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 This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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. Perumal, et al. Expires January 17, 2013 [Page 1] Internet-Draft STUN Usage for Consent/Liveness July 2012 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 Perumal, et al. Expires January 17, 2013 [Page 2] Internet-Draft STUN Usage for Consent/Liveness July 2012 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 Perumal, et al. Expires January 17, 2013 [Page 3] Internet-Draft STUN Usage for Consent/Liveness July 2012 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. Perumal, et al. Expires January 17, 2013 [Page 4] Internet-Draft STUN Usage for Consent/Liveness July 2012 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 Perumal, et al. Expires January 17, 2013 [Page 5] Internet-Draft STUN Usage for Consent/Liveness July 2012 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 Perumal, et al. Expires January 17, 2013 [Page 6] Internet-Draft STUN Usage for Consent/Liveness July 2012 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? Perumal, et al. Expires January 17, 2013 [Page 7] Internet-Draft STUN Usage for Consent/Liveness July 2012 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. Perumal, et al. Expires January 17, 2013 [Page 8] Internet-Draft STUN Usage for Consent/Liveness July 2012 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 Perumal, et al. 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