< draft-ietf-abfab-arch-00.txt   draft-ietf-abfab-arch-01.txt >
ABFAB J. Howlett ABFAB J. Howlett
Internet-Draft JANET(UK) Internet-Draft JANET(UK)
Intended status: Informational S. Hartman Intended status: Informational S. Hartman
Expires: January 30, 2012 Painless Security Expires: September 11, 2012 Painless Security
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
E. Lear E. Lear
Cisco Systems GmbH Cisco Systems GmbH
July 29, 2011 March 10, 2012
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-ietf-abfab-arch-00.txt draft-ietf-abfab-arch-01.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 access management. Most of this effort has space of federated access management. Most of this effort has
focused on two use-cases: network and web-based access. However, the focused on two use-cases: network and web-based access. However, the
solutions to these use-cases that have been proposed and deployed solutions to these use-cases that have been proposed and deployed
tend to have few common building blocks in common. 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 security mechanisms for both federated and non- the commonly used security mechanisms for both federated and non-
federated access management, including RADIUS, Diameter, GSS, GS2, federated access management, including the Remote Authentication Dial
EAP and SAML. The architecture addresses the problem of federated In User Service (RADIUS) and the Diameter protocol, the Generic
access management to primarily non-web-based services, in a manner Security Service (GSS), the GS2 family, the Extensible Authentication
that will scale to large numbers of identity providers, relying Protocol (EAP) and the Security Assertion Markup Language (SAML).
parties, and federations. 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 identity providers, relying parties, and
federations.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 11, 2012.
This Internet-Draft will expire on January 30, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. An Overview of Federation . . . . . . . . . . . . . . . . 5 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 5
1.3. Challenges to Contemporary Federation . . . . . . . . . . 8 1.3. Challenges to Contemporary Federation . . . . . . . . . . 8
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 8 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 8
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 11 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 11
1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 11 1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 12
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 13 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1. Federation Substrate . . . . . . . . . . . . . . . . . . . 13 2.1. Relying Party to Identity Provider . . . . . . . . . . . . 14
2.1.1. Discovery, Rules Determination, and Technical Trust . 14 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 17
2.2. Subject To Identity Provider . . . . . . . . . . . . . . . 16 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 18
2.3. Application to Service . . . . . . . . . . . . . . . . . . 17
2.4. Personalization Layer . . . . . . . . . . . . . . . . . . 19
2.5. Tieing Layers Together . . . . . . . . . . . . . . . . . . 19
3. Application Security Services . . . . . . . . . . . . . . . . 21 3. Application Security Services . . . . . . . . . . . . . . . . 21
3.1. Server (Mutual) Authentication . . . . . . . . . . . . . . 21 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 21
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 22 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 22
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 23 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 23
3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 24 3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 24
4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 25 4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 25
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 26 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 26
5.1. What entities collect and use data? . . . . . . . . . . . 26 5.1. What Entities collect and use Data? . . . . . . . . . . . 26
5.2. Relationship between User's and other Entities . . . . . . 27 5.2. Relationship between User's and other Entities . . . . . . 27
5.3. What Data about the User is likely Needed to be 5.3. What Data about the User is likely Needed to be
Collected? . . . . . . . . . . . . . . . . . . . . . . . . 27 Collected? . . . . . . . . . . . . . . . . . . . . . . . . 27
5.4. What is the Identification Level of the Data? . . . . . . 27 5.4. What is the Identification Level of the Data? . . . . . . 27
5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 28 5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 28
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 29 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 29
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 29 6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 29
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 29 6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 29
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30 7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
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to that particular Relying Party. Federated access management to that particular Relying Party. Federated access management
therefore provides various strategies for protecting the Subject's therefore provides various strategies for protecting the Subject's
privacy. Other privacy aspects typically of concern are the privacy. Other privacy aspects typically of concern are the
policy for releasing personal data about the Subjectfrom the IdP policy for releasing personal data about the Subjectfrom the IdP
to the RP, the purpose of the usage, the retention period of the to the RP, the purpose of the usage, the retention period of the
data, and many more. data, and many more.
Provisioning Provisioning
Sometimes a Relying Party needs, or would like, to know more about Sometimes a Relying Party needs, or would like, to know more about
a subject that an affiliation or pseudonym. For example, a a subject than an affiliation or a pseudonym. For example, a
Relying Party may want the Subject's email address or name. Some Relying Party may want the Subject's email address or name. Some
federated access management technologies provide the ability for federated access management technologies provide the ability for
the IdP to provision this information, either on request by by the the IdP to provision this information, either on request by the RP
RP or unsolicited. or unsolicited.
1.1. Terminology 1.1. Terminology
This document uses identity management and privacy terminology from This document uses identity management and privacy terminology from
[I-D.hansen-privacy-terminology]. In particular, this document uses [I-D.iab-privacy-terminology]. In particular, this document uses the
the terms pseudonymity, unlinkability, anonymity, and identity terms identity provider, relying party, (data) subject, identifier,
management. pseudonymity, unlinkability, and anonymity.
We make one note about the IdP: in this architecture, the IdP In this architecture the IdP consists of the following components: an
consists of the following components: an EAP server, a radius server, EAP server, a RADIUS or a Diameter server, and optionally a SAML
and optionally a SAML Assertion service. The IdP is also responsible Assertion service.
for authentication, even though it may rely upon other components
within a domain for such an operation. The reader is advised that This document uses the term Network Access Identifier (NAI), as
for succinctness, in most cases the term IdP is used, except where defined in [RFC4282].
additional clarity seems appropriate.
1.2. An Overview of Federation 1.2. An Overview of Federation
In the previous section we introduced the following actors: In the previous section we introduced the following actors:
o the Subject, o the Subject,
o the Identity Provider, and o the Identity Provider, and
o the Relying Party. o the Relying Party.
These entities and their relationships are illustrated graphically in These entities and their relationships are illustrated graphically in
Figure 1. Figure 1.
,----------\ ,---------\ ,----------\ ,---------\
| Identity | Federation | Relying | | Identity | Federation | Relying |
| Provider + <-------------------> + Party | | Provider + <-------------------> + Party |
`----------' '---------' `----------' '---------'
< <
\ \
\ Identity \ Authentication
\ management \
\ \
\ \
\ \
\ +------------+ \ +---------+
\ | | \ | | O
v| Subject | v| Client | \|/ Subject
| | | | |
+------------+ +---------+ / \
Figure 1: General federation framework model Figure 1: Entities and their Relationships
A federation typically this relationship encompasses operational A federation typically this relationship encompasses operational
specifications and legal rules: specifications and legal rules:
Operational Specifications: Operational Specifications:
This includes the technical specifications (e.g. protocols used to This includes the technical specifications (e.g. protocols used to
communicate between the three parties), process standards, communicate between the three parties), process standards,
policies, identity proofing, credential and authentication policies, identity proofing, credential and authentication
algorithm requirements, performance requirements, assessment and algorithm requirements, performance requirements, assessment and
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and every RP; on an Internet scale this setup requires the and every RP; on an Internet scale this setup requires the
introduction of the multi-lateral federation concept, as the introduction of the multi-lateral federation concept, as the
management of such pair-wise relationships would otherwise prove management of such pair-wise relationships would otherwise prove
burdensome. burdensome.
While many of the non-technical aspects of federation, such as While many of the non-technical aspects of federation, such as
business practices and legal arrangements, are outside the scope of business practices and legal arrangements, are outside the scope of
the IETF they still impact the architectural setup on how to ensure the IETF they still impact the architectural setup on how to ensure
the dynamic establishment of trust. the dynamic establishment of trust.
Some deployments are sometimes required to deploy complex technical Some deployments demand the deployment of sophisticated technical
infrastructure, including message routing intermediaries, to offer infrastructure, including message routing intermediaries, to offer
the required technical functionality, while in other deployments the required technical functionality. In other deployments fewer
those are missing. technical components are needed.
Figure 1 also shows the relationship between the IdP and the Subject. Figure 1 also shows the relationship between the IdP and the Subject.
Often a real world entity is associated with the Subject; for Often a real world entity is associated with the Subject; for
example, a person or some software. example, a person or some software.
The IdP will typically have a long-term relationship with the The IdP will typically have a long-term relationship with the
Subject. This relationship would typically involve the IdP Subject. This relationship would typically involve the IdP
positively identifying and credentialling the Subject (for example, positively identifying and credentialling the Subject (for example,
at time of enrollment in the context of employment within an at time of enrollment in the context of employment within an
organisation). The relationship will often be instantiated within an organisation). The relationship will often be instantiated within an
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It is, for example, entirely compatible with a relationship between 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 the IdP and Subject that is only as weak as completing a web form and
confirming the verification email. confirming the verification email.
However, the nature and quality of the relationship between the However, the nature and quality of the relationship between the
Subject and the IdP is an important contributor to the level of trust 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 that an RP may attribute to an assertion describing a Subject made by
an IdP. This is sometimes described as the Level of Assurance. an IdP. This is sometimes described as the Level of Assurance.
Similarly it is also important to note that, in the general case, Similarly it is also important to note that, in the general case,
there is no requirement of a long-term relationship betweem the RP there is no requirement of a long-term relationship between the RP
and the Subject. This is a property of federation that yields many and the Subject. This is a property of federation that yields many
of its benefits. However, federation does not preclude the of its benefits. However, federation does not preclude the
possibility relationship between the RP and the Subject, should needs possibility of a pre-existing relationship existing between the RP
dictate. and the Subject, nor that they may use the introduction to create a
new long-term relationship independent of the federation.
Finally, it is important to reiterate that in some scenarios there Finally, it is important to reiterate that in some scenarios there
might indeed be a human behind the device denoted as Subject and in might indeed be a human behind the device denoted as Subject and in
other cases there is no human involved in the actual protocol other cases there is no human involved in the actual protocol
execution. execution.
1.3. Challenges to Contemporary Federation 1.3. Challenges to Contemporary Federation
As the number of such federated services has proliferated, however, As the number of federated services has proliferated, however, the
the role of the individual has become ambiguous in certain role of the individual can become ambiguous in certain circumstances.
circumstances. For example, a school might provide online access to For example, a school might provide online access to a student's
grades to a parent who is also a teacher. She must clearly grades to their parents for review, and to the student's teacher for
distinguish her role upon access. After all, she is probably not modifying the grades. A teacher who is also a parent must clearly
allowed to edit her own child's grades. distinguish here role upon access.
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(s) a user
associated with. This is true for both the web and non-web case, but is associated with. This is true for both the web and non-web case,
particularly acute for the latter ans many non-web authentication but is particularly acute for the latter as many non-web
systems are not semantically rich enough on their own to allow for authentication systems are not semantically rich enough on their own
such ambiguities. For instance, in the case of an email provider, to allow for such ambiguities. For instance, in the case of an email
the use of SMTP and IMAP protocols does not on its own provide for a provider, the use of SMTP and IMAP protocols does not on its own
way to select a federation. However, the building blocks do exist to provide for a way to select a federation. However, the building
add this functionality. blocks do exist to add this functionality.
1.4. An Overview of ABFAB-based Federation 1.4. An Overview of ABFAB-based Federation
The previous section described the general model of federation, and The previous section described the general model of federation, and
its the application of federated access management. This section its the application of federated access management. This section
provides a brief overview of ABFAB in the context of this model. provides a brief overview of ABFAB in the context of this model.
The steps taken generally in an ABFAB federated authentication/ The steps taken generally in an ABFAB federated authentication/
authorization exchange are as follows: authorization exchange are as follows:
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3. Client Application provides NAI to RP: At the conclusion of 3. Client Application provides NAI to RP: At the conclusion of
mechanism selection the NAI must be provided to the RP for mechanism selection the NAI must be provided to the RP for
discovery. discovery.
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 the RADIUS/Diameter request to
encapsulates a GSS/EAP access request to an IdP. This may or an IdP, which encapsulates the EAP access request. 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 and it makes whatever SAML Attribute Requests through a AAA
attribute. XXX- Check order of SAML attribute request. attribute.
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 EAP peer and the EAP
are exchanged between the principal and the IdP until a result server, i.e., the principal and the IdP in our identity
is determined. The number and content of those messages will management terminology, until the result of the authentication
depend on the EAP method. If the IdP is unable to authenticate protocol is determined. The number and content of those
the principal, the process concludes here. As part of this messages will depend on the EAP method. If the IdP is unable to
process, the principal will, under protection of EAP, assert the authenticate the principal, the process concludes here. As part
identity of the RP to which it intends to authenticate. of this process, the principal will, under protection of EAP,
assert the identity of the RP to which it intends to
authenticate.
8. Successful Authentication: At the very least the IdP (its EAP 8. Successful Authentication: At the very least the IdP (its EAP
server) and EAP peer / subject have authenticated one another. server) and EAP peer / subject have authenticated one another.
As a result of this step, the subject and the IdP hold two As a result of this step, the subject and the IdP hold two
cryptographic keys- a Master Session Key (MSK), and an Extended cryptographic keys- a Master Session Key (MSK), and an Extended
MSK (EMSK). If the asserted identity of the RP by the principal MSK (EMSK). If the asserted identity of the RP by the principal
matches the identity the RP itself asserted, there is some matches the identity the RP itself asserted, there is some
confidence that the RP is now authenticated to the IdP. confidence that the RP is now 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
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authorization identies. It will apply these results in an authorization identies. It will apply these results in an
application-specific way. application-specific way.
12. RP returns results to principal: Once the RP has a response it 12. RP returns results to principal: Once the RP has a response it
must inform the client application of the result. If all has must inform the client application of the result. If all has
gone well, all are authenticated, and the application proceeds gone well, all are authenticated, and the application proceeds
with appropriate authorization levels. with appropriate authorization levels.
An example communication flow is given below: An example communication flow is given below:
Relying Party Client App IdP Relying Client Identity
Party App Provider
| (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
| | | | | |
|<=====(4)====================>| Discovery |<=====(4)====================>| Discovery
| | | | | |
|>=====(5)====================>| Access request from RP to IdP |>=====(5)====================>| Access request from RP to IdP
| | | | | |
| |< - - (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) RP Processes results. (11) RP processes | |
results | |
| | | | | |
|>----(12)----->| | Results to client app. |>----(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
1.5. Design Goals 1.5. Design Goals
Our key design goals are as follows: Our key design goals are as follows:
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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
as well as to the end host for application integration, those changes as well as to the client for application integration, those changes
are kept at a minimum. A mechanism that can demonstrate deployment are kept at a minimum. A mechanism that can demonstrate deployment
benefits (based on ease of update of existing software, low benefits (based on ease of update of existing software, low
implementation effort, etc.)is preferred and there may be a need to implementation effort, etc.) is preferred and there may be a need to
specify multiple mechanisms to support the range of different specify multiple mechanisms to support the range of different
deployment scenarios. deployment scenarios.
There are a number of ways for encapsulating EAP into an application 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 protocol. For ease of integration with a wide range of non-Web based
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 The architecture consists of several buiding blocks, which is shown
discusses the individual layers. graphically in Figure 2. The subsections below explain relationship
of the protocol components in more detail.
2.1. Federation Substrate +--------------+
| Identity |
| Provider |
| (IdP) |
+-^----------^-+
* EAP o RADIUS/
* o Diameter
--v----------v--
/// \\\
// \\
| Federation |
| Substrate |
\\ //
\\\ ///
--^----------^--
* EAP o RADIUS/
* o Diameter
+-------------+ +-v----------v--+
| |<---------------->| |
| Client | EAP/EAP Method | Relying Party |
| Application |<****************>| (RP) |
| | GSS-API | |
| |<---------------->| |
| | Application | |
| | Protocol | |
| |<================>| |
+-------------+ +---------------+
The federation substrate is responsible for the connunication between Legend:
<****>: Client-to-IdP Exchange
<---->: Client-to-RP Exchange
<oooo>: RP-to-IdP Exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled
Figure 2: ABFAB Protocol Instantiation
2.1. Relying Party to Identity Provider
The federation substrate is responsible for the communication 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.
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.
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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.
2.1.1. Discovery, Rules Determination, and Technical Trust
One demand that the AAA substrate must make of the upper layers is 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 they must properly identify the end points of the communication.
That is- it must be possible for the AAA client at the RP to That is- it must be possible for the AAA client at the RP to
determine where to send each RADIUS or Diameter message. Without determine where to send each RADIUS or Diameter message. Without
this requirement, it would be the RP's responsibility to determine this requirement, it would be the RP's responsibility to determine
the identity of the principal on its own, without the assistance of the identity of the principal on its own, without the assistance of
an IdP. This architecture makes use of the Network Access Identifier an IdP. This architecture makes use of the Network Access Identifier
(NAI), where the IdP is indicated in the realm component [RFC4282]. (NAI), where the IdP is indicated in the realm component [RFC4282].
The NAI is represented and consumed by the GSS-API layer as 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 GSS_C_NT_USER_NAME as specified in [RFC2743]. The GSS-API EAp
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Real-world deployments are likely to be mixtures of these basic Real-world deployments are likely to be mixtures of these basic
approaches. For example, it will be quite common for an RP to route 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 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 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 that rather than being directly reachable, an IDP may have a proxy
within its organization. Federations MAY provide a traditional AAA within its organization. Federations MAY provide a traditional AAA
proxy interface even if they also provide another mechanism for proxy interface even if they also provide another mechanism for
increased efficiency or security. increased efficiency or security.
2.2. Subject To Identity Provider 2.2. Client To Identity Provider
Traditional web federation does not describe how a subject Traditional web federation does not describe how a subject interacts
communicates with an identity provider. As a result, this with an identity provider for authentication. 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
adequately validated they are talking to the intended server. By adequately validated they are talking to the intended server. By
giving control of the authentication interface to a potential giving control of the authentication interface to a potential
attacker, then the security of the system may be reduced and phishing attacker, then the security of the system may be reduced and phishing
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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.
2.3. Application to Service 2.3. Client to Relying Party
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 the 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. In effect, using a GSS-API SASL integration is also addressed. In effect, using a GSS-API
mechanism with SASL simply requires placing some headers on the front mechanism with SASL simply requires placing some headers on 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
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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.
2.4. Personalization Layer
The AAA framework provides a way to transport statements from the
identity provider to the relying party. However, we also need to say
more about the content of these statements. In simple cases,
attributes particular to the AAA protocol can be defined. However in
more complicated situations it is strongly desirable to re-use an
existing protocol for asking questions and receiving information
about subjects. SAML is used for this.
SAML usage may be as simple as the identity provider including a SAML
Response message in the AAA response. Alternatively the relying
party may generate a SAML request XXX to whom, how, and at what
point? (see above XXX).
2.5. Tieing Layers Together
+--------------+
| 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
3. 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.
3.1. Server (Mutual) Authentication 3.1. 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, unfortunately, does not explicitly talk about what mutual
means. Within the GSS-API community successful mutual authentication authentication means. Within this document we therefore define it as
has come to mean:
o If a target name is supplied by the initiator, then the initiator o If a target name is supplied by the initiator, then the initiator
trusts that the supplied target name describes the acceptor. This trusts that the supplied target name describes the acceptor. This
implies both that appropriate cryptographic exchanges took place implies both that appropriate cryptographic exchanges took place
for the initiator to make such a trust decision, and that after for the initiator to make such a trust decision, and that after
evaluating the results of these exchanges, the initiator's policy evaluating the results of these exchanges, the initiator's policy
trusts that the target name is accurate. trusts that the target name is accurate.
o The initiator trusts that its idea of the acceptor name correctly o The initiator trusts that its idea of the acceptor name correctly
names the entity it is communicating with. names the entity it is communicating with.
skipping to change at page 26, line 12 skipping to change at page 26, line 12
would return. (Otherwise, the IdP might as well make the query to would return. (Otherwise, the IdP might as well make the query to
the attribute authority and then resign it.) the attribute authority and then resign it.)
5. Privacy Considerations 5. Privacy Considerations
Sharing identity information raises privacy violations and as Sharing identity information raises privacy violations and as
described throughout this document an existing architecture is re- described throughout this document an existing architecture is re-
used for a different usage environment. As such, a discussion about used for a different usage environment. As such, a discussion about
the privacy properties has to take these pre-conditions into the privacy properties has to take these pre-conditions into
consideration. We use the approach suggested in consideration. We use the approach suggested in
[I-D.morris-privacy-considerations] to shed light into what data is [I-D.iab-privacy-considerations] to shed light into what data is
collected and used by which entity, what the relationship between collected and used by which entity, what the relationship between
these entities and the end user is, what data about the user is these entities and the end user is, what data about the user is
likely needed to be collected, and what the identification level of likely needed to be collected, and what the identification level of
the data is. the data is.
5.1. What entities collect and use data? 5.1. What Entities collect and use Data?
Figure 2 shows the architecture with the involved entities. Message Figure 2 shows the architecture with the involved entities. Message
exchanges are exchanged between the client application, via the exchanges are exchanged between the client application, via the
relying part to the AAA server. There will likely be intermediaries relying part to the AAA server. There will likely be intermediaries
between the relying party and the AAA server, labeled generically as between the relying party and the AAA server, labeled generically as
"federation". "federation".
In order for the relying party to route messages to the AAA server it In order for the relying party to route messages to the AAA server it
is necessary for the client application to provide enough information is necessary for the client application to provide enough information
to enable the identification of the AAA server's domain. While often to enable the identification of the AAA server's domain. While often
skipping to change at page 30, line 7 skipping to change at page 30, line 7
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.
7. Security Considerations 7. Security Considerations
This entire document is about security. A future version of the This document describes the architecture for Application Bridging for
document will highlight some important security concepts. Federated Access Beyond Web (ABFAB) and security is therefore the
main focus. This section highlights the main communication channels
and their security properties:
Client-to-RP Channel:
This communication channel is secured by TLS executed between the
client and the RP. The channel binding material is provided by
any certificates and the final message (i.e., a cryptographic
token for the channel). Authentication may be provided by the RP
to the client but a deployment without authentication at the TLS
layer is possible as well. In addition, there is a channel
between the GSS requestor and the GSS acceptor, but the keying
material is provided by a "third party" to both entities. The
client can derive keying material locally, but the RP gets the
material from the IdP. There is no cryptographic binding on this
channel until the EAP processing has finished and the MSK is
transferred from the IdP to the RP.
RP-to-IdP Channel:
The security of this communication channel is mainly provided by
the functionality offered via RADIUS and Diameter. At the time of
writing there are no end-to-end security mechanisms standardized
and thereby the architecture has to rely on hop-by-hop security
with trusted AAA entities or, as an alternative but possible
deployment variant, direct communication between the AAA client to
the AAA server. Note that the authorization result the IdP
provides to the RP in the form of a SAML assertion may, however,
be protected such that the SAML related components are secured
end-to-end.
Client-to-IdP Channel:
This communication interaction is accomplished with the help of
EAP and EAP methods. The offered security protection will depend
on the EAP method that is chosen but a minimum requirement fis to
offer mutual authentication, and key derivation. The IdP is
responsible during this process to determine that the RP that is
communication to the client over the RP-to-IdP channel is the same
one talking to the IdP. This is accomplished via the EAP channel
binding.
8. IANA Considerations 8. IANA Considerations
This document does not require actions by IANA. This document does not require actions by IANA.
9. Acknowledgments 9. Acknowledgments
We would like to thank Mayutan Arumaithurai and Klaas Wierenga for We would like to thank Mayutan Arumaithurai and Klaas Wierenga for
their feedback. Additionally, we would like to thank Eve Maler, their feedback. Additionally, we would like to thank Eve Maler,
Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, and Luke Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, and Luke
Howard for their feedback on the federation terminology question. Howard for their feedback on the federation terminology question.
Furthermore, we would like to thank Klaas Wierenga for his review of Furthermore, we would like to thank Klaas Wierenga for his review of
the pre-00 draft version. the pre-00 draft version.
We would like to thank Jim Schaad for his detailed review of the -00
working group draft version.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2743] Linn, J., "Generic Security Service Application Program [RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", "Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000. RFC 2865, June 2000.
skipping to change at page 33, line 34 skipping to change at page 33, line 34
Dial In User Service) Support For Extensible Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003. Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072, Authentication Protocol (EAP) Application", RFC 4072,
August 2005. August 2005.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005. Network Access Identifier", RFC 4282, December 2005.
[I-D.hansen-privacy-terminology] [I-D.iab-privacy-terminology]
Hansen, M. and H. Tschofenig, "Terminology for Talking Hansen, M., Tschofenig, H., and R. Smith, "Privacy
about Privacy by Data Minimization: Anonymity, Terminology", draft-iab-privacy-terminology-00 (work in
Unlinkability, Undetectability, Unobservability, progress), January 2012.
Pseudonymity, and Identity Management",
draft-hansen-privacy-terminology-02 (work in progress),
March 2011.
[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-02 (work in progress), July 2011. draft-ietf-abfab-gss-eap-05 (work in progress),
March 2012.
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, "A Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A
Flexible Authentication Framework for the Transport Layer Flexible Authentication Framework for the Transport Layer
Security (TLS) Protocol using the Extensible Security (TLS) Protocol using the Extensible
Authentication Protocol (EAP)", draft-nir-tls-eap-12 (work Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work
in progress), June 2011. in progress), December 2011.
[I-D.ietf-oauth-v2] [I-D.ietf-oauth-v2]
Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Protocol", draft-ietf-oauth-v2-20 (work 2.0 Authorization Protocol", draft-ietf-oauth-v2-25 (work
in progress), July 2011. in progress), March 2012.
[I-D.morris-privacy-considerations] [I-D.iab-privacy-considerations]
Aboba, B., Morris, J., Peterson, J., and H. Tschofenig, Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., and
"Privacy Considerations for Internet Protocols", J. Morris, "Privacy Considerations for Internet
draft-morris-privacy-considerations-03 (work in progress), Protocols", draft-iab-privacy-considerations-01 (work in
March 2011. progress), October 2011.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible [RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005. Wireless LANs", RFC 4017, March 2005.
[RFC5106] Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y., [RFC5106] Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y.,
and F. Bersani, "The Extensible Authentication Protocol- and F. Bersani, "The Extensible Authentication Protocol-
Internet Key Exchange Protocol version 2 (EAP-IKEv2) Internet Key Exchange Protocol version 2 (EAP-IKEv2)
Method", RFC 5106, February 2008. Method", RFC 5106, February 2008.
 End of changes. 51 change blocks. 
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