draft-ietf-tokbind-https-05.txt   draft-ietf-tokbind-https-06.txt 
Internet Engineering Task Force A. Popov Internet Engineering Task Force A. Popov
Internet-Draft M. Nystroem Internet-Draft M. Nystroem
Intended status: Standards Track Microsoft Corp. Intended status: Standards Track Microsoft Corp.
Expires: January 8, 2017 D. Balfanz, Ed. Expires: February 27, 2017 D. Balfanz, Ed.
A. Langley A. Langley
Google Inc. Google Inc.
J. Hodges J. Hodges
Paypal Paypal
July 7, 2016 August 26, 2016
Token Binding over HTTP Token Binding over HTTP
draft-ietf-tokbind-https-05 draft-ietf-tokbind-https-06
Abstract Abstract
This document describes a collection of mechanisms that allow HTTP This document describes a collection of mechanisms that allow HTTP
servers to cryptographically bind authentication tokens (such as servers to cryptographically bind authentication tokens (such as
cookies and OAuth tokens) to TLS [RFC5246] connections. cookies and OAuth tokens) to TLS [RFC5246] connections.
We describe both _first-party_ and _federated_ scenarios. In a We describe both _first-party_ and _federated_ scenarios. In a
first-party scenario, an HTTP server is able to cryptographically first-party scenario, an HTTP server is able to cryptographically
bind the security tokens it issues to a client, and which the client bind the security tokens it issues to a client, and which the client
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 8, 2017. This Internet-Draft will expire on February 27, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. The Sec-Token-Binding Header Field . . . . . . . . . . . . . 4 2. The Sec-Token-Binding Header Field . . . . . . . . . . . . . 4
2.1. HTTPS Token Binding Key Pair Scoping . . . . . . . . . . 4 2.1. HTTPS Token Binding Key Pair Scoping . . . . . . . . . . 4
3. First-party Use Cases . . . . . . . . . . . . . . . . . . . . 5 3. First-party Use Cases . . . . . . . . . . . . . . . . . . . . 5
4. Federation Use Cases . . . . . . . . . . . . . . . . . . . . 5 4. Federation Use Cases . . . . . . . . . . . . . . . . . . . . 5
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. HTTP Redirects . . . . . . . . . . . . . . . . . . . . . 7 4.3. HTTP Redirects . . . . . . . . . . . . . . . . . . . . . 7
4.4. Negotiated Key Parameters . . . . . . . . . . . . . . . . 9 4.4. Negotiated Key Parameters . . . . . . . . . . . . . . . . 9
4.5. Federation Example . . . . . . . . . . . . . . . . . . . 9 4.5. Federation Example . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 5. Implementation Considerations . . . . . . . . . . . . . . . . 12
5.1. Security Token Replay . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
5.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS 6.1. Security Token Replay . . . . . . . . . . . . . . . . . . 12
Versions . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS
5.3. Sensitivity of the Sec-Token-Binding Header . . . . . . . 12 Versions . . . . . . . . . . . . . . . . . . . . . . . . 13
5.4. Securing Federated Sign-On Protocols . . . . . . . . . . 13 6.3. Sensitivity of the Sec-Token-Binding Header . . . . . . . 13
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15 6.4. Securing Federated Sign-On Protocols . . . . . . . . . . 14
6.1. Scoping of Token Binding Keys . . . . . . . . . . . . . . 15 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
6.2. Life Time of Token Binding Keys . . . . . . . . . . . . . 16 7.1. Scoping of Token Binding Keys . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7.2. Life Time of Token Binding Keys . . . . . . . . . . . . . 16
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 7.3. Correlation . . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
The Token Binding Protocol [I-D.ietf-tokbind-protocol] defines a The Token Binding Protocol [I-D.ietf-tokbind-protocol] defines a
Token Binding ID for a TLS connection between a client and a server. Token Binding ID for a TLS connection between a client and a server.
The Token Binding ID of a TLS connection is related to a private key, The Token Binding ID of a TLS connection is related to a private key,
that the client proves possession of to the server, and is long-lived that the client proves possession of to the server, and is long-lived
(i.e., subsequent TLS connections between the same client and server (i.e., subsequent TLS connections between the same client and server
have the same Token Binding ID). When issuing a security token (e.g. have the same Token Binding ID). When issuing a security token (e.g.
an HTTP cookie or an OAuth token) to a client, the server can include an HTTP cookie or an OAuth token) to a client, the server can include
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Once a client and server have negotiated the Token Binding Protocol Once a client and server have negotiated the Token Binding Protocol
with HTTP/1.1 or HTTP/2 (see [I-D.ietf-tokbind-protocol] and with HTTP/1.1 or HTTP/2 (see [I-D.ietf-tokbind-protocol] and
[I-D.ietf-tokbind-negotiation]), clients MUST include the Sec-Token- [I-D.ietf-tokbind-negotiation]), clients MUST include the Sec-Token-
Binding header field in their HTTP requests. The ABNF of the Sec- Binding header field in their HTTP requests. The ABNF of the Sec-
Token-Binding header field is (in [RFC7230] style, see also [RFC7231] Token-Binding header field is (in [RFC7230] style, see also [RFC7231]
Section 8.3): Section 8.3):
Sec-Token-Binding = EncodedTokenBindingMessage Sec-Token-Binding = EncodedTokenBindingMessage
The header field name is "Sec-Token-Binding", and The header field name is "Sec-Token-Binding" and its value is a
EncodedTokenBindingMessage is a base64url encoding (see [RFC4648] base64url encoding of the TokenBindingMessage defined in
Section 5) of the TokenBindingMessage as defined in [I-D.ietf-tokbind-protocol] using the URL- and filename-safe
[I-D.ietf-tokbind-protocol]. character set described in Section 5 of [RFC4648], with all trailing
pad characters '=' omitted and without the inclusion of any line
breaks, whitespace, or other additional characters.
For example: For example:
Sec-Token-Binding: <base64url-encoded TokenBindingMessage> Sec-Token-Binding: <base64url-encoded TokenBindingMessage>
The TokenBindingMessage MUST contain one TokenBinding structure with The TokenBindingMessage MUST contain one TokenBinding structure with
TokenBindingType of provided_token_binding, which MUST be signed with TokenBindingType of provided_token_binding, which MUST be signed with
the Token Binding private key used by the client for connections the Token Binding private key used by the client for connections
between itself and the server that the HTTP request is sent to between itself and the server that the HTTP request is sent to
(clients use different Token Binding keys for different servers, see (clients use different Token Binding keys for different servers, see
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The Token Binding key pair scoping for those key pairs generated in The Token Binding key pair scoping for those key pairs generated in
the context of the first-party and federation use cases defined in the context of the first-party and federation use cases defined in
this specification (below), and to be used for binding HTTP cookies this specification (below), and to be used for binding HTTP cookies
MUST be at the granularity of "effective top-level domain (public MUST be at the granularity of "effective top-level domain (public
suffix) + 1" (eTLD+1), i.e., at the same granularity at which cookies suffix) + 1" (eTLD+1), i.e., at the same granularity at which cookies
can be set (see [RFC6265]). Key pairs used to bind other application can be set (see [RFC6265]). Key pairs used to bind other application
tokens, such as OAuth tokens, SHOULD adhere to the above eTLD+1 tokens, such as OAuth tokens, SHOULD adhere to the above eTLD+1
scoping requirement for those tokens being employed in first-party or scoping requirement for those tokens being employed in first-party or
federation scenarios as described below, e.g., OAuth refresh tokens federation scenarios as described below, e.g., OAuth refresh tokens
or Open ID Connect "ID Tokens". See also Section 6.1, below. or Open ID Connect "ID Tokens". See also Section 7.1, below.
Scoping rules for other HTTP-based application contexts are outside Scoping rules for other HTTP-based application contexts are outside
the scope of this specification. the scope of this specification.
3. First-party Use Cases 3. First-party Use Cases
In a first-party use case, an HTTP server issues a security token In a first-party use case, an HTTP server issues a security token
such as a cookie (or similar) to a client, and expects the client to such as a cookie (or similar) to a client, and expects the client to
return the security token at a later time, e.g., in order to return the security token at a later time, e.g., in order to
authenticate. Binding the security token to the TLS connection authenticate. Binding the security token to the TLS connection
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about the Token Binding used between the client and the Token about the Token Binding used between the client and the Token
Consumer to the Token Provider. Consumer to the Token Provider.
As illustrated in Section 4.5, when a client receives this header As illustrated in Section 4.5, when a client receives this header
field, it should take the TokenBindingID of the provided TokenBinding field, it should take the TokenBindingID of the provided TokenBinding
from the referrer and create a referred TokenBinding with it to from the referrer and create a referred TokenBinding with it to
include in the TokenBindingMessage on the redirect request. In other include in the TokenBindingMessage on the redirect request. In other
words, the Token Binding message in the redirect request to the Token words, the Token Binding message in the redirect request to the Token
Provider now includes one provided binding and one referred binding, Provider now includes one provided binding and one referred binding,
the latter constructed from the binding between the client and the the latter constructed from the binding between the client and the
Token Consumer. Note that that the referred token binding is sent Token Consumer.
only on the request resulting from the redirect and not on any
subsequent requests to the Token Provider When a client receives the Include-Referred-Token-Binding-ID header,
it includes the referred token binding even if both the Token
Provider and the Token Consumer fall under the same eTLD+1 and the
provided and referred token binding IDs are the same. Note that the
referred token binding is sent only on the request resulting from the
redirect and not on any subsequent requests to the Token Provider.
If the Include-Referred-Token-Binding-ID header field is received in If the Include-Referred-Token-Binding-ID header field is received in
response to a request that did not include the Token-Binding header response to a request that did not include the Token-Binding header
field, the client MUST ignore the Include-Referred-Token-Binding-ID field, the client MUST ignore the Include-Referred-Token-Binding-ID
header field. header field.
This header field has only meaning if the HTTP status code is 301, This header field has only meaning if the HTTP status code is 301,
302, 303, 307 or 308, and MUST be ignored by the client for any other 302, 303, 307 or 308, and MUST be ignored by the client for any other
status codes. If the client supports the Token Binding Protocol, and status codes. If the client supports the Token Binding Protocol, and
has negotiated the Token Binding Protocol with both the Token has negotiated the Token Binding Protocol with both the Token
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between the client and Token Provider, use different key parameters. between the client and Token Provider, use different key parameters.
The client MUST use the key parameters negotiated with the Token The client MUST use the key parameters negotiated with the Token
Consumer in the referred_token_binding TokenBinding of the Consumer in the referred_token_binding TokenBinding of the
TokenBindingMessage, even if those key parameters are different from TokenBindingMessage, even if those key parameters are different from
the ones negotiated with the origin that the header field is sent to. the ones negotiated with the origin that the header field is sent to.
Token Providers SHOULD support all the Token Binding key parameters Token Providers SHOULD support all the Token Binding key parameters
specified in the [I-D.ietf-tokbind-protocol]. If a token provider specified in the [I-D.ietf-tokbind-protocol]. If a token provider
does not support the key parameters specified in the does not support the key parameters specified in the
referred_token_binding TokenBinding in the TokenBindingMessage, it referred_token_binding TokenBinding in the TokenBindingMessage, it
MUST issue an unbound token. MUST NOT issue a bound token.
4.5. Federation Example 4.5. Federation Example
The diagram below shows a typical HTTP Redirect-based Web Browser SSO The diagram below shows a typical HTTP Redirect-based Web Browser SSO
Profile (no artifact, no callbacks), featuring binding of, e.g., a Profile (no artifact, no callbacks), featuring binding of, e.g., a
TLS Token Binding ID into an OpenID Connect "ID Token". TLS Token Binding ID into an OpenID Connect "ID Token".
Legend: Legend:
+------------+------------------------------------------------------+ +------------+------------------------------------------------------+
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| ID Token w/TBID1, issued for TC | | ID Token w/TBID1, issued for TC |
| | | | | |
| | | | | |
| | | | | |
| 4. user is signed-on, any security-relevant cookie(s)| | 4. user is signed-on, any security-relevant cookie(s)|
| that are set SHOULD contain TBID1 | | that are set SHOULD contain TBID1 |
|<------------------------------| | |<------------------------------| |
| | | | | |
| | | | | |
5. Security Considerations 5. Implementation Considerations
5.1. Security Token Replay HTTPS-based applications may have multi-party use cases other than,
or in addition to, the HTTP redirect-based signaling-and-conveyance
of referred token bindings, as presented above in Section 4.3.
Thus, generic Token Binding implementations intended to support any
HTTPS-based client-side application (e.g., so-called "native
applications"), should provide means for applications to have Token
Binding messages, containing Token Binding IDs of various
application-specified Token Binding types and for application-
specified TLS connections, conveyed over an application-specified
HTTPS connection, i.e., within the TokenBindingMessage conveyed by
the Sec-Token-Binding header field.
However, such applications MUST only convey Token Binding IDs to
other servers if the server associated with a Token Binding ID
explicitly signals to do so, e.g., by returning an Include-Referred-
Token-Binding-ID HTTP response header field.
NOTE: See Section 7 "Privacy Considerations", for privacy guidance
regarding the use of this functionality.
6. Security Considerations
6.1. Security Token Replay
The goal of the Federated Token Binding mechanisms is to prevent The goal of the Federated Token Binding mechanisms is to prevent
attackers from exporting and replaying tokens used in protocols attackers from exporting and replaying tokens used in protocols
between the client and Token Consumer, thereby impersonating between the client and Token Consumer, thereby impersonating
legitimate users and gaining access to protected resources. Bound legitimate users and gaining access to protected resources. Bound
tokens can still be replayed by malware present in the client. In tokens can still be replayed by malware present in the client. In
order to export the token to another machine and successfully replay order to export the token to another machine and successfully replay
it, the attacker also needs to export the corresponding private key. it, the attacker also needs to export the corresponding private key.
The Token Binding private key is therefore a high-value asset and The Token Binding private key is therefore a high-value asset and
MUST be strongly protected, ideally by generating it in a hardware MUST be strongly protected, ideally by generating it in a hardware
security module that prevents key export. security module that prevents key export.
5.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions 6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions
The Token Binding protocol relies on the exported key material (EKM) The Token Binding protocol relies on the exported key material (EKM)
value [RFC5705] to associate a TLS connection with a TLS Token value [RFC5705] to associate a TLS connection with a TLS Token
Binding. The triple handshake attack [TRIPLE-HS] is a known Binding. The triple handshake attack [TRIPLE-HS] is a known
vulnerability in TLS 1.2 and older TLS versions, allowing the vulnerability in TLS 1.2 and older TLS versions, allowing the
attacker to synchronize keying material between TLS connections. The attacker to synchronize keying material between TLS connections. The
attacker can then successfully replay bound tokens. For this reason, attacker can then successfully replay bound tokens. For this reason,
the Token Binding protocol MUST NOT be negotiated with these TLS the Token Binding protocol MUST NOT be negotiated with these TLS
versions, unless the Extended Master Secret [RFC7627] and versions, unless the Extended Master Secret [RFC7627] TLS extension
Renegotiation Indication [RFC5746] TLS extensions have also been has also been negotiated. In addition, TLS renegotiation MUST NOT be
negotiated. initiated or allowed, unless the Renegotiation Indication [RFC5746]
TLS extension has been negotiated.
5.3. Sensitivity of the Sec-Token-Binding Header 6.3. Sensitivity of the Sec-Token-Binding Header
The purpose of the Token Binding protocol is to convince the server The purpose of the Token Binding protocol is to convince the server
that the client that initiated the TLS connection controls a certain that the client that initiated the TLS connection controls a certain
key pair. For the server to correctly draw this conclusion after key pair. For the server to correctly draw this conclusion after
processing the Sec-Token-Binding header field, certain secrecy and processing the Sec-Token-Binding header field, certain secrecy and
integrity requirements must be met. integrity requirements must be met.
For example, the client's private Token Binding key must be kept For example, the client's private Token Binding key must be kept
secret by the client. If the private key is not secret, then another secret by the client. If the private key is not secret, then another
actor in the system could create a valid Token Binding header field, actor in the system could create a valid Token Binding header field,
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example, if S has a feature that lets account holders see their example, if S has a feature that lets account holders see their
activity history on S). activity history on S).
Therefore, we need to protect the integrity of the Sec-Token-Binding Therefore, we need to protect the integrity of the Sec-Token-Binding
header field. One origin should not be able to set the Sec-Token- header field. One origin should not be able to set the Sec-Token-
Binding header field (through a DOM API or otherwise) that the User Binding header field (through a DOM API or otherwise) that the User
Agent uses with another origin. Employing the "Sec-" header field Agent uses with another origin. Employing the "Sec-" header field
prefix helps to meet this requirement by denoting the header field prefix helps to meet this requirement by denoting the header field
name to be a "forbidden header name", see [fetch-spec]. name to be a "forbidden header name", see [fetch-spec].
5.4. Securing Federated Sign-On Protocols 6.4. Securing Federated Sign-On Protocols
As explained above, in a federated sign-in scenario a client will As explained above, in a federated sign-in scenario a client will
prove possession of two different key pairs to a Token Provider: One prove possession of two different key pairs to a Token Provider: One
key pair is the "provided" Token Binding key pair (which the client key pair is the "provided" Token Binding key pair (which the client
normally uses with the Token Provider), and the other is the normally uses with the Token Provider), and the other is the
"referred" Token Binding key pair (which the client normally uses "referred" Token Binding key pair (which the client normally uses
with the Token Consumer). The Token Provider is expected to issue a with the Token Consumer). The Token Provider is expected to issue a
token that is bound to the referred Token Binding key. token that is bound to the referred Token Binding key.
Both proofs (that of the provided Token Binding key and that of the Both proofs (that of the provided Token Binding key and that of the
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referred Token Binding key in an application-level message as part of referred Token Binding key in an application-level message as part of
the redirect URL) is one way to assure that the man-in-the-middle the redirect URL) is one way to assure that the man-in-the-middle
between client and Token Consumer cannot affect the communication of between client and Token Consumer cannot affect the communication of
the referred Token Binding key to the Token Provider. the referred Token Binding key to the Token Provider.
Therefore, the Sec-Token-Binding header field in the federated sign- Therefore, the Sec-Token-Binding header field in the federated sign-
on use case contains both, a proof of possession of the provided on use case contains both, a proof of possession of the provided
Token Binding key, as well as a proof of possession of the referred Token Binding key, as well as a proof of possession of the referred
Token Binding key. Token Binding key.
6. Privacy Considerations 7. Privacy Considerations
6.1. Scoping of Token Binding Keys 7.1. Scoping of Token Binding Keys
Clients use different Token Binding key pairs for different servers, Clients use different Token Binding key pairs for different servers,
so as to not allow Token Binding to become a tracking tool across so as to not allow Token Binding to become a tracking tool across
different servers. However, the scoping of the Token Binding key different servers. However, the scoping of the Token Binding key
pairs to servers varies according to the scoping rules of the pairs to servers varies according to the scoping rules of the
application protocol ([I-D.ietf-tokbind-protocol] section 4.1). application protocol ([I-D.ietf-tokbind-protocol] section 4.1).
In the case of HTTP cookies, servers may use Token Binding to secure In the case of HTTP cookies, servers may use Token Binding to secure
their cookies. These cookies can be attached to any sub-domain of their cookies. These cookies can be attached to any sub-domain of
effective top-level domains, and clients therefore should use the effective top-level domains, and clients therefore should use the
same Token Binding key across such subdomains. This will ensure that same Token Binding key across such subdomains. This will ensure that
any server capable of receiving the cookie will see the same Token any server capable of receiving the cookie will see the same Token
Binding ID from the client, and thus be able to verify the token Binding ID from the client, and thus be able to verify the token
binding of the cookie. See Section 2.1, above. binding of the cookie. See Section 2.1, above.
6.2. Life Time of Token Binding Keys 7.2. Life Time of Token Binding Keys
Token Binding keys do not have an expiration time. This means that Token Binding keys do not have an expiration time. This means that
they can potentially be used by a server to track a user across an they can potentially be used by a server to track a user across an
extended period of time (similar to a long-lived cookie). HTTPS extended period of time (similar to a long-lived cookie). HTTPS
clients such as web user agents should therefore provide a user clients such as web user agents should therefore provide a user
interface for discarding Token Binding keys (similar to the interface for discarding Token Binding keys (similar to the
affordances provided to delete cookies). affordances provided to delete cookies).
If a user agent provides modes such as private browsing mode in which If a user agent provides modes such as private browsing mode in which
the user is promised that browsing state such as cookies are the user is promised that browsing state such as cookies are
discarded after the session is over, the user agent should also discarded after the session is over, the user agent should also
discard Token Binding keys from such modes after the session is over. discard Token Binding keys from such modes after the session is over.
Generally speaking, users should be given the same level of control Generally speaking, users should be given the same level of control
over life time of Token Binding keys as they have over cookies or over life time of Token Binding keys as they have over cookies or
other potential tracking mechanisms. other potential tracking mechanisms.
7. IANA Considerations 7.3. Correlation
An application's various communicating endpoints, that receive Token
Binding IDs for TLS connections other than their own, obtain
information about the application's other TLS connections (in this
context, "an application" is a combination of client-side and server-
side components, communicating over HTTPS, where the client side may
be either or both web browser-based or native application-based).
These other Token Binding IDs can serve as correlation handles for
the endpoints of the other connections. If the receiving endpoints
are otherwise aware of these other connections, then no additional
information is being exposed. For instance, if in a redirect-based
federation protocol, the Identity Provider and Relying Party already
possess URLs for one another, also having Token Binding IDs for these
connections does not provide additional correlation information. If
not, then, by providing the other Token Binding IDs, additional
information is exposed that can be used to correlate the other
endpoints. In such cases, a privacy analysis of enabled correlations
and their potential privacy impacts should be performed as part of
the application design decisions of how, and whether, to utilize
Token Binding.
Also, applications must take care to only reveal Token Binding IDs to
other endpoints if the server associated with a Token Binding ID
explicitly signals to do so, see Section 5
"Implementation Considerations".
Finally, care should be taken to ensure that unrelated applications
do not obtain information about each other's Token Bindings. For
instance, a Token Binding implementation shared between multiple
applications on a given system should prevent unrelated applications
from obtaining each other's Token Binding information. This may be
accomplished by using techniques such as application isolation and
key segregation, depending upon system capabilities.
8. IANA Considerations
Below are the Internet Assigned Numbers Authority (IANA) Permanent Below are the Internet Assigned Numbers Authority (IANA) Permanent
Message Header Field registration information per [RFC3864]. Message Header Field registration information per [RFC3864].
Header field name: Sec-Token-Binding Header field name: Sec-Token-Binding
Applicable protocol: HTTP Applicable protocol: HTTP
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): this one
Header field name: Include-Referred-Token-Binding-ID Header field name: Include-Referred-Token-Binding-ID
Applicable protocol: HTTP Applicable protocol: HTTP
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): this one
[[TODO: possibly add further considerations wrt the behavior of the [[TODO: possibly add further considerations wrt the behavior of the
above header fields, per <https://tools.ietf.org/html/ above header fields, per <https://tools.ietf.org/html/
rfc7231#section-8.3>]] rfc7231#section-8.3>]]
skipping to change at page 16, line 43 skipping to change at page 18, line 14
Header field name: Include-Referred-Token-Binding-ID Header field name: Include-Referred-Token-Binding-ID
Applicable protocol: HTTP Applicable protocol: HTTP
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): this one
[[TODO: possibly add further considerations wrt the behavior of the [[TODO: possibly add further considerations wrt the behavior of the
above header fields, per <https://tools.ietf.org/html/ above header fields, per <https://tools.ietf.org/html/
rfc7231#section-8.3>]] rfc7231#section-8.3>]]
8. Acknowledgements 9. Acknowledgements
This document incorporates comments and suggestions offered by Eric This document incorporates comments and suggestions offered by Eric
Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony
Nadalin, Michael Jones, Bill Cox, Nick Harper, Brian Campbell and Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell,
others. and others.
9. References 10. References
9.1. Normative References 10.1. Normative References
[fetch-spec] [fetch-spec]
WhatWG, "Fetch", Living Standard , WhatWG, "Fetch", Living Standard ,
<https://fetch.spec.whatwg.org/>. <https://fetch.spec.whatwg.org/>.
[I-D.ietf-tokbind-negotiation] [I-D.ietf-tokbind-negotiation]
Popov, A., Nystrom, M., Balfanz, D., and A. Langley, Popov, A., Nystrom, M., Balfanz, D., and A. Langley,
"Transport Layer Security (TLS) Extension for Token "Transport Layer Security (TLS) Extension for Token
Binding Protocol Negotiation", draft-ietf-tokbind- Binding Protocol Negotiation", draft-ietf-tokbind-
negotiation-03 (work in progress), July 2016. negotiation-03 (work in progress), July 2016.
[I-D.ietf-tokbind-protocol] [I-D.ietf-tokbind-protocol]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J. Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "The Token Binding Protocol Version 1.0", draft- Hodges, "The Token Binding Protocol Version 1.0", draft-
ietf-tokbind-protocol-07 (work in progress), July 2016. ietf-tokbind-protocol-08 (work in progress), July 2016.
[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, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004,
<http://www.rfc-editor.org/info/rfc3864>. <http://www.rfc-editor.org/info/rfc3864>.
skipping to change at page 18, line 19 skipping to change at page 19, line 36
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>. <http://www.rfc-editor.org/info/rfc7231>.
[RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for [RFC7541] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015, HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<http://www.rfc-editor.org/info/rfc7541>. <http://www.rfc-editor.org/info/rfc7541>.
9.2. Informative References 10.2. Informative References
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication "Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010, Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
<http://www.rfc-editor.org/info/rfc5746>. <http://www.rfc-editor.org/info/rfc5746>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012, RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>. <http://www.rfc-editor.org/info/rfc6749>.
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