draft-ietf-avtcore-6222bis-01.txt   draft-ietf-avtcore-6222bis-02.txt 
Network Working Group A. Begen Network Working Group A. Begen
Internet-Draft Cisco Internet-Draft Cisco
Obsoletes: 6222 (if approved) C. Perkins Obsoletes: 6222 (if approved) C. Perkins
Intended status: Standards Track University of Glasgow Intended status: Standards Track University of Glasgow
Expires: September 12, 2013 D. Wing Expires: October 15, 2013 D. Wing
Cisco Cisco
E. Rescorla E. Rescorla
RTFM, Inc. RTFM, Inc.
March 11, 2013 April 13, 2013
Guidelines for Choosing RTP Control Protocol (RTCP) Guidelines for Choosing RTP Control Protocol (RTCP)
Canonical Names (CNAMEs) Canonical Names (CNAMEs)
draft-ietf-avtcore-6222bis-01 draft-ietf-avtcore-6222bis-02
Abstract Abstract
The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a
persistent transport-level identifier for an RTP endpoint. While the persistent transport-level identifier for an RTP endpoint. While the
Synchronization Source (SSRC) identifier of an RTP endpoint may Synchronization Source (SSRC) identifier of an RTP endpoint may
change if a collision is detected or when the RTP application is change if a collision is detected or when the RTP application is
restarted, its RTCP CNAME is meant to stay unchanged, so that RTP restarted, its RTCP CNAME is meant to stay unchanged, so that RTP
endpoints can be uniquely identified and associated with their RTP endpoints can be uniquely identified and associated with their RTP
media streams. media streams.
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This Internet-Draft will expire on September 12, 2013. This Internet-Draft will expire on October 15, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Deficiencies with Earlier Guidelines for Choosing an RTCP 3. Deficiencies with Earlier Guidelines for Choosing an RTCP
CNAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 CNAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Choosing an RTCP CNAME . . . . . . . . . . . . . . . . . . . . 4 4. Choosing an RTCP CNAME . . . . . . . . . . . . . . . . . . . 4
4.1. Persistent RTCP CNAMEs versus Per-Session RTCP CNAMEs . . . 4 4.1. Persistent RTCP CNAMEs versus Per-Session RTCP CNAMEs . . 4
4.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 5
5. Procedure to Generate a Unique Identifier . . . . . . . . . . . 6 5. Procedure to Generate a Unique Identifier . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6.1. Considerations on Uniqueness of RTCP CNAMEs . . . . . . . . 7 6.1. Considerations on Uniqueness of RTCP CNAMEs . . . . . . . 7
6.2. Session Correlation Based on RTCP CNAMEs . . . . . . . . . 7 6.2. Session Correlation Based on RTCP CNAMEs . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
In Section 6.5.1 of the RTP specification, [RFC3550], there are a In Section 6.5.1 of the RTP specification, [RFC3550], there are a
number of recommendations for choosing a unique RTCP CNAME for an RTP number of recommendations for choosing a unique RTCP CNAME for an RTP
endpoint. However, in practice, some of these methods are not endpoint. However, in practice, some of these methods are not
guaranteed to produce a unique RTCP CNAME. [RFC6222] updated the guaranteed to produce a unique RTCP CNAME. [RFC6222] updated the
guidelines for choosing RTCP CNAMEs, superseding those presented in guidelines for choosing RTCP CNAMEs, superseding those presented in
Section 6.5.1 of [RFC3550]. Unfortunately, some parts of the new Section 6.5.1 of [RFC3550]. Unfortunately, some parts of the new
algorithms are rather complicated and also produce RTCP CNAMEs which algorithms are rather complicated and also produce RTCP CNAMEs which
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has to use the same RTCP CNAME for its audio RTP session and for its has to use the same RTCP CNAME for its audio RTP session and for its
video RTP session. Another example might be to synchronize the video RTP session. Another example might be to synchronize the
layers of a layered audio codec, where the same RTCP CNAME has to be layers of a layered audio codec, where the same RTCP CNAME has to be
used for each layer. used for each layer.
A longer-term persistent RTCP CNAME is sometimes useful to facilitate A longer-term persistent RTCP CNAME is sometimes useful to facilitate
third-party monitoring, consistent with [RFC3550]. One such use third-party monitoring, consistent with [RFC3550]. One such use
might be to allow network management tools to correlate the ongoing might be to allow network management tools to correlate the ongoing
quality of service for a participant across multiple RTP sessions for quality of service for a participant across multiple RTP sessions for
fault diagnosis, and to understand long-term network performance fault diagnosis, and to understand long-term network performance
statistics. An implementation that wishes to discourage this type of statistics. An application developer that wishes to discourage this
third-party monitoring can generate a unique RTCP CNAME for each RTP type of third-party monitoring can choose to generate a unique RTCP
session, or group of related RTP sessions, that it joins. Such a CNAME for each RTP session, or group of related RTP sessions, that
per-session RTCP CNAME cannot be used for traffic analysis, and so the application will join. Such a per-session RTCP CNAME cannot be
provides some limited form of privacy (note that there are non-RTP used for traffic analysis, and so provides some limited form of
means that can be used by a third party to correlate RTP sessions, so privacy. Note that there are non-RTP means that can be used by a
the use of per-session RTCP CNAMEs will not prevent a determined third party to correlate RTP sessions, so the use of per-session RTCP
traffic analyst from monitoring such sessions). CNAMEs will not prevent a determined traffic analyst from monitoring
such sessions.
This memo defines several different ways by which an implementation This memo defines several different ways by which an implementation
can choose an RTCP CNAME. It is possible, and legitimate, for can choose an RTCP CNAME. It is possible, and legitimate, for
independent implementations to make different choices of RTCP CNAME independent implementations to make different choices of RTCP CNAME
when running on the same host. This can hinder third-party when running on the same host. This can hinder third-party
monitoring, unless some external means is provided to configure a monitoring, unless some external means is provided to configure a
persistent choice of RTCP CNAME for those implementations. persistent choice of RTCP CNAME for those implementations.
Note that there is no backwards compatibility issue (with [RFC3550]- Note that there is no backwards compatibility issue (with
compatible implementations) introduced in this memo, since the RTCP [RFC3550]-compatible implementations) introduced in this memo, since
CNAMEs are opaque strings to remote peers. the RTCP CNAMEs are opaque strings to remote peers.
4.2. Requirements 4.2. Requirements
RTP endpoints will choose to generate RTCP CNAMEs that are persistent RTP endpoints will choose to generate RTCP CNAMEs that are persistent
or per-session. An RTP endpoint that wishes to generate a persistent or per-session. An RTP endpoint that wishes to generate a persistent
RTCP CNAME MUST use one of the following two methods: RTCP CNAME MUST use one of the following two methods:
o To produce a long-term persistent RTCP CNAME, an RTP endpoint MUST o To produce a long-term persistent RTCP CNAME, an RTP endpoint MUST
generate and store a Universally Unique IDentifier (UUID) generate and store a Universally Unique IDentifier (UUID)
[RFC4122] for use as the "host" part of its RTCP CNAME. The UUID [RFC4122] for use as the "host" part of its RTCP CNAME. The UUID
MUST be version 1, 2, or 4, as described in [RFC4122], with the MUST be version 1, 2, or 4, as described in [RFC4122], with the
"urn:uuid:" stripped, resulting in a 36-octet printable string "urn:uuid:" stripped, resulting in a 36-octet printable string
representation. representation.
o To produce a short-term persistent RTCP CNAME, an RTP endpoint o To produce a short-term persistent RTCP CNAME, an RTP endpoint
MUST either (a) use the numeric representation of the layer-2 MUST either (a) use the numeric representation of the layer-2
(Media Access Control (MAC)) address of the interface that is used (Media Access Control (MAC)) address of the interface that is used
to initiate the RTP session as the "host" part of its RTCP CNAME to initiate the initial set of RTP sessions as the "host" part of
or (b) generate and use an identifier by following the procedure its RTCP CNAME or (b) generate and use an identifier by following
described in Section 5. In either case, the procedure is the procedure described in Section 5. In either case, the
performed once per initialization of the software. After procedure is performed once per initialization of the software.
obtaining an identifier in case of (a), the 48 bits are converted After obtaining an identifier in case of (a), the 48 bits are
to the standard colon-separated hexadecimal format [RFC5342], converted to the standard colon-separated hexadecimal format
e.g., "00:23:32:af:9b:aa", resulting in a 17-octet printable [RFC5342], e.g., "00:23:32:af:9b:aa", resulting in a 17-octet
string representation. In case of (b), minimally the least printable string representation. In case of (b), minimally the
significant 96 bits SHOULD be converted to ASCII using Base64 least significant 96 bits SHOULD be converted to ASCII using
encoding [RFC4648] (to compromise between packet size and Base64 encoding [RFC4648] (to compromise between packet size and
uniqueness - refer to Section 6.1). If 96 bits are used, the uniqueness - refer to Section 6.1). If 96 bits are used, the
resulting string will be 16 octets. resulting string will be 16 octets.
In the two cases above, the "user@" part of the RTCP CNAME MAY be In the two cases above, the "user@" part of the RTCP CNAME MAY be
omitted on single-user systems and MAY be replaced by an opaque token omitted on single-user systems and MAY be replaced by an opaque token
on multi-user systems, to preserve privacy. on multi-user systems, to preserve privacy.
An RTP endpoint that wishes to generate a per-session RTCP CNAME MUST An RTP endpoint that wishes to generate a per-session RTCP CNAME MUST
use the following method: use the following method:
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used for multiple RTP sessions that are to be correlated. However, used for multiple RTP sessions that are to be correlated. However,
such a specification needs to be reviewed and approved before such a specification needs to be reviewed and approved before
deployment. deployment.
The mechanisms described in this document are to be used to generate The mechanisms described in this document are to be used to generate
RTCP CNAMEs, and they are not to be used for generating general- RTCP CNAMEs, and they are not to be used for generating general-
purpose unique identifiers. purpose unique identifiers.
5. Procedure to Generate a Unique Identifier 5. Procedure to Generate a Unique Identifier
The algorithm described below is intended to be used for locally To locally produce a unique identifier, we simply generate a
generated unique identifiers. It is based on simply generating a cryptographically pseudorandom value as described in [RFC4086]. This
cryptographically pseudorandom value [RFC4086]. This value MUST be value MUST be at least 96 bits but MAY be longer.
at least 96 bits but MAY be longer.
The biggest bottleneck to implementation of this algorithm is the The biggest bottleneck to implementation of this algorithm is the
availability of an appropriate cryptographically secure PRNG availability of an appropriate cryptographically secure pseudorandom
(CSPRNG). In any setting which already has a secure PRNG, this number generator (CSPRNG). In any setting which already has a secure
algorithm described is far simpler than the algorithm described in PRNG, this algorithm described is far simpler than the algorithm
Section 5 of [RFC6222]. SIP stacks [RFC3261] are required to use described in Section 5 of [RFC6222]. SIP stacks [RFC3261] are
cryptographically random numbers to generate To and From tags required to use cryptographically random numbers to generate To and
(Section 19.3). RTCWEB implementations From tags (Section 19.3). RTCWEB implementations
[I-D.ietf-rtcweb-security-arch] will need to have secure PRNGs to [I-D.ietf-rtcweb-security-arch] will need to have secure PRNGs to
implement ICE [RFC5245] and DTLS-SRTP [RFC5764]. And, of course, implement ICE [RFC5245] and DTLS-SRTP [RFC5764]. And, of course,
essentially every Web browser already supports TLS, which requires a essentially every Web browser already supports TLS, which requires a
secure PRNG. secure PRNG.
6. Security Considerations 6. Security Considerations
The security considerations of [RFC3550] apply to this memo. The security considerations of [RFC3550] apply to this memo.
6.1. Considerations on Uniqueness of RTCP CNAMEs 6.1. Considerations on Uniqueness of RTCP CNAMEs
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which does not require that RTCP CNAMEs are unique within a session which does not require that RTCP CNAMEs are unique within a session
but instead says that condition SHOULD hold. As described in the but instead says that condition SHOULD hold. As described in the
Security Considerations section of [RFC3550], because each Security Considerations section of [RFC3550], because each
participant in a session is free to choose its own RTCP CNAME, they participant in a session is free to choose its own RTCP CNAME, they
can do so in such a way as to impersonate another participant. That can do so in such a way as to impersonate another participant. That
is, participants are trusted to not impersonate each other. No is, participants are trusted to not impersonate each other. No
recommendation for generating RTCP CNAMEs can prevent this recommendation for generating RTCP CNAMEs can prevent this
impersonation, because an attacker can neglect the stipulation. impersonation, because an attacker can neglect the stipulation.
Secure RTP (SRTP) [RFC3711] keeps unauthorized entities out of an RTP Secure RTP (SRTP) [RFC3711] keeps unauthorized entities out of an RTP
session, but it does not aim to prevent impersonation attacks from session, but it does not aim to prevent impersonation attacks from
unauthorized entities. authorized entities.
Because of the properties of the PRNG, there is no significant Because of the properties of the PRNG, there is no significant
privacy/linkability difference between long and short RTCP CNAMEs. privacy/linkability difference between long and short RTCP CNAMEs.
However, the requirement to generate unique RTCP CNAMEs implies a However, the requirement to generate unique RTCP CNAMEs implies a
certain minimum length. A length of 96 bits allows on the order of certain minimum length. A length of 96 bits allows on the order of
2^{40} RTCP CNAMEs globally before there is a large chance of 2^{40} RTCP CNAMEs globally before there is a large chance of
collision (there is about a 50% chance of one collision after 2^{48} collision (there is about a 50% chance of one collision after 2^{48}
RTCP CNAMEs). RTCP CNAMEs).
6.2. Session Correlation Based on RTCP CNAMEs 6.2. Session Correlation Based on RTCP CNAMEs
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8. Acknowledgments 8. Acknowledgments
Thanks to Marc Petit-Huguenin, who suggested using UUIDs in Thanks to Marc Petit-Huguenin, who suggested using UUIDs in
generating RTCP CNAMEs. Also, thanks to David McGrew for providing generating RTCP CNAMEs. Also, thanks to David McGrew for providing
text for the Security Considerations section in RFC 6222. text for the Security Considerations section in RFC 6222.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC3550] Schulzrinne, H., Casner, S., [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Frederick, R., and V. Jacobson, Jacobson, "RTP: A Transport Protocol for Real-Time
"RTP: A Transport Protocol for Applications", STD 64, RFC 3550, July 2003.
Real-Time Applications", STD 64,
RFC 3550, July 2003.
[RFC2119] Bradner, S., "Key words for use [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
in RFCs to Indicate Requirement Requirement Levels", BCP 14, RFC 2119, March 1997.
Levels", BCP 14, RFC 2119,
March 1997.
[RFC4122] Leach, P., Mealling, M., and R. [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Salz, "A Universally Unique Unique IDentifier (UUID) URN Namespace", RFC 4122, July
IDentifier (UUID) URN 2005.
Namespace", RFC 4122, July 2005.
[RFC4648] Josefsson, S., "The Base16, [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Base32, and Base64 Data Encodings", RFC 4648, October 2006.
Encodings", RFC 4648,
October 2006.
[RFC5342] Eastlake, D., "IANA [RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
Considerations and IETF Protocol for IEEE 802 Parameters", BCP 141, RFC 5342, September
Usage for IEEE 802 Parameters", 2008.
BCP 141, RFC 5342,
September 2008.
[RFC4086] Eastlake, D., Schiller, J., and [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.
Requirements for Security",
BCP 106, RFC 4086, June 2005.
9.2. Informative References 9.2. Informative References
[RFC6222] Begen, A., Perkins, C., and D. [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for
Wing, "Guidelines for Choosing Choosing RTP Control Protocol (RTCP) Canonical Names
RTP Control Protocol (RTCP) (CNAMEs)", RFC 6222, April 2011.
Canonical Names (CNAMEs)",
RFC 6222, April 2011.
[RFC1918] Rekhter, Y., Moskowitz, R., [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP
E. Lear, "Address Allocation for 5, RFC 1918, February 1996.
Private Internets", BCP 5,
RFC 1918, February 1996.
[RFC3022] Srisuresh, P. and K. Egevang, [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
"Traditional IP Network Address Address Translator (Traditional NAT)", RFC 3022, January
Translator (Traditional NAT)", 2001.
RFC 3022, January 2001.
[RFC3711] Baugher, M., McGrew, D., [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)",
Norrman, "The Secure Real-time RFC 3711, March 2004.
Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4941] Narten, T., Draves, R., and S. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Krishnan, "Privacy Extensions Extensions for Stateless Address Autoconfiguration in
for Stateless Address IPv6", RFC 4941, September 2007.
Autoconfiguration in IPv6",
RFC 4941, September 2007.
[RFC5245] Rosenberg, J., "Interactive [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT)
(ICE): A Protocol for Network Traversal for Offer/Answer Protocols", RFC 5245, April
Address Translator (NAT) 2010.
Traversal for Offer/Answer
Protocols", RFC 5245,
April 2010.
[RFC5764] McGrew, D. and E. Rescorla, [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
"Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure
Security (DTLS) Extension to Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.
Establish Keys for the Secure
Real-time Transport Protocol
(SRTP)", RFC 5764, May 2010.
[RFC3261] Rosenberg, J., Schulzrinne, H., [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
Camarillo, G., Johnston, A., A., Peterson, J., Sparks, R., Handley, M., and E.
Peterson, J., Sparks, R., Schooler, "SIP: Session Initiation Protocol", RFC 3261,
Handley, M., and E. Schooler, June 2002.
"SIP: Session Initiation
Protocol", RFC 3261, June 2002.
[I-D.ietf-rtcweb-security-arch] Rescorla, E., "RTCWEB Security [I-D.ietf-rtcweb-security-arch]
Architecture", draft-ietf- Rescorla, E., "RTCWEB Security Architecture", draft-ietf-
rtcweb-security-arch-06 (work in rtcweb-security-arch-06 (work in progress), January 2013.
progress), January 2013.
[I-D.rescorla-avtcore-random-cname] Rescorla, E., "Random algorithm [I-D.rescorla-avtcore-random-cname]
for RTP CNAME generation", draft Rescorla, E., "Random algorithm for RTP CNAME generation",
-rescorla-avtcore-random-cname- draft-rescorla-avtcore-random-cname-00 (work in progress),
00 (work in progress), July 2012.
July 2012.
Authors' Addresses Authors' Addresses
Ali Begen Ali Begen
Cisco Cisco
181 Bay Street 181 Bay Street
Toronto, ON M5J 2T3 Toronto, ON M5J 2T3
CANADA CANADA
EMail: abegen@cisco.com EMail: abegen@cisco.com
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
Glasgow G12 8QQ Glasgow G12 8QQ
UK UK
EMail: csp@csperkins.org EMail: csp@csperkins.org
Dan Wing Dan Wing
Cisco Systems, Inc. Cisco Systems, Inc.
170 West Tasman Drive 170 West Tasman Drive
San Jose, California 95134 San Jose, California 95134
USA USA
EMail: dwing@cisco.com EMail: dwing@cisco.com
Eric Rescorla Eric Rescorla
RTFM, Inc. RTFM, Inc.
2064 Edgewood Drive 2064 Edgewood Drive
Palo Alto, CA 94303 Palo Alto, CA 94303
USA USA
Phone: +1 650 678 2350 Phone: +1 650 678 2350
EMail: ekr@rtfm.com EMail: ekr@rtfm.com
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