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RFC 2905 - AAA Authorization Application Examples

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Network Working Group                                      J. Vollbrecht
Request for Comments: 2905                      Interlink Networks, Inc.
Category: Informational                                       P. Calhoun
                                                  Sun Microsystems, Inc.
                                                              S. Farrell
                                                  Baltimore Technologies
                                                              L. Gommans
                                                 Enterasys Networks EMEA
                                                                G. Gross
                                                     Lucent Technologies
                                                            B. de Bruijn
                                                 Interpay Nederland B.V.
                                                              C. de Laat
                                                      Utrecht University
                                                             M. Holdrege
                                                               D. Spence
                                                Interlink Networks, Inc.
                                                             August 2000

                 AAA Authorization Application Examples

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.


   This memo describes several examples of applications requiring
   authorization.  Each application is described in terms of a
   consistent framework, and specific authorization requirements of each
   application are given.  This material was not contributed by the
   working groups responsible for the applications and should not be
   considered prescriptive for how the applications will meet their
   authorization needs.  Rather the intent is to explore the fundamental
   needs of a variety of different applications with the view of
   compiling a set of requirements that an authorization protocol will
   need to meet in order to be generally useful.

Table of Contents

   1. Introduction ................................................    3
   2. PPP Dialin with Roaming .....................................    4
      2.1. Descriptive Model ......................................    4
      2.2. Authorization Requirements .............................    6
   3. Mobile-IP ...................................................    6
      3.1. Relationship to the Framework ..........................   10
      3.2. Minimized Internet Traversal ...........................   10
      3.3. Key Distribution .......................................   10
      3.4. Mobile-IP Authorization Requirements ...................   11
   4. Bandwidth Broker ............................................   12
      4.1. Model Description ......................................   13
      4.2. Components of the Two-Tier Model .......................   13
      4.3. Identification of Contractual Relationships ............   13
           4.3.1. Single-Domain Case ..............................   14
           4.3.2. Multi-Domain Case ...............................   15
      4.4. Identification of Trust Relationships ..................   16
      4.5. Communication Models and Trust Relationships ...........   18
      4.6. Bandwidth Broker Communication Models ..................   19
           4.6.1. Concepts ........................................   19
       Intra-Domain Authorization ...............   19
       Inter-Domain Authorization ...............   19
           4.6.2. Bandwidth Broker Work Phases ....................   20
           4.6.3. Inter-Domain Signaling ..........................   20
       Phase 0 ..................................   20
       Phase 1 ..................................   20
           4.6.4. Bandwidth Broker Communication Architecture .....   22
           4.6.5. Two-Tier Inter-Domain Model .....................   23
       Session Initialization ...................   23
       Service Setup ............................   23
       Service Cancellation .....................   24
       Service Renegotiation ....................   24
       RAR and RAA ..............................   24
       Session Maintenance ......................   24
       Intra-domain Interface Protocol ..........   24
      4.7. Requirements ...........................................   24
   5. Internet Printing ...........................................   25
      5.1. Trust Relationships ....................................   26
      5.2. Use of Attribute Certificates ..........................   27
      5.3. IPP and the Authorization Descriptive Model ............   28
   6. Electronic Commerce .........................................   29
      6.1. Model Description ......................................   30
           6.1.1. Identification of Components ....................   30
           6.1.2. Identification of Contractual Relationships .....   31
           6.1.3. Identification of Trust Relationships ...........   32
       Static Trust Relationships ...............   33
       Dynamic Trust Relationships ..............   35

           6.1.4. Communication Model .............................   35
      6.2. Multi Domain Model .....................................   37
      6.3. Requirements ...........................................   38
   7. Computer Based Education and Distance Learning ..............   40
      7.1. Model Description ......................................   40
           7.1.1. Identification of Components ....................   40
           7.1.2. Identification of Contractual Relationships .....   41
           7.1.3. Identification of Trust Relationships ...........   43
           7.1.4. Sequence of Requests ............................   44
      7.2. Requirements ...........................................   46
   8. Security Considerations .....................................   47
   Glossary .......................................................   47
   References .....................................................   48
   Authors' Addresses .............................................   50
   Full Copyright Statement .......................................   53

1.  Introduction

   This document is one of a series of three documents under
   consideration by the AAAarch RG dealing with the authorization
   requirements for AAA protocols.  The three documents are:

         AAA Authorization Framework [2]
         AAA Authorization Requirements [3]
         AAA Authorization Application Examples (this document)

   In this memo, we examine several important Internet applications that
   require authorization.  For each application, we present a model
   showing how it might do authorization and then map that model back to
   the framework presented in [2].  We then present the authorization
   requirements of the application as well as we presently understand
   them.  The requirements presented in this memo have been collected
   together, generalized, and presented in [3].

   The intent of this memo is to validate and illustrate the framework
   presented in [2] and to motivate the requirements presented in [3].
   This work is intended to be in alignment with the work of the various
   working groups responsible for the authorization applications
   illustrated.  This memo should not, however, be regarded as
   authoritative for any of the applications illustrated.  Where
   authoritative documents exist or are in development, they are listed
   in the references at the end of this document.

   The work for this memo was done by a group that originally was the
   Authorization subgroup of the AAA Working Group of the IETF.  When
   the charter of the AAA working group was changed to focus on MobileIP
   and NAS requirements, the AAAarch Research Group was chartered within
   the IRTF to continue and expand the architectural work started by the
   Authorization subgroup.  This memo is one of four which were created
   by the subgroup.  This memo is a starting point for further work
   within the AAAarch Research Group.  It is still a work in progress
   and is published so that the work will be available for the AAAarch
   subgroup and others working in this area, not as a definitive
   description of architecture or requirements.

   This document uses the terms 'MUST', 'SHOULD' and 'MAY', and their
   negatives, in the way described in RFC 2119 [4].

2.  PPP Dialin with Roaming

   In this section, we present an authorization model for dialin network
   access in terms of the framework presented in [2].  Included in the
   model are the multi-domain considerations required for roaming [5].
   Detailed requirements for network access protocols are presented in

2.1.  Descriptive Model

   The PPP dialin application uses the pull sequence as discussed in
   [2].  The roaming case uses the roaming pull sequence, also discussed
   in [2].  This sequence is redrawn using dialin roaming terminology in
   figure 1, below.

            +------+      +-------------------------+
            |      |      | Home ISP                |
            |      |      | (User Home Organization)|
            |      |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |      |  |                   |  |
            |      |      |  +-------------------+  |
            |      |      |             /|\  |      |
            |      |      +--------------+---+------+
            |      |                     |   |
            |      |                     |3  |4
            |      |                     |   |
            |      |      +--------------+---+------+
            |      |      | Visited ISP  |   |      |
            |      |      |              |  \|/     |
            | User |      |  +-------------------+  |
            |      |      |  |    AAA Server     |  |
            |      |      |  |                   |  |
            |      |      |  +-------------------+  |
            |      |      |             /|\  |      |
            |      |      |              |2  |5     |
            |      |      |              |  \|/     |
            |      |   1  |  +-------------------+  |
            |      |------+->| NAS (Service      |  |
            |      |<-----+--|      Equipment)   |  |
            |      |   6  |  +-------------------+  |
            |      |      |  (Service Provider)     |
            +------+  PPP +-------------------------+

            Fig. 1 -- Dialin Authorization
                      Based on Roaming Pull Sequence

   In this model, the User dials in to a Network Access Server (NAS)
   provided by the visited (or foreign) ISP (the Service Provider in the
   general model). The User is authenticated using a protocol such as
   PAP, CHAP, or EAP which is encapsulated in PPP frames (1).  Because
   the User has not yet gained access to the network, he or she cannot
   send IP datagrams to a AAA server. At this point, the User can only
   communicate with the NAS (Service Equipment).  The NAS forwards the
   User's authentication/ authorization request including the Network
   Access Identifier (NAI) [7] to a AAA server in its own domain via
   RADIUS [8] or a successor AAA protocol (2).  The visited ISP's AAA
   server examines the realm from the NAI and forwards the request to
   the User's home domain AAA server (3).  The home domain AAA server
   authenticates the user and authorizes access according to a roaming
   agreement.  The home domain AAA server may return service parameters

   (e.g. Idle-Timeout) to the visited ISP's AAA server (4) which
   forwards them to the NAS, possibly adding additional service
   parameters (5).  The NAS completes PPP session initialization (6).

   In the future, this model may be expanded in several ways [9].  For
   instance, Authentication and Authorization may be done in separate
   passes using different servers in order to support specialized forms
   of authentication.  Or to better support roaming, a broker may be
   inserted between the visited ISP and the home ISP.  Or authorization
   may be supported based on other identifiers such as the caller ID and
   called ID obtained from the PSTN (e.g., using ANI and DNIS).

2.2.  Authorization Requirements

   The following requirements are identified in [9] for authorizing PPP
   dialin service using roaming.

   -  Authorization separate from authentication should be allowed when
      necessary, but the AAA protocol MUST allow for a single message to
      request both authentication and authorization.

   -  The AAA protocol MUST be "proxyable", meaning that a AAA Server or
      PDP MUST be able to forward the request to another AAA Server or
      PDP, which may or may not be within the same administrative

   -  The AAA protocol MUST allow for intermediate brokers to add their
      own local Authorization information to a request or response.

   -  When a broker is involved, the protocol MUST provide end to end

   -  The broker MUST be able to return a forwarding address to a
      requester, allowing two nodes to communicate together.

   -  The protocol MUST provide the following features (per user

      1. One Authentication, One Authorization
      2. One Authentication, Multiple Authorization
      3. Multiple Authentication, Multiple Authorization

3.  Mobile-IP

   The Mobile-IP protocol is used to manage mobility of an IP host
   across IP subnets [10].  Recent activity within the Mobile-IP Working
   Group has defined the interaction between Mobile-IP and AAA in order
   to provide:

      -  Better scaling of security associations
      -  Mobility across administrative domain boundaries
      -  Dynamic assignment of Home Agent

   The Mobile IP protocol, as defined in [10], works well when all
   mobile nodes belong to the same administrative domain.  Some of the
   current work within the Mobile IP Working Group is to allow Mobile IP
   to scale across administrative domains.  This changes the trust model
   that is currently defined in [10].

   The requirements for Mobile-IP authorization are documented in [11].
   In this section, we develop a multi-domain model for Mobile-IP
   authorization and present it in the terms of the framework presented
   in [2].

   Figure 2 depicts the new AAA trust model for Mobile-IP.  In this
   model each network contains mobile nodes (MN) and a AAA server (AAA).
   Each mobility device shares a security association (SA) with the AAA
   server within its own home network.  This means that none of the
   mobility devices initially share a security association.  Both
   administrative domains' AAA servers can either share a security
   association, or can have a security association with an intermediate

                             Broker AAA
                             |        |
                             |  AAA   |
                       /=====|        |=====\
                      //     +--------+     \\
            Foreign  // SA                SA \\   Home
              AAA   //                        \\  AAA
             +--------+                      +--------+
             |        |          SA          |        |
             |  AAA   |======================|  AAA   |
             |        | (in lieu of broker)  |        |
             +--------+                      +--------+
                 ||                           ||    ||
              SA ||                        SA ||    || SA
                 ||                           ||    ||
                 ||                           ||    ||
             +---------+              +---------+  +---------+
             |         |              |         |  |         |
             |   FA    |              |   HA    |  |   MN    |
             |         |              |         |  |         |
             +---------+              +---------+  +---------+

                    Fig. 2 -- Mobile-IP AAA Trust Model

   Figure 3 provides an example of a Mobile-IP network that includes
   AAA. In the integrated Mobile-IP/AAA Network, it is assumed that each
   mobility agent shares a security association between itself and its
   local AAA server.  Further, the Home and Foreign AAA servers both
   share a security association with the broker's AAA server.  Lastly,
   it is assumed that each mobile node shares a trust relationship with
   its home AAA Server.

           Visited Access      Broker          Home IP
           Provider Network    Network         Network
             +--------+      +--------+      +--------+
             |        |      |        |      |        |
             |  AAA   |------|  AAA   |------|  AAA   |
             |        |      |        |      |        |
             +--------+      +--------+      +--------+
                  |                              |
                  |                              |
              AAA |                              | AAA
                  |                              |
                  |                              |
             +---------+                    +---------+
             |         |                    |         |
             |   FA    |                    |   HA    |
             |         |                    |         |
             +---------+                    +---------+
                  |   Visited Access     Home Network
                  |  Provider Network       -Private Network
           Mobile |                         -Home Provider
             IP   |                         -Home ISP
             | Mobile |
             | Node   |

    Fig. 3 -- General Wireless IP Architecture for Mobile-IP AAA

   In this example, a Mobile Node appears within a foreign network and
   issues a registration to the Foreign Agent.  Since the Foreign Agent
   does not share any security association with the Home Agent, it sends
   a AAA request to its local AAA server, which includes the
   authentication information and the Mobile-IP registration request.
   The Mobile Node cannot communicate directly with the home AAA Server
   for two reasons:

      -  It does not have access to the network.  The registration
         request is sent by the Mobile Node to request access to the
      -  The Mobile Node may not have an IP address, and may be
         requesting that one be assigned to it by its home provider.

   The Foreign AAA Server will determine whether the request can be
   satisfied locally through the use of the Network Access Identifier
   [7] provided by the Mobile Node.  The NAI has the format of
   user@realm and the AAA Server uses the realm portion of the NAI to
   identify the Mobile Node's home AAA Server. If the Foreign AAA Server
   does not share any security association with the Mobile Node's home
   AAA Server, it may forward the request to its broker.  If the broker
   has a relationship with the home network, it can forward the request,
   otherwise a failed response is sent back to the Foreign AAA Server.

   When the home AAA Server receives the AAA Request, it authenticates
   the user and begins the authorization phase.  The authorization phase
   includes the generation of:

      -  Dynamic Session Keys to be distributed among all Mobility
      -  Optional Dynamic assignment of a Home Agent
      -  Optional Dynamic assignment of a Home Address (note this could
         be done by the Home Agent).
      -  Optional Assignment of QOS parameters for the Mobile Node [12]

   Once authorization is complete, the home AAA Server issues an
   unsolicited AAA request to the Home Agent, which includes the
   information in the original AAA request as well as the authorization
   information generated by the home AAA server.  The Home Agent
   retrieves the Registration Request from the AAA request and processes
   it, then generates a Registration Reply that is sent back to the home
   AAA server in a AAA response.  The message is forwarded through the
   broker back to the Foreign AAA server, and finally to the Foreign

   The AAA servers maintain session state information based on the
   authorization information.  If a Mobile Node moves to another Foreign
   Agent within the foreign domain, a request to the foreign AAA server
   can immediately be done in order to immediately return the keys that
   were issued to the previous Foreign Agent.  This minimizes an
   additional round trip through the internet when micro mobility is
   involved, and enables smooth hand-off.

3.1.  Relationship to the Framework

   Mobile-IP uses the roaming pull model described in [2].  The Mobile
   Node is the User.  The Foreign Network is the Service Provider with
   the Foreign Agent as the Service Equipment.  The Home Network is the
   User Home Organization.  Note that the User Home Organization
   operates not only a AAA Server, but also the Home Agent.  Note, also,
   that a broker has been inserted between the Service Provider and the
   User Home Organization.

3.2.  Minimized Internet Traversal

   Although it would have been possible for the AAA interactions to be
   performed for basic authentication and authorization, and the
   Registration flow to be sent directly to the Home Agent from the
   Foreign Agent, one of the key Mobile-IP AAA requirements is to
   minimize Internet Traversals. Including the Registration Request and
   Replies in the AAA messages allows for a single traversal to
   authenticate the user, perform authorization and process the
   Registration Request.  This streamlined approach is required in order
   to minimize the latency involved in getting wireless (cellular)
   devices access to the network.  New registrations should not increase
   the connect time more than what the current cellular networks

3.3.  Key Distribution

   In order to allow the scaling of wireless data access across
   administrative domains, it is necessary to minimize the security
   associations required. This means that each Foreign Agent does not
   share a security association with each Home Agent on the Internet.
   The Mobility Agents share a security association with their local AAA
   server, which in turn shares a security association with other AAA
   servers.  Again, the use of brokers, as defined by the Roaming
   Operations (roamops) Working Group, allows such services to scale by
   allowing the number of relationships established by the providers to
   be reduced.

   After a Mobile Node is authenticated, the authorization phase
   includes the generation of Sessions Keys.  Specifically, three keys
   are generated:

      -  k1 - Key to be shared between the Mobile Node and the Home
      -  k2 - Key to be shared between the Mobile Node and the Foreign
      -  k3 - Key to be shared between the Foreign Agent and the Home

   Each Key is propagated to each mobility device through the AAA
   protocol (for the Foreign and Home Agent) and via Mobile-IP for the
   Mobile Node (since the Mobile Node does not interface directly with
   the AAA servers).

   Figure 4 depicts the new security associations used for Mobile-IP
   message integrity using the keys derived by the AAA server.

             +--------+                      +--------+
             |        |          k3          |        |
             |   FA   |======================|   HA   |
             |        |                      |        |
             +--------+                      +--------+
                   \\                          //
                    \\ k2                  k1 //
                     \\      +--------+      //
                      \\     |        |     //
                       \=====|   MN   |=====/
                             |        |

       Fig. 4 -- Security Association after Key Distribution

   Once the session keys have been established and propagated, the
   mobility devices can exchange registration information directly
   without the need of the AAA infrastructure.  However the session keys
   have a lifetime, after which the AAA infrastructure must be used in
   order to acquire new session keys.

3.4.  Mobile-IP Authorization Requirements

   To summarize, Mobile-IP has the following authorization requirements:

   1. Mobile-IP requires an AAA protocol that makes use of the pull

   2. Mobile-IP requires broker support, and data objects must contain
      data integrity and confidentiality end-to-end.  This means that
      neither the broker nor any other intermediate AAA node should be
      able to decrypt the data objects, but they must be able to verify
      the objects' validity.

   3. Authorization includes Resource Management.  This allows the AAA
      servers to maintain a snapshot of a mobile node's current
      location, keying information, etc.

   4. Due to the nature of the service being offered, it is imperative
      that the AAA transaction add minimal latency to the connect time.
      Ideally, the AAA protocol should allow for a single round trip for
      authentication and authorization.

   5. If the AAA protocol allows for the Mobile-IP registration messages
      to be embedded within the authentication/authorization request,
      this will further reduce the number of round trips required and
      hence reduce the connect time.

   6. It must be possible to pass Mobile-IP specific key management data
      along with the authorization data.  This allows the AAA server to
      act as a Key Distribution Center (KDC).

   7. It must be possible to pass other application-specific data units
      such as home agent selection and home address assignment to be
      carried along with the authorization data units.

   8. The authorization response should allow for diffserv (QOS)
      profiles, which can be used by the mobility agents to provide some
      quality of service to the mobile node.

   9. The AAA protocol must allow for unsolicited messages to be sent to
      a "client", such as the AAA client running on the Home Agent.

4.  Bandwidth Broker

   This section describes authorization aspects derived from the
   Bandwidth Broker architecture as discussed within the Internet2 Qbone
   BB Advisory Council.  We use authorization model concepts to identify
   contract relationships and trust relationships, and we present
   possible message exchanges.  We will derive a set of authorization
   requirements for Bandwidth Brokers from our architectural model.  The
   Internet 2 Qbone BB Advisory Council researches a single and multi-
   domain implementation based on 2-tier authorization concepts.  A 3-
   tier model is considered as a future work item and therefore not part
   of this description. Information concerning the Internet 2 Bandwidth
   Broker work and its concepts can be found at:


   The material in this section is based on [13] which is a work in
   progress of the Internet2 Qbone BB Advisory Council.

4.1.  Model Description

   The establishment of a model involves four steps:

   1. identification of the components that are involved and what they
      are called in this specific environment,
   2. identification of the relationships between the involved parties
      that are based on some form of agreement,
   3. identification of the relationships that are based on trust, and
   4. consideration of the sequence of messages exchanged between

4.2.  Components of the Two-Tier Model for Bandwidth Brokerage

   We will consider the components of a bandwidth broker transaction in
   the context of the conceptual entities defined in [2].  The bandwidth
   broker two-tier model recognizes a User and the Service Provider
   controlling the Service Equipment.

   The components are as follows:

   -  The Service User (User) -- A person or process willing to use
      certain level of QoS by requesting the allocation of a
      quantifiable amount of resource between a selected destination and
      itself.  In bandwidth broker terms, the User is called a Service
      User, capable of generating a Resource Allocation Request (RAR).

   -  The Bandwidth Broker (Service Provider) -- a function that
      authorizes allocation of a specified amount of bandwidth resource
      between an identified source and destination based on a set of
      policies.  In this context we refer to this function as the
      Bandwidth Broker.  A Bandwidth Broker is capable of managing the
      resource availability within a network domain it controls.

   Note: a 3-tier model involving a User Home Organization is recognized
   in [13], however its development is left for future study and
   therefore it is not discussed in this document.

4.3.  Identification of Contractual Relationships

   Authorizations to obtain bandwidth are based on contractual
   relationships. In both the single and multi-domain cases, the current
   Bandwidth Broker model assumes that a User always has a contractual
   relationship with the service domain to which it is connected.

4.3.1.  Single-Domain Case

   In the single-domain case, the User has a contract with a single
   Service Provider in a single service domain.

                                    |             |
                                    | +---------+ |
                                    | |Bandwidth| |
                  +-------+         | |Broker   | |
                  |       |         | |         | |
                  |Service|         | +---------+ |
                  |User   |=========|             |
                  |       |         | +---------+ |
                  |       |         | | Network | |
                  +-------+         | | Routing | |
                                    | | Devices | |
                                    | +---------+ |
                                    | Autonomous  |
                                    | Service     |
                                    | Domain      |
                  ==== contractual

     Fig. 5 -- Two-Tier Single Domain Contractual Relationships

4.3.2.  Multi-Domain Case

   In the multi-domain case, the User has a contract with a single
   Service Provider.  This Service Provider has a contract with
   neighboring Service Providers.  This model is used when independent
   autonomous networks establish contracts with each other.

                        +-------------+        +-------------+
                        |             |        |             |
                        | +---------+ |        | +---------+ |
                        | |Bandwidth| |        | |Bandwidth| |
      +-------+         | |Broker   | |        | |Broker   | |
      |       |         | |         | |        | |         | |
      |Service|         | +---------+ |        | +---------+ |
      |User   |=========|             |========|             |
      |       |         | +---------+ |        | +---------+ |
      |       |         | | Network | |        | | Network | |
      +-------+         | | Routing | |        | | Routing | |
                        | | Devices | |        | | Devices | |
                        | +---------+ |        | +---------+ |
                        | Autonomous  |        | Autonomous  |
                        | Service     |        | Service     |
                        | Domain A    |        | Domain B    |
                        +-------------+        +-------------+

      ==== contractual

     Fig. 6 -- Two-Tier Multi-Domain Contractual Relationships

4.4.  Identification of Trust Relationships

   Contractual relationships may be independent of how trust, which is
   necessary to facilitate authenticated and possibly secure
   communication, is implemented.  There are several alternatives in the
   Bandwidth Broker environment to create trusted relationships.
   Figures 7 and 8 show two alternatives that are options in the two-
   tier Bandwidth Broker model.

                        +-------------+        +-------------+
                        |             |        |             |
                        | +---------+ |        | +---------+ |
                        | |Bandwidth| |        | |Bandwidth| |
      +-------+         | |Broker   | |        | |Broker   | |
      |       O***********O         O************O         | |
      |Service|         | +----O----+ |        | +----O----+ |
      |User   |=========|      *      |========|      *      |
      |       |         | +----0----+ |        | +----O----+ |
      |       |         | |Network  | |        | |Network  | |
      +-------+         | |Routing  | |        | |Routing  | |
                        | |Devices  | |        | |Devices  | |
                        | +---------+ |        | +---------+ |
                        | Autonomous  |        | Autonomous  |
                        | Service     |        | Service     |
                        | Domain A    |        | Domain B    |
                        +-------------+        +-------------+

      ==== contractual relationship
      O**O trust relationship

     Fig. 7 -- Two-Tier Multi-Domain Trust Relationships, alt 1

                        +-------------+        +-------------+
                        |             |        |             |
                        | +---------+ |        | +---------+ |
                        | |Bandwidth| |        | |Bandwidth| |
      +-------+         | |Broker   | |        | |Broker   | |
      |       |         | |         | |        | |         | |
      |Service|         | +----O----+ |        | +----O----+ |
      |User   |=========|      *      |========|      *      |
      |       |         | +----O----+ |        | +----O----+ |
      |       O***********O Network O************O Network | |
      +-------+         | | Routing | |        | | Routing | |
                        | | Devices | |        | | Devices | |
                        | +---------+ |        | +---------+ |
                        | Autonomous  |        | Autonomous  |
                        | Service     |        | Service     |
                        | Domain A    |        | Domain B    |
                        +-------------+        +-------------+

      ==== contractual relationship
      O**O trust relationship

     Fig. 8 -- Two-Tier Multi-Domain Trust Relationships, alt 2

   Although [13] does not recommend specifics regarding this question,
   the document recognizes the need for trust relationships.  In the
   first model, a trust relationship, based on some form of
   authentication method, is created between the User and the Bandwidth
   Broker and among Bandwidth Brokers.  In the second model, which
   enjoys some popularity in enterprise networks, the trust relationship
   may be established via the wiring closet and the knowledge of which
   physical router port or MAC address is connected to which user.  The
   router-Bandwidth Broker relationship may be established physically or
   by some other authentication method or secure channel.

   A Certificate Authority (CA) based trust relationship is shown in
   figure 9.  In this figure, a CA signs public key certificates, which
   then can be used in encrypted message exchanges using public keys
   that are trusted by all involved.  As a first step, each involved
   party must register with the CA so it can join a trust domain.  The
   Router-Bandwidth Broker relationship may be established as described
   in the two previous figures.  An interesting observation regarding
   this kind of model is that the bandwidth broker in domain B may route
   information to the user via the bandwidth broker in domain A without
   BB1 being able to read the information (using end-to-end security).
   This model creates a meshed trust relationship via a tree like CA

                               |  Certificate      |
           ....................|  Authority        |
          :                  ..|                   |..
          :                 :  +-------------------+  :
          :                 :                         :
          :                 :                         :
          :  ***************:***********************  :
          :  *          +---:---------+        +---*--:------+
          :  *          |   :         |        |   *  :      |
          :  *          | +-:-------+ |        | +-O--:----+ |
          :  *          | |{C}      | |        | |   {C}   | |
      +---:--O+         | |Bandwidth| |        | |Bandwidth| |
      |  {C}  O***********O Broker  O************O Broker  | |
      |Service|         | +----O----+ |        | +----O----+ |
      |User   |=========|      *      |========|      *      |
      |       |         | +----0----+ |        | +----O----+ |
      |       |         | |Network  | |        | |Network  | |
      +-------+         | |Routing  | |        | |Routing  | |
                        | |Devices  | |        | |Devices  | |
                        | +---------+ |        | +---------+ |
                        | Autonomous  |        | Autonomous  |
                        | Service     |        | Service     |
                        | Domain A    |        | Domain B    |
                        +-------------+        +-------------+

      ==== contractual relationship
      O**O trust relationship
      {C}. certification process

     Fig. 9 -- Two-Tier Multi-Domain Trust Relationships, alt 3

4.5.  Communication Models and Trust Relationships

   When describing the Bandwidth Broker communication model, it is
   important to recognize that trust relationships between components
   must ensure secure and authenticated communication between the
   involved components.  As the Internet 2 Qbone Bandwidth Broker work
   does not recommend any particular trust relationship model, we make
   the same assumptions as [13].  In theory, the trust model and
   communication model can be independent, however communication
   efficiency will determine the most logical approach.

4.6.  Bandwidth Broker Communication Models

4.6.1.  Concepts

   The current Internet 2 Qbone Bandwidth Broker discussion describes a
   two-tier model, where a Bandwidth Broker accepts Resource Allocation
   Requests (RAR's) from users belonging to its domain or RAR's
   generated by upstream Bandwidth Brokers from adjacent domains.  Each
   Bandwidth Broker will manage one service domain and subsequently
   provide authorization based on a policy that decides whether a
   request can be honored.  Intra-Domain Authorization

   Admission Authorization or Connection Admission Control (CAC) for
   intra-domain communication is performed using whatever method is
   appropriate for determining availability of resources within the
   domain. Generally a Bandwidth Broker configures its service domain to
   certain levels of service.  RAR's are subsequently accommodated using
   a policy-based decision.  Inter-Domain Authorization

   Service Level Specifications (SLS's) provide the basis for handling
   inter-domain bandwidth authorization requests.  A Bandwidth Broker
   monitors both the state of its network components and the state of
   its connections to neighboring networks.  SLS's are translations of
   SLA's established between Autonomous Service Domains.  Each Bandwidth
   Broker will initialize itself so it is aware of existing SLS's.
   SLS's are established in a unidirectional sense.  Two SLS's must
   govern a bi-directional connection.  SLS's are established on the
   level of aggregate data-flows and the resources (bandwidth)
   provisioned for these flows.

   A Bandwidth Broker may honor an inter-domain RAR by applying policy
   decisions determining that a particular RAR does fit into a pre-
   established SLS.  If successful, the Bandwidth Broker will authorize
   the usage of the bandwidth.  If unsuccessful, the Bandwidth Broker
   may deny the request or approve the request after it has re-
   negotiated the SLS with its downstream Bandwidth Broker.

   A separate Policy Manager may be involved in the CAC decision.  The
   Internet 2 Qbone Bandwidth Broker discussion recognizes an ideal
   environment where Bandwidth Brokers and Policy Managers work together
   to provide CAC using integrated policy services [13].

4.6.2.  Bandwidth Broker Work Phases

   The Internet 2 Qbone Bandwidth Broker discussion proposes development
   of the Bandwidth Broker model in several phases:

   -  Phase 0: Local Admission.  RAR's are only handled within a local
      domain. SLS's are pre-established using manual methods (fax, e-

   -  Phase 1: Informed Admission.  RAR's spanning multiple domains are
      authorized based on information obtained from one or more
      Bandwidth Brokers along the path.

   -  Phase 2: Dynamic SLS admission.  Bandwidth Brokers can dynamically
      set up new SLS's.

   Although the local admission case is addressed, the current Internet
   2 Qbone Bandwidth Broker work is currently concerned with solving
   multi-domain problems in order to allow individual Bandwidth Brokers
   to inter-operate as identified in phase 0 or 1.

4.6.3.  Inter-Domain Signaling  Phase 0

   In phase 0 implementations, no electronic signaling between Bandwidth
   Brokers is performed and SLS negotiation will be performed manually
   (phone, email etc) by network operators.  An RAR is only handled
   within the domain and may originate from a User or ingress router.  Phase 1

   Here a CAC decision is made on information obtained from downstream
   Bandwidth Brokers.  This information could come from the next hop
   Bandwidth Broker or all Bandwidth Brokers downstream to the

   Two fundamental signaling approaches between Bandwidth Brokers have
   been identified for the Informed Admission case.  These are
   illustrated in figure 10.

   +-------+         +-------+         +-------+         +-------+
   |       |         |       |         |       |         |       |
   |       |RAR      |       |    1    |       |   2     |       |
   | User  |-------->|       |-------->|       |-------->|       |
   |       |     RAA | BB1   |    4    |  BB2  |   3     |  BB3  |
   |       |<--------|       |<--------|       |<--------|       |
   |       |         |       |         |       |         |       |
   |       |         |       |         |       |         |       |
   +-------+         +-------+         +-------+         +-------+

   A)End-to-end signaling

   +-------+         +-------+         +-------+         +-------+
   |       |         |       |         |       |         |       |
   |       |RAR      |       |    1    |       |   3     |       |
   | User  |-------->|       |-------->|       |-------->|       |
   |       |     RAA | BB1   |    2    |  BB2  |   4     |  BB3  |
   |       |<--------|       |<--------|       |<--------|       |
   |       |    7    |       |    6    |       |   5     |       |
   |       |<--------|       |<--------|       |<--------|       |
   +-------+         +-------+         +-------+         +-------+

   B) Immediate response signaling.

            Fig. 10 -- Fundamental Signalling Approaches

   -  End to End signaling.  An RAR from a User to BB1 is forwarded to
      BB2 (1). BB2 will forward the request to BB3 (2).  If BB3 is the
      destination of the request, BB3 will authorize the request and
      reply to BB2 (3).  BB2 will then reply to BB1 (4), and BB1 will
      send a Resource Allocation Answer (RAA) back to the User to
      complete the authorization.

   -  Immediate response signaling.  This is the case where BB1 will
      want to authorize an RAR from its domain and forwards the
      authorization request to BB2 (1).  If BB2 approves, the response
      is immediately returned to BB1 (2).  BB1 will send an RAA back to
      the User.  If the authorization was positive BB2 will forward
      subsequently a request to the next BB, BB3 (3).  BB3 authorizes
      the request and responds to BB2 (4).  If the response is negative
      (5), BB2 will cancel the authorization it previously issued to BB1
      (6) and this will result in a cancellation from BB1 to the user
      (7).  In this case the RAA authorization is valid until revoked by

4.6.4.  Bandwidth Broker Communication Architecture

   Figure 11 shows components of the discussed Bandwidth Broker
   architecture with its interfaces.

   -  An intra-domain interface allows communication with all the
      service components within the network that the Bandwidth Broker

   -  An inter-domain interface allows communication between Bandwidth
      Brokers of different autonomous networks.

   -  A user/application interface allows the Bandwidth Broker to be
      managed manually.  Requests can be sent from the User or a host

   -  A policy manager interface allows implementation of complex policy
      management or admission control.

   -  A routing table interface allows the Bandwidth Broker to
      understand the network topology.

   -  An NMS interface allows coordination of network provisioning and

           adjacent BB <---------------------------> adjacent BB
                      |       | inter-domain |       |
                      |        --------------  ------|
          application |                       |  PM  |
          server  \   |                       |iface |
                   \  |-------   ---------+    ------|
                    ->| user/ | | simple  |    ------|
          user/host-->| app   | | policy  |   | NMS  |
                    ->| iface | | services|   |iface |
                   /  |-------   ---------+    ------|
          network /   |                              |
          operator    |  -------          -------    |
                      | | data  |        |routing|   |
                      | | store |        |info   |   |
                      | |       |        |       |   |
                      |  -------          -------    |
                      |                              |
                      |       ----------------       |
                      |      | intra-domain   |      |
        edge router(s) <---------------------------> edge router(s)

              Fig. 11 -- Bandwidth Broker Architecture

4.6.5.  Two-Tier Inter-Domain Bandwidth Broker Communication Model  Session Initialization

   Before Bandwidth Brokers can configure services between two adjacent
   domains, they have to establish and initialize a relationship.  No
   authentication is used; therefore any trust relationship is implicit.
   Part of the initialization is an exchange of topology information
   (list of adjacent Bandwidth Brokers).  Service Setup

   The Bandwidth Broker must first be configured in regard to agreed
   bi-lateral service levels.  All resources allocated to a particular
   level of provisioned service must be reserved in each domain.

   A Service Setup Request (SSR) is generated  (on demand by the
   operator or at startup of the system) and forwarded to a downstream
   Bandwidth Broker.  The downstream Bandwidth Broker will check the

   consistency with its own service level specifications and respond
   with Setup Answer message (SA) agreements. This message exchange
   confirms and identifies pre-established service authorization levels.  Service Cancellation

   A Service Cancellation (SC) message may cancel a service
   authorization. This message may be initiated by the operator or by an
   expiration date. A Cancellation Answer (CA) is returned.  Service Renegotiation

   An (optional) Service-Renegotiation message (SR) may allow a
   Bandwidth Broker to re-negotiate an existing service.  This message
   may be initiated by the operator or automatically when a certain
   threshold is reached.  Renegotiations happen within the margins of a
   pre-established authorization.  Resource Allocation Request and Resource Allocation Answer

   An RAR allocates a requested level of service on behalf of the User
   and when available it will decide on the admittance of a certain User
   to the service. A Bandwidth Broker may receive an RAR via either the
   intra-domain or inter-domain interface.  The RAR must refer to the
   Service SetUp Identification (SSU_ID), which binds a request to a
   certain authorization. A Resource Allocation Answer (RAA) confirms or
   rejects a request or it may indicate an "in progress" state.  Session Maintenance

   A certain level of session maintenance is required to keep Bandwidth
   Brokers aware of each other.  This must be implemented using time-
   outs and keep-alive messages.  This will help Bandwidth Brokers to
   notice when other Bandwidth Brokers disappear.  Intra-domain Interface Protocol

   The Intra-domain interface protocol used between a Bandwidth Broker
   and the routers it controls may be COPS, SNMP, or Telnet Command Line

4.7.  Requirements

   From the above descriptions we derive the following requirements.

   -  The Authorization mechanism may require trust relationships to be
      established before any requests can be made from the User to the
      Service Provider.  Currently trust relationship establishment is

   -  A confirmation of authorization is required in order to initialize
      the system.

   -  A negation of static authorization is required to shut down
      certain services.

   -  A renegotiation of static authorization is required to alter
      services (SLS's).

   -  Dynamic authorization requests (RAR) must fit into pre-established
      static authorizations (SLS's).

   -  Dynamic authorization requests (RAR) may be answered by an "in
      progress state" answer.

   -  Provisions must be made to allow reconstruction of authorization
      states after a Bandwidth Broker re-initializes.

5.  Internet Printing

   The Internet Printing Protocol, IPP [14], has some potentially
   complex authorization requirements, in particular with the "print-
   by-reference" model.  The following attempts to describe some
   possible ways in which an authorization solution for this aspect of
   IPP might work, and to relate these to the framework described in
   [2].  This is not a product of the IPP working group, and is meant
   only to illustrate some issues in authorization in order to establish
   requirements for a "generic" protocol to support AAA functions across
   many applications.

   IPP print-by-reference allows a user to request a print service to
   print a particular file.  The user creates a request to print a
   particular file on a printer (or one of a group of printers).  The
   key aspect is that the request includes only the file name and not
   the file content. The print service must then read the file from a
   file server prior to printing.  Both the file server and the print
   server must authorize the request.  Once initiated, printing will be
   done without intervention of the user; i.e., the file will be sent
   directly to the print service rather than through the user to the

5.1.  Trust Relationships

   The assumption is that the Printer and File Server may be owned and
   operated by different organizations.  There appear to be two models
   for how "agreements" can be set up.

   1. User has agreement with Print Server; Print Server has agreement
      with File Server.

   2. User has agreements with both File and Print Server directly.

   In case 1, the user has a trust relationship with the Print Service
   AAA Server.  The Printer forwards the request to the File Server. The
   File Server authorizes the Printer and determines if the Printer is
   allowed access to the file.  Note that while there may be some cases
   where a Print Server may on its own be allowed access to files
   (perhaps some "public files", or that can only be printed on certain
   "secure" printers), it is normally the case that files are associated
   with users and not with printers.  This is not a good "generic" model
   as it tends to make the print service an attractive point of attack.

            +------+       +----------------------+
            |      |       | File Service         |----+
            |      |       | AAA Server           |<-+ |
            |      |       +----------------------+  | |
            |      |       |                      |  | |
            |      |       | File Server          |  | |
            |      |       |                      |  | |
            | User |       +----------------------+  | |
            |      |                                 | |
            |      |                                 | |
            |      |                                 | |
            |      |       +----------------------+  | |
            |      |------>| Print Service        |--+ |
            |      |<------| AAA Server           |<---+
            |      |       +----------------------+
            |      |       | Print Server         |
            |      |       |  and Printer         |
            +------+       +----------------------+

          Fig. 12 -- Case 1
                     User authorizes with Print Service.
                     Printer authorizes with File Service.

   In case 2, the user must have a trust relationship with both the file
   and print services so that each can verify the service appropriate to
   the User.  In this case, the User first contacts the File Service AAA
   Server and requests that it enable authorization for the Print

   Service to access the file.  This might be done in various ways, for
   example the File Service AAA Server may return a token to the User
   which can (via the Print Service) be presented to the File Server to
   enable access.

               +------+       +----------------------+
               |      |------>| File Service         |
               |      |<------| AAA Server           |
               |      |       +----------------------+
               |      |
               |      |       +----------------------+
               |      |       | File Server          |
               | User |       +----------------------+
               |      |              /|\  |
               |      |               |   |
               |      |               |  \|/
               |      |       +----------------------+
               |      |------>| Print Service        |
               |      |<------| AAA Server           |
               |      |       +----------------------+
               |      |       | Print Server         |
               |      |       |  and Printer         |
               +------+       +----------------------+

         Fig. 13 -- Case 2
                    User authorizes File and Print Service.
                    Must create binding for session between
                    Print Service and File Service.

5.2.  Use of Attribute Certificates in Print-by-Reference

   The print-by-reference case provides a good example of the use of
   attribute certificates as discussed in [2].  If we describe case 2
   above in terms of attribute certificates (ACs) we get the diagram
   shown in figure 14.

      +------+       +----------------------+
      |      |------>| File Service         |
      |      |<------| AAA Server           |
      |      |Get AC +----------------------+
      |      |
      |      |       +----------------------+
      |      |       | File Server          |----+
      |      |       |                      |<-+ |
      | User |       +----------------------+  | |
      |      |                                 | |
      |      |   +---authorize passing AC      | |<---Create session
      |      |   |                             | |    Using AC
      |      |   V   +----------------------+  | |
      |      |------>| Print Service        |  | |
      |      |<------| AAA Server           |  | |
      |      |       +----------------------+  | |
      |      |       | Print Server         |--+ |
      |      |       |  and Printer         |<---+
      +------+       +----------------------+

       Fig. 14 -- Using Attribute Certificates in IPP Authorization

   In this case, the User gets an AC from the File Service's AAA Server
   which is signed by the File Service AAA Server and contains a set of
   attributes describing what the holder of the AC is allowed to do. The
   User then authorizes with the Print Service AAA Server and passes the
   AC in the authorization request.  The Printer establishes a session
   with the File Server, passing it the AC.  The File Server trusts the
   AC because it is signed by the File Service AAA Server and allows (or
   disallows) the session.

   It is interesting to note that an AC could also be created and signed
   by the User, and passed from the Print Server to the File Server. The
   File Server would need to be able to recognize the User's signature.
   Yet another possibility is that the Print Service AAA Server could
   simply authenticate the User and then request an AC from the File
   Service AAA Server.

5.3.  IPP and the Authorization Descriptive Model

   The descriptive model presented in [2] includes four basic elements:
   User, User Home Organization, Service Provider AAA Server, and
   Service Equipment.

   Mapping these to IPP, the User is the same, the User Home
   Organization (if included) is the same.  The Service Provider AAA
   Server and the Service Equipment  are expected to be closely coupled
   on the same processor.  In other words, the interface between the

   Print Service AAA Server and the Printer as well as that between the
   File Service AAA Server and the File Server is an internal one that
   will not require a formal protocol (although some standard API might
   be useful).

   The concept of a Resource Manager (see [2]) has some interesting
   twists relative to IPP.  Once started, the user is not involved in
   the service, but until printing is complete it seems useful that any
   of the parties in the authorization process be allowed to query for
   status or to cancel the print session.   The user needs a way to
   "bind" to a particular session, and may have to reauthorize to be
   allowed to access Resource Manager information.

6.  Electronic Commerce

   This section describes the authorization aspects of an e-commerce
   architecture typically used in Europe.  We will use this model to
   identify contractual and trust relationships and message exchanges.
   We will then identify a set of authorization requirements for e-

   Whereas most e-commerce protocols focus on authentication and message
   integrity, e-commerce exchanges as described by the Internet Open
   Trading Protocol (trade) Working Group in [15] also involve
   authorization.  This section will examine one e-commerce protocol
   called SET (Secure Electronic Transaction) that provides for credit
   and debit card payments.  We will analyze the authorization aspects
   from an architectural viewpoint.  We will apply concepts and terms
   defined in [2].

   We are not here proposing SET as a standard authorization protocol.
   Rather, we are examining the SET model as a way of understanding the
   e-commerce problem domain so that we can derive requirements that an
   authorization protocol would have to meet in order to be used in that

   E-commerce protocols and mechanisms such as those described in [16]
   may not only be important to allow customers to shop safely in
   Cyberspace, but may also be important for purchases of Internet
   services as well.  With emerging technologies allowing Internet
   transport services to be differentiated, an inherently more complex
   pricing model will be required as well as additional payment methods.
   Flexible authorization of services will be an important aspect to
   allow, for example, globally roaming users ad hoc allocation of
   premium bandwidth with an ISP who is authorized to accept certain
   credit card brands.

6.1.  Model Description

   The establishment of a model involves four steps:

   1. identification of the components that are involved and what they
      are called in this specific environment,
   2. identification of the relationships between the involved parties
      that are based on some form of agreement,
   3. identification of the relationships that are based on trust, and
   4. consideration of the sequence of messages exchanged between

6.1.1.  Identification of Components

   We will consider the components of an electronic commerce transaction
   in the context of the conceptual entities defined in [2].

   -  The Cardholder (User) -- the person or organization that is to
      receive and pay for the goods or services after a request to
      purchase has been received.  In SET terms this is called a

   -  The Issuer (User Home Organization) -- the financial organization
      that guarantees to pay for authorized transactions to purchase
      goods or services on behalf of the User when using a debit or
      credit card it issues.  The financial organization (typically a
      bank or Brand Organization) will transfer money from the user
      account to the account the party to which the User instructs it to
      send the payment. The issued card authorizes the User to use the
      card for payments to merchants who are authorized to accept the
      card.  In SET terms this organization is called the Issuer.  This
      organization is considered "home" to the Cardholder.

   -  The Merchant (Service Provider) -- the organization from whom the
      purchase is being made and who is legally responsible for
      providing the goods or services and receives the benefit of the
      payment made.  In SET terms this organization is called a
      Merchant.  The Cardholder is considered to be "foreign" to the

   -  The Acquirer (Broker) -- the organization that processes credit or
      debit card transactions.  Although in reality this function may be
      rather complex and may span several organizations, we will simply
      assume this organization to be a Brand Organization fulfilling the
      role of the Acquirer as defined in SET.  The Acquirer establishes
      an account with the Merchant.  The Acquirer operates a Payment
      Gateway that will accept payment authorization requests from

      authorized merchants and provide responses from the issuer.  The
      Acquirer will forward an authorization request to the Issuer.  The
      Acquirer is considered "home" to the Merchant.

   As the SET document [16] notes, a Brand Organization (credit card
   organization) may handle both the Issuer function and Acquirer
   function that operates a Payment Gateway.  For simplicity, we
   therefore assume that the authorization role of Broker (Acquirer) and
   User Home Organization (Issuer) both belong to the Brand

   In order to be more descriptive we now use the SET terms.  In the
   requirements section these terms are mapped back into the
   authorization framework terms again.

6.1.2.  Identification of Contractual Relationships

   Contractual relationships are illustrated in figure 15, below.

   -  The Cardholder has a contractual relationship with the card
      Issuer.  The Cardholder holds an account with the Issuer and
      obtains an account number.

   -  The Merchant has a contractual relationship with the Acquirer.
      The Merchant obtains a Merchant ID from the Acquirer.

   -  In the real world there may be no direct contractual relationship
      between the Issuer and the Acquirer.  The contractual
      relationships allowing an Acquirer to relay a payment
      authorization request to an Issuer may be very complex and
      distributed over multiple organizations. For simplicity, however,
      we assume there are contracts in place allowing an Acquirer to
      request payment authorization from an Issuer.  These contracts are
      facilitated by the Brand Organization.  Therefore, in our
      simplified example, the Acquirer and Issuer belong to the same
      Brand Organization.  The Acquirer operates a Payment Gateway for
      which it needs a Bank Identification Number (BIN).

               +----------------+       +------------------------+
               | Issuer         |       | Acquirer               |
               | (User Home     |       | (Broker)               |
               |  Organization) |       |  +------------------+  |
               |                |=======|  |  Payment         |  |
               |                |       |  |  Gateway         |  |
               |                |       |  +------------------+  |
               |                |       |                        |
               +----------------+       +------------------------+
                       ||                             ||
                       ||                             ||
                       ||                             ||
               +----------------+       +--------------------+
               | Cardholder     |       | Merchant           |
               | (User)         |       | (Service Provider) |---+
               |                |       |                    |   |
               |                |       |                    |   |
               |                |       +--------------------+   |
               |                |         |                      |
               |                |         | Fulfillment          |
               |                |         |                      |
               +----------------+         +----------------------+

                    Fig. 15 -- SET Contractual Relationships

6.1.3.  Identification of Trust Relationships

   It is important to recognize that there are two kinds of trust
   relationships: static and dynamic trust relationships.  Static trust
   relationships in SET are established by means of a registration
   process that will request a certificate to be issued to the party
   that needs to be trusted and authorized to be part of a SET
   transaction.  Dynamic trust is created at the time of a payment
   transaction and its subsequent authorization request.  Note that at
   the issue phase of a certificate, based on identification and
   registration, the user of the certificate gets an implicit static
   authorization and a means of authenticating and securing messages.
   For this purpose a Certificate Authority (CA) will issue certificates
   that are used to sign and/or encrypt messages exchanged according to
   the SET protocol.  Static Trust Relationships

   In the discussion that follows, refer to figure 16, below.

                               | Root  |
                               |  CA   |
                               +-------+     CA = Certificate Authority
                                   |        {C} = Certificate
                        |        Brand    |
                        |         CA      |
                          |        |    |
                          |        | +-------+
                          |        | |Payment|
   +----------------+     |        | |Gateway| +----------------------+
   | Issuer         |     |        | |  CA   | | Acquirer             |
   | (User Home     | +----------+ | +-------+ | (Broker)             |
   |  Organization) | |Cardholder| |    |      |  +----------------+  |
   |                | |    CA    | |    +------+--+-{C} Payment    |  |
   |                | +----------+ |       3   |  |     Gateway    |  |
   |                |     |        |           |  +----------------+  |
   |                |     |   +---------+      |                      |
   +----------------+     |   | Merchant|      +----------------------+
                          |   |    CA   |
                          |   +---------+
                          |        |
   +----------------+     |        |           +--------------------+
   | Cardholder     |     |        |           | Merchant           |
   | (User)         |     |        |           | (Service Provider) |--+
   |            {C}-+-----+        |           |                    |  |
   |                |  1           +-----------+-{C}                |  |
   |                |                    2     |                    |  |
   |                |                          |                    |  |
   |                |                          +--------------------+  |
   |                |                            |                     |
   |                |                            | Fulfillment         |
   |                |                            |                     |
   +----------------+                            +---------------------+

         Fig. 16 -- SET Trust Relationships within a Brand Domain

   -  The Brand Organization operates a Brand CA and is therefore the
      holder of the common trust within the described domain.  All
      involved parties (Cardholder, Issuer, Merchant and Acquirer) are
      members of the same trust domain.  We will identify three separate

      CA's which issue a certificate on behalf of the Issuer, the
      Acquirer and the Brand Organization.  The Brand CA, according to a
      tree like hierarchy, certifies all underlying CA's.  The Brand CA
      obtains its trust from a single Root Certificate Authority.
      Before any party can obtain a Certificate from a CA, the party
      must have some form of contractual relationship.

   -  After an account has been established with the Issuer, the
      Cardholder has to register with a Cardholder CA (CCA) through a
      series of registration steps (1) as defined in the SET protocol.
      If the CCA approves the registration, the Cardholder will obtain a
      Cardholder Certificate.  The CCA may be operated by the Brand
      Organization on behalf of the Issuer.  The Cardholder Certificate
      is an electronic representation of the payment card.  This process
      creates a trust relationship between the Cardholder and the Brand.
      After the cardholder has received the Cardholder Certificate, the
      Cardholder is authorized to perform payments to an authorized

   -  After the Merchant has obtained a Merchant ID from the Acquirer,
      the Merchant has to register with the Merchant CA (MCA) through a
      series of registration steps (2) as defined in the SET protocol.
      If the MCA approves the registration, the Merchant will obtain a
      Merchant Certificate.  This process creates a trust relationship
      between the Merchant and the Brand.  The MCA may be operated by
      the Brand Organization on behalf of the Acquirer.  After
      registration, the Merchant is authorized to accept payment
      requests from Cardholders and to send authorization requests to
      the Acquirer's Payment Gateway.

   -  After the Acquirer has obtained a valid Bank Identification Number
      (BIN), the Acquirer must register with the Payment Gateway CA
      (PCA) in order to obtain a Payment Gateway Certificate (3).  The
      Payment Gateway Certificate authorizes the Gateway to accept
      payment authorization requests originating from Merchants within
      its trust domain.

   -  The Acquirer and Issuer have a trust relationship via the Brand
      Organization.  The trust relationship is not ensured by procedures
      or a mechanism defined by SET, as this is a problem solved by
      agreements between financial organizations facilitating the
      payment service.  Again, for simplicity, we assume that the
      relationship ensures that payment authorization requests received
      by the Acquirer's gateway will be forwarded in a secure and
      efficient way to the Issuer and its response is handled in the
      same way.  Dynamic Trust Relationships

   Note that there is no prior established static trust relationship
   between the Cardholder and the Merchant, as a Cardholder does not
   have to register with a Merchant or vice versa.  The trust
   relationship is dynamically created during the communication process
   and is based on the common relationship with the Brand.  By means of
   digital signatures using public key cryptography, the Cardholder's
   software is able to verify that the Merchant is authorized to accept
   the Brand Organization's credit card.  The merchant is able to verify
   that the Cardholder has been authorized to use the Brand
   Organization's credit card.

6.1.4.  Communication Model

   The purchase request from Cardholder to Merchant and subsequent
   payment authorization exchange between Merchant and Acquirer is
   illustrated in figure 17 and described below.

         +----------------+       +------------------------+
         | Issuer         |       | Acquirer               |
         | (User Home     |       | (Broker)               |
         |  Organization) |       |  +------------------+  |
         |                |<------+--|  Payment         |  |
         |                |   5   |  |  Gateway         |  |
         |                |-------+->|                  |  |
         |                |   6   |  +------------------+  |
         |                |       |        /|\  |          |
         +----------------+       +---------+---+----------+
                                            |4  |7
                                            |  \|/
         +----------------+       +--------------------+
         | Cardholder     |       | Merchant           |
         | (User)         |       | (Service Provider) |---+
         |                |------>|                    |   |
         |                |   1   |                    |   |
         |                |<------|                    |   |
         |                |   2   |                    |   |
         |                |------>|                    |   |
         |                |   3   |                    |   |
         |                |<------|                    |   |
         |                |   8   |                    |   |
         |                |       |                 |  |   |
         |                |       +-----------------+--+   |
         |                |         |               |9     |
         |                |<--------| Fulfillment  \|/     |
         |                |   10    |                      |
         +----------------+         +----------------------+

                  Fig. 17 -- Communication Sequence

   1. The Cardholder shops and decides to purchase some goods at
      merchant.com. The Cardholder has selected a list of goods and the
      Merchant's software has subsequently prepared an order form for
      the Cardholder indicating the price, the terms and conditions, and
      the accepted payment methods.  The SET transaction starts at the
      moment the Cardholder indicates that he or she wants to pay for
      the goods using a certain payment brand.  The Cardholder software
      sends a request to the Merchant that initiates the payment

   2. The Merchant checks the order and signs it and returns it to the
      Cardholder including a certificate from the Acquirer's Gateway
      that allows the Cardholder to encrypt payment instructions that
      are only relevant to the Gateway and not to the Merchant (e.g.,
      the Cardholder's credit card information).  The Cardholder also
      includes his or her own certificate.

   3. The Cardholder now verifies both certificates (the software has
      the CA's root certificate).  The Cardholder software generates a
      message containing the order information and the payment
      instructions that is signed by the Cardholder.  Using the Gateway
      Certificate, it will encrypt the Payment Instruction so that it
      will only be readable by the Gateway.  The Cardholder will include
      his or her certificate.

   4. The Merchant verifies the Cardholder certificate and checks the
      message integrity.  He or she will now process the payment and
      issue a payment authorization request to the gateway.  The payment
      authorization request contains the Cardholder's certificate and
      both Merchant certificates.

   5. The Gateway verifies the Merchant's signature certificate and that
      the Merchant signed the authorization request.  Next it will
      obtain the account information and payment instructions and will
      check the message integrity and the Cardholder's certificate.  If
      everything is in proper order it will send an authorization
      request to the Issuer via a secure bank network.

   6. The issuer returns the authorization.

   7. The Acquirer's Gateway generates an authorization response which
      includes the gateway's certificate.

   8. The Merchant checks the authorization response and completes the
      process by forwarding a purchase response to the Cardholder.

   9. The Merchant software authorizes the delivery of the purchased

   10. The Cardholder receives the purchased goods.

6.2.  Multi Domain Model

   In the previous "single" domain case we already assume that there are
   multiple Cardholders, Merchants, Issuers and Acquirers.  However all
   these parties belong to a single trust domain as there is only a
   single CCA, MCA and PCA.  The trust relationship between multiple
   cardholders and multiple Issuers go via a single CCA in the same way
   as the trust relationship between an Acquirer and a Merchant uses the
   same MCA.  The multi-domain case arises when there are multiple
   domains of CCA's, MCA's and PCA's.  In SET these domains reside under
   a particular Geopolitical CA (GCA) which is illustrated in figure 18.

                        |  Root CA  |
                        |           |
      +-----------------------------------------------------+ |
      |                   Brand CA                          | |
      |                                                     |-+
      +-----------------------------------------------------+ |
      |                   Geopolitical CA                   | |
      |                                                     |-+
            |                 |                    |
            |                 |                    |
       +----|--------+    +---|-------+    +-------|----------+
      +------------+ |   +----------+ |   +-----------------+ |
      | Cardholder | |   | Merchant | |   | Payment Gateway | |
      |     CA     |-+   |    CA    |-+   |       CA        |-+
      +------------+     +----------+     +-----------------+

         Fig. 18 -- SET Certificate Management Architecture

   A GCA may represent a country or region.  The architecture defines a
   trust hierarchy needed to manage and verify SET Certificates as these
   need to be issued, renewed or revoked.  Each geopolitical region may
   have different policies for issuing, renewing or revoking
   certificates. However once certificates have been issued, Cardholders
   and Merchants belonging to different GCA's can still be recognized as
   belonging to the same Brand.  This will allow a European Cardholder
   to purchase goods in the U.S.  The U.S. Acquirer's gateway will
   recognize that the Cardholder belongs to the same Brand and will
   therefore accept a payment authorization request.

6.3.  Requirements

   Many e-commerce environments do not use SET.  Other mechanisms exist
   based on SSL, XML, and S/MIME.  Also a mechanism that uses SET only
   for the payment authorization to the Gateway exists and is known as
   half SET.  However, using the model described in this document, we
   can derive a fairly comprehensive set of protocol requirements for
   e-commerce.  In these requirements, the SET terms are replaced again
   by the descriptive model terms:

      Cardholder = User
      Merchant = Service Provider
      Issuer = User Organization
      Acquirer = Broker

   1. The Authorization mechanism must allow trust relationships to be
      established before any requests can be made from the User to the
      Service Provider and from the Service Provider via a Broker to the
      User Organization.  This process will enable the parties to
      communicate securely by creating an authenticated channel and, by
      so doing, implicitly authorizing its usage.

   2. Upon receipt of any request or response, entities need to be able
      to verify whether the transmitting party is still authorized to
      send this request or response.

   3. The User must be able to authorize the Service Provider to request
      an authorization from the User Home Organization.

   4. The User must be able to authorize fulfillment of a proposed
      service offer from the Service Provider.

   Other requirements related to the authorization process:


   5. For any authorization request or response, the receiving party
      needs to verify that the content of the message has not been


   6. The User must be able to pass information relevant to the session
      authorization process to the User Home Organization via a Broker
      and the Service Provider without allowing the Broker or the
      Service Provider to examine its content.

   7. The User Home Organization must be able to communicate information
      relevant to the session authorization via the Broker and the
      Service Provider to the User without allowing the Broker or the
      Service Provider to examine its content.


   8. There is a need for a recorded, authenticated and authorized
      agreement about the request for and delivery of service.

7.  Computer Based Education and Distance Learning

   This section describes the authorization aspects of computer based
   distance learning environments.  In this section we will model the
   relationships and working practices in a hypothetical university
   environment where a student enrolls in courses, attends lectures, and
   takes the corresponding exams from remote locations (distance
   learning) or via computer equipment (computer based education).  When
   completed successfully, a student is authorized to enroll in a set of
   subsequent courses according to his or her curriculum requirements.
   Completion of required courses with passing grades results in

   Although this section specifically describes an example of a student
   taking courses at a faculty (department) of the university, the
   resulting requirements should also be valid for other applications in
   similar environments, e.g. library loans, electronic abstract and
   reprint services, computer and network access, use of copy machines,
   budget management, store retrievals, use of coffee machines and
   building access.

   It is important to recognize that the AAA environment we are
   describing also needs to be managed.  For example, for an application
   such as budget management, it is necessary to delegate budget
   authority from a central financial department to budget managers in
   education or faculty groups.  An AAA environment must allow creation
   of policy rules either by certain individuals or by other AAA servers
   with authorization to do so.

7.1.  Model Description

   The establishment of the model involves four steps:

   1. identification of the components that are involved and what they
      are called in this specific environment,

   2. identification of the contractual relationships between the
      involved parties,

   3. identification of the relationships that are based on trust, and

   4. consideration of the sequence of messages exchanged between

7.1.1.  Identification of Components

   We will consider the components of a distance learning environment in
   the context of the conceptual entities defined in [2].

   -  The Student (User) -- the person enrolling in a course (Service)
      and taking the corresponding exam.

   -  The Educator (Service Equipment) -- the education content server
      for which the content is delivered by the Professor.

   -  The Educator Authorization Module (Service Provider AAA Server).
      This module must check at the service access point whether the
      student complies with the requirements for enrolling in the
      course.  The authorization may be based on both local (by the
      professor) and remote policies (originating from the faculty).
      Rules must allow enough flexibility to prevent students from being
      falsely denied access to courses.  Strict rules must only be
      applied at graduation time.

   -  The Faculty (Service Provider) -- the organization (department in
      U.S. terms) which controls the Service "Equipment" of which the
      Educator is one example.

   -  The Curriculum Commission (Part of User Home Organization) -- body
      responsible for creating rules by which a student is allowed to
      enroll in a certain course and how this course will count toward
      his or her graduation requirements.  Students may legally take any
      course available at any time, however the Curriculum Commission
      will decide whether this course will contribute towards their
      graduation.  When a Student registers with a certain Educator, the
      Educator may check with the Curriculum Commission AAA server
      whether the course will count towards graduation and confirm this
      with the student.

   -  The Student Administration (Part of User Home Organization) -- the
      administrative organization that authorizes students to enroll in
      courses if certain criteria, including financial criteria, are
      met.  Next to the student, the Student Administration will keep
      track of any exam results for the student and will issue a
      graduation certificate when all criteria are met.

7.1.2.  Identification of Contractual Relationships

   Contractual relationships are illustrated in figure 19, below. Based
   on contract relationships,specific trust relationships are created as

   Although not shown in figure 19, it is assumed that the university
   has contractual relationships with the faculties in which every
   faculty is allowed and obligated to build, maintain and present one
   or more specific studies.

                     | +-----------------------------------------+ |
                     | |          Faculty administration         | |
                     | |+----------------+     +----------------+| |
                     | |O Student        |     | Curriculum     || |
                     | *| Administration O*****O Commission     || |
                     |*|| AAA Server     |     | AAA Server     || |
                     */|+---O------O-----+     +-----O------O---+| |
                    *//|    *       *               *       *    | |
                   *// +----*---------*-----------*---------*----+ |
                  *//|      *   ||      *       *     ||    *      |
                 *// |      *   ||        *   *       ||    *      |
                *//  |      *   ||          *         ||    *      |
               *//   |      *   ||        *   *       ||    *      |
              *//    |      *   ||      *       *     ||    *      |
             *//     | +----*---------*--+     +--*---------*----+ |
            *//      | |    *       *    |     |    *       *      |
           *//       | |+---O------O----+|     |+----O------O---+| |
          *//        | || Educator A    ||     || Educator B    || |
         *//         | || AAA Server    ||     || AAA Server    || |
        *//          | || Service admin.||     || Service admin.|| |
       *//           | |+---O-----------+|     |+-----------O---+| |
      *//            | |    *            |     |            *    | |
   +-O-------+       | |    *            |     |            *    | |
   |         |       | |+---O-----------+|     |+-----------O---+| |
   | Student |       | || Educator      ||     || Educator      || |
   |         |       | || Course A      ||     || Course B      || |
   |         |       | |+---------------+|     |+---------------+| |
   +---------+       | +-----------------+     +-----------------+ |
                     |                   Faculty                   |

                     // = contractual relationship
                     ** = trust relationship

       Fig. 19 -- Contractual relationships - single domain case

   As shown in figure 19, the Student has a contractual relationship
   with the Faculty.  The contract allows the Student to pursue a course
   of study consisting of a set of courses.  Courses are presented to
   the Students by the Educators.  A course of study may consist of
   courses from different Faculties.

   Faculties have contracts among them allowing Students from one
   Faculty to enroll in courses from other Faculties.

   Faculties instantiate Educators based on a contract between the
   Faculty Administration and the professor implementing and managing
   the Educator. Authorization is based on policy rules defined by one
   or more parties in the contractual relationships.  For example, a
   professor has a policy to give the course only in the afternoon and
   the Faculty has a policy to give the course to their own students and
   students from faculty-x but not, when oversubscribed, to faculty-y

7.1.3.  Identification of Trust Relationships

   Figure 19 illustrates relevant trust relationships which statically
   enable AAA entities to communicate certain attributes in our
   simplified example. However, in order for the illustrated entities to
   work, other trust relationships that are not illustrated must already
   be in existence:

   -  A trust relationship based on a contract between the Faculty and
      the university enables a faculty to create and teach specific
      courses belonging to a course of study.

   -  Although not further detailed in this example, it is worth noting
      that trust relationships between faculties authorize students from
      one faculty to enroll in courses with other faculties.

   -  A professor responsible for the content of the Educator has a
      trust relationship with the administration of the faculty.
      Through this relationship, the faculty enables the professor to
      teach one or more courses fitting the requirements of the
      Curriculum Commission.

   Figure 19 illustrates the following trust relationships:

   -  When a person wants to become a Student of a Faculty, the contract
      requires the Student to register with the Student Administration
      of the Faculty.  If the requirements for registration are met, a
      trust relationship with the Faculty enables the Student to
      register for courses.  For this purpose, the Student
      Administration will issue a student card which contains a student
      ID and information about the Faculty he or she is admitted to.
      The Student Administration will only admit Students who pay the
      necessary fees and have met certain prerequisites.  The Student
      Administration will also keep track of Student grades and will
      ultimately issue a certificate at graduation. The Student
      Administration AAA server has access to relevant student data and
      will only issue grade information and other student-related
      information to authorized parties which have a specified means of

   -  The Curriculum Commission AAA server needs a trust relationship
      with the Student Administration AAA server in order to obtain
      grade information to check whether a student has met the required
      course prerequisites.  The Curriculum Commission creates certain
      rules within its AAA server which are evaluated when a particular
      student attempts to register for a particular course in order to
      give an advisory to the student.

   -  The Educator AAA server needs a trust relationship with the
      Student Administrator AAA server in order to verify whether this
      particular Student is in good standing with the Faculty.  Only
      authorized Educator AAA servers may send requests to the Student
      Administration AAA server.

   -  The Educator AAA server needs a trust relationship with the
      Curriculum Commission AAA server in order to allow the Educator to
      obtain an advisory for the Student whether this course is
      consistent with his or her curriculum or whether the student meets
      the course prerequisites.  Only authorized Educator AAA servers
      may send requests to the Curriculum AAA Server.

7.1.4.  Sequence of Requests

   For the sake of simplicity, we take the example of a student from the
   same faculty as the professor.

   In this example the following interactions take place for a
   hypothetical course (see figure 20).

                   |                                              |
                   |  +----------------+  6   +----------------+  |
                   |  | Student        |----->| Curriculum     |  |
                   |  | Administration |<-----| Commission     |  |
                   |  | AAA Server     |  5   | AAA Server     |  |
                   |  +----------------+    _ +----------------+  |
                   |    /|\ |               /|/                   |
                   |     |  |              / /                    |
                   |  2,8|  |3            / /6                    |
                   |     |  |           4/ /                      |
                   |     |  |           / /                       |
                   |     |  |          / /                        |
                   |     | \|/        /|/                         |
                   |  +---------------+ --     +---------------+  |
                   |  | Educator A    |        | Educator B    |  |
                   |  | AAA Server    |        | AAA Server    |  |
                   |  +---------------+        +---------------+  |
                   |    /|\ |                                     |
                   |2,4,8|  |3,6                                  |
   +---------+     |     | \|/                                    |
   |         | 1,7 |  +---------------+        +---------------+  |
   | Student |------->| Educator      |        | Educator      |  |
   |         |<-------| Course A      |        | Course B      |  |
   |         | 7,8 |  +---------------+        +---------------+  |
   +---------+     |                   Faculty                    |

           Fig. 20 -- AAA transactions - single domain case

   1. After the Professor has set up the Service Equipment (Educator)
      students come to it presenting their ID (college card,
      name+faculty) and ask to be admitted to the course.

   2. The Educator checks the ID to determine it is indeed dealing with
      a student from the faculty.  This can include a check with the
      Student Administration.

   3. The Student Administration replies to the Educator AAA Server, and
      the Educator AAA Server replies to the Educator.

   4. The Educator checks the request of the Student against its own
      policy (courses only in the afternoon) and checks with the
      Curriculum Commission whether this student is advised to take the
      course.  The necessary information is not normally known to or
      maintained by the professor.

   5. The Curriculum Commission may check against the Student
      Administration to see if the Student had the necessary grades for
      the previous courses according to the policies set by the
      Curriculum Commission.

   6. The Student Administration replies to the Curriculum Commission,
      the Curriculum Commission replies to the Educator AAA Server, and
      the Educator AAA Server replies to the Educator.

   7. If now authorized, the Student is presented the material and the
      Student returns completed exams.

   8. If the Student passes the tests, the Educator informs both the
      Student and the Student Administration that the Student has

7.2.  Requirements

   We identify the following requirements for an AAA server environment
   for this example:

   1. It must be possible to delegate authority to contracted partners.
      Although this requirement is not explicit in the limited example,
      the relationship between University and Faculty may require
      delegation of authority regarding the curriculum to the Faculty.
      In the case of budget management, this requirement is evident.

   2. A system to manage the delegated authority must be established.
      It is possible that this is just another AAA server environment.
      This comes from the fact that one partner requires the presence of
      specific rules to be in the AAA server of another partner.  For
      example, the Faculty must be sure that certain checks are
      performed by the Educator's AAA server.

   3. AAA requests must either be evaluated at the AAA server queried or
      else parts of the request must be forwarded to another AAA server
      which can decide further on the request.  As such, it must be
      possible to build a network of AAA servers in which each makes the
      decisions it is authorized to make by the relationships among the
      entities, e.g., a request from the Educator to the Curriculum
      Commission may result in a request to the Student Administration.

   4. Transaction logs must be maintained to support non-repudiation for
      the grades of the students.  This recording should be time-stamped
      and allow signing by authorized entities.  A student should sign
      for taking an exam and this should be kept by the Educator's AAA

      server.  After grading, the professor should be able to sign a
      grade and send it to the Student Administrator and the Student
      Administrator's AAA server should log and timestamp this event.

   5. Three types of AAA messages are required:

      -  authorization requests and responses for obtaining
      -  notification messages for accounting purposes, and
      -  information requests and responses for getting information
         regarding the correct construction of requests and for querying
         the database of notifications.

8.  Security Considerations

   The authorization applications discussed in this document are modeled
   on the framework presented in [2].  Security considerations relative
   to the authorization framework are discussed in [2].

   Specific security aspects of each authorization application presented
   in this document are discussed in the relevant section, above.

   Security aspects of the applications, themselves, are discussed in
   the references cited below.


   Attribute Certificate -- structure containing authorization
      attributes which is digitally signed using public key

   Contract Relationship -- a relation established between two or more
      business entities where terms and conditions determine the
      exchange of goods or services.

   Distributed Service -- a service that is provided by more than one
      Service Provider acting in concert.

   Dynamic Trust Relationship -- a secure relationship which is
      dynamically created between two entities who may never have had
      any prior relationship. This relationship can be created if the
      involved entities have a mutually trusted third party. Example: A
      merchant trusts a cardholder at the time of a payment transaction
      because they both are known by a credit card organization.

   Policy Decision Point (PDP) -- The point where policy decisions are

   Policy Enforcement Point (PEP) -- The point where the policy
      decisions are actually enforced.

   Resource Manager -- the component of an AAA Server which tracks the
      state of sessions associated with the AAA Server or its associated
      Service Equipment and provides an anchor point from which a
      session can be controlled, monitored, and coordinated.

   Roaming -- An authorization transaction in which the Service Provider
      and the User Home Organization are two different organizations.
      (Note that the dialin application is one for which roaming has
      been actively considered, but this definition encompasses other
      applications as well.)

   Security Association -- a collection of security contexts, between a
      pair of nodes, which may be applied to protocol messages exchanged
      between them. Each context indicates an authentication algorithm
      and mode, a secret (a shared key, or appropriate public/private
      key pair), and a style of replay protection in use. [14]

   Service Equipment -- the equipment which provides a service.

   Service Provider -- an organization which provides a service.

   Static Trust Relationship -- a pre-established secure relationship
      between two entities created by a trusted party.  This
      relationship facilitates the exchange of AAA messages with a
      certain level of security and traceability. Example: A network
      operator (trusted party) who has access to the wiring closet
      creates a connection between a user's wall outlet and a particular
      network port.  The user is thereafter trusted -- to a certain
      level -- to be connected to this particular network port.

   User -- the entity seeking authorization to use a resource or a

   User Home Organization (UHO) -- An organization with whom the User
      has a contractual relationship which can authenticate the User and
      may be able to authorize access to resources or services.


   [1]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [2]  Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., Gross,
        G., de Bruijn, B., de Laat, C., Holdrege, M. and D. Spence, "AAA
        Authorization Framework", RFC 2904, August 2000.

   [3]  Farrell, S., Vollbrecht, J., Calhoun, P., Gommans, L., Gross,
        G., de Bruijn, B., de Laat, C., Holdrege, M. and D. Spence, "AAA
        Authorization Requirements", RFC 2906, August 2000.

   [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [5]  Aboba, B. and G. Zorn, "Criteria for Evaluating Roaming
        Protocols", RFC 2477, January 1999.

   [6]  Beadles, Mark Anthony, and David Mitton, "Criteria for
        Evaluating Network Access Server Protocols", Work in Progress.

   [7]  Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
        2486, January 1999.

   [8]  Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
        Authentication Dial In User Service (RADIUS)", RFC 2138, April

   [9]  Calhoun, P. and G. Zorn, "Roamops Authentication/Authorization
        Requirements", Work in Progress.

   [10] Perkins, C., "IP Mobility Support", RFC 2002, October 1996.

   [11] Glass, Steven, et al, "Mobile IP Authentication, Authorization,
        and Accounting Requirements", Work in Progress.

   [12] Hiller, Tom, et al., "cdma2000 Wireless Data Requirements for
        AAA", Work in Progress.

   [13] Neilson, Rob, Jeff Wheeler, Francis Reichmeyer, and Susan Hares,
        "A Discussion of Bandwidth Broker Requirements for Internet2
        Qbone Deployment", ver. 0.7, August 1999,

   [14] deBry, R., "Internet Printing Protocol/1.0: Model and
        Semantics", RFC 2566, April 1999.

   [15] Burdett, D., "Internet Open Trading Protocol - IOTP", RFC 2801,
        April 2000.

   [16] "SET Secure Electronic Transaction Specification Book 1:
        Business Description", Version 1.0, May 31, 1997,

Authors' Addresses

   John R. Vollbrecht
   Interlink Networks, Inc.
   775 Technology Drive, Suite 200
   Ann Arbor, MI  48108

   Phone: +1 734 821 1205
   Fax:   +1 734 821 1235
   EMail: jrv@interlinknetworks.com

   Pat R. Calhoun
   Network and Security Research Center, Sun Labs
   Sun Microsystems, Inc.
   15 Network Circle
   Menlo Park, California, 94025

   Phone:  +1 650 786 7733
   Fax:    +1 650 786 6445
   EMail:  pcalhoun@eng.sun.com

   Stephen Farrell
   Baltimore Technologies
   61 Fitzwilliam Lane
   Dublin 2

   Phone:  +353 1 647 7406
   Fax:    +353 1 647 7499
   EMail:  stephen.farrell@baltimore.ie

   Leon Gommans
   Enterasys Networks EMEA
   Kerkplein 24
   2841 XM  Moordrecht
   The Netherlands

   Phone: +31 182 379279
   email: gommans@cabletron.com
          or at University of Utrecht:

   George M. Gross
   Lucent Technologies
   184 Liberty Corner Road, m.s. LC2N-D13
   Warren, NJ 07059

   Phone:  +1 908 580 4589
   Fax:    +1 908-580-4991
   EMail:  gmgross@lucent.com

   Betty de Bruijn
   Interpay Nederland B.V.
   Eendrachtlaan 315
   3526 LB Utrecht
   The Netherlands

   Phone: +31 30 2835104
   EMail: betty@euronet.nl

   Cees T.A.M. de Laat
   Physics and Astronomy dept.
   Utrecht University
   Pincetonplein 5,
   3584CC Utrecht

   Phone: +31 30 2534585
   Phone: +31 30 2537555
   EMail: delaat@phys.uu.nl

   Matt Holdrege
   223 Ximeno Ave.
   Long Beach, CA 90803

   EMail: matt@ipverse.com

   David W. Spence
   Interlink Networks, Inc.
   775 Technology Drive, Suite 200
   Ann Arbor, MI  48108

   Phone: +1 734 821 1203
   Fax:   +1 734 821 1235
   EMail: dspence@interlinknetworks.com

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