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AAA Working Group                                            S. Farrell
INTERNET-DRAFT                                   Baltimore Technologies
Expires in six months                                     J. Vollbrecht
                                                    Merit Network, Inc.
                                                             P. Calhoun
                                                 Sun Microsystems, Inc.
                                                             L. Gommans
                                                 Cabletron Systems EMEA
                                                               G. Gross
                                                    Lucent Technologies
                                                           B. de Bruijn
                                                Interpay Nederland B.V.
                                                             C. de Laat
                                                     Utrecht University
                                                            M. Holdrege
                                                    Lucent Technologies
                                                              D. Spence
                                                    Merit Network, Inc.
                                                           October 1999


                      AAA Authorization Requirements
               <draft-ietf-aaa-authorization-reqs-01.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of [RFC2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


Abstract

   This document specifies the requirements that AAA protocols must
   meet in order to support authorization services in the Internet. The
   requirements have been elicited from a study of a range of
   applications including mobile-IP, roamops and others.



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Table Of Contents


   Status of this Memo.............................................1
   Abstract........................................................1
   Table Of Contents...............................................2
   1. Introduction.................................................2
   2. Requirements.................................................3
       2.1  Authorization Information..............................3
       2.2  Security of authorization information..................6
       2.3  Time...................................................8
       2.4  Topology...............................................9
       2.5  Application Proxying..................................11
       2.6  Trust Model...........................................11
       2.7  Not just transactions.................................13
       2.8  Administration........................................14
       2.9  Bytes on-the-wire.....................................15
       2.10 Interfaces............................................16
       2.11 Negotiation...........................................16
   3. Security Considerations.....................................18
   4. References..................................................18
   Author's Addresses.............................................19
   Full Copyright Statement.......................................20


1. Introduction

   <<Comments are in angle-brackets like this. Where text was added
   late in the editing process, requirements are marked "late
   entrant".>>

   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
   in this document are to be interpreted as described in [RFC2119].

   This document is one of a series of three documents prepared by the
   AAA WG authorization subgroup dealing with the authorization
   requirements for AAA protocols. The three documents are:

        AAA Authorization Framework [FRMW]
        AAA Authorization Requirements (this document)
        AAA Authorization Application Examples [SAMP]

   The process followed in producing this document was to analyze the
   requirements from [SAMP] based on a common understanding of the AAA
   authorization framework [FRMW]. This document assumes familiarity
   with both the general issues involved in authorization and, in
   particular, the reader will benefit from a reading of [FRMW] where,
   for example, definitions of terms can be found.





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2. Requirements

   Requirements are grouped under headings for convenience; this
   grouping is not significant.

   Definitions and explanations of some of the technical terms used in
   this document may be found in [FRMW].

   Each requirement is presented as a succinct (usually a sentence or
   two) statement. Most are followed by a paragraph of explanatory
   material, which sometimes contains an example. Fully described
   examples may be found in [SAMP].

   The requirements presented are not intended to be "orthogonal", that
   is, some of them repeat, or overlap, with others.

2.1 Authorization Information


2.1.1   Authorization decisions MUST be able to be based on information
     about the requestor, the service/method requested, and the
     operating environment (authorization information). AAA protocols
     are required to transport this information.

   This simply states the requirement for a protocol and an access
   decision function, which takes inputs, based on the requestor, the
   resource requested and the environment.

2.1.2   It MUST be possible to represent authorization information as
     sets of attributes. It MAY be possible to represent authorization
     information as objects.

   This states that authorization information must be decomposable into
   sets of attributes. It is not intended to imply any particular
   mechanism for representing attributes.

2.1.3   It MUST be possible to package authorization information so
     that the authorization information for multiple services or
     applications can be carried in a single message in a AAA or
     application protocol.

   This states that a protocol, which always required separate AAA
   messages/transactions for each service/application, would not meet
   the requirement. For example, it should be possible for a single AAA
   message/transaction to be sufficient to allow both network and
   application access.

2.1.4   Standard attributes types SHOULD be defined which are relevant
     to many Internet applications/services (e.g.  identity
     information, group information, ...)




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   There are many attributes that are used in lots of contexts, and
   these should only be defined once, in order to promote
   interoperability and prevent duplication of effort.

2.1.5   Authorization decisions MUST NOT be limited to being based on
     identity information, i.e. AAA protocols MUST support the use of
     non-identifying information, e.g. to support role based access
     control (RBAC).

   Authorization based on clearances, roles, groups or other
   information is required to be supported. A AAA protocol that only
   carried identity information would not meet the requirement.

2.1.6   Authorization data MAY include limits in addition to attributes
     which are directly "owned" by end entities.

   This states that some attributes do not simply represent attributes
   of an entity, for example a spending limit of IRú1,000 is not an
   intrinsic attribute of an entity. This also impacts on the access
   decision function, in that the comparison to be made is not a simple
   equality match.

2.1.7   It MUST be possible for other (non-AAA) protocols to define
     their own attribute types, which can then be carried within an
     authorization package in a AAA or application protocol.

   This states that the attributes that are significant in an
   authorization decision, may be application protocol dependent. For
   example, many attribute types are defined by [RFC2138] and support
   for the semantics of these attributes will be required. Of course,
   only AAA entities that are aware of the added attribute types can
   make use of them.

2.1.8   It SHOULD be possible for administrators of deployed systems to
     define their own attribute types, which can then be carried within
     an authorization package in a AAA or application protocol.

   This states that the attributes that are significant in an
   authorization decision, may be dependent on a closed environment.
   For example, many organizations have a well-defined scheme of
   seniority, which can be used to determine access levels. Of course,
   only AAA entities that are aware of the added attribute types can
   make use of them.

2.1.9   It SHOULD be possible to define new attribute types without
     central administration and control of attribute name space.

   A centralized or distributed registration scheme of some sort is
   needed if collisions in attribute type allocations are to be
   avoided. However a AAA protocol which always requires use of such a
   centralized registration would not meet the requirement. Of course,
   collisions should be avoided where possible.


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2.1.10  It MUST be possible to define attribute types so that an
     instance of an attribute in a single AAA message can have multiple
     values.

   This states that a protocol which does not allow multiple instances
   of an attribute in a message/transaction would not meet the
   requirement.  For example it should be possible to have a "group"
   attribute which contains more than one groupname (or number or
   whatever).

2.1.11  If MUST be possible to distinguish different instances of the
     same authorization attribute type or value, on the basis of
     "security domain" or "authority".

   This recognizes that it is important to be able to distinguish
   between attributes based not only on their value. For example, all
   NT domains (which use the English language) have an Administrators
   group, an access decision function has to be able to determine to
   which of these groups the requestor belongs.

2.1.12  AAA protocols MUST specify mechanisms for updating the rules
     which will be used to control authorization decisions.

   This states that a AAA protocol that cannot provide a mechanism for
   distributing authorization rules is not sufficient. For example,
   this could be used to download ACLs to a PDP.

   Note that this is not meant to mean that this AAA protocol mechanism
   must always be used, simply that it must be available for use. In
   particular, storing authorization rules in a trusted repository (in
   many cases an LDAP server) will in many cases be used instead of
   such a AAA protocol mechanism.  Neither does this requirement call
   for a standardized format for authorization rules, merely that there
   be a mechanism for transporting these.

2.1.13  The AAA protocol MUST allow for chains of AAA entities to be
     involved in an authorization decision.

   This states that more than one AAA server may have to be involved in
   a single authorization decision. This may occur either due to a
   decision being spread across more than one "domain" or in order to
   distribute authorization within a single "domain".

2.1.14  The AAA protocol MUST allow for intermediate AAA entities to
     add their own local authorization information to a AAA request or
     response.

   This states that where more than one AAA entity is involved in an
   authorization decision each of the AAA entities may manipulate the
   AAA messages involved either by adding more information or by
   processing parts of the information.



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2.1.15  AAA entities MAY be either be deployed independently or
     integrated with application entities.

   This states that the AAA entities may either be implemented as AAA
   servers or integrated with application entities.

2.1.16  The AAA protocol MUST support the creation and encoding of
     rules that are to be active inside one AAA server based on
     attributes published by another AAA server. The level of
     authorization of the requesting AAA Server MAY govern the view on
     attributes.

   This states that one AAA entity may have to distribute authorization
   rules to another, and that the AAA entity that receives the rules
   may only be seeing part of the story.

   <<late entrant>>
2.1.17  AAA protocols MAY have to support the idea of critical and non-
     critical attribute types.

   This is analogous to the use of the criticality flag in public key
   certificate extensions.

2.1.18  A AAA protocol MUST allow authorization rules to be expressed
     in terms of combinations of other authorization rules which have
     been evaluated.

   For example, access may only be granted if the requestor is member
   of the backup users group and not a member of the administrator's
   group. Note that this requirement does not state which types of
   combinations are to be supported.

2.1.19  It SHOULD be possible to make authorization decisions based on
     the geographic location of a requestor, service or AAA entity.

   This is just an example of an authorization attribute type, notable
   because it requires different underlying implementation mechanisms.

2.1.20  It SHOULD be possible to make authorization decisions based on
     the identity or the equipment used by a requestor, service or AAA
     entity.

   This is just an example of an authorization attribute type, notable
   because it may require different underlying implementation
   mechanisms (if IPSec isn't available).

   <<late entrant>>
2.1.21  When there are multiple instances of a given attribute, there
     must be an unambiguous mechanism by which a receiving peer can
     determine the value of specified instance.

2.2 Security of authorization information


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2.2.1   It MUST be possible for authorization information to be
     communicated securely in AAA and application protocols.
     Mechanisms that preserve authenticity, integrity and privacy for
     this information MUST be specified.

   This states that there must be a well-defined method for securing
   authorization information, not that such methods must always be
   used. Whether support for these mechanisms is to be required for
   conformance is left open. In particular, mechanisms must be provided
   so that a service administrator in the middle of a chain cannot read
   or change authorization information being sent between other AAA
   entities.

2.2.2   AAA protocols MUST allow for use of an appropriate level of
     security for authorization information. AAA protocols MUST be able
     to support both highly secure and less secure mechanisms for data
     integrity/confidentiality etc.

   It is important that AAA protocols do not mandate too heavy a
   security overhead, thus the security mechanisms specified donÆt
   always need to be used (though not using them may affect the
   authorization decision).

2.2.3   The security requirements MAY differ between different parts of
     a package of authorization information.

   Some parts may require confidentiality and integrity, some may only
   require integrity. This effectively states that we require something
   like selective field security mechanisms. For example, information
   required to gain access to a network may have to be in clear, whilst
   information required for access to an application within that
   network may have to be encrypted in the AAA protocol.

2.2.4   AAA protocols MUST provide mechanisms that prevent intermediate
     administrators breaching security.

   This is a basic requirement to prevent man-in-the-middle attacks,
   for example where an intermediate administrator changes AAA messages
   on the fly.

2.2.5   AAA protocols MUST NOT open up replay attacks based on replay
     of the authorization information.

   For example, a AAA protocol should not allow flooding attacks where
   the attacker replays AAA messages that require the recipient to use
   a lot of CPU or communications before the replay is detected.

2.2.6   AAA protocols MUST be capable of leveraging any underlying peer
     entity authentication mechanisms that may have been applied - this
     MAY provide additional assurance that the owner of the
     authorization information is the same as the authenticated entity.



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   For example, if IPSec provides sufficient authentication, then it
   must be possible to omit AAA protocol authentication.

2.2.7   End-to-end confidentiality, integrity, peer-entity-
     authentication, or non-repudiation MAY be required for packages of
     authorization information.

   This states that confidentiality, (resp. the other security
   services), may have to be provided for parts of a AAA message, even
   where it is transmitted via other AAA entities. It does allow that
   such a AAA message may also contain non-confidential, resp. the
   other security services), parts. In addition, intermediate AAA
   entities may themselves be considered end-points for end-to-end
   security services applied to other parts of the AAA message.

2.2.8   AAA protocols MUST be usable even in environments where no peer
     entity authentication is required (e.g. a network address on a
     secure LAN may be enough to decide).

   This requirement (in a sense the opposite of 2.2.6), indicates the
   level of flexibility that is required in order to make the AAA
   protocol useful across a broad range of applications/services.

2.2.9   AAA protocols MUST specify "secure" defaults for all protocol
     options. Implementations of AAA entities MUST use these "secure"
     defaults unless otherwise configured/administered.

   This states that the out-of-the-box configuration must be "secure",
   for example, authorization decisions should result in denial of
   access until a AAA entity is configured. Note that the
   interpretation of "secure" will vary on a case-by-case basis, though
   the principle remains the same.

2.3 Time

2.3.1   Authorization information MUST be timely, which means that it
     MUST expire and in some cases MAY be revoked before expiry.

   This states that authorization information itself is never to be
   considered valid for all time, every piece of authorization
   information must have associated either an explicit or implicit
   validity period or time-to-live.

2.3.2   AAA protocols MUST provide mechanisms for revoking
     authorization information, in particular privileges.

   Where the validity or time-to-live is long, it may be necessary to
   revoke the authorization information, e.g. where someone leaves a
   company. Note that this requirement does not mandate a particular
   scheme for revocation, so that it is not a requirement for
   blacklists or CRLs.



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2.3.3   A set of attributes MAY have an associated validity period -
     such that that the set MUST only be used for authorization
     decisions during that period. The validity period may be
     relatively long, (e.g. months) or short (hours, minutes).

   This states that explicit validity periods are, in some cases,
   needed at the field level.

2.3.4   Authorization decisions MAY be time sensitive. Support for e.g.
     "working hours" or equivalent MUST be possible.

   This states that the AAA protocol must be able to support the
   transmission of time control attributes, although it does not
   mandate that AAA protocols must include a standard way of expressing
   the "working hours" type constraint.

2.3.5   It MUST be possible to support authorization decisions that
     produce time dependent results.

   For example, an authorization result may be that service should be
   provided for a certain period. In such cases a AAA protocol must be
   able to transport this information, possibly as a specific result of
   the authorization decision, or, as an additional "termination of
   service" AAA message transmitted later.

2.3.6   It MUST be possible to support models where the authorization
     information is issued in well in advance of an authorization
     decision rather than near the time of the authorization decision.

   This is required in order to support pre-paid (as opposed to
   subscription) scenarios (e.g. for VoIP).

2.3.7   It SHOULD be possible to support models where the authorization
     decision is made in advance of a service request.

   This is for some applications such as backup, where actions are
   scheduled for future dates. It also covers applications that require
   reservation of resources.

2.3.8   A AAA mechanism must allow time stamp information to be carried
     along with authorization information (e.g. for non-repudiation).

   The PKIX WG is developing a time stamp protocol, which can be used
   as part of a non-repudiation solution. In some environments it may
   be necessary that certain AAA protocol messages are timestamped (by
   a trusted authority) and that the timestamps are forwarded within
   subsequent AAA messages.

2.4 Topology

2.4.1   AAA protocols MUST be able to support the use of the push, pull
     and agent models.


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   This states that a protocol that only supported one model, say pull,
   would not meet the requirements of all the applications. The models
   are defined in [FRMW].

2.4.2   In transactions/sessions, which involve more than one AAA
     entity, each æhopÆ MAY use a different push/pull/agent model.

   For example, in the mobile IP case, a "foreign" AAA server might
   pull authorization information from a broker, whereas the broker
   might push some authorization information to a "home" AAA server.

2.4.3   AAA Protocols MUST cater for applications and services where
     the entities involved in the application or AAA protocols belong
     to different (security) domains.

   This states that it must be possible for any AAA protocol message to
   cross security or administrative domain boundaries. Typically,
   higher levels of security will be applied when crossing such
   boundaries, and accounting mechanisms may also have to be more
   stringent.

2.4.4   AAA protocols MUST support roaming.

   Roaming here may also be thought of as "away-from-home" operation.
   For example, this is a fundamental requirement for the mobile IP
   case.

2.4.5   AAA protocols SHOULD support dynamic mobility

   Dynamic mobility here means that a client moves from one domain to
   another, without having to completely re-establish e.g. whatever AAA
   session information is being maintained.

2.4.6   An authorization decision MAY have to be made before the
     requestor has any other connection to a network.

   For example, this means that the requestor canÆt go anywhere on the
   network to fetch anything and must do requests via an
   application/service or via an intermediate AAA entity. The AAA
   protocol should not overexpose such a server to denial-of-service
   attacks.

2.4.7   AAA protocols MUST support the use of intermediate AAA entities
     which take part in authorization transactions but which donÆt
     "own" any of the end entities or authorization data.

   In some environments (e.g. roamops), these entities are termed
   brokers (though these are not the same as bandwidth brokers in the
   QoS environment).

2.4.8   AAA protocols MAY support cases where an intermediate AAA
     entity returns a forwarding address to a requestor or AAA entity,


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     in order that the requestor or originating AAA entity can contact
     another AAA entity.

   This requirement recognizes that there will be routing issues with
   AAA servers, and that this requires that AAA protocols are able to
   help with such routing. For example, in the mobile IP case, a broker
   may be required, in part to allow the foreign and home AAA servers
   to get in contact.

2.4.9   It MUST be possible for an access decision function to discover
     the AAA server of a requestor. If the requestor provides
     information used in this discovery process then the access
     decision function MUST be able to verify this information in a
     trusted manner.

   This states that not only do AAA servers have to be able to find one
   another, but that sometimes an application entity may have to find
   an appropriate AAA server.

2.5 Application Proxying

2.5.1   AAA protocols MUST support cases where applications use
     proxies, that is, an application entity (C), originates a service
     request to a peer (I) and this intermediary (I) also initiates a
     service request on behalf of the client (C) to a final target (T).
     AAA protocols MUST be such that the authorization decision made at
     T, MAY depend on the authorization information associated with C
     and/or with I. This "application proxying" must not introduce new
     security weaknesses in the AAA protocols. There MAY be chains of
     application proxies of any length.

   Note that this requirement addresses application layer proxying -
   not chains of AAA servers. For example, a chain of HTTP proxies
   might each want to restrict the content they serve to the "outside".
   As the HTTP GET message goes from HTTP proxy to HTTP proxy, this
   requirement states that it must be possible that the authorization
   decisions made at each stage can depend on the user at the browser,
   and not say, solely on the previous HTTP proxyÆs identity. Of course
   there may only be a single AAA server involved, or there may be
   many.

2.5.2   Where there is a chain of application proxies, the AAA protocol
     flows at each stage MAY be independent, i.e. the first hop may use
     the push model, the second pull, the third the agent model.

   This simply restates a previous requirement (no. 2.4.7), to make it
   clear that this also applies when application proxying is being
   used.

2.6 Trust Model




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2.6.1   AAA entities MUST be able to make decisions about which other
     AAA entities are trusted for which sorts of authorization
     information.

   This is analogous to a requirement in pubic key infrastructures:
   Just because someone can produce a cryptographically correct public
   key certificate doesnÆt mean that I should trust them for anything,
   in particular, I might trust the issuer for some purposes, but not
   for others.

2.6.2   AAA protocols MUST allow entities to be trusted for different
     purposes, trust MUST NOT be an all-or-nothing issue.

   This relates the packaging (no. 2.1.3) and trust (no. 2.6.1)
   requirements. For example, a AAA entity may trust some parts of an
   authorization package but not others.


2.6.3   A confirmation of authorization MAY be required in order to
     initialize or resynchronize a AAA entity.

   This states that a AAA entity may need to process some AAA protocol
   messages in order to initialize itself. In particular, a AAA entity
   may need to check that a previous AAA message remains "valid", e.g.
   at boot-time.

2.6.4   A negation of static authorization MAY be required to shut down
     certain services.

   This is the converse of 2.6.5 above. It means that a AAA entity may
   be "told" by another that a previous AAA message is no longer
   "valid". See also 2.3.2 and 2.7.6.

2.6.5   It MUST be possible to configure sets of AAA entities that
     belong to a local domain, so that they are mutually trusting, but
     so that any external trust MUST be via some nominated subset of
     AAA entities.

   This states that for efficiency or organizational reasons, it must
   be possible to set up some AAA servers through which all "external"
   AAA services are handled. It also states that it must be possible to
   do this without over-burdening the "internal-only" AAA servers with
   onerous security mechanisms, just because some AAA servers do handle
   external relations.

2.6.6   Intermediate AAA entities in a chain MUST be able to refuse a
     connection approved by an earlier entity in the chain.

   For example, in mobile IP the home network may authorize a
   connection, but the foreign network may refuse to allow the
   connection due to the settings chosen by the home network, say if
   the home network will refuse to pay.


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2.6.7   It SHOULD be possible to modify authorization for resources
     while a session is in progress without destroying other session
     information.

   For example, a "parent" AAA server should be able to modify the
   authorization state of sessions managed by a "child" AAA server, say
   by changing the maximum number of simultaneous sessions which are
   allowed.

2.7 Not just transactions

2.7.1   Authorization decisions MAY be context sensitive, AAA protocols
     MUST enable such decisions.

   This states that AAA protocols need to support cases where the
   authorization depends, (perhaps even only depends), on the current
   state of the system, e.g. only seven sessions allowed, seventh
   decision depends on existence of six current sessions. Since the
   context might involve more than one service, the AAA protocol is
   likely to have to offer some support.

2.7.2   AAA protocols SHOULD support both the authorization of
     transactions and continuing authorization of sessions.

   This states that AAA entities may have to maintain state and act
   when the state indicates some condition has been met.

2.7.3   Within a single session or transaction, it MUST be possible to
     interleave authentication, authorization and accounting AAA
     messages.

   This states, that e.g. a session may have to use initial
   authentication, authorization and accounting AAA message(s), but
   also have to include e.g. re-authentication every 30 minutes, or a
   continuous "drip-drip" of accounting AAA messages.

2.7.4   Authorization decisions may result in a "not ready" answer.

   This states that yes and no are not the only outcomes of an
   authorization decision. In particular, if the AAA entity cannot yet
   give a decision, it might have to return such a result. This is
   analogous to how public key certification requests are sometimes
   handled in PKI management protocols.

2.7.5   A AAA entity MAY re-direct a AAA request that it has received.

   This states that if entity "a" asks "b", then "b" may say: "don't
   ask me, ask 'c'". This is analogous to HTTP re-direction (status
   code 307).

2.7.6   AAA protocols SHOULD allow a AAA entity to "take back" an
     authorization.


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   The expectation is that AAA protocols will support the ability of a
   AAA entity to signal an application or other AAA entity that an
   authorization (possibly previously granted by a third AAA entity) is
   no longer valid.

2.8 Administration

2.8.1   It MUST be possible for authorization data to be administered
     on behalf of the end entities and AAA entities.

   This requirement indicates that administration of AAA has to be
   considered as part of protocol design - a AAA protocol, which
   required all AAA entities act independent of all other AAA entities,
   would not meet the requirement.

2.8.2   Centralizable administration of all features SHOULD be
     supported.

   It should be possible (if it meets the domain requirements) to
   centralize or distribute the administration of AAA.

2.8.3   AAA protocols SHOULD support cases where the user (as opposed
     to an administrator) authorizes a transaction.

   For example, a user might want to control anti-spam measures or
   authorize things like a purchase. In such cases, the user is acting
   somewhat like an administrator.

2.8.4   One AAA entity MAY create authorization rules for another AAA
     entity.

   This is required to properly support delegation of authority,
   however when allowed, this must be able to be done in a secure
   fashion.

2.8.5   AAA protocols SHOULD support failure recovery when one AAA
     entity in a chain of AAA entities that maintain state about a
     session fails.

   For example, in a network access situation it may be required that a
   AAA server which has crashed be able to determine how many sessions
   are in progress, in order to make the "next" authorization decision.

2.8.6   It SHOULD be possible for a AAA entity to query the
     authorization state of another AAA entity.

   This may be required as part of a failure recovery procedure.

2.8.7   AAA protocols MUST be able to support "hot fail-over" for
     server components without loss of state information.

   This states that AAA protocols must be able to support cases where,
   when a server is no longer operable, a secondary server can

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   automatically be brought "live" without losing important state
   information.

2.9 Bytes on-the-wire

2.9.1   Authorization separate from authentication SHOULD be allowed
     when necessary, but the AAA protocols MUST also allow for a single
     message to request both authentication and authorization.

   AAA protocols have to allow a split between authentication and
   authorization so that different mechanisms are used for each. This
   states that sometimes both types of information need to be carried
   in the same message.

2.9.2   In order to minimize resource usage (e.g. reduce roundtrips) it
     MUST be possible to embed AAA PDUs into other protocols.

   This states that the AAA protocol authorization packages must be
   defined so that they can also be carried in other protocols. For
   example, depending on AAA protocol header information in order to
   reference an authorization package could cause a protocol to fail to
   meet the requirement.


2.9.3   A AAA protocol MAY provide mechanisms for replication of state
     information.

   This can be required e.g. to support resiliency in cases where hot
   fail-over is required. Note that AAA protocols are of course,
   subject to normal protocol design requirements to do with
   reliability, no single-point-of-failure etc even though these are
   not all specified here.

2.9.4   A AAA protocol SHOULD allow the possibility for implementation
     of a gateway function between the AAA protocol and other legacy
     AAA related protocols.

   For example, some form of support for [RFC2138] as a legacy protocol
   is very likely to be required. Of course, the use of such a gateway
   is almost certain to mean not meeting some other requirements, (e.g.
   end-to-end security), for transactions routed through the gateway.
   There is no implication that such gateway functionality needs to be
   a separate server.

2.9.5   A AAA protocol MUST be able to support use of a wide range of
     primitive data types, including RFC2277.

   For example, various sized, signed and unsigned integers, possibly
   including multi-precision integers will almost certainly need to be
   transported. Floating point support according to ANSI IEEE 754-1985
   may also be required.



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2.9.6   A AAA protocol transport SHOULD support being optimized for a
     long-term exchange of small packets in a stream between a pair of
     hosts.

   NASes typically have a high number of transactions/second, so the
   AAA protocol MUST allow the flow of requests to be controlled in
   order for the server to make efficient use of it's receive buffers.

2.9.7   A AAA protocol MUST provide support for load balancing.

   In the event that a peer's cannot receive any immediate requests,
   the AAA protocol MUST allow for an implementation to balance the
   load of requests among a set of peers.

2.10    Interfaces

2.10.1  It SHOULD be possible that authorization data can be used for
     application purposes.

   For example, in web access, if the authorization data includes a
   group name, mechanisms to make this data available to the
   application so that it can modify the URL originally requested are
   desirable.

2.10.2  It SHOULD be possible that authorization data can be used to
     mediate the response to a request.

   For example, with web access the clearance attribute value may
   affect the content of the HTTP response message.

2.10.3  AAA protocols SHOULD be able to operate in environments where
     requestors are not pre-registered (at least for authorization
     purposes, but possibly also for authentication purposes).

   This is necessary to be able to scale a AAA solution where there are
   many requestors.

2.10.4  AAA protocols MUST be able to support a linkage between
     authorization and accounting mechanisms.

   Motherhood and apple-pie.

2.10.5  AAA protocols MUST be able to support accountability (audit/
     non-repudiation) mechanisms.

   Sometimes, an authorization decision will be made where the
   requestor has not authenticated. In such cases, it must be possible
   that the authorization data used is linked to audit or other
   accountability mechanisms. Note that this requirement does not call
   for mandatory support for digital signatures, or other parts of a
   non-repudiation solution.

2.11    Negotiation

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2.11.1  AAA protocols MUST support the ability to refer to sets of
     authorization packages in order to allow peers negotiate a common
     set.

   Given that peers may support different combinations of authorization
   attribute types and packages, the requirement states that protocol
   support is required to ensure that the peers use packages supported
   by both peers.

2.11.2  It MUST be possible to negotiate authorization packages between
     AAA entities that are not in direct communication.

   This states that where, e.g. a broker is involved, the end AAA
   servers might still need to negotiate.

2.11.3  Where negotiation fails to produce an acceptable common
     supported set then access MUST be denied.

   For example, a server cannot grant access if it cannot understand
   the attributes of the requestor.

2.11.4  Where negotiation fails to produce an acceptable common
     supported set then it SHOULD be possible to generate an error
     indication to be sent to another AAA entity.

   If negotiation fails, then some administrator intervention is often
   required, and protocol support for this should be provided.

2.11.5  It MUST be possible to pre-provision the result of a
     negotiation, but in such cases, the AAA protocol MUST include a
     confirmation of the "negotiation result".

   Even if the supported packages of a peer are configured, this must
   be confirmed before assuming both sides are similarly configured.

2.11.6  For each application making use of a AAA protocol, there MUST
     be one inter-operable IETF standards-track specification of the
     authorization package types that are "mandatory to implement".

   This requirement assures that communicating peers can count on
   finding at least one IETF specified inter-operable AAA protocol
   dialect provided they are doing authorization for a common
   application specific problem domain. This does not preclude the
   negotiation of commonly understood but private AAA protocol
   authorization package types (e.g. vendor specific).

2.11.7  It SHOULD also be possible to rank AAA negotiation options in
     order of preference.

   This states that, when negotiating, peers must be able to indicate
   preferences as well as capabilities.


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2.11.8  The negotiation mechanisms used by AAA protocols SHOULD NOT be
     vulnerable to a "bidding-down" attack.

   A "bidding-down" attack is where an attacker forces the negotiating
   parties to choose the "weakest" option available. This is analogous
   to forcing 40-bit encryption on a link. The requirement highlights
   that protocol support is needed to prevent such attacks, for example
   by including the negotiation messages as part of a later MAC
   calculation, if authentication has produced a shared secret.

   <<late entrant>>
2.11.9  A peer MUST NOT send an attribute within an authorization
     package or attribute that was not agreed to by a prior successful
     negotiation. If this AAA protocol violation occurs, then it MUST
     be possible to send an error indication to the misbehaving peer,
     and generate an error indication to the network operator.

   <<late entrant>>
2.11.10 A peer MUST declare all of the sets of the authorization
     packages that it understands in its initial negotiation bid
     message.


3. Security Considerations

   This document includes specific security requirements.

   This document does not state any detailed requirements for the
   interplay with authentication, accounting or accountability (audit).
   A AAA protocol, which meets all of the above requirements, may still
   leave vulnerabilities due to such interactions. Such issues must be
   considered as part of AAA protocol design.

4. References

  [FRMW]      Vollbrecht et al., "AAA Authorization Framework",
               draft-ietf-aaa-authz-arch-00.txt, October 1999.
  [RFC2026]   Bradner, S., "The Internet Standards Process -- Revision
               3", RFC 2026, BCP 9, October 1996.
  [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, March 1997.
  [RFC2138]   Rigney, C., et al., "Remote Authentication Dial In User
               Service (RADIUS)", RFC2138, April 1997.
  [RFC2277]   Alvestrand, H., "IETF Policy on Character Sets and
               Languages", RFC2277, January 1998.
  [SAMP]      Vollbrecht et al., "AAA Authorization Application
               Examples", draft-ietf-aaa-authz-samp-00.txt, October
               1999.






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Author's Addresses

   Stephen Farrell                     John R. Vollbrecht
   Baltimore Technologies              Merit Network, Inc.
   61/62 Fitzwilliam Lane              4251 Plymouth Rd., Suite 2000
   Dublin 2,                           Ann Arbor, MI  48105
   IRELAND                             USA
   Phone: +353-1-647-7300              Phone: +1 734 763 1206
   Fax: +353-1-647-7499                Fax: +1 734 647 3745
   stephen.farrell@baltimore.ie        EMail: jrv@merit.edu

   Pat R. Calhoun                      Leon Gommans
   Network and Security Research       Cabletron Systems EMEA
   Center, Sun Labs                    Kerkplein 24
   Sun Microsystems, Inc.              2841 XM  Moordrecht
   15 Network Circle                   The Netherlands
   Menlo Park, California, 94025       Phone: +31 182 379278
   USA                                 Email: gommans@cabletron.com
   Phone:  +1 650 786 7733
   Fax:  +1 650 786 6445
   EMail:  pcalhoun@eng.sun.com

   George M. Gross                     Betty de Bruijn
   Lucent Technologies                 Interpay Nederland B.V.
   184 Liberty Corner Road, m.s.       Eendrachtlaan 315
   LC2N-D13                            3526 LB Utrecht
   Warren, NJ 07059                    The Netherlands
   USA                                 Phone: +31 30 2835104
   Phone:  +1 908 580 4589             Email: betty@euronet.nl
   Fax:  +1 908 580 7430
   Email:  gmgross@lucent.com

   Cees T.A.M. de Laat                 Matt Holdrege
   Physics and Astronomy dept.         Lucent Technologies
   Utrecht University                  1701 Harbor Bay Pkwy.
   Pincetonplein 5,                    Alameda, CA 94502
   3584CC Utrecht                      USA
   Netherlands                         Phone:  +1 510 747 2711
   Phone: +31 30 2534585               Email:  holdrege@lucent.com
   Phone: +31 30 2537555
   EMail: delaat@phys.uu.nl

   David W. Spence
   Merit Network, Inc.
   4251 Plymouth Rd., Suite 2000
   Ann Arbor, MI  48105
   USA
   Phone: +1 734 615 2630
   Fax: +1 734 647 3745
   EMail: dwspence@merit.edu



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