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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ABFAB J. Howlett 3 Internet-Draft JANET(UK) 4 Intended status: Informational S. Hartman 5 Expires: October 20, 2013 Painless Security 6 H. Tschofenig 7 Nokia Siemens Networks 8 E. Lear 9 Cisco Systems GmbH 10 J. Schaad 11 Soaring Hawk Consulting 12 April 18, 2013 14 Application Bridging for Federated Access Beyond Web (ABFAB) 15 Architecture 16 draft-ietf-abfab-arch-06.txt 18 Abstract 20 Over the last decade a substantial amount of work has occurred in the 21 space of federated access management. Most of this effort has 22 focused on two use cases: network access and web-based access. 23 However, the solutions to these use cases that have been proposed and 24 deployed tend to have few common building blocks in common. 26 This memo describes an architecture that makes use of extensions to 27 the commonly used security mechanisms for both federated and non- 28 federated access management, including the Remote Authentication Dial 29 In User Service (RADIUS) and the Diameter protocol, the Generic 30 Security Service (GSS), the GS2 family, the Extensible Authentication 31 Protocol (EAP) and the Security Assertion Markup Language (SAML). 32 The architecture addresses the problem of federated access management 33 to primarily non-web-based services, in a manner that will scale to 34 large numbers of identity providers, relying parties, and 35 federations. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at http://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on October 20, 2013. 54 Copyright Notice 56 Copyright (c) 2013 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (http://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 72 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 73 1.1.1. Channel Binding . . . . . . . . . . . . . . . . . . . 6 74 1.2. An Overview of Federation . . . . . . . . . . . . . . . . 7 75 1.3. Challenges for Contemporary Federation . . . . . . . . . 10 76 1.4. An Overview of ABFAB-based Federation . . . . . . . . . . 10 77 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . 13 78 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 14 79 2.1. Relying Party to Identity Provider . . . . . . . . . . . 15 80 2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . 16 81 2.1.2. Discovery and Rules Determination . . . . . . . . . . 18 82 2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 19 83 2.1.4. AAA Security . . . . . . . . . . . . . . . . . . . . 20 84 2.1.5. SAML Assertions . . . . . . . . . . . . . . . . . . . 21 85 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 23 86 2.2.1. Extensible Authentication Protocol (EAP) . . . . . . 23 87 2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 25 88 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 25 89 2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 26 90 2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . 27 91 2.3.3. Reauthentication . . . . . . . . . . . . . . . . . . 28 92 3. Application Security Services . . . . . . . . . . . . . . . . 28 93 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . 28 94 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 29 95 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . 30 96 3.4. Additional GSS-API Services . . . . . . . . . . . . . . . 32 98 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 32 99 4.1. Entities and their roles . . . . . . . . . . . . . . . . 33 100 4.2. Privacy Aspects of ABFAB Communication Flows . . . . . . 34 101 4.2.1. Client to RP . . . . . . . . . . . . . . . . . . . . 34 102 4.2.2. Client to IdP (via Federation Substrate) . . . . . . 35 103 4.2.3. IdP to RP (via Federation Substrate) . . . . . . . . 36 104 4.3. Relationship between User and Entities . . . . . . . . . 36 105 4.4. Accounting Information . . . . . . . . . . . . . . . . . 37 106 4.5. Collection and retention of data and identifiers . . . . 37 107 4.6. User Participation . . . . . . . . . . . . . . . . . . . 38 108 5. Deployment Considerations . . . . . . . . . . . . . . . . . . 38 109 5.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 38 110 5.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . 38 111 6. Security Considerations . . . . . . . . . . . . . . . . . . . 38 112 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 113 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40 114 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 115 9.1. Normative References . . . . . . . . . . . . . . . . . . 40 116 9.2. Informative References . . . . . . . . . . . . . . . . . 41 117 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 119 1. Introduction 121 The Internet uses numerous security mechanisms to manage access to 122 various resources. These mechanisms have been generalized and scaled 123 over the last decade through mechanisms such as Simple Authentication 124 and Security Layer (SASL) with the Generic Security Server 125 Application Program Interface (GSS-API) (known as the GS2 family) 126 [RFC5801], Security Assertion Markup Language (SAML) 127 [OASIS.saml-core-2.0-os], and the Authentication, Authorization, and 128 Accounting (AAA) architecture as embodied in RADIUS [RFC2865] and 129 Diameter [RFC3588]. 131 A Relying Party (RP) is the entity that manages access to some 132 resource. The entity that is requesting access to that resource is 133 often described as the Client. Many security mechanisms are 134 manifested as an exchange of information between these entities. The 135 RP is therefore able to decide whether the Client is authorized, or 136 not. 138 Some security mechanisms allow the RP to delegate aspects of the 139 access management decision to an entity called the Identity Provider 140 (IdP). This delegation requires technical signaling, trust and a 141 common understanding of semantics between the RP and IdP. These 142 aspects are generally managed within a relationship known as a 143 'federation'. This style of access management is accordingly 144 described as 'federated access management'. 146 Federated access management has evolved over the last decade through 147 specifications like SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth 148 [RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits 149 of federated access management include: 151 Single or Simplified sign-on: 153 An Internet service can delegate access management, and the 154 associated responsibilities such as identity management and 155 credentialing, to an organization that already has a long-term 156 relationship with the Client. This is often attractive for 157 Relying Parties who frequently do not want these responsibilities. 158 The Client also requires fewer credentials, which is also 159 desirable. 161 Data Minimization and User Participation: 163 Often a Relying Party does not need to know the identity of a 164 Client to reach an access management decision. It is frequently 165 only necessary for the Relying Party know specific attributes 166 about the subject, for example, that the Subject is affiliated 167 with a particular organization or has a certain role or 168 entitlement. Sometimes the RP only needs to know a pseudonym of 169 the Subject. 171 Prior to the release of attributes to the RP from the IdP, the IdP 172 will check configuration and policy to determine if the attributes 173 are to be released. There is currently no direct client 174 participation in this decision. 176 Provisioning: 178 Sometimes a Relying Party needs, or would like, to know more about 179 a client than an affiliation or a pseudonym. For example, a 180 Relying Party may want the Client's email address or name. Some 181 federated access management technologies provide the ability for 182 the IdP to supply this information, either on request by the RP or 183 unsolicited. 185 This memo describes the Application Bridging for Federated Access 186 Beyond the Web (ABFAB) architecture. This architecture makes use of 187 extensions to the commonly used security mechanisms for both 188 federated and non-federated access management, including the RADIUS 189 and the Diameter protocols, the Generic Security Service (GSS), the 190 GS2 family, the Extensible Authentication Protocol (EAP) and SAML. 191 The architecture addresses the problem of federated access management 192 primarily for non-web-based services. It does so in a manner that 193 will scale to large numbers of identity providers, relying parties, 194 and federations. 196 1.1. Terminology 198 This document uses identity management and privacy terminology from 199 [I-D.iab-privacy-considerations]. In particular, this document uses 200 the terms identity provider, relying party, identifier, pseudonymity, 201 unlinkability, and anonymity. 203 In this architecture the IdP consists of the following components: an 204 EAP server, a RADIUS or a Diameter server, and optionally a SAML 205 Assertion service. 207 This document uses the term Network Access Identifier (NAI), as 208 defined in [I-D.ietf-radext-nai]. An NAI consists of a realm 209 identifier, which is associated with an IdP and a username which is 210 associated with a specific client of the IdP. 212 One of the problems people will find with reading this document is 213 that the terminology sometimes appears to be inconsistent. This is 214 due the fact that the terms used by the different standards we are 215 referencing are not consistent. In general the document uses either 216 a the ABFAB term or the term associated with the standard under 217 discussion as appropriate. For reference we include this table which 218 maps the different terms into a single table. 220 +--------------+--------------+-----------------+-------------------+ 221 | Protocol | Subject | Relying Party | Identity Provider | 222 +--------------+--------------+-----------------+-------------------+ 223 | ABFAB | Client | Relying Party | Identity Provider | 224 | | | (RP) | (IdP) | 225 | | | | | 226 | | Initiator | Acceptor | | 227 | | | | | 228 | | | Server | | 229 | | | | | 230 | SAML | Subject | Service | Issuer | 231 | | | Provider | | 232 | | | | | 233 | GSS-API | Initiator | Acceptor | | 234 | | | | | 235 | EAP | EAP peer | | EAP server | 236 | | | | | 237 | AAA | | AAA Client | AAA server | 238 | | | | | 239 | RADIUS | user | NAS | RADIUS server | 240 | | | | | 241 | | | RADIUS client | | 242 +--------------+--------------+-----------------+-------------------+ 244 Note that in some cases a cell has been left empty; in these cases 245 there is no direct name that represents this concept. 247 1.1.1. Channel Binding 249 This document uses the term channel binding with two different 250 meanings. 252 EAP channel binding is used to provide GSS-API naming semantics. 253 Channel binding sends a set of attributes from the peer to the EAP 254 server either as part of the EAP conversation or as part of a secure 255 association protocol. In addition, attributes are sent in the 256 backend protocol from the authenticator to the EAP server. The EAP 257 server confirms the consistency of these attributes and provides the 258 confirmation back to the peer. In this document, channel binding 259 without qualification refers to EAP channel binding. 261 GSS-API channel binding provides protection against man-in-the-middle 262 attacks when GSS-API is used for authentication inside of some 263 tunnel; it is similar to a facility called cryptographic binding in 264 EAP. The binding works by each side deriving a cryptographic value 265 from the tunnel itself and then using that cryptographic value to 266 prove to the other side that it knows the value. 268 See [RFC5056] for a discussion of the differences between these two 269 facilities. 271 Typically when considering channel binding, people think of channel 272 binding in combination with mutual authentication. This is 273 sufficiently common that without additional qualification channel 274 binding should be assumed to imply mutual authentication. Without 275 mutual authentication, only one party knows that the endpoints are 276 correct. That's sometimes useful. Consider for example a user who 277 wishes to access a protected resource from a shared whiteboard in a 278 conference room. The whiteboard is the initiator; it does not need 279 to actually authenticate that it is talking to the correct resource 280 because the user will be able to recognize whether the displayed 281 content is correct. If channel binding is used without mutual 282 authentication, it is effectively a request to disclose the resource 283 in the context of a particular channel. Such an authentication would 284 be similar in concept to a holder-of-key SAML assertion. However, 285 also note that while it is not happening in the protocol, mutual 286 authentication is happening in the overall system: the user is able 287 to visually authenticate the content. This is consistent with all 288 uses of channel binding without protocol level mutual authentication 289 found so far. 291 1.2. An Overview of Federation 293 In the previous section we introduced the following entities: 295 o the Client, 297 o the Identity Provider, and 299 o the Relying Party. 301 The final entity that needs to be introduced is the Individual. An 302 Individual is a human being that is using the Client. In any given 303 situation, an Individual may or may not exist. Clients can act 304 either as front ends for Individuals or they may be independent 305 entities that are setup and allowed to run autonomously. An example 306 of such an entity can be found in the trust routing protocol where 307 the routers use ABFAB to authenticate to each other. 309 These entities and their relationships are illustrated graphically in 310 Figure 1. 312 ,----------\ ,---------\ 313 | Identity | Federation | Relying | 314 | Provider + <-------------------> + Party | 315 `----------' '---------' 316 < 317 \ 318 \ Authentication 319 \ 320 \ 321 \ 322 \ 323 \ +---------+ 324 \ | | O 325 v| Client | \|/ Individual 326 | | | 327 +---------+ / \ 329 Figure 1: Entities and their Relationships 331 The relationships between the entities in Figure 1 are: 333 Federation 335 The Identity Provider and the Relying Parties are part of a 336 Federation. The relationship may be direct (they have an explicit 337 trust relationship) or transitive (the trust relationship is 338 mediated by one or more entities). The federation relationship is 339 governed by a federation agreement. Within a single federation, 340 there may be multiple Identity Providers as well as multiple 341 Relying Parties. A federation is governed by a federation 342 agreement. 344 Authentication 346 There is a direct relationship between the Client and the Identity 347 Provider by which the entities trust and can securely authenticate 348 each other. 350 A federation agreement typically encompasses operational 351 specifications and legal rules: 353 Operational Specifications: 355 These include the technical specifications (e.g. protocols used 356 to communicate between the three parties), process standards, 357 policies, identity proofing, credential and authentication 358 algorithm requirements, performance requirements, assessment and 359 audit criteria, etc. The goal of operational specifications is to 360 provide enough definition that the system works and 361 interoperability is possible. 363 Legal Rules: 365 The legal rules take the legal framework into consideration and 366 provide contractual obligations for each entity. The rules define 367 the responsibilities of each party and provide further 368 clarification of the operational specifications. These legal 369 rules regulate the operational specifications, make operational 370 specifications legally binding to the participants, define and 371 govern the rights and responsibilities of the participants. The 372 legal rules may, for example, describe liability for losses, 373 termination rights, enforcement mechanisms, measures of damage, 374 dispute resolution, warranties, etc. 376 The Operational Specifications can demand the usage of a 377 sophisticated technical infrastructure, including requirements on the 378 message routing intermediaries, to offer the required technical 379 functionality. In other environments, the Operational Specifications 380 require fewer technical components in order to meet the required 381 technical functionality. 383 The Legal Rules include many non-technical aspects of federation, 384 such as business practices and legal arrangements, which are outside 385 the scope of the IETF. The Legal Rules can still have an impact on 386 the architectural setup or on how to ensure the dynamic establishment 387 of trust. 389 While a federation agreement is often discussed within the context of 390 formal relationships, such as between an enterprise and an employee 391 or a government and a citizen, a federation agreement does not have 392 to require any particular level of formality. For an IdP and a 393 Client, it is sufficient for a relationship to be established by 394 something as simple as using a web form and confirmation email. For 395 an IdP and an RP, it is sufficient for the IdP to publish contact 396 information along with a public key and for the RP to use that data. 397 Within the framework of ABFAB, it will generally be required that a 398 mechanism exists for the IdP to be able to trust the identity of the 399 RP, if this is not present then the IdP cannot provide the assurances 400 to the client that the identity of the RP has been established. 402 The nature of federation dictates that there is some form of 403 relationship between the identity provider and the relying party. 404 This is particularly important when the relying party wants to use 405 information obtained from the identity provider for access management 406 decisions and when the identity provider does not want to release 407 information to every relying party (or only under certain 408 conditions). 410 While it is possible to have a bilateral agreement between every IdP 411 and every RP; on an Internet scale this setup requires the 412 introduction of the multi-lateral federation concept, as the 413 management of such pair-wise relationships would otherwise prove 414 burdensome. 416 The IdP will typically have a long-term relationship with the Client. 417 This relationship typically involves the IdP positively identifying 418 and credentialing the Client (for example, at time of employment 419 within an organization). When dealing with individuals, this process 420 is called identity proofing [NIST-SP.800-63]. The relationship will 421 often be instantiated within an agreement between the IdP and the 422 Client (for example, within an employment contract or terms of use 423 that stipulates the appropriate use of credentials and so forth). 425 The nature and quality of the relationship between the Subject and 426 the IdP is an important contributor to the level of trust that an RP 427 may attribute to an assertion describing a Client made by an IdP. 428 This is sometimes described as the Level of Assurance 429 [NIST-SP.800-63]. 431 Federation does not require an a priori relationship or a long-term 432 relationship between the RP and the Client; it is this property of 433 federation that yields many of its benefits. However, federation 434 does not preclude the possibility of a pre-existing relationship 435 between the RP and the Client, nor that they may use the introduction 436 to create a new long-term relationship independent of the federation. 438 Finally, it is important to reiterate that in some scenarios there 439 might indeed be an Individual behind the Client and in other cases 440 the Client may be autonomous. 442 1.3. Challenges for Contemporary Federation 444 As the number of federated services has proliferated, the role of the 445 individual can become ambiguous in certain circumstances. For 446 example, a school might provide online access for a student's grades 447 to their parents for review, and to the student's teacher for 448 modification. A teacher who is also a parent must clearly 449 distinguish her role upon access. 451 Similarly, as the number of federations proliferates, it becomes 452 increasingly difficult to discover which identity provider(s) a user 453 is associated with. This is true for both the web and non-web case, 454 but is particularly acute for the latter as many non-web 455 authentication systems are not semantically rich enough on their own 456 to allow for such ambiguities. For instance, in the case of an email 457 provider, the use of SMTP and IMAP protocols do not have the ability 458 for the server to get additional information, beyond the clients NAI, 459 in order to provide additional input to decide between multiple 460 federations it may be associated with. However, the building blocks 461 do exist to add this functionality. 463 1.4. An Overview of ABFAB-based Federation 465 The previous section described the general model of federation, and 466 the application of federated access management. This section 467 provides a brief overview of ABFAB in the context of this model. 469 In this example, a client is attempting to connect to a server in 470 order to either get access to some data or perform some type of 471 transaction. In order for the client to mutually authenticate with 472 the server, the following steps are taken in an ABFAB federated 473 architecture: 475 1. Client Configuration: The Client Application is configured with 476 an NAI assigned by the IdP. It is also configured with any 477 keys, certificates, passwords or other secret and public 478 information needed to run the EAP protocols between it and the 479 IdP. 481 2. Authentication mechanism selection: The GSS-EAP GSS-API 482 mechanism is selected for authentication/authorization. 484 3. Client provides an NAI to RP: The client application sets up a 485 transport to the RP and begins the GSS-EAP authentication. In 486 response, the RP sends an EAP request message (nested in the 487 GSS-EAP protocol) asking for the Client's name. The Client 488 sends an EAP response with an NAI name form that, at a minimum, 489 contains the realm portion of its full NAI. 491 4. Discovery of federated IdP: The RP uses pre-configured 492 information or a federation proxy to determine what IdP to use 493 based on policy and the realm portion of the provided Client 494 NAI. This is discussed in detail below (Section 2.1.2). 496 5. Request from Relying Party to IdP: Once the RP knows who the IdP 497 is, it (or its agent) will send a RADIUS/Diameter request to the 498 IdP. The RADIUS/Diameter access request encapsulates the EAP 499 response. At this stage, the RP will likely have no idea who 500 the client is. The RP sends its identity to the IdP in AAA 501 attributes, and it may send a SAML Attribute Requests in a AAA 502 attribute. The AAA network checks that the identity claimed by 503 the RP is valid. 505 6. IdP begins EAP with the client: The IdP sends an EAP message to 506 the client with an EAP method to be used. The IdP SHOULD NOT 507 re-request the clients name in this message, but clients need to 508 be able to handle it. In this case the IdP MUST accept a realm 509 only in order to protect the client's name from the RP. The 510 available and appropriate methods are discussed below in this 511 memo (Section 2.2.1). 513 7. The EAP protocol is run: A bunch of EAP messages are passed 514 between the client (EAP peer) and the IdP (EAP server), until 515 the result of the authentication protocol is determined. The 516 number and content of those messages depends on the EAP method 517 selected. If the IdP is unable to authenticate the client, the 518 IdP sends a EAP failure message to the RP. As part of the EAP 519 protocol, the client sends a channel bindings EAP message to the 520 IdP (Section 2.2.2). In the channel binding message the client 521 identifies, among other things, the RP to which it is attempting 522 to authenticate. The IdP checks the channel binding data from 523 the client with that provided by the RP via the AAA protocol. 524 If the bindings do not match the IdP sends an EAP failure 525 message to the RP. 527 8. Successful EAP Authentication: At this point, the IdP (EAP 528 server) and client (EAP peer) have mutually authenticated each 529 other. As a result, the subject and the IdP hold two 530 cryptographic keys: a Master Session Key (MSK), and an Extended 531 MSK (EMSK). At this point the client has a level of assurance 532 about the identity of the RP based on the name checking the IdP 533 has done using the RP naming information from the AAA framework 534 and from the client (by the channel binding data). 536 9. Local IdP Policy Check: At this stage, the IdP checks local 537 policy to determine whether the RP and client are authorized for 538 a given transaction/service, and if so, what if any, attributes 539 will be released to the RP. If the IdP gets a policy failure, 540 it sends an EAP failure message to the RP.[[Should this be an 541 EAP failure to the client as well?]] (The RP will have done its 542 policy checks during the discovery process.) 544 10. IdP provide the RP with the MSK: The IdP sends a positive result 545 EAP to the RP, along with an optional set of AAA attributes 546 associated with the client (usually as one or more SAML 547 assertions). In addition, the EAP MSK is returned to the RP. 549 11. RP Processes Results: When the RP receives the result from the 550 IdP, it should have enough information to either grant or refuse 551 a resource access request. It may have information that 552 associates the client with specific authorization identities. 553 If additional attributes are needed from the IdP the RP may make 554 a new SAML Request to the IdP. It will apply these results in 555 an application-specific way. 557 12. RP returns results to client: Once the RP has a response it must 558 inform the client application of the result. If all has gone 559 well, all are authenticated, and the application proceeds with 560 appropriate authorization levels. The client can now complete 561 the authentication of the RP by the use of the EAP MSK value. 563 An example communication flow is given below: 565 Relying Client Identity 566 Party App Provider 568 | (1) | Client Configuration 569 | | | 570 |<-----(2)----->| | Mechanism Selection 571 | | | 572 |<-----(3)-----<| | NAI transmitted to RP 573 | | | 574 |<=====(4)====================>| Discovery 575 | | | 576 |>=====(5)====================>| Access request from RP to IdP 577 | | | 578 | |< - - (6) - -<| EAP method to Client 579 | | | 580 | |< - - (7) - ->| EAP Exchange to authenticate 581 | | | Client 582 | | | 583 | | (8 & 9) Local Policy Check 584 | | | 585 |<====(10)====================<| IdP Assertion to RP 586 | | | 587 (11) | | RP processes results 588 | | | 589 |>----(12)----->| | Results to client app. 591 ----- = Between Client App and RP 592 ===== = Between RP and IdP 593 - - - = Between Client App and IdP 595 1.5. Design Goals 597 Our key design goals are as follows: 599 o Each party of a transaction will be authenticated, although 600 perhaps not identified, and the client will be authorized for 601 access to a specific resource. 603 o Means of authentication is decoupled so as to allow for multiple 604 authentication methods. 606 o The architecture requires no sharing of long term private keys 607 between clients and servers. 609 o The system will scale to large numbers of identity providers, 610 relying parties, and users. 612 o The system will be designed primarily for non-Web-based 613 authentication. 615 o The system will build upon existing standards, components, and 616 operational practices. 618 Designing new three party authentication and authorization protocols 619 is hard and fraught with risk of cryptographic flaws. Achieving 620 widespread deployment is even more difficult. A lot of attention on 621 federated access has been devoted to the Web. This document instead 622 focuses on a non-Web-based environment and focuses on those protocols 623 where HTTP is not used. Despite the increased excitement for 624 layering every protocol on top of HTTP there are still a number of 625 protocols available that do not use HTTP-based transports. Many of 626 these protocols are lacking a native authentication and authorization 627 framework of the style shown in Figure 1. 629 2. Architecture 631 We have already introduced the federated access architecture, with 632 the illustration of the different actors that need to interact, but 633 did not expand on the specifics of providing support for non-Web 634 based applications. This section details this aspect and motivates 635 design decisions. The main theme of the work described in this 636 document is focused on re-using existing building blocks that have 637 been deployed already and to re-arrange them in a novel way. 639 Although this architecture assumes updates to the relying party, the 640 client application, and the Identity Provider, those changes are kept 641 at a minimum. A mechanism that can demonstrate deployment benefits 642 (based on ease of update of existing software, low implementation 643 effort, etc.) is preferred and there may be a need to specify 644 multiple mechanisms to support the range of different deployment 645 scenarios. 647 There are a number of ways for encapsulating EAP into an application 648 protocol. For ease of integration with a wide range of non-Web based 649 application protocols the usage of the GSS-API was chosen. A 650 description of the technical specification can be found in 651 [I-D.ietf-abfab-gss-eap]. 653 The architecture consists of several building blocks, which is shown 654 graphically in Figure 2. In the following sections, we discuss the 655 data flow between each of the entities, the protocols used for that 656 data flow and some of the trade-offs made in choosing the protocols. 658 +--------------+ 659 | Identity | 660 | Provider | 661 | (IdP) | 662 +-^----------^-+ 663 * EAP o RADIUS/ 664 * o Diameter 665 --v----------v-- 666 /// \\\ 667 // \\ 668 | Federation | 669 | Substrate | 670 \\ // 671 \\\ /// 672 --^----------^-- 673 * EAP o RADIUS/ 674 * o Diameter 675 +-------------+ +-v----------v--+ 676 | | | | 677 | Client | EAP/EAP Method | Relying Party | 678 | Application |<****************>| (RP) | 679 | | GSS-API | | 680 | |<---------------->| | 681 | | Application | | 682 | | Protocol | | 683 | |<================>| | 684 +-------------+ +---------------+ 686 Legend: 688 <****>: Client-to-IdP Exchange 689 <---->: Client-to-RP Exchange 690 : RP-to-IdP Exchange 691 <====>: Protocol through which GSS-API/GS2 exchanges are tunneled 693 Figure 2: ABFAB Protocol Instantiation 695 2.1. Relying Party to Identity Provider 697 Communications between the Relying Party and the Identity Provider is 698 done by the federation substrate. This communication channel is 699 responsible for: 701 o Establishing the trust relationship between the RP and the IdP. 703 o Determining the rules governing the relationship. 705 o Conveying authentication packets from the client to the IdP and 706 back. 708 o Providing the means of establishing a trust relationship between 709 the RP and the client. 711 o Providing a means for the RP to obtain attributes about the client 712 from the IdP. 714 The ABFAB working group has chosen the AAA framework for the messages 715 transported between the RP and IdP. The AAA framework supports the 716 requirements stated above as follows: 718 o The AAA backbone supplies the trust relationship between the RP 719 and the IdP. 721 o The agreements governing a specific AAA backbone contains the 722 rules governing the relationships within the AAA federation. 724 o A method exists for carrying EAP packets within RADIUS [RFC3579] 725 and Diameter [RFC4072]. 727 o The use of EAP channel binding [RFC6677] along with the core ABFAB 728 protocol provide the pieces necessary to establish the identities 729 of the RP and the client, while EAP provides the cryptographic 730 methods for the RP and the client to validate they are talking to 731 each other. 733 o A method exists for carrying SAML packets within RADIUS 734 [I-D.ietf-abfab-aaa-saml] and Diameter (work in progress) which 735 allows the RP to query attributes about the client from the IdP. 737 Future protocols that support the same framework but do different 738 routing may be used in the future. One such effort is to setup a 739 framework that creates a trusted point-to-point channel on the fly. 741 2.1.1. AAA, RADIUS and Diameter 743 Interestingly, for network access authentication the usage of the AAA 744 framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite 745 successful from a deployment point of view. To map to the 746 terminology used in Figure 1 to the AAA framework the IdP corresponds 747 to the AAA server, the RP corresponds to the AAA client, and the 748 technical building blocks of a federation are AAA proxies, relays and 749 redirect agents (particularly if they are operated by third parties, 750 such as AAA brokers and clearing houses). The front-end, i.e. the 751 end host to AAA client communication, is in case of network access 752 authentication offered by link layer protocols that forward 753 authentication protocol exchanges back-and-forth. An example of a 754 large scale RADIUS-based federation is EDUROAM [2]. 756 By using the AAA framework, ABFAB gets a lot of mileage as many of 757 the federation agreements already exist and merely need to be 758 expanded to cover the ABFAB additions. The AAA framework has already 759 addressed some of the problems outlined above. For example, 761 o It already has a method for routing requests based on a domain. 763 o It already has an extensible architecture allowing for new 764 attributes to be defined and transported. 766 o Pre-existing relationships can be re-used. 768 The astute reader will notice that RADIUS and Diameter have 769 substantially similar characteristics. Why not pick one? RADIUS and 770 Diameter are deployed in different environments. RADIUS can often be 771 found in enterprise and university networks, and is also in use by 772 fixed network operators. Diameter, on the other hand, is deployed by 773 mobile operators. Another key difference is that today RADIUS is 774 largely transported upon UDP. We leave as a deployment decision, 775 which protocol will be appropriate. The protocol defines all the 776 necessary new AAA attributes as RADIUS attributes. A future document 777 would define the same AAA attributes for a Diameter environment. We 778 also note that there exist proxies which convert from RADIUS to 779 Diameter and back. This makes it possible for both to be deployed in 780 a single federation substrate. 782 Through the integrity protection mechanisms in the AAA framework, the 783 identity provider can establish technical trust that messages are 784 being sent by the appropriate relying party. Any given interaction 785 will be associated with one federation at the policy level. The 786 legal or business relationship defines what statements the identity 787 provider is trusted to make and how these statements are interpreted 788 by the relying party. The AAA framework also permits the relying 789 party or elements between the relying party and identity provider to 790 make statements about the relying party. 792 The AAA framework provides transport for attributes. Statements made 793 about the subject by the identity provider, statements made about the 794 relying party and other information are transported as attributes. 796 One demand that the AAA substrate makes of the upper layers is that 797 they must properly identify the end points of the communication. It 798 must be possible for the AAA client at the RP to determine where to 799 send each RADIUS or Diameter message. Without this requirement, it 800 would be the RP's responsibility to determine the identity of the 801 client on its own, without the assistance of an IdP. This 802 architecture makes use of the Network Access Identifier (NAI), where 803 the IdP is indicated by the realm component [I-D.ietf-radext-nai]. 804 The NAI is represented and consumed by the GSS-API layer as 805 GSS_C_NT_USER_NAME as specified in [RFC2743]. The GSS-API EAP 806 mechanism includes the NAI in the EAP Response/Identity message. 808 2.1.2. Discovery and Rules Determination 810 While we are using the AAA protocols to communicate with the IdP, the 811 RP may have multiple federation substrates to select from. The RP 812 has a number of criteria that it will use in selecting which of the 813 different federations to use: 815 o The federation selected must be able to communicate with the IdP. 817 o The federation selected must match the business rules and 818 technical policies required for the RP security requirements. 820 The RP needs to discover which federation will be used to contact the 821 IdP. The first selection criteria used during discovery is going to 822 be the name of the IdP to be contacted. The second selection 823 criteria used during discovery is going to be the set of business 824 rules and technical policies governing the relationship; this is 825 called rules determination. The RP also needs to establish technical 826 trust in the communications with the IdP. 828 Rules determination covers a broad range of decisions about the 829 exchange. One of these is whether the given RP is permitted to talk 830 to the IdP using a given federation at all, so rules determination 831 encompasses the basic authorization decision. Other factors are 832 included, such as what policies govern release of information about 833 the client to the RP and what policies govern the RP's use of this 834 information. While rules determination is ultimately a business 835 function, it has significant impact on the technical exchanges. The 836 protocols need to communicate the result of authorization. When 837 multiple sets of rules are possible, the protocol must disambiguate 838 which set of rules are in play. Some rules have technical 839 enforcement mechanisms; for example in some federations 840 intermediaries validate information that is being communicated within 841 the federation. 843 At the time of writing no protocol mechanism has been specified to 844 allow a AAA client to determine whether a AAA proxy will indeed be 845 able to route AAA requests to a specific IdP. The AAA routing is 846 impacted by business rules and technical policies that may be quite 847 complex and at the present time, the route selection is based on 848 manual configuration. 850 2.1.3. Routing and Technical Trust 852 Several approaches to having messages routed through the federation 853 substrate are possible. These routing methods can most easily be 854 classified based on the mechanism for technical trust that is used. 855 The choice of technical trust mechanism constrains how rules 856 determination is implemented. Regardless of what deployment strategy 857 is chosen, it is important that the technical trust mechanism be able 858 to validate theg identities of both parties to the exchange. The 859 trust mechanism must to ensure that the entity acting as IdP for a 860 given NAI is permitted to be the IdP for that realm, and that any 861 service name claimed by the RP is permitted to be claimed by that 862 entity. Here are the categories of technical trust determination: 864 AAA Proxy: 865 The simplest model is that an RP is an AAA client and can send the 866 request directly to an AAA proxy. The hop-by-hop integrity 867 protection of the AAA fabric provides technical trust. An RP can 868 submit a request directly to a federation. Alternatively, a 869 federation disambiguation fabric can be used. Such a fabric takes 870 information about what federations the RP is part of and what 871 federations the IdP is part of and routes a message to the 872 appropriate federation. The routing of messages across the fabric 873 plus attributes added to requests and responses provides rules 874 determination. For example, when a disambiguation fabric routes a 875 message to a given federation, that federation's rules are chosen. 876 Name validation is enforced as messages travel across the fabric. 877 The entities near the RP confirm its identity and validate names 878 it claims. The fabric routes the message towards the appropriate 879 IdP, validating the IdP's name in the process. The routing can be 880 statically configured. Alternatively a routing protocol could be 881 developed to exchange reachability information about given a IdP 882 and to apply policy across the AAA fabric. Such a routing 883 protocol could flood naming constraints to the appropriate points 884 in the fabric. 886 Trust Broker: 888 Instead of routing messages through AAA proxies, some trust broker 889 could establish keys between entities near the RP and entities 890 near the IdP. The advantage of this approach is efficiency of 891 message handling. Fewer entities are needed to be involved for 892 each message. Security may be improved by sending individual 893 messages over fewer hops. Rules determination involves decisions 894 made by trust brokers about what keys to grant. Also, associated 895 with each credential is context about rules and about other 896 aspects of technical trust including names that may be claimed. A 897 routing protocol similar to the one for AAA proxies is likely to 898 be useful to trust brokers in flooding rules and naming 899 constraints. 901 Global Credential: 902 A global credential such as a public key and certificate in a 903 public key infrastructure can be used to establish technical 904 trust. A directory or distributed database such as the Domain 905 Name System is used by the RP to discover the endpoint to contact 906 for a given NAI. Either the database or certificates can provide 907 a place to store information about rules determination and naming 908 constraints. Provided that no intermediates are required (or 909 appear to be required) and that the RP and IdP are sufficient to 910 enforce and determine rules, rules determination is reasonably 911 simple. However applying certain rules is likely to be quite 912 complex. For example if multiple sets of rules are possible 913 between an IdP and RP, confirming the correct set is used may be 914 difficult. This is particularly true if intermediates are 915 involved in making the decision. Also, to the extent that 916 directory information needs to be trusted, rules determination may 917 be more complex. 919 Real-world deployments are likely to be mixtures of these basic 920 approaches. For example, it will be quite common for an RP to route 921 traffic to a AAA proxy within an organization. That proxy could then 922 use any of the three methods to get closer to the IdP. It is also 923 likely that rather than being directly reachable, the IdP may have a 924 proxy on the edge of its organization. Federations will likely 925 provide a traditional AAA proxy interface even if they also provide 926 another mechanism for increased efficiency or security. 928 2.1.4. AAA Security 930 For the AAA framework there are two different places where security 931 needs to be examined. The first is the security that is in place for 932 the links in the AAA backbone being used. The second is the nodes 933 that the backbone consists of. 935 The default link security for RADIUS is showing its age as it uses 936 MD5 and a shared secret to both obfuscate passwords and to provide 937 integrity on the RADIUS messages. While some EAP methods have 938 designed in the ability to protect the client authentication 939 credentials, the MSK returned from the IDP to the RP is protected 940 only by the RADIUS security. In many environments this is considered 941 to be insufficient, especially as not all attributes are obfuscated 942 and can thus leak information to a passive eavesdropper. The use of 943 RADIUS with TLS [RFC6614] and/or DTLS [I-D.ietf-radext-dtls] 944 addresses these attacks. The same level of security is included in 945 the base Diameter specifications. 947 2.1.5. SAML Assertions 949 For the traditional use of AAA frameworks, network access, the only 950 requirement that was necessary to grant access was an affirmative 951 response from the IdP. In the ABFAB world, the RP may need to get 952 additional information about the client before granting access. 953 ABFAB therefore has a requirement that it can transport an arbitrary 954 set of attributes about the client from the IdP to the RP. 956 Security Assertions Markup Language (SAML) [OASIS.saml-core-2.0-os] 957 was designed in order to carry an extensible set of attributes about 958 a subject. Since SAML is extensible in the attribute space, ABFAB 959 has no immediate needs to update the core SAML specifications for our 960 work. It will be necessary to update IdPs that need to return SAML 961 assertions to RPs and for both the IdP and the RP to implement a new 962 SAML profile designed to carry SAML assertions in AAA. The new 963 profile can be found in RFCXXXX [I-D.ietf-abfab-aaa-saml]. As SAML 964 statements will frequently be large, RADIUS servers and clients that 965 deal with SAML statements will need to implement RFC XXXX 966 [I-D.perez-radext-radius-fragmentation] 968 There are several issues that need to be highlighted: 970 o The security of SAML assertions. 972 o Namespaces and mapping of SAML attributes. 974 o Subject naming of entities. 976 o Making multiple queries about the subject(s). 978 o Level of Assurance for authentication. 980 SAML assertions have an optional signature that can be used to 981 protect and provide origination of the assertion. These signatures 982 are normally based on asymmetric key operations and require that the 983 verifier be able to check not only the cryptographic operation, but 984 also the binding of the originators name and the public key. In a 985 federated environment it will not always be possible for the RP to 986 validate the binding, for this reason the technical trust established 987 in the federation is used as an alternate method of validating the 988 origination and integrity of the SAML Assertion. 990 Attributes placed in SAML assertions can have different namespaces 991 assigned to the same name. In many, but not all, cases the 992 federation agreements will determine what attributes can be used in a 993 SAML statement. This means that the RP needs to map from the 994 federation names, types and semantics into the ones that the policies 995 of the RP are written in. In other cases the federation substrate 996 may modify the SAML assertions in transit to do the necessary 997 namespace, naming and semantic mappings as the assertion crosses the 998 different boundaries in the federation. If the proxies are modifying 999 the SAML Assertion, then they will obviously remove any signatures as 1000 they would no longer validate. In this case the technical trust is 1001 the required mechanism for validating the integrity of the assertion. 1002 Finally, the attributes may still be in the namespace of the 1003 originating IdP. When this occurs the RP will need to get the 1004 required mapping operations from the federation agreements and do the 1005 appropriate mappings itself. 1007 The RADIUS SAML RFC [I-D.ietf-abfab-aaa-saml] has define a new SAML 1008 name format that corresponds to the NAI name form defined by RFC XXXX 1009 [I-D.ietf-radext-nai]. This allows for easy name matching in many 1010 cases as the name form in the SAML statement and the name form used 1011 in RADIUS or Diameter will be the same. In addition to the NAI name 1012 form, the document also defines a pair of implicit name forms 1013 corresponding to the Client and the Client's machine. These implicit 1014 name forms are based on the Identity-Type enumeration defined in TEAP 1015 [I-D.ietf-emu-eap-tunnel-method]. If the name form returned in a 1016 SAML statement is not based on the NAI, then it is a requirement on 1017 the EAP server that it validate that the subject of the SAML 1018 assertion, if any, is equivalent to the subject identified by the NAI 1019 used in the RADIUS or Diameter session. 1021 RADIUS has the ability to deal with multiple SAML queries for those 1022 EAP Servers which follow RFC 5080 [RFC5080]. In this case a State 1023 attribute will always be returned with the Access-Accept. The EAP 1024 client can then send a new Access-Request with the State attribute 1025 and the new SAML Request Multiple SAML queries can then be done by 1026 making a new Access-Request using the State attribute returned in the 1027 last Access-Accept to link together the different RADIUS sessions. 1029 Some RPs need to ensure that specific criteria are met during the 1030 authentication process. This need is met by using Levels of 1031 Assurance. The way a Level of Assurance is communicated to the RP 1032 from the EAP server is by the use of a SAML Authentication Request 1033 using the Authentication Profile from RFC XXX 1034 [I-D.ietf-abfab-aaa-saml] When crossing boundaries between different 1035 federations, either the policy specified will need to be shared 1036 between the two federations, the policy will need to be mapped by the 1037 proxy server on the boundary or the proxy server on the boundary will 1038 need to supply information the EAP server so that it can do the 1039 required mapping. If this mapping is not done, then the EAP server 1040 will not be able to enforce the desired Level of Assurance as it will 1041 not understand the policy requirements. 1043 2.2. Client To Identity Provider 1045 Looking at the communications between the client and the IdP, the 1046 following items need to be dealt with: 1048 o The client and the IdP need to mutually authenticate each other. 1050 o The client and the IdP need to mutually agree on the identity of 1051 the RP. 1053 ABFAB selected EAP for the purposes of mutual authentication and 1054 assisted in creating some new EAP channel binding documents for 1055 dealing with determining the identity of the RP. A framework for the 1056 channel binding mechanism has been defined in RFC 6677 [RFC6677] that 1057 allows the IdP to check the identity of the RP provided by the AAA 1058 framework with that provided by the client. 1060 2.2.1. Extensible Authentication Protocol (EAP) 1062 Traditional web federation does not describe how a subject interacts 1063 with an identity provider for authentication. As a result, this 1064 communication is not standardized. There are several disadvantages 1065 to this approach. Since the communication is not standardized, it is 1066 difficult for machines to correctly enter their credentials with 1067 different authentications, where Individuals can correctly identify 1068 the entire mechanism on the fly. The use of browsers for 1069 authentication restricts the deployment of more secure forms of 1070 authentication beyond plaintext username and password known by the 1071 server. In a number of cases the authentication interface may be 1072 presented before the subject has adequately validated they are 1073 talking to the intended server. By giving control of the 1074 authentication interface to a potential attacker, the security of the 1075 system may be reduced and phishing opportunities introduced. 1077 As a result, it is desirable to choose some standardized approach for 1078 communication between the subject's end-host and the identity 1079 provider. There are a number of requirements this approach must 1080 meet. 1082 Experience has taught us one key security and scalability 1083 requirement: it is important that the relying party not get 1084 possession of the long-term secret of the client. Aside from a 1085 valuable secret being exposed, a synchronization problem can develop 1086 when the client changes keys with the IdP. 1088 Since there is no single authentication mechanism that will be used 1089 everywhere there is another associated requirement: The 1090 authentication framework must allow for the flexible integration of 1091 authentication mechanisms. For instance, some IdPs require hardware 1092 tokens while others use passwords. A service provider wants to 1093 provide support for both authentication methods, and other methods 1094 from IdPs not yet seen. 1096 These requirements can be met by utilizing standardized and 1097 successfully deployed technology, namely by the Extensible 1098 Authentication Protocol (EAP) framework [RFC3748]. Figure 2 1099 illustrates the integration graphically. 1101 EAP is an end-to-end framework; it provides for two-way communication 1102 between a peer (i.e. client or individual) through the authenticator 1103 (i.e., relying party) to the back-end (i.e., identity provider). 1104 Conveniently, this is precisely the communication path that is needed 1105 for federated identity. Although EAP support is already integrated 1106 in AAA systems (see [RFC3579] and [RFC4072]) several challenges 1107 remain: 1109 o The first is how to carry EAP payloads from the end host to the 1110 relying party. 1112 o Another is to verify statements the relying party has made to the 1113 subject, confirm these statements are consistent with statements 1114 made to the identity provider and confirm all the above are 1115 consistent with the federation and any federation-specific policy 1116 or configuration. 1118 o Another challenge is choosing which identity provider to use for 1119 which service. 1121 The EAP method used for ABFAB needs to meet the following 1122 requirements: 1124 o It needs to provide mutual authentication of the client and IdP. 1126 o It needs to support channel binding. 1128 As of this writing, the only EAP method that meets these criteria is 1129 TEAP [I-D.ietf-emu-eap-tunnel-method] either alone (if client 1130 certificates are used) or with an inner EAP method that does mutual 1131 authentication. 1133 2.2.2. EAP Channel Binding 1135 EAP channel binding is easily confused with a facility in GSS-API 1136 also called channel binding. GSS-API channel binding provides 1137 protection against man-in-the-middle attacks when GSS-API is used as 1138 authentication inside some tunnel; it is similar to a facility called 1139 cryptographic binding in EAP. See [RFC5056] for a discussion of the 1140 differences between these two facilities and Section 6.1 for how GSS- 1141 API channel binding is handled in this mechanism. 1143 The client knows, in theory, the name of the RP that it attempted to 1144 connect to, however in the event that an attacker has intercepted the 1145 protocol, the client and the IdP need to be able to detect this 1146 situation. A general overview of the problem along with a 1147 recommended way to deal with the channel binding issues can be found 1148 in RFC 6677 [RFC6677]. 1150 Since that document was published, a number of possible attacks were 1151 found and methods to address these attacks have been outlined in 1152 [I-D.ietf-emu-crypto-bind]. 1154 2.3. Client to Relying Party 1156 The final set of interactions between parties to consider are those 1157 between the client and the RP. In some ways this is the most complex 1158 set since at least part of it is outside the scope of the ABFAB work. 1159 The interactions between these parties include: 1161 o Running the protocol that implements the service that is provided 1162 by the RP and desired by the client. 1164 o Authenticating the client to the RP and the RP to the client. 1166 o Providing the necessary security services to the service protocol 1167 that it needs beyond authentication. 1169 o Deal with client re-authentication where desired. 1171 2.3.1. GSS-API 1173 One of the remaining layers is responsible for integration of 1174 federated authentication into the application. There are a number of 1175 approaches that applications have adopted for security. So, there 1176 may need to be multiple strategies for integration of federated 1177 authentication into applications. However, we have started with a 1178 strategy that provides integration to a large number of application 1179 protocols. 1181 Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645] 1182 and several non-IETF applications support the Generic Security 1183 Services Application Programming Interface [RFC2743]. Many 1184 applications such as IMAP, SMTP, XMPP and LDAP support the Simple 1185 Authentication and Security Layer (SASL) [RFC4422] framework. These 1186 two approaches work together nicely: by creating a GSS-API mechanism, 1187 SASL integration is also addressed. In effect, using a GSS-API 1188 mechanism with SASL simply requires placing some headers on the front 1189 of the mechanism and constraining certain GSS-API options. 1191 GSS-API is specified in terms of an abstract set of operations which 1192 can be mapped into a programming language to form an API. When 1193 people are first introduced to GSS-API, they focus on it as an API. 1194 However, from the prospective of authentication for non-web 1195 applications, GSS-API should be thought of as a protocol not an API. 1196 It consists of some abstract operations such as the initial context 1197 exchange, which includes two sub-operations (gss_init_sec_context and 1198 gss_accept_sec_context). An application defines which abstract 1199 operations it is going to use and where messages produced by these 1200 operations fit into the application architecture. A GSS-API 1201 mechanism will define what actual protocol messages result from that 1202 abstract message for a given abstract operation. So, since this work 1203 is focusing on a particular GSS-API mechanism, we generally focus on 1204 protocol elements rather than the API view of GSS-API. 1206 The API view has significant value. Since the abstract operations 1207 are well defined, the set of information that a mechanism gets from 1208 the application is well defined. Also, the set of assumptions the 1209 application is permitted to make is generally well defined. As a 1210 result, an application protocol that supports GSS-API or SASL is very 1211 likely to be usable with a new approach to authentication including 1212 this one with no required modifications. In some cases, support for 1213 a new authentication mechanism has been added using plugin interfaces 1214 to applications without the application being modified at all. Even 1215 when modifications are required, they can often be limited to 1216 supporting a new naming and authorization model. For example, this 1217 work focuses on privacy; an application that assumes it will always 1218 obtain an identifier for the client will need to be modified to 1219 support anonymity, unlinkability or pseudonymity. 1221 So, we use GSS-API and SASL because a number of the application 1222 protocols we wish to federate support these strategies for security 1223 integration. What does this mean from a protocol standpoint and how 1224 does this relate to other layers? This means we need to design a 1225 concrete GSS-API mechanism. We have chosen to use a GSS-API 1226 mechanism that encapsulates EAP authentication. So, GSS-API (and 1227 SASL) encapsulate EAP between the end-host and the service. The AAA 1228 framework encapsulates EAP between the relying party and the identity 1229 provider. The GSS-API mechanism includes rules about how initiators 1230 and services are named as well as per-message security and other 1231 facilities required by the applications we wish to support. 1233 2.3.2. Protocol Transport 1235 The transport of data between the client and the relying party is not 1236 provided by GSS-API. GSS-API creates and consumes messages, but it 1237 does not provide the transport itself, instead the protocol using 1238 GSS-API needs to provide the transport. In many cases HTTP or HTTPS 1239 is used for this transport, but other transports are perfectly 1240 acceptable. The core GSS-API document [RFC2743] provides some 1241 details on what requirements exist. 1243 In addition we highlight the following: 1245 o The transport does not need to provide either privacy or 1246 integrity. After GSS-EAP has finished negotiation, GSS-API can be 1247 used to provide both services. If the negotiation process itself 1248 needs protection from eavesdroppers then the transport would need 1249 to provide the necessary services. 1251 o The transport needs to provide reliable transport of the messages. 1253 o The transport needs to ensure that tokens are delivered in order 1254 during the negotiation process. 1256 o GSS-API messages need to be delivered atomically. If the 1257 transport breaks up a message it must also reassemble the message 1258 before delivery. 1260 2.3.3. Reauthentication 1262 TBD. 1264 3. Application Security Services 1266 One of the key goals is to integrate federated authentication into 1267 existing application protocols and where possible, existing 1268 implementations of these protocols. Another goal is to perform this 1269 integration while meeting the best security practices of the 1270 technologies used to perform the integration. This section describes 1271 security services and properties required by the EAP GSS-API 1272 mechanism in order to meet these goals. This information could be 1273 viewed as specific to that mechanism. However, other future 1274 application integration strategies are very likely to need similar 1275 services. So, it is likely that these services will be expanded 1276 across application integration strategies if new application 1277 integration strategies are adopted. 1279 3.1. Authentication 1281 GSS-API provides an optional security service called mutual 1282 authentication. This service means that in addition to the initiator 1283 providing (potentially anonymous or pseudonymous) identity to the 1284 acceptor, the acceptor confirms its identity to the initiator. 1285 Especially for the ABFAB context, this service is confusingly named. 1286 We still say that mutual authentication is provided when the identity 1287 of an acceptor is strongly authenticated to an anonymous initiator. 1289 RFC 2743, unfortunately, does not explicitly talk about what mutual 1290 authentication means. Within this document we therefore define it 1291 as: 1293 o If a target name is configured for the initiator, then the 1294 initiator trusts that the supplied target name describes the 1295 acceptor. This implies both that appropriate cryptographic 1296 exchanges took place for the initiator to make such a trust 1297 decision, and that after evaluating the results of these 1298 exchanges, the initiator's policy trusts that the target name is 1299 accurate. 1301 o If no target name is configured for the initiator, then the 1302 initiator trusts that the acceptor name, supplied by the acceptor, 1303 correctly names the entity it is communicating with. 1305 o Both the initiator and acceptor have the same key material for 1306 per-message keys and both parties have confirmed they actually 1307 have the key material. In EAP terms, there is a protected 1308 indication of success. 1310 Mutual authentication is an important defense against certain aspects 1311 of phishing. Intuitively, clients would like to assume that if some 1312 party asks for their credentials as part of authentication, 1313 successfully gaining access to the resource means that they are 1314 talking to the expected party. Without mutual authentication, the 1315 server could "grant access" regardless of what credentials are 1316 supplied. Mutual authentication better matches this user intuition. 1318 It is important, therefore, that the GSS-EAP mechanism implement 1319 mutual authentication. That is, an initiator needs to be able to 1320 request mutual authentication. When mutual authentication is 1321 requested, only EAP methods capable of providing the necessary 1322 service can be used, and appropriate steps need to be taken to 1323 provide mutual authentication. While a broader set of EAP methods 1324 could be supported by not requiring mutual authentication, it was 1325 decided that the client needs to always have the ability to request 1326 it. In some cases the IdP and the RP will not support mutual 1327 authentication, however the client will always be able to detect this 1328 and make an appropriate security decision. 1330 The AAA infrastructure MAY hide the initiator's identity from the 1331 GSS-API acceptor, providing anonymity between the initiator and the 1332 acceptor. At this time, whether the identity is disclosed is 1333 determined by EAP server policy rather than by an indication from the 1334 initiator. Also, initiators are unlikely to be able to determine 1335 whether anonymous communication will be provided. For this reason, 1336 initiators are unlikely to set the anonymous return flag from 1337 GSS_Init_Sec_context. 1339 3.2. GSS-API Channel Binding 1341 [RFC5056] defines a concept of channel binding which is used prevent 1342 man-in-the-middle attacks. The channel binding works by taking a 1343 cryptographic value from the transport security and checks that both 1344 sides of the GSS-API conversation know this value. Transport Layer 1345 Security (TLS) is the most common transport security layer used for 1346 this purpose. 1348 It needs to be stressed that RFC 5056 channel binding (also called 1349 GSS-API channel binding when GSS-API is involved) is not the same 1350 thing as EAP channel binding. GSS-API channel binding is used for 1351 detecting Man-In-The-Middle attacks. EAP channel binding is used for 1352 mutual authentication and acceptor naming checks. Details are 1353 discussed in the mechanisms specification [I-D.ietf-abfab-gss-eap]. 1354 A fuller description of the differences between the facilities can be 1355 found in RFC 5056 [RFC5056]. 1357 The use of TLS can provide both encryption and integrity on the 1358 channel. It is common to provide SASL and GSS-API with these other 1359 security services. 1361 One of the benefits that the use of TLS provides, is that client has 1362 the ability to validate the name of the server. However this 1363 validation is predicated on a couple of things. The TLS sessions 1364 needs to be using certificates and not be an anonymous session. The 1365 client and the TLS need to share a common trust point for the 1366 certificate used in validating the server. TLS provides its own 1367 server authentication. However there are a variety of situations 1368 where this authentication is not checked for policy or usability 1369 reasons. Even when it is checked, if the trust infrastructure behind 1370 the TLS authentication is different from the trust infrastructure 1371 behind the GSS-API mutual authentication then confirming the end- 1372 points using both trust infrastructures is likely to enhance 1373 security. If the endpoints of the GSS-API authentication are 1374 different than the endpoints of the lower layer, this is a strong 1375 indication of a problem such as a man-in-the-middle attack. Channel 1376 binding provides a facility to determine whether these endpoints are 1377 the same. 1379 The GSS-EAP mechanism needs to support channel binding. When an 1380 application provides channel binding data, the mechanism needs to 1381 confirm this is the same on both sides consistent with the GSS-API 1382 specification. 1384 3.3. Host-Based Service Names 1386 IETF security mechanisms typically take a host name and perhaps a 1387 service, entered by a user, and make some trust decision about 1388 whether the remote party in the interaction is the intended party. 1389 This decision can be made by the use of certificates, pre-configured 1390 key information or a previous leap of trust. GSS-API has defined a 1391 relatively flexible name convention, however most of the IETF 1392 applications that use GSS-API (including SSH, NFS, IMAP, LDAP and 1393 XMPP) have chosen to use a more restricted naming convention based on 1394 the host name. The GSS-EAP mechanism needs to support host-based 1395 service names in order to work with existing IETF protocols. 1397 The use of host-based service names leads to a challenging trust 1398 delegation problem. Who is allowed to decide whether a particular 1399 host name maps to a specific entity. Possible solutions to this 1400 problem have been looked at. 1402 o The public-key infrastructure (PKI) used by the web has chosen to 1403 have a number of trust anchors (root certificate authorities) each 1404 of which can map any host name to a public key. 1406 o A number of GSS-API mechanisms, such as Kerberos [RFC1964], have 1407 split the problem into two parts. A new concept called a realm is 1408 introduced, the realm is responsible for host mapping within that 1409 realm. The mechanism then decides what realm is responsible for a 1410 given name. This is the approach adopted by ABFAB. 1412 GSS-EAP defines a host naming convention that takes into account the 1413 host name, the realm, the service and the service parameters. An 1414 example of GSS-API service name is "xmpp/foo@example.com". This 1415 identifies the XMPP service on the host foo in the realm example.com. 1416 Any of the components, except for the service name may be omitted 1417 from a name. When omitted, then a local default would be used for 1418 that component of the name. 1420 While there is no requirement that realm names map to Fully Qualified 1421 Domain Names (FQDN) within DNS, in practice this is normally true. 1422 Doing so allows for the realm portion of service names and the 1423 portion of NAIs to be the same. It also allows for the use of DNS in 1424 locating the host of a service while establishing the transport 1425 channel between the client and the relying party. 1427 It is the responsibility of the application to determine the server 1428 that it is going to communicate with, GSS-API has the ability to help 1429 confirm that the server is the desired server but not to determine 1430 the name of the server to use. It is also the responsibility of the 1431 application to determine how much of the information identifying the 1432 service needs to be validated by the ABFAB system. The information 1433 that needs to be validated is used to build up the service name 1434 passed into the GSS-EAP mechanism. What information is to be 1435 validated will depend on both what information was provided by the 1436 client, and what information is considered significant. If the 1437 client only cares about getting a specific service, then the host and 1438 realm that provides the service does not need to be validated. 1440 In many cases applications may retrieve information about providers 1441 of services from DNS. When Service Records (SRV) and Naming 1442 Authority Pointer (NAPTR) records are used to help find a host that 1443 provides a service, the security requirements on the referrals is 1444 going to interact with the information used in the service name. If 1445 a host name is returned from the DNS referrals, and the host name is 1446 to be validated by GS-EAP, then it makes sense that the referrals 1447 themselves should be secure. On the other hand, if the host name 1448 returned is not validated, i.e. only the service is passed in, then 1449 it is less important that the host name be obtained in a secure 1450 manner. 1452 Another issue that needs to be addressed for host-based service names 1453 is that they do not work ideally when different instances of a 1454 service are running on different ports. If the services are 1455 equivalent, then it does not matter. However if there are 1456 substantial differences in the quality of the service that 1457 information needs to be part of the validation process. If one has 1458 just a host name and not a port in the information being validated, 1459 then this is not going to be a successful strategy. 1461 3.4. Additional GSS-API Services 1463 GSS-API provides per-message security services that can provide 1464 confidentiality and/or integrity. Some IETF protocols such as NFS 1465 and SSH take advantage of these services. As a result GSS-EAP needs 1466 to support these services. As with mutual authentication, per- 1467 message services will limit the set of EAP methods that can be used 1468 to those that generate a Master Session Key (MSK). Any EAP method 1469 that produces an MSK is able to support per-message security services 1470 described in [RFC2743]. 1472 GSS-API provides a pseudo-random function. This function generates a 1473 pseudo-random sequence using the shared private key as the seed for 1474 the bytes generated. This provides an algorithm that both the 1475 initiator and acceptor can run in order to arrive at the same key 1476 value. The use of this feature allows for an application to generate 1477 keys or other shared secrets for use in other places in the protocol. 1478 In this regards, it is similar in concept to the TLS extractor (RFC 1479 5705 [RFC5705].). While no current IETF protocols require this, non- 1480 IETF protocols are expected to take advantage of this in the near 1481 future. Additionally, a number of protocols have found the TLS 1482 extractor to be useful in this regards so it is highly probably that 1483 IETF protocols may also start using this feature. 1485 4. Privacy Considerations 1487 ABFAB, as an architecture designed to enable federated authentication 1488 and allow for the secure transmission of identity information between 1489 entities, obviously requires careful consideration around privacy and 1490 the potential for privacy violations. 1492 This section examines the privacy related information presented in 1493 this document, summarising the entities that are involved in ABFAB 1494 communications and what exposure they have to identity information. 1495 In discussing these privacy considerations in this section, we use 1496 terminology and ideas from [I-D.iab-privacy-considerations]. 1498 Note that the ABFAB architecture uses at its core several existing 1499 technologies and protocols; detailed privacy discussion around these 1500 is not examined. This section instead focuses on privacy 1501 considerations specifically related to overall architecture and usage 1502 of ABFAB. 1504 +--------+ +---------------+ +--------------+ 1505 | Client | <---> | RP | <---> | AAA Client | 1506 +--------+ +---------------+ +--------------+ 1507 ^ 1508 | 1509 v 1510 +---------------+ +--------------+ 1511 | SAML Server | | AAA Proxy(s) | 1512 +---------------+ +--------------+ 1513 ^ ^ 1514 | | 1515 v v 1516 +------------+ +---------------+ +--------------+ 1517 | EAP Server | <---> | IdP | <---> | AAA Server | 1518 +------------+ +---------------+ +--------------+ 1520 Figure 3: Entities and Data Flow 1522 4.1. Entities and their roles 1524 Categorizing the ABFAB entities shown in the Figure 3 according to 1525 the taxonomy of terms from [I-D.iab-privacy-considerations] the 1526 entities shown in Figure 3 is somewhat complicated as during the 1527 various phases of ABFAB communications the roles of each entity 1528 changes. The three main phases of relevance are the Client to RP 1529 communication phase, the Client to IdP (via the Federation Substrate) 1530 phase, and the IdP to RP (via the Federation Substrate) phase. 1532 In the Client to RP communication phase, we have: 1534 Initiator: Client. 1536 Observers: Client, RP. 1538 Recipient: RP. 1540 In the Client to IdP (via the Federation Substrate) communication 1541 phase, we have: 1543 Initiator: Client. 1545 Observers: Client, RP, AAA Client, AAA Proxy(s), AAA Server, IdP. 1547 Recipient: IdP 1549 In the IdP to Relying party (via the Federation Substrate) 1550 communication phase, we have: 1552 Initiator: IdP. 1554 Observers: IdP, AAA Server, AAA Proxy(s), AAA Client, RP. 1556 Recipient: RP 1558 Eavesdroppers and Attackers can reside on any communication link 1559 between entities in Figure 3. 1561 The Federation Substrate consists of all of the AAA entities. In 1562 some cases the AAA Proxies entities may not exist as the AAA Client 1563 can talk directly to the AAA Server. Specifications such as the 1564 Trust Router Protocol and RADIUS dynamic discovery 1565 [I-D.ietf-radext-dynamic-discovery] can be used to shorten the path 1566 between the AAA client and the AAA server (and thus stop these AAA 1567 Proxies from being Observers), however even in these circumstances 1568 there may be AAA Proxies in the path. 1570 In Figure 3 the IdP has been divided into multiple logical pieces, in 1571 actual implementations these pieces will frequently be tightly 1572 coupled. The links between these pieces provide the greatest 1573 opportunity for attackers and eavesdroppers to acquire information, 1574 however, as they are all under the control of a single entity they 1575 are also the easiest to have tightly secured. 1577 4.2. Privacy Aspects of ABFAB Communication Flows 1579 In the ABFAB architecture, there are a few different types of data 1580 and identifiers in use. The best way to understand them, and the 1581 potential privacy impacts of them, is to look at each phase of 1582 communication in ABFAB. 1584 4.2.1. Client to RP 1586 The flow of data between the client and the RP is divided into two 1587 parts. The first part consists of all of the data exchanged as part 1588 of the ABFAB authentication process. The second part consists of all 1589 of the data exchanged after the authentication process has been 1590 finished. 1592 During the initial communications phase, the client sends an NAI (see 1593 [I-D.ietf-radext-nai]) to the RP. Many EAP methods (but not all) 1594 allow for the client to disclose an NAI to the in a form that 1595 includes only a realm during this communications phase. This is the 1596 minimum amount of identity information necessary for ABFAB to work - 1597 it indicates an IdP that the principal has a relationship with. EAP 1598 methods that do not allow this will necessarily also reveal an 1599 identifier for the principal in the IdP realm (e.g. a username). 1601 The data exchanged after the authentication process can have privacy 1602 and authentication using the GSS-API services. If the overall 1603 application protocol allows for the process of re-authentication, 1604 then the same privacy impliciations as discussed in previous 1605 paragraph apply. 1607 4.2.2. Client to IdP (via Federation Substrate) 1609 This phase sees a secure TLS tunnel initiated between the Client and 1610 the IdP via the RP and federation substrate. The process is 1611 initiated by the RP using the realm information given to it by the 1612 client. Once set up, the tunnel is used to send credentials to IdP 1613 to authenticate. 1615 Various operational information is transported between RP and IdP, 1616 over the AAA infrastructure, for example using RADIUS headers. As no 1617 end-to-end security is provided by AAA, all AAA entities on the path 1618 between the RP and IdP have the ability to eavesdrop on this 1619 information unless additional security measures are taken (such as 1620 the use of TLS for RADIUS [I-D.ietf-radext-dtls]). Some of this 1621 information may form identifiers or explicit identity information: 1623 o The Relying Party knows the IP address of the Client. It is 1624 possible that the Relying Party could choose to expose this IP 1625 address by including it in a RADIUS header such as Calling Station 1626 ID. This is a privacy consideration to take into account of the 1627 application protocol. 1629 o The EAP MSK is transported between the IdP and the RP over the AAA 1630 infrastructure, for example through RADIUS headers. This is a 1631 particularly important privacy consideration, as any AAA Proxy 1632 that has access to the EAP MSK is able to decrypt and eavesdrop on 1633 any traffic encrypted using that EAP MSK (i.e. all communications 1634 between the Client and IdP). 1636 o Related to the above, the AAA server has access to the material 1637 necessary to derive the session key, thus the AAA server can 1638 observe any traffic encrypted between the Client and RP. This 1639 "feature" was" chosen as a simplification and to make performance 1640 faster; if it was decided that this trade-off was not desireable 1641 for privacy and security reasons, then extensions to ABFAB that 1642 make use of techniques such as Diffie-Helman key exchange would 1643 mitigate against this. 1645 The choice of EAP method used has other potential privacy 1646 implications. For example, if the EAP method in use does not support 1647 trust anchors to enable mutual authentication, then there are no 1648 guarantees that the IdP is who it claims to be, and thus the full NAI 1649 including a username and a realm might be sent to any entity 1650 masquerading as a particular IdP. 1652 Note that ABFAB has not specified any AAA accounting requirements. 1653 Implementations that use the accounting portion of AAA should 1654 consider privacy appropriately when designing this aspect. 1656 4.2.3. IdP to RP (via Federation Substrate) 1658 In this phase, the IdP communicates with the RP informing it as to 1659 the success or failure of authentication of the user, and optionally, 1660 the sending of identity information about the principal. 1662 As in the previous flow (Client to IdP), various operation 1663 information is transported between IdP and RP over the AAA 1664 infrastructure, and the same privacy considerations apply. However, 1665 in this flow, explicit identity information about the authenticated 1666 principal can be sent from the IdP to the RP. This information can 1667 be sent through RADIUS headers, or using SAML 1668 [I-D.ietf-abfab-aaa-saml]. This can include protocol specific 1669 identitifiers, such as SAML NameIDs, as well as arbitrary attribute 1670 information about the principal. What information will be released 1671 is controlled by policy on the Identity Provider. As before, when 1672 sending this through RADIUS headers, all AAA entities on the path 1673 between the RP and IdP have the ability to eavesdrop unless 1674 additional security measures are taken (such as the use of TLS for 1675 RADIUS [I-D.ietf-radext-dtls]). When sending this using SAML, as 1676 specified in [I-D.ietf-abfab-aaa-saml], confidentiality of the 1677 information should however be guaranteed as [I-D.ietf-abfab-aaa-saml] 1678 requires the use of TLS for RADIUS. 1680 4.3. Relationship between User and Entities 1682 o Between User and IdP - the IdP is an entity the user will have a 1683 direct relationship with, created when the organisation that 1684 operates the entity provisioned and exchanged the user's 1685 credentials. Privacy and data protection guarantees may form a 1686 part of this relationship. 1688 o Between User and RP - the RP is an entity the user may or may not 1689 have a direct relationship with, depending on the service in 1690 question. Some services may only be offered to those users where 1691 such a direct relationship exists (for particularly sensitive 1692 services, for example), while some may not require this and would 1693 instead be satisfied with basic federation trust guarantees 1694 between themselves and the IdP). This may well include the option 1695 that the user stays anonymous with respect to the RP (though 1696 obviously never to the IdP). If attempting to preserve privacy 1697 through the mitigation of data minimisation, then the only 1698 attribute information about individuals exposed to the RP should 1699 be that which is strictly necessary for the operation of the 1700 service. 1702 o Between User and Federation substrate - the user is highly likely 1703 to have no knowledge of, or relationship with, any entities 1704 involved with the federation substrate (not that the IdP and/or RP 1705 may, however). Knowledge of attribute information about 1706 individuals for these entities is not necessary, and thus such 1707 information should be protected in such a way as to prevent access 1708 to this information from being possible. 1710 4.4. Accounting Information 1712 Alongside the core authentication and authorization that occurs in 1713 AAA communications, accounting information about resource consumption 1714 may be delivered as part of the accounting exchange during the 1715 lifetime of the granted application session. 1717 4.5. Collection and retention of data and identifiers 1719 In cases where Relying Parties do not require to identify a 1720 particular individual when an individual wishes to make use of their 1721 service, the ABFAB architecture enable anonymous or pseudonymous 1722 access. Thus data and identifiers other than pseudonyms and 1723 unlinkable attribute information need not be stored and retained. 1725 However, in cases where Relying Parties require the ability to 1726 identify a particular individual (e.g. so they can link this 1727 identity information to a particular account in their service, or 1728 where identity information is required for audit purposes), the 1729 service will need to collect and store such information, and to 1730 retain it for as long as they require. Deprovisioning of such 1731 accounts and information is out of scope for ABFAB, but obviously for 1732 privacy protection any identifiers collected should be deleted when 1733 they are no longer needed. 1735 4.6. User Participation 1737 In the ABFAB architecture, by its very nature users are active 1738 participants in the sharing of their identifiers as they initiate the 1739 communications exchange every time they wish to access a server. 1740 They are, however, not involved in control of the set of information 1741 related to them that transmitted from the IdP to RP for authorisation 1742 purposes; rather, this is under the control of policy on the IdP. 1743 Due to the nature of the AAA communication flows, with the current 1744 ABFAB architecture there is no place for a process of gaining user 1745 consent for the information to be released from IdP to RP. 1747 5. Deployment Considerations 1749 5.1. EAP Channel Binding 1751 Discuss the implications of needing EAP channel binding. 1753 5.2. AAA Proxy Behavior 1755 Discuss deployment implications of our proxy requirements. 1757 6. Security Considerations 1759 This document describes the architecture for Application Bridging for 1760 Federated Access Beyond Web (ABFAB) and security is therefore the 1761 main focus. This section highlights the main communication channels 1762 and their security properties: 1764 Client-to-RP Channel: 1766 The channel binding material is provided by any certificates and 1767 the final message (i.e., a cryptographic token for the channel). 1768 Authentication may be provided by the RP to the client but a 1769 deployment without authentication at the TLS layer is possible as 1770 well. In addition, there is a channel between the GSS requestor 1771 and the GSS acceptor, but the keying material is provided by a 1772 "third party" to both entities. The client can derive keying 1773 material locally, but the RP gets the material from the IdP. In 1774 the absence of a transport that provides encryption and/or 1775 integrity, the channel between the client and the RP has no 1776 ability to have any cryptographic protection until the EAP 1777 authentication has been completed and the MSK is transferred from 1778 the IdP to the RP. 1780 RP-to-IdP Channel: 1782 The security of this communication channel is mainly provided by 1783 the functionality offered via RADIUS and Diameter. At the time of 1784 writing there are no end-to-end security mechanisms standardized 1785 and thereby the architecture has to rely on hop-by-hop security 1786 with trusted AAA entities or, as an alternative but possible 1787 deployment variant, direct communication between the AAA client to 1788 the AAA server. Note that the authorization result the IdP 1789 provides to the RP in the form of a SAML assertion may, however, 1790 be protected such that the SAML related components are secured 1791 end-to-end. 1793 The MSK is transported from the IdP to the RP over this channel. 1794 As no end-to-end security is provided by AAA, all AAA entities on 1795 the path between the RP and IdP have the ability to eavesdrop if 1796 no additional security measures are taken. One such measure is to 1797 use a transport between the client and the IdP that provides 1798 confidentiality. 1800 Client-to-IdP Channel: 1802 This communication interaction is accomplished with the help of 1803 EAP and EAP methods. The offered security protection will depend 1804 on the EAP method that is chosen but a minimum requirement is to 1805 offer mutual authentication, and key derivation. The IdP is 1806 responsible during this process to determine that the RP that is 1807 communication to the client over the RP-to-IdP channel is the same 1808 one talking to the IdP. This is accomplished via the EAP channel 1809 binding. 1811 Partial list of issues to be addressed in this section: Privacy, 1812 SAML, Trust Anchors, EAP Algorithm Selection, Diameter/RADIUS/AAA 1813 Issues, Naming of Entities, Protection of passwords, Channel Binding, 1814 End-point-connections (TLS), Proxy problems 1816 When a pseudonym is generated as a unique long term identifier for a 1817 Subject by an IdP, care MUST be taken in the algorithm that it cannot 1818 easily be reverse engineered by the service provider. If it can be 1819 reversed then the service provider can consult an oracle to determine 1820 if a given unique long term identifier is associated with a different 1821 known identifier. 1823 7. IANA Considerations 1825 This document does not require actions by IANA. 1827 8. Acknowledgments 1829 We would like to thank Mayutan Arumaithurai and Klaas Wierenga for 1830 their feedback. Additionally, we would like to thank Eve Maler, 1831 Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, Paul Leach, 1832 and Luke Howard for their feedback on the federation terminology 1833 question. 1835 Furthermore, we would like to thank Klaas Wierenga for his review of 1836 the pre-00 draft version. 1838 9. References 1840 9.1. Normative References 1842 [RFC2743] Linn, J., "Generic Security Service Application Program 1843 Interface Version 2, Update 1", RFC 2743, January 2000. 1845 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 1846 "Remote Authentication Dial In User Service (RADIUS)", RFC 1847 2865, June 2000. 1849 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 1850 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 1852 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 1853 Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 1854 3748, June 2004. 1856 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 1857 Dial In User Service) Support For Extensible 1858 Authentication Protocol (EAP)", RFC 3579, September 2003. 1860 [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 1861 Authentication Protocol (EAP) Application", RFC 4072, 1862 August 2005. 1864 [I-D.ietf-abfab-gss-eap] 1865 Hartman, S. and J. Howlett, "A GSS-API Mechanism for the 1866 Extensible Authentication Protocol", draft-ietf-abfab-gss- 1867 eap-09 (work in progress), August 2012. 1869 [I-D.ietf-abfab-aaa-saml] 1870 Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding, 1871 Profiles, Name Identifier Format, and Confirmation Methods 1872 for SAML", draft-ietf-abfab-aaa-saml-05 (work in 1873 progress), February 2013. 1875 [I-D.ietf-radext-nai] 1876 DeKok, A., "The Network Access Identifier", draft-ietf- 1877 radext-nai-02 (work in progress), January 2013. 1879 [RFC6677] Hartman, S., Clancy, T., and K. Hoeper, "Channel-Binding 1880 Support for Extensible Authentication Protocol (EAP) 1881 Methods", RFC 6677, July 2012. 1883 9.2. Informative References 1885 [RFC2903] de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and 1886 D. Spence, "Generic AAA Architecture", RFC 2903, August 1887 2000. 1889 [I-D.nir-tls-eap] 1890 Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A 1891 Flexible Authentication Framework for the Transport Layer 1892 Security (TLS) Protocol using the Extensible 1893 Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work 1894 in progress), December 2011. 1896 [I-D.ietf-oauth-v2] 1897 Hardt, D., "The OAuth 2.0 Authorization Framework", draft- 1898 ietf-oauth-v2-31 (work in progress), August 2012. 1900 [I-D.iab-privacy-considerations] 1901 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1902 Morris, J., Hansen, M., and R. Smith, "Privacy 1903 Considerations for Internet Protocols", draft-iab-privacy- 1904 considerations-03 (work in progress), July 2012. 1906 [I-D.perez-radext-radius-fragmentation] 1907 Perez-Mendez, A., Lopez, R., Pereniguez-Garcia, F., Lopez- 1908 Millan, G., Lopez, D., and A. DeKok, "Support of 1909 fragmentation of RADIUS packets", draft-perez-radext- 1910 radius-fragmentation-05 (work in progress), February 2013. 1912 [RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible 1913 Authentication Protocol (EAP) Method Requirements for 1914 Wireless LANs", RFC 4017, March 2005. 1916 [RFC5106] Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y., 1917 and F. Bersani, "The Extensible Authentication Protocol- 1918 Internet Key Exchange Protocol version 2 (EAP-IKEv2) 1919 Method", RFC 5106, February 2008. 1921 [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", RFC 1922 1964, June 1996. 1924 [RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol 1925 Specification", RFC 2203, September 1997. 1927 [RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J., 1928 and R. Hall, "Generic Security Service Algorithm for 1929 Secret Key Transaction Authentication for DNS (GSS-TSIG)", 1930 RFC 3645, October 2003. 1932 [RFC2138] Rigney, C., Rigney, C., Rubens, A.C., Simpson, W.A., and 1933 S. Willens, "Remote Authentication Dial In User Service 1934 (RADIUS)", RFC 2138, April 1997. 1936 [RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch, 1937 "Generic Security Service Application Program Interface 1938 (GSS-API) Authentication and Key Exchange for the Secure 1939 Shell (SSH) Protocol", RFC 4462, May 2006. 1941 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 1942 Security Layer (SASL)", RFC 4422, June 2006. 1944 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 1945 Channels", RFC 5056, November 2007. 1947 [RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication 1948 Dial In User Service (RADIUS) Implementation Issues and 1949 Suggested Fixes", RFC 5080, December 2007. 1951 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 1952 Layer Security (TLS)", RFC 5705, March 2010. 1954 [RFC5801] Josefsson, S. and N. Williams, "Using Generic Security 1955 Service Application Program Interface (GSS-API) Mechanisms 1956 in Simple Authentication and Security Layer (SASL): The 1957 GS2 Mechanism Family", RFC 5801, July 2010. 1959 [RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849, 1960 April 2010. 1962 [RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga, 1963 "Transport Layer Security (TLS) Encryption for RADIUS", 1964 RFC 6614, May 2012. 1966 [OASIS.saml-core-2.0-os] 1967 Cantor, S., Kemp, J., Philpott, R., and E. Maler, 1968 "Assertions and Protocol for the OASIS Security Assertion 1969 Markup Language (SAML) V2.0", OASIS Standard saml- 1970 core-2.0-os, March 2005. 1972 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 1973 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 1974 D. Spence, "AAA Authorization Framework", RFC 2904, August 1975 2000. 1977 [I-D.ietf-emu-crypto-bind] 1978 Hartman, S., Wasserman, M., and D. Zhang, "EAP Mutual 1979 Cryptographic Binding", draft-ietf-emu-crypto-bind-03 1980 (work in progress), March 2013. 1982 [I-D.ietf-emu-eap-tunnel-method] 1983 Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna, 1984 "Tunnel EAP Method (TEAP) Version 1", draft-ietf-emu-eap- 1985 tunnel-method-05 (work in progress), February 2013. 1987 [I-D.ietf-radext-dtls] 1988 DeKok, A., "DTLS as a Transport Layer for RADIUS", draft- 1989 ietf-radext-dtls-03 (work in progress), January 2013. 1991 [I-D.ietf-radext-dynamic-discovery] 1992 Winter, S. and M. McCauley, "NAI-based Dynamic Peer 1993 Discovery for RADIUS/TLS and RADIUS/DTLS", draft-ietf- 1994 radext-dynamic-discovery-06 (work in progress), February 1995 2013. 1997 [WS-TRUST] 1998 Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin, 1999 M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS 2000 Standard ws-trust-200902, February 2009, . 2003 [NIST-SP.800-63] 2004 Burr, W., Dodson, D., and W. Polk, "Electronic 2005 Authentication Guideline", NIST Special Publication 2006 800-63, April 2006. 2008 Authors' Addresses 2009 Josh Howlett 2010 JANET(UK) 2011 Lumen House, Library Avenue, Harwell 2012 Oxford OX11 0SG 2013 UK 2015 Phone: +44 1235 822363 2016 Email: Josh.Howlett@ja.net 2018 Sam Hartman 2019 Painless Security 2021 Email: hartmans-ietf@mit.edu 2023 Hannes Tschofenig 2024 Nokia Siemens Networks 2025 Linnoitustie 6 2026 Espoo 02600 2027 Finland 2029 Phone: +358 (50) 4871445 2030 Email: Hannes.Tschofenig@gmx.net 2031 URI: http://www.tschofenig.priv.at 2033 Eliot Lear 2034 Cisco Systems GmbH 2035 Richtistrasse 7 2036 Wallisellen, ZH CH-8304 2037 Switzerland 2039 Phone: +41 44 878 9200 2040 Email: lear@cisco.com 2042 Jim Schaad 2043 Soaring Hawk Consulting 2045 Email: ietf@augustcellars.com