draft-ietf-mmusic-securityprecondition-00.txt   draft-ietf-mmusic-securityprecondition-01.txt 
Internet Engineering Task Force Flemming Andreasen Internet Engineering Task Force Flemming Andreasen
MMUSIC Working Group Dan Wing MMUSIC Working Group Dan Wing
INTERNET-DRAFT Internet-Draft
EXPIRES: August 2005 Cisco Systems Expires: April 2006 Cisco Systems
February, 2005 October, 2005
Security Preconditions for Security Preconditions for
Session Description Protocol Media Streams Session Description Protocol Media Streams
<draft-ietf-mmusic-securityprecondition-00.txt> <draft-ietf-mmusic-securityprecondition-01.txt>
Status of this memo Status of this memo
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Copyright (C) The Internet Society (2005). All Rights Reserved. Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract Abstract
This document defines a new security precondition for the Session This document defines a new security precondition for the Session
Description Protocol precondition framework described in RFC 3312. Description Protocol precondition framework described in RFCs 3312
A security precondition can be used to delay session establishment and 4032. A security precondition can be used to delay session
or modification until media stream security has been negotiated establishment or modification until media stream security has been
successfully. negotiated successfully.
1 Notational Conventions............................................2 1 Notational Conventions............................................2
2 Introduction......................................................2 2 Introduction......................................................2
3 Security Precondition Definition..................................3 3 Security Precondition Definition..................................3
4 Examples..........................................................5 4 Examples..........................................................5
4.1 SDP Security Descriptions Example.............................5 4.1 SDP Security Descriptions Example.............................5
4.2 Key Management Extension for SDP Example......................7 4.2 Key Management Extension for SDP Example......................8
5 Security Considerations..........................................10 5 Security Considerations..........................................10
6 IANA Considerations..............................................10 6 IANA Considerations..............................................11
7 Acknowledgements.................................................10 7 Acknowledgements.................................................11
8 Authors' Addresses...............................................11 8 Authors' Addresses...............................................11
9 Normative References.............................................11 9 Normative References.............................................12
10 Informative References.........................................11 10 Informative References.........................................12
11 Intellectual Property Statement................................13 11 Intellectual Property Statement................................14
1 Notational Conventions 1 Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT", The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2 Introduction 2 Introduction
The concept of a Session Description Protocol (SDP) [SDP] The concept of a Session Description Protocol (SDP) [SDP]
precondition is defined in [RFC3312] and [RFC3312upd]. A precondition is defined in [RFC3312] as updated by [RFC4032]. A
precondition is a condition that has to be satisfied for a given precondition is a condition that has to be satisfied for a given
media stream in order for session establishment or modification to media stream in order for session establishment or modification to
proceed. When the precondition is not met, session progress is proceed. When the precondition is not met, session progress is
delayed until the precondition is satisfied, or the session delayed until the precondition is satisfied or the session
establishment fails. For example, RFC 3312 defines the Quality of establishment fails. For example, RFC 3312 defines the Quality of
Service precondition, which is used to ensure availability of Service precondition, which is used to ensure availability of
network resources prior to establishing (i.e. alerting) a call. network resources prior to establishing (i.e. alerting) a call.
Media streams can either be provided in cleartext and with no Media streams can either be provided in cleartext and with no
integrity checks, or some kind of media security can be applied, integrity protection, or some kind of media security can be applied,
e.g., confidentiality and/or message integrity. For example, the e.g., confidentiality and/or message integrity. For example, the
Audio/Video profile of the Real-Time Transfer protocol (RTP) Audio/Video profile of the Real-Time Transfer protocol (RTP)
[RFC3551] is normally used without any security services whereas the [RFC3551] is normally used without any security services whereas the
Secure Real-time Transport Protocol (SRTP) [SRTP] is always used Secure Real-time Transport Protocol (SRTP) [SRTP] is always used
with security services. When media stream security is being with security services. When media stream security is being
negotiated, e.g., using the mechanism defined in SDP Security negotiated, e.g., using the mechanism defined in SDP Security
Descriptions [SDESC], both the offerer and the answerer need to know Descriptions [SDESC], both the offerer and the answerer need to know
the cryptographic parameters being used for the media stream; the the cryptographic parameters being used for the media stream; the
offerer may provide multiple choices for the cryptographic offerer may provide multiple choices for the cryptographic
parameters, or the cryptographic parameters selected by the answerer parameters, or the cryptographic parameters selected by the answerer
may differ from those of the offerer (e.g. the key used in one 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 direction versus the other). In such cases, to avoid media
offerer must receive the answer prior to receiving any media packets clipping, the offerer must receive the answer prior to receiving any
from the answerer. This can be achieved by using a security media packets from the answerer. This can be achieved by using a
precondition, which is used to ensure the successful negotiation of security precondition, which ensures the successful negotiation of
media stream security prior to session establishment or media stream security parameters prior to session establishment or
modification. modification.
3 Security Precondition Definition 3 Security Precondition Definition
The security precondition type is defined by the string "sec" and The security precondition type is defined by the string "sec" and
hence we modify the grammar found in RFC 3312 as follows: hence we modify the grammar found in RFC 3312 as follows:
precondition-type = "sec" | "qos" | token precondition-type = "sec" | "qos" | token
RFC 3312 defines support for two kinds of status types, namely RFC 3312 defines support for two kinds of status types, namely
segmented and end-to-end. The security precondition-type defined segmented and end-to-end. The security precondition-type defined
here MUST be used with the end-to-end status type; use of the here MUST be used with the end-to-end status type; use of the
segmented status type is undefined. segmented status type is undefined.
An entity that wishes to delay session establishment or modification An entity that wishes to delay session establishment or modification
until media stream security has been established uses the security until media stream security has been established uses the security
precondition-type in an offer. When a mandatory security precondition-type in an offer. When a mandatory security
precondition is received in an offer, session establishment or precondition is received in an offer, session establishment or
modification MUST be delayed until the security precondition has modification MUST be delayed until the security precondition has
been met, i.e. parameters for a secure media stream are known to been met, i.e. cryptographic parameters (cipher, key, etc.) for a
have been negotiated in the direction(s) required. A secure media secure media stream are known to have been negotiated in the
stream is here defined as a media stream that uses some kind of direction(s) required. A secure media stream is here defined as a
security service, e.g. message integrity, confidentiality or both, media stream that uses some kind of security service, e.g. message
regardless of the cryptographic strength of the mechanisms being integrity, confidentiality or both, regardless of the cryptographic
used. strength of the mechanisms being used.
As an extreme example of this, Secure RTP (SRTP) using the NULL As an extreme example of this, Secure RTP (SRTP) using the NULL
encryption algorithm and no message authentication/integrity would encryption algorithm and no message integrity would satisfy the
satisfy the above whereas use of plain RTP would not. Note above whereas use of plain RTP would not. Note though, that use
though, that use of SRTP without authentication is discouraged. of SRTP without authentication is discouraged.
The delay of session establishment defined here implies that that The delay of session establishment defined here implies that
alerting of the called party MUST NOT occur and media for which alerting of the called party MUST NOT occur and media for which
security is being negotiated MUST NOT be exchanged until the security is being negotiated MUST NOT be exchanged until the
precondition has been satisfied. In cases where secure media and precondition has been satisfied. In cases where secure media and
other non-secure data is multiplexed on a media stream, e.g. when other non-secure data is multiplexed on a media stream, e.g. when
Interactive Connectivity Establishment [ICE] is being used, the non- Interactive Connectivity Establishment [ICE] is being used, the non-
secure data is allowed to be exchanged irrespective of the status of secure data is allowed to be exchanged prior to the security
the security precondition. precondition being satisfied.
The direction tags defined in RFC 3312 are interpreted as follows: The direction tags defined in RFC 3312 are interpreted as follows:
* send: Media stream security negotiation is at a stage where it is * send: Media stream security negotiation is at a stage where it is
possible to send secure media packets to the other party and the possible to send secure media packets to the other party and the
other party will be able to process them correctly. The other party will be able to process them correctly. The
definition of "media packets" includes all packets that make up definition of "media packets" includes all packets that make up
the media stream. In the case of Secure RTP for example, it the media stream. In the case of Secure RTP for example, it
includes SRTP as well as SRTCP. When media and non-media packets includes SRTP as well as SRTCP. When media and non-media packets
are multiplexed on a given media stream, e.g. as when ICE is being are multiplexed on a given media stream, e.g. when ICE is being
used, the requirement applies to the media packets only. used, the requirement applies to the media packets only.
* recv: Media stream security negotiation is at a stage where it is * recv: Media stream security negotiation is at a stage where it is
possible to receive and correctly process secure media stream possible to receive and correctly process secure media stream
packets sent by the other party. packets sent by the other party.
The precise criteria for determining when the other party is able to The precise criteria for determining when the other party is able to
correctly process secure media stream packets depends on the secure correctly process secure media stream packets depends on the secure
media stream protocol being used as well as the mechanism by which media stream protocol being used as well as the mechanism by which
the required cryptographic parameters are negotiated. the required cryptographic parameters are negotiated.
We here provide details for SRTP negotiated through SDP security We here provide details for SRTP negotiated through SDP security
descriptions [SDESC]: descriptions as defined in [SDESC]:
* When the offerer requests the "send" security precondition, it * When the offerer requests the "send" security precondition, it
needs to receive the answer before the security precondition is needs to receive the answer before the security precondition is
satisfied. The reason for this is twofold. First, the offerer satisfied. The reason for this is twofold. First, the offerer
needs to know where to send the media to. Secondly, in the case needs to know where to send the media to. Secondly, in the case
where alternative cryptographic parameters are offered, the where alternative cryptographic parameters are offered, the
offerer needs to know which set was selected. The answerer does offerer needs to know which set was selected. The answerer does
not know when the answer is actually received by the offerer not know when the answer is actually received by the offerer
(which in turn will satisfy the precondition), and hence the (which in turn will satisfy the precondition), and hence the
answerer needs to use the confirm-status attribute [RFC3312]. answerer needs to use the confirm-status attribute [RFC3312].
This will make the offerer generate a new offer showing the This will make the offerer generate a new offer showing the
updated status of the precondition. updated status of the precondition.
* When the offerer requests the "recv" security precondition, it * When the offerer requests the "recv" security precondition, it
also needs to receive the answer before the security precondition also needs to receive the answer before the security precondition
is satisfied. The reason for this is straightforward: The answer is satisfied. The reason for this is straightforward: The answer
contains the cryptographic parameters that will be used by the contains the cryptographic parameters that will be used by the
answerer for sending media to the offerer. answerer for sending media to the offerer; prior to receipt of
these cryptographic parameters the offerer is unable to
authenticate or decrypt media.
When security preconditions are used with the Key Management When security preconditions are used with the Key Management
Extensions for Session Description Protocol (SDP) [KMGMT], the Extensions for Session Description Protocol (SDP) [KMGMT], the
details depend on the actual key management protocol being used. details depend on the actual key management protocol being used.
After an initial offer/answer sequence in which the security
precondition is requested, any subsequent offer/answer sequence for
the purpose of updating the status of the precondition SHOULD use
the same key material as the initial offer/answer sequence. This
means that the key-mgmt attribute lines [KMGMT] or crypto attribute
lines [SDESC] in SDP offers that are sent in response to SDP answers
containing a confirm-status field [RFC3312] SHOULD repeat the same
data as that sent in the previous SDP offer. If applicable to the
key management protocol or SDP security description, the SDP answers
to these SDP offers SHOULD repeat the same data in the key-mgmt
attribute lines [KMGMT] or crypto attribute lines [SDESC] as that
sent in the previous SDP answer.
Of course, this duplication of key exchange during precondition
establishment is not to be interpreted as a replay attack. This
issue may be solved if, e.g. the SDP implementation recognizes that
the key management protocol data is identical in the second
offer/answer exchange and avoids forwarding the information to the
security layer for further processing.
Security preconditions may have a strength-tag of either "mandatory" Security preconditions may have a strength-tag of either "mandatory"
or "optional". When a mandatory security precondition is offered, or "optional". When a mandatory security precondition is offered,
and the answerer cannot satisfy the security precondition, e.g. and the answerer cannot satisfy the security precondition, e.g.
because the offer does not include any parameters related to because the offer does not include any parameters related to
establishing a secure media stream, the offer MUST be rejected as establishing a secure media stream, the offer MUST be rejected as
described in RFC 3312. When an optional security precondition is described in RFC 3312. When an optional security precondition is
offered, the answerer MUST generate its answer SDP as soon as offered, the answerer MUST generate its answer SDP as soon as
possible; since session progress is not delayed in this case, possible; since session progress is not delayed in this case,
clipping may occur. If the answerer wants to avoid clipping and clipping may occur. If the answerer wants to avoid clipping and
delay session progress until the offerer has received the answer, delay session progress until the offerer has received the answer,
skipping to change at page 7, line 15 skipping to change at page 7, line 44
preconditions, and both are now satisfied, A immediately sends an preconditions, and both are now satisfied, A immediately sends an
updated offer (3) to B showing that the security preconditions are updated offer (3) to B showing that the security preconditions are
satisfied: satisfied:
m=audio 20000 RTP/SAVP 0 m=audio 20000 RTP/SAVP 0
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
a=curr:sec e2e sendrecv a=curr:sec e2e sendrecv
a=des:sec mandatory e2e sendrecv a=des:sec mandatory e2e sendrecv
a=crypto:foo... a=crypto:foo...
Note that we here use PRACK [RFC3262] instead of UPDATE [RFC3311]
since the precondition is satisfied immediately, and the original
offer/answer exchange is complete)
SDP4: Upon receiving the updated offer, B updates its local status SDP4: Upon receiving the updated offer, B updates its local status
table based on the rules in RFC 3312 which yields the following: table based on the rules in RFC 3312 which yields the following:
Direction | Current | Desired Strength | Confirm Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+---------- -----------+----------+------------------+----------
send | yes | mandatory | no send | yes | mandatory | no
recv | yes | mandatory | no recv | yes | mandatory | no
B responds with an answer (4) which contains the current status of B responds with an answer (4) which contains the current status of
the security precondition (i.e., sendrecv) from B's point of view: the security precondition (i.e., sendrecv) from B's point of view:
skipping to change at page 9, line 15 skipping to change at page 9, line 51
the send and receive direction and hence the resulting answer SDP the send and receive direction and hence the resulting answer SDP
becomes: becomes:
m=audio 30000 RTP/SAVP 0 m=audio 30000 RTP/SAVP 0
c=IN IP4 192.0.2.4 c=IN IP4 192.0.2.4
a=curr:sec e2e none a=curr:sec e2e none
a=des:sec mandatory e2e sendrecv a=des:sec mandatory e2e sendrecv
a=conf:sec e2e sendrecv a=conf:sec e2e sendrecv
a=key-mgmt:mikey AQAFgM0X... a=key-mgmt:mikey AQAFgM0X...
Note that the actual MIKEY data in the answer differs from that in
the offer, however we have only shown the initial and common part of
the MIKEY value in the above.
SDP3: When A receives the answer, A updates its local status table SDP3: When A receives the answer, A updates its local status table
based on the rules in RFC 3312. A now knows all the security based on the rules in RFC 3312. A now knows all the security
parameters of both the send and receive direction and hence A's parameters of both the send and receive direction and hence A's
local status table is updated as follows: local status table is updated as follows:
Direction | Current | Desired Strength | Confirm Direction | Current | Desired Strength | Confirm
-----------+----------+------------------+---------- -----------+----------+------------------+----------
send | yes | mandatory | yes send | yes | mandatory | yes
recv | yes | mandatory | yes recv | yes | mandatory | yes
skipping to change at page 10, line 53 skipping to change at page 11, line 40
IANA is hereby requested to register a RFC 3312 precondition type IANA is hereby requested to register a RFC 3312 precondition type
called "sec" with the name "Security precondition". The reference called "sec" with the name "Security precondition". The reference
for this precondition type is the current document. for this precondition type is the current document.
7 Acknowledgements 7 Acknowledgements
The security precondition was defined in earlier draft versions of The security precondition was defined in earlier draft versions of
RFC 3312. RFC 3312 contains an extensive list of people who worked RFC 3312. RFC 3312 contains an extensive list of people who worked
on those earlier draft versions which are acknowledged here as well. on those earlier draft versions which are acknowledged here as well.
The authors would like to thank Mark Baugher, Gonzalo Camarillo, and The authors would additionally like to thank Mark Baugher, Gonzalo
Paul Kyzivat for their comments on this document. Camarillo, Paul Kyzivat and Thomas Stach for their comments on this
document.
8 Authors' Addresses 8 Authors' Addresses
Flemming Andreasen Flemming Andreasen
Cisco Systems, Inc. Cisco Systems, Inc.
499 Thornall Street, 8th Floor 499 Thornall Street, 8th Floor
Edison, New Jersey 08837 USA Edison, New Jersey 08837 USA
EMail: fandreas@cisco.com EMail: fandreas@cisco.com
Dan Wing Dan Wing
Cisco Systems, Inc. Cisco Systems, Inc.
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 USA San Jose, CA 95134 USA
EMail: dwing@cisco.com EMail: dwing@cisco.com
9 Normative References 9 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3312] G. Camarillo, W. Marshall, J. Rosenberg, "Integration of [RFC3312] G. Camarillo, W. Marshall, J. Rosenberg, "Integration of
Resource Management and Session Initiation Protocol (SIP)", RFC Resource Management and Session Initiation Protocol (SIP)", RFC
3312, October 2002. 3312, October 2002.
[RFC4032] G. Camarillo and P. Kyzivat, "Update to the Session
Initiation Protocol (SIP) Preconditions Framework", RFC 4032, March
2005.
[RFC2327] M. Handley and V. Jacobson, "SDP: Session Description [RFC2327] M. Handley and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998. Protocol", RFC 2327, April 1998.
[SIP] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. [SIP] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, E. Schooler, "SIP: Session Peterson, R. Sparks, M. Handley, E. Schooler, "SIP: Session
Initiation Protocol", RFC 3261, June 2002. Initiation Protocol", RFC 3261, June 2002.
10 Informative References 10 Informative References
[SDESC] F. Andreasen, M. Baugher, and D. Wing, "SDP Security [SDESC] F. Andreasen, M. Baugher, and D. Wing, "SDP Security
Descriptions for Media Streams", work in progress Descriptions for Media Streams", work in progress
[RFC3551] H. Schulzrinne, and S. Casner "RTP Profile for Audio and [RFC3551] H. Schulzrinne, and S. Casner "RTP Profile for Audio and
Video Conferences with Minimal Control", RFC 3550, July 2003. Video Conferences with Minimal Control", RFC 3550, July 2003.
[SRTP] M. Baugher, D. McGrew, M. Naslund, E. Carrara, K. Norrman, [SRTP] M. Baugher, D. McGrew, M. Naslund, E. Carrara, K. Norrman,
"The Secure Real-time Transport Protocol", RFC 3711, March 2004. "The Secure Real-time Transport Protocol", RFC 3711, March 2004.
[RFC3312upd] G. Camarillo and P. Kyzivat, "Update to the Session
Initiation Protocol (SIP) Preconditions Framework", IETF, work-in-
progress.
[ICE] J. Rosenberg, "Interactive Connectivity Establishment (ICE): A [ICE] J. Rosenberg, "Interactive Connectivity Establishment (ICE): A
Methodology for Network Address Translator (NAT) Traversal for Methodology for Network Address Translator (NAT) Traversal for
Multimedia Session Establishment Protocols", IETF, work-in-progress. Multimedia Session Establishment Protocols", IETF, work-in-progress.
[KMGMT] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K. [KMGMT] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K.
Norrman, "Key Management Extensions for Session Description Protocol Norrman, "Key Management Extensions for Session Description Protocol
(SDP) and Real Time Streaming Protocol (RTSP)", IETF, work-in- (SDP) and Real Time Streaming Protocol (RTSP)", IETF, work-in-
progress. progress.
[MIKEY] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K. [MIKEY] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, August 2004. Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, August 2004.
[RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol (SIP)", RFC
3262, June 2002.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method," RFC 3311, September 2002.
11 Intellectual Property Statement 11 Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such in this document or the extent to which any license under such
rights might or might not be available; nor does it represent that rights might or might not be available; nor does it represent that
it has made any independent effort to identify any such rights. it has made any independent effort to identify any such rights.
Information on the IETF's procedures with respect to rights in IETF Information on the IETF's procedures with respect to rights in IETF
Documents can be found in BCP 78 and BCP 79. Documents can be found in BCP 78 and BCP 79.
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