Internet DRAFT - draft-mdns-ice-candidates
draft-mdns-ice-candidates
RTCWEB Y. Fablet
Internet-Draft Apple Inc.
Intended status: Informational June 29, 2018
Expires: December 31, 2018
Using Multicast DNS to protect privacy when exposing ICE candidates
draft-mdns-ice-candidates-00
Abstract
WebRTC applications rely on ICE candidates to enable peer-to-peer
connections between clients in as many network configurations as
possible. To maximize the probability to create a direct peer-to-
peer connection, client private IP addresses are often exposed
without user consent. This is currently used as a way to track
users. This document describes a way to share IP addresses with
other clients while preserving client privacy. This is achieved by
obfuscating IP addresses using dynamically generated names resolvable
through Multicast DNS [RFC6763].
Status of This Memo
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This Internet-Draft will expire on December 31, 2018.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Privacy Concerns . . . . . . . . . . . . . . . . . . . . . . 3
3. Principle . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. ICE Candidate Gathering . . . . . . . . . . . . . . . . . 3
3.2. ICE Candidate Processing . . . . . . . . . . . . . . . . 4
4. Privacy Guidelines . . . . . . . . . . . . . . . . . . . . . 4
4.1. APIs leaking IP addresses . . . . . . . . . . . . . . . . 4
4.2. Generated names reuse . . . . . . . . . . . . . . . . . . 5
4.3. Specific execution contexts . . . . . . . . . . . . . . . 5
5. Specification Requirements . . . . . . . . . . . . . . . . . 5
6. Informative References . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
As detailed in [IPHandling], exposing client private IP addresses
allows maximizing the probability to successfully create a connection
between two clients. This information is also used by many web sites
as a way to fingerprint and identify users without their consent.
The first approach exposes client private IP addresses by default, as
can be seen from websites such as [IPLeak]. The second approach
implemented in the WebKit engine enforces the following policy:
1. By default, use mode 3 as defined in [IPHandling]: any host ICE
candidate is filtered out.
2. Use mode 2 as defined in [IPHandling] if there is an explicit
user action to trust the web site: host ICE candidates are
exposed to the web site based on the use of
navigator.mediaDevices.getUserMedia, which typically prompts the
user to grant or deny access to cameras/microphones.
The second approach supports most common audio/video conference
applications but leads to failing or suboptimal connections for
applications relying solely on data channel. This is particularly an
issue on unmanaged networks, typically home or small offices where
NAT loopback might not be supported.
To overcome the shortcomings of the above two approaches, this
document proposes to register dynamically generated names using
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Multicast DNS when gathering ICE candidates. These dynamically
generated names are used to replace private IP addresses in host ICE
candidates. Only clients that can resolve these dynamically
generated names using Multicast DNS will get access to the actual
client IP address.
2. Privacy Concerns
The gathering of ICE candidates without user consent is a well-known
fingerprinting technique to track users. This is particularly a
concern when users are connected through a NAT which is a usual
configuration. In such a case, knowing both the private IP address
and the public IP address will usually identify uniquely the user
device. Additionally, Internet web sites can more easily attack
intranet web sites when knowing the intranet IP address range.
A successful WebRTC connection between two peers is also a potential
thread to user privacy. When a WebRTC connection latency is close to
zero, the probability is high that the two peers are running on the
same device. Browsers often isolate contexts one from the other.
Private browsing mode contexts usually do not share any information
with regular browsing contexts. The WebKit engine isolates third-
party iframes in various ways (cookies, ITP) to prevent user
tracking. Enabling a web application to determine that two contexts
run in the same device would defeat some of the protections provided
by modern browsers.
3. Principle
This section uses the concept of ICE agent as define in [RFC5245].
In the remainder of the document, it is assumed that each browser
execution context has its own ICE agent.
3.1. ICE Candidate Gathering
For any host ICE candidate gathered by a browsing context as part of
[RFC5245] section 4.1.1, obfuscation of the candidate is done as
follows:
1. Check whether the context ICE agent registered a name resolving
to the ICE host candidate IP address.
2. If the ICE agent registered the name, replace the IP address of
the ICE host candidate with the name with ".local" appended to
it. Expose the candidate and abort these steps.
3. Generate a random unique name, typically a version 4 UUID as
defined in [RFC4122].
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4. Register the unique name using Multicast DNS.
5. If registering of the unique name fails, abort these steps. The
candidate is not exposed.
6. Store the name and its related IP address in the ICE agent for
future reuse.
7. Replace the IP address of the ICE host candidate with the name
with ".local" appended to it. Expose the candidate.
3.2. ICE Candidate Processing
For any remote host ICE candidate received by the ICE agent, the
following procedure is used:
1. If the connection-address field value of the ICE candidate does
not finish by ".local", process the candidate as defined in
[RFC5245].
2. Otherwise, remove the ".local" suffix to the value and resolve it
using Multicast DNS.
3. If it resolves to an IP address, replace the value of the ICE
host candidate by the resolved IP address and continue processing
of the candidate.
4. Otherwise, ignore the candidate.
Multicast DNS resolution might end up retrieving both an IPv4 and
IPv6 address. In that case, the IPv6 address may be used preferably
to the IPv4 address.
4. Privacy Guidelines
4.1. APIs leaking IP addresses
When there is no user consent, the following filtering should be done
to prevent private IP address leakage:
1. host ICE candidates with an IP address are not exposed as ICE
candidate events.
2. Server reflexive ICE candidate raddr field is set to 0.0.0.0 and
rport to 0.
3. SDP does not expose any a=candidate line corresponding to a host
ICE candidate which contains an IP address.
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4. RTCIceCandidateStats dictionaries exposed to web pages do not
contain any 'ip' member if related to a host ICE candidate.
4.2. Generated names reuse
Dynamically generated names can be used to track users if used too
often. Conversely, registering too many names will also generate
useless processing. The proposed rule is to create and register a
new generated name for a given IP address on a per execution context.
4.3. Specific execution contexts
Privacy might also be breached if two execution contexts can identify
whether they are run in the same device based on a successful peer-
to-peer connection. The proposed rule is to not register any name
using Multicast DNS for any ICE agent belonging to:
1. A third-party browser execution context, i.e. a context that is
not same origin as the top level execution context.
2. A private browsing execution context.
5. Specification Requirements
The proposal relies on identifying and resolving any Multicast DNS
based ICE candidates as part of adding/processing a remote candidate.
[ICESDP] section 4.1 could be updated to explicitly allow Multicast
DNS names in the connection-address field.
The proposal relies on adding the ability to register Multicast DNS
names at ICE gathering time. This could be described in [ICESDP]
and/or [WebRTCSpec].
The proposal allows updating [IPHandling] so that mode 2 is not the
mode used by default when user consent is not required. Instead, the
default mode could be defined as mode 3 with Multicast DNS based ICE
candidates.
6. Informative References
[ICESDP] Keranen, A., "Session Description Protocol (SDP) Offer/
Answer procedures for Interactive Connectivity
Establishment (ICE)", April 2018,
<https://tools.ietf.org/html/
draft-ietf-mmusic-ice-sip-sdp>.
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[IPHandling]
Shieh, G., "WebRTC IP Address Handling Requirements",
April 2018, <https://tools.ietf.org/html/
draft-ietf-rtcweb-ip-handling>.
[IPLeak] "IP/DNS Detect", n.d., <https://ipleak.net>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<https://www.rfc-editor.org/info/rfc5245>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[WebRTCSpec]
Bruaroey, J., "The WebRTC specification", n.d.,
<https://w3c.github.io/webrtc-pc/>.
Author's Address
Youenn Fablet
Apple Inc.
Email: youenn@apple.com
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