wdiff draft-ietf-rtcweb-stun-consent-freshness-07.txt draft-ietf-rtcweb-stun-consent-freshness-08.txt

RTCWEB M. Perumal
Internet-Draft Ericsson
Intended status: Standards Track D. Wing
Expires: March 19, April 30, 2015 R. Ravindranath
T. Reddy
Cisco Systems
M. Thomson
Mozilla
September 15,
October 27, 2014

STUN Usage for Consent Freshness
draft-ietf-rtcweb-stun-consent-freshness-07
draft-ietf-rtcweb-stun-consent-freshness-08

Abstract

To prevent sending excessive traffic to an endpoint, periodic consent
needs to be obtained from that remote endpoint.

This document describes a consent mechanism using a new Session
Traversal Utilities for NAT (STUN) usage. This same mechanism can
also determine connection loss ("liveness") with a remote peer.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on March 19, April 30, 2015.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Design Considerations . . . . . . . . . . . . . . . . . . . . 3
4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Expiration of Consent . . . . . . . . . . . . . . . . . . 4 3
4.2. Immediate Revocation of Consent . . . . . . . . . . . . . 5
5. Connection Liveness DiffServ Treatment for Consent . . . . . . . . . . . . . . . 5
6. DTLS applicability . . . . . . . . . . 5
6. DiffServ Treatment for Consent packets . . . . . . . . . . . 6
7. W3C API Implications Recommendations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8

1. Introduction

To prevent attacks on peers, RTP endpoints have to ensure the remote peer wants
is willing to receive traffic. This is performed both when the
session is first established to the remote peer using Interactive
Connectivity Establishment ICE [RFC5245] connectivity checks, and
periodically for the duration of the session using the procedures
defined in this document.

When a session is first established, ICE implementations obtain an
initial consent to send by performing STUN connectivity checks as part of
ICE. That initial consent is not described further in this document
and it is assumed that ICE is being used for that initial consent.

Related to consent is loss of connectivity ("liveness"). Many
applications want notification of connection loss to take appropriate
actions (e.g., alert the user, try switching to a different
interface). checks. This
document describes a new STUN usage with exchange of request and
response messages to verify that verifies the remote peer's ongoing consent to
receive
traffic, and the absence of which for traffic. This consent expires after a period of time indicates a
loss of liveness.

When a (full) and
needs to be continually renewed, which ensures that consent can be
terminated.

This applies to full ICE implementation interworks with an ICE-lite
implementation the implementations. An ICE-lite implementation
will not generate consent checks, but will just just respond to consent
checks it receives. ICE-lite implementation do not require any
changes to respond to consent checks.

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].

Consent: It is the The mechanism of obtaining permission to send traffic to a certain remote
transport address. This is the initial Initial consent to
send traffic, which is obtained by using ICE or a TCP
handshake.

Consent Freshness: Permission to continue sending traffic to a
certain transport address. This is performed by the procedure
described in this document.

Session Liveness: Detecting loss of connectivity to a certain
transport address. This is performed by the procedure described
in this document. Maintaining and renewing consent over time.

Transport Address: The remote peer's IP address and (UDP UDP or TCP) TCP port
number.

3. Design Considerations

Although ICE requires periodic keepalive traffic to keep NAT bindings
alive (Section 10 of [RFC5245], [RFC6263]), those keepalives are sent
as STUN Indications which are send-and-forget, and do not evoke a
response. A response is necessary both for consent to continue sending traffic, as well as to verify session liveness.
traffic. Thus, we need a request/response mechanism for consent
freshness. ICE can be used for that mechanism because ICE
implementations are already required to continue listening for ICE
messages, as described in section 10 of [RFC5245].

4. Solution

There are two ways consent to send traffic is revoked: expiration of
consent and immediate revocation of consent, which are discussed in
the following sections.

4.1. Expiration of Consent

A WebRTC implementation [I-D.ietf-rtcweb-overview], which implements
full ICE, MUST perform a combined performs consent freshness and session liveness test using STUN request/response
as described below:

An endpoint MUST NOT send application data (e.g., RTP, RTCP, SCTP,
DTLS), over paced STUN connectivity checks toward any
transport protocol (e.g., UDP, TCP) on an ICE-
initiated connection address unless the receiving endpoint consents to receive the
data. That is, no application data (e.g., RTP or DTLS) can be sent
until consent is obtained. After a successful ICE connectivity check
on a particular transport address, subsequent consent MUST be obtained following
the procedure described in this document. The consent
expires after a fixed amount of time. During ICE restart

Explicit consent
checks MUST continue to be sent on previously validated pair, and
MUST be responded send is obtained by sending an STUN binding
request to on the previously validated pair, until remote peer's transport address and receiving a
matching, authenticated, non-error STUN binding response from the
remote peer's transport address. These STUN binding requests and
responses are authenticated using the same short-term credentials as
the initial ICE
restart completes. exchange.

Note: Although TCP has its own consent mechanism (TCP
acknowledgements), consent is necessary over a TCP connection
because it could be translated to a UDP connection (e.g.,
[RFC6062]).

Explicit

Initial consent to send is obtained by sending granted as a result of a successful ICE
connectivity check on a particular transport address, and expires 30
seconds after an ICE binding
request to candidate par has been selected. Once an ICE
candidate pair has been selected, consent for the remote peer's Transport Address and receiving a
matching, authenticated, non-error ICE candidate pairs
lasts for 30 seconds. That is, if a valid STUN binding response
corresponding to any STUN request sent in the last 30 seconds has not
been received from the remote peer's Transport Address. These ICE binding requests and
responses are authenticated using the same short-term credentials as transport address, the initial ICE exchange. Implementations endpoint
MUST cease sending data if
their transmission on that 5-tuple. STUN consent responses
received after consent expires. expiry do not re-establish consent, and may be
discarded or cause an ICMP error.

To prevent expiry of consent, a STUN binding request MUST can be sent every N milliseconds, where N is chosen randomly
with each
periodically. To prevent synchronization of consent check in the checks, each
interval [.8N, 1.2N] (to prevent
network synchronization), where N SHOULD MUST be 5000. Using the value
5000 milliseconds randomized from between 0.8 and that 20% randomization range, N would be 1.2 times the basic
period. Implementations SHOULD set a default interval of 5 seconds,
resulting in a
value period between 4000 and 6000. These STUN binding requests for consent
are not re-transmitted. checks of 4 to 6 seconds.

Each STUN binding request for consent re-
calculates a new random value N and MUST use a new
cryptographically-random [RFC4086] STUN transaction ID.

The initial Consent to send traffic is obtained by ICE. Consent
expires after 30 seconds. That is, if a valid Each STUN
binding requests for consent is transmitted once only. Hence, the
sender cannot assume that it will receive a response
corresponding to for each consent
request, and a response might be for a previous request (rather than
for the most recently sent request). Consent expiration causes
immediate termination of all outstanding STUN consent transactions.
Each STUN transaction is maintained until one of the following
criteria is fulfilled:

o A STUN requests sent in the last 30 seconds
has not been received from the remote peer's Transport Address, response associated with the
endpoint MUST cease transmission on that 5-tuple. transaction is received; or

o A STUN response associated to a newer transaction is received.

To meet the security needs of consent, an untrusted application
(e.g., JavaScript) JavaScript or signaling servers) MUST NOT be able to obtain or
control the STUN transaction ID, because that enables spoofing of
STUN responses, falsifying consent.

To prevent attacks on the peer during ICE restart, an endpoint that
continues to send traffic on the previously validated candidate pair
during ICE restart MUST continue to perform consent freshness on that
candidate pair as described earlier.

While TCP affords some protection from off-path attackers ([RFC5961],
[RFC4953]), there is still a risk an attacker could cause a TCP
sender to send packets forever by spoofing ACKs. To prevent such an attack,
consent checks MUST be performed over all transport connections,
including TCP. In this way, an off-path attacker spoofing TCP
segments can not cause a TCP sender to send packets
longer than once the consent timer
expires (30 seconds).

An endpoint that is not sending any application traffic data does not need to obtain consent which can slightly conserve its resources.
maintain consent. 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, data, it needs to first obtain
consent if its consent has expired.

4.2. Immediate Revocation of Consent

The previous section explained how consent expires due to a timeout.

In some cases it is useful to signal a connection that consent is terminated, terminated
rather than relying on a timeout. This is done by immediately
revoking consent.

Consent for sending traffic on the media or application data channel is immediately revoked by
receipt of an authenticated message that closes the connection (e.g.,
a TLS fatal alert) or receipt of a valid and authenticated STUN
response with error code Forbidden (403).
Those Note however that consent
revocation messages can be lost on the network, so an
implementation wanting to immediately revoke endpoint could
resend these messages, or wait for consent needs to
remember those credentials until consent expiry (30 seconds). expire.

Receipt of an unauthenticated message that closes a connection (e.g.,
TCP FIN) does not indicate revocation of consent. Thus, an endpoint
receiving an unauthenticated end-of-session message SHOULD continue
sending media (over connectionless transport) or attempt to re-
establish the connection (over connection-oriented transport) until
consent expires or it receives an authenticated message revoking
consent.

Note that an authenticated SRTCP BYE does not terminate consent; it
only indicates the associated SRTP source has quit.

5. Connection Liveness

A connection is considered "live" if packets are received from a
remote endpoint within an application-dependent period. An
application can request a notification when there are no packets
received for a certain period (configurable).

Similarly, if packets haven't been received within a certain period,
an application can request a consent check (heartbeat) be generated.
These two time intervals might be controlled by the same
configuration item.

Sending consent checks (heartbeats) at a high rate could allow a
malicious application to generate congestion, so applications MUST
NOT be able to send heartbeats at an average rate of more than 1 per
second.

6. DiffServ Treatment for Consent packets

It is RECOMMENDED that STUN consent checks use the same Diffserv
Codepoint markings as the ICE connectivity checks described in
section
Section 7.1.2.4 of [RFC5245] for a given 5-tuple.

Note: It is possible that different Diffserv Codepoints are used by
different media over the same transport address
[I-D.ietf-tsvwg-rtcweb-qos]. Such a case is outside the scope of
this document.

6. DTLS applicability

The DTLS applicability is identical to what is described in
Section 4.2 of [RFC7350].

7. W3C API Implications

For the consent freshness and liveness test the Recommendations

The W3C specification
should MAY provide APIs as described below:

1. Ability for the browser following API to notify the JavaScript that provide
feedback and control over consent:

1. Generate an event when consent
freshness has failed expired for a 5-tuple and the browser has stopped
transmitting on that 5-tuple.

2. Ability for the JavaScript to start and stop liveness test and
set the liveness test interval.

3. Ability for the browser to notify the JavaScript given 5-tuple,
meaning that a liveness
test transmission of data has failed for a ceased. This could
indicate what application data is affected, such as media stream. or data
channels.

8. Security Considerations

This document describes a security mechanism.

The security considerations discussed in [RFC5245] should also be
taken into account.

SRTP is encrypted and authenticated with symmetric keys; that is,
both sender and receiver know the keys. With two party sessions,
receipt of an authenticated packet from the single remote party is a
strong assurance the packet came from that party. However, when a
session involves more than two parties, all of whom know each others
keys, any of those parties could have sent (or spoofed) the packet.
Such shared key distributions are possible with some MIKEY [RFC3830]
modes, Security Descriptions [RFC4568], and EKT
[I-D.ietf-avtcore-srtp-ekt]. Thus, in such shared keying
distributions, receipt of an authenticated SRTP packet is not
sufficient to verify consent.

9. IANA Considerations

This document does not require any action from IANA.

10. Acknowledgement

Thanks to Eric Rescorla, Harald Alvestrand, Bernard Aboba, Magnus
Westerland, Cullen Jennings, Christer Holmberg, Simon Perreault, Paul
Kyzivat, Emil Ivov, and Jonathan Lennox Lennox, Inaki Baz Castillo, Rajmohan
Banavi and Christian Groves for their valuable inputs and comments.
Thanks to Christer Holmberg for doing a through review.

11. References

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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
(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.

11.2. Informative References

[I-D.ietf-avtcore-srtp-ekt]
Mattsson, J., McGrew, D. D., and D. Wing, "Encrypted Key
Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-02 draft-ietf-avtcore-srtp-ekt-03
(work in progress), February October 2014.

[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-11 draft-ietf-rtcweb-overview-12
(work in progress), August October 2014.

[I-D.ietf-tsvwg-rtcweb-qos]
Dhesikan, S., Jennings, C., Druta, D., Jones, P., and J.
Polk, "DSCP and other packet markings for RTCWeb QoS",
draft-ietf-tsvwg-rtcweb-qos-02 (work in progress), June
2014.

[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004.

[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media
Streams", RFC 4568, July 2006.

[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC
4953, July 2007.

[RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
Robustness to Blind In-Window Attacks", RFC 5961, August
2010.

[RFC6062] Perreault, S. and J. Rosenberg, "Traversal Using Relays
around NAT (TURN) Extensions for TCP Allocations", RFC
6062, November 2010.

[RFC7350] Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport
Layer Security (DTLS) as Transport for Session Traversal
Utilities for NAT (STUN)", RFC 7350, August 2014.

Authors' Addresses

Muthu Arul Mozhi Perumal
Ericsson
Ferns Icon
Doddanekundi, Mahadevapura
Bangalore, Karnataka 560037
India

Email: muthu.arul@gmail.com

Dan Wing
Cisco Systems
821 Alder Drive
Milpitas, California 95035
USA

Email: dwing@cisco.com

Ram Mohan Ravindranath
Cisco Systems
Cessna Business Park
Sarjapur-Marathahalli Outer Ring Road
Bangalore, Karnataka 560103
India

Email: rmohanr@cisco.com
Tirumaleswar Reddy
Cisco Systems
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India

Email: tireddy@cisco.com

Martin Thomson
Mozilla
Suite 300
650 Castro Street
Mountain View, California 94041
US

Email: martin.thomson@gmail.com