< draft-ietf-abfab-arch-01.txt   draft-ietf-abfab-arch-02.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: September 11, 2012 Painless Security Expires: November 25, 2012 Painless Security
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
E. Lear E. Lear
Cisco Systems GmbH Cisco Systems GmbH
March 10, 2012 J. Schaad
Soaring Hawk Consulting
May 24, 2012
Application Bridging for Federated Access Beyond Web (ABFAB) Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture Architecture
draft-ietf-abfab-arch-01.txt draft-ietf-abfab-arch-02.txt
Abstract Abstract
Over the last decade a substantial amount of work has occurred in the Over the last decade a substantial amount of work has occurred in the
space of federated 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 4 skipping to change at page 2, line 6
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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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 September 11, 2012.
This Internet-Draft will expire on November 25, 2012.
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.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. An Overview of Federation . . . . . . . . . . . . . . . . 5 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 6
1.3. Challenges to Contemporary Federation . . . . . . . . . . 8 1.3. Challenges to Contemporary Federation . . . . . . . . . . 9
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 8 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 9
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 11 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 12
1.6. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 12 1.6. Client to Relying Party Transport . . . . . . . . . . . . 13
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.7. Use of AAA . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1. Relying Party to Identity Provider . . . . . . . . . . . . 14 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2. Client To Identity Provider . . . . . . . . . . . . . . . 17 2.1. Relying Party to Identity Provider . . . . . . . . . . . . 16
2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 18 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 19
3. Application Security Services . . . . . . . . . . . . . . . . 21 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 20
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 21 3. Application Security Services . . . . . . . . . . . . . . . . 23
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 22 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 23
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 23 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 24
3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 24 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 25
4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 25 3.4. Per-Message Tokens . . . . . . . . . . . . . . . . . . . . 26
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 26 4. Future Work: Attribute Providers . . . . . . . . . . . . . . . 27
5.1. What Entities collect and use Data? . . . . . . . . . . . 26 5. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 28
5.2. Relationship between User's and other Entities . . . . . . 27 5.1. What Entities collect and use Data? . . . . . . . . . . . 28
5.2. Relationship between User's and other Entities . . . . . . 29
5.3. What Data about the User is likely Needed to be 5.3. What Data about the User is likely Needed to be
Collected? . . . . . . . . . . . . . . . . . . . . . . . . 27 Collected? . . . . . . . . . . . . . . . . . . . . . . . . 29
5.4. What is the Identification Level of the Data? . . . . . . 27 5.4. What is the Identification Level of the Data? . . . . . . 29
5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 28 5.5. Privacy Challenges . . . . . . . . . . . . . . . . . . . . 30
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 29 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 31
6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 29 6.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 31
6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 29 6.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 31
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.1. Normative References . . . . . . . . . . . . . . . . . . . 33 10.1. Normative References . . . . . . . . . . . . . . . . . . . 36
10.2. Informative References . . . . . . . . . . . . . . . . . . 33 10.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
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 SASL/GS2 [RFC5801], over the last decade through mechanisms such as Simple Authentication
Security Assertion Markup Language (SAML) [OASIS.saml-core-2.0-os], and Security Layer (SASL) with the Generic Security Server
RADIUS [RFC2865], and Diameter [RFC3588]. Application Program Interface (GSS-API) (known as the GS2 family)
[RFC5801], Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os], 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 Subject. 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 Subject is authorised, 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 signalling, 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], and such standards as SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth
OAuth [RFC5849], [I-D.ietf-oauth-v2]. The benefits of federated [RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits
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 may also therefore require fewer credentials, which is The Subject may also therefore require fewer credentials, which is
often desirable. often desirable.
Privacy: Privacy:
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 to establish, for example, only necessary for the Relying Party to establish, for example,
that the Subject is affiliated with a particular organisation or that the Subject is affiliated with a particular organisation or
has a certain role or entitlement. Sometimes the RP does require has a certain role or entitlement. Sometimes the RP does require
an identifier for the Subject (for example, so that it can an identifier for the Subject (for example, so that it can
recognise the Subject subsequently); in this case, it is common recognise the Subject subsequently); in this case, it is a common
practise for the IdP to only release a pseudonym that is specific practise for the IdP to only release a pseudonym that is specific
to that particular Relying Party. Federated access management to that particular Relying Party. Federated access management
therefore provides various strategies for protecting the Subject's therefore provides various strategies for protecting the Subject's
privacy. Other privacy aspects typically of concern are the privacy. Other privacy aspects typically of concern are the
policy for releasing personal data about the Subjectfrom the IdP policy for releasing personal data about the Subject from the IdP
to the RP, the purpose of the usage, the retention period of the to the RP, the purpose of the usage, the retention period of the
data, and many more. data, and many more.
Provisioning Provisioning
Sometimes a Relying Party needs, or would like, to know more about Sometimes a Relying Party needs, or would like, to know more about
a subject 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 provision this information, either on request by the RP the IdP to supply this information, either on request by the RP or
or unsolicited. unsolicited.
This memo describes the Application Bridging for Federated Access
Beyond the Web (ABFAB) architecture. This architecture makes use of
extensions to the commonly used security mechanisms for both
federated and non-federated access management, including the RADIUS
and the Diameter protocol, the Generic Security Service (GSS), the
GS2 family, the Extensible Authentication Protocol (EAP) and SAML.
The architecture addresses the problem of federated access management
to primarily non-web-based services, in a manner that will scale to
large numbers of identity providers, relying parties, 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-terminology]. In particular, this document uses the
terms identity provider, relying party, (data) subject, identifier, terms identity provider, relying party, (data) subject, identifier,
pseudonymity, unlinkability, and anonymity. 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].
One of the problems people will find with reading this document is
that the terminology somestimes appears to be inconsistant. This is
do 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
either a consistant term or the term associated with the standard
under discussion as appropriate. For reference we include this table
which maps the different terms into a single table.
+----------+------------+-------------------+-----------------------+
| Protocol | Subject | Relying Party | Identity Provider |
+----------+------------+-------------------+-----------------------+
| ABFAB | Subject | Relying Party | Identity Provider |
| | | (RP) | (IdP) |
| | | | |
| | Principal | | |
| | | | |
| SAML | | | |
| | | | |
| GSS-API | | | |
| | | | |
| EAP | EAP client | | EAP server |
| | | | |
| | EAP peer | | |
| | | | |
| SASL | | | |
| | | | |
| AAA | | AAA Client | AAA server |
| | | | |
| RADIUS | client | NAS | RADIUS server |
+----------+------------+-------------------+-----------------------+
Note that in some cases a cell has been left empty, in these cases
there is no direct name that represents this concept.
Note to reviewers - I have most likely missed some entries in the
table. Please provide me with both correct names from the protocol
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 Subject,
o the Identity Provider, and o the Identity Provider, and
o the Relying Party. o the Relying Party.
skipping to change at page 6, line 24 skipping to change at page 7, line 24
\ \
\ \
\ +---------+ \ +---------+
\ | | O \ | | O
v| Client | \|/ Subject v| Client | \|/ Subject
| | | | | |
+---------+ / \ +---------+ / \
Figure 1: Entities and their Relationships Figure 1: Entities and their Relationships
A federation typically this relationship encompasses operational A federation agreement typically encompasses operational
specifications and legal rules: specifications and legal rules:
Operational Specifications: Operational Specifications:
This includes the technical specifications (e.g. protocols used to These includes the technical specifications (e.g. protocols used
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 these specifications to make the audit criteria, etc. The goal of these specifications to make the
system work and to accomplish interoperability. system work and to accomplish interoperability.
Legal Rules: Legal Rules:
The legal rules take existing laws into consideration and provide The legal rules take existing laws into consideration and provide
contractual obligations to provide further clarification and contractual obligations to provide further clarification and
define responsibilities. These legal rules regulate the define responsibilities. These legal rules regulate the
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Similarly it is also important to note that, in the general case, Similarly it is also important to note that, in the general case,
there is no requirement of a long-term relationship between the RP there is no requirement of a long-term relationship between the RP
and the Subject. This is a property of federation that yields many and the Subject. This is a property of federation that yields many
of its benefits. However, federation does not preclude the of its benefits. However, federation does not preclude the
possibility of a pre-existing relationship existing between the RP possibility of a pre-existing relationship existing between the RP
and the Subject, nor that they may use the introduction to create a and the Subject, nor that they may use the introduction to create a
new long-term relationship independent of the federation. new long-term relationship independent of the federation.
Finally, it is important to reiterate that in some scenarios there Finally, it is important to reiterate that in some scenarios there
might indeed be a human behind the device denoted as Subject and in might indeed be a human behind the device denoted as Client and in
other cases there is no human involved in the actual protocol other cases there is no human involved in the actual protocol
execution. execution.
1.3. Challenges to Contemporary Federation 1.3. Challenges to Contemporary Federation
As the number of federated services has proliferated, however, the As the number of federated services has proliferated, the role of the
role of the individual can become ambiguous in certain circumstances. individual can become ambiguous in certain circumstances. For
For example, a school might provide online access to a student's example, a school might provide online access for a student's grades
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
modifying the grades. A teacher who is also a parent must clearly modifying the grades. A teacher who is also a parent must clearly
distinguish here role upon access. distinguish here role upon access.
Similarly, as the number of federations proliferates, it becomes Similarly, as the number of federations proliferates, it becomes
increasingly difficult to discover which identity provider(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 does not on its own
provide for a way to select a federation. However, the building provide for a way to select a federation. However, the building
blocks do exist to add this functionality. blocks do exist to add this functionality.
1.4. An Overview of ABFAB-based Federation 1.4. An Overview of ABFAB-based Federation
The previous section described the general model of federation, and The previous section described the general model of federation, and
its the application of federated access management. This section its the application of federated access management. This section
provides a brief overview of ABFAB in the context of this model. provides a brief overview of ABFAB in the context of this model.
The steps taken generally in an ABFAB federated authentication/ The steps taken in an ABFAB federated authentication/authorization
authorization exchange are as follows: exchange are as follows:
1. Principal provides NAI to Application: Somehow the client is 1. Principal provides an NAI to Application: The client application
configured with at least the realm portion of an NAI, which is configured with an NAI. The provided name contains, at a
represents the IdP to be discovered. minimum, the realm of an NAI. The realm represents the IdP to
be discovered.
2. Authentication mechanism selection: this is the step necessary 2. Authentication mechanism selection: The GSS-EAP SASL/GS2
to indicate that the GSS-EAP SASL/GS2 mechanism will be used for mechanism is selected for authentication/authorization.
authentication/authorization.
3. Client Application provides NAI to RP: At the conclusion of 3. Client Application provides the NAI to RP: The client
mechanism selection the NAI must be provided to the RP for application setups a transport to the RP and begins the GSS-EAP
discovery. authentication. The RP initiates the EAP protocol to the client
application, and the client provides the NAI to the RP in the
form of the EAP response.
4. Discovery of federated IdP: This is discussed in detail below. 4. Discovery of federated IdP: The RP uses pre-configured
Either the RP is configured with authorized IdPs, or it makes information or a federation proxy to determine what IdP to use
use of a federation proxy. based on policy and the provided NAI. This is discussed in
detail below.
5. Request from Relying Party to IdP: Once the RP knows who the IdP 5. Request from Relying Party to IdP: Once the RP knows who the IdP
is, it or its agent will forward the RADIUS/Diameter request to is, it (or its agent) will send a RADIUS/Diameter request to the
an IdP, which encapsulates the EAP access request. This may or IdP. The RADIUS/Diameter access request encapsulates the EAP
may not contain a SAML request as a series of attributes. At response. At this stage, the RP will likely have no idea who
this stage, the RP will likely have no idea who the principal the principal is. The RP claims its identity to the IdP in AAA
is. The RP claims its identity to the IdP in AAA attributes, attributes, and it may contain a SAML Attribute Requests in a
and it makes whatever SAML Attribute Requests through a AAA AAA attribute.
attribute.
6. IdP informs the principal of which EAP method to use: The 6. IdP informs the principal of which EAP method to use: The
available and appropriate methods are discussed below in this available and appropriate methods are discussed below in this
memo. memo.
7. A bunch of EAP messages happen between the EAP peer and the EAP 7. The EAP protocol is run: A bunch of EAP messages are passed
server, i.e., the principal and the IdP in our identity between the EAP peer and the EAP server, i.e., the principal and
management terminology, until the result of the authentication the IdP in our identity management terminology, until the result
protocol is determined. The number and content of those of the authentication protocol is determined. The number and
messages will depend on the EAP method. If the IdP is unable to content of those messages will depend on the EAP method. If the
authenticate the principal, the process concludes here. As part IdP is unable to authenticate the principal, the process
of this process, the principal will, under protection of EAP, concludes here. As part of the EAP protocol, the principal will
assert the identity of the RP to which it intends to create a channel bindings message to the IdP identifying, among
authenticate. other things, the RP to which it is attempting to authenticate.
The IdP checks the channel binding data from the principal with
that provided by the RP via the AAA protocol. If the bindings
do not match the IdP fails the EAP protocol.
8. Successful Authentication: At the very least the IdP (its EAP 8. Successful Authentication: The IdP (its EAP server) and EAP peer
server) and EAP peer / subject have authenticated one another. / subject have mutually authenticated each other. As a result
As a result of this step, the subject and the IdP hold two of this step, the subject and the IdP hold two cryptographic
cryptographic keys- a Master Session Key (MSK), and an Extended keys- a Master Session Key (MSK), and an Extended MSK (EMSK).
MSK (EMSK). If the asserted identity of the RP by the principal There is some confidence that the RP is the one the principal is
matches the identity the RP itself asserted, there is some communicating with as the channel binding data validated. This
confidence that the RP is now authenticated to the IdP. allows for a claim of authentication for the RP to the
principal.
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 subject are authorized
for a given transaction/service, and if so, what if any, for a given transaction/service, and if so, what if any,
attributes will be released to the RP. Additional policy checks attributes will be released to the RP. The RP will have done
will likely have been made earlier just through the process of it's policy checks during the discovery process.
discovery.
10. Response from the IdP to the Relying Party: Once the IdP has 10. Response from the IdP to the Relying Party: Once the IdP has
made a determination of whether and how to authenticate or made a determination of whether and how to authenticate and
authorize the principal to the RP, it returns either a negative authorize the principal to the RP, it returns either a negative
AAA result to the RP, or it returns a positive result to the RP, AAA result to the RP, or it returns a positive result to the RP,
along with an optional set of AAA attributes associated with the along with an optional set of AAA attributes associated with the
principal that could include one or more SAML assertions. In principal that could include one or more SAML assertions. In
addition, an EAP MSK is returned to the subject. 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 leads a resource access request. It may have information that
it to make additional attribute queries. It may have associates the principal with specific authorization identities.
information that associates the principal with specific If additional attributes are needed from the IdP the RP may make
authorization identies. It will apply these results in an a new SAML Request to the IdP. It will apply these results in
application-specific way. an application-specific way.
12. RP returns results to principal: Once the RP has a response it 12. RP returns results to principal: Once the RP has a response it
must inform the client application of the result. If all has must inform the client application of the result. If all has
gone well, all are authenticated, and the application proceeds gone well, all are authenticated, and the application proceeds
with appropriate authorization levels. with appropriate authorization levels.
An example communication flow is given below: An example communication flow is given below:
Relying Client Identity Relying Client Identity
Party App Provider Party App Provider
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| | | | | |
| |< - - (6) - -<| EAP method to Principal | |< - - (6) - -<| EAP method to Principal
| | | | | |
| |< - - (7) - ->| EAP Exchange to authenticate | |< - - (7) - ->| EAP Exchange to authenticate
| | | Principal | | | Principal
| | | | | |
| | (8 & 9) Local Policy Check | | (8 & 9) Local Policy Check
| | | | | |
|<====(10)====================<| IdP Assertion to RP |<====(10)====================<| IdP Assertion to RP
| | | | | |
(11) RP processes | | | | (11) RP processes results
results | |
| | | | | |
|>----(12)----->| | Results to client app. |>----(12)----->| | Results to client app.
----- = Between Client App and RP ----- = Between Client App and RP
===== = Between RP and IdP ===== = Between RP and IdP
- - - = Between Client App and IdP - - - = Between Client App and IdP
1.5. Design Goals 1.5. Design Goals
Our key design goals are as follows: Our key design goals are as follows:
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is hard and frought with risk of cryptographic flaws. Achieving is hard and frought with risk of cryptographic flaws. Achieving
widespead deployment is even more difficult. A lot of attention on widespead deployment is even more difficult. A lot of attention on
federated access has been devoted to the Web. This document instead federated access has been devoted to the Web. This document instead
focuses on a non-Web-based environment and focuses on those protocols focuses on a non-Web-based environment and focuses on those protocols
where HTTP is not used. Despite the increased excitement for where HTTP is not used. Despite the increased excitement for
layering every protocol on top of HTTP there are still a number of layering every protocol on top of HTTP there are still a number of
protocols available that do not use HTTP-based transports. Many of protocols available that do not use HTTP-based transports. Many of
these protocols are lacking a native authentication and authorization these protocols are lacking a native authentication and authorization
framework of the style shown in Figure 1. framework of the style shown in Figure 1.
1.6. Use of AAA 1.6. Client to Relying Party Transport
The transport of data between the client and the relying part is not
provided by GSS-API. GSS-API creates and consumes messages, but it
does not provide the transport itself, instead the protocol using
GSS-API needs to provide the transport. In many cases HTTP or HTTPS
is used for this transport, but other transports are perfectly
acceptable. The core GSS-API document [RFC2743] provides some
details on what requirements exist.
In addition we highlight the following:
o The transport does not need to provide either privacy or
integrity. After GSS-EAP has finished negotiation, GSS-API can be
used to provide both services. If the negotiation process itself
needs protection from eavesdroppers then the transport would need
to provide the necessary services.
o The transport needs to provide reliable transport of the messages.
o The transport needs to ensure that tokens are delivered in order
during the negotiation process.
o GSS-API messages need to be delivered atomically. If the
transport breaks up a message it must also reassemble the message
before delivery.
1.7. Use of AAA
Interestingly, for network access authentication the usage of the AAA Interestingly, for network access authentication the usage of the AAA
framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite
successful from a deployment point of view. To map the terminology successful from a deployment point of view. To map the terminology
used in Figure 1 to the AAA framework the IdP corresponds to the AAA 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 server, the RP corresponds to the AAA client, and the technical
building blocks of a federation are AAA proxies, relays and redirect building blocks of a federation are AAA proxies, relays and redirect
agents (particularly if they are operated by third parties, such as agents (particularly if they are operated by third parties, such as
AAA brokers and clearing houses). The front-end, i.e. the end host AAA brokers and clearing houses). The front-end, i.e. the end host
to AAA client communication, is in case of network access to AAA client communication, is in case of network access
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business relationship defines what statements the identity provider business relationship defines what statements the identity provider
is trusted to make and how these statements are interpreted by the is trusted to make and how these statements are interpreted by the
relying party. The AAA framework also permits the relying party or relying party. The AAA framework also permits the relying party or
elements between the relying party and identity provider to make elements between the relying party and identity provider to make
statements about the relying party. statements about the relying party.
The AAA framework provides transport for attributes. Statements made The AAA framework provides transport for attributes. Statements made
about the subject by the identity provider, statements made about the about the subject by the identity provider, statements made about the
relying party and other information is transported as attributes. relying party and other information is transported as attributes.
One demand that the AAA substrate must make of the upper layers is One demand that the AAA substrate makes of the upper layers is that
that they must properly identify the end points of the communication. they must properly identify the end points of the communication. It
That is- it must be possible for the AAA client at the RP to must be possible for the AAA client at the RP to determine where to
determine where to send each RADIUS or Diameter message. Without send each RADIUS or Diameter message. Without this requirement, it
this requirement, it would be the RP's responsibility to determine would be the RP's responsibility to determine the identity of the
the identity of the principal on its own, without the assistance of principal on its own, without the assistance of an IdP. This
an IdP. This architecture makes use of the Network Access Identifier architecture makes use of the Network Access Identifier (NAI), where
(NAI), where the IdP is indicated in the realm component [RFC4282]. the IdP is indicated in the realm component [RFC4282]. The NAI is
The NAI is represented and consumed by the GSS-API layer as represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME
GSS_C_NT_USER_NAME as specified in [RFC2743]. The GSS-API EAp as specified in [RFC2743]. The GSS-API EAP mechanism includes the
mechanism includes the NAI in the EAP Response/Identity message. NAI in the EAP Response/Identity message.
The RP needs to discover which federation will be used to contact the The RP needs to discover which federation will be used to contact the
IDP. As part of this process, the RP determines the set of business IDP. As part of this process, the RP determines the set of business
rules and technical policies governing the relationship; this is rules and technical policies governing the relationship; this is
called rules determination. The RP also needs to establish technical called rules determination. The RP also needs to establish technical
trust in the communications with the IDP. trust in the communications with the IDP.
Rules determination covers a broad range of decisions about the Rules determination covers a broad range of decisions about the
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
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giving control of the authentication interface to a potential giving control of the authentication interface to a potential
attacker, then the security of the system may be reduced and phishing attacker, then the security of the system may be reduced and phishing
opportunities introduced. 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 in requirement: it is important that the relying party not get
possession of the long-term secret of the entity being authenticated possession of the long-term secret of the client. Aside from a
by the AAA server. Aside from a valuable secret being exposed, a valuable secret being exposed, a synchronization problem can develop
synchronization problem can also often develop. Since there is no when the client changes keys with the IdP.
single authentication mechanism that will be used everywhere there is
another associated requirement: The authentication framework must Since there is no single authentication mechanism that will be used
allow for the flexible integration of authentication mechanisms. For everywhere there is another associated requirement: The
instance, some identity providers may require hardware tokens while authentication framework must allow for the flexible integration of
others may use passwords. A service provider would want to support authentication mechanisms. For instance, some IdPs require hardware
both sorts of federations, and others. tokens while others use passwords. A service provider wants to
provide support for both authentication methods, and other methods
from IdPs not yet seen.
Fortunately, these requirements can be met by utilizing standardized Fortunately, these requirements can be met by utilizing standardized
and successfully deployed technology, namely by the Extensible and 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,service client or principal) through the between a peer (i.e,service client or principal) through the
authenticator (i.e., service provider) to the back-end (i.e., authenticator (i.e., service provider) to the back-end (i.e.,
identity provider). Conveniently, this is precisely the identity provider). Conveniently, this is precisely the
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GSS-API provides an optional security service called mutual GSS-API provides an optional security service called mutual
authentication. This service means that in addition to the initiator authentication. This service means that in addition to the initiator
providing (potentially anonymous or pseudonymous) identity to the providing (potentially anonymous or pseudonymous) identity to the
acceptor, the acceptor confirms its identity to the initiator. acceptor, the acceptor confirms its identity to the initiator.
Especially for the ABFAB context, this service is confusingly named. Especially for the ABFAB context, this service is confusingly named.
We still say that mutual authentication is provided when the identity We still say that mutual authentication is provided when the identity
of an acceptor is strongly authenticated to an anonymous initiator. of an acceptor is strongly authenticated to an anonymous initiator.
RFC 2743, 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 as authentication means. Within this document we therefore define it
as:
o If a target name is supplied by the initiator, then the initiator o If a target name is supplied by the initiator, then the initiator
trusts that the supplied target name describes the acceptor. This trusts that the supplied target name describes the acceptor. This
implies both that appropriate cryptographic exchanges took place implies both that appropriate cryptographic exchanges took place
for the initiator to make such a trust decision, and that after for the initiator to make such a trust decision, and that after
evaluating the results of these exchanges, the initiator's policy evaluating the results of these exchanges, the initiator's policy
trusts that the target name is accurate. trusts that the target name is accurate.
o The initiator trusts that its idea of the acceptor name correctly o If no target name is supplied by the initiator, then the initiator
names the entity it is communicating with. trusts that its idea of the acceptor name correctly 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
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It is important, therefore, that the GSS-EAP mechanism implement It is important, therefore, that the GSS-EAP mechanism implement
mutual authentication. That is, an initiator needs to be able to mutual authentication. That is, an initiator needs to be able to
request mutual authentication. When mutual authentication is request mutual authentication. When mutual authentication is
requested, only EAP methods capabale of providing the necessary requested, only EAP methods capabale of providing the necessary
service can be used, and appropriate steps need to be taken to service can be used, and appropriate steps need to be taken to
provide mutual authentication. A broader set of EAP methods could be provide mutual authentication. A broader set of EAP methods could be
supported when a particular application does not request mutual supported when a particular application does not request mutual
authentication. It is an open question whether the mechanism will authentication. It is an open question whether the mechanism will
permit this. permit this.
The AAA infrastructure MAY hide the peer's identity from the GSS-API
acceptor, providing anonymity between the peer and initiator. At
this time, whether the identity is disclosed is determined by EAP
server policy rather than by an indication from the peer. Also,
peers are unlikely to be able to determine whether anonymous
communication will be provided. For this reason, peers are unlikely
to set the anonymous return flag from GSS_Init_Sec_context.
3.2. GSS-API Channel Binding 3.2. GSS-API Channel Binding
[RFC5056] defines a concept of channel binding to prevent man-in-the- [RFC5056] defines a concept of channel binding to prevent man-in-the-
middle attacks. It is common to provide SASL and GSS-API with middle attacks. It is common to provide SASL and GSS-API with
another layer to provide transport security; Transport Layer Security another layer to provide transport security; Transport Layer Security
(TLS) is the most common such layer. TLS provides its own server (TLS) is the most common such layer. TLS provides its own server
authentication. However there are a variety of situations where this authentication. However there are a variety of situations where this
authentication is not checked for policy or usability reasons. Even authentication is not checked for policy or usability reasons. Even
when it is checked, if the trust infrastructure behind the TLS when it is checked, if the trust infrastructure behind the TLS
authentication is different from the trust infrastructure behind the authentication is different from the trust infrastructure behind the
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7. Security Considerations 7. 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
and their security properties: and their security properties:
Client-to-RP Channel: Client-to-RP Channel:
This communication channel is secured by TLS executed between the The channel binding material is provided by any certificates and
client and the RP. The channel binding material is provided by the final message (i.e., a cryptographic token for the channel).
any certificates and the final message (i.e., a cryptographic Authentication may be provided by the RP to the client but a
token for the channel). Authentication may be provided by the RP deployment without authentication at the TLS layer is possible as
to the client but a deployment without authentication at the TLS well. In addition, there is a channel between the GSS requestor
layer is possible as well. In addition, there is a channel and the GSS acceptor, but the keying material is provided by a
between the GSS requestor and the GSS acceptor, but the keying "third party" to both entities. The client can derive keying
material is provided by a "third party" to both entities. The material locally, but the RP gets the material from the IdP. In
client can derive keying material locally, but the RP gets the the absence of a transport that provides encryption and/or
material from the IdP. There is no cryptographic binding on this integrity, the channel between the client and the RP has no
channel until the EAP processing has finished and the MSK is ability to have any cryptographic protection until the EAP
transferred from the IdP to the RP. authentication has been completed and the MSK is transfered from
the IdP to the RP.
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.
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
no additional security measures are taken. One such measure is to
use a transport between the client and the IdP that provides
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 fis 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,
SAML, Trust Anchors, EAP Algorithm Selection, Diameter/RADIUS/AAA
Issues, Naming of Entities, Protection of passwords, Channel Binding,
End-point-connections (TLS), Proxy problems
8. IANA Considerations 8. IANA Considerations
This document does not require actions by IANA. This document does not require actions by IANA.
9. Acknowledgments 9. Acknowledgments
We would like to thank Mayutan Arumaithurai and Klaas Wierenga for We would like to thank Mayutan Arumaithurai and Klaas Wierenga for
their feedback. Additionally, we would like to thank Eve Maler, their feedback. Additionally, we would like to thank Eve Maler,
Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, and Luke Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, and Luke
Howard for their feedback on the federation terminology question. Howard for their feedback on the federation terminology question.
Furthermore, we would like to thank Klaas Wierenga for his review of Furthermore, we would like to thank Klaas Wierenga for his review of
the pre-00 draft version. the pre-00 draft version.
We would like to thank Jim Schaad for his detailed review of the -00
working group draft version.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2743] Linn, J., "Generic Security Service Application Program [RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", "Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000. RFC 2865, June 2000.
skipping to change at page 33, line 35 skipping to change at page 36, line 35
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] [I-D.iab-privacy-terminology]
Hansen, M., Tschofenig, H., and R. Smith, "Privacy Hansen, M., Tschofenig, H., Smith, R., and A. Cooper,
Terminology", draft-iab-privacy-terminology-00 (work in "Privacy Terminology and Concepts",
progress), January 2012. 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-05 (work in progress), draft-ietf-abfab-gss-eap-07 (work in progress), May 2012.
March 2012.
10.2. Informative References 10.2. Informative References
[I-D.nir-tls-eap] [I-D.nir-tls-eap]
Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A
Flexible Authentication Framework for the Transport Layer Flexible Authentication Framework for the Transport Layer
Security (TLS) Protocol using the Extensible Security (TLS) Protocol using the Extensible
Authentication Protocol (EAP)", draft-nir-tls-eap-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 Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Protocol", draft-ietf-oauth-v2-25 (work 2.0 Authorization Framework", draft-ietf-oauth-v2-26 (work
in progress), March 2012. in progress), May 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., and
J. Morris, "Privacy Considerations for Internet J. Morris, "Privacy Considerations for Internet
Protocols", draft-iab-privacy-considerations-01 (work in Protocols", draft-iab-privacy-considerations-02 (work in
progress), October 2011. progress), March 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 36, line 5 skipping to change at page 38, line 21
Cantor, S., Kemp, J., Philpott, R., and E. Maler, Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion "Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core- Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2.0-os, March 2005.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904, D. Spence, "AAA Authorization Framework", RFC 2904,
August 2000. August 2000.
[WS-TRUST]
Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin,
M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS
Standard ws-trust-200902, February 2009, <http://
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>
Authors' Addresses Authors' Addresses
Josh Howlett Josh Howlett
JANET(UK) JANET(UK)
skipping to change at line 1365 skipping to change at page 40, line 40
URI: http://www.tschofenig.priv.at URI: http://www.tschofenig.priv.at
Eliot Lear Eliot Lear
Cisco Systems GmbH Cisco Systems GmbH
Richtistrasse 7 Richtistrasse 7
Wallisellen, ZH CH-8304 Wallisellen, ZH CH-8304
Switzerland Switzerland
Phone: +41 44 878 9200 Phone: +41 44 878 9200
Email: lear@cisco.com Email: lear@cisco.com
Jim Schaad
Soaring Hawk Consulting
Email: ietf@augustcellars.com
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