Behave Muthu A M. Perumal
Internet-Draft D. Wing
Intended status: Standards Track R. Ram Mohan
Expires: January 17, 2013 Cisco Systems
H. Kaplan
Acme Packet
July 16, 2012
STUN Usage for Consent Freshness and Session Liveness
draft-muthu-behave-consent-freshness-01
Abstract
Verification of peer consent is necessary in WebRTC deployments to
ensure that a malicious JavaScript cannot use the browser as a
platform for launching attacks. A related problem is session
liveness. WebRTC applications may want to detect connection failure
and take appropriate actions. This document describes a STUN usage
that enables a WebRTC browser to perform the following on a candidate
pair ICE is using for a media component after session establishment:
1. Verify the peer consent for continuing to receive traffic.
2. Dectect connection failure.
This also serves the purpose of refreshing NAT bindings.
Status of this Memo
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This Internet-Draft will expire on January 17, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 4
5. Design Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. STUN Consent Method . . . . . . . . . . . . . . . . . . . . . . 5
7. STUN Consent Method Processing . . . . . . . . . . . . . . . . 6
7.1. Generating a Consent Request . . . . . . . . . . . . . . . 6
7.2. Receiving a Consent Request . . . . . . . . . . . . . . . . 6
7.3. Generating a Consent Response . . . . . . . . . . . . . . . 7
7.4. Receiving a Consent Response . . . . . . . . . . . . . . . 7
8. Performing Consent Freshness . . . . . . . . . . . . . . . . . 7
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Generating Consent Freshness Response . . . . . . . . . . . . . 7
11. SDP Extension for Consent Freshness . . . . . . . . . . . . . . 7
12. Interaction with Keepalives used for Refreshing NAT
Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
13. Open Items . . . . . . . . . . . . . . . . . . . . . . . . . . 7
14. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
16. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 8
17. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Consent verification is the mechanism using which WebRTC
implementations can verify the peer consent for receiving traffic on
candidate media transport addresses. This has two parts
1. Verifying peer consent for receiving traffic on candidate media
transport addresses at session establishment.
2. Verifying peer consent for continuing to receive traffic on
candidate media transport addresses after session establishment.
WebRTC implements are required to perform STUN connectivity checks at
session establishment as part of ICE procedures [RFC5245]. This
takes care of the first part of the consent verification described
above.
After session establishment ICE requires STUN Binding indications to
be used for refreshing NAT bindings for a candidate pair ICE is using
for a media component. Since a STUN Binding indication does not
evoke a response, it cannot be used for the second part of the
consent verification describes above.
A related problem is session liveness. WebRTC applications may want
to detect connection failure on candidate media transport addresses
after session establishment and take appropriate actions. Again, the
STUN Binding indications in ICE sent after session establishment
cannot be used for determining session liveness.
This document describes a STUN usage based on STUN request/response
that enables a WebRTC browser to perform the following on a candidate
pair ICE is using for a media component after session establishment:
1. Verify the peer consent for continuing to receive traffic.
2. Dectect connection failure.
This also serves the purpose of refreshing NAT bindings.
2. Terminology
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 [RFC2119].
3. Definitions
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Consent Freshness: It is the mechanism of verifying peer consent for
continuing to receive traffic on a candidate pair ICE is using for
a media component after ICE has concluded. This document uses
completion of session establishment synonymous with the conclusion
of ICE.
Session Liveness: It is the mechanism of detecting connectivity on a
candidate pair ICE is using for a media component after ICE has
concluded.
Transport Address: The combination of an IP address and port number
(such as a UDP or TCP port number).
4. Solution Overview
The solution uses two timers:
1. A consent timer Tc whose value is determined by the browser.
2. A packet receipt timer whose value is determined by the
application.
A WebRTC browser performs a combined consent freshness and session
liveness test using STUN resuest/respose as described below:
o Starts a consent timer Tc (no less than 15 sec).
o Starts a packet receipt timer Tr (no less than 500 msec);
application configurable.
o When either timer expires it starts a STUN transaction.
o When the STUN transaction succeeds, it re-starts both timers.
o When the STUN transaction fails
* If the transaction was started by timer Tc, it stops sending
traffic on that candidate pair.
* Else, it notifies the application of the failure and continues.
o It resets timer Tr on receiving any packet from the other side.
While consent freshness serves as a circuit breaker (if there is a
failure the WebRTC browser stops sending all traffic on that
candidate pair), determining session liveness serves the purpose of
notifying the application of connectivity failure so that the
application can take appropriate action.
5. Design Considerations
As described earlier in this document, STUN indications are not
suitable for performing consent freshness. Hence, performing consent
freshness requires the use of STUN request/response.
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ICE requires the usage of message integrity with STUN using its
short-term credential mechanism. The need for this mechanism goes
beyond just security and is required for the correct operation of the
ICE connectivity check procedures; without message integrity the
connectivity checks can yield false positives, as described in
Appendix B section B.4 of RFC5245. However, this problem is not
applicable for consent freshness, since consent freshness is
performed only after ICE concludes.
One of the reasons for ICE choosing STUN Binding indications for
keepalives is because Binding indication allows integrity to be
disabled, allowing for better performance. This is useful for large-
scale endpoints, such as PSTN gateways and SBCs as described in
Appendix B section B.10 of RFC5245
STUN requires the 96 bits transaction ID to be uniformly and randomly
chosen from the interval 0 .. 2**96-1, and be cryptographically
random. This is good enough security against an off-path attacker.
Though ICE specifies STUN Binding indications to be used for
keepalives, it requires that an agent be prepared to receive
connectivity check as well. If a connectivity check is received, a
response is generated, but there is no impact on ICE processing, as
described in section 10 of RFC5245.
Reusing STUN Binding request/response allows browsers to interoperate
with existing ICE implementations; even ICE-lite implementations.
This is considered very important.
Conclusion: Considering all the above, there seems to be a rough
consensus in the RTCWEB WG for reusing the STUN Binding request/
response for determining consent freshness and session liveness. The
current thought is that the cost of the SHA-1 computation is not a
good enough justification for the pain a new method would cause with
existing IEC implementations.
6. STUN Consent Method
The STUN message type field from the STUN specification [RFC5389] is
shown below
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2 3 4 5 6 7 8 9 A B C D E F
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|M|M|M|M|C|M|M|M|C|M|M|M|M|
|b|a|9|8|7|1|6|5|4|0|3|2|1|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of STUN Message Type Field
Here the bits in the message type field are shown as most significant
(Mb) through least significant (M0). C1 and C0 represent a 2-bit
encoding of the class. Mb through M0 represent a 12-bit encoding of
the method. The Consent method is encoded as 0b000000000010.
A Consent request has class=0b00 (request) and method=0b000000000010
(Consent) and is encoded into the first 16 bits of the STUN header as
0x0002.
A Consent success response has class=0b10 (success response) and
method=0b000000000010 (Consent) and is encoded into the first 16 bits
of the STUN header as 0x0102.
A Consent error response has class=0b11 (error response) and
method=0b000000000010 (Consent) and is encoded into the first 16 bits
of the STUN header as 0x0112.
A Consent indication has class=0b01 (indication) and
method=0b000000000010 (Consent) and is encoded into the first 16 bits
of the STUN header as 0x0012.
7. STUN Consent Method Processing
Processing of the STUN Consent method is similar to the processing of
the STUN Binding method except that the procedures pertaining to the
message integrity and short/long-term credential mechanisms are not
applicable. In particular, the USERNAME and MESSAGE-INTEGRITY
attributes are not included in a Consent request or response.
7.1. Generating a Consent Request
TBD
7.2. Receiving a Consent Request
TBD
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7.3. Generating a Consent Response
TBD
7.4. Receiving a Consent Response
TBD
8. Performing Consent Freshness
TBD
9. Examples
TBD
10. Generating Consent Freshness Response
A STUN agent receiving a consent freshness request for a candidate
pair ICE is using for a media component MUST generate a STUN Consent
response.
11. SDP Extension for Consent Freshness
TBD
12. Interaction with Keepalives used for Refreshing NAT Bindings
An implementation that performs the procedures described in this
document has no need to also perform the keepalives described in ICE
[RFC5245] or RTP keepalive [RFC6263], as they both force recurring
messages to be sent over the UDP port used by RTP. Thus, an
implementation that performs the procedures described in this
document SHOULD NOT also do the keepalives described in ICE [RFC5245]
or RTP keepalives [RFC6263] for the UDP port used for RTP.
13. Open Items
1. Should STUN Binding request/response be reused for determining
consent freshness and session liveness, considering
interoperability with existing ICE and ICE-lite implementation
even at the cost of the incurred SHA-1 computation?
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2. If the RTCP port is different from the RTP port, does RTCP need
consent freshness and session liveness tests?
14. Security Considerations
TBD
15. IANA Considerations
TBD
16. Acknowledgement
Thanks to Eric Rescorla, Harald Alvestrand, Martin Thomson, Bernard
Aboba, Cullen Jennings and Simon Perreault for their valuable inputs
and comments
17. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / RTP
Control Protocol (RTCP) Flows", RFC 6263, June 2011.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
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Authors' Addresses
Muthu Arul Mozhi Perumal
Cisco Systems
Cessna Business Park
Sarjapur-Marathahalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: mperumal@cisco.com
Dan Wing
Cisco Systems
821 Alder Drive
Milpitas, California 95035
USA
Email: dwing@cisco.com
Ram Mohan R
Cisco Systems
Cessna Business Park
Sarjapur-Marathahalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: rmohanr@cisco.com
Hadriel Kaplan
Acme Packet
Email: hkaplan@acmepacket.com
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