< draft-ietf-abfab-arch-03.txt   draft-ietf-abfab-arch-04.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 10, 2013 Painless Security Expires: April 25, 2013 Painless Security
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
E. Lear E. Lear
Cisco Systems GmbH Cisco Systems GmbH
J. Schaad J. Schaad
Soaring Hawk Consulting Soaring Hawk Consulting
July 9, 2012 October 22, 2012
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-ietf-abfab-arch-03.txt draft-ietf-abfab-arch-04.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
skipping to change at page 2, line 7 skipping to change at page 2, line 7
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 10, 2013. This Internet-Draft will expire on April 25, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 10 skipping to change at page 3, line 10
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . 6 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 6
1.3. Challenges to Contemporary Federation . . . . . . . . . . 9 1.3. Challenges for Contemporary Federation . . . . . . . . . . 9
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 9 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 10
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 12 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 13
1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 13 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.7. Use of GSS-API . . . . . . . . . . . . . . . . . . . . . . 14 2.1. Relying Party to Identity Provider . . . . . . . . . . . . 15
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . . 16
2.1. Relying Party to Identity Provider . . . . . . . . . . . . 16 2.1.2. Discovery and Rules Determination . . . . . . . . . . 17
2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . . 17 2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 18
2.1.2. Discovery and Rules Determination . . . . . . . . . . 18
2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19
2.1.4. SAML Assertions . . . . . . . . . . . . . . . . . . . 20 2.1.4. SAML Assertions . . . . . . . . . . . . . . . . . . . 20
2.2. Client To Identity Provider . . . . . . . . . . . . . . . 22 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 21
2.2.1. Extensible Authentication Protocol (EAP) . . . . . . . 22 2.2.1. Extensible Authentication Protocol (EAP) . . . . . . . 21
2.2.2. Channel Binding . . . . . . . . . . . . . . . . . . . 23 2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 23
2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 23 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 23
2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 24 2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . . 25 2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . . 25
3. Application Security Services . . . . . . . . . . . . . . . . 26 3. Application Security Services . . . . . . . . . . . . . . . . 26
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 26 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 26
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 27 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 27
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 28 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 28
3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 29 3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 29
4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 30 4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 30
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 31 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 31
5.1. What Entities collect and use Data? . . . . . . . . . . . 31 5.1. Entities and their roles . . . . . . . . . . . . . . . . . 31
5.2. Relationship between User's and other Entities . . . . . . 32 5.2. Relationship between user and entities . . . . . . . . . . 32
5.3. What Data about the User is likely Needed to be 5.3. Data and Identifiers in use . . . . . . . . . . . . . . . 32
Collected? . . . . . . . . . . . . . . . . . . . . . . . . 32 5.3.1. NAI . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4. What is the Identification Level of the Data? . . . . . . 32 5.3.2. Identity Information . . . . . . . . . . . . . . . . . 33
5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 33 5.3.3. Accounting Information . . . . . . . . . . . . . . . . 33
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 34 5.3.4. Collection and retention of data and identifiers . . . 33
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 34 5.4. User Participation . . . . . . . . . . . . . . . . . . . . 34
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 34 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . . . 35 6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 35
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 35
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38 7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . . 39 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
10.1. Normative References . . . . . . . . . . . . . . . . . . . 40
10.2. Informative References . . . . . . . . . . . . . . . . . . 40 10.2. Informative References . . . . . . . . . . . . . . . . . . 40
Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . . Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . .
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction 1. Introduction
The Internet uses numerous security mechanisms to manage access to The Internet uses numerous security mechanisms to manage access to
various resources. These mechanisms have been generalized and scaled various resources. These mechanisms have been generalized and scaled
over the last decade through mechanisms such as Simple Authentication over the last decade through mechanisms such as Simple Authentication
and Security Layer (SASL) with the Generic Security Server and Security Layer (SASL) with the Generic Security Server
Application Program Interface (GSS-API) (known as the GS2 family) Application Program Interface (GSS-API) (known as the GS2 family)
[RFC5801], Security Assertion Markup Language (SAML) [RFC5801], Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os], RADIUS [RFC2865], and Diameter [RFC3588]. [OASIS.saml-core-2.0-os], and the Authentication, Authorization, and
Accounting (AAA) architecture as embodied in RADIUS [RFC2865] and
Diameter [RFC3588].
A Relying Party (RP) is the entity that manages access to some A Relying Party (RP) is the entity that manages access to some
resource. The actor that is requesting access to that resource is resource. The actor that is requesting access to that resource is
often described as the Subject. Many security mechanisms are often described as the Client. Many security mechanisms are
manifested as an exchange of information between these actors. The manifested as an exchange of information between these actors. The
RP is therefore able to decide whether the Subject is authorised, or RP is therefore able to decide whether the Client is authorized, or
not. not.
Some security mechanisms allow the RP to delegate aspects of the Some security mechanisms allow the RP to delegate aspects of the
access management decision to an actor called the Identity Provider access management decision to an actor called the Identity Provider
(IdP). This delegation requires technical signaling, trust and a (IdP). This delegation requires technical signaling, trust and a
common understanding of semantics between the RP and IdP. These common understanding of semantics between the RP and IdP. These
aspects are generally managed within a relationship known as a aspects are generally managed within a relationship known as a
'federation'. This style of access management is accordingly 'federation'. This style of access management is accordingly
described as 'federated access management'. described as 'federated access management'.
Federated access management has evolved over the last decade through Federated access management has evolved over the last decade through
such standards as SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth specifications like SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth
[RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits [RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits
of federated access management include: of federated access management include:
Single or Simplified sign-on: Single or Simplified sign-on:
An Internet service can delegate access management, and the An Internet service can delegate access management, and the
associated responsibilities such as identity management and associated responsibilities such as identity management and
credentialing, to an organisation that already has a long-term credentialing, to an organisation that already has a long-term
relationship with the Subject. This is often attractive for relationship with the Subject. This is often attractive for
Relying Parties who frequently do not want these responsibilities. Relying Parties who frequently do not want these responsibilities.
The Subject also requires fewer credentials, which is also The Subject also requires fewer credentials, which is also
desirable. desirable.
Privacy: Data Minimization and User Participation:
Often a Relying Party does not need to know the identity of a Often a Relying Party does not need to know the identity of a
Subject to reach an access management decision. It is frequently Subject to reach an access management decision. It is frequently
only necessary for the Relying Party know specific attributes only necessary for the Relying Party know specific attributes
about the subject, for example, that the Subject is affiliated about the subject, for example, that the Subject is affiliated
with a particular organisation or has a certain role or with a particular organisation or has a certain role or
entitlement. Sometimes the RP does not need to know the identity entitlement. Sometimes the RP only needs to know a pseudonym of
of the Subject, but does require a unique identifier for the the Subject.
Subject (for example, so that it can recognise the Subject
subsequently); in this case, it is a common practise for the IdP Prior to the release of attributes to the IdP from the IdP, the
to only release a pseudonym that is specific to that particular IdP will check configuration and policy to determine if the
Relying Party. Federated access management therefore provides attributes are to be released. There is currently no direct
various strategies for protecting the Subject's privacy. Other client participation in this decision.
privacy aspects typically of concern are the policy for releasing
personal data about the Subject from the IdP to the RP, the
purpose of the usage, the retention period of the 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 than an affiliation or a 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 supply this information, either on request by the RP or the IdP to supply this information, either on request by the RP or
unsolicited. unsolicited.
This memo describes the Application Bridging for Federated Access This memo describes the Application Bridging for Federated Access
Beyond the Web (ABFAB) architecture. This architecture makes use of Beyond the Web (ABFAB) architecture. This architecture makes use of
extensions to the commonly used security mechanisms for both extensions to the commonly used security mechanisms for both
federated and non-federated access management, including the RADIUS federated and non-federated access management, including the RADIUS
and the Diameter protocol, the Generic Security Service (GSS), the and the Diameter protocols, the Generic Security Service (GSS), the
GS2 family, the Extensible Authentication Protocol (EAP) and SAML. GS2 family, the Extensible Authentication Protocol (EAP) and SAML.
The architecture addresses the problem of federated access management The architecture addresses the problem of federated access management
to primarily non-web-based services, in a manner that will scale to primarily for non-web-based services. It does so in a manner that
large numbers of identity providers, relying parties, and will scale to large numbers of identity providers, relying parties,
federations. and federations.
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.iab-privacy-terminology]. In particular, this document uses the [I-D.iab-privacy-considerations]. In particular, this document uses
terms identity provider, relying party, (data) subject, identifier, the terms identity provider, relying party, (data) subject,
pseudonymity, unlinkability, and anonymity. identifier, pseudonymity, unlinkability, and anonymity.
In this architecture the IdP consists of the following components: an In this architecture the IdP consists of the following components: an
EAP server, a RADIUS or a Diameter server, and optionally a SAML EAP server, a RADIUS or a Diameter server, and optionally a SAML
Assertion service. Assertion service.
This document uses the term Network Access Identifier (NAI), as This document uses the term Network Access Identifier (NAI), as
defined in [RFC4282]. defined in [RFC4282]. An NAI consists of a realm identifier, which
is associated with an IdP and a username which is associated with a
specific client of the IdP.
One of the problems people will find with reading this document is One of the problems people will find with reading this document is
that the terminology sometimes appears to be inconsistent. This is that the terminology sometimes appears to be inconsistent. This is
due the fact that the terms used by the different standards we are due the fact that the terms used by the different standards we are
picking up don't use the same terms. In general the document uses picking up don't use the same terms. In general the document uses
either a consistent term or the term associated with the standard either a consistent term or the term associated with the standard
under discussion as appropriate. For reference we include this table under discussion as appropriate. For reference we include this table
which maps the different terms into a single table. which maps the different terms into a single table.
+----------+------------+-------------------+-----------------------+ +----------+-----------+--------------------+-----------------------+
| Protocol | Subject | Relying Party | Identity Provider | | Protocol | Subject | Relying Party | Identity Provider |
+----------+------------+-------------------+-----------------------+ +----------+-----------+--------------------+-----------------------+
| ABFAB | Subject | Relying Party | Identity Provider | | ABFAB | Client | Relying Party (RP) | Identity Provider |
| | | (RP) | (IdP) | | | | | (IdP) |
| | | | | | | | | |
| | Principal | | | | | Initiator | Acceptor | |
| | | | | | | | | |
| | Client | | | | SAML | Subject | Service Provider | Issuer |
| | | | | | | | | |
| SAML | Subject | Service Provider | Issuer | | GSS-API | Initiator | Acceptor | |
| | | | | | | | | |
| GSS-API | Initiator | Acceptor | | | EAP | EAP peer | | EAP server |
| | | | | | | | | |
| EAP | EAP client | | EAP server | | AAA | | AAA Client | AAA server |
| | | | | | | | | |
| | EAP peer | | | | RADIUS | user | NAS | RADIUS server |
| | | | | | | | | |
| SASL | | | | | | | RADIUS client | |
| | | | | +----------+-----------+--------------------+-----------------------+
| AAA | | AAA Client | AAA server |
| | | | |
| RADIUS | client | NAS | RADIUS server |
+----------+------------+-------------------+-----------------------+
Note that in some cases a cell has been left empty, in these cases Note that in some cases a cell has been left empty, in these cases
there is no direct name that represents this concept. there is no direct name that represents this concept.
Note to reviewers - I have most likely missed some entries in the Note to reviewers - I have most likely missed some entries in the
table. Please provide me with both correct names from the protocol table. Please provide me with both correct names from the protocol
and missing names that are used in the text below. and missing names that are used in the text below.
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 Client,
o the Identity Provider, and o the Identity Provider, and
o the Relying Party. o the Relying Party.
One additional actor in can be an Individual. An individual is a
human being that is using a client. Individuals may or may not exist
in any given deployment. The client may be either a front end on an
individual or an independent automated entity.
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 |
`----------' '---------' `----------' '---------'
< <
\ \
\ Authentication \ Authentication
\
\ \
\ \
\ \
\ \ +---------+
\ +---------+ \ | | O
\ | | O v| Client | \|/ Individual
v| Client | \|/ Principal | | |
| | | +---------+ / \
+---------+ / \
Figure 1: Entities and their Relationships Figure 1: Entities and their Relationships
The relationships between the entities in Figure 1 are:
Federation
The Identity Provider and the Relying Parties are part of a
Federation. The relationship may be direct (they have an explicit
trust relationship) or transitive (the trust releationship is
mediated by one or more entities). The federation relationship is
governed by a federation agreement. Within a single federation,
there may be multiple Identity Providers as well as multiple
Relying Parties. A federation is governed by a federation
agreement.
Authentication
There is a direct relationship between the Client and the Identity
Provider by which the entities trust and can securely authenticate
each other.
A federation agreement typically encompasses operational A federation agreement typically encompasses operational
specifications and legal rules: specifications and legal rules:
Operational Specifications: Operational Specifications:
These includes the technical specifications (e.g. protocols used These includes the technical specifications (e.g. protocols used
to communicate between the three parties), process standards, to 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
audit criteria, etc. The goal of operational specifications is to audit criteria, etc. The goal of operational specifications is to
provide enough definition that the system works and provide enough definition that the system works and
interoperability is possible. interoperability is possible.
Legal Rules: Legal Rules:
The legal rules takes the legal framework into consideration and The legal rules take the legal framework into consideration and
provides contractual obligations for each entity, defines the provides contractual obligations for each entity. The rules
responsibilities and provides further clarification of the define the responsibilities of each party and provide further
operational specifications. These legal rules regulate the clarification of the operational specifications. These legal
operational specifications, make operational specifications rules regulate the operational specifications, make operational
legally binding to the participants, define and govern the rights specifications legally binding to the participants, define and
and responsibilities of the participants. The legal rules may, govern the rights and responsibilities of the participants. The
for example, describe liability for losses, termination rights, legal rules may, for example, describe liability for losses,
enforcement mechanisms, measures of damage, dispute resolution, termination rights, enforcement mechanisms, measures of damage,
warranties, etc. dispute resolution, warranties, etc.
The Operational Specifications can demand the usage of a
sophisticated technical infrastructure, including requirements on the
message routing intermediaries, to offer the required technical
functionality. In other environments, the Operational Specifications
require fewer technical components in order to meet the required
technical functionality.
The Legal Rules include many non-technical aspects of federation,
such as business practices and legal arrangements, which are outside
the scope of the IETF. The Legal Rules can still have an impact the
architectural setup or on how to ensure the dynamic establishment of
trust.
While a federation agreement is often discussed within the context of
formal relationships, such as between an enterprise and an employee
or a government and a citizen, a federation agreement does not have
to require any particular level of formality. For an IdP and a
Client, it is sufficient for a relationship to be established by
something as simple as using a web form and confirmation email. For
an IdP and an RP, it is sufficient for the IdP to publish contact
information along with a public key and for the RP to use that data.
With in the framework of ABFAB, it will generally be required that a
mechanism exists for the IdP to be able to trust the identity of the
RP, if this is not present then the IdP cannot provide the assurances
to the client that the identity of the RP has been established.
The nature of federation dictates that there is some form of The nature of federation dictates that there is some form of
relationship between the identity provider and the relying party. relationship between the identity provider and the relying party.
This is particularly important when the relying party wants to use This is particularly important when the relying party wants to use
information obtained from the identity provider for access management information obtained from the identity provider for access management
decisions and when the identity provider does not want to release decisions and when the identity provider does not want to release
information to every relying party (or only under certain information to every relying party (or only under certain
conditions). conditions).
While it is possible to have a bilateral agreement between every IdP While it is possible to have a bilateral agreement between every IdP
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 The IdP will typically have a long-term relationship with the Client.
business practices and legal arrangements, are outside the scope of This relationship typically involves the IdP positively identifying
the IETF, they still impact the architectural setup on how to ensure and credentialing the Client (for example, at time of employment
the dynamic establishment of trust. within an organization). The relationship will often be instantiated
within an agreement between the IdP and the Client (for example,
Some deployments demand the deployment of sophisticated technical within an employment contract or terms of use that stipulates the
infrastructure, including message routing intermediaries, to offer appropriate use of credentials and so forth).
the required technical functionality. In other deployments fewer
technical components are needed.
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 credentialing 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 formal
relationships, such as between an enterprise and an employee or a
government and a citizen, federation does not in require any
particular level of formality. For an IdP and a subject, it is
entirely compatible with a relationship between the IdP and Subject
that is only Requiems completing a web form and confirming the
verification email. For an IdP and an RP, it is entirely compatible
with the IdP publishing a usage point and the RP using that data.
However, the nature and quality of the relationship between the The nature and quality of the relationship between the Subject and
Subject and the IdP is an important contributor to the level of trust the IdP is an important contributor to the level of trust that an RP
that an RP may attribute to an assertion describing a Subject made by may attribute to an assertion describing a Client made by an IdP.
an IdP. This is sometimes described as the Level of Assurance. This is sometimes described as the Level of Assurance.
Federation does not imposes requirement of an a priori relationship Federation does not require an a priori relationship or a long-term
or a long-term relationship between the RP and the Subject. This is relationship between the RP and the Client; it is this property of
a property of federation that yields many of its benefits. However, federation that yields many of its benefits. However, federation
federation does not preclude the possibility of a pre-existing does not preclude the possibility of a pre-existing relationship
relationship existing between the RP and the Subject, nor that they between the RP and the Client, nor that they may use the introduction
may use the introduction to create a new long-term relationship to create a new long-term relationship independent of the federation.
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 Client and in might indeed be an Individual behind the Client and in other cases
other cases there is no human involved in the actual protocol the Client may be autonomous.
execution.
1.3. Challenges to Contemporary Federation 1.3. Challenges for Contemporary Federation
As the number of federated services has proliferated, the role of the As the number of federated services has proliferated, the role of the
individual can become ambiguous in certain circumstances. For individual can become ambiguous in certain circumstances. For
example, a school might provide online access for a student's grades example, a school might provide online access for a student's grades
to their parents for review, and to the student's teacher for to their parents for review, and to the student's teacher for
modification. A teacher who is also a parent must clearly modification. A teacher who is also a parent must clearly
distinguish her role upon access. distinguish her 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(s) a user increasingly difficult to discover which identity provider(s) a user
is associated with. This is true for both the web and non-web case, is associated with. This is true for both the web and non-web case,
but is particularly acute for the latter as many non-web but is particularly acute for the latter as many non-web
authentication systems are not semantically rich enough on their own authentication systems are not semantically rich enough on their own
to allow for such ambiguities. For instance, in the case of an email to allow for such ambiguities. For instance, in the case of an email
provider, the use of SMTP and IMAP protocols does not on its own provider, the use of SMTP and IMAP protocols do not have the ability
provide for a way to select a federation. However, the building for the server to get additional information, beyond the clients NAI,
blocks do exist to add this functionality. in order to provide additional input to decide between multiple
federations it may be associated with. However, the building 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 in an ABFAB federated authentication/authorization In this example, a client is attempting to connect to a server in
exchange are as follows: order to either get access to some data or perform some type of
transaction. In order for the client to mutually authenticate with
the server, the following steps are taken in an ABFAB federated
architecture:
1. Principal provides an NAI to Application: The client application 1. Client Configuration: The Client Application is configured with
is configured with an NAI. The provided name contains, at a an NAI assigned by the IdP. It is also configured with any
minimum, the realm of an NAI. The realm represents the IdP to keys, certificates, passwords or other secret and public
be discovered. information needed to run the EAP protocols between it and the
IdP.
2. Authentication mechanism selection: The GSS-EAP SASL/GS2 2. Authentication mechanism selection: The GSS-EAP GSS-API
mechanism is selected for authentication/authorization. mechanism is selected for authentication/authorization.
3. Client Application provides the NAI to RP: The client 3. Client provides an NAI to RP: The client application sets up a
application setups a transport to the RP and begins the GSS-EAP transport to the RP and begins the GSS-EAP authentication. In
authentication. The RP initiates the EAP protocol to the client response, the RP sends an EAP request message (nested in the
application, and the client provides the NAI to the RP in the GSS-EAP protocol) asking for the Client's name. The Client
form of the EAP response. sends an EAP response with an NAI name form that at a minimum,
contains the realm portion of it's full NAI.
4. Discovery of federated IdP: The RP uses pre-configured 4. Discovery of federated IdP: The RP uses pre-configured
information or a federation proxy to determine what IdP to use information or a federation proxy to determine what IdP to use
based on policy and the provided NAI. This is discussed in based on policy and the realm portion of the provided Client
detail below (Section 2.1.2). NAI. This is discussed in detail below (Section 2.1.2).
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 send a RADIUS/Diameter request to the is, it (or its agent) will send a RADIUS/Diameter request to the
IdP. The RADIUS/Diameter access request encapsulates the EAP IdP. The RADIUS/Diameter access request encapsulates the EAP
response. At this stage, the RP will likely have no idea who response. At this stage, the RP will likely have no idea who
the client is. The RP claims its identity to the IdP in AAA the client is. The RP sends its identity to the IdP in AAA
attributes, and it may contain a SAML Attribute Requests in a attributes, and it may send a SAML Attribute Requests in a AAA
AAA attribute. attribute. The AAA network checks that the identity claimed by
the RP is valid.
6. IdP informs the client of which EAP method to use: The available 6. IdP begins EAP with the client: The IdP sends an EAP message to
and appropriate methods are discussed below in this the client with an EAP method to be run. The IdP may re-request
memo.[anchor4] the clients name in this message, but this is unexpected
behavior. The available and appropriate methods are discussed
below in this memo (Section 2.2.1).
7. The EAP protocol is run: A bunch of EAP messages are passed 7. The EAP protocol is run: A bunch of EAP messages are passed
between the EAP peer and the EAP server, i.e., the client and between the client (EAP peer) and the IdP (EAP server), until
the IdP in our identity management terminology, until the result the result of the authentication protocol is determined. The
of the authentication protocol is determined. The number and number and content of those messages depends on the EAP method
content of those messages will depend on the EAP method. If the selected. If the IdP is unable to authenticate the client, the
IdP is unable to authenticate the client, the process concludes IdP sends a EAP failure message to the RP. As part of the EAP
here. As part of the EAP protocol, the client will create a protocol, the client sends a channel bindings EAP message to the
channel bindings message to the IdP identifying, among other IdP (Section 2.2.2). In the channel binding message the client
things, the RP to which it is attempting to authenticate. The identifies, among other things, the RP to which it is attempting
IdP checks the channel binding data from the client with that to authenticate. The IdP checks the channel binding data from
provided by the RP via the AAA protocol. If the bindings do not the client with that provided by the RP via the AAA protocol.
match the IdP fails the EAP protocol. If the bindings do not match the IdP sends an EAP failure
message to the RP.
8. Successful Authentication: The IdP (its EAP server) and EAP peer 8. Successful EAP Authentication: At this point, the IdP (EAP
/ subject have mutually authenticated each other. As a result server) and client (EAP peer) have mutually authenticated each
of this step, the subject and the IdP hold two cryptographic other. As a result, the subject and the IdP hold two
keys- a Master Session Key (MSK), and an Extended MSK (EMSK). cryptographic keys: a Master Session Key (MSK), and an Extended
There is some confidence that the RP is the one the client is MSK (EMSK). At this point the client has a level of assurance
communicating with as the channel binding data validated. This about the identity of the RP based on the name checking the IdP
allows for a claim of authentication for the RP to the client. has done using the RP naming information from the AAA framework
and from the client (by the channel binding data).
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 subject are authorized policy to determine whether the RP and client are authorized for
for a given transaction/service, and if so, what if any, a given transaction/service, and if so, what if any, attributes
attributes will be released to the RP. The RP will have done will be released to the RP. If the IdP gets a policy failure,
its policy checks during the discovery process. it sends an EAP failure message to the RP.[anchor4] (The RP will
have done its policy checks during the discovery process.)
10. Response from the IdP to the Relying Party: Once the IdP has 10. IdP provide the RP with the MSK: The IdP sends a positive result
made a determination of whether and how to authenticate and EAP to the RP, along with an optional set of AAA attributes
authorize the client to the RP, it returns either a negative AAA associated with the client (usually as one or more SAML
result to the RP, or it returns a positive result to the RP, assertions). In addition, the EAP MSK is returned to the RP.
along with an optional set of AAA attributes associated with the
client (usually as one or more SAML assertions). In addition,
an EAP MSK is returned to the RP.
11. RP Processes Results: When the RP receives the result from the 11. RP Processes Results: When the RP receives the result from the
IdP, it should have enough information to either grant or refuse IdP, it should have enough information to either grant or refuse
a resource access request. It may have information that a resource access request. It may have information that
associates the client with specific authorization identities. associates the client with specific authorization identities.
If additional attributes are needed from the IdP the RP may make If additional attributes are needed from the IdP the RP may make
a new SAML Request to the IdP. It will apply these results in a new SAML Request to the IdP. It will apply these results in
an application-specific way. an application-specific way.
12. RP returns results to client: Once the RP has a response it must 12. RP returns results to client: Once the RP has a response it must
inform the client application of the result. If all has gone inform the client application of the result. If all has gone
well, all are authenticated, and the application proceeds with well, all are authenticated, and the application proceeds with
appropriate authorization levels. appropriate authorization levels. The client can now complete
the authentication of the RP by the use of the EAP MSK value.
An example communication flow is given below: An example communication flow is given below:
Relying Client Identity Relying Client Identity
Party App Provider Party App Provider
| (1) | Client App gets NAI (somehow) | (1) | Client Configuration
| | | | | |
|<-----(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 Client | |< - - (6) - -<| EAP method to Client
| | | | | |
| |< - - (7) - ->| EAP Exchange to authenticate | |< - - (7) - ->| EAP Exchange to authenticate
| | | Client | | | Client
| | | | | |
| | (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:
o Each party of a transaction will be authenticated, and the client o Each party of a transaction will be authenticated, although
will be authorized for access to a specific resource. perhaps not identified, and the client 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
keys. keys between clients and servers.
o The system will scale to large numbers of identity providers, o The system will scale to large numbers of identity providers,
relying parties, and users. relying parties, and users.
o The system will be designed primarily for non-Web-based o The system will be designed primarily for non-Web-based
authentication. authentication.
o The system will build upon existing standards, components, and o The system will build upon existing standards, components, and
operational practices. operational practices.
skipping to change at page 13, line 25 skipping to change at page 14, line 5
is hard and fraught with risk of cryptographic flaws. Achieving is hard and fraught 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.
1.6. Use of AAA
Interestingly, for network access authentication the usage of the AAA
framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
successful from a deployment point of view. To map the terminology
used in Figure 1 to the AAA framework the IdP corresponds to the AAA
server, the RP corresponds to the AAA client, and the technical
building blocks of a federation are AAA proxies, relays and redirect
agents (particularly if they are operated by third parties, such as
AAA brokers and clearing houses). The front-end, i.e. the end host
to AAA client communication, is in case of network access
authentication offered by link layer protocols that forward
authentication protocol exchanges back-and-forth. An example of a
large scale RADIUS-based federation is EDUROAM [2].
By using the AAA framework, ABFAB gets a lot of mileage as many of
the federation agreements already exist and merely need to be
expanded to cover the ABFAB additions. The AAA framework has already
addressed some of the problems outlined above. For example,
o It already needs a method of doing routing of requests based on a
domain.
o It already has an extensible architecture allowing for new
attributes to be defined and transported.
o Pre-existing relationships can be re-used.
1.7. Use of GSS-API
Expand here
2. Architecture 2. Architecture
We have already introduced the federated access architecture, with We have 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
did not expand on the specifics of providing support for non-Web 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 the relying party, the Although this architecture assumes updates to the relying party, the
client application and the Identity Provider, those changes are kept client application, and the Identity Provider, those changes are kept
at a minimum. A mechanism that can demonstrate deployment benefits at a minimum. A mechanism that can demonstrate deployment benefits
(based on ease of update of existing software, low implementation (based on ease of update of existing software, low implementation
effort, etc.) is preferred and there may be a need to specify effort, etc.) is preferred and there may be a need to specify
multiple mechanisms to support the range of different deployment multiple mechanisms to support the range of different deployment
scenarios. 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. A
Encapsulating EAP into the GSS-API also allows EAP to be used in 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].[anchor9] [I-D.nir-tls-eap].[anchor7]
The architecture consists of several building blocks, which is shown The architecture consists of several building blocks, which is shown
graphically in Figure 2. In the following sections, we discuss the graphically in Figure 2. In the following sections, we discuss the
data flow between each of the entities, the protocols used for that data flow between each of the entities, the protocols used for that
data flow and some of the trade-offs made in choosing the protocols. data flow and some of the trade-offs made in choosing the protocols.
+--------------+ +--------------+
| Identity | | Identity |
| Provider | | Provider |
| (IdP) | | (IdP) |
skipping to change at page 16, line 38 skipping to change at page 15, line 38
| | Application | | | | Application | |
| | Protocol | | | | Protocol | |
| |<================>| | | |<================>| |
+-------------+ +---------------+ +-------------+ +---------------+
Legend: Legend:
<****>: Client-to-IdP Exchange <****>: Client-to-IdP Exchange
<---->: Client-to-RP Exchange <---->: Client-to-RP Exchange
<oooo>: RP-to-IdP Exchange <oooo>: RP-to-IdP Exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunnelled <====>: Protocol through which GSS-API/GS2 exchanges are tunneled
Figure 2: ABFAB Protocol Instantiation Figure 2: ABFAB Protocol Instantiation
2.1. Relying Party to Identity Provider 2.1. Relying Party to Identity Provider
Communications between the Relying Part and the Identity Provider is Communications between the Relying Party and the Identity Provider is
done by the federation substrate. This communication channel is done by the federation substrate. This communication channel is
responsible for: responsible for:
o Establishing the trust relationship between the RP and the IdP. o Establishing the trust relationship between the RP and the IdP.
o Determining the Rules governing the relationship. o Determining the rules governing the relationship.
o Conveying packets between the RP and IdP.
o Providing the means of establishing a trust relationship between o Conveying EAP packets between the RP and IdP.
the RP and the client.
The ABFAB working group has chosen the AAA framework for the messages The ABFAB working group has chosen the AAA framework for the messages
transported between the RP and IdP. This allows for the standard AAA transported between the RP and IdP. This allows for the current AAA
framework to be used to establish the trust relationship between the protocols to be used to establish the trust relationship between the
RP and the IdP while allowing other newer routing mechanisms using RP and the IdP. Future protocols that support the same framework but
the same message format to be used in the future. The ABFAB protocol do different routing may be used in the future. There is currently
itself details the method of establishing the trust relationship an effort to setup a framework that creates a trusted point-to-point
between the RP and the client. channel on the fly. The ABFAB protocol itself details the method of
establishing the trust relationship between the RP and the client.
2.1.1. AAA, RADIUS and Diameter 2.1.1. AAA, RADIUS and Diameter
The IETF has defined a federation framework already with the Interestingly, for network access authentication the usage of the AAA
Authentication, Authorization and Accounting (AAA) framework framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
[RFC2903], [RFC2904]. Two implementations of the AAA framework exist successful from a deployment point of view. To map the terminology
in RADIUS [RFC2138] and Diameter [RFC3588] protocols. The existence used in Figure 1 to the AAA framework the IdP corresponds to the AAA
of these protocols allows us to re-use a pair of existing protocols server, the RP corresponds to the AAA client, and the technical
that have been widely deployed and are reasonable well understood. building blocks of a federation are AAA proxies, relays and redirect
These protocols are nicely designed so that they can carry additional agents (particularly if they are operated by third parties, such as
attributes with minimal changes to either the protocol or existing AAA brokers and clearing houses). The front-end, i.e. the end host
AAA servers. to AAA client communication, is in case of network access
authentication offered by link layer protocols that forward
authentication protocol exchanges back-and-forth. An example of a
large scale RADIUS-based federation is EDUROAM [2].
By using the AAA framework, ABFAB gets a lot of mileage as many of
the federation agreements already exist and merely need to be
expanded to cover the ABFAB additions. The AAA framework has already
addressed some of the problems outlined above. For example,
o It already has a method for routing requests based on a domain.
o It already has an extensible architecture allowing for new
attributes to be defined and transported.
o Pre-existing relationships can be re-used.
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? RADIUS and
difference is that today RADIUS is largely transported upon UDP, and Diameter are deployed in different environments. RADIUS can often be
its use is largely, though not exclusively, intra-domain. Diameter found in enterprise and university networks, and is also in use by
itself was designed to scale to broader uses. We leave as a fixed network operators. Diameter, on the other hand, is deployed by
deployment decision, which protocol will be appropriate. The mobile operators. Another key difference is that today RADIUS is
protocol defines all the necessary new AAA attributes as RADIUS largely transported upon UDP. We leave as a deployment decision,
attributes, this allows for the same structures and attributes to be which protocol will be appropriate. The protocol defines all the
used in both RADIUS and Diameter. We also note that there exist necessary new AAA attributes as RADIUS attributes. A future document
proxies which convert from RADIUS to Diameter and back. This makes would defined the same AAA attributes for a Diameter environment. We
it possible for both to be deployed in a single federation substrate. also note that there exist proxies which convert from RADIUS to
Diameter and back. This makes it possible for both to be deployed in
a single federation substrate.
Through the integrity protection mechanisms in the AAA framework, the Through the integrity protection mechanisms in the AAA framework, the
identity provider can establish technical trust that messages are identity provider can establish technical trust that messages are
being sent by the appropriate relying party. Any given interaction being sent by the appropriate relying party. Any given interaction
will be associated with one federation at the policy level. The will be associated with one federation at the policy level. The
legal or business relationship defines what statements the identity legal or business relationship defines what statements the identity
provider is trusted to make and how these statements are interpreted provider is trusted to make and how these statements are interpreted
by the relying party. The AAA framework also permits the relying by the relying party. The AAA framework also permits the relying
party or elements between the relying party and identity provider to party or elements between the relying party and identity provider to
make statements about the relying party. make statements about the relying party.
skipping to change at page 18, line 50 skipping to change at page 18, line 17
exchange. One of these is whether the given RP is permitted to talk 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 to the IdP using a given federation at all, so rules determination
encompasses the basic authorization decision. Other factors are encompasses the basic authorization decision. Other factors are
included, such as what policies govern release of information about 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 the principal to the RP and what policies govern the RP's use of this
information. While rules determination is ultimately a business information. While rules determination is ultimately a business
function, it has significant impact on the technical exchanges. The function, it has significant impact on the technical exchanges. The
protocols need to communicate the result of authorization. When protocols need to communicate the result of authorization. When
multiple sets of rules are possible, the protocol must disambiguate multiple sets of rules are possible, the protocol must disambiguate
which set of rules are in play. Some rules have technical which set of rules are in play. Some rules have technical
enforcement mechanisms; for example in some federations intermediates enforcement mechanisms; for example in some federations
validate information that is being communicated within the intermediaries validate information that is being communicated within
federation. the federation.
ABFAB has not formally defined any part of discovery at this point. ABFAB has not formally defined any part of discovery at this point.
The process of specifying and evaluating the business rules and The process of specifying and evaluating the business rules and
technical policies is too complex to provide a simple framework. technical policies is too complex to provide a simple framework.
There is not currently a way to know if a AAA proxy is able to There is not currently a way to know if a AAA proxy is able to
communicate with a specific IdP, although this may change with some communicate with a specific IdP, although this may change with some
of the routing protocols that are being considered. At the present of the routing protocols that are being considered. At the present
time, the discovery process is going to be a manual configuration time, the discovery process is going to be a manual configuration
process. process.
2.1.3. Routing and Technical Trust 2.1.3. Routing and Technical Trust
Several approaches to having messages routed through the federation Several approaches to having messages routed through the federation
substrate are possible. These routing methods can most easily be substrate are possible. These routing methods can most easily be
classified based on the mechanism for technical trust that is used. classified based on the mechanism for technical trust that is used.
The choice of technical trust mechanism constrains how rules The choice of technical trust mechanism constrains how rules
determination is implemented. Regardless of what deployment strategy determination is implemented. Regardless of what deployment strategy
is chosen, it is important that the technical trust mechanism is chosen, it is important that the technical trust mechanism be able
constrain the names of both parties to the exchange. The trust to validate the names of both parties to the exchange. The trust
mechanism ought to ensure that the entity acting as IdP for a given mechanism must to ensure that the entity acting as IdP for a given
NAI is permitted to be the IdP for that realm, and that any service NAI is permitted to be the IdP for that realm, and that any service
name claimed by the RP is permitted to be claimed by that entity. name claimed by the RP is permitted to be claimed by that entity.
Here are the categories of technical trust determination: Here are the categories of technical trust determination:
AAA Proxy: AAA Proxy:
The simplest model is that an RP supports a request directly to an 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 AAA proxy. The hop-by-hop integrity protection of the AAA fabric
provides technical trust. An RP can submit a request directly to provides technical trust. An RP can submit a request directly to
a federation. Alternatively, a federation disambiguation fabric a federation. Alternatively, a federation disambiguation fabric
can be used. Such a fabric takes information about what can be used. Such a fabric takes information about what
federations the RP is part of and what federations the IdP is part federations the RP is part of and what federations the IdP is part
of and routes a message to the appropriate federation. The of and routes a message to the appropriate federation. The
routing of messages across the fabric plus attributes added to routing of messages across the fabric plus attributes added to
requests and responses provides rules determination. For example, requests and responses provides rules determination. For example,
when a disambiguation fabric routes a message to a given when a disambiguation fabric routes a message to a given
federation, that federation's rules are chosen. Naming is federation, that federation's rules are chosen. Name validation
enforced as messages travel across the fabric. The entities near is enforced as messages travel across the fabric. The entities
the RP confirm its identity and validate names it claims. The near the RP confirm its identity and validate names it claims.
fabric routes the message towards the appropriate IdP, validating The fabric routes the message towards the appropriate IdP,
the IdP's name in the process. The routing can be statically validating the IdP's name in the process. The routing can be
configured. Alternatively a routing protocol could be developed statically configured. Alternatively a routing protocol could be
to exchange reachability information about given IdPs and to apply developed to exchange reachability information about given IdPs
policy across the AAA fabric. Such a routing protocol could flood and to apply policy across the AAA fabric. Such a routing
naming constraints to the appropriate points in the fabric. protocol could flood naming constraints to the appropriate points
in the fabric.
Trust Broker: Trust Broker:
Instead of routing messages through AAA proxies, some trust broker Instead of routing messages through AAA proxies, some trust broker
could establish keys between entities near the RP and entities could establish keys between entities near the RP and entities
near the IdP. The advantage of this approach is efficiency of near the IdP. The advantage of this approach is efficiency of
message handling. Fewer entities are needed to be involved for message handling. Fewer entities are needed to be involved for
each message. Security may be improved by sending individual each message. Security may be improved by sending individual
messages over fewer hops. Rules determination involves decisions messages over fewer hops. Rules determination involves decisions
made by trust brokers about what keys to grant. Also, associated made by trust brokers about what keys to grant. Also, associated
with each credential is context about rules and about other with each credential is context about rules and about other
skipping to change at page 21, line 17 skipping to change at page 20, line 31
was designed in order to carry an extensible set of attributes about was designed in order to carry an extensible set of attributes about
a subject. Since SAML is extensible in the attribute space, ABFAB a subject. Since SAML is extensible in the attribute space, ABFAB
has no immediate needs to update the core SAML specifications for our has no immediate needs to update the core SAML specifications for our
work. It will be necessary to update IdPs that need to return SAML work. It will be necessary to update IdPs that need to return SAML
assertions to IdPs and for both the IdP and the RP to implement a new assertions to IdPs and for both the IdP and the RP to implement a new
SAML profile designed to carry SAML assertions in AAA. The new SAML profile designed to carry SAML assertions in AAA. The new
profile can be found in RFCXXXX [I-D.ietf-abfab-aaa-saml]. profile can be found in RFCXXXX [I-D.ietf-abfab-aaa-saml].
There are two issues that need to be highlighted: There are two issues that need to be highlighted:
o The security of SAML Assertions. o The security of SAML assertions.
o Namespaces and mapping of SAML attributes. o Namespaces and mapping of SAML attributes.
SAML Assertions have an optional signature that can be used to SAML assertions have an optional signature that can be used to
protect and provide origination of the assertion. These signatures protect and provide origination of the assertion. These signatures
are normally based on asymmetric key operations and require that the are normally based on asymmetric key operations and require that the
verifier be able to check not only the cryptographic operation, but verifier be able to check not only the cryptographic operation, but
also the binding of the originators name and the public key. In a also the binding of the originators name and the public key. In a
federated environment it will not always be possible for the RP to federated environment it will not always be possible for the RP to
validate the binding, for this reason the technical trust established validate the binding, for this reason the technical trust established
in the federation is used as an alternate method of validating the in the federation is used as an alternate method of validating the
origination and integrity of the SAML Assertion. origination and integrity of the SAML Assertion.
Attributes placed in SAML Assertions can have different namespaces Attributes placed in SAML assertions can have different namespaces
assigned to the same name. In many, but not all, cases a the assigned to the same name. In many, but not all, cases the
federation agreements will determine what attributes can be used in a federation agreements will determine what attributes can be used in a
SAML statement. This means that the RP needs to map from the SAML statement. This means that the RP needs to map from the
federation names, types and semantics into the onces that the federation names, types and semantics into the ones that the policies
policies of the RP are written in. In other cases the federation of the RP are written in. In other cases the federation substrate
substrate may modify the SAML Assertions in transit to do the may modify the SAML assertions in transit to do the necessary
necessary namespace, naming and semantic mappings as the assertion namespace, naming and semantic mappings as the assertion crosses the
crosses the different boundaries in the federation. If the proxies different boundaries in the federation. If the proxies are modifying
are modifying the SAML Assertion, then will obviously remove any the SAML Assertion, then will obviously remove any signatures on the
signatures on the SAML Assertions as they would no longer validate. SAML assertions as they would no longer validate. In this case the
In this case the technical trust is the required mechanism for technical trust is the required mechanism for validating the
validating the integrity of the assertion. In the last case, the integrity of the assertion. Finally, the attributes may still be in
attributes may still be in the namespace of the originating IdP. the namespace of the originating IdP. When this occurs the RP will
When this occurs the RP will need to get the required mapping need to get the required mapping operations from the federation
operations from the federation agreements and do the appropriate agreements and do the appropriate mappings itself.
mappings itself.
2.2. Client To Identity Provider 2.2. Client To Identity Provider
Looking at the communications between the client and the IdP, the Looking at the communications between the client and the IdP, the
following items need to be dealt with: following items need to be dealt with:
o The client and the IdP need to mutually authenticate each other. o The client and the IdP need to mutually authenticate each other.
o The client and the IdP need to mutually agree on the identity of o The client and the IdP need to mutually agree on the identity of
the RP. the RP.
ABFAB selected EAP for the purposes of mutual authentication and ABFAB selected EAP for the purposes of mutual authentication and
assisted in creating some new EAP channel binding documents for assisted in creating some new EAP channel binding documents for
dealing with determining the identity of the RP. ABFAB has defined dealing with determining the identity of the RP. A framework for the
and specified a new channel binding mechanism that operates as an EAP channel binding mechanism has been defined in RFC 6677 [RFC6677] that
method for the purpose of agreeing on the identity of the RP. allows the IdP to check the identity of the RP provided by the AAA
framework with that provided by the client.
2.2.1. Extensible Authentication Protocol (EAP) 2.2.1. Extensible Authentication Protocol (EAP)
Traditional web federation does not describe how a subject interacts Traditional web federation does not describe how a subject interacts
with an identity provider for authentication. 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. Since the communication is not standardized, it is
rather than humans that use some sort of programatic credential. In difficult for machines to correctly enter their credentials with
addition, use of browsers for authentication restricts the deployment different authentications, where Individuals can correctly identify
of more secure forms of authentication beyond plaintext username and the entyr mechanism on the fly. The use of browsers for
password known by the server. In a number of cases the authentication restricts the deployment of more secure forms of
authentication interface may be presented before the subject has authentication beyond plaintext username and password known by the
adequately validated they are talking to the intended server. By server. In a number of cases the authentication interface may be
giving control of the authentication interface to a potential presented before the subject has adequately validated they are
attacker, then the security of the system may be reduced and phishing talking to the intended server. By giving control of the
opportunities introduced. authentication interface to a potential attacker, then the security
of the system may be reduced and phishing opportunities introduced.
As a result, it is desirable to choose some standardized approach for As a result, it is desirable to choose some standardized approach for
communication between the subject's end-host and the identity communication between the subject's end-host and the identity
provider. There are a number of requirements this approach must provider. There are a number of requirements this approach must
meet. meet.
Experience has taught us one key security and scalability Experience has taught us one key security and scalability
requirement: it is important that the relying party not get requirement: it is important that the relying party not get
possession of the long-term secret of the client. Aside from a possession of the long-term secret of the client. Aside from a
valuable secret being exposed, a synchronization problem can develop valuable secret being exposed, a synchronization problem can develop
skipping to change at page 23, line 32 skipping to change at page 22, line 44
o Another is to verify statements the relying party has made to the o Another is to verify statements the relying party has made to the
subject, confirm these statements are consistent with statements subject, confirm these statements are consistent with statements
made to the identity provider and confirm all the above are made to the identity provider and confirm all the above are
consistent with the federation and any federation-specific policy consistent with the federation and any federation-specific policy
or configuration. or configuration.
o Another challenge is choosing which identity provider to use for o Another challenge is choosing which identity provider to use for
which service. which service.
2.2.2. Channel Binding The EAP method used for ABFAB needs to meet the following
requirements:
o It needs to provide mutual authentication of the client and IdP.
o It needs to support channel binding.
As of this writing, the only EAP method that meets these criteria is
TEAP [I-D.ietf-emu-eap-tunnel-method] either alone (if client
certificates are used) or with an inner EAP method that does mutual
authentication.
2.2.2. EAP Channel Binding
EAP channel binding is easily confused with a facility in GSS-API
also called channel binding. GSS-API channel binding provides
protection against man-in-the-middle attacks when GSS-API is used as
authentication inside some tunnel; it is similar to a facility called
cryptographic binding in EAP. See [RFC5056] for a discussion of the
differences between these two facilities and Section 6.1 for how GSS-
API channel binding is handled in this mechanism.
The client knows, in theory, the name of the RP that it attempted to The client knows, in theory, the name of the RP that it attempted to
connect to, however in the event that an attacker has intercepted the connect to, however in the event that an attacker has intercepted the
protocol, the client and the IdP need to be able to detect this protocol, the client and the IdP need to be able to detect this
situation. A general overview of the problem can be found in situation. A general overview of the problem along with a
[I-D.hartman-emu-mutual-crypto-bind]. recommended way to deal with the channel binding issues can be found
in RFC 6677 [RFC6677].
The recommended way to deal with channel binding can be found in RFC Since that document was published, a number of possible attacks were
XXXX [I-D.ietf-emu-chbind]. found and methods to address these attacks have been outlined in
[I-D.hartman-emu-mutual-crypto-bind].
2.3. Client to Relying Party 2.3. Client to Relying Party
The final set of interactions between parties to consider are those The final set of interactions between parties to consider are those
between the client and the RP. In some ways this is the most complex between the client and the RP. In some ways this is the most complex
set since at least part of it is outside the scope of the ABFAB work. set since at least part of it is outside the scope of the ABFAB work.
The interactions between these parties include: The interactions between these parties include:
o Running the protocol that implements the web service that is o Running the protocol that implements the service that is provided
provided by the RP and desired by the client. by the RP and desired by the client.
o Authenticating the client to the RP and the RP to the client. o Authenticating the client to the RP and the RP to the client.
o Providing the necessary security services to the web service o Providing the necessary security services to the service protocol
protocol that it needs beyond authentication. that it needs beyond authentication.
2.3.1. GSS-API 2.3.1. GSS-API
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.
skipping to change at page 26, line 34 skipping to change at page 26, line 34
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, unfortunately, does not explicitly talk about what mutual RFC 2743, unfortunately, does not explicitly talk about what mutual
authentication means. Within this document we therefore define it authentication means. Within this document we therefore define it
as: as:
o If a target name is supplied by the initiator, then the initiator o If a target name is supplied to 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 If no target name is supplied by the initiator, then the initiator o If no target name is supplied to the initiator, then the initiator
trusts that its idea of the acceptor name correctly names the trusts that the acceptor name, supplied by the acceptor, correctly
entity it is communicating with. names the entity it is communicating with.
o Both the initiator and acceptor have the same key material for o Both the initiator and acceptor have the same key material for
per-message keys and both parties have confirmed they actually per-message keys and both parties have confirmed they actually
have the key material. In EAP terms, there is a protected have the key material. In EAP terms, there is a protected
indication of success. indication of success.
Mutual authentication is an important defense against certain aspects Mutual authentication is an important defense against certain aspects
of phishing. Intuitively, users would like to assume that if some of phishing. Intuitively, users would like to assume that if some
party asks for their credentials as part of authentication, party asks for their credentials as part of authentication,
successfully gaining access to the resource means that they are successfully gaining access to the resource means that they are
skipping to change at page 27, line 47 skipping to change at page 27, line 47
GSS-API mutual authentication then confirming the end-points using GSS-API mutual authentication then confirming the end-points using
both trust infrastructures is likely to enhance security. If the both trust infrastructures is likely to enhance security. If the
endpoints of the GSS-API authentication are different than the endpoints of the GSS-API authentication are different than the
endpoints of the lower layer, this is a strong indication of a endpoints of the lower layer, this is a strong indication of a
problem such as a man-in-the-middle attack. Channel binding provides problem such as a man-in-the-middle attack. Channel binding provides
a facility to determine whether these endpoints are the same. a facility to determine whether these endpoints are the same.
The GSS-EAP mechanism needs to support channel binding. When an The GSS-EAP mechanism needs to support channel binding. When an
application provides channel binding data, the mechanism needs to application provides channel binding data, the mechanism needs to
confirm this is the same on both sides consistent with the GSS-API confirm this is the same on both sides consistent with the GSS-API
specification. XXXThere is an open question here as to the details; specification.
today RFC 5554 governs. We could use that and the current draft
assumes we will. However in Beijing we became aware of some changes
to these details that would make life much better for GSS
authentication of HTTP. We should resolve this with kitten and
replace this note with a reference to the spec we're actually
following.
Typically when considering channel binding, people think of channel Typically when considering channel binding, people think of channel
binding in combination with mutual authentication. This is binding in combination with mutual authentication. This is
sufficiently common that without additional qualification channel sufficiently common that without additional qualification channel
binding should be assumed to imply mutual authentication. Without binding should be assumed to imply mutual authentication. Without
mutual authentication, only one party knows that the endpoints are mutual authentication, only one party knows that the endpoints are
correct. That's sometimes useful. Consider for example a user who correct. That's sometimes useful. Consider for example a user who
wishes to access a protected resource from a shared whiteboard in a wishes to access a protected resource from a shared whiteboard in a
conference room. The whiteboard is the initiator; it does not need conference room. The whiteboard is the initiator; it does not need
to actually authenticate that it is talking to the correct resource to actually authenticate that it is talking to the correct resource
skipping to change at page 28, line 48 skipping to change at page 28, line 42
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.
Using host-based service names leads to a challenging trust Using host-based service names leads to a challenging trust
delegation problem. Who is allowed to decide whether a particular delegation problem. Who is allowed to decide whether a particular
hostname maps to an entity. The public-key infrastructure (PKI) used hostname maps to an entity. The public-key infrastructure (PKI) used
by the web has chosen to have a number of trust anchors (root by the web has chosen to have a number of trust anchors (root
certificate authorities) each of wich can map any name to a public certificate authorities) each of which can map any name to a public
key. A number of GSS-API mechanisms suchs as Kerberos [RFC1964] key. A number of GSS-API mechanisms, such as Kerberos [RFC1964],
split the problem into two parts. A new concept called a realm is split the problem into two parts. A new concept called a realm is
introduced. Then the mechanism decides what realm is responsible for introduced. Then the mechanism decides what realm is responsible for
a given name. That realm is responsible for deciding if the acceptor a given name. That realm is responsible for deciding if the acceptor
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.
3.4. 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 EAP method that produces a Master Session Key (MSK) is able to
support per-message security services. support per-message security services described in [X].
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
skipping to change at page 31, line 7 skipping to change at page 31, line 7
provide a URI to the RP that contains a token of some form. The form 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 of communications between the IdP and attribute provider as well as
other considerations are left for the future. One thing we can say other considerations are left for the future. One thing we can say
now is that the IdP would merely be asserting who the attribute now is that the IdP would merely be asserting who the attribute
authority is, and not the contents of what the attribute authority authority is, and not the contents of what the attribute authority
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 ABFAB, as an architecture designed to enable federated authentication
described throughout this document an existing architecture is re- and allow for the secure transmission of identity information between
used for a different usage environment. As such, a discussion about entities, obviously requires careful consideration around privacy and
the privacy properties has to take these pre-conditions into the potential for privacy violations.
consideration. We use the approach suggested in
[I-D.iab-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? This section examines the privacy related information presented in
this document, summarising the entities that are involved in ABFAB
communications and what exposure they have to identity information.
In discussing these privacy considerations in this section, we use
terminology and ideas from [I-D.iab-privacy-considerations].
Figure 2 shows the architecture with the involved entities. Message Note that the ABFAB architecture uses at its core several existing
exchanges are exchanged between the client application, via the technologies and protocols; detailed privacy discussion around these
relying part to the AAA server. There will likely be intermediaries is not examined. This section instead focuses on privacy
between the relying party and the AAA server, labeled generically as considerations specifically related to overall architecture and usage
"federation". of ABFAB.
In order for the relying party to route messages to the AAA server it 5.1. Entities and their roles
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 In an ABFAB environment, there are four distinct types of entities
linked to a user. Additionally, a sequence of authentication involved in communication paths. Figure 2 shows the ABFAB
protocol exchanges may be linked together. Depending on the chosen architecture with these entity types. We have:
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 o The client application: usually a piece of software running on a
user's device. This communicates with a service (the Relying
Party) that the user wishes to interact with.
The AAA server is a first-party site the user typically has a o The Identity Provider: The home AAA server for the user.
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? o The Relying Party: The service the user wishes to connect to.
The data that is likely going to be collected as part of a protocol o The federation substrate: A set of entities through which messages
exchange with application access at the relying party is accounting pass on their path between RP and AAA server.
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? As described in detail earlier in this document, when a user wishes
to access a Relying Party, a secure tunnel is set up between their
client application and their Identity Provider (via the Relying Party
and the federation substrate) through which credentials are
exchanged. An indication of success or failure, alongside a set of
AAA attributes about a principal is then passed from the Identity
Provider to the Relying Party (usually in the form of a SAML
assertion).
With regard to identification there are several protocol layers that 5.2. Relationship between user and entities
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 o Between User and Identity Provider - the identity Provider is an
but rather re-uses existing mechanisms the level of identification entity the user will have a direct relationship with, created when
heavily depends on the selected mechanisms. The following two the organisation that operates the entity provisioned and
examples aim to illustrate the amount of existing work with respect exchanged the user's credentials. Privacy and data protection
to decrease exposure of personal data. guarantees may form a part of this relationship.
1. When designing EAP methods a number of different requirements may o Between User and Relying Party - the Relying Party is an entity
need to get considered; some of them are conflicting. RFC 4017 the user may or may not have a direct relationship with, depending
[RFC4017], for example, tried to list requirements for EAP on the service in question. Some services may only be offered to
methods utilized for network access over Wireless LANs. It also those users where such a direct relationship exists (for
recommends the end-user identity hiding requirement, which is particularly sensitive services, for example), while some may not
privacy-relevant. Some EAP methods, such as EAP-IKEv2 [RFC5106], require this and would instead be satisfied with basic federation
also fulfill this requirement. trust guarantees between themselves and the Identity Provider).
This may well include the option that the user stays anonymous
with respect to the Relying Party (though obviously not to the
Identity Provider). If attempting to preserve privacy through the
mitigation of data minimisation, then the only attribute
information about individuals exposed to the Relying Party should
be that which is strictly necessary for the operation of the
service.
2. EAP, as the layer encapsulating EAP method specific information, o Between User and Federation substrate - the user is highly likely
needs identity information to allow routing requests towards the to have no knowledge of, or relationship with, any entities
user's home AAA server. This information is carried within the involved with the federation substrate (not that the Identity
Network Access Identifier (NAI) and the username part of the NAI Provider and/or Relying Party may, however). Knowledge of
(as supported by RFC 4282 [RFC4282]) can be obfuscated. attribute information about individuals for these entities is not
necessary, and thus such information should be protected in such a
way as to prevent access to this information from being possible.
5.5. Privacy Challenges 5.3. Data and Identifiers in use
While a lot of standarization work was done to avoid leakage of In the ABFAB architecture, there are a few different types of data
identity information to intermediaries (such as eavesdroppers on the and identifiers in use.
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 5.3.1. NAI
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 In order for the Relying Party to be able to route messages to enable
amount of information exchanged with other parties over time, as an EAP transaction to occur between client application and the
well as the possibility to control the amount of information correct identity Provider, it is necessary for the client application
exposed via an explict consent is limited. This is partially due to provide enough information to the Relying Party to enable the
the nature of application capabilities at the time of network identification of the correct Identity Provider. This takes the form
access authentication. However, with the envisioned extension of of an Network Access Identifier (NAI) (as specified in [RFC4282]).
the usage, as described in this document, it is desirable to Note that an NAI can have inner and outer forms in a AAA
offer these capabilities. architecture.
o The outer part of NAI is exposed to the Relying Party; this can
simply contain realm information. Doing so (i.e. not including
user identification details such as a username) minimises the data
given to the Relying Part to that which is purely necessary to
support the necessary routing decision.
o The inner part of NAI is sent through the secure tunnel as
established by the EAP protocol; this form of the NAI will contain
credentials for the user suitable for authenticating them
successfully (e.g. a username and password). Since the entire
purpose of the secure tunnel is to protect communications between
client application (EAP client) and Identity Provider (EAP
server), then it is considered secure from eavesdroppers or
malicious intermediaries and no further privacy discussion is
necessary.
5.3.2. Identity Information
As a part of the ABFAB process, after a successful authentication has
occurred between client application and Identity Provider, an
indication of this success is sent to the Relying Party. Alongside
this message, information about the user may be returned through AAA
attributes, usually in form of a SAML assertion. This information is
arbitrary and may include either only attributes that prevent an
individual from being identified by the Relying Party (thus enabling
anonymous or pseudonymous access) or attributes that contain
personally identifiable information.
Depending on the method used, this information carried through AAA
attributes may or may not be accessible to intermediaries involved in
communications - e.g. in the case of RADIUS and unencrypted SAML,
these headers are plain text and could be seen by any observer,
whereas if using RADSEC or encrypted SAML, these headers are
protected from observers. Obviously, where the protection of the
privacy of an individual is required then this information needs to
be protected by some appropriate means.
5.3.3. Accounting Information
Alongside the core authentication and authorization that occurs in
AAA communications, accounting information about resource consumption
may be delivered as part of the accounting exchange during the
lifetime of the granted application session.
5.3.4. Collection and retention of data and identifiers
In cases where Relying Parties do not require to identify a
particular individual when an individual wishes to make use of their
service, the ABFAB architecture enable anonymous or pseudonymous
access. Thus data and identifiers other than pseudonyms and
unlinkable attribute information need not be stored and retained.
However, in cases where Relying Parties require the ability to
identify a particular individual (e.g. so they can link this identity
information to a particular account in their service, or where
identity information is required for audit purposes), the service
will need to collect and store such information, and to retain it for
as long as they require. Deprovisioning of such accounts and
information is out of scope for ABFAB, but obviously for privacy
protection any identifiers collected should be deleted when they are
no longer needed.
5.4. User Participation
In the ABFAB architecture, by its very nature users are active
participants in the sharing of their identifiers as they initiate the
communications exchange every time they wish to access a server.
They are, however, not involved in control of the set of information
related to them that transmitted from Identity Provider to Relying
Party for authorisation purposes.
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 35, line 52 skipping to change at page 36, line 52
As no end-to-end security is provided by AAA, all AAA entities on As no end-to-end security is provided by AAA, all AAA entities on
the path between the RP and IdP have the ability to eavesdrop if the path between the RP and IdP have the ability to eavesdrop if
no additional security measures are taken. One such measure is to no additional security measures are taken. One such measure is to
use a transport between the client and the IdP that provides use a transport between the client and the IdP that provides
confidentiality. confidentiality.
Client-to-IdP Channel: Client-to-IdP Channel:
This communication interaction is accomplished with the help of This communication interaction is accomplished with the help of
EAP and EAP methods. The offered security protection will depend EAP and EAP methods. The offered security protection will depend
on the EAP method that is chosen but a minimum requirement fis to on the EAP method that is chosen but a minimum requirement is to
offer mutual authentication, and key derivation. The IdP is offer mutual authentication, and key derivation. The IdP is
responsible during this process to determine that the RP that 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 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 one talking to the IdP. This is accomplished via the EAP channel
binding. binding.
Partial list of issues to be addressed in this section: Privacy, Partial list of issues to be addressed in this section: Privacy,
SAML, Trust Anchors, EAP Algorithm Selection, Diameter/RADIUS/AAA SAML, Trust Anchors, EAP Algorithm Selection, Diameter/RADIUS/AAA
Issues, Naming of Entities, Protection of passwords, Channel Binding, Issues, Naming of Entities, Protection of passwords, Channel Binding,
End-point-connections (TLS), Proxy problems End-point-connections (TLS), Proxy problems
When a psuedonym is generated as a unique long term identifier for a
Subject by an IdP, care MUST be taken in the algorithm that it cannot
easily be reverse engineered by the service provider. If it can be
reversed then the service provider can consult an oracle to determine
if a given unique long term identifier is associated with a different
known identifier.
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, Paul Leach,
Howard for their feedback on the federation terminology question. and Luke 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.
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.
skipping to change at page 39, line 34 skipping to change at page 40, 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.iab-privacy-terminology]
Hansen, M., Tschofenig, H., Smith, R., and A. Cooper,
"Privacy Terminology and Concepts",
draft-iab-privacy-terminology-01 (work in progress),
March 2012.
[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-08 (work in progress), June 2012. draft-ietf-abfab-gss-eap-09 (work in progress),
August 2012.
[I-D.ietf-abfab-aaa-saml] [I-D.ietf-abfab-aaa-saml]
Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding
and Profiles for SAML", draft-ietf-abfab-aaa-saml-03 (work and Profiles for SAML", draft-ietf-abfab-aaa-saml-04 (work
in progress), March 2012. in progress), October 2012.
[I-D.ietf-emu-chbind] [RFC6677] Hartman, S., Clancy, T., and K. Hoeper, "Channel-Binding
Hartman, S., Clancy, T., and K. Hoeper, "Channel Binding Support for Extensible Authentication Protocol (EAP)
Support for EAP Methods", draft-ietf-emu-chbind-16 (work Methods", RFC 6677, July 2012.
in progress), May 2012.
10.2. Informative References 10.2. Informative References
[RFC2903] de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and [RFC2903] de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and
D. Spence, "Generic AAA Architecture", RFC 2903, D. Spence, "Generic AAA Architecture", RFC 2903,
August 2000. August 2000.
[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-13 (work Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work
in progress), December 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 Hardt, D., "The OAuth 2.0 Authorization Framework",
2.0 Authorization Framework", draft-ietf-oauth-v2-28 (work draft-ietf-oauth-v2-31 (work in progress), August 2012.
in progress), June 2012.
[I-D.iab-privacy-considerations] [I-D.iab-privacy-considerations]
Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., and Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
J. Morris, "Privacy Considerations for Internet Morris, J., Hansen, M., and R. Smith, "Privacy
Protocols", draft-iab-privacy-considerations-02 (work in Considerations for Internet Protocols",
progress), March 2012. draft-iab-privacy-considerations-03 (work in progress),
July 2012.
[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.
skipping to change at page 41, line 42 skipping to change at page 42, line 36
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.
[I-D.hartman-emu-mutual-crypto-bind] [I-D.hartman-emu-mutual-crypto-bind]
Hartman, S., Wasserman, M., and D. Zhang, "EAP Mutual Hartman, S., Wasserman, M., and D. Zhang, "EAP Mutual
Cryptographic Binding", Cryptographic Binding",
draft-hartman-emu-mutual-crypto-bind-00 (work in draft-hartman-emu-mutual-crypto-bind-00 (work in
progress), March 2012. progress), March 2012.
[I-D.ietf-emu-eap-tunnel-method]
Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel EAP Method (TEAP) Version 1",
draft-ietf-emu-eap-tunnel-method-04 (work in progress),
October 2012.
[WS-TRUST] [WS-TRUST]
Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin, Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin,
M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS
Standard ws-trust-200902, February 2009, <http:// Standard ws-trust-200902, February 2009, <http://
docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>. docs.oasis-open.org/ws-sx/ws-trust/v1.4/ws-trust.html>.
URIs URIs
[1] <http://www.openid.net> [1] <http://www.openid.net>
[2] <http://www.eduroam.org> [2] <http://www.eduroam.org>
Editorial Comments Editorial Comments
[anchor4] JLS: Add section on discussion EAP methods and [anchor4] JLS: Should this be an EAP failure to the client as well?
requirements there on
[anchor9] JLS: I don't believe this is a true statement - check it [anchor7] JLS: I don't believe this is a true statement - check it
with Josh and Sam. with Josh and Sam.
Authors' Addresses Authors' Addresses
Josh Howlett Josh Howlett
JANET(UK) JANET(UK)
Lumen House, Library Avenue, Harwell Lumen House, Library Avenue, Harwell
Oxford OX11 0SG Oxford OX11 0SG
UK UK
 End of changes. 109 change blocks. 
511 lines changed or deleted 576 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/