draft-ietf-rtcweb-stun-consent-freshness-03.txt   draft-ietf-rtcweb-stun-consent-freshness-04.txt 
RTCWEB M. Perumal RTCWEB M. Perumal
Internet-Draft D. Wing Internet-Draft D. Wing
Intended status: Standards Track R. Ravindranath Intended status: Standards Track R. Ravindranath
Expires: November 20, 2014 T. Reddy Expires: December 19, 2014 T. Reddy
Cisco Systems Cisco Systems
M. Thomson M. Thomson
Mozilla Mozilla
May 19, 2014 June 17, 2014
STUN Usage for Consent Freshness STUN Usage for Consent Freshness
draft-ietf-rtcweb-stun-consent-freshness-03 draft-ietf-rtcweb-stun-consent-freshness-04
Abstract Abstract
To prevent sending excessive traffic to an endpoint, periodic consent To prevent sending excessive traffic to an endpoint, periodic consent
needs to be obtained from that remote endpoint. needs to be obtained from that remote endpoint.
This document describes a consent mechanism using a new STUN usage. This document describes a consent mechanism using a new STUN usage.
This same mechanism can also determine connection loss ("liveness") This same mechanism can also determine connection loss ("liveness")
with a remote peer. with a remote peer.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 20, 2014. This Internet-Draft will expire on December 19, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Design Considerations . . . . . . . . . . . . . . . . . . . . 3 3. Design Considerations . . . . . . . . . . . . . . . . . . . . 3
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3 4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 3 4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 3
4.2. Immediate Revocation of Consent . . . . . . . . . . . . . 4 4.2. Immediate Revocation of Consent . . . . . . . . . . . . . 5
5. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 5 5. Connection Liveness . . . . . . . . . . . . . . . . . . . . . 5
6. DiffServ Treatment for Consent packets . . . . . . . . . . . 5 6. DiffServ Treatment for Consent packets . . . . . . . . . . . 5
7. W3C API Implications . . . . . . . . . . . . . . . . . . . . 5 7. W3C API Implications . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7 11.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Example Implementation . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
To prevent attacks on peers, RTP endpoints have to ensure the remote To prevent attacks on peers, RTP endpoints have to ensure the remote
peer wants to receive traffic. This is performed both when the peer wants to receive traffic. This is performed both when the
session is first established to the remote peer using ICE session is first established to the remote peer using ICE
connectivity checks, and periodically for the duration of the session connectivity checks, and periodically for the duration of the session
using the procedures defined in this document. using the procedures defined in this document.
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required to perform STUN connectivity checks as part of ICE required to perform STUN connectivity checks as part of ICE
[RFC5245]. That initial consent is not described further in this [RFC5245]. That initial consent is not described further in this
document and it is assumed that ICE is being used for that initial document and it is assumed that ICE is being used for that initial
consent. consent.
Related to consent is loss of connectivity ("liveness"). Many Related to consent is loss of connectivity ("liveness"). Many
applications want notification of connection loss to take appropriate applications want notification of connection loss to take appropriate
actions (e.g., alert the user, try switching to a different actions (e.g., alert the user, try switching to a different
interface). interface).
This document describes a new STUN usage with a request and response This document describes a new STUN usage with exchange of request and
messages which verifies the remote peer's consent to receive traffic, response messages to verify the remote peer's consent to receive
and can also detect loss of liveness. traffic, and the absence of which for a period of time indicates a
loss of liveness.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 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].
Consent: It is the mechanism of obtaining permission to send traffic Consent: It is the mechanism of obtaining permission to send traffic
to a certain transport address. This is the initial consent to to a certain transport address. This is the initial consent to
send traffic, which is obtained by ICE or a TCP handshake. send traffic, which is obtained by ICE or a TCP handshake.
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Although ICE requires periodic keepalive traffic to keep NAT bindings Although ICE requires periodic keepalive traffic to keep NAT bindings
alive (Section 10 of [RFC5245], [RFC6263]), those keepalives are sent alive (Section 10 of [RFC5245], [RFC6263]), those keepalives are sent
as STUN Indications which are send-and-forget, and do not evoke a as STUN Indications which are send-and-forget, and do not evoke a
response. A response is necessary both for consent to continue response. A response is necessary both for consent to continue
sending traffic, as well as to verify session liveness. Thus, we sending traffic, as well as to verify session liveness. Thus, we
need a request/response mechanism for consent freshness. ICE can be need a request/response mechanism for consent freshness. ICE can be
used for that mechanism because ICE already requires ICE agents used for that mechanism because ICE already requires ICE agents
continue listening for ICE messages, as described in section 10 of continue listening for ICE messages, as described in section 10 of
[RFC5245]. [RFC5245].
4. Solution Overview 4. Solution
There are two ways consent to send traffic is revoked: expiration of There are two ways consent to send traffic is revoked: expiration of
consent and immediate revocation of consent, which are discussed in consent and immediate revocation of consent, which are discussed in
the following sections. the following sections.
4.1. Expiration of Consent 4.1. Expiration of Consent
A WebRTC browser performs a combined consent freshness and session A WebRTC browser performs a combined consent freshness and session
liveness test using STUN request/response as described below: liveness test using STUN request/response as described below:
An endpoint MUST NOT send application data (e.g., RTP, RTCP, SCTP, An endpoint MUST NOT send application data (e.g., RTP, RTCP, SCTP,
DTLS) on an ICE-initiated connection unless the receiving endpoint DTLS) on an ICE-initiated connection unless the receiving endpoint
consents to receive the data. After a successful ICE connectivity consents to receive the data. After a successful ICE connectivity
check on a particular transport address, subsequent consent MUST be check on a particular transport address, subsequent consent MUST be
obtained following the procedure described in this document. The obtained following the procedure described in this document. The
consent expires after a fixed amount of time. consent expires after a fixed amount of time.
Explicit consent to send is indicated by sending an ICE binding Explicit consent to send is obtained by sending an ICE binding
request to the remote peer's Transport Address and receiving a request to the remote peer's Transport Address and receiving a
matching and authenticated ICE binding response from the inverted matching, authenticated, non-error ICE binding response from the
remote peer's Transport Address. These ICE binding requests and inverted remote peer's Transport Address. These ICE binding requests
responses are authenticated using the same short-term credentials as and responses are authenticated using the same short-term credentials
the initial ICE exchange, but using a new (fresh) transaction-id each as the initial ICE exchange. Implementations MUST cease sending data
time consent needs to be refreshed. Implementations MUST obtain if their consent expires. To prevent expiry of consent, a STUN
fresh consent before their existing consent expires. If an ICE binding request is sent every N milliseconds, where N SHOULD be 5000
binding response is not received within 1.5 times the previous round milliseconds and MUST be randomized at least 20% above and 20% below
trip time, another ICE binding request is sent using the a new that value (to prevent prevent network synchronization). Using the
(fresh) transaction-id (so that round-trip time can be calculated), value 5000 milliseconds and that 20% randomization range, N would be
and re-transmissions MUST NOT be sent more frequently than every a value between 4000 and 6000. These STUN binding requests for
500ms or the smoothed round-trip time (from previous consent consent are not re-transmitted. Each STUN binding request for
freshness checks or RTP round-trip time), whichever is less. For the consent re-calculates a new random value N and a new
purposes of this document, receipt of an ICE response with the cryptographically-random [RFC4086] STUN transaction ID.
matching transaction-id of its request with a valid MESSAGE-INTEGRITY
is considered a consent response.
The initial Consent to send traffic is obtained by ICE. Consent The initial Consent to send traffic is obtained by ICE. Consent
expires after 30 seconds. That is, if a valid STUN binding response expires after 30 seconds. That is, if a valid STUN binding response
corresponding to one of the STUN requests sent in the last 30 seconds corresponding to one of the STUN requests sent in the last 30 seconds
has not been received from the inverted 5-tuple, the endpoint MUST has not been received from the inverted 5-tuple, the endpoint MUST
cease transmission on that 5-tuple. cease transmission on that 5-tuple.
To meet the security needs of consent, an untrusted application To meet the security needs of consent, an untrusted application
(e.g., JavaScript) MUST NOT be able to obtain or control the ICE (e.g., JavaScript) MUST NOT be able to obtain or control the STUN
transaction-id, because that enables spoofing STUN responses, transaction ID, because that enables spoofing STUN responses,
falsifying consent falsifying consent.
An endpoint that is only receiving application traffic (recvonly) While TCP affords some protection from off-path attackers ([RFC5961],
does not need to obtain consent which can slightly conserve its [RFC4953]), there is still a risk an attacker could cause a TCP
resources. However, the endpoint needs to ensure its NAT or firewall sender to send packets forever by spoofing ACKs. To prevent such an
mappings persist which can be done using keepalive or other attack, consent checks MUST be performed over all WebRTC-initiated
techniques (see Section 10 of [RFC5245] and see [RFC6263]). If the transport connections, including TCP. In this way, an off-path
endpoint wants send application traffic, it needs to first obtain attacker spoofing TCP segments can not cause a TCP sender to send
consent if its consent expired. packets longer than the consent timer (30 seconds).
An endpoint that is not sending any application traffic does not need
to obtain consent which can slightly conserve its resources.
However, the endpoint needs to ensure its NAT or firewall mappings
persist which can be done using keepalive or other techniques (see
Section 10 of [RFC5245] and see [RFC6263]). If the endpoint wants to
send application traffic, it needs to first obtain consent if its
consent has expired.
4.2. Immediate Revocation of Consent 4.2. Immediate Revocation of Consent
The previous section explained how consent expires due to a timeout. The previous section explained how consent expires due to a timeout.
In some cases it is useful to signal a connection is terminated, In some cases it is useful to signal a connection is terminated,
rather than relying on a timeout. This is done by immediately rather than relying on a timeout. This is done by immediately
revoking consent. revoking consent.
Consent for sending traffic on the media or data channel is revoked Consent for sending traffic on the media or data channel is
by receipt of a an authenticated message that closes the connection immediately revoked by receipt of a an authenticated message that
(for instance, a TLS fatal alert). closes the connection (e.g., a TLS fatal alert) or receipt of a valid
and authenticated STUN response with error code Forbidden (403).
Receipt of an unauthenticated message that closes a connection (e.g., Receipt of an unauthenticated message that closes a connection (e.g.,
TCP FIN) does not indicate revocation of consent. Thus, an endpoint TCP FIN) does not indicate revocation of consent. Thus, an endpoint
receiving an unauthenticated end-of-session message SHOULD continue receiving an unauthenticated end-of-session message SHOULD continue
sending media (over connectionless transport) or attempt to re- sending media (over connectionless transport) or attempt to re-
establish the connection (over connection-oriented transport) until establish the connection (over connection-oriented transport) until
consent expires or it receives an authenticated message revoking consent expires or it receives an authenticated message revoking
consent. consent.
Note that an authenticated SRTCP BYE does not terminate consent; it
only indicates the associated SRTP source has quit.
5. Connection Liveness 5. Connection Liveness
A connection is considered "live" if packets are received from a A connection is considered "live" if packets are received from a
remote endpoint within an application-dependent period. An remote endpoint within an application-dependent period. An
application can request a notification when there are no packets application can request a notification when there are no packets
received for a certain period (configurable). received for a certain period (configurable).
Similarly, if packets haven't been received within a certain period, Similarly, if packets haven't been received within a certain period,
an application can request a consent check (heartbeat) be generated. an application can request a consent check (heartbeat) be generated.
These two time intervals might be controlled by the same These two time intervals might be controlled by the same
configuration item. configuration item.
Sending consent checks (heartbeats) at a high rate could allow a Sending consent checks (heartbeats) at a high rate could allow a
malicious application to generate congestion, so applications MUST malicious application to generate congestion, so applications MUST
NOT be able to send heartbeats faster than 1 per second. NOT be able to send heartbeats at an average rate of more than 1 per
second.
6. DiffServ Treatment for Consent packets 6. DiffServ Treatment for Consent packets
It is RECOMMENDED that STUN consent checks use the same Diffserv It is RECOMMENDED that STUN consent checks use the same Diffserv
Codepoint markings as the media packets sent on that transport Codepoint markings as the ICE connectivity checks described in
address. This follows the recommendation of ICE connectivity check section 7.1.2.4 of [RFC5245] for a given 5-tuple.
described in section 7.1.2.4 of [RFC5245].
Note: It is possible that different Diffserv Codepoints are used by Note: It is possible that different Diffserv Codepoints are used by
different media over the same transport address different media over the same transport address
[I-D.ietf-tsvwg-rtcweb-qos]. In that case, what should this document
recommend as the Codepoint for STUN consent packets ? [I-D.ietf-tsvwg-rtcweb-qos]. Such a case is outside the scope of
this document.
7. W3C API Implications 7. W3C API Implications
For the consent freshness and liveness test the W3C specification For the consent freshness and liveness test the W3C specification
should provide APIs as described below: should provide APIs as described below:
1. Ability for the browser to notify the JavaScript that a consent 1. Ability for the browser to notify the JavaScript that consent
freshness transaction has failed for a media stream and the freshness has failed for a 5-tuple and the browser has stopped
browser has stopped transmitting for that stream. transmitting on that 5-tuple.
2. Ability for the JavaScript to start and stop liveness test and 2. Ability for the JavaScript to start and stop liveness test and
set the liveness test interval. set the liveness test interval.
3. Ability for the browser to notify the JavaScript that a liveness 3. Ability for the browser to notify the JavaScript that a liveness
test has failed for a media stream. test has failed for a media stream.
8. Security Considerations 8. Security Considerations
This document describes a security mechanism. This document describes a security mechanism.
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SRTP is encrypted and authenticated with symmetric keys; that is, SRTP is encrypted and authenticated with symmetric keys; that is,
both sender and receiver know the keys. With two party sessions, both sender and receiver know the keys. With two party sessions,
receipt of an authenticated packet from the single remote party is a receipt of an authenticated packet from the single remote party is a
strong assurance the packet came from that party. However, when a strong assurance the packet came from that party. However, when a
session involves more than two parties, all of whom know each others session involves more than two parties, all of whom know each others
keys, any of those parties could have sent (or spoofed) the packet. keys, any of those parties could have sent (or spoofed) the packet.
Such shared key distributions are possible with some MIKEY [RFC3830] Such shared key distributions are possible with some MIKEY [RFC3830]
modes, Security Descriptions [RFC4568], and EKT modes, Security Descriptions [RFC4568], and EKT
[I-D.ietf-avtcore-srtp-ekt]. Thus, in such shared keying [I-D.ietf-avtcore-srtp-ekt]. Thus, in such shared keying
distributions, receipt of an authenticated SRTP packet is not distributions, receipt of an authenticated SRTP packet is not
sufficient. sufficient to verify consent.
9. IANA Considerations 9. IANA Considerations
This document does not require any action from IANA. This document does not require any action from IANA.
10. Acknowledgement 10. Acknowledgement
Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus
Westerland, Cullen Jennings and Simon Perreault for their valuable Westerland, Cullen Jennings, Christer Holmberg and Simon Perreault
inputs and comments. for their valuable inputs and comments.
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, April Traversal for Offer/Answer Protocols", RFC 5245, April
2010. 2010.
[RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / RTP Keeping Alive the NAT Mappings Associated with RTP / RTP
Control Protocol (RTCP) Flows", RFC 6263, June 2011. Control Protocol (RTCP) Flows", RFC 6263, June 2011.
11.2. Informative References 11.2. Informative References
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rtcweb-qos-00 (work in progress), April 2014. rtcweb-qos-00 (work in progress), April 2014.
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K. [RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830, Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004. August 2004.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, July 2006. Streams", RFC 4568, July 2006.
Appendix A. Example Implementation [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC
4953, July 2007.
This section describes one possible implementation algorithm of
consent. This section is non-normative and provided for reference
only.
The solution uses three values:
1. A consent timer, Tc, whose value is set to 30 seconds.
2. A packet receipt timer, Tr, whose value is determined by the
application. Tr can be greater than 1 but less than 30 seconds
and has a default value of 5 seconds.
3. A consent timeout, Tf, which is how many seconds elapse without a
consent response before the browser ceases transmission of media.
Its value is be 30 seconds or less.
4. A retransmission Timer, Tret, whose value is determined by the
RTT of a given path. The duration of this timer is set to 1.5
times of (500 ms or the smoothened round-trip time (from previous
consent freshness checks or RTP round-trip time)), whichever is
less.
A WebRTC browser performs a combined consent freshness and session
liveness test using STUN request/response as described below:
Every Tc seconds, the WebRTC browser sends a STUN Binding Request to
the peer. The difference from ICE connectivity check is that there
is no exponential back off for retransmissions.
If a valid STUN Binding Response is received, the consent timer is
reset to the time of receiving the response and fires again Tc
seconds later.
If a valid STUN Binding Response is not received after Tret [RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
milliseconds, the STUN Binding Request is retransmitted (with a new Robustness to Blind In-Window Attacks", RFC 5961, August
Transaction ID). As long as a valid STUN Binding Response is not 2010.
received, this retransmission is repeated every Tret milliseconds
until Tf seconds have elapsed or a valid response is received. If no
valid response is received after Tf seconds, the WebRTC browser quits
transmitting traffic to this remote peer. The streams that are being
sent on a flow(5-tuple) for which a consent has failed will be
stopped. If the default value of Tf is 30 seconds then media
transmission will stop Consent (Tf) expires.
Authors' Addresses Authors' Addresses
Muthu Arul Mozhi Perumal Muthu Arul Mozhi Perumal
Cisco Systems Cisco Systems
Cessna Business Park Cessna Business Park
Sarjapur-Marathahalli Outer Ring Road Sarjapur-Marathahalli Outer Ring Road
Bangalore, Karnataka 560103 Bangalore, Karnataka 560103
India India
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