< draft-ietf-abfab-arch-07.txt   draft-ietf-abfab-arch-08.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 31, 2014 Painless Security Expires: May 7, 2014 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 30, 2013 November 3, 2013
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-ietf-abfab-arch-07.txt draft-ietf-abfab-arch-08.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 access and web-based access. focused on two use cases: network access and web-based access.
However, the solutions to these use cases that have been proposed and However, the solutions to these use cases that have been proposed and
deployed tend to have few common building blocks in common. deployed tend to have few common building blocks in common.
This memo describes an architecture that makes use of extensions to This memo describes an architecture that makes use of extensions to
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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 31, 2014. This Internet-Draft will expire on May 7, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1. Channel Binding . . . . . . . . . . . . . . . . . . . 6 1.1.1. Channel Binding . . . . . . . . . . . . . . . . . . . 6
1.2. An Overview of Federation . . . . . . . . . . . . . . . . 7 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 7
1.3. Challenges for Contemporary Federation . . . . . . . . . 10 1.3. Challenges for Contemporary Federation . . . . . . . . . 11
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 11 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 11
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . 14 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . 14
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 14 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1. Relying Party to Identity Provider . . . . . . . . . . . 16 2.1. Relying Party to Identity Provider . . . . . . . . . . . 16
2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . 17 2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . 17
2.1.2. Discovery and Rules Determination . . . . . . . . . . 18 2.1.2. Discovery and Rules Determination . . . . . . . . . . 18
2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19 2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19
2.1.4. AAA Security . . . . . . . . . . . . . . . . . . . . 20 2.1.4. AAA Security . . . . . . . . . . . . . . . . . . . . 21
2.1.5. SAML Assertions . . . . . . . . . . . . . . . . . . . 21 2.1.5. SAML Assertions . . . . . . . . . . . . . . . . . . . 21
2.2. Client To Identity Provider . . . . . . . . . . . . . . . 23 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 23
2.2.1. Extensible Authentication Protocol (EAP) . . . . . . 23 2.2.1. Extensible Authentication Protocol (EAP) . . . . . . 24
2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 25 2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 25
2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 25 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 26
2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 26 2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . 27 2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . 28
2.3.3. Reauthentication . . . . . . . . . . . . . . . . . . 27 2.3.3. Reauthentication . . . . . . . . . . . . . . . . . . 28
3. Application Security Services . . . . . . . . . . . . . . . . 28 3. Application Security Services . . . . . . . . . . . . . . . . 28
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . 28 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . 29
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 29 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 30
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . 30 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . 31
3.4. Additional GSS-API Services . . . . . . . . . . . . . . . 32 3.4. Additional GSS-API Services . . . . . . . . . . . . . . . 33
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 32 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 33
4.1. Entities and their roles . . . . . . . . . . . . . . . . 33 4.1. Entities and their roles . . . . . . . . . . . . . . . . 34
4.2. Privacy Aspects of ABFAB Communication Flows . . . . . . 34 4.2. Privacy Aspects of ABFAB Communication Flows . . . . . . 35
4.2.1. Client to RP . . . . . . . . . . . . . . . . . . . . 34 4.2.1. Client to RP . . . . . . . . . . . . . . . . . . . . 35
4.2.2. Client to IdP (via Federation Substrate) . . . . . . 35 4.2.2. Client to IdP (via Federation Substrate) . . . . . . 36
4.2.3. IdP to RP (via Federation Substrate) . . . . . . . . 36 4.2.3. IdP to RP (via Federation Substrate) . . . . . . . . 37
4.3. Relationship between User and Entities . . . . . . . . . 37 4.3. Relationship between User and Entities . . . . . . . . . 38
4.4. Accounting Information . . . . . . . . . . . . . . . . . 37 4.4. Accounting Information . . . . . . . . . . . . . . . . . 38
4.5. Collection and retention of data and identifiers . . . . 37 4.5. Collection and retention of data and identifiers . . . . 38
4.6. User Participation . . . . . . . . . . . . . . . . . . . 38 4.6. User Participation . . . . . . . . . . . . . . . . . . . 39
5. Security Considerations . . . . . . . . . . . . . . . . . . . 38 5. Security Considerations . . . . . . . . . . . . . . . . . . . 39
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.1. Normative References . . . . . . . . . . . . . . . . . . 40 8.1. Normative References . . . . . . . . . . . . . . . . . . 41
8.2. Informative References . . . . . . . . . . . . . . . . . 41 8.2. Informative References . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
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], and the Authentication, Authorization, and [OASIS.saml-core-2.0-os], and the Authentication, Authorization, and
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associated responsibilities such as identity management and associated responsibilities such as identity management and
credentialing, to an organization that already has a long-term credentialing, to an organization that already has a long-term
relationship with the Client. This is often attractive as Relying relationship with the Client. This is often attractive as Relying
Parties frequently do not want these responsibilities. The Client Parties frequently do not want these responsibilities. The Client
also requires fewer credentials, which is also desirable. also requires fewer credentials, which is also desirable.
Data Minimization and User Participation: 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
Client to reach an access management decision. It is frequently Client to reach an access management decision. It is frequently
only necessary for the Relying Party know specific attributes only necessary for the Relying Party to know specific attributes
about the client, for example, that the client is affiliated with about the client, for example, that the client is affiliated with
a particular organization or has a certain role or entitlement. a particular organization or has a certain role or entitlement.
Sometimes the RP only needs to know a pseudonym of the client. Sometimes the RP only needs to know a pseudonym of the client.
Prior to the release of attributes to the RP from the IdP, the IdP Prior to the release of attributes to the RP from the IdP, the IdP
will check configuration and policy to determine if the attributes will check configuration and policy to determine if the attributes
are to be released. There is currently no direct client are to be released. There is currently no direct client
participation in this decision. participation in this decision.
Provisioning: Provisioning:
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This document uses the term Network Access Identifier (NAI), as This document uses the term Network Access Identifier (NAI), as
defined in [I-D.ietf-radext-nai]. An NAI consists of a realm defined in [I-D.ietf-radext-nai]. An NAI consists of a realm
identifier, which is associated with an IdP and a username which is identifier, which is associated with an IdP and a username which is
associated with a specific client of the IdP. 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
referencing are not consistent. In general the document uses either referencing are not consistent. In general the document uses either
a the ABFAB term or the term associated with the standard under the ABFAB term or the term associated with the standard under
discussion as appropriate. For reference we include this table which discussion as appropriate. For reference we include this table which
maps the different terms into a single table. maps the different terms into a single table.
+--------------+--------------+-----------------+-------------------+ +------------+-------------+---------------------+------------------+
| Protocol | Client | Relying Party | Identity Provider | | Protocol | Client | Relying Party | Identity |
+--------------+--------------+-----------------+-------------------+ | | | | Provider |
| ABFAB | Client | Relying Party | Identity Provider | +------------+-------------+---------------------+------------------+
| | | (RP) | (IdP) | | ABFAB | Client | Relying Party (RP) | Identity |
| | | | | | | | | Provider (IdP) |
| | Initiator | Acceptor | | | | | | |
| | | | | | | Initiator | Acceptor | |
| | | Server | | | | | | |
| | | | | | | | Server | |
| SAML | Subject | Service | Issuer | | | | | |
| | | Provider | | | SAML | Subject | Service Provider | Issuer |
| | | | | | | | | |
| GSS-API | Initiator | Acceptor | | | GSS-API | Initiator | Acceptor | |
| | | | | | | | | |
| EAP | EAP peer | | EAP server | | EAP | EAP peer | EAP Authenticator | EAP server |
| | | | | | | | | |
| AAA | | AAA Client | AAA server | | AAA | | AAA Client | AAA server |
| | | | | | | | | |
| RADIUS | user | NAS | RADIUS server | | RADIUS | user | NAS | RADIUS server |
| | | | | | | | | |
| | | RADIUS client | | | | | RADIUS client | |
+--------------+--------------+-----------------+-------------------+ +------------+-------------+---------------------+------------------+
Table 1. Terminology
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 name that represents the entity. there is no name that represents the entity.
1.1.1. Channel Binding 1.1.1. Channel Binding
This document uses the term channel binding with two different This document uses the term channel binding with two different
meanings. meanings.
EAP channel binding is used to provide GSS-API naming semantics. EAP channel binding is used to provide GSS-API naming semantics. EAP
Channel binding sends a set of attributes from the peer to the EAP channel binding sends a set of attributes from the peer to the EAP
server either as part of the EAP conversation or as part of a secure server either as part of the EAP conversation or as part of a secure
association protocol. In addition, attributes are sent in the association protocol. In addition, attributes are sent in the
backend protocol from the authenticator to the EAP server. The EAP backend protocol from the EAP authenticator to the EAP server. The
server confirms the consistency of these attributes and provides the EAP server confirms the consistency of these attributes and provides
confirmation back to the peer. In this document, channel binding the confirmation back to the peer. In this document, channel binding
without qualification refers to EAP channel binding. without qualification refers to EAP channel binding.
GSS-API channel binding provides protection against man-in-the-middle GSS-API channel binding provides protection against man-in-the-middle
attacks when GSS-API is used for authentication inside of some attacks when GSS-API is used for authentication inside of some
tunnel; it is similar to a facility called cryptographic binding in tunnel; it is similar to a facility called cryptographic binding in
EAP. The binding works by each side deriving a cryptographic value EAP. The binding works by each side deriving a cryptographic value
from the tunnel itself and then using that cryptographic value to from the tunnel itself and then using that cryptographic value to
prove to the other side that it knows the value. prove to the other side that it knows the value.
See [RFC5056] for a discussion of the differences between these two See [RFC5056] for a discussion of the differences between these two
facilities. However, the difference can be summarized as GSS-API facilities. However, the difference can be summarized as GSS-API
channel binding says that there is nobody between the client and the channel binding says that there is nobody between the client and the
authenticator while EAP channel binding allows the client to have EAP authenticator while EAP channel binding allows the client to have
knowledge about attributes of the authenticator (such as it's name). knowledge about attributes of the EAP authenticator (such as its
name).
Typically when considering channel binding, people think of channel Typically when considering both EAP and GSS-API channel binding,
binding in combination with mutual authentication. This is people think of channel binding in combination with mutual
sufficiently common that without additional qualification channel authentication. This is sufficiently common that without additional
binding should be assumed to imply mutual authentication. Without qualification channel binding should be assumed to imply mutual
mutual authentication, only one party knows that the endpoints are authentication. In GSS-API, without mutualtion only the acceptor has
correct. That's sometimes useful. Consider for example a user who authenticated the initator. Similarly in EAP, only the EAP server
wishes to access a protected resource from a shared whiteboard in a has authenticated the peer. That's sometimes useful. Consider for
conference room. The whiteboard is the initiator; it does not need example a user who wishes to access a protected resource for a shared
to actually authenticate that it is talking to the correct resource whiteboard in a conference room. The whiteboard is the acceptor; it
because the user will be able to recognize whether the displayed knows that the initiator is authorized to give it a presentation and
content is correct. If channel binding is used without mutual the user can validate the whitebord got the correct presentation by
authentication, it is effectively a request to disclose the resource visual means. (The presention should not be confiduatal in this
in the context of a particular channel. Such an authentication would case.) If channel binding is used without mutual authentication, it
be similar in concept to a holder-of-key SAML assertion. However, is effectively a request to disclose the resource in the context of a
also note that while it is not happening in the protocol, mutual particular channel. Such an authentication would be similar in
authentication is happening in the overall system: the user is able concept to a holder-of-key SAML assertion. However, also note that
to visually authenticate the content. This is consistent with all while it is not happening in the protocol, mutual authentication is
uses of channel binding without protocol level mutual authentication happening in the overall system: the user is able to visually
found so far. authenticate the content. This is consistent with all uses of
channel binding without protocol level mutual authentication found so
far.
1.2. An Overview of Federation 1.2. An Overview of Federation
In the previous section we introduced the following entities: In the previous section we introduced the following entities:
o the Client, o the Client,
o the Identity Provider, and o the Identity Provider, and
o the Relying Party. o the Relying Party.
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The relationships between the entities in Figure 1 are: The relationships between the entities in Figure 1 are:
Federation Federation
The Identity Provider and the Relying Parties are part of a The Identity Provider and the Relying Parties are part of a
Federation. The relationship may be direct (they have an explicit Federation. The relationship may be direct (they have an explicit
trust relationship) or transitive (the trust relationship is trust relationship) or transitive (the trust relationship is
mediated by one or more entities). The federation relationship is mediated by one or more entities). The federation relationship is
governed by a federation agreement. Within a single federation, governed by a federation agreement. Within a single federation,
there may be multiple Identity Providers as well as multiple there may be multiple Identity Providers as well as multiple
Relying Parties. A federation is governed by a federation Relying Parties.
agreement.
Authentication Authentication
There is a direct relationship between the Client and the Identity There is a direct relationship between the Client and the Identity
Provider by which the entities trust and can securely authenticate Provider by which the entities trust and can securely authenticate
each other. each other.
A federation agreement typically encompasses operational A federation agreement typically encompasses operational
specifications and legal rules: specifications and legal rules:
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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
the application of access management within the federation. This the application of access management within the federation. This
section provides a brief overview of ABFAB in the context of this section provides a brief overview of ABFAB in the context of this
model. model.
In this example, a client is attempting to connect to a server in In this example, a client is attempting to connect to a server in
order to either get access to some data or perform some type of order to either get access to some data or perform some type of
transaction. In order for the client to mutually authenticate with transaction. In order for the client to mutually authenticate with
the server, the following steps are taken in an ABFAB federated the server, the following steps are taken in an ABFAB architecture:
architecture:
1. Client Configuration: The Client Application is configured with 1. Client Configuration: The Client Application is configured with
an NAI assigned by the IdP. It is also configured with any an NAI assigned by the IdP. It is also configured with any
keys, certificates, passwords or other secret and public keys, certificates, passwords or other secret and public
information needed to run the EAP protocols between it and the information needed to run the EAP protocols between it and the
IdP. IdP.
2. Authentication mechanism selection: The GSS-EAP GSS-API 2. Authentication mechanism selection: The GSS-EAP GSS-API
mechanism is selected for authentication/authorization. mechanism is selected for authentication/authorization.
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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 realm portion of the provided Client based on policy and the realm portion of the provided Client
NAI. This is discussed in 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 sends its identity to the IdP in AAA the client is. The RP sends its identity to the IdP in AAA
attributes, and it may send a SAML Attribute Requests in a AAA attributes, and it may send a SAML Attribute Request in a AAA
attribute. The AAA network checks that the identity claimed by attribute. The AAA network checks that the identity claimed by
the RP is valid. the RP is valid.
6. IdP begins EAP with the client: The IdP sends an EAP message to 6. IdP begins EAP with the client: The IdP sends an EAP message to
the client with an EAP method to be used. The IdP SHOULD NOT the client with an EAP method to be used. The IdP SHOULD NOT
re-request the clients name in this message, but clients need to re-request the clients name in this message, but clients need to
be able to handle it. In this case the IdP MUST accept a realm be able to handle it. In this case the IdP MUST accept a realm
only in order to protect the client's name from the RP. The only in order to protect the client's name from the RP. The
available and appropriate methods are discussed below in this available and appropriate methods are discussed below in this
memo (Section 2.2.1). 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 client (EAP peer) and the IdP (EAP server), until between the client (EAP peer) and the IdP (EAP server), until
the result of the authentication protocol is determined. The the result of the authentication protocol is determined. The
number and content of those messages depends on the EAP method number and content of those messages depends on the EAP method
selected. If the IdP is unable to authenticate the client, the selected. If the IdP is unable to authenticate the client, the
IdP sends a EAP failure message to the RP. As part of the EAP IdP sends an EAP failure message to the RP. As part of the EAP
protocol, the client sends a channel bindings EAP message to the protocol, the client sends a channel bindings EAP message to the
IdP (Section 2.2.2). In the channel binding message the client IdP (Section 2.2.2). In the channel binding message the client
identifies, among other things, the RP to which it is attempting identifies, among other things, the RP to which it is attempting
to authenticate. The IdP checks the channel binding data from to authenticate. The IdP checks the channel binding data from
the client with that provided by the RP via the AAA protocol. the client with that provided by the RP via the AAA protocol.
If the bindings do not match the IdP sends an EAP failure If the bindings do not match the IdP sends an EAP failure
message to the RP. message to the RP.
8. Successful EAP Authentication: At this point, the IdP (EAP 8. Successful EAP Authentication: At this point, the IdP (EAP
server) and client (EAP peer) have mutually authenticated each server) and client (EAP peer) have mutually authenticated each
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and from the client (by the channel binding data). 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 client are authorized for policy to determine whether the RP and client are authorized for
a given transaction/service, and if so, what if any, attributes a given transaction/service, and if so, what if any, attributes
will be released to the RP. If the IdP gets a policy failure, will be released to the RP. If the IdP gets a policy failure,
it sends an EAP failure message to the RP.[[Should this be an it sends an EAP failure message to the RP.[[Should this be an
EAP failure to the client as well?]] (The RP will have done its EAP failure to the client as well?]] (The RP will have done its
policy checks during the discovery process.) policy checks during the discovery process.)
10. IdP provide the RP with the MSK: The IdP sends a positive result 10. IdP provides the RP with the MSK: The IdP sends a positive
EAP to the RP, along with an optional set of AAA attributes result EAP to the RP, along with an optional set of AAA
associated with the client (usually as one or more SAML attributes associated with the client (usually as one or more
assertions). In addition, the EAP MSK is returned to the RP. SAML assertions). In addition, the 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
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manual configuration. manual configuration.
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 be able is chosen, it is important that the technical trust mechanism be able
to validate theg identities of both parties to the exchange. The to validate the identities of both parties to the exchange. The
trust mechanism must to ensure that the entity acting as IdP for a trust mechanism must ensure that the entity acting as IdP for a given
given NAI is permitted to be the IdP for that realm, and that any NAI is permitted to be the IdP for that realm, and that any service
service name claimed by the RP is permitted to be claimed by that name claimed by the RP is permitted to be claimed by that entity.
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 is an AAA client and can send the The simplest model is that an RP is an AAA client and can send the
request directly to an AAA proxy. The hop-by-hop integrity request directly to an AAA proxy. The hop-by-hop integrity
protection of the AAA fabric provides technical trust. An RP can protection of the AAA fabric provides technical trust. An RP can
submit a request directly to a federation. Alternatively, a submit a request directly to the correct federation.
federation disambiguation fabric can be used. Such a fabric takes Alternatively, a federation disambiguation fabric can be used.
information about what federations the RP is part of and what Such a fabric takes information about what federations the RP is
federations the IdP is part of and routes a message to the part of and what federations the IdP is part of and routes a
appropriate federation. The routing of messages across the fabric message to the appropriate federation. The routing of messages
plus attributes added to requests and responses provides rules across the fabric plus attributes added to requests and responses
determination. For example, when a disambiguation fabric routes a provides rules determination. For example, when a disambiguation
message to a given federation, that federation's rules are chosen. fabric routes a message to a given federation, that federation's
Name validation is enforced as messages travel across the fabric. rules are chosen. Name validation is enforced as messages travel
The entities near the RP confirm its identity and validate names across the fabric. The entities near the RP confirm its identity
it claims. The fabric routes the message towards the appropriate and validate names it claims. The fabric routes the message
IdP, validating the IdP's name in the process. The routing can be towards the appropriate IdP, validating the name of the IdP in the
statically configured. Alternatively a routing protocol could be process. The routing can be statically configured. Alternatively
developed to exchange reachability information about given a IdP a routing protocol could be developed to exchange reachability
and to apply policy across the AAA fabric. Such a routing information about a given IdP and to apply policy across the AAA
protocol could flood naming constraints to the appropriate points fabric. Such a routing protocol could flood naming constraints to
in the fabric. 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
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namespace, naming and semantic mappings as the assertion crosses the namespace, naming and semantic mappings as the assertion crosses the
different boundaries in the federation. If the proxies are modifying different boundaries in the federation. If the proxies are modifying
the SAML Assertion, then they will obviously remove any signatures as the SAML Assertion, then they will obviously remove any signatures as
they would no longer validate. In this case the technical trust is they would no longer validate. In this case the technical trust is
the required mechanism for validating the integrity of the assertion. the required mechanism for validating the integrity of the assertion.
Finally, the attributes may still be in the namespace of the Finally, the attributes may still be in the namespace of the
originating IdP. When this occurs the RP will need to get the originating IdP. When this occurs the RP will need to get the
required mapping operations from the federation agreements and do the required mapping operations from the federation agreements and do the
appropriate mappings itself. appropriate mappings itself.
The RADIUS SAML RFC [I-D.ietf-abfab-aaa-saml] has define a new SAML The RADIUS SAML RFC [I-D.ietf-abfab-aaa-saml] has defined a new SAML
name format that corresponds to the NAI name form defined by RFC XXXX name format that corresponds to the NAI name form defined by RFC XXXX
[I-D.ietf-radext-nai]. This allows for easy name matching in many [I-D.ietf-radext-nai]. This allows for easy name matching in many
cases as the name form in the SAML statement and the name form used cases as the name form in the SAML statement and the name form used
in RADIUS or Diameter will be the same. In addition to the NAI name in RADIUS or Diameter will be the same. In addition to the NAI name
form, the document also defines a pair of implicit name forms form, the document also defines a pair of implicit name forms
corresponding to the Client and the Client's machine. These implicit corresponding to the Client and the Client's machine. These implicit
name forms are based on the Identity-Type enumeration defined in TEAP name forms are based on the Identity-Type enumeration defined in TEAP
[I-D.ietf-emu-eap-tunnel-method]. If the name form returned in a [I-D.ietf-emu-eap-tunnel-method]. If the name form returned in a
SAML statement is not based on the NAI, then it is a requirement on SAML statement is not based on the NAI, then it is a requirement on
the EAP server that it validate that the subject of the SAML the EAP server that it validate that the subject of the SAML
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tokens while others use passwords. A service provider wants to tokens while others use passwords. A service provider wants to
provide support for both authentication methods, and other methods provide support for both authentication methods, and other methods
from IdPs not yet seen. from IdPs not yet seen.
These requirements can be met by utilizing standardized and These requirements can be met by utilizing standardized and
successfully deployed technology, namely by the Extensible successfully deployed technology, namely by the Extensible
Authentication Protocol (EAP) framework [RFC3748]. Figure 2 Authentication Protocol (EAP) framework [RFC3748]. Figure 2
illustrates the integration graphically. illustrates the integration graphically.
EAP is an end-to-end framework; it provides for two-way communication EAP is an end-to-end framework; it provides for two-way communication
between a peer (i.e. client or individual) through the authenticator between a peer (i.e. client or individual) through the EAP
(i.e., relying party) to the back-end (i.e., identity provider). authenticator (i.e., relying party) to the back-end (i.e., identity
Conveniently, this is precisely the communication path that is needed provider). Conveniently, this is precisely the communication path
for federated identity. Although EAP support is already integrated that is needed for federated identity. Although EAP support is
in AAA systems (see [RFC3579] and [RFC4072]) several challenges already integrated in AAA systems (see [RFC3579] and [RFC4072])
remain: several challenges remain:
o The first is how to carry EAP payloads from the end host to the o The first is how to carry EAP payloads from the end host to the
relying party. relying party.
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
client, confirm these statements are consistent with statements client, 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 of 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.
The EAP method used for ABFAB needs to meet the following The EAP method used for ABFAB needs to meet the following
requirements: requirements:
o It needs to provide mutual authentication of the client and IdP. o It needs to provide mutual authentication of the client and IdP.
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certificates are used) or with an inner EAP method that does mutual certificates are used) or with an inner EAP method that does mutual
authentication. authentication.
2.2.2. EAP Channel Binding 2.2.2. EAP Channel Binding
EAP channel binding is easily confused with a facility in GSS-API EAP channel binding is easily confused with a facility in GSS-API
also called channel binding. GSS-API channel binding provides also called channel binding. GSS-API channel binding provides
protection against man-in-the-middle attacks when GSS-API is used as protection against man-in-the-middle attacks when GSS-API is used as
authentication inside some tunnel; it is similar to a facility called authentication inside some tunnel; it is similar to a facility called
cryptographic binding in EAP. See [RFC5056] for a discussion of the cryptographic binding in EAP. See [RFC5056] for a discussion of the
differences between these two facilities and Section 6.1 for how GSS- differences between these two facilities.
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 along with a situation. A general overview of the problem along with a
recommended way to deal with the channel binding issues can be found recommended way to deal with the channel binding issues can be found
in RFC 6677 [RFC6677]. in RFC 6677 [RFC6677].
Since that document was published, a number of possible attacks were Since that document was published, a number of possible attacks were
found and methods to address these attacks have been outlined in found and methods to address these attacks have been outlined in
[I-D.ietf-emu-crypto-bind]. [I-D.ietf-emu-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 the parties to consider are
between the client and the RP. In some ways this is the most complex those between the client and the RP. In some ways this is the most
set since at least part of it is outside the scope of the ABFAB work. complex set since at least part of it is outside the scope of the
The interactions between these parties include: ABFAB work. The interactions between these parties include:
o Running the protocol that implements the service that is provided o Running the protocol that implements the service that is 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 service protocol o Providing the necessary security services to the service protocol
that it needs beyond authentication. that it needs beyond authentication.
o Deal with client re-authentication where desired. o Deal with client re-authentication where desired.
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For example, this work focuses on privacy; an application that For example, this work focuses on privacy; an application that
assumes it will always obtain an identifier for the client will need assumes it will always obtain an identifier for the client will need
to be modified to support anonymity, unlinkability or pseudonymity. to be modified to support anonymity, unlinkability or pseudonymity.
So, we use GSS-API and SASL because a number of the application So, we use GSS-API and SASL because a number of the application
protocols we wish to federate support these strategies for security protocols we wish to federate support these strategies for security
integration. What does this mean from a protocol standpoint and how integration. What does this mean from a protocol standpoint and how
does this relate to other layers? This means we need to design a does this relate to other layers? This means we need to design a
concrete GSS-API mechanism. We have chosen to use a GSS-API concrete GSS-API mechanism. We have chosen to use a GSS-API
mechanism that encapsulates EAP authentication. So, GSS-API (and mechanism that encapsulates EAP authentication. So, GSS-API (and
SASL) encapsulate EAP between the end-host and the service. The AAA SASL) encapsulates EAP between the end-host and the service. The AAA
framework encapsulates EAP between the relying party and the identity framework encapsulates EAP between the relying party and the identity
provider. The GSS-API mechanism includes rules about how initiators provider. The GSS-API mechanism includes rules about how initiators
and services are named as well as per-message security and other and services are named as well as per-message security and other
facilities required by the applications we wish to support. facilities required by the applications we wish to support.
2.3.2. Protocol Transport 2.3.2. Protocol Transport
The transport of data between the client and the relying party is not The transport of data between the client and the relying party is not
provided by GSS-API. GSS-API creates and consumes messages, but it provided by GSS-API. GSS-API creates and consumes messages, but it
does not provide the transport itself, instead the protocol using does not provide the transport itself, instead the protocol using
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o The transport needs to ensure that tokens are delivered in order o The transport needs to ensure that tokens are delivered in order
during the negotiation process. during the negotiation process.
o GSS-API messages need to be delivered atomically. If the o GSS-API messages need to be delivered atomically. If the
transport breaks up a message it must also reassemble the message transport breaks up a message it must also reassemble the message
before delivery. before delivery.
2.3.3. Reauthentication 2.3.3. Reauthentication
TBD. There are circumstances where the server will want to have the client
reauthenticate itself. These include very long sessions, where the
original authentication is time limited or cases where in order to
complete an operation a different authentication is required. GSS-
EAP does not have any mechanism for the server to initiate a
reauthentication as all authentication operations start from the
client. If a protocol using GSS-EAP needs to support
reauthentication that is initiated by the server, then a request from
the server to the client for the reauthentiction to start needs to be
placed in the protocol.
Clients can re-use the existing secure connection established by GSS-
API to run the new authentication in by calling GSS_Init_sec_context.
At this point a full reauthentication will be done.
3. Application Security Services 3. Application Security Services
One of the key goals is to integrate federated authentication into One of the key goals is to integrate federated authentication into
existing application protocols and where possible, existing existing application protocols and where possible, existing
implementations of these protocols. Another goal is to perform this implementations of these protocols. Another goal is to perform this
integration while meeting the best security practices of the integration while meeting the best security practices of the
technologies used to perform the integration. This section describes technologies used to perform the integration. This section describes
security services and properties required by the EAP GSS-API security services and properties required by the EAP GSS-API
mechanism in order to meet these goals. This information could be mechanism in order to meet these goals. This information could be
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found in RFC 5056 [RFC5056]. found in RFC 5056 [RFC5056].
The use of TLS can provide both encryption and integrity on the The use of TLS can provide both encryption and integrity on the
channel. It is common to provide SASL and GSS-API with these other channel. It is common to provide SASL and GSS-API with these other
security services. security services.
One of the benefits that the use of TLS provides, is that client has One of the benefits that the use of TLS provides, is that client has
the ability to validate the name of the server. However this the ability to validate the name of the server. However this
validation is predicated on a couple of things. The TLS sessions validation is predicated on a couple of things. The TLS sessions
needs to be using certificates and not be an anonymous session. The needs to be using certificates and not be an anonymous session. The
client and the TLS need to share a common trust point for the client and the TLS server need to share a common trust point for the
certificate used in validating the server. TLS provides its own certificate used in validating the server. TLS provides its own
server authentication. However there are a variety of situations server authentication. However there are a variety of situations
where this authentication is not checked for policy or usability where this authentication is not checked for policy or usability
reasons. Even when it is checked, if the trust infrastructure behind reasons. When the TLS authentication is checked, if the trust
the TLS authentication is different from the trust infrastructure infrastructure behind the TLS authentication is different from the
behind the GSS-API mutual authentication then confirming the end- trust infrastructure behind the GSS-API mutual authentication then
points using both trust infrastructures is likely to enhance confirming the end-points using both trust infrastructures is likely
security. If the endpoints of the GSS-API authentication are to enhance security. If the endpoints of the GSS-API authentication
different than the endpoints of the lower layer, this is a strong are different than the endpoints of the lower layer, this is a strong
indication of a problem such as a man-in-the-middle attack. Channel indication of a problem such as a man-in-the-middle attack. Channel
binding provides a facility to determine whether these endpoints are binding provides a facility to determine whether these endpoints are
the same. 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. specification.
3.3. Host-Based Service Names 3.3. Host-Based Service Names
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This decision can be made by the use of certificates, pre-configured This decision can be made by the use of certificates, pre-configured
key information or a previous leap of trust. GSS-API has defined a key information or a previous leap of trust. GSS-API has defined a
relatively flexible name convention, however most of the IETF relatively flexible name convention, however most of the IETF
applications that use GSS-API (including SSH, NFS, IMAP, LDAP and applications that use GSS-API (including SSH, NFS, IMAP, LDAP and
XMPP) have chosen to use a more restricted naming convention based on XMPP) have chosen to use a more restricted naming convention based on
the host name. The GSS-EAP mechanism needs to support host-based the host name. The GSS-EAP mechanism needs to support host-based
service names in order to work with existing IETF protocols. service names in order to work with existing IETF protocols.
The use of host-based service names leads to a challenging trust The use of 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
host name maps to a specific entity. Possible solutions to this host name maps to a specific entity? Possible solutions to this
problem have been looked at. problem have been looked at.
o The public-key infrastructure (PKI) used by the web has chosen to o The public-key infrastructure (PKI) used by the web has chosen to
have a number of trust anchors (root certificate authorities) each have a number of trust anchors (root certificate authorities) each
of which can map any host name to a public key. of which can map any host name to a public key.
o A number of GSS-API mechanisms, such as Kerberos [RFC1964], have o A number of GSS-API mechanisms, such as Kerberos [RFC1964], have
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, the realm is responsible for host mapping within that introduced, the realm is responsible for host mapping within that
realm. The mechanism then decides what realm is responsible for a realm. The mechanism then decides what realm is responsible for a
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that component of the name. that component of the name.
While there is no requirement that realm names map to Fully Qualified While there is no requirement that realm names map to Fully Qualified
Domain Names (FQDN) within DNS, in practice this is normally true. Domain Names (FQDN) within DNS, in practice this is normally true.
Doing so allows for the realm portion of service names and the Doing so allows for the realm portion of service names and the
portion of NAIs to be the same. It also allows for the use of DNS in portion of NAIs to be the same. It also allows for the use of DNS in
locating the host of a service while establishing the transport locating the host of a service while establishing the transport
channel between the client and the relying party. channel between the client and the relying party.
It is the responsibility of the application to determine the server It is the responsibility of the application to determine the server
that it is going to communicate with, GSS-API has the ability to help that it is going to communicate with; GSS-API has the ability to help
confirm that the server is the desired server but not to determine confirm that the server is the desired server but not to determine
the name of the server to use. It is also the responsibility of the the name of the server to use. It is also the responsibility of the
application to determine how much of the information identifying the application to determine how much of the information identifying the
service needs to be validated by the ABFAB system. The information service needs to be validated by the ABFAB system. The information
that needs to be validated is used to build up the service name that needs to be validated is used to build up the service name
passed into the GSS-EAP mechanism. What information is to be passed into the GSS-EAP mechanism. What information is to be
validated will depend on both what information was provided by the validated will depend on both what information was provided by the
client, and what information is considered significant. If the client, and what information is considered significant. If the
client only cares about getting a specific service, then the host and client only cares about getting a specific service, then the host and
realm that provides the service does not need to be validated. realm that provides the service does not need to be validated.
In many cases applications may retrieve information about providers Applications may retrieve information about providers of services
of services from DNS. When Service Records (SRV) and Naming from DNS. Service Records (SRV) and Naming Authority Pointer (NAPTR)
Authority Pointer (NAPTR) records are used to help find a host that records are used to help find a host that provides a service; however
provides a service, the security requirements on the referrals is the necessity of having DNSSEC on the queries depends on how the
going to interact with the information used in the service name. If information is going to be used. If the host name returned is not
a host name is returned from the DNS referrals, and the host name is going to be validated by EAP channel binding, because only the
to be validated by GS-EAP, then it makes sense that the referrals service is being validated, then DNSSEC is not required. However, if
themselves should be secure. On the other hand, if the host name the host name is going to be validated by EAP channel binding then
returned is not validated, i.e. only the service is passed in, then DNSSEC needs to be use to ensure that the correct host name is
it is less important that the host name be obtained in a secure validated. In general, if the information that is returned from the
manner. DNS query is to be validated, then it needs to be obtained in a
secure manner.
Another issue that needs to be addressed for host-based service names Another issue that needs to be addressed for host-based service names
is that they do not work ideally when different instances of a is that they do not work ideally when different instances of a
service are running on different ports. If the services are service are running on different ports. If the services are
equivalent, then it does not matter. However if there are equivalent, then it does not matter. However if there are
substantial differences in the quality of the service that substantial differences in the quality of the service that
information needs to be part of the validation process. If one has information needs to be part of the validation process. If one has
just a host name and not a port in the information being validated, just a host name and not a port in the information being validated,
then this is not going to be a successful strategy. then this is not going to be a successful strategy.
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GSS-API provides per-message security services that can provide GSS-API provides per-message security services that can provide
confidentiality and/or integrity. Some IETF protocols such as NFS confidentiality and/or integrity. Some IETF protocols such as NFS
and SSH take advantage of these services. As a result GSS-EAP needs and SSH take advantage of these services. As a result GSS-EAP needs
to support these services. As with mutual authentication, per- to support these services. As with mutual authentication, per-
message services will limit the set of EAP methods that can be used message services will limit the set of EAP methods that can be used
to those that generate a Master Session Key (MSK). Any EAP method to those that generate a Master Session Key (MSK). Any EAP method
that produces an MSK is able to support per-message security services that produces an MSK is able to support per-message security services
described in [RFC2743]. described in [RFC2743].
GSS-API provides a pseudo-random function. This function generates a GSS-API provides a pseudo-random function. This function generates a
pseudo-random sequence using the shared private key as the seed for pseudo-random sequence using the shared session key as the seed for
the bytes generated. This provides an algorithm that both the the bytes generated. This provides an algorithm that both the
initiator and acceptor can run in order to arrive at the same key initiator and acceptor can run in order to arrive at the same key
value. The use of this feature allows for an application to generate value. The use of this feature allows for an application to generate
keys or other shared secrets for use in other places in the protocol. keys or other shared secrets for use in other places in the protocol.
In this regards, it is similar in concept to the TLS extractor (RFC In this regards, it is similar in concept to the TLS extractor (RFC
5705 [RFC5705].). While no current IETF protocols require this, non- 5705 [RFC5705].). While no current IETF protocols require this, non-
IETF protocols are expected to take advantage of this in the near IETF protocols are expected to take advantage of this in the near
future. Additionally, a number of protocols have found the TLS future. Additionally, a number of protocols have found the TLS
extractor to be useful in this regards so it is highly probably that extractor to be useful in this regards so it is highly probable that
IETF protocols may also start using this feature. IETF protocols may also start using this feature.
4. Privacy Considerations 4. Privacy Considerations
ABFAB, as an architecture designed to enable federated authentication ABFAB, as an architecture designed to enable federated authentication
and allow for the secure transmission of identity information between and allow for the secure transmission of identity information between
entities, obviously requires careful consideration around privacy and entities, obviously requires careful consideration around privacy and
the potential for privacy violations. the potential for privacy violations.
This section examines the privacy related information presented in This section examines the privacy related information presented in
this document, summarising the entities that are involved in ABFAB this document, summarizing the entities that are involved in ABFAB
communications and what exposure they have to identity information. communications and what exposure they have to identity information.
In discussing these privacy considerations in this section, we use In discussing these privacy considerations in this section, we use
terminology and ideas from [I-D.iab-privacy-considerations]. terminology and ideas from [I-D.iab-privacy-considerations].
Note that the ABFAB architecture uses at its core several existing Note that the ABFAB architecture uses at its core several existing
technologies and protocols; detailed privacy discussion around these technologies and protocols; detailed privacy discussion around these
is not examined. This section instead focuses on privacy is not examined. This section instead focuses on privacy
considerations specifically related to overall architecture and usage considerations specifically related to overall architecture and usage
of ABFAB. of ABFAB.
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Eavesdroppers and Attackers can reside on any communication link Eavesdroppers and Attackers can reside on any communication link
between entities in Figure 3. between entities in Figure 3.
The Federation Substrate consists of all of the AAA entities. In The Federation Substrate consists of all of the AAA entities. In
some cases the AAA Proxies entities may not exist as the AAA Client some cases the AAA Proxies entities may not exist as the AAA Client
can talk directly to the AAA Server. Specifications such as the can talk directly to the AAA Server. Specifications such as the
Trust Router Protocol and RADIUS dynamic discovery Trust Router Protocol and RADIUS dynamic discovery
[I-D.ietf-radext-dynamic-discovery] can be used to shorten the path [I-D.ietf-radext-dynamic-discovery] can be used to shorten the path
between the AAA client and the AAA server (and thus stop these AAA between the AAA client and the AAA server (and thus stop these AAA
Proxies from being Observers), however even in these circumstances Proxies from being Observers); however even in these circumstances
there may be AAA Proxies in the path. there may be AAA Proxies in the path.
In Figure 3 the IdP has been divided into multiple logical pieces, in In Figure 3 the IdP has been divided into multiple logical pieces, in
actual implementations these pieces will frequently be tightly actual implementations these pieces will frequently be tightly
coupled. The links between these pieces provide the greatest coupled. The links between these pieces provide the greatest
opportunity for attackers and eavesdroppers to acquire information, opportunity for attackers and eavesdroppers to acquire information,
however, as they are all under the control of a single entity they however, as they are all under the control of a single entity they
are also the easiest to have tightly secured. are also the easiest to have tightly secured.
4.2. Privacy Aspects of ABFAB Communication Flows 4.2. Privacy Aspects of ABFAB Communication Flows
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ABFAB to work - it indicates an IdP that the principal has a ABFAB to work - it indicates an IdP that the principal has a
relationship with. EAP methods that do not allow this will relationship with. EAP methods that do not allow this will
necessarily also reveal an identifier for the principal in the IdP necessarily also reveal an identifier for the principal in the IdP
realm (e.g. a username). realm (e.g. a username).
The data shared during the initial communication phase may be The data shared during the initial communication phase may be
protected by a channel protocol such as TLS. This will prevent the protected by a channel protocol such as TLS. This will prevent the
leak of information to passive eavesdroppers, however an active leak of information to passive eavesdroppers, however an active
attacker may still be able to setup as a man-in-the-middle. The attacker may still be able to setup as a man-in-the-middle. The
client may not be able to validate the certificates (if any) provided client may not be able to validate the certificates (if any) provided
by the service, defering the check of the identity of the RP until by the service, deferring the check of the identity of the RP until
the completion of the ABFAB authentication protocol (i.e., using EAP the completion of the ABFAB authentication protocol (i.e., using EAP
channel binding). channel binding).
The data exchanged after the authentication process can have privacy The data exchanged after the authentication process can have privacy
and authentication using the GSS-API services. If the overall and authentication using the GSS-API services. If the overall
application protocol allows for the process of re-authentication, application protocol allows for the process of re-authentication,
then the same privacy impliciations as discussed in previous then the same privacy implications as discussed in previous
paragraphs apply. paragraphs apply.
4.2.2. Client to IdP (via Federation Substrate) 4.2.2. Client to IdP (via Federation Substrate)
This phase sees a secure TLS tunnel initiated between the Client and This phase sees a secure TLS tunnel initiated between the Client and
the IdP via the RP and federation substrate. The process is the IdP via the RP and federation substrate. The process is
initiated by the RP using the realm information given to it by the initiated by the RP using the realm information given to it by the
client. Once set up, the tunnel is used to send credentials to IdP client. Once set up, the tunnel is used to send credentials to IdP
to authenticate. to authenticate.
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infrastructure, for example through RADIUS headers. This is a infrastructure, for example through RADIUS headers. This is a
particularly important privacy consideration, as any AAA Proxy particularly important privacy consideration, as any AAA Proxy
that has access to the EAP MSK is able to decrypt and eavesdrop on that has access to the EAP MSK is able to decrypt and eavesdrop on
any traffic encrypted using that EAP MSK (i.e. all communications any traffic encrypted using that EAP MSK (i.e. all communications
between the Client and IdP). between the Client and IdP).
o Related to the above, the AAA server has access to the material o Related to the above, the AAA server has access to the material
necessary to derive the session key, thus the AAA server can necessary to derive the session key, thus the AAA server can
observe any traffic encrypted between the Client and RP. This observe any traffic encrypted between the Client and RP. This
"feature" was" chosen as a simplification and to make performance "feature" was" chosen as a simplification and to make performance
faster; if it was decided that this trade-off was not desireable faster; if it was decided that this trade-off was not desirable
for privacy and security reasons, then extensions to ABFAB that for privacy and security reasons, then extensions to ABFAB that
make use of techniques such as Diffie-Helman key exchange would make use of techniques such as Diffie-Helman key exchange would
mitigate against this. mitigate against this.
The choice of EAP method used has other potential privacy The choice of EAP method used has other potential privacy
implications. For example, if the EAP method in use does not support implications. For example, if the EAP method in use does not support
trust anchors to enable mutual authentication, then there are no trust anchors to enable mutual authentication, then there are no
guarantees that the IdP is who it claims to be, and thus the full NAI guarantees that the IdP is who it claims to be, and thus the full NAI
including a username and a realm might be sent to any entity including a username and a realm might be sent to any entity
masquerading as a particular IdP. masquerading as a particular IdP.
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the success or failure of authentication of the user, and optionally, the success or failure of authentication of the user, and optionally,
the sending of identity information about the principal. the sending of identity information about the principal.
As in the previous flow (Client to IdP), various operation As in the previous flow (Client to IdP), various operation
information is transported between IdP and RP over the AAA information is transported between IdP and RP over the AAA
infrastructure, and the same privacy considerations apply. However, infrastructure, and the same privacy considerations apply. However,
in this flow, explicit identity information about the authenticated in this flow, explicit identity information about the authenticated
principal can be sent from the IdP to the RP. This information can principal can be sent from the IdP to the RP. This information can
be sent through RADIUS headers, or using SAML be sent through RADIUS headers, or using SAML
[I-D.ietf-abfab-aaa-saml]. This can include protocol specific [I-D.ietf-abfab-aaa-saml]. This can include protocol specific
identitifiers, such as SAML NameIDs, as well as arbitrary attribute identifiers, such as SAML NameIDs, as well as arbitrary attribute
information about the principal. What information will be released information about the principal. What information will be released
is controlled by policy on the Identity Provider. As before, when is controlled by policy on the Identity Provider. As before, when
sending this through RADIUS headers, all AAA entities on the path sending this through RADIUS headers, all AAA entities on the path
between the RP and IdP have the ability to eavesdrop unless between the RP and IdP have the ability to eavesdrop unless
additional security measures are taken (such as the use of TLS for additional security measures are taken (such as the use of TLS for
RADIUS [I-D.ietf-radext-dtls]). When sending this using SAML, as RADIUS [I-D.ietf-radext-dtls]). When sending this using SAML, as
specified in [I-D.ietf-abfab-aaa-saml], confidentiality of the specified in [I-D.ietf-abfab-aaa-saml], confidentiality of the
information should however be guaranteed as [I-D.ietf-abfab-aaa-saml] information should however be guaranteed as [I-D.ietf-abfab-aaa-saml]
requires the use of TLS for RADIUS. requires the use of TLS for RADIUS.
4.3. Relationship between User and Entities 4.3. Relationship between User and Entities
o Between User and IdP - the IdP is an entity the user will have a o Between User and IdP - the IdP is an entity the user will have a
direct relationship with, created when the organisation that direct relationship with, created when the organization that
operates the entity provisioned and exchanged the user's operates the entity provisioned and exchanged the user's
credentials. Privacy and data protection guarantees may form a credentials. Privacy and data protection guarantees may form a
part of this relationship. part of this relationship.
o Between User and RP - the RP is an entity the user may or may not o Between User and RP - the RP is an entity the user may or may not
have a direct relationship with, depending on the service in have a direct relationship with, depending on the service in
question. Some services may only be offered to those users where question. Some services may only be offered to those users where
such a direct relationship exists (for particularly sensitive such a direct relationship exists (for particularly sensitive
services, for example), while some may not require this and would services, for example), while some may not require this and would
instead be satisfied with basic federation trust guarantees instead be satisfied with basic federation trust guarantees
between themselves and the IdP). This may well include the option between themselves and the IdP). This may well include the option
that the user stays anonymous with respect to the RP (though that the user stays anonymous with respect to the RP (though
obviously never to the IdP). If attempting to preserve privacy obviously never to the IdP). If attempting to preserve privacy
through the mitigation of data minimisation, then the only through the mitigation of data minimization, then the only
attribute information about individuals exposed to the RP should attribute information about individuals exposed to the RP should
be that which is strictly necessary for the operation of the be that which is strictly necessary for the operation of the
service. service.
o Between User and Federation substrate - the user is highly likely o Between User and Federation substrate - the user is highly likely
to have no knowledge of, or relationship with, any entities to have no knowledge of, or relationship with, any entities
involved with the federation substrate (not that the IdP and/or RP involved with the federation substrate (not that the IdP and/or RP
may, however). Knowledge of attribute information about may, however). Knowledge of attribute information about
individuals for these entities is not necessary, and thus such individuals for these entities is not necessary, and thus such
information should be protected in such a way as to prevent access information should be protected in such a way as to prevent access
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4.4. Accounting Information 4.4. Accounting Information
Alongside the core authentication and authorization that occurs in Alongside the core authentication and authorization that occurs in
AAA communications, accounting information about resource consumption AAA communications, accounting information about resource consumption
may be delivered as part of the accounting exchange during the may be delivered as part of the accounting exchange during the
lifetime of the granted application session. lifetime of the granted application session.
4.5. Collection and retention of data and identifiers 4.5. Collection and retention of data and identifiers
In cases where Relying Parties do not require to identify a In cases where Relying Parties are not required to identify a
particular individual when an individual wishes to make use of their particular individual when an individual wishes to make use of their
service, the ABFAB architecture enable anonymous or pseudonymous service, the ABFAB architecture enables anonymous or pseudonymous
access. Thus data and identifiers other than pseudonyms and access. Thus data and identifiers other than pseudonyms and
unlinkable attribute information need not be stored and retained. unlinkable attribute information need not be stored and retained.
However, in cases where Relying Parties require the ability to However, in cases where Relying Parties require the ability to
identify a particular individual (e.g. so they can link this identity identify a particular individual (e.g. so they can link this identity
information to a particular account in their service, or where information to a particular account in their service, or where
identity information is required for audit purposes), the service identity information is required for audit purposes), the service
will need to collect and store such information, and to retain it for will need to collect and store such information, and to retain it for
as long as they require. Deprovisioning of such accounts and as long as they require. Deprovisioning of such accounts and
information is out of scope for ABFAB, but obviously for privacy information is out of scope for ABFAB, but obviously for privacy
protection any identifiers collected should be deleted when they are protection any identifiers collected should be deleted when they are
no longer needed. no longer needed.
4.6. User Participation 4.6. User Participation
In the ABFAB architecture, by its very nature users are active In the ABFAB architecture, by its very nature users are active
participants in the sharing of their identifiers as they initiate the participants in the sharing of their identifiers as they initiate the
communications exchange every time they wish to access a server. communications exchange every time they wish to access a server.
They are, however, not involved in control of the set of information They are, however, not involved in control of the set of information
related to them that transmitted from the IdP to RP for authorisation related to them that transmitted from the IdP to RP for authorization
purposes; rather, this is under the control of policy on the IdP. purposes; rather, this is under the control of policy on the IdP.
Due to the nature of the AAA communication flows, with the current Due to the nature of the AAA communication flows, with the current
ABFAB architecture there is no place for a process of gaining user ABFAB architecture there is no place for a process of gaining user
consent for the information to be released from IdP to RP. consent for the information to be released from IdP to RP.
5. Security Considerations 5. Security Considerations
This document describes the architecture for Application Bridging for This document describes the architecture for Application Bridging for
Federated Access Beyond Web (ABFAB) and security is therefore the Federated Access Beyond Web (ABFAB) and security is therefore the
main focus. This section highlights the main communication channels main focus. This section highlights the main communication channels
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RP-to-IdP Channel: RP-to-IdP Channel:
The security of this communication channel is mainly provided by The security of this communication channel is mainly provided by
the functionality offered via RADIUS and Diameter. At the time of the functionality offered via RADIUS and Diameter. At the time of
writing there are no end-to-end security mechanisms standardized writing there are no end-to-end security mechanisms standardized
and thereby the architecture has to rely on hop-by-hop security and thereby the architecture has to rely on hop-by-hop security
with trusted AAA entities or, as an alternative but possible with trusted AAA entities or, as an alternative but possible
deployment variant, direct communication between the AAA client to deployment variant, direct communication between the AAA client to
the AAA server. Note that the authorization result the IdP the AAA server. Note that the authorization result the IdP
provides to the RP in the form of a SAML assertion may, however, provides to the RP in the form of a SAML assertion may; however,
be protected such that the SAML related components are secured be protected such that the SAML related components are secured
end-to-end. end-to-end.
The MSK is transported from the IdP to the RP over this channel. The MSK is transported from the IdP to the RP over this channel.
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.
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