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RFC2906 - AAA Authorization Requirements

王朝other·作者佚名  2008-05-31
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Network Working Group S. Farrell

Request for Comments: 2906 Baltimore Technologies

Category: Informational J. Vollbrecht

Interlink Networks, Inc.

P. Calhoun

Sun Microsystems, Inc.

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 Requirements

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 document specifies the requirements that Authentication

Authorization Accounting (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.

Table Of Contents

1. Introduction.................................................2

2. Requirements.................................................3

2.1 Authorization Information..............................3

2.2 Security of authorization information..................7

2.3 Time...................................................9

2.4 Topology..............................................10

2.5 Application Proxying..................................12

2.6 Trust Model...........................................12

2.7 Not just transactions.................................14

2.8 Administration........................................15

2.9 Bytes on-the-wire.....................................16

2.10 Interfaces............................................17

2.11 Negotiation...........................................18

3. Security Considerations.....................................19

4. References..................................................20

Authors' Addresses.............................................20

Full Copyright Statement.......................................23

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 [FRMW]

AAA Authorization Requirements (this document)

AAA Authorization Application Examples [SAMP]

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.

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.

The key Words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"

in this document are to be interpreted as described in [RFC2119].

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, ...)

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 IR 1,000 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.

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.

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.

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).

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

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 don't

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. 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.

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.

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 "hop" 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 can't 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 don't "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, 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 proxy's 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

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 public key infrastructures:

Just because someone can produce a cryptographically correct public

key certificate does not 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.

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.

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

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.

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

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.

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.

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.

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, J., Calhoun, P., Farrell, S., Gommans, L.,

Gross, G., de Bruijn, B., de Laat, C., Holdrege, M. and D.

Spence, "AAA Authorization Framework", RFC2904, August

2000.

[RFC2026] Bradner, S., "The Internet Standards Process -- Revision

3", BCP 9, RFC2026, October 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC2119, March 1997.

[RFC2138] Rigney, C., Rubens, A., Simpson, W. and S. Willens,

"Remote Authentication Dial In User Service (RADIUS)", RFC

2138, April 1997.

[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and

Languages", RFC2277, January 1998.

[SAMP] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,

Gross, G., de Bruijn, B., de Laat, C., Holdrege, M. and D.

Spence, "AAA Authorization Application Examples", RFC

2905, August 2000.

Authors' Addresses

Stephen Farrell

Baltimore Technologies

61/62 Fitzwilliam Lane

Dublin 2,

IRELAND

Phone: +353-1-647-7300

Fax: +353-1-647-7499

EMail: stephen.farrell@baltimore.ie

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

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

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

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

Full Copyright Statement

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

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFCEditor function is currently provided by the

Internet Society.

 
 
 
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