< draft-ietf-rtcweb-security-10.txt   draft-ietf-rtcweb-security-11.txt >
RTC-Web E. Rescorla RTC-Web E. Rescorla
Internet-Draft RTFM, Inc. Internet-Draft RTFM, Inc.
Intended status: Standards Track January 22, 2018 Intended status: Standards Track February 1, 2019
Expires: July 26, 2018 Expires: August 5, 2019
Security Considerations for WebRTC Security Considerations for WebRTC
draft-ietf-rtcweb-security-10 draft-ietf-rtcweb-security-11
Abstract Abstract
WebRTC is a protocol suite for use with real-time applications that WebRTC is a protocol suite for use with real-time applications that
can be deployed in browsers - "real time communication on the Web". can be deployed in browsers - "real time communication on the Web".
This document defines the WebRTC threat model and analyzes the This document defines the WebRTC threat model and analyzes the
security threats of WebRTC in that model. security threats of WebRTC in that model.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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
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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 July 26, 2018. This Internet-Draft will expire on August 5, 2019.
Copyright Notice Copyright Notice
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document authors. All rights reserved. document authors. All rights reserved.
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not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Browser Threat Model . . . . . . . . . . . . . . . . . . 4 3. The Browser Threat Model . . . . . . . . . . . . . . . . . . 4
3.1. Access to Local Resources . . . . . . . . . . . . . . . . 5 3.1. Access to Local Resources . . . . . . . . . . . . . . . . 5
3.2. Same Origin Policy . . . . . . . . . . . . . . . . . . . 5 3.2. Same-Origin Policy . . . . . . . . . . . . . . . . . . . 5
3.3. Bypassing SOP: CORS, WebSockets, and consent to 3.3. Bypassing SOP: CORS, WebSockets, and consent to
communicate . . . . . . . . . . . . . . . . . . . . . . . 6 communicate . . . . . . . . . . . . . . . . . . . . . . . 6
4. Security for WebRTC Applications . . . . . . . . . . . . . . 7 4. Security for WebRTC Applications . . . . . . . . . . . . . . 7
4.1. Access to Local Devices . . . . . . . . . . . . . . . . . 7 4.1. Access to Local Devices . . . . . . . . . . . . . . . . . 7
4.1.1. Threats from Screen Sharing . . . . . . . . . . . . . 8 4.1.1. Threats from Screen Sharing . . . . . . . . . . . . . 8
4.1.2. Calling Scenarios and User Expectations . . . . . . . 8 4.1.2. Calling Scenarios and User Expectations . . . . . . . 8
4.1.2.1. Dedicated Calling Services . . . . . . . . . . . 8 4.1.2.1. Dedicated Calling Services . . . . . . . . . . . 9
4.1.2.2. Calling the Site You're On . . . . . . . . . . . 9 4.1.2.2. Calling the Site You're On . . . . . . . . . . . 9
4.1.3. Origin-Based Security . . . . . . . . . . . . . . . . 9 4.1.3. Origin-Based Security . . . . . . . . . . . . . . . . 10
4.1.4. Security Properties of the Calling Page . . . . . . . 11 4.1.4. Security Properties of the Calling Page . . . . . . . 11
4.2. Communications Consent Verification . . . . . . . . . . . 12 4.2. Communications Consent Verification . . . . . . . . . . . 12
4.2.1. ICE . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.1. ICE . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.2. Masking . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.2. Masking . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.3. Backward Compatibility . . . . . . . . . . . . . . . 13 4.2.3. Backward Compatibility . . . . . . . . . . . . . . . 14
4.2.4. IP Location Privacy . . . . . . . . . . . . . . . . . 14 4.2.4. IP Location Privacy . . . . . . . . . . . . . . . . . 15
4.3. Communications Security . . . . . . . . . . . . . . . . . 15 4.3. Communications Security . . . . . . . . . . . . . . . . . 15
4.3.1. Protecting Against Retrospective Compromise . . . . . 16 4.3.1. Protecting Against Retrospective Compromise . . . . . 16
4.3.2. Protecting Against During-Call Attack . . . . . . . . 17 4.3.2. Protecting Against During-Call Attack . . . . . . . . 17
4.3.2.1. Key Continuity . . . . . . . . . . . . . . . . . 17 4.3.2.1. Key Continuity . . . . . . . . . . . . . . . . . 17
4.3.2.2. Short Authentication Strings . . . . . . . . . . 18 4.3.2.2. Short Authentication Strings . . . . . . . . . . 18
4.3.2.3. Third Party Identity . . . . . . . . . . . . . . 18 4.3.2.3. Third Party Identity . . . . . . . . . . . . . . 19
4.3.2.4. Page Access to Media . . . . . . . . . . . . . . 19 4.3.2.4. Page Access to Media . . . . . . . . . . . . . . 19
4.3.3. Malicious Peers . . . . . . . . . . . . . . . . . . . 20 4.3.3. Malicious Peers . . . . . . . . . . . . . . . . . . . 20
4.4. Privacy Considerations . . . . . . . . . . . . . . . . . 20 4.4. Privacy Considerations . . . . . . . . . . . . . . . . . 20
4.4.1. Correlation of Anonymous Calls . . . . . . . . . . . 20 4.4.1. Correlation of Anonymous Calls . . . . . . . . . . . 20
4.4.2. Browser Fingerprinting . . . . . . . . . . . . . . . 20 4.4.2. Browser Fingerprinting . . . . . . . . . . . . . . . 21
5. Security Considerations . . . . . . . . . . . . . . . . . . . 20 5. Security Considerations . . . . . . . . . . . . . . . . . . . 21
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Changes Since -04 . . . . . . . . . . . . . . . . . . . . . . 21 8. Changes Since -04 . . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . 21 9.1. Normative References . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . 21 9.2. Informative References . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 24 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
The Real-Time Communications on the Web (RTCWEB) working group is The Real-Time Communications on the Web (RTCWEB) working group has
tasked with standardizing protocols for real-time communications standardized protocols for real-time communications between Web
between Web browsers, generally called "WebRTC" browsers, generally called "WebRTC" [I-D.ietf-rtcweb-overview]. The
[I-D.ietf-rtcweb-overview]. The major use cases for WebRTC major use cases for WebRTC technology are real-time audio and/or
technology are real-time audio and/or video calls, Web conferencing, video calls, Web conferencing, and direct data transfer. Unlike most
and direct data transfer. Unlike most conventional real-time conventional real-time systems, (e.g., SIP-based [RFC3261] soft
systems, (e.g., SIP-based[RFC3261] soft phones) WebRTC communications phones) WebRTC communications are directly controlled by some Web
are directly controlled by some Web server. A simple case is shown server. A simple case is shown below.
below.
+----------------+ +----------------+
| | | |
| Web Server | | Web Server |
| | | |
+----------------+ +----------------+
^ ^ ^ ^
/ \ / \
HTTP / \ HTTP HTTP / \ HTTP
or / \ or or / \ or
WebSockets / \ WebSockets WebSockets / \ WebSockets
v v v v
JS API JS API JS API JS API
+-----------+ +-----------+ +-----------+ +-----------+
| | Media | | | | Media | |
| Browser |<---------->| Browser | | Browser |<---------->| Browser |
| | | | | | | |
+-----------+ +-----------+ +-----------+ +-----------+
Alice Bob
Figure 1: A simple WebRTC system Figure 1: A simple WebRTC system
In the system shown in Figure 1, Alice and Bob both have WebRTC In the system shown in Figure 1, Alice and Bob both have WebRTC-
enabled browsers and they visit some Web server which operates a enabled browsers and they visit some Web server which operates a
calling service. Each of their browsers exposes standardized calling service. Each of their browsers exposes standardized
JavaScript calling APIs (implementated as browser built-ins) which JavaScript calling APIs (implementated as browser built-ins) which
are used by the Web server to set up a call between Alice and Bob. are used by the Web server to set up a call between Alice and Bob.
The Web server also serves as the signaling channel to transport The Web server also serves as the signaling channel to transport
control messages between the browsers. While this system is control messages between the browsers. While this system is
topologically similar to a conventional SIP-based system (with the topologically similar to a conventional SIP-based system (with the
Web server acting as the signaling service and browsers acting as Web server acting as the signaling service and browsers acting as
softphones), control has moved to the central Web server; the browser softphones), control has moved to the central Web server; the browser
simply provides API points that are used by the calling service. As simply provides API points that are used by the calling service. As
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denial of service attacks. Any successful system will need to be denial of service attacks. Any successful system will need to be
resistant to this and other attacks. resistant to this and other attacks.
A companion document [I-D.ietf-rtcweb-security-arch] describes a A companion document [I-D.ietf-rtcweb-security-arch] describes a
security architecture intended to address the issues raised in this security architecture intended to address the issues raised in this
document. document.
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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. The Browser Threat Model 3. The Browser Threat Model
The security requirements for WebRTC follow directly from the The security requirements for WebRTC follow directly from the
requirement that the browser's job is to protect the user. Huang et requirement that the browser's job is to protect the user. Huang et
al. [huang-w2sp] summarize the core browser security guarantee as: al. [huang-w2sp] summarize the core browser security guarantee as:
Users can safely visit arbitrary web sites and execute scripts Users can safely visit arbitrary web sites and execute scripts
provided by those sites. provided by those sites.
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NETWORK ATTACKERS, who are able to control your network. Network NETWORK ATTACKERS, who are able to control your network. Network
attackers correspond to the [RFC3552] "Internet Threat Model". Note attackers correspond to the [RFC3552] "Internet Threat Model". Note
that for non-HTTPS traffic, a network attacker is also a Web that for non-HTTPS traffic, a network attacker is also a Web
attacker, since it can inject traffic as if it were any non-HTTPS Web attacker, since it can inject traffic as if it were any non-HTTPS Web
site. Thus, when analyzing HTTP connections, we must assume that site. Thus, when analyzing HTTP connections, we must assume that
traffic is going to the attacker. traffic is going to the attacker.
3.1. Access to Local Resources 3.1. Access to Local Resources
While the browser has access to local resources such as keying While the browser has access to local resources such as keying
material, files, the camera and the microphone, it strictly limits or material, files, the camera, and the microphone, it strictly limits
forbids web servers from accessing those same resources. For or forbids web servers from accessing those same resources. For
instance, while it is possible to produce an HTML form which will instance, while it is possible to produce an HTML form which will
allow file upload, a script cannot do so without user consent and in allow file upload, a script cannot do so without user consent and in
fact cannot even suggest a specific file (e.g., /etc/passwd); the fact cannot even suggest a specific file (e.g., /etc/passwd); the
user must explicitly select the file and consent to its upload. user must explicitly select the file and consent to its upload.
[Note: in many cases browsers are explicitly designed to avoid [Note: in many cases browsers are explicitly designed to avoid
dialogs with the semantics of "click here to screw yourself", as dialogs with the semantics of "click here to bypass security checks",
extensive research shows that users are prone to consent under such as extensive research shows that users are prone to consent under
circumstances.] such circumstances.]
Similarly, while Flash programs (SWFs) [SWF] can access the camera Similarly, while Flash programs (SWFs) [SWF] can access the camera
and microphone, they explicitly require that the user consent to that and microphone, they explicitly require that the user consent to that
access. In addition, some resources simply cannot be accessed from access. In addition, some resources simply cannot be accessed from
the browser at all. For instance, there is no real way to run the browser at all. For instance, there is no real way to run
specific executables directly from a script (though the user can of specific executables directly from a script (though the user can of
course be induced to download executable files and run them). course be induced to download executable files and run them).
3.2. Same Origin Policy 3.2. Same-Origin Policy
Many other resources are accessible but isolated. For instance, Many other resources are accessible but isolated. For instance,
while scripts are allowed to make HTTP requests via the while scripts are allowed to make HTTP requests via the
XMLHttpRequest() API those requests are not allowed to be made to any XMLHttpRequest() API (see [XmlHttpRequest]) those requests are not
server, but rather solely to the same ORIGIN from whence the script allowed to be made to any server, but rather solely to the same
came [RFC6454] (although CORS [CORS] and WebSockets [RFC6455] provide ORIGIN from whence the script came [RFC6454] (although CORS [CORS]
a escape hatch from this restriction, as described below.) This SAME and WebSockets [RFC6455] provide a escape hatch from this
ORIGIN POLICY (SOP) prevents server A from mounting attacks on server restriction, as described below.) This SAME ORIGIN POLICY (SOP)
B via the user's browser, which protects both the user (e.g., from prevents server A from mounting attacks on server B via the user's
misuse of his credentials) and the server B (e.g., from DoS attack). browser, which protects both the user (e.g., from misuse of his
credentials) and the server B (e.g., from DoS attack).
More generally, SOP forces scripts from each site to run in their More generally, SOP forces scripts from each site to run in their
own, isolated, sandboxes. While there are techniques to allow them own, isolated, sandboxes. While there are techniques to allow them
to interact, those interactions generally must be mutually consensual to interact, those interactions generally must be mutually consensual
(by each site) and are limited to certain channels. For instance, (by each site) and are limited to certain channels. For instance,
multiple pages/browser panes from the same origin can read each multiple pages/browser panes from the same origin can read each
other's JS variables, but pages from the different origins--or even other's JS variables, but pages from the different origins--or even
iframes from different origins on the same page--cannot. iframes from different origins on the same page--cannot.
3.3. Bypassing SOP: CORS, WebSockets, and consent to communicate 3.3. Bypassing SOP: CORS, WebSockets, and consent to communicate
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The most obvious threats are simply those of "oversharing". I.e., The most obvious threats are simply those of "oversharing". I.e.,
the user may believe they are sharing a window when in fact they are the user may believe they are sharing a window when in fact they are
sharing an application, or may forget they are sharing their whole sharing an application, or may forget they are sharing their whole
screen, icons, notifications, and all. This is already an issue with screen, icons, notifications, and all. This is already an issue with
existing screen sharing technologies and is made somewhat worse if a existing screen sharing technologies and is made somewhat worse if a
partially trusted site is responsible for asking for the resource to partially trusted site is responsible for asking for the resource to
be shared rather than having the user propose it. be shared rather than having the user propose it.
A less obvious threat involves the impact of screen sharing on the A less obvious threat involves the impact of screen sharing on the
Web security model. A key part of the Same Origin Policy is that Web security model. A key part of the Same-Origin Policy is that
HTML or JS from site A can reference content from site B and cause HTML or JS from site A can reference content from site B and cause
the browser to load it, but (unless explicitly permitted) cannot see the browser to load it, but (unless explicitly permitted) cannot see
the result. However, if a web application from a site is screen the result. However, if a web application from a site is screen
sharing the browser, then this violates that invariant, with serious sharing the browser, then this violates that invariant, with serious
security consequences. For example, an attacker site might request security consequences. For example, an attacker site might request
screen sharing and then briefly open up a new Window to the user's screen sharing and then briefly open up a new Window to the user's
bank or webmail account, using screen sharing to read the resulting bank or webmail account, using screen sharing to read the resulting
displayed content. A more sophisticated attack would be open up a displayed content. A more sophisticated attack would be open up a
source view window to a site and use the screen sharing result to source view window to a site and use the screen sharing result to
view anti cross-site request forgery tokens. view anti cross-site request forgery tokens.
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representative" windows that appear on many shopping sites. In this representative" windows that appear on many shopping sites. In this
case, the user's expectation is that they are calling the site case, the user's expectation is that they are calling the site
they're actually visiting. However, it is unlikely that they want to they're actually visiting. However, it is unlikely that they want to
provide a general consent to such a site; just because I want some provide a general consent to such a site; just because I want some
information on a car doesn't mean that I want the car manufacturer to information on a car doesn't mean that I want the car manufacturer to
be able to activate my microphone whenever they please. Thus, this be able to activate my microphone whenever they please. Thus, this
suggests the need for a second consent mechanism where I only grant suggests the need for a second consent mechanism where I only grant
consent for the duration of a given call. As described in consent for the duration of a given call. As described in
Section 3.1, great care must be taken in the design of this interface Section 3.1, great care must be taken in the design of this interface
to avoid the users just clicking through. Note also that the user to avoid the users just clicking through. Note also that the user
interface chrome must clearly display elements showing that the call interface chrome, which is the representation through which the user
is continuing in order to avoid attacks where the calling site just interacts with the user agent itself, must clearly display elements
leaves it up indefinitely but shows a Web UI that implies otherwise. showing that the call is continuing in order to avoid attacks where
the calling site just leaves it up indefinitely but shows a Web UI
that implies otherwise.
4.1.3. Origin-Based Security 4.1.3. Origin-Based Security
Now that we have seen another use case, we can start to reason about Now that we have seen another use case, we can start to reason about
the security requirements. the security requirements.
As discussed in Section 3.2, the basic unit of Web sandboxing is the As discussed in Section 3.2, the basic unit of Web sandboxing is the
origin, and so it is natural to scope consent to origin. origin, and so it is natural to scope consent to origin.
Specifically, a script from origin A MUST only be allowed to initiate Specifically, a script from origin A MUST only be allowed to initiate
communications (and hence to access camera and microphone) if the communications (and hence to access camera and microphone) if the
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cases. As discussed above, individual consent puts the user's cases. As discussed above, individual consent puts the user's
approval in the UI flow for every call. Not only does this quickly approval in the UI flow for every call. Not only does this quickly
become annoying but it can train the user to simply click "OK", at become annoying but it can train the user to simply click "OK", at
which point the consent becomes useless. Thus, while it may be which point the consent becomes useless. Thus, while it may be
necessary to have individual consent in some case, this is not a necessary to have individual consent in some case, this is not a
suitable solution for (for instance) the calling service case. Where suitable solution for (for instance) the calling service case. Where
necessary, in-flow user interfaces must be carefully designed to necessary, in-flow user interfaces must be carefully designed to
avoid the risk of the user blindly clicking through. avoid the risk of the user blindly clicking through.
The other two options are designed to restrict calls to a given The other two options are designed to restrict calls to a given
target. Callee-oriented consent provided by the calling site not target. Callee-oriented consent provided by the calling site would
work well because a malicious site can claim that the user is calling not work well because a malicious site can claim that the user is
any user of his choice. One fix for this is to tie calls to a calling any user of his choice. One fix for this is to tie calls to
cryptographically established identity. While not suitable for all a cryptographically-established identity. While not suitable for all
cases, this approach may be useful for some. If we consider the case cases, this approach may be useful for some. If we consider the case
of advertising, it's not particularly convenient to require the of advertising, it's not particularly convenient to require the
advertiser to instantiate an iframe on the hosting site just to get advertiser to instantiate an iframe on the hosting site just to get
permission; a more convenient approach is to cryptographically tie permission; a more convenient approach is to cryptographically tie
the advertiser's certificate to the communication directly. We're the advertiser's certificate to the communication directly. We're
still tying permissions to origin here, but to the media origin (and- still tying permissions to origin here, but to the media origin (and-
or destination) rather than to the Web origin. or destination) rather than to the Web origin.
[I-D.ietf-rtcweb-security-arch] describes mechanisms which facilitate [I-D.ietf-rtcweb-security-arch] describes mechanisms which facilitate
this sort of consent. this sort of consent.
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Note that this attack does not depend on the media being insecure. Note that this attack does not depend on the media being insecure.
Because the call is to the attacker, it is also encrypted to him. Because the call is to the attacker, it is also encrypted to him.
Moreover, it need not be executed immediately; the attacker can Moreover, it need not be executed immediately; the attacker can
"infect" the origin semi-permanently (e.g., with a web worker or a "infect" the origin semi-permanently (e.g., with a web worker or a
popped-up window that is hidden under the main window.) and thus be popped-up window that is hidden under the main window.) and thus be
able to bug me long after I have left the infected network. This able to bug me long after I have left the infected network. This
risk is created by allowing calls at all from a page fetched over risk is created by allowing calls at all from a page fetched over
HTTP. HTTP.
Even if calls are only possible from HTTPS [RFC2818] sites, if the Even if calls are only possible from HTTPS [RFC2818] sites, if those
site embeds active content (e.g., JavaScript) that is fetched over sites include active content (e.g., JavaScript) from an untrusted
HTTP or from an untrusted site, because that JavaScript is executed site, that JavaScript is executed in the security context of the page
in the security context of the page [finer-grained]. Thus, it is [finer-grained]. This could lead to compromise of a call even if the
also dangerous to allow WebRTC functionality from HTTPS origins that parent page is safe. Note: this issue is not restricted to PAGES
embed mixed content. Note: this issue is not restricted to PAGES which contain untrusted content. If a page from a given origin ever
which contain mixed content. If a page from a given origin ever loads JavaScript from an attacker, then it is possible for that
loads mixed content then it is possible for a network attacker to attacker to infect the browser's notion of that origin semi-
infect the browser's notion of that origin semi-permanently. permanently.
4.2. Communications Consent Verification 4.2. Communications Consent Verification
As discussed in Section 3.3, allowing web applications unrestricted As discussed in Section 3.3, allowing web applications unrestricted
network access via the browser introduces the risk of using the network access via the browser introduces the risk of using the
browser as an attack platform against machines which would not browser as an attack platform against machines which would not
otherwise be accessible to the malicious site, for instance because otherwise be accessible to the malicious site, for instance because
they are topologically restricted (e.g., behind a firewall or NAT). they are topologically restricted (e.g., behind a firewall or NAT).
In order to prevent this form of attack as well as cross-protocol In order to prevent this form of attack as well as cross-protocol
attacks it is important to require that the target of traffic attacks it is important to require that the target of traffic
skipping to change at page 12, line 44 skipping to change at page 13, line 9
matter there are a large number of Web sites which can act as data matter there are a large number of Web sites which can act as data
sources, so an attacker can at least use downlink bandwidth with sources, so an attacker can at least use downlink bandwidth with
existing Web APIs. However, this potential DoS vector reinforces the existing Web APIs. However, this potential DoS vector reinforces the
need for adequate congestion control for WebRTC protocols to ensure need for adequate congestion control for WebRTC protocols to ensure
that they play fair with other demands on the user's bandwidth. that they play fair with other demands on the user's bandwidth.
4.2.1. ICE 4.2.1. ICE
Verifying receiver consent requires some sort of explicit handshake, Verifying receiver consent requires some sort of explicit handshake,
but conveniently we already need one in order to do NAT hole- but conveniently we already need one in order to do NAT hole-
punching. ICE [RFC5245] includes a handshake designed to verify that punching. ICE [RFC8445] includes a handshake designed to verify that
the receiving element wishes to receive traffic from the sender. It the receiving element wishes to receive traffic from the sender. It
is important to remember here that the site initiating ICE is is important to remember here that the site initiating ICE is
presumed malicious; in order for the handshake to be secure the presumed malicious; in order for the handshake to be secure the
receiving element MUST demonstrate receipt/knowledge of some value receiving element MUST demonstrate receipt/knowledge of some value
not available to the site (thus preventing the site from forging not available to the site (thus preventing the site from forging
responses). In order to achieve this objective with ICE, the STUN responses). In order to achieve this objective with ICE, the STUN
transaction IDs must be generated by the browser and MUST NOT be made transaction IDs must be generated by the browser and MUST NOT be made
available to the initiating script, even via a diagnostic interface. available to the initiating script, even via a diagnostic interface.
Verifying receiver consent also requires verifying the receiver wants Verifying receiver consent also requires verifying the receiver wants
to receive traffic from a particular sender, and at this time; for to receive traffic from a particular sender, and at this time; for
example a malicious site may simply attempt ICE to known servers that example a malicious site may simply attempt ICE to known servers that
are using ICE for other sessions. ICE provides this verification as are using ICE for other sessions. ICE provides this verification as
well, by using the STUN credentials as a form of per-session shared well, by using the STUN credentials as a form of per-session shared
secret. Those credentials are known to the Web application, but secret. Those credentials are known to the Web application, but
would need to also be known and used by the STUN-receiving element to would need to also be known and used by the STUN-receiving element to
be useful. be useful.
There also needs to be some mechanism for the browser to verify that There also needs to be some mechanism for the browser to verify that
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The message/reply pair must be generated in such a way that an The message/reply pair must be generated in such a way that an
attacker who controls the Web application cannot forge them, attacker who controls the Web application cannot forge them,
generally by having the message contain some secret value that must generally by having the message contain some secret value that must
be incorporated (e.g., echoed, hashed into, etc.). Non-ICE be incorporated (e.g., echoed, hashed into, etc.). Non-ICE
candidates for this role (in cases where the legacy endpoint has a candidates for this role (in cases where the legacy endpoint has a
public address) include: public address) include:
o STUN checks without using ICE (i.e., the non-RTC-web endpoint sets o STUN checks without using ICE (i.e., the non-RTC-web endpoint sets
up a STUN responder.) up a STUN responder.)
o Use or RTCP as an implicit reachability check. o Use of RTCP as an implicit reachability check.
In the RTCP approach, the WebRTC endpoint is allowed to send a In the RTCP approach, the WebRTC endpoint is allowed to send a
limited number of RTP packets prior to receiving consent. This limited number of RTP packets prior to receiving consent. This
allows a short window of attack. In addition, some legacy endpoints allows a short window of attack. In addition, some legacy endpoints
do not support RTCP, so this is a much more expensive solution for do not support RTCP, so this is a much more expensive solution for
such endpoints, for which it would likely be easier to implement ICE. such endpoints, for which it would likely be easier to implement ICE.
For these two reasons, an RTCP-based approach does not seem to For these two reasons, an RTCP-based approach does not seem to
address the security issue satisfactorily. address the security issue satisfactorily.
In the STUN approach, the WebRTC endpoint is able to verify that the In the STUN approach, the WebRTC endpoint is able to verify that the
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those for initial consent, though are perhaps weaker since the those for initial consent, though are perhaps weaker since the
threats is less severe. threats is less severe.
4.2.4. IP Location Privacy 4.2.4. IP Location Privacy
Note that as soon as the callee sends their ICE candidates, the Note that as soon as the callee sends their ICE candidates, the
caller learns the callee's IP addresses. The callee's server caller learns the callee's IP addresses. The callee's server
reflexive address reveals a lot of information about the callee's reflexive address reveals a lot of information about the callee's
location. In order to avoid tracking, implementations may wish to location. In order to avoid tracking, implementations may wish to
suppress the start of ICE negotiation until the callee has answered. suppress the start of ICE negotiation until the callee has answered.
In addition, either side may wish to hide their location from the
In addition, either side may wish to hide their location entirely by other side entirely by forcing all traffic through a TURN server.
forcing all traffic through a TURN server.
In ordinary operation, the site learns the browser's IP address, In ordinary operation, the site learns the browser's IP address,
though it may be hidden via mechanisms like Tor though it may be hidden via mechanisms like Tor
[http://www.torproject.org] or a VPN. However, because sites can [http://www.torproject.org] or a VPN. However, because sites can
cause the browser to provide IP addresses, this provides a mechanism cause the browser to provide IP addresses, this provides a mechanism
for sites to learn about the user's network environment even if the for sites to learn about the user's network environment even if the
user is behind a VPN that masks their IP address. Implementations user is behind a VPN that masks their IP address. Implementations
may wish to provide settings which suppress all non-VPN candidates if may wish to provide settings which suppress all non-VPN candidates if
the user is on certain kinds of VPN, especially privacy-oriented the user is on certain kinds of VPN, especially privacy-oriented
systems such as Tor. systems such as Tor.
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Finally, we consider a problem familiar from the SIP world: Finally, we consider a problem familiar from the SIP world:
communications security. For obvious reasons, it MUST be possible communications security. For obvious reasons, it MUST be possible
for the communicating parties to establish a channel which is secure for the communicating parties to establish a channel which is secure
against both message recovery and message modification. (See against both message recovery and message modification. (See
[RFC5479] for more details.) This service must be provided for both [RFC5479] for more details.) This service must be provided for both
data and voice/video. Ideally the same security mechanisms would be data and voice/video. Ideally the same security mechanisms would be
used for both types of content. Technology for providing this used for both types of content. Technology for providing this
service (for instance, SRTP [RFC3711], DTLS [RFC6347] and DTLS-SRTP service (for instance, SRTP [RFC3711], DTLS [RFC6347] and DTLS-SRTP
[RFC5763]) is well understood. However, we must examine this [RFC5763]) is well understood. However, we must examine this
technology to the WebRTC context, where the threat model is somewhat technology in the WebRTC context, where the threat model is somewhat
different. different.
In general, it is important to understand that unlike a conventional In general, it is important to understand that unlike a conventional
SIP proxy, the calling service (i.e., the Web server) controls not SIP proxy, the calling service (i.e., the Web server) controls not
only the channel between the communicating endpoints but also the only the channel between the communicating endpoints but also the
application running on the user's browser. While in principle it is application running on the user's browser. While in principle it is
possible for the browser to cut the calling service out of the loop possible for the browser to cut the calling service out of the loop
and directly present trusted information (and perhaps get consent), and directly present trusted information (and perhaps get consent),
practice in modern browsers is to avoid this whenever possible. "In- practice in modern browsers is to avoid this whenever possible. "In-
flow" modal dialogs which require the user to consent to specific flow" modal dialogs which require the user to consent to specific
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During-call attack by calling service. During-call attack by calling service.
The calling service is compromised during the call it wishes to The calling service is compromised during the call it wishes to
attack (often called an "active attack"). attack (often called an "active attack").
Providing security against the former type of attack is practical Providing security against the former type of attack is practical
using the techniques discussed in Section 4.3.1. However, it is using the techniques discussed in Section 4.3.1. However, it is
extremely difficult to prevent a trusted but malicious calling extremely difficult to prevent a trusted but malicious calling
service from actively attacking a user's calls, either by mounting a service from actively attacking a user's calls, either by mounting a
MITM attack or by diverting them entirely. (Note that this attack Man-in-the-Middle (MITM) attack or by diverting them entirely. (Note
applies equally to a network attacker if communications to the that this attack applies equally to a network attacker if
calling service are not secured.) We discuss some potential communications to the calling service are not secured.) We discuss
approaches and why they are likely to be impractical in some potential approaches and why they are likely to be impractical
Section 4.3.2. in Section 4.3.2.
4.3.1. Protecting Against Retrospective Compromise 4.3.1. Protecting Against Retrospective Compromise
In a retrospective attack, the calling service was uncompromised In a retrospective attack, the calling service was uncompromised
during the call, but that an attacker subsequently wants to recover during the call, but that an attacker subsequently wants to recover
the content of the call. We assume that the attacker has access to the content of the call. We assume that the attacker has access to
the protected media stream as well as having full control of the the protected media stream as well as having full control of the
calling service. calling service.
If the calling service has access to the traffic keying material (as If the calling service has access to the traffic keying material (as
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[cranor-wolf], it seems extremely unlikely that any key continuity [cranor-wolf], it seems extremely unlikely that any key continuity
mechanism will be effective rather than simply annoying. mechanism will be effective rather than simply annoying.
Moreover, it is trivial to bypass even this kind of mechanism. Moreover, it is trivial to bypass even this kind of mechanism.
Recall that unlike the case of SSH, the browser never directly gets Recall that unlike the case of SSH, the browser never directly gets
the peer's identity from the user. Rather, it is provided by the the peer's identity from the user. Rather, it is provided by the
calling service. Even enabling a mechanism of this type would calling service. Even enabling a mechanism of this type would
require an API to allow the calling service to tell the browser "this require an API to allow the calling service to tell the browser "this
is a call to user X". All the calling service needs to do to avoid is a call to user X". All the calling service needs to do to avoid
triggering a key continuity warning is to tell the browser that "this triggering a key continuity warning is to tell the browser that "this
is a call to user Y" where Y is close to X. Even if the user is a call to user Y" where Y is confusable with X. Even if the user
actually checks the other side's name (which all available evidence actually checks the other side's name (which all available evidence
indicates is unlikely), this would require (a) the browser to trusted indicates is unlikely), this would require (a) the browser to trusted
UI to provide the name and (b) the user to not be fooled by similar UI to provide the name and (b) the user to not be fooled by similar
appearing names. appearing names.
4.3.2.2. Short Authentication Strings 4.3.2.2. Short Authentication Strings
ZRTP [RFC6189] uses a "short authentication string" (SAS) which is ZRTP [RFC6189] uses a "short authentication string" (SAS) which is
derived from the key agreement protocol. This SAS is designed to be derived from the key agreement protocol. This SAS is designed to be
compared by the users (e.g., read aloud over the the voice channel or compared by the users (e.g., read aloud over the the voice channel or
skipping to change at page 19, line 6 skipping to change at page 19, line 23
simply ignore such indicators even in the rather more dire case of simply ignore such indicators even in the rather more dire case of
mixed content warnings. mixed content warnings.
4.3.2.3. Third Party Identity 4.3.2.3. Third Party Identity
The conventional approach to providing communications identity has of The conventional approach to providing communications identity has of
course been to have some third party identity system (e.g., PKI) to course been to have some third party identity system (e.g., PKI) to
authenticate the endpoints. Such mechanisms have proven to be too authenticate the endpoints. Such mechanisms have proven to be too
cumbersome for use by typical users (and nearly too cumbersome for cumbersome for use by typical users (and nearly too cumbersome for
administrators). However, a new generation of Web-based identity administrators). However, a new generation of Web-based identity
providers (BrowserID, Federated Google Login, Facebook Connect, providers (BrowserID, Federated Google Login, Facebook Connect, OAuth
OAuth, OpenID, WebFinger), has recently been developed and use Web [RFC6749], OpenID [OpenID], WebFinger [RFC7033]), has recently been
technologies to provide lightweight (from the user's perspective) developed and use Web technologies to provide lightweight (from the
third-party authenticated transactions. It is possible to use user's perspective) third-party authenticated transactions. It is
systems of this type to authenticate WebRTC calls, linking them to possible to use systems of this type to authenticate WebRTC calls,
existing user notions of identity (e.g., Facebook adjacencies). linking them to existing user notions of identity (e.g., Facebook
Specifically, the third-party identity system is used to bind the adjacencies). Specifically, the third-party identity system is used
user's identity to cryptographic keying material which is then used to bind the user's identity to cryptographic keying material which is
to authenticate the calling endpoints. Calls which are authenticated then used to authenticate the calling endpoints. Calls which are
in this fashion are naturally resistant even to active MITM attack by authenticated in this fashion are naturally resistant even to active
the calling site. MITM attack by the calling site.
Note that there is one special case in which PKI-style certificates Note that there is one special case in which PKI-style certificates
do provide a practical solution: calls from end-users to large sites. do provide a practical solution: calls from end-users to large sites.
For instance, if you are making a call to Amazon.com, then Amazon can For instance, if you are making a call to Amazon.com, then Amazon can
easily get a certificate to authenticate their media traffic, just as easily get a certificate to authenticate their media traffic, just as
they get one to authenticate their Web traffic. This does not they get one to authenticate their Web traffic. This does not
provide additional security value in cases in which the calling site provide additional security value in cases in which the calling site
and the media peer are one in the same, but might be useful in cases and the media peer are one in the same, but might be useful in cases
in which third parties (e.g., ad networks or retailers) arrange for in which third parties (e.g., ad networks or retailers) arrange for
calls but do not participate in them. calls but do not participate in them.
skipping to change at page 19, line 43 skipping to change at page 20, line 11
manipulated by the calling site. Obviously, if the site can modify manipulated by the calling site. Obviously, if the site can modify
or view the media, then the user is not getting the level of or view the media, then the user is not getting the level of
assurance they would expect from being able to authenticate their assurance they would expect from being able to authenticate their
peer. In many cases, this is acceptable because the user values peer. In many cases, this is acceptable because the user values
site-based special effects over complete security from the site. site-based special effects over complete security from the site.
However, there are also cases where users wish to know that the site However, there are also cases where users wish to know that the site
cannot interfere. In order to facilitate that, it will be necessary cannot interfere. In order to facilitate that, it will be necessary
to provide features whereby the site can verifiably give up access to to provide features whereby the site can verifiably give up access to
the media streams. This verification must be possible both from the the media streams. This verification must be possible both from the
local side and the remote side. I.e., I must be able to verify that local side and the remote side. I.e., I must be able to verify that
the person I am calling has engaged a secure media mode. In order to the person I am calling has engaged a secure media mode (see
achieve this it will be necessary to cryptographically bind an Section 4.3.3). In order to achieve this it will be necessary to
indication of the local media access policy into the cryptographic cryptographically bind an indication of the local media access policy
authentication procedures detailed in the previous sections. into the cryptographic authentication procedures detailed in the
previous sections.
4.3.3. Malicious Peers 4.3.3. Malicious Peers
One class of attack that we do not generally try to prevent is One class of attack that we do not generally try to prevent is
malicious peers. For instance, no matter what confidentiality malicious peers. For instance, no matter what confidentiality
measures you employ the person you are talking to might record the measures you employ the person you are talking to might record the
call and publish it on the Internet. Similarly, we do not attempt to call and publish it on the Internet. Similarly, we do not attempt to
prevent them from using voice or video processing technology from prevent them from using voice or video processing technology from
hiding or changing their appearance. While technologies (DRM, etc.) hiding or changing their appearance. While technologies (DRM, etc.)
do exist to attempt to address these issues, they are generally not do exist to attempt to address these issues, they are generally not
skipping to change at page 20, line 27 skipping to change at page 20, line 39
unwanted calls. In general, this is in the scope of the calling unwanted calls. In general, this is in the scope of the calling
site, though because WebRTC does offer some forms of strong site, though because WebRTC does offer some forms of strong
authentication, that may be useful as part of a defense against such authentication, that may be useful as part of a defense against such
attacks. attacks.
4.4. Privacy Considerations 4.4. Privacy Considerations
4.4.1. Correlation of Anonymous Calls 4.4.1. Correlation of Anonymous Calls
While persistent endpoint identifiers can be a useful security While persistent endpoint identifiers can be a useful security
feature (see Section 4.3.2.1 they can also represent a privacy threat feature (see Section 4.3.2.1) they can also represent a privacy
in settings where the user wishes to be anonymous. WebRTC provides a threat in settings where the user wishes to be anonymous. WebRTC
number of possible persistent identifiers such as DTLS certificates provides a number of possible persistent identifiers such as DTLS
(if they are reused between connections) and RTCP CNAMES (if certificates (if they are reused between connections) and RTCP CNAMES
generated according to [RFC6222] rather than the privacy preserving (if generated according to [RFC6222] rather than the privacy
mode of [RFC7022]). In order to prevent this type of correlation, preserving mode of [RFC7022]). In order to prevent this type of
browsers need to provide mechanisms to reset these identifiers (e.g., correlation, browsers need to provide mechanisms to reset these
with the same lifetime as cookies). Moreover, the API should provide identifiers (e.g., with the same lifetime as cookies). Moreover, the
mechanisms to allow sites intended for anonymous calling to force the API should provide mechanisms to allow sites intended for anonymous
minting of fresh identifiers. In addition, IP addresses can be a calling to force the minting of fresh identifiers. In addition, IP
source of call linkage [I-D.ietf-rtcweb-ip-handling] addresses can be a source of call linkage
[I-D.ietf-rtcweb-ip-handling]
4.4.2. Browser Fingerprinting 4.4.2. Browser Fingerprinting
Any new set of API features adds a risk of browser fingerprinting, Any new set of API features adds a risk of browser fingerprinting,
and WebRTC is no exception. Specifically, sites can use the presence and WebRTC is no exception. Specifically, sites can use the presence
or absence of specific devices as a browser fingerprint. In general, or absence of specific devices as a browser fingerprint. In general,
the API needs to be balanced between functionality and the the API needs to be balanced between functionality and the
incremental fingerprint risk. incremental fingerprint risk. See [Fingerprinting]
5. Security Considerations 5. Security Considerations
This entire document is about security. This entire document is about security.
6. Acknowledgements 6. Acknowledgements
Bernard Aboba, Harald Alvestrand, Dan Druta, Cullen Jennings, Alan Bernard Aboba, Harald Alvestrand, Dan Druta, Cullen Jennings, Alan
Johnston, Hadriel Kaplan (S 4.2.1), Matthew Kaufman, Martin Thomson, Johnston, Hadriel Kaplan (S 4.2.1), Matthew Kaufman, Martin Thomson,
Magnus Westerlund. Magnus Westerlund.
skipping to change at page 21, line 45 skipping to change at page 22, line 11
o Added a section describing screen sharing threats. o Added a section describing screen sharing threats.
o Assorted editorial changes. o Assorted editorial changes.
9. References 9. References
9.1. Normative References 9.1. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References 9.2. Informative References
[abarth-rtcweb] [abarth-rtcweb]
Barth, A., "Prompting the user is security failure", RTC- Barth, A., "Prompting the user is security failure", RTC-
Web Workshop, September 2010. Web Workshop, September 2010.
[CORS] van Kesteren, A., "Cross-Origin Resource Sharing", January [CORS] van Kesteren, A., "Cross-Origin Resource Sharing", January
2014. 2014.
skipping to change at page 22, line 22 skipping to change at page 22, line 41
Symposium, 2009, August 2009. Symposium, 2009, August 2009.
[farus-conversion] [farus-conversion]
Farrus, M., Erro, D., and J. Hernando, "Speaker Farrus, M., Erro, D., and J. Hernando, "Speaker
Recognition Robustness to Voice Conversion", January 2008. Recognition Robustness to Voice Conversion", January 2008.
[finer-grained] [finer-grained]
Barth, A. and C. Jackson, "Beware of Finer-Grained Barth, A. and C. Jackson, "Beware of Finer-Grained
Origins", W2SP, 2008, July 2008. Origins", W2SP, 2008, July 2008.
[Fingerprinting]
W3C, "Fingerprinting Guidance for Web Specification
Authors (Draft)", November 2013.
[huang-w2sp] [huang-w2sp]
Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C. Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
Jackson, "Talking to Yourself for Fun and Profit", W2SP, Jackson, "Talking to Yourself for Fun and Profit", W2SP,
2011, May 2011. 2011, May 2011.
[I-D.ietf-rtcweb-ip-handling] [I-D.ietf-rtcweb-ip-handling]
Uberti, J. and G. Shieh, "WebRTC IP Address Handling Uberti, J., "WebRTC IP Address Handling Requirements",
Requirements", draft-ietf-rtcweb-ip-handling-04 (work in draft-ietf-rtcweb-ip-handling-11 (work in progress),
progress), July 2017. November 2018.
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19 Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017. (work in progress), November 2017.
[I-D.ietf-rtcweb-security-arch] [I-D.ietf-rtcweb-security-arch]
Rescorla, E., "WebRTC Security Architecture", draft-ietf- Rescorla, E., "WebRTC Security Architecture", draft-ietf-
rtcweb-security-arch-13 (work in progress), October 2017. rtcweb-security-arch-17 (work in progress), November 2018.
[kain-conversion] [kain-conversion]
Kain, A. and M. Macon, "Design and Evaluation of a Voice Kain, A. and M. Macon, "Design and Evaluation of a Voice
Conversion Algorithm based on Spectral Envelope Mapping Conversion Algorithm based on Spectral Envelope Mapping
and Residual Prediction", Proceedings of ICASSP, May and Residual Prediction", Proceedings of ICASSP, May
2001, May 2001. 2001, May 2001.
[OpenID] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "Fingerprinting Guidance for Web
Specification Authors (Draft)", November 2014.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, <https://www.rfc- DOI 10.17487/RFC2818, May 2000,
editor.org/info/rfc2818>. <https://www.rfc-editor.org/info/rfc2818>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, <https://www.rfc- DOI 10.17487/RFC3261, June 2002,
editor.org/info/rfc3261>. <https://www.rfc-editor.org/info/rfc3261>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, <https://www.rfc- DOI 10.17487/RFC3552, July 2003,
editor.org/info/rfc3552>. <https://www.rfc-editor.org/info/rfc3552>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004, RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>. <https://www.rfc-editor.org/info/rfc3711>.
[RFC3760] Gustafson, D., Just, M., and M. Nystrom, "Securely [RFC3760] Gustafson, D., Just, M., and M. Nystrom, "Securely
Available Credentials (SACRED) - Credential Server Available Credentials (SACRED) - Credential Server
Framework", RFC 3760, DOI 10.17487/RFC3760, April 2004, Framework", RFC 3760, DOI 10.17487/RFC3760, April 2004,
<https://www.rfc-editor.org/info/rfc3760>. <https://www.rfc-editor.org/info/rfc3760>.
[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
January 2006, <https://www.rfc-editor.org/info/rfc4251>. January 2006, <https://www.rfc-editor.org/info/rfc4251>.
[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, DOI 10.17487/RFC4568, July 2006, Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
<https://www.rfc-editor.org/info/rfc4568>. <https://www.rfc-editor.org/info/rfc4568>.
[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>.
[RFC5479] Wing, D., Ed., Fries, S., Tschofenig, H., and F. Audet, [RFC5479] Wing, D., Ed., Fries, S., Tschofenig, H., and F. Audet,
"Requirements and Analysis of Media Security Management "Requirements and Analysis of Media Security Management
Protocols", RFC 5479, DOI 10.17487/RFC5479, April 2009, Protocols", RFC 5479, DOI 10.17487/RFC5479, April 2009,
<https://www.rfc-editor.org/info/rfc5479>. <https://www.rfc-editor.org/info/rfc5479>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework [RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer (SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <https://www.rfc-editor.org/info/rfc5763>. 2010, <https://www.rfc-editor.org/info/rfc5763>.
skipping to change at page 24, line 20 skipping to change at page 24, line 40
[RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for
Choosing RTP Control Protocol (RTCP) Canonical Names Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAMEs)", RFC 6222, DOI 10.17487/RFC6222, April 2011, (CNAMEs)", RFC 6222, DOI 10.17487/RFC6222, April 2011,
<https://www.rfc-editor.org/info/rfc6222>. <https://www.rfc-editor.org/info/rfc6222>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011, <https://www.rfc- DOI 10.17487/RFC6454, December 2011,
editor.org/info/rfc6454>. <https://www.rfc-editor.org/info/rfc6454>.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011, RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>. <https://www.rfc-editor.org/info/rfc6455>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla, [RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla,
"Guidelines for Choosing RTP Control Protocol (RTCP) "Guidelines for Choosing RTP Control Protocol (RTCP)
Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022, Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022,
September 2013, <https://www.rfc-editor.org/info/rfc7022>. September 2013, <https://www.rfc-editor.org/info/rfc7022>.
[RFC7033] Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
"WebFinger", RFC 7033, DOI 10.17487/RFC7033, September
2013, <https://www.rfc-editor.org/info/rfc7033>.
[RFC7675] Perumal, M., Wing, D., Ravindranath, R., Reddy, T., and M. [RFC7675] Perumal, M., Wing, D., Ravindranath, R., Reddy, T., and M.
Thomson, "Session Traversal Utilities for NAT (STUN) Usage Thomson, "Session Traversal Utilities for NAT (STUN) Usage
for Consent Freshness", RFC 7675, DOI 10.17487/RFC7675, for Consent Freshness", RFC 7675, DOI 10.17487/RFC7675,
October 2015, <https://www.rfc-editor.org/info/rfc7675>. October 2015, <https://www.rfc-editor.org/info/rfc7675>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[SWF] Adobe, "SWF File Format Specification Version 19", April [SWF] Adobe, "SWF File Format Specification Version 19", April
2013. 2013.
[whitten-johnny] [whitten-johnny]
Whitten, A. and J. Tygar, "Why Johnny Can't Encrypt: A Whitten, A. and J. Tygar, "Why Johnny Can't Encrypt: A
Usability Evaluation of PGP 5.0", Proceedings of the 8th Usability Evaluation of PGP 5.0", Proceedings of the 8th
USENIX Security Symposium, 1999, August 1999. USENIX Security Symposium, 1999, August 1999.
[XmlHttpRequest]
van Kesteren, A., "XMLHttpRequesti Level 2", January 2012.
Author's Address Author's Address
Eric Rescorla Eric Rescorla
RTFM, Inc. RTFM, Inc.
2064 Edgewood Drive 2064 Edgewood Drive
Palo Alto, CA 94303 Palo Alto, CA 94303
USA USA
Phone: +1 650 678 2350 Phone: +1 650 678 2350
Email: ekr@rtfm.com Email: ekr@rtfm.com
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