One document matched: draft-tschofenig-moonshot-ps-00.txt
MOONSHOT H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Standards Track July 5, 2010
Expires: January 6, 2011
Federated Authentication Beyond The Web: Problem Statement and
Requirements
draft-tschofenig-moonshot-ps-00.txt
Abstract
It is quite common that application developers and system architects
are in a need for authentication and authorization support in a
distributed environment. At least three parties need to cooperate,
namely the end host, the identity provider, and the relying party.
At the end of the exchange the identity provider asserts identity
information or certain attributes to the relying party without
exposing the user's long-term secret to the relying party.
While the problem sounds challenging and interesting but it is not
new. In fact, various IETF groups have produced specifications to
solve this problem, such as Kerberos, RADIUS, and Diameter. Outside
the IETF various Single-Sign-On solution for HTTP-based applications
have been developed as well.
The reader might therefore wonder why there is need for new work
given the existence of readily available solutions. This document
tries to answer this question in a compact fashion.
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
Task Force (IETF). Note that other groups may also distribute
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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 January 6, 2011.
Copyright Notice
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Internet-Draft Federated Auth. Beyond The Web: PS July 2010
Copyright (c) 2010 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Assumptions and Requirements . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
7. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The typical setup for a three party protocol has the following few
entities involved. Figure 1 shows the situation. It might surprise
that there are actually four parties; we will address the invisible
party in the middle a little bit later.
With three party protocols there are a number of different protocol
variants possible, as the available crypto-literature shows. We will
not discuss the different options in this document. What is relevant
is that a real world entity is behind the end host and responsible
for establishing some form of contract with the identity provider,
even if it is only as weak as completing a web form and to confirm
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 (or the user). 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.
We assume that the identity provider and the relying party belong to
different administrative domains. Very often 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 does require some intermediary, the "stuff-
in-the-middle". Please note that the lack of scalability is not
caused by technical limitations but rather by business limitations
since the agreements between identity providers and the relying
parties are often business contracts, i.e. they are about money. The
"stuff-in-the-middle" is a placeholder for technical interoperability
as well as business practices and operational arrangements, many
aspects are outside the scope of the IETF.
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-----
/- -\
// \\
/ \
---- | | ----
///- -\\\ | | ///- -\\\
/ \ | Stuff-in- | / \
| |-+ the-Middle +-| |
| Identity | | | | Relying |
| Provider | | | | Party |
| | | | | |
\ / \ / \ /
\\\- -/// \\ // \\\- -///
---- \- -/ ----
< ----- >
\ /
\ /
\ /
\ /
\ /
\ /
\ +------------+ /
\ | | /
v| End Host |v
| |
| |
+------------+
Figure 1: Three Party Authentication Framework
Designing new three party authentication and authorization protocols
is hard and cryptographic flaws common in designs. Achieving
widespead deployment is even more difficult. The HTTP-based Web has
enjoyed a lot of attention from the industry with respect to this
problem and some amount of success can be noticed even though many of
the business aspects with the "stuff-in-the-middle" still has to be
sorted out. This document does not focus on an HTTP-based
environment and instead 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 an authentication and authorization framework of the style
shown in Figure 1.
Interestingly, for network access authentication the usage of the AAA
framework with RADIUS and Diameter 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
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server, the relying party corresponds to the AAA client, and the
"stuff-in-the-middle" are AAA proxies and relays (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.
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
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 [RFC2119].
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3. Assumptions and Requirements
Some requirements restrict the solution space more than others. In
this particular case the main requirement is to re-use an existing
infrastructure, namely the AAA framework. Briefly stated: The
solution MUST make use of the AAA infrastructure (RADIUS and
Diameter). Ideally, modifications at AAA servers SHOULD be kept at a
minimum. Modifications to the AAA infrastructure that affect
operational aspects MUST NOT be made.
The next requirement concerns security: The relying party MUST NOT
get in possession of the long-term secret of the entity that is
authenticated towards the AAA server. 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.
Those who are familiar with the AAA framework might now think
about the Extensible Authentication Protocol (EAP) framework. It
is standardized, and deployed. The choices are limited.
Assuming that this design decision is taken for granted the remaining
work is with the integration of the AAA infrastructure into non-Web-
based application protocols. Figure 2 shows it graphically.
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+--------------+ business
|AAA Server | agreements
|(Identity | <......+
|Provider) | .
| | .
+------------+-+ .
--^----------|-- . .
///// | | \\\\\ .
// | | \\ .
| | AAA | |.
| | protocol | |.
| | | |.
\\ | | // .
\\\\\ | | ///// .
--|----------|-- . .
Authentication | | .
and Security | v .
+-------------+ Layer +-+----------+--+ .
| |<---------------->| |<-.....+
| Application | | Server Side |
| @ End Host | Application | Application |
| |<================>|(Relying Party)|
+-------------+ Application +---------------+
Data
Figure 2: Front-End Integration
The front-end (end-host to relying party) MUST be integrated the
authentication framework of the back-end.
The changes to the end host and the changes to the relying party
SHOULD be kept at a minimum. A mechanism MUST be preferred that can
demonstrate deployment benefits (based on easy of update of existing
software, smaller implementation effort, etc.).
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4. Security Considerations
This entire document is about security.
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5. IANA Considerations
This document does not require actions by IANA.
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6. Acknowledgments
The author would like to thank Sam Hartman for a discussion about all
aspects of the "Federated Authentication Beyond The Web" effort when
he was visiting MIT in June 2010.
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7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Author's Address
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
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