When a security precondition is
received in an offer, session establishment or modification MUST be
delayed until the security precondition has been met, i.e. a secure
media stream is known to have been established by both the offerer
and answerer. A secure media stream is here defined as a media
stream that uses some kind of security service, e.g. encryption,
integrity protection or both, regardless of the cryptographic
strength of the mechanisms being used.
As an extreme example of this, use of the NULL encryption
algorithm would satisfy the above. Use of no encryption mechanism
however would not.
The direction attributes are interpreted as follows:
* send: The offerer/answerer has established security parameters
for sending media, and the offerer/answerer knows the other party
has enough information to process such packets, e.g. the other
party has learned the cryptographic algorithm and key.
* recv: The offerer/answerer has established security parameters
for receiving media, and the offerer/answerer knows the other
party has enough information to generate such packets, e.g. the
other party has learned the cryptographic algorithm and key.
If it is not possible to satisfy the security precondition, e.g.
because the offer does not include any parameters related to
establishing a secure media stream, the offer MUST be rejected as
described in RFC 3312.
4. Examples
The call flow of Figure 1 shows a basic session establishment using
SDP security descriptions [SDESC] and security descriptions for the
secure media stream (SRTP in this case). The SDP descriptions of
this example are shown below - we have omitted the details of the
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INTERNET-DRAFT Security Preconditions February, 2004
SDP security descriptions for clarity of the security precondition
described here:
SDP1: A includes the end-to-end security precondition in the initial
offer as well as a crypto parameter (see [SDESC]), which includes
keying material that can be used by A to generate media packets.
Since B does not know any of the security parameters yet, the
current status is set to none:
m=audio 20000 RTP/SAVP 0
c=IN IP4 192.0.2.1
a=curr:sec e2e none
a=des:sec mandatory e2e sendrecv
a=crypto:foo...
SDP2: When B receives the offer, and generates an answer, B knows
the security parameters of both A and B, however A does not know the
security parameters that will be used by B, so the current status is
set to none. B requests A to confirm when A knows the parameters
used in the send and receive direction by both:
m=audio 30000 RTP/SAVP 0
c=IN IP4 192.0.2.4
a=curr:sec e2e none
a=des:sec mandatory e2e sendrecv
a=conf:sec e2e sendrecv
a=crypto:bar...
SDP3: When A receives the answer, A now knows the security
parameters of both A and B. A also knows that B knows those
parameters and hence A immediately sends an updated offer (3) to B
showing that the security precondition has been satisfied:
m=audio 20000 RTP/SAVP 0
c=IN IP4 192.0.2.1
a=curr:sec e2e sendrecv
a=des:sec mandatory e2e sendrecv
a=crypto:foo...
SDP4: Upon receiving the updated offer, B now knows that both A and
B know the security parameters and hence B responds with an answer
(4) which contains the current status of the security precondition
(i.e., sendrecv) from B's point of view:
m=audio 30000 RTP/SAVP 0
c=IN IP4 192.0.2.4
a=curr:sec e2e sendrecv
a=des:sec mandatory e2e sendrecv
At this point in time, session establishment resumes and B returns a
180 (Ringing) response (5).
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A B
| |
|-------------(1) INVITE SDP1--------------->|
| |
|<------(2) 183 Session Progress SDP2--------|
| |
|----------------(3) PRACK SDP3------------->|
| |
|<-----------(4) 200 OK (PRACK) SDP4---------|
| |
|<-------------(5) 180 Ringing---------------|
| |
| |
| |
Figure 1: Example using the security precondition
5. Security Considerations
TBD
6. IANA Considerations
IANA is hereby requested to register a RFC 3312 precondition type
called "sec" with the name "Security precondition". The reference
for this precondition type is the current document.
7. Acknowledgements
The security precondition was defined in earlier draft versions of
RFC 3312. RFC 3312 contains an extensive list of people who worked
on those earlier draft versions which are acknowledged here as well.
Thanks to Paul Kyzivat who optimized the example message flow.
8. Authors' Addresses
Flemming Andreasen
Cisco Systems, Inc.
499 Thornall Street, 8th Floor
Edison, New Jersey 08837 USA
EMail: fandreas@cisco.com
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Mark Baugher
5510 SW Orchid Street
Portland, Oregon 97219 USA
EMail: mbaugher@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134 USA
EMail: dwing@cisco.com
9. Normative References
[RFC3312] G. Camarillo, W. Marshall, J. Rosenberg, "Integration of
Resource Management and Session Initiation Protocol (SIP)", RFC
3312, October 2002.
[RFC2327] M. Handley and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
10. Informative References
[SDESC] F. Andreasen, M. Baugher, and D. Wing, "SDP Security
Descriptions for Media Streams", work in progress
[RFC3551] H. Schulzrinne, and S. Casner "RTP Profile for Audio and
Video Conferences with Minimal Control", RFC 3550, July 2003.
[SRTP] M. Baugher, R. Blom, E. Carrara, D. McGrew, M. Naslund, K.
Norrman, D. Oran, "The Secure Real-time Transport Protocol", May
2003, http://search.ietf.org/internet-drafts/draft-ietf-avt-srtp-
08.txt, Work in Progress
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