< draft-lear-abfab-arch-01.txt   draft-lear-abfab-arch-02.txt >
ABFAB J. Howlett ABFAB J. Howlett
Internet-Draft JANET(UK) Internet-Draft JANET(UK)
Intended status: Informational S. Hartmann Intended status: Informational S. Hartman
Expires: June 24, 2011 Painless Security Expires: September 10, 2011 Painless Security
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
E. Lear E. Lear
Cisco Systems GmbH Cisco Systems GmbH
December 21, 2010 March 9, 2011
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-lear-abfab-arch-01.txt draft-lear-abfab-arch-02.txt
Abstract Abstract
Over the last decade a substantial amount of work has occurred in the Over the last decade a substantial amount of work has occurred in the
space of federated authentication and authorization. Most of this space of federated access management. Most of this effort has
effort has focused on two common use cases: network and web-based focused on two use-cases: network and web-based access. However, the
access, with few common building blocks within the architecture. solutions to these use-cases that have been proposed and deployed
tend to have few common building blocks in common.
This memo describes an architecture that makes use of extensions to This memo describes an architecture that makes use of extensions to
the commonly used mechanisms for both federated and non-federated the commonly used security mechanisms for both federated and non-
authentication and authorization, including Radius/Diameter, GSS/GS2, federated access management, including RADIUS, Diameter, GSS, GS2,
and SAML, to primarily address non-web based authentication, in a EAP and SAML. The architecture addresses the problem of federated
access management to primarily non-web-based services, in a manner
that will scale to large numbers of federations. that will scale to large numbers of federations.
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
Copyright (c) 2010 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Federation Description . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 7 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 5
1.3. Use of Radius . . . . . . . . . . . . . . . . . . . . . . 8 1.3. Challenges to Contemporary Federation . . . . . . . . . . 8
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 8
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Federation Substrate . . . . . . . . . . . . . . . . . . . 10 1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. Subject To Identity Provider . . . . . . . . . . . . . . . 12 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3. Application to Service . . . . . . . . . . . . . . . . . . 13 2.1. Federation Substrate . . . . . . . . . . . . . . . . . . . 13
3.4. Personalization Layer . . . . . . . . . . . . . . . . . . 14 2.1.1. Discovery, Rules Determination, and Technical Trust . 14
3.5. Tieing Layers Together . . . . . . . . . . . . . . . . . . 14 2.2. Subject To Identity Provider . . . . . . . . . . . . . . . 16
4. Application Security Services . . . . . . . . . . . . . . . . 16 2.3. Application to Service . . . . . . . . . . . . . . . . . . 17
4.1. Server (Mutual) Authentication . . . . . . . . . . . . . . 16 2.4. Personalization Layer . . . . . . . . . . . . . . . . . . 19
4.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 17 2.5. Tieing Layers Together . . . . . . . . . . . . . . . . . . 19
4.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 18 3. Application Security Services . . . . . . . . . . . . . . . . 21
4.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 19 3.1. Server (Mutual) Authentication . . . . . . . . . . . . . . 21
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 20 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 22
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 21 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 23
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 21 3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 24
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 21 4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 22 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 26
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 5.1. What entities collect and use data? . . . . . . . . . . . 26
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 5.2. Relationship between User's and other Entities . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.3. What Data about the User is likely Needed to be
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25 Collected? . . . . . . . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . . 25 5.4. What is the Identification Level of the Data? . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 28
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 29
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 29
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 29
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1. Normative References . . . . . . . . . . . . . . . . . . . 33
10.2. Informative References . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction 1. Introduction
XXX This document is a first draft. Comments and contributions are The Internet uses numerous security mechanisms to manage access to
requested. various resources. These mechanisms have been generalized and scaled
over the last decade through mechanisms such as SASL/GS2 [RFC5801],
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], Security Assertion Markup Language (SAML) [OASIS.saml-core-2.0-os],
Radius, and Diameter. So-called "federated" access has evolved over RADIUS, and Diameter.
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 A Relying Party (RP) is the entity that manages access to some
information from a domain to allow for authentication and resource. The actor that is requesting access to that resource is
authorization. often described as the Subject. Many security mechanisms are
manifested as an exchange of information between these actors. The
RP is therefore able to decide whether the Subject is authorised, or
not.
o Individual users are able to make use of a single credential to Some security mechanisms allow the RP to delegate aspects of the
authenticate to such services. access management decision to an actor called the Identity Provider
(IdP). This delegation requires technical signalling, trust and a
common understanding of semantics between the RP and IdP. These
aspects are generally managed within a relationship known as a
'federation'. This style of access management is accordingly
described as 'federated access management'.
Federated access management has evolved over the last decade through
such standards as SAML, OpenID [1], and OAUTH [RFC5849]. The
benefits of federated access management include:
o Single or Simplified sign-on. An Internet service can delegate
access management, and the associated responsibilities such as
identity management and credentialing, to an organisation that
already has a long-term relationship with the Subject. This is
often attractive for Relying Parties who frequently do not want
these responsibilities. The Subject may also therefore require
fewer credentials, which is often desirable.
o Privacy. Often a Relying Party does not need to know the identity
of a Subject to reach an access management decision. It is
frequently only necessary for the Relying Party to establish, for
example, that the Subject is affiliated with a particular
organisation or has a certain role or entitlement. Sometimes the
RP does require an identifier for the Subject (for example, so
that it can recognise the Subject subsequently); in this case, it
is common practise for the IdP to only release a pseudonym that is
specific to that particular Relying Party. Federated access
management therefore provides various strategies for protecting
the Subject's privacy.
o Provisioning. Sometimes a Relying Party needs, or would like, to
know more about a subject that an affiliation or pseudonym. For
example, a Relying Party may want the Subject's email address or
name. Some federated access management technologies provide the
ability for the IdP to provision this information, either on
request by by the RP or unsolicited.
1.1. Terminology
This document uses identity management and privacy terminology from
[I-D.hansen-privacy-terminology]. In particular, this document uses
the terms pseudonymity, unlinkability, anonymity.
We make one note about the IdP: in this architecture, the IdP
consists of the following components: an EAP server, a radius server,
and optionally a SAML Assertion service. The IdP is also responsible
for authentication, even though it may rely upon other components
within a domain for such an operation. The reader is advised that
for succinctness, in most cases the term IdP is used, except where
additional clarity seems appropriate.
1.2. An Overview of Federation
In the previous section we introduced the following actors:
o the Subject,
o the Identity Provider, and
o the Relying Party.
These entities and their relationships are illustrated graphically in
Figure 1.
,----------\ ,---------\
| Identity | Federation | Relying |
| Provider + <-------------------> + Party |
`----------' '---------'
<
\
\ Identity
\ management
\
\
\
\ +------------+
\ | |
v| Subject |
| |
+------------+
Figure 1: General federation framework model
Figure 1 shows the federation relationship between the IdP and RP.
Typically this relationship encompasses the following:
o Technical infrastructure. This infrastructure is generally used
to support signalling and trust establishment between the IdP and
RP.
o Policy framework. This framework is generally used to establish
expectations between an IdP and RP that may facilitate stronger
trust and common semantics.
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 access management
decisions and when the identity provider does not want to release
information to every relying party (or only under certain
conditions).
In a federation, policy is agreed upon by some form of administrative
management. The policy and infrastructure are then instantiated
through an operational framework. This may include the measurement
of compliance in some fashion. To support the more generic
deployment case, we assume that the identity provider and the RP
belong to different administrative domains.
While it is possible to have a bilateral agreement between every IdP
and every RP; on an Internet scale this setup requires the
introduction of the multi-lateral federation concept, as the
management of such pair-wise relationships would otherwise prove
burdensome.
While many of the non-technical aspects of 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.
Some deployments are sometimes required to deploy complex technical
infrastructure including message routing intermediaries to offer the
required technical functionality while in other deployments those are
missing.
Figure 1 also shows the relationship between the IdP and the Subject.
Often a real world entity is associated with the Subject; for
example, a person or some software.
The IdP will typically have a long-term relationship with the
Subject. This relationship would typically involve the IdP
positively identifying and credentialling the Subject (for example,
at time of enrollment in the context of employment within an
organisation). The relationship will often be instantiated within an
agreement between the IdP and the Subject (for example, within an
employment contract or terms of use that stipulates the appropriate
use of credentials and so forth).
While federation is often discussed within the context of relatively
formal relationships, such as between an Enterprise and an Employee
or a Government and a Citizen, federation does not in any way require
this; nor, indeed, does it require any particular level of formality.
It is, for example, entirely compatible with a relationship between
the IdP and Subject that is only as weak as completing a web form and
confirming the verification email.
However, the nature and quality of the relationship between the
Subject and the IdP is an important contributor to the level of trust
that an RP may attribute to an assertion describing a Subject made by
an IdP. This is sometimes described as the Level of Assurance.
Similarly it is also important to note that, in the general case,
there is no requirement of a relationship betweem the RP and the
Subject. This is a property of federation that yields many of its
benefits. However, federation does not preclude the possibility
relationship between the RP and the Subject, should needs dictate.
Finally, it is important to reiterate that in some scenarios there
might indeed be a human behind the device denoted as Subject and in
other cases there is no human involved in the actual protocol
execution.
1.3. Challenges to Contemporary Federation
JH: Much more content needed!
As the number of such federated services has proliferated, however, As the number of such federated services has proliferated, however,
the role of the individual has become ambiguous in certain the role of the individual has become ambiguous in certain
circumstances. For example, a school might provide online access to circumstances. For example, a school might provide online access to
grades to a parent who is also a teacher. She must clearly grades to a parent who is also a teacher. She must clearly
distinguish her role upon access. After all, she is probably not distinguish her role upon access. After all, she is probably not
allowed to edit her own child's grades. allowed to edit her own child's grades.
Similarly, as the number of federations proliferates, it becomes Similarly, as the number of federations proliferates, it becomes
increasingly difficult to discover which identity provider a user is increasingly difficult to discover which identity provider a user is
associated with. This is true for both the web and non-web case, but associated with. This is true for both the web and non-web case, but
particularly acute for the latter ans many non-web authentication particularly acute for the latter ans many non-web authentication
systems are not semantically rich enough on their own to allow for systems are not semantically rich enough on their own to allow for
such ambiguities. For instance, in the case of an email provider, 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 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 way to select a federation. However, the building blocks do exist to
add this functionality. add this functionality.
1.1. Federation Description 1.4. An Overview of ABFAB-based Federation
The typical setup for a three party protocol involves the following
entities:
o the End Host,
o the Identity Provider, and
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.
To support the more generic deployment case, we assume that the The previous section described the general model of federation, and
identity provider and the relying party belong to different its the application of federated access management. This section
administrative domains. The nature of federation dictates that there provides a brief overview of ABFAB in the context of this model.
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.
The steps taken generally in an ABFAB federated authentication/ The steps taken generally in an ABFAB federated authentication/
authorization exchange are as follows (XXX not complete): authorization exchange are as follows:
1. Principal provides NAI to Application: Somehow the client is 1. Principal provides NAI to Application: Somehow the client is
configured with at least the realm portion of an NAI, which configured with at least the realm portion of an NAI, which
represents the IdP to be discovered. represents the IdP to be discovered.
2. Authentication mechanism selection: this is the step necessary 2. Authentication mechanism selection: this is the step necessary
to indicate that the GSS-EAP SASL/GS2 mechanism will be used for to indicate that the GSS-EAP SASL/GS2 mechanism will be used for
authentication/authorization. authentication/authorization.
3. Client Application provides NAI to RP: At the conclusion of 3. Client Application provides NAI to RP: At the conclusion of
skipping to change at page 6, line 47 skipping to change at page 9, line 10
4. Discovery of federated IdP: This is discussed in detail below. 4. Discovery of federated IdP: This is discussed in detail below.
Either the RP is configured with authorized IdPs, or it makes Either the RP is configured with authorized IdPs, or it makes
use of a federation proxy. use of a federation proxy.
5. Request from Relying Party to IdP: Once the RP knows who the IdP 5. Request from Relying Party to IdP: Once the RP knows who the IdP
is, it or its agent will forward RADIUS request that is, it or its agent will forward RADIUS request that
encapsulates a GSS/EAP access request to an IdP. This may or encapsulates a GSS/EAP access request to an IdP. This may or
may not contain a SAML request as a series of attributes.. At may not contain a SAML request as a series of attributes.. At
this stage, the RP will likely have no idea who the principal this stage, the RP will likely have no idea who the principal
is. The RP claims its identity to the IdP in AAA attributes. is. The RP claims its identity to the IdP in AAA attributes,
and it makes whatever SAML Attribute Requests through a AAA
attribute. XXX- Check order of SAML attribute request.
6. IdP informs the principal of which EAP method to use: The 6. IdP informs the principal of which EAP method to use: The
available and appropriate methods are discussed below in this available and appropriate methods are discussed below in this
memo. memo.
7. A bunch of EAP messages happen between the endpoints: Messages 7. A bunch of EAP messages happen between the endpoints: Messages
are exchanged between the principal and the IdP until a result are exchanged between the principal and the IdP until a result
is determined. The number and content of those messages will is determined. The number and content of those messages will
depend on the EAP method. If the IdP is unable to authenticate depend on the EAP method. If the IdP is unable to authenticate
the principal, the process concludes here. As part of this the principal, the process concludes here. As part of this
process, the principal will, under protection of EAP, assert the process, the principal will, under protection of EAP, assert the
identity of the RP to which it intends to authenticate. identity of the RP to which it intends to authenticate.
8. Successful Authentication: At the very least the EAP server / 8. Successful Authentication: At the very least the IdP (its EAP
IdP has authenticated the principal, and the principal has server) and EAP peer / subject have authenticated one another.
authenticated the IdP. As a result of this step, the principal As a result of this step, the subject and the IdP hold two
and the EAP server hold two cryptographic keys- a Master Session cryptographic keys- a Master Session Key (MSK), and an Extended
Key (MSK), and an Extended MSK (EMSK). If the asserted identity MSK (EMSK). If the asserted identity of the RP by the principal
of the RP by the principal matches the identity the RP itself matches the identity the RP itself asserted, there is some
asserted, there is some confidence that the RP is now confidence that the RP is now authenticated to the IdP.
authenticated to the IdP.
9. Local IdP Policy Check: At this stage, the IdP checks local 9. Local IdP Policy Check: At this stage, the IdP checks local
policy to determine whether the RP and principal are authorized policy to determine whether the RP and subject are authorized
for the assertion to be made. Additional policy checks will for a given transaction/service, and if so, what if any,
likely have been made earlier just through the process of attributes will be released to the RP. Additional policy checks
discovery (see later discussion). will likely have been made earlier just through the process of
discovery.
10. Response from the IdP to the Relying Party: Once the IdP has 10. Response from the IdP to the Relying Party: Once the IdP has
made a determination of whether and how to authenticate or made a determination of whether and how to authenticate or
authorize the principal to the RP, it returns either a negative authorize the principal to the RP, it returns either a negative
answer to the RP, or it returns the identity of the principal to AAA result to the RP, or it returns a positive result to the RP,
the RP, as well as an optional set of attributes associated with along with an optional set of AAA attributes associated with the
the principal. XXX XXX XXX this needs work!!! principal that could include one or more SAML assertions. In
addition, an EAP MSK is returned to the subject.
11. Return results to principal: Once the RP has a response it must 11. RP Processes Results. When the RP receives the result from the
inform the client application of the result. If all has gone IdP, it should have enough information to either grant or refuse
well, all are authenticated, and the application proceeds with a resource access request. It may have information that leads
appropriate authorization levels. it to make additional attribute queries. It may have
information that associates the principal with specific
authorization identies. It will apply these results in an
application-specific way.
12. RP returns results to principal: Once the RP has a response it
must inform the client application of the result. If all has
gone well, all are authenticated, and the application proceeds
with appropriate authorization levels.
An example communication flow is given below: An example communication flow is given below:
Relying Party Client App IdP Relying Party Client App IdP
| (1) | Client App gets NAI (somehow) | (1) | Client App gets NAI (somehow)
| | | | | |
|<-----(2)----->| | Mechanism Selection |<-----(2)----->| | Mechanism Selection
| | | | | |
|<-----(3)-----<| | NAI transmitted to RP |<-----(3)-----<| | NAI transmitted to RP
skipping to change at page 8, line 26 skipping to change at page 10, line 36
| | | | | |
| |< - - (6) - -<| EAP method to Principal | |< - - (6) - -<| EAP method to Principal
| | | | | |
| |< - - (7) - ->| EAP Exchange to authenticate | |< - - (7) - ->| EAP Exchange to authenticate
| | | Principal | | | Principal
| | | | | |
| | (8 & 9) Local Policy Check | | (8 & 9) Local Policy Check
| | | | | |
|<====(10)====================<| IdP Assertion to RP |<====(10)====================<| IdP Assertion to RP
| | | | | |
|>----(11)----->| | Results to client app. | | | (11) RP Processes results.
| | |
|>----(12)----->| | Results to client app.
----- = Between Client App and RP ----- = Between Client App and RP
===== = Between RP and IdP ===== = Between RP and IdP
- - - = Between Client App and IdP - - - = Between Client App and IdP
1.2. Design Goals 1.5. Design Goals
Our key design goals are as follows: Our key design goals are as follows:
o Each party of a transaction will be authenticated, and the o Each party of a transaction will be authenticated, and the
principal will be authorized for access to a specific resource . principal will be authorized for access to a specific resource .
o Means of authentication is decoupled so as to allow for multiple o Means of authentication is decoupled so as to allow for multiple
authentication methods. authentication methods.
o Hence, the architecture requires no sharing of long term private o Hence, the architecture requires no sharing of long term private
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is hard and frought with risk of cryptographic flaws. Achieving is hard and frought with risk of cryptographic flaws. Achieving
widespead deployment is even more difficult. A lot of attention on widespead deployment is even more difficult. A lot of attention on
federated access has been devoted to the Web. This document instead federated access has been devoted to the Web. This document instead
focuses on a non-Web-based environment and focuses on those protocols focuses on a non-Web-based environment and focuses on those protocols
where HTTP is not used. Despite the increased excitement for where HTTP is not used. Despite the increased excitement for
layering every protocol on top of HTTP there are still a number of layering every protocol on top of HTTP there are still a number of
protocols available that do not use HTTP-based transports. Many of protocols available that do not use HTTP-based transports. Many of
these protocols are lacking a native authentication and authorization these protocols are lacking a native authentication and authorization
framework of the style shown in Figure 1. framework of the style shown in Figure 1.
1.3. Use of Radius 1.6. Use of AAA
Interestingly, for network access authentication the usage of the AAA Interestingly, for network access authentication the usage of the AAA
framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
successful from a deployment point of view. To map the terminology successful from a deployment point of view. To map the terminology
used in Figure 1 to the AAA framework the identity provider used in Figure 1 to the AAA framework the IdP corresponds to the AAA
corresponds to the AAA server, the relying party corresponds to the server, the RP corresponds to the AAA client, and the technical
AAA client, and the technical building blocks of a federation are AAA building blocks of a federation are AAA proxies, relays and redirect
proxies, relays and redirect agents (particularly if they are agents (particularly if they are operated by third parties, such as
operated by third parties, such as AAA brokers and clearing houses). AAA brokers and clearing houses). The front-end, i.e. the end host
The front-end, i.e. the end host to AAA client communication, is in to AAA client communication, is in case of network access
case of network access authentication offered by link layer protocols authentication offered by link layer protocols that forward
that forward authentication protocol exchanges back-and-forth. An authentication protocol exchanges back-and-forth. An example of a
example of a large scale Radius-based federation is EDUROAM [1]. large scale RADIUS-based federation is EDUROAM [2].
Is it possible to design a system that builds on top of successful Is it possible to design a system that builds on top of successful
protocols to offer non-Web-based protocols with a solid starting protocols to offer non-Web-based protocols with a solid starting
point for authentication and authorization in a distributed system? point for authentication and authorization in a distributed system?
2. Terminology 2. Architecture
This document uses identity management and privacy terminology from
[I-D.hansen-privacy-terminology].
3. Architecture
Section 1 already introduced the federated access architecture, with Section 1 already introduced the federated access architecture, with
the illustration of the different actors that need to interact, but the illustration of the different actors that need to interact, but
it did not expand on the specifics of providing support for non-Web it did not expand on the specifics of providing support for non-Web
based applications. This section details this aspect and motivates based applications. This section details this aspect and motivates
design decisions. The main theme of the work described in this design decisions. The main theme of the work described in this
document is focused on re-using existing building blocks that have document is focused on re-using existing building blocks that have
been deployed already and to re-arrange them in a novel way. been deployed already and to re-arrange them in a novel way.
Although this architecture assumes updates to both the relying party Although this architecture assumes updates to both the relying party
skipping to change at page 11, line 35 skipping to change at page 13, line 35
application protocols the usage of the GSS-API was chosen. application protocols the usage of the GSS-API was chosen.
Encapsulating EAP into the GSS-API also allows EAP to be used in Encapsulating EAP into the GSS-API also allows EAP to be used in
SASL. A description of the technical specification can be found 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 [I-D.ietf-abfab-gss-eap]. Other alternatives exist as well and may
be considered later, such as "TLS using EAP Authentication" be considered later, such as "TLS using EAP Authentication"
[I-D.nir-tls-eap]. [I-D.nir-tls-eap].
There are several architectural layers in the system; this section There are several architectural layers in the system; this section
discusses the individual layers. discusses the individual layers.
3.1. Federation Substrate 2.1. Federation Substrate
The federation substrate is responsible for the connunication between The federation substrate is responsible for the connunication between
the relying party and the identity provider. This layer is the relying party and the identity provider. This layer is
responsible for the inter-domain communication and for the technical responsible for the inter-domain communication and for the technical
mechanisms necessary to establish inter-domain trust. mechanisms necessary to establish inter-domain trust.
A key design goal is the re-use of an existing infrastructure, we A key design goal is the re-use of an existing infrastructure, we
build upon the AAA framework as utilized by RADIUS [RFC2138] and build upon the AAA framework as utilized by RADIUS [RFC2138] and
Diameter [RFC3588]. Since this document does not aim to re-describe Diameter [RFC3588]. Since this document does not aim to re-describe
the AAA framework the interested reader is referred to [RFC2904]. the AAA framework the interested reader is referred to [RFC2904].
Building on the AAA infrastructure, and RADIUS and Diameter as Building on the AAA infrastructure, and RADIUS and Diameter as
protocols, modifications to that infrastructure is to be avoided. protocols, modifications to that infrastructure is to be avoided.
Also, modifications to AAA servers should be kept at a minimum. Also, modifications to AAA servers should be kept at a minimum.
One demand that the AAA substrate must make of the upper layers is
that they must properly identify the end points of the communication.
That is- it must be possible for the AAA server at the RP to
determine where to send each radius or diameter message. Otherwise,
it is the RP's responsibility to determine the identity of the
principal on its own, without the assistance of an IdP. This
architecture makes use of the Network Access Identifier (NAI), where
the IdP is indicated in the realm component [RFC4282]. The NAI is
represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME
as specified in [RFC2743]. XXX Where is EAP here?
Once an IdP has been determined by the RP, it or its proxy agent must
determine whether or not the IdP itself is authorized to make
assertions, as it will likely not blindly accept any old provider.
Federations serve this purpose. This architecture provides for three
approaches to resolve whether an IdP is authorized:
Static Configuration: In this case, the federation provides the RP
or its proxy agent with a static list of IdPs that it may trust.
Federation Dynamic Referral In this case, the federation provides a
proxy of its own that will in some way authorize the IdP to the
RP, and visa versa, as not all RPs may be authorized to use all
IdPs for all purposes within a federation. N.B., because the
identity of the principal is likely unknown at this point, it will
not be possible for a federation to authorize an IdP to an RP
based on the identity of the principal.
Federation Proxy: In this case, the authentication request is
forwarded to a federation proxy, who then further forwards the
request to the IdP.
In the first two cases, it is expected that RPs will be configured to
consult multiple federations, as a matter of practice. The first
successful query is sufficient for the RP to then contact the IdP's
AAA server.
The astute reader will notice that RADIUS and Diameter have The astute reader will notice that RADIUS and Diameter have
substantially similar characteristics. Why not pick one? A key substantially similar characteristics. Why not pick one? A key
difference is that today RADIUS is largely transported upon UDP, and difference is that today RADIUS is largely transported upon UDP, and
its use is largely, though not exclusively, intra-domain. Diameter its use is largely, though not exclusively, intra-domain. Diameter
itself was designed to scale to broader uses. We leave as a itself was designed to scale to broader uses. We leave as a
deployment decision, which protocol will be appropriate. deployment decision, which protocol will be appropriate.
Through the integrity protection mechanisms in the AAA framework, the Through the integrity protection mechanisms in the AAA framework, the
relying party can establish technical trust that messages are being relying party can establish technical trust that messages are being
sent by the appropriate relying party. Any given interaction will be sent by the appropriate relying party. Any given interaction will be
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business relationship defines what statements the identity provider business relationship defines what statements the identity provider
is trusted to make and how these statements are interpreted by the is trusted to make and how these statements are interpreted by the
relying party. The AAA framework also permits the relying party or relying party. The AAA framework also permits the relying party or
elements between the relying party and identity provider to make elements between the relying party and identity provider to make
statements about the relying party. statements about the relying party.
The AAA framework provides transport for attributes. Statements made The AAA framework provides transport for attributes. Statements made
about the subject by the identity provider, statements made about the about the subject by the identity provider, statements made about the
relying party and other information is transported as attributes. relying party and other information is transported as attributes.
3.2. Subject To Identity Provider 2.1.1. Discovery, Rules Determination, and Technical Trust
One demand that the AAA substrate must make of the upper layers is
that they must properly identify the end points of the communication.
That is- it must be possible for the AAA client at the RP to
determine where to send each RADIUS or Diameter message. Without
this requirement, it would be the RP's responsibility to determine
the identity of the principal on its own, without the assistance of
an IdP. This architecture makes use of the Network Access Identifier
(NAI), where the IdP is indicated in the realm component [RFC4282].
The NAI is represented and consumed by the GSS-API layer as
GSS_C_NT_USER_NAME as specified in [RFC2743]. The GSS-API EAp
mechanism includes the NAI in the EAP Response/Identity message.
The RP needs to discover which federation will be used to contact the
IDP. As part of this process, the RP determines the set of business
rules and technical policies governing the relationship; this is
called rules determination. The RP also needs to establish technical
trust in the communications with the IDP.
Rules determination covers a broad range of decisions about the
exchange. One of these is whether the given RP is permitted to talk
to the IDP using a given federation at all, so rules determination
encompasses the basic authorization decision. Other factors are
included, such as what policies govern release of information about
the principal to the RP and what policies govern the RP's use of this
information. While rules determination is ultimately a business
function, it has significant impact on the technical exchanges. The
protocols need to communicate the result of authorization. When
multiple sets of rules are possible, the protocol must disambiguate
which set of rules are in play. Some rules have technical
enforcement mechanisms; for example in some federations intermediates
validate information that is being communicated within the
federation.
Several deployment approaches are possible. These can most easily be
classified based on the mechanism for technical trust that is used.
The choice of technical trust mechanism constrains how rules
determination is implemented. Regardless of what deployment strategy
is chosen, the technical trust mechanism MUST constrain the names of
both parties to the exchange. The trust mechanism MUST make sure
that the entity acting as IDP for a given NAI is permitted to be the
IDP for that realm. The mechanism MUST make sure that any service
name claimed by the RP is permitted to be claimed by that entity.
Here are the categories of technical trust determination:
AAA Proxy: The simplest model is that an RP supports a request
directly to an AAA proxy. The hop-by-hop integrity protection of
the AAA fabric provides technical trust. An RP can submit a
request directly to a federation. Alternatively, a federation
disambiguation fabric can be used. Such a fabric takes
information about what federations the RP is part of and what
federations the IDP is part of and routes a message to the
appropriate federation. The routing of messages across the fabric
plus attributes added to requests and responses provides rules
determination. For example, when a disambiguation fabric routes a
message to a given federation, that federation's rules are chosen.
Naming is enforced as messages travel across the fabric. The
entities near the RP confirm its identity and validate names it
claims. The fabric routes the message towards the appropriate
IDP, validating the IDP's name in the process. The routing can be
statically configured. Alternatively a routing protocol could be
developed to exchange reachability information about given IDPs
and to apply policy across the AAA fabric. Such a routing
protocol could flood naming constraints to the appropriate points
in the fabric.
Trust Broker: Instead of routing messages through AAA proxies, some
trust broker could establish keys between entities near the RP and
entities near the IDP. The advantage of this approach is
efficiency of message handling. Fewer entities are needed to be
involved for each message. Security may be improved by sending
individual messages over fewer hops. Rules determination involves
decisions made by trust brokers about what keys to grant. Also,
associated with each credential is context about rules and about
other aspects of technical trust including names that may be
claimed. A routing protocol similar to the one for AAA proxies is
likely to be useful to trust brokers in flooding rules and naming
constraints.
Global Credential: A global credential such as a public key and
certificate in a public key infrastructure can be used to
establish technical trust. A directory or distributed database
such as the Domain Name System is needed for an RP to discover
what endpoint to contact for a given NAI. Certificates provide a
place to store information about rules determination and naming
constraints. Provided that no intermediates are required and that
the RP and IDP are sufficient to enforce and determine rules,
rules determination is reasonably simple. However applying
certain rules is likely to be quite complex. For example if
multiple sets of rules are possible between an IDP and RP,
confirming the correct set is used may be difficult. This is
particularly true if intermediates are involved in making the
decision. Also, to the extent that directory information needs to
be trusted, rules determination may be more complex.
Real-world deployments are likely to be mixtures of these basic
approaches. For example, it will be quite common for an RP to route
traffic to a AAA proxy within an organization. That proxy MAY use
any of the three methods to get closer to the IDP. It is also likely
that rather than being directly reachable, an IDP may have a proxy
within its organization. Federations MAY provide a traditional AAA
proxy interface even if they also provide another mechanism for
increased efficiency or security.
2.2. Subject To Identity Provider
Traditional web federation does not describe how a subject Traditional web federation does not describe how a subject
communicates with an identity provider. As a result, this communicates with an identity provider. As a result, this
communication is not standardized. There are several disadvantages communication is not standardized. There are several disadvantages
to this approach. It is difficult to have subjects that are machines to this approach. It is difficult to have subjects that are machines
rather than humans that use some sort of programatic credential. In rather than humans that use some sort of programatic credential. In
addition, use of browsers for authentication restricts the deployment addition, use of browsers for authentication restricts the deployment
of more secure forms of authentication beyond plaintext username and of more secure forms of authentication beyond plaintext username and
password known by the server. In a number of cases the password known by the server. In a number of cases the
authentication interface may be presented before the subject has authentication interface may be presented before the subject has
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EAP support is already integrated in AAA systems (see [RFC3579] and EAP support is already integrated in AAA systems (see [RFC3579] and
[RFC4072]) several challenges remain: one is to carry EAP payloads [RFC4072]) several challenges remain: one is to carry EAP payloads
from the end host to the relying party. Another is to verify from the end host to the relying party. Another is to verify
statements the relying party has made to the subject, confirm these statements the relying party has made to the subject, confirm these
statements are consistent with statements made to the identity statements are consistent with statements made to the identity
provider and confirm all the above are consistent with the federation provider and confirm all the above are consistent with the federation
and any federation-specific policy or configuration. Another and any federation-specific policy or configuration. Another
challenge is choosing which identity provider to use for which challenge is choosing which identity provider to use for which
service. service.
3.3. Application to Service 2.3. Application to Service
One of the remaining layers is responsible for integration of One of the remaining layers is responsible for integration of
federated authentication into the application. There are a number of federated authentication into the application. There are a number of
approaches that applications have adopted for security. So, there approaches that applications have adopted for security. So, there
may need to be multiple strategies for integration of federated may need to be multiple strategies for integration of federated
authentication into applications. However, we have started with a authentication into applications. However, we have started with a
strategy that provides integration to a large number of application strategy that provides integration to a large number of application
protocols. protocols.
Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645] Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645]
and several non-IETF applications support the Generic Security and several non-IETF applications support the Generic Security
Services Application Programming Interface [RFC2743]. Many Services Application Programming Interface [RFC2743]. Many
applications such as IMAP, SMTP, XMPP and LDAP support e Simple applications such as IMAP, SMTP, XMPP and LDAP support e Simple
Authentication and Security Layer (SASL) [RFC4422] framework. These Authentication and Security Layer (SASL) [RFC4422] framework. These
two approaches work together nicely: by creating a GSS-API mechanism, two approaches work together nicely: by creating a GSS-API mechanism,
SASL integration is also addressed [RFC5801]. In effect, using a SASL integration is also addressed. In effect, using a GSS-API
GSS-API mechanism with SASL simply requires placing some headers on mechanism with SASL simply requires placing some headers on the front
the front of the mechanism and constraining certain GSS-API options. of the mechanism and constraining certain GSS-API options.
GSS-API is specified in terms of an abstract set of operations which GSS-API is specified in terms of an abstract set of operations which
can be mapped into a programming language to form an API. When can be mapped into a programming language to form an API. When
people are first introduced to GSS-API, they focus on it as an API. people are first introduced to GSS-API, they focus on it as an API.
However, from the prospective of authentication for non-web However, from the prospective of authentication for non-web
applications, GSS-API should be thought of as a protocol not an API. applications, GSS-API should be thought of as a protocol not an API.
It consists of some abstract operations such as the initial context It consists of some abstract operations such as the initial context
exchange, which includes two sub-operations (gss_init_sec_context and exchange, which includes two sub-operations (gss_init_sec_context and
gss_accept_sec_context). An application defines which abstract gss_accept_sec_context). An application defines which abstract
operations it is going to use and where messages produced by these operations it is going to use and where messages produced by these
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integration. What does this mean from a protocol standpoint and how integration. What does this mean from a protocol standpoint and how
does this relate to other layers? This means we need to design a does this relate to other layers? This means we need to design a
concrete GSS-API mechanism. We have chosen to use a GSS-API concrete GSS-API mechanism. We have chosen to use a GSS-API
mechanism that encapsulates EAP authentication. So, GSS-API (and mechanism that encapsulates EAP authentication. So, GSS-API (and
SASL) encapsulate EAP between the end-host and the service. The AAA SASL) encapsulate EAP between the end-host and the service. The AAA
framework encapsulates EAP between the relying party and the identity framework encapsulates EAP between the relying party and the identity
provider. The GSS-API mechanism includes rules about how principals provider. The GSS-API mechanism includes rules about how principals
and services are named as well as per-message security and other and services are named as well as per-message security and other
facilities required by the applications we wish to support. facilities required by the applications we wish to support.
3.4. Personalization Layer 2.4. Personalization Layer
The AAA framework provides a way to transport statements from the The AAA framework provides a way to transport statements from the
identity provider to the relying party. However, we also need to say identity provider to the relying party. However, we also need to say
more about the content of these statements. In simple cases, more about the content of these statements. In simple cases,
attributes particular to the AAA protocol can be defined. However in attributes particular to the AAA protocol can be defined. However in
more complicated situations it is strongly desirable to re-use an more complicated situations it is strongly desirable to re-use an
existing protocol for asking questions and receiving information existing protocol for asking questions and receiving information
about subjects. SAML is used for this. about subjects. SAML is used for this.
SAML usage may be as simple as the identity provider including a SAML SAML usage may be as simple as the identity provider including a SAML
Response message in the AAA response. Alternatively the relying Response message in the AAA response. Alternatively the relying
party may generate a SAML request. party may generate a SAML request XXX to whom, how, and at what
point? (see above XXX).
3.5. Tieing Layers Together 2.5. Tieing Layers Together
+--------------+ +--------------+
| AAA Server | | AAA Server |
| (Identity | | (Identity |
| Provider) | | Provider) |
+-^----------^-+ +-^----------^-+
* EAP | RADIUS/ * EAP | RADIUS/
* | Diameter * | Diameter
--v----------v-- --v----------v--
/// \\\ /// \\\
// \\ *** // \\ ***
skipping to change at page 17, line 5 skipping to change at page 21, line 5
Legend: Legend:
<****>: End-to-end exchange <****>: End-to-end exchange
<---->: Hop-by-hop exchange <---->: Hop-by-hop exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled <====>: Protocol through which GSS-API/GS2 exchanges are tunnelled
Figure 2: Architecture for Federated Access of non-Web based Figure 2: Architecture for Federated Access of non-Web based
Applications Applications
4. Application Security Services 3. Application Security Services
One of the key goals is to integrate federated authentication into One of the key goals is to integrate federated authentication into
existing application protocols and where possible, existing existing application protocols and where possible, existing
implementations of these protocols. Another goal is to perform this implementations of these protocols. Another goal is to perform this
integration while meeting the best security practices of the integration while meeting the best security practices of the
technologies used to perform the integration. This section describes technologies used to perform the integration. This section describes
security services and properties required by the EAP GSS-API security services and properties required by the EAP GSS-API
mechanism in order to meet these goals. This information could be mechanism in order to meet these goals. This information could be
viewed as specific to that mechanism. However, other future viewed as specific to that mechanism. However, other future
application integration strategies are very likely to need similar application integration strategies are very likely to need similar
services. So, it is likely that these services will be expanded services. So, it is likely that these services will be expanded
across application integration strategies if new application across application integration strategies if new application
integration strategies are adopted. integration strategies are adopted.
4.1. Server (Mutual) Authentication 3.1. Server (Mutual) Authentication
GSS-API provides an optional security service called mutual GSS-API provides an optional security service called mutual
authentication. This service means that in addition to the initiator authentication. This service means that in addition to the initiator
providing (potentially anonymous or pseudonymous) identity to the providing (potentially anonymous or pseudonymous) identity to the
acceptor, the acceptor confirms its identity to the initiator. acceptor, the acceptor confirms its identity to the initiator.
Especially for the ABFAB context, this service is confusingly named. Especially for the ABFAB context, this service is confusingly named.
We still say that mutual authentication is provided when the identity We still say that mutual authentication is provided when the identity
of an acceptor is strongly authenticated to an anonymous initiator. of an acceptor is strongly authenticated to an anonymous initiator.
RFC 2743 does not explicitly talk about what mutual authentication RFC 2743 does not explicitly talk about what mutual authentication
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The GSS-EAP mechanism MUST implement mutual authentication. That is, The GSS-EAP mechanism MUST implement mutual authentication. That is,
an initiator needs to be able to request mutual authentication. When an initiator needs to be able to request mutual authentication. When
mutual authentication is requested, only EAP methods capabale of mutual authentication is requested, only EAP methods capabale of
providing the necessary service can be used, and appropriate steps providing the necessary service can be used, and appropriate steps
need to be taken to provide mutual authentication. A broader set of need to be taken to provide mutual authentication. A broader set of
EAP methods could be supported when a particular application does not EAP methods could be supported when a particular application does not
request mutual authentication. It is an open question whether the request mutual authentication. It is an open question whether the
mechanism will permit this. mechanism will permit this.
4.2. GSS-API Channel Binding 3.2. GSS-API Channel Binding
[RFC5056] defines a concept of channel binding to prevent man-in-the- [RFC5056] defines a concept of channel binding to prevent man-in-the-
middle attacks. It is common to provide SASL and GSS-API with middle attacks. It is common to provide SASL and GSS-API with
another layer to provide transport security; Transport Layer Security another layer to provide transport security; Transport Layer Security
(TLS) is the most common such layer. TLS provides its own server (TLS) is the most common such layer. TLS provides its own server
authentication. However there are a variety of situations where this authentication. However there are a variety of situations where this
authentication is not checked for policy or usability reasons. Even authentication is not checked for policy or usability reasons. Even
when it is checked, if the trust infrastructure behind the TLS when it is checked, if the trust infrastructure behind the TLS
authentication is different from the trust infrastructure behind the authentication is different from the trust infrastructure behind the
GSS-API mutual authentication. If the endpoints of the GSS-API GSS-API mutual authentication. If the endpoints of the GSS-API
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the user is able to visually authenticate the content. This is the user is able to visually authenticate the content. This is
consistent with all uses of channel binding without protocol level consistent with all uses of channel binding without protocol level
mutual authentication found so far. mutual authentication found so far.
RFC 5056 channel binding (also called GSS-API channel binding when RFC 5056 channel binding (also called GSS-API channel binding when
GSS-API is involved) is not the same thing as EAP channel binding. GSS-API is involved) is not the same thing as EAP channel binding.
EAP channel binding is also used in the ABFAB context in order to EAP channel binding is also used in the ABFAB context in order to
implement acceptor naming and mutual authentication. Details are implement acceptor naming and mutual authentication. Details are
discussed in the mechanisms specification [I-D.ietf-abfab-gss-eap]. discussed in the mechanisms specification [I-D.ietf-abfab-gss-eap].
4.3. Host-Based Service Names 3.3. Host-Based Service Names
IETF security mechanisms typically take the name of a service entered IETF security mechanisms typically take the name of a service entered
by a user and make some trust decision about whether the remote party by a user and make some trust decision about whether the remote party
in an interaction is the intended party. GSS-API has a relatively in an interaction is the intended party. GSS-API has a relatively
flexible naming architecture. However most of the IETF applications flexible naming architecture. However most of the IETF applications
that use GSS-API, including SSH, NFS, IMAP, LDAP and XMPP, have that use GSS-API, including SSH, NFS, IMAP, LDAP and XMPP, have
chosen to use host-based service names when they use GSS-API. In chosen to use host-based service names when they use GSS-API. In
this model, the initiator names an acceptor based on a service such this model, the initiator names an acceptor based on a service such
as "imap" or "host" (for login services such as SSH) and a host name. as "imap" or "host" (for login services such as SSH) and a host name.
skipping to change at page 20, line 5 skipping to change at page 24, line 5
entity is allowed to claim the name. ABFAB needs to adopt this entity is allowed to claim the name. ABFAB needs to adopt this
approach. approach.
Host-based service names do not work ideally when different instances Host-based service names do not work ideally when different instances
of a service are running on different ports. Also, these do not work of a service are running on different ports. Also, these do not work
ideally when SRV record or other insecure referrals are used. ideally when SRV record or other insecure referrals are used.
The GSS-EAP mechanism needs to support host-based service names in The GSS-EAP mechanism needs to support host-based service names in
order to work with existing IETF protocols. order to work with existing IETF protocols.
4.4. Per-Message Tokens 3.4. Per-Message Tokens
GSs-API provides per-message security services that can provide GSS-API provides per-message security services that can provide
confidentiality and integrity. Some IETF protocols such as NFS and confidentiality and integrity. Some IETF protocols such as NFS and
SSH take advantage of these services. As a result GSS-EAP needs to SSH take advantage of these services. As a result GSS-EAP needs to
support these services. As with mutual authentication, per-message support these services. As with mutual authentication, per-message
services will limit the set of EAP methods that are available. Any services will limit the set of EAP methods that are available. Any
method that produces a Master Session Key (MSK) should be able to method that produces a Master Session Key (MSK) should be able to
support per-message security services. support per-message security services.
GSS-API provides a pseudo-random function. While the pseudo-random GSS-API provides a pseudo-random function. While the pseudo-random
function does not involve sending data over the wire, it provides an function does not involve sending data over the wire, it provides an
algorithm that both the initiator and acceptor can run in order to algorithm that both the initiator and acceptor can run in order to
arrive at the same key value. This is useful for designs where a arrive at the same key value. This is useful for designs where a
successful authentication is used to key some other function. This successful authentication is used to key some other function. This
is similar in concept to the TLS extractor. No current IETF is similar in concept to the TLS extractor. No current IETF
protocols require this. However GSS-EAP supports this service protocols require this. However GSS-EAP supports this service
because it is valuable for the future and easy to do given per- because it is valuable for the future and easy to do given per-
message services. Non-IETF protocols are expected to take advantage message services. Non-IETF protocols are expected to take advantage
of this in the near future. of this in the near future.
4. Future Work: Attribute Providers
This architecture provides for a federated authentication and
authorization framework between IdPs, RPs, principals, and subjects.
It does not at this time provide for a means to retrieve attributes
from 3rd parties. However, it envisions such a possibility. We note
that in any extension to the model, an attribute provider must be
authorized to release specific attributes to a specific RP for a
specific principal. In addition, we note that it is an open question
beyond this architecture as to how the RP should know to trust a
particular attribute provider.
There are a number of possible technical means to provide attribute
provider capabilities. One possible approach is for the IdP to
provide a signed attribute request to RP that it in turn will provide
to the attribute authority. Another approach would be for the IdP to
provide a URI to the RP that contains a token of some form. The form
of communications between the IdP and attribute provider as well as
other considerations are left for the future. One thing we can say
now is that the IdP would merely be asserting who the attribute
authority is, and not the contents of what the attribute authority
would return. (Otherwise, the IdP might as well make the query to
the attribute authority and then resign it.)
5. Privacy Considerations 5. Privacy Considerations
Sharing identity information may lead to privacy violations. A Sharing identity information raises privacy violations and as
future verison of this document will provide a discussion of privacy described throughout this document an existing architecture is re-
considerations in a federated access environment. used for a different usage environment. As such, a discussion about
the privacy properties has to take these pre-conditions into
consideration. We use the approach suggested in
[I-D.morris-privacy-considerations] to shed light into what data is
collected and used by which entity, what the relationship between
these entities and the end user is, what data about the user is
likely needed to be collected, and what the identification level of
the data is.
5.1. What entities collect and use data?
Figure 2 shows the architecture with the involved entities. Message
exchanges are exchanged between the client application, via the
relying part to the AAA server. There will likely be intermediaries
between the relying party and the AAA server, labeled generically as
"federation".
In order for the relying party to route messages to the AAA server it
is necessary for the client application to provide enough information
to enable the identification of the AAA server's domain. While often
the username is attached to the domain (in the form of a Network
Access Identity (NAI) this is not necessary for the actual protocol
operation. The EAP server component within the AAA server needs to
authenticate the user and therefore needs to execute the respective
authentication protocol. Once the authentication exchange is
complete authorization information needs to be conveyed to the
relying party to grant the user the necessary application rights.
Information about resource consumption may be delivered as part of
the accounting exchange during the lifetime of the granted
application session.
The authentication exchange may reveal an identifier that can be
linked to a user. Additionally, a sequence of authentication
protocol exchanges may be linked together. Depending on the chosen
authentication protocol information at varying degrees may be
revealed to all parties along the communication path. This
authorization information exchange may disclose identity information
about the user. While accounting information is created by the
relying party it is likely to needed by intermediaries in the
federation for financial settlement purposes and will be stored for
billing, fraud detection, statistical purposes, and for service
improvement by the AAA server operator.
5.2. Relationship between User's and other Entities
The AAA server is a first-party site the user typically has a
relationship with. This relationship will be created at the time
when the security credentials are exchange and provisioned. The
relying party and potential intermediares in the federation are
typically operate under the contract of the first-party site. The
user typically does not know about the intermediaries in the
federation nor does he have any relationship with them. The protocol
interaction triggered by the client application happens with the
relying party at the time of application access. The relying party
does not have a direct contractual relationship with the user but
depending on the application the interaction may expose the brand of
the application running by the relying party to the end user via some
user interface.
5.3. What Data about the User is likely Needed to be Collected?
The data that is likely going to be collected as part of a protocol
exchange with application access at the relying party is accounting
information and authorization information. This information is
likely to be kept beyond the terminated application usage for trouble
shooting, statistical purposes, etc. There is also like to be
additional data collected to to improve application service usage by
the relying party that is not conveyed to the AAA server as part of
the accounting stream.
5.4. What is the Identification Level of the Data?
With regard to identification there are several protocol layers that
need to be considered separately. First, there is the EAP method
exchange, which as an authentication and key exchange protocol has
properties related to identification and protocol linkage. Second,
there is identification at the EAP layer for routing of messages.
Then, in the exchange between the client application and the relying
party the identification depends on the underlying application layer
protocol the EAP/GSS-API exchange is tunneled over. Finally, there
is the backend exchange via the AAA infrastructure, which involves a
range of RADIUS and Diameter extensions and yet to be defined
extensions, such as encoding authorization information inside SAML
assertions.
Since this document does not attempt to define any of these exchanges
but rather re-uses existing mechanisms the level of identification
heavily depends on the selected mechanisms. The following two
examples aim to illustrate the amount of existing work with respect
to decrease exposure of personal data.
1. When designing EAP methods a number of different requirements may
need to get considered; some of them are conflicting. RFC 4017
[RFC4017], for example, tried to list requirements for EAP
methods utilized for network access over Wireless LANs. It also
recommends the end-user identity hiding requirement, which is
privacy-relevant. Some EAP methods, such as EAP-IKEv2 [RFC5106],
also fulfill this requirement.
2. EAP, as the layer encapsulating EAP method specific information,
needs identity information to allow routing requests towards the
user's home AAA server. This information is carried within the
Network Access Identifier (NAI) and the username part of the NAI
(as supported by RFC 4282 [RFC4282]) can be obfuscated.
5.5. Privacy Challenges
While a lot of standarization work was done to avoid leakage of
identity information to intermediaries (such as eavesdroppers on the
communication path between the client application and the relying
party) in the area of authentication and key exchange protocols.
However, from current deployments the weak aspects with respect to
security are:
1. Today business contracts are used to create federations between
identity providers and relying parties. These contracts are not
only financial agreements but they also define the rules about
what information is exchanged between the AAA server and the
relying party and the potential involvement of AAA proxies and
brokers as intermediaries. While these contracts are openly
available for university federations they are not public in case
of commercial deployments. Quite naturally, there is a lack of
transparency for external parties.
2. In today's deployments the ability for users to determine the
amount of information exchanged with other parties over time, as
well as the possibility to control the amount of information
exposed via an explict consent is limited. This is partially due
the nature of application capabilities at the time of network
access authentication. However, with the envisioned extension of
the usage, as described in this document, it is desirable to
offer these capabilities.
6. Deployment Considerations 6. Deployment Considerations
6.1. EAP Channel Binding 6.1. EAP Channel Binding
Discuss the implications of needing EAP channel binding. Discuss the implications of needing EAP channel binding.
6.2. AAA Proxy Behavior 6.2. AAA Proxy Behavior
Discuss deployment implications of our proxy requirements. Discuss deployment implications of our proxy requirements.
skipping to change at page 26, line 45 skipping to change at page 33, line 45
Pfitzmann, A., Hansen, M., and H. Tschofenig, "Terminology Pfitzmann, A., Hansen, M., and H. Tschofenig, "Terminology
for Talking about Privacy by Data Minimization: Anonymity, for Talking about Privacy by Data Minimization: Anonymity,
Unlinkability, Undetectability, Unobservability, Unlinkability, Undetectability, Unobservability,
Pseudonymity, and Identity Management", Pseudonymity, and Identity Management",
draft-hansen-privacy-terminology-01 (work in progress), draft-hansen-privacy-terminology-01 (work in progress),
August 2010. August 2010.
[I-D.ietf-abfab-gss-eap] [I-D.ietf-abfab-gss-eap]
Hartman, S. and J. Howlett, "A GSS-API Mechanism for the Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol", Extensible Authentication Protocol",
draft-ietf-abfab-gss-eap-00 (work in progress), draft-ietf-abfab-gss-eap-01 (work in progress),
October 2010. February 2011.
10.2. Informative References 10.2. Informative References
[I-D.nir-tls-eap] [I-D.nir-tls-eap]
Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "TLS Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "TLS
using EAP Authentication", draft-nir-tls-eap-08 (work in using EAP Authentication", draft-nir-tls-eap-10 (work in
progress), July 2010. progress), February 2011.
[I-D.morris-privacy-considerations]
Aboba, B., Morris, J., Peterson, J., and H. Tschofenig,
"Privacy Considerations for Internet Protocols",
draft-morris-privacy-considerations-02 (work in progress),
November 2010.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005.
[RFC5106] Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y.,
and F. Bersani, "The Extensible Authentication Protocol-
Internet Key Exchange Protocol version 2 (EAP-IKEv2)
Method", RFC 5106, February 2008.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996. RFC 1964, June 1996.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol [RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997. Specification", RFC 2203, September 1997.
[RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J., [RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J.,
and R. Hall, "Generic Security Service Algorithm for and R. Hall, "Generic Security Service Algorithm for
Secret Key Transaction Authentication for DNS (GSS-TSIG)", Secret Key Transaction Authentication for DNS (GSS-TSIG)",
skipping to change at page 27, line 37 skipping to change at page 35, line 5
Security Layer (SASL)", RFC 4422, June 2006. Security Layer (SASL)", RFC 4422, June 2006.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007. Channels", RFC 5056, November 2007.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security [RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010. GS2 Mechanism Family", RFC 5801, July 2010.
[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.
[OASIS.saml-core-2.0-os] [OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler, Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion "Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core- Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2.0-os, March 2005.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904, D. Spence, "AAA Authorization Framework", RFC 2904,
August 2000. August 2000.
URIs URIs
[1] <http://www.eduroam.org> [1] <http://www.openid.net>
[2] <http://www.eduroam.org>
Authors' Addresses Authors' Addresses
Josh Howlett Josh Howlett
JANET(UK) JANET(UK)
Lumen House, Library Avenue, Harwell
Oxford OX11 0SG
UK
Phone: Phone: +44 1235 822363
Email: Josh.Howlett@ja.net Email: Josh.Howlett@ja.net
Sam Hartman Sam Hartman
Painless Security Painless Security
Phone: Phone:
Email: hartmans-ietf@mit.edu Email: hartmans-ietf@mit.edu
Hannes Tschofenig Hannes Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
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