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rfc:rfc2905

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
                                                               ipVerse
                                                             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.

Abstract

 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.

Vollbrecht, et al. Informational [Page 1] RFC 2905 AAA Authorization Application Examples August 2000

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
              4.6.1.1. Intra-Domain Authorization ...............   19
              4.6.1.2. Inter-Domain Authorization ...............   19
         4.6.2. Bandwidth Broker Work Phases ....................   20
         4.6.3. Inter-Domain Signaling ..........................   20
              4.6.3.1. Phase 0 ..................................   20
              4.6.3.2. Phase 1 ..................................   20
         4.6.4. Bandwidth Broker Communication Architecture .....   22
         4.6.5. Two-Tier Inter-Domain Model .....................   23
              4.6.5.1. Session Initialization ...................   23
              4.6.5.2. Service Setup ............................   23
              4.6.5.3. Service Cancellation .....................   24
              4.6.5.4. Service Renegotiation ....................   24
              4.6.5.5. RAR and RAA ..............................   24
              4.6.5.6. Session Maintenance ......................   24
              4.6.5.7. 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
              6.1.3.1. Static Trust Relationships ...............   33
              6.1.3.2. Dynamic Trust Relationships ..............   35

Vollbrecht, et al. Informational [Page 2] RFC 2905 AAA Authorization Application Examples August 2000

         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.

Vollbrecht, et al. Informational [Page 3] RFC 2905 AAA Authorization Application Examples August 2000

 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
 [6].

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.

Vollbrecht, et al. Informational [Page 4] RFC 2905 AAA Authorization Application Examples August 2000

          +------+      +-------------------------+
          |      |      | 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

Vollbrecht, et al. Informational [Page 5] RFC 2905 AAA Authorization Application Examples August 2000

 (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.
  1. 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.
  1. 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
    domain.
  1. The AAA protocol MUST allow for intermediate brokers to add their

own local Authorization information to a request or response.

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

security.

  1. The broker MUST be able to return a forwarding address to a

requester, allowing two nodes to communicate together.

  1. The protocol MUST provide the following features (per user

session):

    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:

Vollbrecht, et al. Informational [Page 6] RFC 2905 AAA Authorization Application Examples August 2000

  1. Better scaling of security associations
  2. Mobility across administrative domain boundaries
  3. 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.
                           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

Vollbrecht, et al. Informational [Page 7] RFC 2905 AAA Authorization Application Examples August 2000

 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:

Vollbrecht, et al. Informational [Page 8] RFC 2905 AAA Authorization Application Examples August 2000

  1. It does not have access to the network. The registration

request is sent by the Mobile Node to request access to the

       network.
    -  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:
  1. Dynamic Session Keys to be distributed among all Mobility

Agents

  1. Optional Dynamic assignment of a Home Agent
  2. Optional Dynamic assignment of a Home Address (note this could

be done by the Home Agent).

  1. 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
 Agent.
 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.

Vollbrecht, et al. Informational [Page 9] RFC 2905 AAA Authorization Application Examples August 2000

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
 provide.

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:
  1. k1 - Key to be shared between the Mobile Node and the Home

Agent

  1. k2 - Key to be shared between the Mobile Node and the Foreign

Agent

  1. k3 - Key to be shared between the Foreign Agent and the Home

Agent

Vollbrecht, et al. Informational [Page 10] RFC 2905 AAA Authorization Application Examples August 2000

 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
    model.
 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.

Vollbrecht, et al. Informational [Page 11] RFC 2905 AAA Authorization Application Examples August 2000

 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:
    http://www.merit.edu/working.groups/i2-qbone-bb
 The material in this section is based on [13] which is a work in
 progress of the Internet2 Qbone BB Advisory Council.

Vollbrecht, et al. Informational [Page 12] RFC 2905 AAA Authorization Application Examples August 2000

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
    components.

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:
  1. 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).
  1. 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.

Vollbrecht, et al. Informational [Page 13] RFC 2905 AAA Authorization Application Examples August 2000

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

Vollbrecht, et al. Informational [Page 14] RFC 2905 AAA Authorization Application Examples August 2000

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

Vollbrecht, et al. Informational [Page 15] RFC 2905 AAA Authorization Application Examples August 2000

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

Vollbrecht, et al. Informational [Page 16] RFC 2905 AAA Authorization Application Examples August 2000

                      +-------------+        +-------------+
                      |             |        |             |
                      | +---------+ |        | +---------+ |
                      | |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
 structure.

Vollbrecht, et al. Informational [Page 17] RFC 2905 AAA Authorization Application Examples August 2000

                             +-------------------+
                             |  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.

Vollbrecht, et al. Informational [Page 18] RFC 2905 AAA Authorization Application Examples August 2000

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.

4.6.1.1. 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.

4.6.1.2. 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].

Vollbrecht, et al. Informational [Page 19] RFC 2905 AAA Authorization Application Examples August 2000

4.6.2. Bandwidth Broker Work Phases

 The Internet 2 Qbone Bandwidth Broker discussion proposes development
 of the Bandwidth Broker model in several phases:
  1. Phase 0: Local Admission. RAR's are only handled within a local

domain. SLS's are pre-established using manual methods (fax, e-

    mail).
  1. Phase 1: Informed Admission. RAR's spanning multiple domains are

authorized based on information obtained from one or more

    Bandwidth Brokers along the path.
  1. 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

4.6.3.1. 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.

4.6.3.2. 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
 destination.
 Two fundamental signaling approaches between Bandwidth Brokers have
 been identified for the Informed Admission case.  These are
 illustrated in figure 10.

Vollbrecht, et al. Informational [Page 20] RFC 2905 AAA Authorization Application Examples August 2000

 +-------+         +-------+         +-------+         +-------+
 |       |         |       |         |       |         |       |
 |       |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
  1. 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.
  1. 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
    7.

Vollbrecht, et al. Informational [Page 21] RFC 2905 AAA Authorization Application Examples August 2000

4.6.4. Bandwidth Broker Communication Architecture

 Figure 11 shows components of the discussed Bandwidth Broker
 architecture with its interfaces.
  1. An intra-domain interface allows communication with all the

service components within the network that the Bandwidth Broker

    controls.
  1. An inter-domain interface allows communication between Bandwidth

Brokers of different autonomous networks.

  1. A user/application interface allows the Bandwidth Broker to be

managed manually. Requests can be sent from the User or a host

    application.
  1. A policy manager interface allows implementation of complex policy

management or admission control.

  1. A routing table interface allows the Bandwidth Broker to

understand the network topology.

  1. An NMS interface allows coordination of network provisioning and

monitoring.

Vollbrecht, et al. Informational [Page 22] RFC 2905 AAA Authorization Application Examples August 2000

         adjacent BB <---------------------------> adjacent BB
                                   |
                                   V
                    +------------------------------+
                    |       | 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

4.6.5.1. 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).

4.6.5.2. 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

Vollbrecht, et al. Informational [Page 23] RFC 2905 AAA Authorization Application Examples August 2000

 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.

4.6.5.3. 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.

4.6.5.4. 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.

4.6.5.5. 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.

4.6.5.6. 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.

4.6.5.7. 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
 Interface.

4.7. Requirements

 From the above descriptions we derive the following requirements.

Vollbrecht, et al. Informational [Page 24] RFC 2905 AAA Authorization Application Examples August 2000

  1. 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
    implicit.
  1. A confirmation of authorization is required in order to initialize

the system.

  1. A negation of static authorization is required to shut down

certain services.

  1. A renegotiation of static authorization is required to alter

services (SLS's).

  1. Dynamic authorization requests (RAR) must fit into pre-established

static authorizations (SLS's).

  1. Dynamic authorization requests (RAR) may be answered by an "in

progress state" answer.

  1. 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
 printer.

Vollbrecht, et al. Informational [Page 25] RFC 2905 AAA Authorization Application Examples August 2000

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

Vollbrecht, et al. Informational [Page 26] RFC 2905 AAA Authorization Application Examples August 2000

 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.

Vollbrecht, et al. Informational [Page 27] RFC 2905 AAA Authorization Application Examples August 2000

    +------+       +----------------------+
    |      |------>| 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

Vollbrecht, et al. Informational [Page 28] RFC 2905 AAA Authorization Application Examples August 2000

 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-
 commerce.
 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
 domain.
 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.

Vollbrecht, et al. Informational [Page 29] RFC 2905 AAA Authorization Application Examples August 2000

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
    components.

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].
  1. 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
    Cardholder.
  1. 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.
  1. 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
    Merchant.
  1. 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

Vollbrecht, et al. Informational [Page 30] RFC 2905 AAA Authorization Application Examples August 2000

    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
 Organization.
 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.
  1. The Cardholder has a contractual relationship with the card

Issuer. The Cardholder holds an account with the Issuer and

    obtains an account number.
  1. The Merchant has a contractual relationship with the Acquirer.

The Merchant obtains a Merchant ID from the Acquirer.

  1. 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).

Vollbrecht, et al. Informational [Page 31] RFC 2905 AAA Authorization Application Examples August 2000

             +----------------+       +------------------------+
             | 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.

Vollbrecht, et al. Informational [Page 32] RFC 2905 AAA Authorization Application Examples August 2000

6.1.3.1. 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
  1. 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

Vollbrecht, et al. Informational [Page 33] RFC 2905 AAA Authorization Application Examples August 2000

    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.
  1. 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
    Merchant.
  1. 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.
  1. 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.
  1. 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.

Vollbrecht, et al. Informational [Page 34] RFC 2905 AAA Authorization Application Examples August 2000

6.1.3.2. 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.

Vollbrecht, et al. Informational [Page 35] RFC 2905 AAA Authorization Application Examples August 2000

       +----------------+       +------------------------+
       | 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
    process.
 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.

Vollbrecht, et al. Informational [Page 36] RFC 2905 AAA Authorization Application Examples August 2000

 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
    goods.
 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.

Vollbrecht, et al. Informational [Page 37] RFC 2905 AAA Authorization Application Examples August 2000

                      +-----------+
                      |  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:

Vollbrecht, et al. Informational [Page 38] RFC 2905 AAA Authorization Application Examples August 2000

    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:
 Integrity
 5. For any authorization request or response, the receiving party
    needs to verify that the content of the message has not been
    altered.
 Confidentiality/Privacy
 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.
 Nonrepudiation
 8. There is a need for a recorded, authenticated and authorized
    agreement about the request for and delivery of service.

Vollbrecht, et al. Informational [Page 39] RFC 2905 AAA Authorization Application Examples August 2000

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
 graduation.
 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
    components.

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].

Vollbrecht, et al. Informational [Page 40] RFC 2905 AAA Authorization Application Examples August 2000

  1. The Student (User) – the person enrolling in a course (Service)

and taking the corresponding exam.

  1. The Educator (Service Equipment) – the education content server

for which the content is delivered by the Professor.

  1. 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.
  1. The Faculty (Service Provider) – the organization (department in

U.S. terms) which controls the Service "Equipment" of which the

    Educator is one example.
  1. 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.
  1. 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
 required.
 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.

Vollbrecht, et al. Informational [Page 41] RFC 2905 AAA Authorization Application Examples August 2000

                   +---------------------------------------------+
                   | +-----------------------------------------+ |
                   | |          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.

Vollbrecht, et al. Informational [Page 42] RFC 2905 AAA Authorization Application Examples August 2000

 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
 students.

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:
  1. 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.
  1. 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.
  1. 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:
  1. 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
    authenticating.

Vollbrecht, et al. Informational [Page 43] RFC 2905 AAA Authorization Application Examples August 2000

  1. 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.
  1. 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.
  1. 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).

Vollbrecht, et al. Informational [Page 44] RFC 2905 AAA Authorization Application Examples August 2000

                 +----------------------------------------------+
                 |                                              |
                 |  +----------------+  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.

Vollbrecht, et al. Informational [Page 45] RFC 2905 AAA Authorization Application Examples August 2000

 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
    passed.

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

Vollbrecht, et al. Informational [Page 46] RFC 2905 AAA Authorization Application Examples August 2000

    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:
  1. authorization requests and responses for obtaining

authorization,

  1. notification messages for accounting purposes, and
  2. 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.

Glossary

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

Vollbrecht, et al. Informational [Page 47] RFC 2905 AAA Authorization Application Examples August 2000

 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
    service.
 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.

References

 [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.

Vollbrecht, et al. Informational [Page 48] RFC 2905 AAA Authorization Application Examples 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
      1997.
 [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,
      http://www.merit.edu/working.groups/i2-qbone-bb/doc/BB_Req7.pdf.
 [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,
      http://www.setco.org/download/set_bk1.pdf.

Vollbrecht, et al. Informational [Page 49] RFC 2905 AAA Authorization Application Examples August 2000

Authors' Addresses

 John R. Vollbrecht
 Interlink Networks, Inc.
 775 Technology Drive, Suite 200
 Ann Arbor, MI  48108
 USA
 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
 USA
 Phone:  +1 650 786 7733
 Fax:    +1 650 786 6445
 EMail:  pcalhoun@eng.sun.com
 Stephen Farrell
 Baltimore Technologies
 61 Fitzwilliam Lane
 Dublin 2
 Ireland
 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:
        l.h.m.gommans@phys.uu.nl

Vollbrecht, et al. Informational [Page 50] RFC 2905 AAA Authorization Application Examples August 2000

 George M. Gross
 Lucent Technologies
 184 Liberty Corner Road, m.s. LC2N-D13
 Warren, NJ 07059
 USA
 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
 Netherlands
 Phone: +31 30 2534585
 Phone: +31 30 2537555
 EMail: delaat@phys.uu.nl
 Matt Holdrege
 ipVerse
 223 Ximeno Ave.
 Long Beach, CA 90803
 EMail: matt@ipverse.com

Vollbrecht, et al. Informational [Page 51] RFC 2905 AAA Authorization Application Examples August 2000

 David W. Spence
 Interlink Networks, Inc.
 775 Technology Drive, Suite 200
 Ann Arbor, MI  48108
 USA
 Phone: +1 734 821 1203
 Fax:   +1 734 821 1235
 EMail: dspence@interlinknetworks.com

Vollbrecht, et al. Informational [Page 52] RFC 2905 AAA Authorization Application Examples August 2000

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Acknowledgement

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Vollbrecht, et al. Informational [Page 53]

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