OAuth H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Informational P. Hunt
Expires: March 10, 2013 Oracle Corporation
September 6, 2012
OAuth 2.0 Security: Going Beyond Bearer Tokens
draft-tschofenig-oauth-security-00.txt
Abstract
The OAuth working group has finished work on the OAuth 2.0 core
protocol as well as the Bearer Token specification. The Bearer Token
is a TLS-based solution for ensuring that neither the interaction
with the Authorization Server (when requesting a token) nor the
interaction with the Resource Server (for accessing a protected
resource) leads to token leakage. There has, however, always been
the desire to develop a security solution that is "better" than
Bearer Tokens (or at least different) where the Client needs to show
possession of some keying material when accessing a Resource Server.
This document tries to capture the discussion and to come up with
requirements to process the work on solutions.
This document aims to discuss threats, security requirements and
desired design properties of an enhanced OAuth security mechanism.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 10, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security and Privacy Threats . . . . . . . . . . . . . . . . . 5
4. Threat Mitigation . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Confidentiality Protection . . . . . . . . . . . . . . . . 7
4.2. Sender Constraint . . . . . . . . . . . . . . . . . . . . 8
4.3. Key Confirmation . . . . . . . . . . . . . . . . . . . . . 8
4.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
OAuth 1.0 [RFC5849] included a mechanism for putting a digital
signature (when using asymmetric keys) and a keyed message digest
(when using symmetric keys) to a resource request when presenting the
OAuth access token. OAuth 2.0 [I-D.ietf-oauth-v2] generalized the
protocol and the Bearer Token security specification
[I-D.ietf-oauth-v2-bearer] is close to publication as an RFC.
Figure 1 shows the OAuth 2.0 exchange at an abstract level and
illustrates the main entities. For most parts of this document the
focus is on the interaction between the Client and the Authorization
Server and between the Client and the Resource Server.
+--------+ +---------------+
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(C)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: OAuth: Abstract Protocol Flow
From a security point of view the following aspects of the OAuth 2.0
specification are worth mentioning:
o Standardization of a JSON-based format and the content of the
access token are still work in progress
[I-D.ietf-oauth-json-web-token]. The same is true for the JSON-
based security mechanisms.
o The interaction to obtain an access token in step #1 mandates to
implement and to use TLS with server-side authentication to
protect the confidentiality of the transmitted information.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document uses the terminology defined in RFC 4949 [RFC4949].
The terms 'keyed hash' and 'keyed message digest' are used
interchangable. For privacy related matters we utilize the
terminology defined in [I-D.iab-privacy-considerations].
This document uses OAuth 2.0 terminology [I-D.ietf-oauth-v2]. In
particular, the terms Client, Resource Server, Authorization Server,
and Access Token are used.
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3. Security and Privacy Threats
The following list presents several common threats against protocols
utilizing some form of tokens. This list of threats is based on NIST
Special Publication 800-63 [NIST800-63]. We exclude a discussion of
threats related to any form of identity proofing and authentication
of the Resource Owner to the Authorization Server since these
procedures are not part of the OAuth 2.0 protocol specificaiton
itself.
Token manufacture/modification:
An attacker may generate a bogus tokens or modify the token
content (such as authentication or attribute statements) of an
existing token, causing Resource Server to grant inappropriate
access to the Client. For example, an attacker may modify the
token to extend the validity period. A Client may modify the
token to have access to information that they should not be able
to view.
Token disclosure: Tokens may contain personal data, such as real
name, age or birthday, payment information, etc.
Token redirect:
An attacker uses the token generated for consumption by the
Resource Server to obtain access to another Resource Server.
Token reuse:
An attacker attempts to use a token that has already been used
once with a Resource Server. The attacker may be an eavesdropper
who observes the communication exchange or, worse, one of the
communication end points. A Client may, for example, leak access
tokens because it cannot keep secrets confidential. A Client may
also re-use access tokens for some other Resource Servers.
Finally, a Resource Server may use a token it had obtained from a
Client and use it with another Resource Server that the Client
interacts with. A Resource Server, offering relatively
unimportant application services, may attempt to use an access
token obtained from a Client to access a high-value service, such
as a payment service, on behalf of the Client using the same
access token.
We excluded one threat from the list, namely 'token repudiation'.
Token repudiation refers to a property whereby a Resource Server is
given an assurance that the Authorization Server cannot deny to have
created a token for the Client. We believe that such a property is
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interesting but most deployments prefer to deal with the violation of
this security property through business actions rather than by using
cryptography.
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4. Threat Mitigation
The purpose of this section is to discuss ways to mitigate the
threats without taking the current working group status into
consideration.
A large range of threats can be mitigated by protecting the content
of the token, using a digital signature or a keyed message digest.
Alternatively, the content of the token could be passed by reference
rather than by value (requiring a separate message exchange to
resolve the reference to the token content). To simplify the
subsequent description we assume that the token itself is digitally
signed by the Authorization Server and therefore cannot be modified.
To deal with token redirect it is important for the Authorization
Server to include the identifier of the intended recipient - the
Resource Server. A Resource Server must not be allowed to accept
access tokens that are not meant for its consumption.
To provide protection against token disclosure two approaches are
possible, namely (a) not to include sensitive information inside the
token or (b) to ensure confidentiality protection. The latter
approach requires at least the communication interaction between the
Client and the Authorization Server as well as the interaction
between the Client and the Resource Server to experience
confidentiality protection. As an example, Transport Layer Security
with a ciphersuite that offers confidentiality protection has to be
applied. Encrypting the token content itself is another alternative.
In our scenario the Authorization Server would, for example, encrypt
the token content with a symmetric key shared with the Resource
Server.
To deal with token reuse more choices are available.
4.1. Confidentiality Protection
In this approach confidentiality protection of the exchange is
provided on the communication interfaces between the Client and the
Resource Server, and between the Client and the Authorization Server.
No eavesdropper on the wire is able to observe the token exchange.
Consequently, a replay by a third party is not possible. An
Authorization Server wants to ensure that it only hands out tokens to
Clients it has authenticated first and who are authorized. For this
purpose, authentication of the Client to the Authorization Server
will be a requirement to ensure adequate protection against a range
of attacks. This is, however, true for the description in
Section 4.2 and Section 4.3 as well. Furthermore, the Client has to
make sure it does not distribute the access token to entities other
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than the intended the Resource Server. For that purpose the Client
will have to authenticate the Resource Server before transmitting the
access token.
4.2. Sender Constraint
Instead of providing confidentiality protection the Authorization
Server could also put the identifier of the Client into the protected
token with the following semantic: 'This token is only valid when
presented by a Client with the following identifer.' When the access
token is then presented to the Resource Server how does it know that
it was provided by the Client? It has to authenticate the Client!
There are many choices for authenticating the Client to the Resource
Server, for example by using client certificates in TLS [RFC5246], or
pre-shared secrets within TLS [RFC4279]. The choice of the preferred
authentication mechanism and credential type may depend on a number
of factors, including
o security properties
o available infrastructure
o library support
o credential cost (financial)
o performance
o integration into the existing IT infrastructure
o operational overhead for configuration and distribution of
credentials
This long list hints to the challenge of selecting at least one
mandatory-to-implement Client authentication mechanism.
4.3. Key Confirmation
A variation of the mechanism of sender authentication described in
Section 4.2 is to replace authentication with the proof-of-possession
of a specific (session) key, i.e. key confirmation. In this model
the Resource Server would not authenticate the Client itself but
would rather verify whether the Client knows the session key
associated with a specific access token. Examples of this approach
can be found with the OAuth 1.0 MAC token [RFC5849], Kerberos
[RFC4120] when utilizing the AP_REQ/AP_REP exchange (see also
[I-D.hardjono-oauth-kerberos] for a comparison between Kerberos and
OAuth), the OAuth 2.0 MAC token [I-D.ietf-oauth-v2-http-mac], and the
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Holder-of-the-Key approach [I-D.tschofenig-oauth-hotk].
To illustrate key confirmation the first examples borrow from
Kerberos and use symmetric key cryptography. Assume that the
Authorization Server shares a long-term secret with the Resource
Server, called K(Authorization Server-Resource Server). This secret
would be established between them in an initial registration phase.
When the Client requests an access token the Authorization Server
creates a fresh and unique session key Ks and places it into the
token encrypted with the long term key K(Authorization Server-
Resource Server). Additionally, the Authorization Server attaches Ks
to the response message to the Client (in addition to the access
token itself) over a confidentiality protected channel. When the
Client sends a request to the Resource Server it has to use Ks to
compute a keyed message digest for the request (in whatever form or
whatever layer). The Resource Server, when receiving the message,
retrieves the access token, verifies it and extracts K(Authorization
Server-Resource Server) to obtain Ks. This key Ks is then used to
verify the keyed message digest of the request message.
Note that in this example one could imagine that the mechanism to
protect the token itself is based on a symmetric key based mechanism
to avoid any form of public key infrastructure but this aspect is not
further elaborated in the scenario.
A similar mechanism can also be designed using asymmetric
cryptography. When the Client requests an access token the
Authorization Server creates an ephemeral public / privacy key pair
(PK/SK) and places the public key PK into the protected token. When
the Authorization Server returns the access token to the Client it
also provides the PK/SK key pair over a confidentiality protected
channel. When the Client sends a request to the Resource Server it
has to use the privacy key SK to sign the request. The Resource
Server, when receiving the message, retrieves the access token,
verifies it and extracts the public key PK. It uses this ephemeral
public key to verify the attached signature.
4.4. Summary
As a high level message, there are various ways how the threats can
be mitigated and while the details of each solution is somewhat
different they all ultimately accomplish the goal.
The three approaches are:
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Confidentiality Protection:
The weak point with this approach, which is briefly described in
Section 4.1, is that the Client has to be careful to whom it
discloses the access token. What can be done with the token
entirely depends on what rights the token entitles the presenter
and what constraints it contains. A token could encode the
identifier of the Client but there are scenarios where the Client
is not authenticated to the Resource Server or where the
identifier of the Client rather represents an application class
rather than a single application instance. As such, it is
possible that certain deployments choose a rather liberal approach
to security and that everyone who is in possession of the access
token is granted access to the data.
Sender Constraint:
The weak point with this approach, which is briefly described in
Section 4.2, is to setup the authentication infrastructure such
that Clients can be authenticated towards Resource Servers.
Additionally, Authorization Server must encode the identifier of
the Client in the token for later verification by the Resource
Server. Depending on the chosen layer for providing Client-side
authentication there may be additional challenges due Web server
load balancing, lack of API access to identity information, etc.
Key Confirmation:
The weak point with this approach, see Section 4.3, is the
increased complexity: a complete key distribution protocol has to
be defined.
In all cases above it has to be ensured that the Client is able to
keep the credentials secret.
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5. Requirements
In an attempt to address the threats described in Section 3 the
Bearer Token, which corresponds to the description in Section 4.1,
was standardized and the work on a JSON-based token format has been
started [I-D.ietf-oauth-json-web-token]. The required capability to
protected the content of a JSON token using integrity and
confidentiality mechanisms is currently work in progress in the IETF
JOSE working group.
Consequently, the purpose of the remaining document is to provide
security that goes beyond the Bearer Token offered security
protection.
Luckily this is not the first security protocol that has been
designed. In trying to seek guidance the authors found RFC 4962
[RFC4962], which gives useful guidelines for designers of
authentication and key management protocols. While RFC 4962 was
written with the AAA framework used for network access authentication
in mind the offered suggestions are useful for the design of other
key management systems as well. The following requirements list
applies OAuth 2.0 terminology to the requirements outlined in RFC
4962.
These requirements include
Cryptographic Algorithm Independent:
The key management protocol MUST be cryptographic algorithm
independent.
Strong, fresh session keys:
Session keys MUST be strong and fresh. Each session deserves an
independent session key, i.e., one that is generated specifically
for the intended use. In context of OAuth this means that keying
material is created in such a way that can only be used by the
combination of a Client instance, protected resource, and
authorization scope.
Limit Key Scope:
Following the principle of least privilege, parties MUST NOT have
access to keying material that is not needed to perform their
role. Any protocol that is used to establish session keys MUST
specify the scope for session keys, clearly identifying the
parties to whom the session key is available.
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Replay Detection Mechanism:
The key management protocol exchanges MUST be replay protected.
Replay protection allows a protocol message recipient to discard
any message that was recorded during a previous legitimate
dialogue and presented as though it belonged to the current
dialogue.
Authenticate All Parties:
Each party in the key management protocol MUST be authenticated to
the other parties with whom they communicate. Authentication
mechanisms MUST maintain the confidentiality of any secret values
used in the authentication process. Secrets MUST NOT be sent to
another party without confidentiality protection.
Authorization:
Client and Resource Server authorization MUST be performed. These
entities MUST demonstrate possession of the appropriate keying
material, without disclosing it. Authorization is REQUIRED
whenever a Client interacts with an Authorization Server. The
authorization checking prevents an elevation of privilege attack,
and it ensures that an unauthorized authorized is detected.
Keying Material Confidentiality and Integrity:
While preserving algorithm independence, confidentiality and
integrity of all keying material MUST be maintained.
Confirm Cryptographic Algorithm Selection:
The selection of the "best" cryptographic algorithms SHOULD be
securely confirmed. The mechanism SHOULD detect attempted roll-
back attacks.
Uniquely Named Keys:
Key management proposals require a robust key naming scheme,
particularly where key caching is supported. The key name
provides a way to refer to a key in a protocol so that it is clear
to all parties which key is being referenced. Objects that cannot
be named cannot be managed. All keys MUST be uniquely named, and
the key name MUST NOT directly or indirectly disclose the keying
material.
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Prevent the Domino Effect:
Compromise of a single Client MUST NOT compromise keying material
held by any other Client within the system, including session keys
and long-term keys. Likewise, compromise of a single Resource
Server MUST NOT compromise keying material held by any other
Resource Server within the system. In the context of a key
hierarchy, this means that the compromise of one node in the key
hierarchy must not disclose the information necessary to
compromise other branches in the key hierarchy. Obviously, the
compromise of the root of the key hierarchy will compromise all of
the keys; however, a compromise in one branch MUST NOT result in
the compromise of other branches. There are many implications of
this requirement; however, two implications deserve highlighting.
First, the scope of the keying material must be defined and
understood by all parties that communicate with a party that holds
that keying material. Second, a party that holds keying material
in a key hierarchy must not share that keying material with
parties that are associated with other branches in the key
hierarchy.
Bind Key to its Context:
Keying material MUST be bound to the appropriate context. The
context includes the following.
* The manner in which the keying material is expected to be used.
* The other parties that are expected to have access to the
keying material.
* The expected lifetime of the keying material. Lifetime of a
child key SHOULD NOT be greater than the lifetime of its parent
in the key hierarchy.
Any party with legitimate access to keying material can determine
its context. In addition, the protocol MUST ensure that all
parties with legitimate access to keying material have the same
context for the keying material. This requires that the parties
are properly identified and authenticated, so that all of the
parties that have access to the keying material can be determined.
The context will include the Client and the Resource Server
identities in more than one form.
Authorization Restriction:
If Client authorization is restricted, then the Client SHOULD be
made aware of the restriction.
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Client Identity Confidentiality:
A Client has identity confidentiality when any party other than
the Resource Server and the Authorization Server cannot
sufficiently identify the Client within the anonymity set. In
comparison to anonymity and pseudonymity, identity confidentiality
is concerned with eavesdroppers and intermediaries. A key
management protocol SHOULD provide this property.
Resource Owner Identity Confidentiality:
Resource servers SHOULD be prevented from knowing the real or
pseudonymous identity of the Resource Owner, since the
Authorization Server is the only entity involved in verifying the
Resource Owner's identity.
Collusion:
Resource Servers that collude can be prevented from using
information related to the Resource Owner to track the individual.
That is, two different Resource Servers can be prevented from
determining that the same Resource Owner has authenticated to both
of them. This requires that each Authorization Server obtains
different keying material as well as different access tokens with
content that does not allow identification of the Resource Owner.
AS-to-RS Relationship Anonymity:
The Authorization Server can be prevented from knowing which
Resource Servers a Resource Owner interacts with. This requires
avoiding direct communication between the Authorization Server and
the Resource Server at the time when access to a protected
resource by the Client is made. Additionally, the Client must not
provide information about the Resource Server in the access token
request. [QUESTION: Is this a desirable property given that it
has other implications for security?]
As an additional requirement a solution MUST enable support for
channel bindings. The concept of channel binding, as defined in
[RFC5056], allows applications to establish that the two end-points
of a secure channel at one network layer are the same as at a higher
layer by binding authentication at the higher layer to the channel at
the lower layer.
Furthermore, there are performance concerns specifically with the
usage of asymmetric cryptography. As such, the requirement can be
phrases as 'faster is better'. [QUESTION: How are we trading the
benefits of asymmetric cryptography against the performance impact?]
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Finally, there are threats that relate to the experience of the
software developer as well as operational policies. For example, a
frequently raised concern is the absent of verifying that the
server's presented identity matches its reference identity so it can
authenticate the communication endpoint and authorize it. Verifying
the server identity in TLS is discussed at length in [RFC6125].
There are also various guesses about what application developers are
able to implement correctly and easily and to what degree they can
rely on third party libraries.[QUESTION: How do we reflect these
requirements in the design?]
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6. Security Considerations
The main focus of this document is on security.
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7. Next Steps
From this description so far a few observations and next steps can be
derived:
1. Bearer Tokens are a viable solution for protecting against the
threats described in Section 3. Further standardization work on
OAuth security mechanisms needs to provide additional security
benefits on top of those provided by the bearer token solution.
2. The requirements listed in Section 5 aim to provide a starting
point for a discussion on a security solution that provides
additional security and privacy benefits for OAuth 2.0.
3. It is likely that implementers will find security solutions hard
to implement and hard to configure right. Additional guidance
and the availability to libraries may help to improve security on
the Internet for OAuth-based implementations. Fundamentally,
there is the question about a design that is based on symmetric
vs. asymmetric cryptography. Ideally, only a single solution
should be developed (or a very small number) since the
differences between different variations of such as protocol are
minor.
4. A standardized solution for the token format is needed to
mitigate a number of attacks and this work is already ongoing
under the name of JWT [I-D.ietf-oauth-json-web-token].
To make progress with the above-mentioned items before the next IETF
meeting in Atlanta I therefore suggest to (a) solicit for document
reviews regarding the JWT document, and (b) progress the work on the
extended OAuth security mechanism. Regarding the latter aspect
consider the following questions:
Threats:
Section 3 lists a few security threats. Are these the threats you
care about? Which threats missing?
Requirements:
The working group has expressed interest to work on an extended
OAuth security mechanism. Assuming that the group wants to
develop a key distribution protocol (as described in Section 4.3)
are the requirements listed in Section 5 complete? Who is
interested to develop early prototypes of support the standards
development?
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8. IANA Considerations
This document does not require actions by IANA.
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9. Acknowledgments
The authors would like to thank the OAuth working group for their
discussion input. A group of regular OAuth participants met at the
IETF #82 meeting in Vancouver to discuss this topic in preparation
for the face-to-face meeting. The participants were:
o John Bradley
o Brian Campbell
o Phil Hunt
o Leif Johansson
o Mike Jones
o Lucy Lynch
o Tony Nadalin
o Klaas Wierenga
This document reuses content from [RFC4962] and the author would like
thank Russ Housely and Bernard Aboba for their work on that document.
Finally, I would like to thank Blaine Cook. This document was
derived from an earlier draft that Blaine and I wrote.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[I-D.ietf-oauth-v2]
Hardt, D., "The OAuth 2.0 Authorization Framework",
draft-ietf-oauth-v2-31 (work in progress), August 2012.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[I-D.ietf-oauth-v2-bearer]
Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage",
draft-ietf-oauth-v2-bearer-23 (work in progress),
August 2012.
[I-D.ietf-oauth-json-web-token]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", draft-ietf-oauth-json-web-token-03 (work in
progress), July 2012.
10.2. Informative References
[RFC4962] Housley, R. and B. Aboba, "Guidance for Authentication,
Authorization, and Accounting (AAA) Key Management",
BCP 132, RFC 4962, July 2007.
[I-D.iab-privacy-considerations]
Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols",
draft-iab-privacy-considerations-03 (work in progress),
July 2012.
[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279,
December 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
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[I-D.hardjono-oauth-kerberos]
Hardjono, T., "OAuth 2.0 support for the Kerberos V5
Authentication Protocol", draft-hardjono-oauth-kerberos-01
(work in progress), December 2010.
[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[I-D.ietf-oauth-v2-http-mac]
Hammer-Lahav, E., "HTTP Authentication: MAC Access
Authentication", draft-ietf-oauth-v2-http-mac-01 (work in
progress), February 2012.
[I-D.tschofenig-oauth-hotk]
Bradley, J., Hunt, P., Nadalin, A., and H. Tschofenig,
"The OAuth 2.0 Authorization Framework: Holder-of-the-Key
Token Usage", draft-tschofenig-oauth-hotk-01 (work in
progress), July 2012.
[NIST800-63]
Burr, W., Dodson, D., Perlner, R., Polk, T., Gupta, S.,
and E. Nabbus, "NIST Special Publication 800-63-1,
INFORMATION SECURITY", December 2008.
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Authors' Addresses
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Phil Hunt
Oracle Corporation
Email: phil.hunt@yahoo.com
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