Internet DRAFT - draft-ietf-abfab-arch
draft-ietf-abfab-arch
ABFAB J. Howlett
Internet-Draft JANET(UK)
Intended status: Informational S. Hartman
Expires: January 22, 2015 Painless Security
H. Tschofenig
ARM Ltd.
E. Lear
Cisco Systems GmbH
J. Schaad
Soaring Hawk Consulting
July 21, 2014
Application Bridging for Federated Access Beyond Web (ABFAB)
Architecture
draft-ietf-abfab-arch-13.txt
Abstract
Over the last decade a substantial amount of work has occurred in the
space of federated access management. Most of this effort has
focused on two use cases: network access and web-based access.
However, the solutions to these use cases that have been proposed and
deployed tend to have few building blocks in common.
This memo describes an architecture that makes use of extensions to
the commonly used security mechanisms for both federated and non-
federated access management, including the Remote Authentication Dial
In User Service (RADIUS) the Generic Security Service Application
Program Interface (GSS-API), the Extensible Authentication Protocol
(EAP) and the Security Assertion Markup Language (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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 22, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1. Channel Binding . . . . . . . . . . . . . . . . . . . 6
1.2. An Overview of Federation . . . . . . . . . . . . . . . . 7
1.3. Challenges for Contemporary Federation . . . . . . . . . 10
1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 10
1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . 13
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1. Relying Party to Identity Provider . . . . . . . . . . . 15
2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . 16
2.1.2. Discovery and Rules Determination . . . . . . . . . . 18
2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19
2.1.4. AAA Security . . . . . . . . . . . . . . . . . . . . 21
2.1.5. SAML Assertions . . . . . . . . . . . . . . . . . . . 21
2.2. Client To Identity Provider . . . . . . . . . . . . . . . 23
2.2.1. Extensible Authentication Protocol (EAP) . . . . . . 23
2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 25
2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 25
2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . 27
2.3.3. Reauthentication . . . . . . . . . . . . . . . . . . 28
3. Application Security Services . . . . . . . . . . . . . . . . 28
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . 28
3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 30
3.3. Host-Based Service Names . . . . . . . . . . . . . . . . 31
3.4. Additional GSS-API Services . . . . . . . . . . . . . . . 32
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4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 33
4.1. Entities and their roles . . . . . . . . . . . . . . . . 34
4.2. Privacy Aspects of ABFAB Communication Flows . . . . . . 35
4.2.1. Client to RP . . . . . . . . . . . . . . . . . . . . 35
4.2.2. Client to IdP (via Federation Substrate) . . . . . . 36
4.2.3. IdP to RP (via Federation Substrate) . . . . . . . . 37
4.3. Relationship between User and Entities . . . . . . . . . 37
4.4. Accounting Information . . . . . . . . . . . . . . . . . 38
4.5. Collection and retention of data and identifiers . . . . 38
4.6. User Participation . . . . . . . . . . . . . . . . . . . 39
5. Security Considerations . . . . . . . . . . . . . . . . . . . 39
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.1. Normative References . . . . . . . . . . . . . . . . . . 40
8.2. Informative References . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction
Numerous security mechanisms have been deployed on the Internet to
manage access to various resources. These mechanisms have been
generalized and scaled over the last decade through mechanisms such
as Simple Authentication and Security Layer (SASL) with the Generic
Security Server Application Program Interface (GSS-API) (known as the
GS2 family) [RFC5801], Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os], and the Authentication, Authorization, and
Accounting (AAA) architecture as embodied in RADIUS [RFC2865] and
Diameter [RFC6733].
A Relying Party (RP) is the entity that manages access to some
resource. The entity that is requesting access to that resource is
often described as the Client. Many security mechanisms are
manifested as an exchange of information between these entities. The
RP is therefore able to decide whether the Client is authorized, or
not.
Some security mechanisms allow the RP to delegate aspects of the
access management decision to an entity called the Identity Provider
(IdP). This delegation requires technical signaling, trust and a
common understanding of semantics between the RP and IdP. These
aspects are generally managed within a relationship known as a
'federation'. This style of access management is accordingly
described as 'federated access management'.
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Federated access management has evolved over the last decade through
specifications like SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth
[RFC6749] and WS-Trust [WS-TRUST]. The benefits of federated access
management include:
Single or Simplified sign-on:
An Internet service can delegate access management, and the
associated responsibilities such as identity management and
credentialing, to an organization that already has a long-term
relationship with the Client. This is often attractive as Relying
Parties frequently do not want these responsibilities. The Client
also requires fewer credentials, which is also desirable.
Data Minimization and User Participation:
Often a Relying Party does not need to know the identity of a
Client to reach an access management decision. It is frequently
only necessary for the Relying Party to know specific attributes
about the client, for example, that the client is affiliated with
a particular organization or has a certain role or entitlement.
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
will check configuration and policy to determine if the attributes
are to be released. There is currently no direct client
participation in this decision.
Provisioning:
Sometimes a Relying Party needs, or would like, to know more about
a client than an affiliation or a pseudonym. For example, a
Relying Party may want the Client's email address or name. Some
federated access management technologies provide the ability for
the IdP to supply this information, either on request by the RP or
unsolicited.
This memo describes the Application Bridging for Federated Access
Beyond the Web (ABFAB) architecture. The architecture addresses the
problem of federated access management primarily for non-web-based
services. This architecture makes use of extensions to the commonly
used security mechanisms for both federated and non-federated access
management, including RADIUS, the Generic Security Service (GSS), the
Extensible Authentication Protocol (EAP) and SAML. The architecture
should be extended to use Diameter in the future. It does so in a
manner that designed to scale to large numbers of identity providers,
relying parties, and federations.
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1.1. Terminology
This document uses identity management and privacy terminology from
[RFC6973]. In particular, this document uses the terms identity
provider, relying party, identifier, pseudonymity, unlinkability, and
anonymity.
In this architecture the IdP consists of the following components: an
EAP server, a RADIUS server, and optionally a SAML Assertion service.
This document uses the term Network Access Identifier (NAI), as
defined in [I-D.ietf-radext-nai]. An NAI consists of a realm
identifier, which is associated with an AAA server and thus an IdP
and a username which is associated with a specific client of the IdP.
One of the problems some people have found with reading this document
is that the terminology sometimes appears to be inconsistent. This
is due the fact that the terms used by the different standards we are
referencing are not consistent with each other. In general the
document uses either the ABFAB 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 | Client | Relying Party | Identity |
| | | | Provider |
+------------+-------------+---------------------+------------------+
| ABFAB | Client | Relying Party (RP) | Identity |
| | | | Provider (IdP) |
| | | | |
| | Initiator | Acceptor | |
| | | | |
| | | Server | |
| | | | |
| SAML | Subject | Service Provider | Issuer |
| | | | |
| GSS-API | Initiator | Acceptor | |
| | | | |
| EAP | EAP peer | EAP Authenticator | EAP server |
| | | | |
| AAA | | AAA Client | AAA server |
| | | | |
| RADIUS | user | NAS | RADIUS server |
| | | | |
| | | RADIUS client | |
+------------+-------------+---------------------+------------------+
Table 1. Terminology
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Note that in some cases a cell has been left empty; in these cases
there is no name that represents the entity.
1.1.1. Channel Binding
This document uses the term channel binding in two different
contexts. The term channel binding has a different meaning in each
of these contexts.
EAP channel binding is used to implement GSS-API naming semantics.
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 association protocol. In addition, attributes are sent in the
backend protocol from the EAP authenticator to the EAP server. The
EAP server confirms the consistency of these attributes and provides
the confirmation back to the peer. In this document, channel binding
without qualification refers to EAP channel binding.
GSS-API channel binding provides protection against man-in-the-middle
attacks when GSS-API is used for authentication inside of some
tunnel; it is similar to a facility called cryptographic binding in
EAP. The binding works by each side deriving a cryptographic value
from the tunnel itself and then using that cryptographic value to
prove to the other side that it knows the value.
See [RFC5056] for a discussion of the differences between these two
facilities. However, the difference can be summarized as GSS-API
channel binding says that there is nobody between the client and the
EAP authenticator while EAP channel binding allows the client to have
knowledge about attributes of the EAP authenticator (such as its
name).
Typically when considering both EAP and GSS-API channel binding,
people think of channel binding in combination with mutual
authentication. This is sufficiently common that without additional
qualification channel binding should be assumed to imply mutual
authentication. In GSS-API, without mutual authentication only the
acceptor has authenticated the initiator. Similarly in EAP, only the
EAP server has authenticated the peer. That's sometimes useful.
Consider for example a user who wishes to access a protected resource
for a shared whiteboard in a conference room. The whiteboard is the
acceptor; it knows that the initiator is authorized to give it a
presentation and the user can validate the whitebord got the correct
presentation by visual means. (The presention should not be
confidential in this case.) If channel binding is used without
mutual authentication, it is effectively a request to disclose the
resource in the context of a particular channel. Such an
authentication would be similar in concept to a holder-of-key SAML
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assertion. However, also note that while it is not happening in the
protocol, mutual authentication is happening in the overall system:
the user is able to visually 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
In the previous section we introduced the following entities:
o the Client,
o the Identity Provider, and
o the Relying Party.
The final entity that needs to be introduced is the Individual. An
Individual is a human being that is using the Client. In any given
situation, an Individual may or may not exist. Clients can act
either as front ends for Individuals or they may be independent
entities that are setup and allowed to run autonomously. An example
of such an independent entity can be found in the trust routing
protocol [2] where the routers use ABFAB to authenticate to each
other.
These entities and their relationships are illustrated graphically in
Figure 1.
,----------\ ,---------\
| Identity | Federation | Relying |
| Provider + <-------------------> + Party |
`----------' '---------'
<
\
\ Authentication
\
\
\
\
\ +---------+
\ | | O
v| Client | \|/ Individual
| | |
+---------+ / \
Figure 1: Entities and their Relationships
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The relationships between the entities in Figure 1 are:
Federation
The Identity Provider and the Relying Parties are part of a
Federation. The relationship may be direct (they have an explicit
trust relationship) or transitive (the trust relationship is
mediated by one or more entities). The federation relationship is
governed by a federation agreement. Within a single federation,
there may be multiple Identity Providers as well as multiple
Relying Parties.
Authentication
There is a direct relationship between the Client and the Identity
Provider. This relationship provides the means by which they
trust each other and can securely authenticate each other.
A federation agreement typically encompasses operational
specifications and legal rules:
Operational Specifications:
The goal of operational specifications is to provide enough
definition that the system works and interoperability is possible.
These include the technical specifications (e.g. protocols used to
communicate between the three parties), process standards,
policies, identity proofing, credential and authentication
algorithm requirements, performance requirements, assessment and
audit criteria, etc.
Legal Rules:
The legal rules take the legal framework into consideration and
provide contractual obligations for each entity. The rules define
the responsibilities of each party and provide further
clarification of the operational specifications. These legal
rules regulate the operational specifications, make operational
specifications legally binding to the participants, define and
govern the rights and responsibilities of the participants. The
legal rules may, for example, describe liability for losses,
termination rights, enforcement mechanisms, measures of damage,
dispute resolution, warranties, etc.
The Operational Specifications can demand the usage of a specific
technical infrastructure, including requirements on the message
routing intermediaries, to offer the required technical
functionality. In other environments, the Operational Specifications
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require fewer technical components in order to meet the required
technical functionality.
The Legal Rules include many non-technical aspects of federation,
such as business practices and legal arrangements, which are outside
the scope of the IETF. The Legal Rules can still have an impact on
the architectural setup or on how to ensure the dynamic establishment
of trust.
While a federation agreement is often discussed within the context of
formal relationships, such as between an enterprise and an employee
or a government and a citizen, a federation agreement does not have
to require any particular level of formality. For an IdP and a
Client, it is sufficient for a relationship to be established by
something as simple as using a web form and confirmation email. For
an IdP and an RP, it is sufficient for the IdP to publish contact
information along with a public key and for the RP to use that data.
Within the framework of ABFAB, it will generally be required that a
mechanism exists for the IdP to be able to trust the identity of the
RP, if this is not present then the IdP cannot provide the assurances
to the client that the identity of the RP has been established.
The nature of federation dictates that there is some form of
relationship between the identity provider and the relying party.
This is particularly important when the relying party wants to use
information obtained from the identity provider for access management
decisions and when the identity provider does not want to release
information to every relying party (or only under certain
conditions).
While it is possible to have a bilateral agreement between every IdP
and every RP; on an Internet scale this setup requires the
introduction of the multi-lateral federation concept, as the
management of such pair-wise relationships would otherwise prove
burdensome.
The IdP will typically have a long-term relationship with the Client.
This relationship typically involves the IdP positively identifying
and credentialing the Client (for example, at time of employment
within an organization). When dealing with individuals, this process
is called identity proofing [NIST-SP.800-63]. The relationship will
often be instantiated within an agreement between the IdP and the
Client (for example, within an employment contract or terms of use
that stipulates the appropriate use of credentials and so forth).
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The nature and quality of the relationship between the Client and the
IdP is an important contributor to the level of trust that an RP may
assign to an assertion describing a Client made by an IdP. This is
sometimes described as the Level of Assurance [NIST-SP.800-63].
Federation does not require an a priori relationship or a long-term
relationship between the RP and the Client; it is this property of
federation that yields many of the federation benefits. However,
federation does not preclude the possibility of a pre-existing
relationship between the RP and the Client, nor that they may use the
introduction to create a new long-term relationship independent of
the federation.
Finally, it is important to reiterate that in some scenarios there
might indeed be an Individual behind the Client and in other cases
the Client may be autonomous.
1.3. Challenges for Contemporary Federation
As the number of federated IdPs and RPs (services) proliferats, the
role of the individual can become ambiguous in certain circumstances.
For example, a school might provide online access for a student's
grades to their parents for review, and to the student's teacher for
modification. A teacher who is also a parent must clearly
distinguish her role upon access.
Similarly, as the number of federations proliferates, it becomes
increasingly difficult to discover which identity provider(s) a user
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
authentication systems are not semantically rich enough on their own
to allow for such ambiguities. For instance, in the case of an email
provider, the SMTP and IMAP protocols do not have the ability for the
server to request information from the client, beyond the clients
NAI, that the server would then use to decide between the multiple
federations it is associated with. However, the building blocks do
exist to add this functionality.
1.4. An Overview of ABFAB-based Federation
The previous section described the general model of federation, and
the application of access management within the federation. This
section provides a brief overview of ABFAB in the context of this
model.
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
transaction. In order for the client to mutually authenticate with
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the server, the following steps are taken in an ABFAB architecture (a
graphical view of the steps can be found in figure Figure 2):
1. Client Configuration: The Client Application is configured with
an NAI assigned by the IdP. It is also configured with any
keys, certificates, passwords or other secret and public
information needed to run the EAP protocols between it and the
IdP.
2. Authentication mechanism selection: The Client Application is
configured to use the GSS-EAP GSS-API mechanism for
authentication/authorization.
3. Client provides an NAI to RP: The client application sets up a
transport to the RP and begins the GSS-EAP authentication. In
response, the RP sends an EAP request message (nested in the
GSS-EAP protocol) asking for the Client's name. The Client
sends an EAP response with an NAI name form that, at a minimum,
contains the realm portion of its full NAI.
4. Discovery of federated IdP: The RP uses pre-configured
information or a federation proxy to determine what IdP to use
based on policy and the realm portion of the provided Client
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
is, it (or its agent) will send a RADIUS request to the IdP.
The RADIUS access request encapsulates the EAP 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 attributes, and it
may send a SAML Attribute Request in a AAA attribute. The AAA
network checks that the identity claimed by the RP is valid.
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
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
only in order to protect the client's name from the RP. The
available and appropriate methods are discussed below in this
memo (Section 2.2.1).
7. The EAP protocol is run: A bunch of EAP messages are passed
between the client (EAP peer) and the IdP (EAP server), until
the result of the authentication protocol is determined. The
number and content of those messages depends on the EAP method
selected. If the IdP is unable to authenticate the client, the
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
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IdP (Section 2.2.2). In the channel binding message the client
identifies, among other things, the RP to which it is attempting
to authenticate. The IdP checks the channel binding data from
the client with that provided by the RP via the AAA protocol.
If the bindings do not match the IdP sends an EAP failure
message to the RP.
8. Successful EAP Authentication: At this point, the IdP (EAP
server) and client (EAP peer) have mutually authenticated each
other. As a result, the client and the IdP hold two
cryptographic keys: a Master Session Key (MSK), and an Extended
MSK (EMSK). At this point the client has a level of assurance
about the identity of the RP based on the name checking the IdP
has done using the RP naming information from the AAA framework
and from the client (by the channel binding data).
9. Local IdP Policy Check: At this stage, the IdP checks local
policy to determine whether the RP and client are authorized for
a given transaction/service, and if so, what if any, attributes
will be released to the RP. If the IdP gets a policy failure,
it sends an EAP failure message to the RP and client. (The RP
will have done its policy checks during the discovery process.)
10. IdP provides the RP with the MSK: The IdP sends a positive
result EAP to the RP, along with an optional set of AAA
attributes associated with the client (usually as one or more
SAML assertions). In addition, the EAP MSK is returned to the
RP.
11. RP Processes Results: When the RP receives the result from the
IdP, it should have enough information to either grant or refuse
a resource access request. It may have information that
associates the client with specific authorization identities.
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
an application-specific way.
12. RP returns results to client: Once the RP has a response it must
inform the client application of the result. If all has gone
well, all are authenticated, and the application proceeds with
appropriate authorization levels. The client can now complete
the authentication of the RP by the use of the EAP MSK value.
Relying Client Identity
Party App Provider
| (1) | Client Configuration
| | |
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|<-----(2)----->| | Mechanism Selection
| | |
|<-----(3)-----<| | NAI transmitted to RP
| | |
|<=====(4)====================>| Discovery
| | |
|>=====(5)====================>| Access request from RP to IdP
| | |
| |< - - (6) - -<| EAP method to Client
| | |
| |< - - (7) - ->| EAP Exchange to authenticate
| | | Client
| | |
| | (8 & 9) Local Policy Check
| | |
|<====(10)====================<| IdP Assertion to RP
| | |
(11) | | RP processes results
| | |
|>----(12)----->| | Results to client app.
----- = Between Client App and RP
===== = Between RP and IdP
- - - = Between Client App and IdP (via RP)
Figure 2: ABFAB Authentication Steps
1.5. Design Goals
Our key design goals are as follows:
o Each party in a transaction will be authenticated, although
perhaps not identified, and the client will be authorized for
access to a specific resource.
o Means of authentication is decoupled from the application protocol
so as to allow for multiple authentication methods with minimal
changes to the application.
o The architecture requires no sharing of long term private keys
between clients and RPs.
o The system will scale to large numbers of identity providers,
relying parties, and users.
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o The system will be designed primarily for non-Web-based
authentication.
o The system will build upon existing standards, components, and
operational practices.
Designing new three party authentication and authorization protocols
is hard and fraught with risk of cryptographic flaws. Achieving
widespread deployment is even more difficult. A lot of attention on
federated access has been devoted to the Web. This document instead
focuses on a non-Web-based environment and focuses on those protocols
where HTTP is not used. Despite the growing trend to layer every
protocol on top of HTTP there are still a number of protocols
available that do not use HTTP-based transports. Many of these
protocols are lacking a native authentication and authorization
framework of the style shown in Figure 1.
2. Architecture
We have already introduced the federated access architecture, with
the illustration of the different actors that need to interact, but
did not expand on the specifics of providing support for non-Web
based applications. This section details this aspect and motivates
design decisions. The main theme of the work described in this
document is focused on re-using existing building blocks that have
been deployed already and to re-arrange them in a novel way.
Although this architecture assumes updates to the relying party, the
client application, and the IdP, those changes are kept at a minimum.
A mechanism that can demonstrate deployment benefits (based on ease
of update of existing software, low implementation effort, etc.) is
preferred and there may be a need to specify multiple mechanisms to
support the range of different deployment scenarios.
There are a number of ways to encapsulate EAP into an application
protocol. For ease of integration with a wide range of non-Web based
application protocols, GSS-API was chosen. The technical
specification of GSS-EAP can be found in [RFC7055].
The architecture consists of several building blocks, which is shown
graphically in Figure 3. In the following sections, we discuss the
data flow between each of the entities, the protocols used for that
data flow and some of the trade-offs made in choosing the protocols.
+--------------+
| Identity |
| Provider |
| (IdP) |
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+-^----------^-+
* EAP o RADIUS
* o
--v----------v--
/// \\\
// \\
| Federation |
| Substrate |
\\ //
\\\ ///
--^----------^--
* EAP o RADIUS
* o
+-------------+ +-v----------v--+
| | | |
| Client | EAP/EAP Method | Relying Party |
| Application |<****************>| (RP) |
| | GSS-API | |
| |<---------------->| |
| | Application | |
| | Protocol | |
| |<================>| |
+-------------+ +---------------+
Legend:
<****>: Client-to-IdP Exchange
<---->: Client-to-RP Exchange
<oooo>: RP-to-IdP Exchange
<====>: Protocol through which GSS-API/GS2 exchanges are tunneled
Figure 3: ABFAB Protocol Instantiation
2.1. Relying Party to Identity Provider
Communications between the Relying Party and the Identity Provider is
done by the federation substrate. This communication channel is
responsible for:
o Establishing the trust relationship between the RP and the IdP.
o Determining the rules governing the relationship.
o Conveying authentication packets from the client to the IdP and
back.
o Providing the means of establishing a trust relationship between
the RP and the client.
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o Providing a means for the RP to obtain attributes about the client
from the IdP.
The ABFAB working group has chosen the AAA framework for the messages
transported between the RP and IdP. The AAA framework supports the
requirements stated above as follows:
o The AAA backbone supplies the trust relationship between the RP
and the IdP.
o The agreements governing a specific AAA backbone contains the
rules governing the relationships within the AAA federation.
o A method exists for carrying EAP packets within RADIUS [RFC3579]
and Diameter [RFC4072].
o The use of EAP channel binding [RFC6677] along with the core ABFAB
protocol provide the pieces necessary to establish the identities
of the RP and the client, while EAP provides the cryptographic
methods for the RP and the client to validate they are talking to
each other.
o A method exists for carrying SAML packets within RADIUS
[I-D.ietf-abfab-aaa-saml] which allows the RP to query attributes
about the client from the IdP.
Protocols that support the same framework, but do different routing
are expected to be defined and used the future. One such effort call
the Trust Router is to setup a framework that creates a trusted
point-to-point channel on the fly [3].
2.1.1. AAA, RADIUS and Diameter
The usage of the AAA framework with RADIUS [RFC2865] and Diameter
[RFC6733] for network access authentication has been successful from
a deployment point of view. To map to the terminology used in Figure
1 to the AAA framework the IdP corresponds to the AAA server, the RP
corresponds to the AAA client, and the technical building blocks of a
federation are AAA proxies, relays and redirect agents (particularly
if they are operated by third parties, such as AAA brokers and
clearing houses). The front-end, i.e. the end host to AAA client
communication, is in case of network access authentication offered by
link layer protocols that forward authentication protocol exchanges
back-and-forth. An example of a large scale RADIUS-based federation
is EDUROAM [4].
By using the AAA framework, ABFAB can be built on the federation
agreements already exist, the agreements can then merely be expanded
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to cover the ABFAB. The AAA framework has already addressed some of
the problems outlined above. For example,
o It already has a method for routing requests based on a domain.
o It already has an extensible architecture allowing for new
attributes to be defined and transported.
o Pre-existing relationships can be re-used.
The astute reader will notice that RADIUS and Diameter have
substantially similar characteristics. Why not pick one? RADIUS and
Diameter are deployed in different environments. RADIUS can often be
found in enterprise and university networks, and is also in use by
fixed network operators. Diameter, on the other hand, is deployed by
mobile operators. Another key difference is that today RADIUS is
largely transported upon UDP. We leave as a deployment decision,
which protocol will be appropriate. The protocol defines all the
necessary new AAA attributes as RADIUS attributes. A future document
could define the same AAA attributes for a Diameter environment. We
also note that there exist proxies which convert from RADIUS to
Diameter and back. This makes it possible for both to be deployed in
a single federation substrate.
Through the integrity protection mechanisms in the AAA framework, the
identity provider can establish technical trust that messages are
being sent by the appropriate relying party. Any given interaction
will be associated with one federation at the policy level. The
legal or business relationship defines what statements the identity
provider is trusted to make and how these statements are interpreted
by the relying party. The AAA framework also permits the relying
party or elements between the relying party and identity provider to
make statements about the relying party.
The AAA framework provides transport for attributes. Statements made
about the client by the identity provider, statements made about the
relying party and other information are transported as attributes.
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One demand that the AAA substrate makes of the upper layers is that
they must properly identify the end points of the communication. It
must be possible for the AAA client at the RP to determine where to
send each RADIUS or Diameter message. Without this requirement, it
would be the RP's responsibility to determine the identity of the
client on its own, without the assistance of an IdP. This
architecture makes use of the Network Access Identifier (NAI), where
the IdP is indicated by the realm component [I-D.ietf-radext-nai].
The NAI is represented and consumed by the GSS-API layer as
GSS_C_NT_USER_NAME as specified in [RFC2743]. The GSS-API EAP
mechanism includes the NAI in the EAP Response/Identity message.
As of the time this document was published, no profiles for the use
of Diameter have been created.
2.1.2. Discovery and Rules Determination
While we are using the AAA protocols to communicate with the IdP, the
RP may have multiple federation substrates to select from. The RP
has a number of criteria that it will use in selecting which of the
different federations to use:
o The federation selected must be able to communicate with the IdP.
o The federation selected must match the business rules and
technical policies required for the RP security requirements.
The RP needs to discover which federation will be used to contact the
IdP. The first selection criterion used during discovery is going to
be the name of the IdP to be contacted. The second selection
criteria used during discovery is going to be the set of business
rules and technical policies governing the relationship; this is
called rules determination. The RP also needs to establish technical
trust in the communications with the IdP.
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Rules determination covers a broad range of decisions about the
exchange. One of these is whether the given RP is permitted to talk
to the IdP using a given federation at all, so rules determination
encompasses the basic authorization decision. Other factors are
included, such as what policies govern release of information about
the client to the RP and what policies govern the RP's use of this
information. While rules determination is ultimately a business
function, it has significant impact on the technical exchanges. The
protocols need to communicate the result of authorization. When
multiple sets of rules are possible, the protocol must disambiguate
which set of rules are in play. Some rules have technical
enforcement mechanisms; for example in some federations
intermediaries validate information that is being communicated within
the federation.
At the time of writing no protocol mechanism has been specified to
allow a AAA client to determine whether a AAA proxy will indeed be
able to route AAA requests to a specific IdP. The AAA routing is
impacted by business rules and technical policies that may be quite
complex and at the present time, the route selection is based on
manual configuration.
2.1.3. Routing and Technical Trust
Several approaches to having messages routed through the federation
substrate are possible. These routing methods can most easily be
classified based on the mechanism for technical trust that is used.
The choice of technical trust mechanism constrains how rules
determination is implemented. Regardless of what deployment strategy
is chosen, it is important that the technical trust mechanism be able
to validate the identities of both parties to the exchange. The
trust mechanism must ensure that the entity acting as IdP for a given
NAI is permitted to be the IdP for that realm, and that any service
name claimed by the RP is permitted to be claimed by that entity.
Here are the categories of technical trust determination:
AAA Proxy:
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
protection of the AAA fabric provides technical trust. An RP can
submit a request directly to the correct federation.
Alternatively, a federation disambiguation fabric can be used.
Such a fabric takes information about what federations the RP is
part of and what federations the IdP is part of and routes a
message to the appropriate federation. The routing of messages
across the fabric plus attributes added to requests and responses
provides rules determination. For example, when a disambiguation
fabric routes a message to a given federation, that federation's
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rules are chosen. Name validation is enforced as messages travel
across the fabric. The entities near the RP confirm its identity
and validate names it claims. The fabric routes the message
towards the appropriate IdP, validating the name of the IdP in the
process. The routing can be statically configured. Alternatively
a routing protocol could be developed to exchange reachability
information about a given IdP and to apply policy across the AAA
fabric. Such a routing protocol could flood naming constraints to
the appropriate points in the fabric.
Trust Broker:
Instead of routing messages through AAA proxies, some trust broker
could establish keys between entities near the RP and entities
near the IdP. The advantage of this approach is efficiency of
message handling. Fewer entities are needed to be involved for
each message. Security may be improved by sending individual
messages over fewer hops. Rules determination involves decisions
made by trust brokers about what keys to grant. Also, associated
with each credential is context about rules and about other
aspects of technical trust including names that may be claimed. A
routing protocol similar to the one for AAA proxies is likely to
be useful to trust brokers in flooding rules and naming
constraints.
Global Credential:
A global credential such as a public key and certificate in a
public key infrastructure can be used to establish technical
trust. A directory or distributed database such as the Domain
Name System is used by the RP to discover the endpoint to contact
for a given NAI. Either the database or certificates can provide
a place to store information about rules determination and naming
constraints. Provided that no intermediates are required (or
appear to be required) and that the RP and IdP are sufficient to
enforce and determine rules, rules determination is reasonably
simple. However applying certain rules is likely to be quite
complex. For example if multiple sets of rules are possible
between an IdP and RP, confirming the correct set is used may be
difficult. This is particularly true if intermediates are
involved in making the decision. Also, to the extent that
directory information needs to be trusted, rules determination may
be more complex.
Real-world deployments are likely to be mixtures of these basic
approaches. For example, it will be quite common for an RP to route
traffic to a AAA proxy within an organization. That proxy could then
use any of the three methods to get closer to the IdP. It is also
likely that rather than being directly reachable, the IdP may have a
proxy on the edge of its organization. Federations will likely
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provide a traditional AAA proxy interface even if they also provide
another mechanism for increased efficiency or security.
2.1.4. AAA Security
For the AAA framework there are two different places where security
needs to be examined. The first is the security that is in place for
the links in the AAA backbone being used. The second are the nodes
that form the AAA backbone.
The default link security for RADIUS is showing its age as it uses
MD5 and a shared secret to both obfuscate passwords and to provide
integrity on the RADIUS messages. While some EAP methods include the
ability to protect the client authentication credentials, the MSK
returned from the IdP to the RP is protected only by the RADIUS
security. In many environments this is considered to be
insufficient, especially as not all attributes are obfuscated and can
thus leak information to a passive eavesdropper. The use of RADIUS
with TLS [RFC6614] and/or DTLS [I-D.ietf-radext-dtls] addresses these
attacks. The same level of security is included in the base Diameter
specifications.
2.1.5. SAML Assertions
For the traditional use of AAA frameworks, network access, an
affirmative response from the IdP can be sufficient to grant access.
In the ABFAB world, the RP may need to get significantly more
additional information about the client before granting access.
ABFAB therefore has a requirement that it can transport an arbitrary
set of attributes about the client from the IdP to the RP.
Security Assertions Markup Language (SAML) [OASIS.saml-core-2.0-os]
was designed in order to carry an extensible set of attributes about
a subject. Since SAML is extensible in the attribute space, ABFAB
has no immediate needs to update the core SAML specifications for our
work. It will be necessary to update IdPs that need to return SAML
assertions to RPs and for both the IdP and the RP to implement a new
SAML profile designed to carry SAML assertions in AAA. The new
profile can be found in RFCXXXX [I-D.ietf-abfab-aaa-saml]. As SAML
statements will frequently be large, RADIUS servers and clients that
deal with SAML statements will need to implement RFC XXXX
[I-D.ietf-radext-radius-fragmentation]
There are several issues that need to be highlighted:
o The security of SAML assertions.
o Namespaces and mapping of SAML attributes.
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o Subject naming of entities.
o Making multiple queries about the subject(s).
o Level of Assurance for authentication.
SAML assertions have an optional signature that can be used to
protect and provide origination of the assertion. These signatures
are normally based on asymmetric key operations and require that the
verifier be able to check not only the cryptographic operation, but
also the binding of the originators name and the public key. In a
federated environment it will not always be possible for the RP to
validate the binding, for this reason the technical trust established
in the federation is used as an alternate method of validating the
origination and integrity of the SAML Assertion.
Attributes in a SAML assertion are identified by a name string. The
name string is either assigned by the SAML issuer context or is
scoped by a namespace (for example a URI or object identifier (OID)).
This means that the same attribute can have different name strings
used to identify it. In many, but not all, cases the federation
agreements will determine what attributes and names can be used in a
SAML statement. This means that the RP needs to map from the SAML
issuer or federation name, type and semantic into the name, type and
semantics that the policies of the RP are written in. In other cases
the federation substrate, in the form of proxies, will modify the
SAML assertions in transit to do the necessary name, type and value
mappings as the assertion crosses boundaries in the federation. If
the proxies are modifying the SAML Assertion, then they will remove
any signatures on the SAML as changing the content of the SAML
statement would invalidate the signature. In this case the technical
trust is the required mechanism for validating the integrity of the
assertion. (The proxy could re-sign the SAML assertion, but the same
issues of establishing trust in the proxy would still exist.)
Finally, the attributes may still be in the namespace of the
originating IdP. When this occurs the RP will need to get the
required mapping operations from the federation agreements and do the
appropriate mappings itself.
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
[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
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
corresponding to the Client and the Client's machine. These implicit
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
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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
assertion, if any, is equivalent to the subject identified by the NAI
used in the RADIUS or Diameter session.
RADIUS has the ability to deal with multiple SAML queries for those
EAP Servers which follow RFC 5080 [RFC5080]. In this case a State
attribute will always be returned with the Access-Accept. The EAP
client can then send a new Access-Request with the State attribute
and the new SAML Request Multiple SAML queries can then be done by
making a new Access-Request using the State attribute returned in the
last Access-Accept to link together the different RADIUS sessions.
Some RPs need to ensure that specific criteria are met during the
authentication process. This need is met by using Levels of
Assurance. The way a Level of Assurance is communicated to the RP
from the EAP server is by the use of a SAML Authentication Request
using the Authentication Profile from RFC XXX
[I-D.ietf-abfab-aaa-saml] When crossing boundaries between different
federations, either the policy specified will need to be shared
between the two federations, the policy will need to be mapped by the
proxy server on the boundary or the proxy server on the boundary will
need to supply information the EAP server so that it can do the
required mapping. If this mapping is not done, then the EAP server
will not be able to enforce the desired Level of Assurance as it will
not understand the policy requirements.
2.2. Client To Identity Provider
Looking at the communications between the client and the IdP, the
following items need to be dealt with:
o The client and the IdP need to mutually authenticate each other.
o The client and the IdP need to mutually agree on the identity of
the RP.
ABFAB selected EAP for the purposes of mutual authentication and
assisted in creating some new EAP channel binding documents for
dealing with determining the identity of the RP. A framework for the
channel binding mechanism has been defined in RFC 6677 [RFC6677] that
allows the IdP to check the identity of the RP provided by the AAA
framework with that provided by the client.
2.2.1. Extensible Authentication Protocol (EAP)
Traditional web federation does not describe how a client interacts
with an identity provider for authentication. As a result, this
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communication is not standardized. There are several disadvantages
to this approach. Since the communication is not standardized, it is
difficult for machines to recognize which entity is going to do the
authentication and thus which credentials to use and where in the
authentication form that the credentials are to be entered. Humans
have a much easier time to correctly deal with these problems. The
use of browsers for authentication restricts the deployment of more
secure forms of authentication beyond plaintext username and password
known by the server. In a number of cases the authentication
interface may be presented before the client has adequately validated
they are talking to the intended server. By giving control of the
authentication interface to a potential attacker, the security of the
system may be reduced and phishing opportunities introduced.
As a result, it is desirable to choose some standardized approach for
communication between the client's end-host and the identity
provider. There are a number of requirements this approach must
meet.
Experience has taught us one key security and scalability
requirement: it is important that the relying party not get
possession of the long-term secret of the client. Aside from a
valuable secret being exposed, a synchronization problem can develop
when the client changes keys with the IdP.
Since there is no single authentication mechanism that will be used
everywhere there is another associated requirement: The
authentication framework must allow for the flexible integration of
authentication mechanisms. For instance, some IdPs require hardware
tokens while others use passwords. A service provider wants to
provide support for both authentication methods, and other methods
from IdPs not yet seen.
These requirements can be met by utilizing standardized and
successfully deployed technology, namely by the Extensible
Authentication Protocol (EAP) framework [RFC3748]. Figure 3
illustrates the integration graphically.
EAP is an end-to-end framework; it provides for two-way communication
between a peer (i.e. client or individual) through the EAP
authenticator (i.e., relying party) to the back-end (i.e., identity
provider). Conveniently, this is precisely the communication path
that is needed for federated identity. Although EAP support is
already integrated in AAA systems (see [RFC3579] and [RFC4072])
several challenges remain:
o The first is how to carry EAP payloads from the end host to the
relying party.
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o Another is to verify statements the relying party has made to the
client, confirm these statements are consistent with statements
made to the identity provider and confirm all of the above are
consistent with the federation and any federation-specific policy
or configuration.
o Another challenge is choosing which identity provider to use for
which service.
The EAP method used for ABFAB needs to meet the following
requirements:
o It needs to provide mutual authentication of the client and IdP.
o It needs to support channel binding.
As of this writing, the only EAP method that meets these criteria is
TEAP [I-D.ietf-emu-eap-tunnel-method] either alone (if client
certificates are used) or with an inner EAP method that does mutual
authentication.
2.2.2. EAP Channel Binding
EAP channel binding is easily confused with a facility in GSS-API
also called channel binding. GSS-API channel binding provides
protection against man-in-the-middle attacks when GSS-API is used as
authentication inside some tunnel; it is similar to a facility called
cryptographic binding in EAP. See [RFC5056] for a discussion of the
differences between these two facilities.
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
protocol, the client and the IdP need to be able to detect this
situation. A general overview of the problem along with a
recommended way to deal with the channel binding issues can be found
in RFC 6677 [RFC6677].
Since that document was published, a number of possible attacks were
found and methods to address these attacks have been outlined in
[RFC7029].
2.3. Client to Relying Party
The final set of interactions between the parties to consider are
those between the client and the RP. In some ways this is the most
complex set since at least part of it is outside the scope of the
ABFAB work. The interactions between these parties include:
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o Running the protocol that implements the service that is provided
by the RP and desired by 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
that it needs beyond authentication.
o Deal with client re-authentication where desired.
2.3.1. GSS-API
One of the remaining layers is responsible for integration of
federated authentication into the application. There are a number of
approaches that applications have adopted for security. So, there
may need to be multiple strategies for integration of federated
authentication into applications. However, we have started with a
strategy that provides integration to a large number of application
protocols.
Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645]
and several non-IETF applications support the Generic Security
Services Application Programming Interface [RFC2743]. Many
applications such as IMAP, SMTP, XMPP and LDAP support the Simple
Authentication and Security Layer (SASL) [RFC4422] framework. These
two approaches work together nicely: by creating a GSS-API mechanism,
SASL integration is also addressed. In effect, using a GSS-API
mechanism with SASL simply requires placing some headers on the front
of the mechanism and constraining certain GSS-API options.
GSS-API is specified in terms of an abstract set of operations which
can be mapped into a programming language to form an API. When
people are first introduced to GSS-API, they focus on it as an API.
However, from the prospective of authentication for non-web
applications, GSS-API should be thought of as a protocol as well as
an API. When looked at as a protocol, it consists of abstract
operations such as the initial context exchange, which includes two
sub-operations (gss_init_sec_context and gss_accept_sec_context). An
application defines which abstract operations it is going to use and
where messages produced by these operations fit into the application
architecture. A GSS-API mechanism will define what actual protocol
messages result from that abstract message for a given abstract
operation. So, since this work is focusing on a particular GSS-API
mechanism, we generally focus on protocol elements rather than the
API view of GSS-API.
The API view of GSS-API does have significant value as well, since
the abstract operations are well defined, the set of information that
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a mechanism gets from the application is well defined. Also, the set
of assumptions the application is permitted to make is generally well
defined. As a result, an application protocol that supports GSS-API
or SASL is very likely to be usable with a new approach to
authentication including this one with no required modifications. In
some cases, support for a new authentication mechanism has been added
using plugin interfaces to applications without the application being
modified at all. Even when modifications are required, they can
often be limited to supporting a new naming and authorization model.
For example, this work focuses on privacy; an application that
assumes it will always obtain an identifier for the client will need
to be modified to support anonymity, unlinkability or pseudonymity.
So, we use GSS-API and SASL because a number of the application
protocols we wish to federate support these strategies for security
integration. What does this mean from a protocol standpoint and how
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
mechanism that encapsulates EAP authentication. So, GSS-API (and
SASL) encapsulates EAP between the end-host and the service. The AAA
framework encapsulates EAP between the relying party and the identity
provider. The GSS-API mechanism includes rules about how initiators
and services are named as well as per-message security and other
facilities required by the applications we wish to support.
2.3.2. Protocol Transport
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
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 confidentiality 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.
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o GSS-API messages need to be delivered atomically. If the
transport breaks up a message it must also reassemble the message
before delivery.
2.3.3. Reauthentication
There are circumstances where the RP 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
One of the key goals is to integrate federated authentication into
existing application protocols and where possible, existing
implementations of these protocols. Another goal is to perform this
integration while meeting the best security practices of the
technologies used to perform the integration. This section describes
security services and properties required by the EAP GSS-API
mechanism in order to meet these goals. This information could be
viewed as specific to that mechanism. However, other future
application integration strategies are very likely to need similar
services. So, it is likely that these services will be expanded
across application integration strategies if new application
integration strategies are adopted.
3.1. Authentication
GSS-API provides an optional security service called mutual
authentication. This service means that in addition to the initiator
providing (potentially anonymous or pseudonymous) identity to the
acceptor, the acceptor confirms its identity to the initiator.
Especially for the ABFAB context, this service is confusingly named.
We still say that mutual authentication is provided when the identity
of an acceptor is strongly authenticated to an anonymous initiator.
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RFC 2743, unfortunately, does not explicitly talk about what mutual
authentication means. Within this document we therefore define
mutual authentication as:
o If a target name is configured for the initiator, then the
initiator trusts that the supplied target name describes the
acceptor. This implies both that appropriate cryptographic
exchanges took place for the initiator to make such a trust
decision, and that after evaluating the results of these
exchanges, the initiator's policy trusts that the target name is
accurate.
o If no target name is configured for the initiator, then the
initiator trusts that the acceptor name, supplied by the acceptor,
correctly names the entity it is communicating with.
o Both the initiator and acceptor have the same key material for
per-message keys and both parties have confirmed they actually
have the key material. In EAP terms, there is a protected
indication of success.
Mutual authentication is an important defense against certain aspects
of phishing. Intuitively, clients would like to assume that if some
party asks for their credentials as part of authentication,
successfully gaining access to the resource means that they are
talking to the expected party. Without mutual authentication, the
server could "grant access" regardless of what credentials are
supplied. Mutual authentication better matches this user intuition.
It is important, therefore, that the GSS-EAP mechanism implement
mutual authentication. That is, an initiator needs to be able to
request mutual authentication. When mutual authentication is
requested, only EAP methods capable of providing the necessary
service can be used, and appropriate steps need to be taken to
provide mutual authentication. While a broader set of EAP methods
could be supported by not requiring mutual authentication, it was
decided that the client needs to always have the ability to request
it. In some cases the IdP and the RP will not support mutual
authentication, however the client will always be able to detect this
and make an appropriate security decision.
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The AAA infrastructure may hide the initiator's identity from the
GSS-API acceptor, providing anonymity between the initiator and the
acceptor. At this time, whether the identity is disclosed is
determined by EAP server policy rather than by an indication from the
initiator. Also, initiators are unlikely to be able to determine
whether anonymous communication will be provided. For this reason,
initiators are unlikely to set the anonymous return flag from
GSS_Init_Sec_context (Section 4.2.1 in [RFC4178].
3.2. GSS-API Channel Binding
[RFC5056] defines a concept of channel binding which is used prevent
man-in-the-middle attacks. The channel binding works by taking a
cryptographic value from the transport security and checks that both
sides of the GSS-API conversation know this value. Transport Layer
Security (TLS) [RFC5246] is the most common transport security layer
used for this purpose.
It needs to be stressed that RFC 5056 channel binding (also called
GSS-API channel binding when GSS-API is involved) is not the same
thing as EAP channel binding. GSS-API channel binding is used for
detecting Man-In-The-Middle attacks. EAP channel binding is used for
mutual authentication and acceptor naming checks. Details are
discussed in the mechanisms specification [RFC7055]. A fuller
description of the differences between the facilities can be found in
RFC 5056 [RFC5056].
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
security services.
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
validation is predicated on a couple of things. The TLS sessions
needs to be using certificates and not be an anonymous session. 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
server authentication. However there are a variety of situations
where this authentication is not checked for policy or usability
reasons. When the TLS authentication is checked, if the trust
infrastructure behind the TLS authentication is different from the
trust infrastructure behind the GSS-API mutual authentication then
confirming the end-points using both trust infrastructures is likely
to enhance security. If the endpoints of the GSS-API authentication
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
binding provides a facility to determine whether these endpoints are
the same.
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The GSS-EAP mechanism needs to support channel binding. When an
application provides channel binding data, the mechanism needs to
confirm this is the same on both sides consistent with the GSS-API
specification.
3.3. Host-Based Service Names
IETF security mechanisms typically take a host name and perhaps a
service, entered by a user, and make some trust decision about
whether the remote party in the interaction is the intended party.
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
relatively flexible name convention, however most of the IETF
applications that use GSS-API (including SSH, NFS, IMAP, LDAP and
XMPP) have chosen to use a more restricted naming convention based on
the host name. The GSS-EAP mechanism needs to support host-based
service names in order to work with existing IETF protocols.
The use of host-based service names leads to a challenging trust
delegation problem. Who is allowed to decide whether a particular
host name maps to a specific entity? Possible solutions to this
problem have been looked at.
o The public-key infrastructure (PKI) used by the web has chosen to
have a number of trust anchors (root certificate authorities) each
of which can map any host name to a public key.
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
introduced, the realm is responsible for host mapping within that
realm. The mechanism then decides what realm is responsible for a
given name. This is the approach adopted by ABFAB.
GSS-EAP defines a host naming convention that takes into account the
host name, the realm, the service and the service parameters. An
example of GSS-API service name is "xmpp/foo@example.com". This
identifies the XMPP service on the host foo in the realm example.com.
Any of the components, except for the service name may be omitted
from a name. When omitted, then a local default would be used for
that component of the name.
While there is no requirement that realm names map to Fully Qualified
Domain Names (FQDN) within DNS, in practice this is normally true.
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
locating the host of a service while establishing the transport
channel between the client and the relying party.
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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
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
application to determine how much of the information identifying the
service needs to be validated by the ABFAB system. The information
that needs to be validated is used to build up the service name
passed into the GSS-EAP mechanism. What information is to be
validated will depend on both what information was provided by the
client, and what information is considered significant. If the
client only cares about getting a specific service, then the host and
realm that provides the service does not need to be validated.
Applications may retrieve information about providers of services
from DNS. Service Records (SRV) [RFC2782] and Naming Authority
Pointer (NAPTR) [RFC3401] records are used to help find a host that
provides a service; however the necessity of having DNSSEC on the
queries depends on how the information is going to be used. If the
host name returned is not going to be validated by EAP channel
binding, because only the service is being validated, then DNSSEC
[RFC4033] is not required. However, if the host name is going to be
validated by EAP channel binding then DNSSEC needs to be use to
ensure that the correct host name is validated. In general, if the
information that is returned from the 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
is that they do not work ideally when different instances of a
service are running on different ports. If the services are
equivalent, then it does not matter. However if there are
substantial differences in the quality of the service that
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,
then this is not going to be a successful strategy.
3.4. Additional GSS-API Services
GSS-API provides per-message security services that can provide
confidentiality and/or integrity. Some IETF protocols such as NFS
and SSH take advantage of these services. As a result GSS-EAP needs
to support these services. As with mutual authentication, per-
message security services will limit the set of EAP methods that can
be used to those that generate a Master Session Key (MSK). Any EAP
method that produces an MSK is able to support per-message security
services described in [RFC2743].
GSS-API provides a pseudo-random function. This function generates a
pseudo-random sequence using the shared session key as the seed for
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the bytes generated. This provides an algorithm that both the
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
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
5705 [RFC5705].). While no current IETF protocols require this, non-
IETF protocols are expected to take advantage of this in the near
future. Additionally, a number of protocols have found the TLS
extractor to be useful in this regards so it is highly probable that
IETF protocols may also start using this feature.
4. Privacy Considerations
ABFAB, as an architecture designed to enable federated authentication
and allow for the secure transmission of identity information between
entities, obviously requires careful consideration around privacy and
the potential for privacy violations.
This section examines the privacy related information presented in
this document, summarizing the entities that are involved in ABFAB
communications and what exposure they have to identity information.
In discussing these privacy considerations in this section, we use
terminology and ideas from [RFC6973].
Note that the ABFAB architecture uses at its core several existing
technologies and protocols; detailed privacy discussion around these
is not examined. This section instead focuses on privacy
considerations specifically related to overall architecture and usage
of ABFAB.
+--------+ +---------------+ +--------------+
| Client | <---> | RP | <---> | AAA Client |
+--------+ +---------------+ +--------------+
^
|
v
+---------------+ +--------------+
| SAML Server | | AAA Proxy(s) |
+---------------+ +--------------+
^ ^
| |
v v
+------------+ +---------------+ +--------------+
| EAP Server | <---> | IdP | <---> | AAA Server |
+------------+ +---------------+ +--------------+
Figure 4: Entities and Data Flow
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4.1. Entities and their roles
Categorizing the ABFAB entities shown in the Figure 4 according to
the taxonomy of terms from [RFC6973] the entities shown in Figure 4
is somewhat complicated as during the various phases of ABFAB
communications the roles of each entity changes. The three main
phases of relevance are the Client to RP communication phase, the
Client to IdP (via the Federation Substrate) phase, and the IdP to RP
(via the Federation Substrate) phase.
In the Client to RP communication phase, we have:
Initiator: Client.
Observers: Client, RP.
Recipient: RP.
In the Client to IdP (via the Federation Substrate) communication
phase, we have:
Initiator: Client.
Observers: Client, RP, AAA Client, AAA Proxy(s), AAA Server, IdP.
Recipient: IdP
In the IdP to Relying party (via the Federation Substrate)
communication phase, we have:
Initiator: RP.
Observers: IdP, AAA Server, AAA Proxy(s), AAA Client, RP.
Recipient: IdP
Eavesdroppers and Attackers can reside on any or all communication
links between entities in Figure 4.
The various entities in the system might also collude or be coerced
into colluding. Some of the significant collusions to look at are:
o If two RPs are colluding, they have the information available to
both nodes. This can be analyzed as if a single RP was offering
multiple services.
o If an RP and a AAA proxy are colluding, then the trust of the
system is broken as the RP would be able to lie about its own
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identity to the IdP. There is no known way to deal with this
situation.
o If multiple AAA proxies are colluding, it can be treated as a
single node for analysis.
The Federation Substrate consists of all of the AAA entities. In
some cases the AAA Proxies entities may not exist as the AAA Client
can talk directly to the AAA Server. Specifications such as the
Trust Router Protocol [5] and RADIUS dynamic discovery
[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
Proxies from being Observers); however even in these circumstances
there may be AAA Proxies in the path.
In Figure 4 the IdP has been divided into multiple logical pieces, in
actual implementations these pieces will frequently be tightly
coupled. The links between these pieces provide the greatest
opportunity for attackers and eavesdroppers to acquire information,
however, as they are all under the control of a single entity they
are also the easiest to have tightly secured.
4.2. Privacy Aspects of ABFAB Communication Flows
In the ABFAB architecture, there are a few different types of data
and identifiers in use. The best way to understand them, and the
potential privacy impacts of them, is to look at each phase of
communication in ABFAB.
4.2.1. Client to RP
The flow of data between the client and the RP is divided into two
parts. The first part consists of all of the data exchanged as part
of the ABFAB authentication process. The second part consists of all
of the data exchanged after the authentication process has been
finished.
During the initial communications phase, the client sends an NAI (see
[I-D.ietf-radext-nai]) to the RP. Many EAP methods (but not all)
allow for the client to disclose an NAI to RP the in a form that
includes only a realm component during this communications phase.
This is the minimum amount of identity information necessary for
ABFAB to work - it indicates an IdP that the principal has a
relationship with. EAP methods that do not allow this will
necessarily also reveal an identifier for the principal in the IdP
realm (e.g. a username).
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The data shared during the initial communication phase may be
protected by a channel protocol such as TLS. This will prevent the
leak of information to passive eavesdroppers, however an active
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
by the service, deferring the check of the identity of the RP until
the completion of the ABFAB authentication protocol (i.e., using EAP
channel binding).
The data exchanged after the authentication process can have privacy
and authentication using the GSS-API services. If the overall
application protocol allows for the process of re-authentication,
then the same privacy implications as discussed in previous
paragraphs apply.
4.2.2. Client to IdP (via Federation Substrate)
This phase sees a secure TLS tunnel initiated between the Client and
the IdP via the RP and federation substrate. The process is
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
to authenticate.
Various operational information is transported between RP and IdP,
over the AAA infrastructure, for example using RADIUS headers. 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 on this
information unless additional security measures are taken (such as
the use of TLS for RADIUS [I-D.ietf-radext-dtls]). Some of this
information may form identifiers or explicit identity information:
o The Relying Party knows the IP address of the Client. It is
possible that the Relying Party could choose to expose this IP
address by including it in a RADIUS header such as Calling Station
ID. This is a privacy consideration to take into account of the
application protocol.
o The EAP MSK is transported between the IdP and the RP over the AAA
infrastructure, for example through RADIUS headers. This is a
particularly important privacy consideration, as any AAA Proxy
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
between the Client and RP). This problem can be mitigted by the
application protocol setting up a secure tunnel between the Client
and the RP and performing a cryptographic binding between the
tunnel and EAP MSK.
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o Related to the above, the AAA server has access to the material
necessary to derive the session key, thus the AAA server can
observe any traffic encrypted between the Client and RP. This
"feature" was chosen as a simplification and to make performance
faster; if it was decided that this trade-off was not desirable
for privacy and security reasons, then extensions to ABFAB that
make use of techniques such as Diffie-Helman key exchange would
mitigate against this.
The choice of EAP method used has other potential privacy
implications. For example, if the EAP method in use does not support
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
including a username and a realm might be sent to any entity
masquerading as a particular IdP.
Note that ABFAB has not specified any AAA accounting requirements.
Implementations that use the accounting portion of AAA should
consider privacy appropriately when designing this aspect.
4.2.3. IdP to RP (via Federation Substrate)
In this phase, the IdP communicates with the RP informing it as to
the success or failure of authentication of the user, and optionally,
the sending of identity information about the principal.
As in the previous flow (Client to IdP), various operation
information is transported between IdP and RP over the AAA
infrastructure, and the same privacy considerations apply. However,
in this flow, explicit identity information about the authenticated
principal can be sent from the IdP to the RP. This information can
be sent through RADIUS headers, or using SAML
[I-D.ietf-abfab-aaa-saml]. This can include protocol specific
identifiers, such as SAML NameIDs, as well as arbitrary attribute
information about the principal. What information will be released
is controlled by policy on the Identity Provider. As before, when
sending this through RADIUS headers, all AAA entities on the path
between the RP and IdP have the ability to eavesdrop unless
additional security measures are taken (such as the use of TLS for
RADIUS [I-D.ietf-radext-dtls]). When sending this using SAML, as
specified in [I-D.ietf-abfab-aaa-saml], confidentiality of the
information should however be guaranteed as [I-D.ietf-abfab-aaa-saml]
requires the use of TLS for RADIUS.
4.3. Relationship between User and Entities
o Between User and IdP - the IdP is an entity the user will have a
direct relationship with, created when the organization that
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operates the entity provisioned and exchanged the user's
credentials. Privacy and data protection guarantees may form a
part of this relationship.
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
question. Some services may only be offered to those users where
such a direct relationship exists (for particularly sensitive
services, for example), while some may not require this and would
instead be satisfied with basic federation trust guarantees
between themselves and the IdP). This may well include the option
that the user stays anonymous with respect to the RP (though
obviously never to the IdP). If attempting to preserve privacy
through the mitigation of data minimization, then the only
attribute information about individuals exposed to the RP should
be that which is strictly necessary for the operation of the
service.
o Between User and Federation substrate - the user is highly likely
to have no knowledge of, or relationship with, any entities
involved with the federation substrate (not that the IdP and/or RP
may, however). Knowledge of attribute information about
individuals for these entities is not necessary, and thus such
information should be protected in such a way as to prevent access
to this information from being possible.
4.4. Accounting Information
Alongside the core authentication and authorization that occurs in
AAA communications, accounting information about resource consumption
may be delivered as part of the accounting exchange during the
lifetime of the granted application session.
4.5. Collection and retention of data and identifiers
In cases where Relying Parties are not required to identify a
particular individual when an individual wishes to make use of their
service, the ABFAB architecture enables anonymous or pseudonymous
access. Thus data and identifiers other than pseudonyms and
unlinkable attribute information need not be stored and retained.
However, in cases where Relying Parties require the ability to
identify a particular individual (e.g. so they can link this identity
information to a particular account in their service, or where
identity information is required for audit purposes), the service
will need to collect and store such information, and to retain it for
as long as they require. Deprovisioning of such accounts and
information is out of scope for ABFAB, but obviously for privacy
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protection any identifiers collected should be deleted when they are
no longer needed.
4.6. User Participation
In the ABFAB architecture, by its very nature users are active
participants in the sharing of their identifiers as they initiate the
communications exchange every time they wish to access a server.
They are, however, not involved in control of the set of information
related to them that transmitted from the IdP to RP for authorization
purposes; rather, this is under the control of policy on the IdP.
Due to the nature of the AAA communication flows, with the current
ABFAB architecture there is no place for a process of gaining user
consent for the information to be released from IdP to RP.
5. Security Considerations
This document describes the architecture for Application Bridging for
Federated Access Beyond Web (ABFAB) and security is therefore the
main focus. Many of the items that are security considerations have
already been discussed in the Privacy Considerations section.
Readers should be sure to read that section as well.
There are many places in this document where TLS is used. While in
some places (i.e. client to RP) anonymous connections can be used, it
is very important that TLS connections within the AAA infrastructure
and between the client and the IdP be fully authenticated and, if
using certificates, that revocation be checked as well. When using
anonymous connections between the client and the RP, all messages and
data exchanged between those two entities will be visible to an
active attacker. In situations where the client is not yet on the
net, the status_request extension [RFC6066] can be used to obtain
revocation checking data inside of the TLS protocol. Clients also
need to get the Trust Anchor for the IdP configured correctly in
order to prevent attacks, this is a hard problem in general and is
going to be even harder for kiosk environments.
Selection of the EAP methods to be permitted by clients and IdPs is
important. The use of a tunneling method such as TEAP
[I-D.ietf-emu-eap-tunnel-method] allows for other EAP methods to be
used while hiding the contents of those EAP exchanges from the RP and
the AAA framework. When considering inner EAP methods the
considerations outlined in [RFC7029] about binding the inner and
outer EAP methods needs to be considered. Finally, one wants to have
the ability to support channel binding in those cases where the
client needs to validate that it is talking to the correct RP.
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In those places where SAML statements are used, RPs will generally be
unable to validate signatures on the SAML statement, either because
it is stripped off by the IdP or because it is unable to validate the
binding between the signer, the key used to sign and the realm
represented by the IdP. For these reasons it is required that IdPs
do the necessary trust checking on the SAML statements and RPs can
trust the AAA infrastructure to keep the SAML statement valid.
When a pseudonym is generated as a unique long term identifier for a
client by an IdP, care must be taken in the algorithm that it cannot
easily be reverse engineered by the service provider. If it can be
reversed then the service provider can consult an oracle to determine
if a given unique long term identifier is associated with a different
known identifier.
6. IANA Considerations
This document does not require actions by IANA.
7. Acknowledgments
We would like to thank Mayutan Arumaithurai, Klaas Wierenga and Rhys
Smith for their feedback. Additionally, we would like to thank Eve
Maler, Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, Paul
Leach, and Luke Howard for their feedback on the federation
terminology question.
Furthermore, we would like to thank Klaas Wierenga for his review of
the pre-00 draft version.
8. References
8.1. Normative References
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
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[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", RFC 4072,
August 2005.
[RFC7055] Hartman, S. and J. Howlett, "A GSS-API Mechanism for the
Extensible Authentication Protocol", RFC 7055, December
2013.
[I-D.ietf-abfab-aaa-saml]
Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding,
Profiles, Name Identifier Format, and Confirmation Methods
for SAML", draft-ietf-abfab-aaa-saml-09 (work in
progress), February 2014.
[I-D.ietf-radext-nai]
DeKok, A., "The Network Access Identifier", draft-ietf-
radext-nai-06 (work in progress), June 2014.
[RFC6677] Hartman, S., Clancy, T., and K. Hoeper, "Channel-Binding
Support for Extensible Authentication Protocol (EAP)
Methods", RFC 6677, July 2012.
8.2. Informative References
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, July
2013.
[I-D.ietf-radext-radius-fragmentation]
Perez-Mendez, A., Lopez, R., Pereniguez-Garcia, F., Lopez-
Millan, G., Lopez, D., and A. DeKok, "Support of
fragmentation of RADIUS packets", draft-ietf-radext-
radius-fragmentation-06 (work in progress), April 2014.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC
1964, June 1996.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
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[RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J.,
and R. Hall, "Generic Security Service Algorithm for
Secret Key Transaction Authentication for DNS (GSS-TSIG)",
RFC 3645, October 2003.
[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
"Generic Security Service Application Program Interface
(GSS-API) Authentication and Key Exchange for the Secure
Shell (SSH) Protocol", RFC 4462, May 2006.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.
[RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication
Dial In User Service (RADIUS) Implementation Issues and
Suggested Fixes", RFC 5080, December 2007.
[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, March 2010.
[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010.
[RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
"Transport Layer Security (TLS) Encryption for RADIUS",
RFC 6614, May 2012.
[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-
core-2.0-os, March 2005.
[RFC7029] Hartman, S., Wasserman, M., and D. Zhang, "Extensible
Authentication Protocol (EAP) Mutual Cryptographic
Binding", RFC 7029, October 2013.
[I-D.ietf-emu-eap-tunnel-method]
Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel EAP Method (TEAP) Version 1", draft-ietf-emu-eap-
tunnel-method-10 (work in progress), January 2014.
[I-D.ietf-radext-dtls]
Howlett, et al. Expires January 22, 2015 [Page 42]
Internet-Draft ABFAB Architecture July 2014
DeKok, A., "DTLS as a Transport Layer for RADIUS", draft-
ietf-radext-dtls-13 (work in progress), July 2014.
[I-D.ietf-radext-dynamic-discovery]
Winter, S. and M. McCauley, "NAI-based Dynamic Peer
Discovery for RADIUS/TLS and RADIUS/DTLS", draft-ietf-
radext-dynamic-discovery-11 (work in progress), March
2014.
[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>.
[NIST-SP.800-63]
Burr, W., Dodson, D., and W. Polk, "Electronic
Authentication Guideline", NIST Special Publication
800-63, April 2006.
[RFC4178] Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The
Simple and Protected Generic Security Service Application
Program Interface (GSS-API) Negotiation Mechanism", RFC
4178, October 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS", RFC 3401, October 2002.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
Authors' Addresses
Howlett, et al. Expires January 22, 2015 [Page 43]
Internet-Draft ABFAB Architecture July 2014
Josh Howlett
JANET(UK)
Lumen House, Library Avenue, Harwell
Oxford OX11 0SG
UK
Phone: +44 1235 822363
Email: Josh.Howlett@ja.net
Sam Hartman
Painless Security
Email: hartmans-ietf@mit.edu
Hannes Tschofenig
ARM Ltd.
110 Fulbourn Rd
Cambridge CB1 9NJ
Great Britain
Email: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Eliot Lear
Cisco Systems GmbH
Richtistrasse 7
Wallisellen, ZH CH-8304
Switzerland
Phone: +41 44 878 9200
Email: lear@cisco.com
Jim Schaad
Soaring Hawk Consulting
Email: ietf@augustcellars.com
Howlett, et al. Expires January 22, 2015 [Page 44]
