ABFAB J. Howlett
Internet-Draft JANET(UK)
Intended status: Informational S. Hartmann
Expires: April 21, 2011 Painless Security
H. Tschofenig
Nokia Siemens Networks
E. Lear
Cisco Systems GmbH
October 18, 2010
Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture
draft-lear-abfab-arch-00.txt
Abstract
Over the last decade a substantial amount of work has occurred in the
space of federated authentication and authorization. Most of this
effort has focused on two common use cases: network and web-based
access, with few common building blocks within the architecture.
This memo describes an architecture that makes use of extensions to
the commonly used mechanisms for both federated and non-federated
authentication and authorization, including Radius/Diameter, GSS/GS2,
and SAML, to primarily address non-web based authentication, in a
that will scale to large numbers of federations.
Status of this Memo
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This Internet-Draft will expire on April 21, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Federation Description . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
XXX This document is a first draft. Comments and contributions are
requested.
The Internet makes uses of numerous authentication methods to grant
access to various resources. These mechanisms have been generalized
and scaled over the last decade through mechanisms such as GS2,
Security Assertion Markup Language (SAML) [OASIS.saml-core-2.0-os],
Radius, and Diameter. So-called "federated" access has evolved over
the last decade between web servers through such standards as SAML,
OpenID, and OAUTH, allowing entire domains of individuals to be
authorized for resources. The key scaling points that have been
addressed are the following:
o An Internet service need not copy manually authentication
information from a domain to allow for authentication and
authorization.
o Individual users are able to make use of a single credential to
authenticate to such services.
As the number of such federated services has proliferated, however,
the role of the individual has become ambiguous in certain
circumstances. For example, a school might provide online access to
grades to a parent who is also a teacher. She must clearly
distinguish her role upon access. After all, she is probably not
allowed to edit her own child's grades.
Similarly, as the number of federations proliferates, it becomes
increasingly difficult to discover which identity provider a user is
associated with. This is true for both the web and non-web case, but
particularly acute for the latter ans many non-web authentication
systems are not semantically rich enough on their own to allow for
such ambiguities. For instance, in the case of an email provider,
the use of SMTP and IMAP protocols does not on its own provide for a
way to select a federation. However, the building blocks do exist to
add this functionality.
1.1. Federation Description
The typical setup for a three party protocol involves the following
entities:
o the End Host,
o the Identity Provider, and
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o the Relying Party.
These entities are illustrated graphically in Figure 1.
-----
/- -\
// \\
/ \
| |
,----------\ | | ,---------\
| Identity | | | | Relying |
| Provider +----+ Federation +---+ Party |
`----------' | | '---------'
< | | >
\ | | /
\ \ / /
\ \\ // /
\ \- -/ /
\ ----- /
\ /
\ +------------+ /
\ | | /
v| End Host |v
| |
+------------+
Figure 1: Three Party Authentication Framework
Figure 1 also shows the logical entity 'Federation'. In a
federation, policy is agreed upon by some form of administrative
management, and then instantiated through an operational framework
that the members use, and where compliance is measured in some
fashion. Some deployments may be required to deploy message routing
intermediaries, such as application layer relays or proxies, to offer
the required technical functionality while in other deployments those
are missing.
Often a real world entity is associated with the end host and
responsible for interacting with the identity provider, even if it is
only as weak as completing a web form and confirming the verification
email. The outcome of this initial registration step is that
credentials are made available to the identity provider and to the
end host. It is important to highlight that in some scenarios there
might indeed be a human behind the device denoted as end host and in
other cases there is no human involved in the actual protocol
execution.
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To support the more generic deployment case, we assume that the
identity provider and the relying party belong to different
administrative domains. The nature of federation dictates that there
is some form of relationship between the identity provider and the
relying party. This is particularly important when the relying party
wants to use information obtained from the identity provider for
authorization decisions and when the identity provider does not want
to release information to every relying party (or only under certain
conditions). While it is possible to have a bilateral agreement
between every identity provider and every relying party; on an
Internet scale this setup requires the introduction of a federation
concept, as the management of such pair-wise relationships would
otherwise prove burdensome. While many of the non-technical aspects
of such a federation, such as business practices and operational
arrangements, are outside the scope of the IETF they still impact the
architecture setup on how to ensure the dynamic establishment of
trust.
Our key design goals are as follows:
o Each party of a transaction will be authenticated, and the
principal will be authorized for access to a specific resource .
o Means of authentication is decoupled so as to allow for multiple
authentication methods.
o Hence, the architecture requires no sharing of long term private
keys.
o The system will scale to large numbers of identity providers,
relying parties, and users.
o The system will be designed primarily for non-Web-based
authentication.
o The system will build upon existing standards, components, and
operational practices.
Designing new three party authentication and authorization protocols
is hard and frought with risk ofcryptographic flaws. Achieving
widespead deployment is even more difficult. A lot of attention on
federated access has been devoted to the Web. This document instead
focuses on a non-Web-based environment and focuses on those protocols
where HTTP is not used. Despite the increased excitement for
layering every protocol on top of HTTP there are still a number of
protocols available that do not use HTTP-based transports. Many of
these protocols are lacking a native authentication and authorization
framework of the style shown in Figure 1.
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Interestingly, for network access authentication the usage of the AAA
framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
successful from a deployment point of view. To map the terminology
used in Figure 1 to the AAA framework the identity provider
corresponds to the AAA server, the relying party corresponds to the
AAA client, and the technical building blocks of a federation are AAA
proxies, relays and redirect agents (particularly if they are
operated by third parties, such as AAA brokers and clearing houses).
The front-end, i.e. the end host to AAA client communication, is in
case of network access authentication offered by link layer protocols
that forward authentication protocol exchanges back-and-forth. An
example of a large scale Radius-based federation is EDUROAM [1].
Is it possible to design a system that builds on top of successful
protocols to offer non-Web-based protocols with a solid starting
point for authentication and authorization in a distributed system?
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2. Terminology
This document uses identity management and privacy terminology from
[I-D.hansen-privacy-terminology].
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3. Architecture
Section 1 already introduced the federated access architecture, with
the illustration of the different actors that need to interact, but
it did not expand on the specifics of providing support for non-Web
based applications. This section details this aspect and motivates
design decisions. The main theme of the work described in this
document is focused on re-using existing building blocks that have
been deployed already and to re-arrange them in a novel way.
A key design goal is the re-use an existing infrastructure, we build
upon the AAA framework as utilized by RADIUS [RFC2138] and Diameter
[RFC3588]. Since this document does not aim to re-describe the AAA
framework the interested reader is referred to [RFC2904]. Building
on the AAA infrastructure, and RADIUS and Diameter as protocols,
modifications to that infrastructure is to be avoided. Also,
modifications to AAA servers should be kept at a minimum.
The astute reader will notice that RADIUS and Diameter have
substantially similar characteristics. Why not pick one? A key
difference is that today RADIUS is largely transported upon TCP, and
its use is largely, though not exclusively, intra-domain. Diameter
itself was designed to scale to broader uses. We leave as a
deployment decision, which protocol will be appropriate.
Experience has taught us one key security and scalability
requirement: it is important that the relying party not get in
possession of the long-term secret of the entity being authenticated
by the AAA server. Aside from a valuable secret being exposed, a
synchronization problem can also often develop. Since there is no
single authentication mechanism that will be used everywhere there is
another associated requirement: The authentication framework must
allow for the flexible integration of authentication mechanisms. For
instance, some identity providers may require hardware tokens while
others may use passwords. A service provider would want to support
both sorts of federations, and others.
Fortunately, these requirements can be met by utilizing standardized
and successfully deployed technology, namely by the Extensible
Authentication Protocol (EAP) framework [RFC3748]. Figure 2
illustrates the integration graphically.
EAP is an end-to-end framework; it provides for two-way communication
between a peer (i.e,service client or principal) through the
authenticator (i.e., service provider) to the back-end (i.e.,
identity provider). Conveniently, this is precisely the
communication path that is needed for federated identity. Although
EAP support is already integrated in AAA systems (see [RFC3579] and
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[RFC4072]) several challenges remain: one is to carry EAP payloads
from the end host to the relying party, and the other is to determine
where identity provider. We will look at these challenges in turn.
[XXX but we don't get to discovery just yet.]
Although this architecture assumes updates to both the relying party
as well as to the end host for application integration, those changes
are kept at a minimum. A mechanism that can demonstrate deployment
benefits (based on ease of update of existing software, low
implementation effort, etc.)is preferred and there may be a need to
specify multiple mechanisms to support the range of different
deployment scenarios.
There are a number of ways for encapsulating EAP into an application
protocol. For ease of integration with a wide range of non-Web based
application protocols the usage of the GSS-API was chosen.
Encapsulating EAP into the GSS-API also allows EAP to be used in
SASL. A description of the technical specification can be found in
[I-D.ietf-abfab-gss-eap]. Other alternatives exist as well and may
be considered later, such as "TLS using EAP Authentication"
[I-D.nir-tls-eap].
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+--------------+
| AAA Server |
| (Identity |
| Provider) |
+-^----------^-+
* EAP | RADIUS/
* | Diameter
--v----------v--
/// \\\
// \\ ***
| Federation | back-
| | end
\\ // ***
\\\ ///
--^----------^--
* EAP | RADIUS/
Application * | Diameter
+-------------+ Data +-v----------v--+
| |<---------------->| |
| Client | EAP/EAP Method | Server Side |
| Application |<****************>| Application |
| @ End Host | GSS-API |(Relying Party)|
| |<---------------->| |
| | Application | |
| | Protocol | |
| |<================>| |
+-------------+ +---------------+
*** front-end ***
Legend:
<****>: End-to-end exchange
<---->: Hop-by-hop exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled
Figure 2: Architecture for Federated Access of non-Web based
Applications
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4. Privacy Considerations
Sharing identity information may lead to privacy violations. A
future verison of this document will provide a discussion of privacy
considerations in a federated access environment.
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5. Security Considerations
This entire document is about security. A future version of the
document will highlight some important security concepts.
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6. IANA Considerations
This document does not require actions by IANA.
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7. Acknowledgments
We would like to thank Mayutan Arumaithurai and Klaas Wierenga for
their feedback. Additionally, we would like to thank Eve Maler,
Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, and Luke
Howard for their feedback on the federation terminology question.
Furthermore, we would like to thank Klaas Wierenga for his review of
the pre-00 draft version.
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8. References
8.1. Normative References
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072,
August 2005.
[I-D.hansen-privacy-terminology]
Pfitzmann, A., Hansen, M., and H. Tschofenig, "Terminology
for Talking about Privacy by Data Minimization: Anonymity,
Unlinkability, Undetectability, Unobservability,
Pseudonymity, and Identity Management",
draft-hansen-privacy-terminology-01 (work in progress),
August 2010.
[I-D.ietf-abfab-gss-eap]
Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol",
draft-ietf-abfab-gss-eap-00 (work in progress),
October 2010.
8.2. Informative References
[I-D.nir-tls-eap]
Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "TLS
using EAP Authentication", draft-nir-tls-eap-08 (work in
progress), July 2010.
[RFC2138] Rigney, C., Rigney, C., Rubens, A., Simpson, W., and S.
Willens, "Remote Authentication Dial In User Service
(RADIUS)", RFC 2138, April 1997.
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[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904,
August 2000.
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URIs
[1] <http://www.eduroam.org>
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Authors' Addresses
Josh Howlett
JANET(UK)
Phone:
Email: Josh.Howlett@ja.net
Sam Hartman
Painless Security
Phone:
Email: hartmans-ietf@mit.edu
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
Eliot Lear
Cisco Systems GmbH
Richtistrasse 7
Wallisellen, ZH CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
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