idnits 2.17.00 (12 Aug 2021) /tmp/idnits52346/draft-ietf-abfab-arch-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 1324: '...A infrastructure MAY hide the initiato...' RFC 2119 keyword, line 1712: '... by an IdP, care MUST be taken in the ...' Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (February 25, 2013) is 3371 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC2903' is defined on line 1779, but no explicit reference was found in the text == Unused Reference: 'RFC4017' is defined on line 1808, but no explicit reference was found in the text == Unused Reference: 'RFC5106' is defined on line 1812, but no explicit reference was found in the text == Unused Reference: 'RFC2138' is defined on line 1828, but no explicit reference was found in the text == Unused Reference: 'RFC2904' is defined on line 1869, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3588 (Obsoleted by RFC 6733) ** Obsolete normative reference: RFC 4282 (Obsoleted by RFC 7542) == Outdated reference: draft-ietf-abfab-gss-eap has been published as RFC 7055 == Outdated reference: draft-ietf-abfab-aaa-saml has been published as RFC 7833 == Outdated reference: draft-ietf-oauth-v2 has been published as RFC 6749 == Outdated reference: draft-iab-privacy-considerations has been published as RFC 6973 == Outdated reference: A later version (-06) exists of draft-perez-radext-radius-fragmentation-05 -- Obsolete informational reference (is this intentional?): RFC 2138 (Obsoleted by RFC 2865) -- Obsolete informational reference (is this intentional?): RFC 5849 (Obsoleted by RFC 6749) == Outdated reference: draft-ietf-emu-crypto-bind has been published as RFC 7029 -- No information found for draft-ietf-emu-eap-tunnel-method - is the name correct? == Outdated reference: draft-ietf-radext-dtls has been published as RFC 7360 Summary: 3 errors (**), 0 flaws (~~), 13 warnings (==), 4 comments (--). 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: August 29, 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 February 25, 2013 14 Application Bridging for Federated Access Beyond Web (ABFAB) 15 Architecture 16 draft-ietf-abfab-arch-05.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 August 29, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . 11 77 1.5. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 13 78 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 15 79 2.1. Relying Party to Identity Provider . . . . . . . . . . . . 16 80 2.1.1. AAA, RADIUS and Diameter . . . . . . . . . . . . . . . 17 81 2.1.2. Discovery and Rules Determination . . . . . . . . . . 19 82 2.1.3. Routing and Technical Trust . . . . . . . . . . . . . 20 83 2.1.4. AAA Security . . . . . . . . . . . . . . . . . . . . . 21 84 2.1.5. SAML Assertions . . . . . . . . . . . . . . . . . . . 22 85 2.2. Client To Identity Provider . . . . . . . . . . . . . . . 24 86 2.2.1. Extensible Authentication Protocol (EAP) . . . . . . . 24 87 2.2.2. EAP Channel Binding . . . . . . . . . . . . . . . . . 25 88 2.3. Client to Relying Party . . . . . . . . . . . . . . . . . 26 89 2.3.1. GSS-API . . . . . . . . . . . . . . . . . . . . . . . 26 90 2.3.2. Protocol Transport . . . . . . . . . . . . . . . . . . 28 91 2.3.3. Reauthentication . . . . . . . . . . . . . . . . . . . 28 92 3. Application Security Services . . . . . . . . . . . . . . . . 29 93 3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 29 94 3.2. GSS-API Channel Binding . . . . . . . . . . . . . . . . . 30 95 3.3. Host-Based Service Names . . . . . . . . . . . . . . . . . 31 96 3.4. Additional GSS-API Services . . . . . . . . . . . . . . . 33 97 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 34 98 4.1. Entities and their roles . . . . . . . . . . . . . . . . . 34 99 4.2. Relationship between user and entities . . . . . . . . . . 35 100 4.3. Data and Identifiers in use . . . . . . . . . . . . . . . 35 101 4.3.1. NAI . . . . . . . . . . . . . . . . . . . . . . . . . 35 102 4.3.2. Identity Information . . . . . . . . . . . . . . . . . 36 103 4.3.3. Accounting Information . . . . . . . . . . . . . . . . 36 104 4.3.4. Collection and retention of data and identifiers . . . 36 105 4.4. User Participation . . . . . . . . . . . . . . . . . . . . 37 106 5. Deployment Considerations . . . . . . . . . . . . . . . . . . 38 107 5.1. EAP Channel Binding . . . . . . . . . . . . . . . . . . . 38 108 5.2. AAA Proxy Behavior . . . . . . . . . . . . . . . . . . . . 38 109 6. Security Considerations . . . . . . . . . . . . . . . . . . . 39 110 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41 111 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42 112 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43 113 9.1. Normative References . . . . . . . . . . . . . . . . . . . 43 114 9.2. Informative References . . . . . . . . . . . . . . . . . . 43 115 Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . . 116 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49 118 1. Introduction 120 The Internet uses numerous security mechanisms to manage access to 121 various resources. These mechanisms have been generalized and scaled 122 over the last decade through mechanisms such as Simple Authentication 123 and Security Layer (SASL) with the Generic Security Server 124 Application Program Interface (GSS-API) (known as the GS2 family) 125 [RFC5801], Security Assertion Markup Language (SAML) 126 [OASIS.saml-core-2.0-os], and the Authentication, Authorization, and 127 Accounting (AAA) architecture as embodied in RADIUS [RFC2865] and 128 Diameter [RFC3588]. 130 A Relying Party (RP) is the entity that manages access to some 131 resource. The actor that is requesting access to that resource is 132 often described as the Client. Many security mechanisms are 133 manifested as an exchange of information between these actors. The 134 RP is therefore able to decide whether the Client is authorized, or 135 not. 137 Some security mechanisms allow the RP to delegate aspects of the 138 access management decision to an actor called the Identity Provider 139 (IdP). This delegation requires technical signaling, trust and a 140 common understanding of semantics between the RP and IdP. These 141 aspects are generally managed within a relationship known as a 142 'federation'. This style of access management is accordingly 143 described as 'federated access management'. 145 Federated access management has evolved over the last decade through 146 specifications like SAML [OASIS.saml-core-2.0-os], OpenID [1], OAuth 147 [RFC5849], [I-D.ietf-oauth-v2] and WS-Trust [WS-TRUST]. The benefits 148 of federated access management include: 150 Single or Simplified sign-on: 152 An Internet service can delegate access management, and the 153 associated responsibilities such as identity management and 154 credentialing, to an organisation that already has a long-term 155 relationship with the Subject. This is often attractive for 156 Relying Parties who frequently do not want these responsibilities. 157 The Subject also requires fewer credentials, which is also 158 desirable. 160 Data Minimization and User Participation: 162 Often a Relying Party does not need to know the identity of a 163 Subject to reach an access management decision. It is frequently 164 only necessary for the Relying Party know specific attributes 165 about the subject, for example, that the Subject is affiliated 166 with a particular organisation or has a certain role or 167 entitlement. Sometimes the RP only needs to know a pseudonym of 168 the Subject. 170 Prior to the release of attributes to the IdP from the IdP, the 171 IdP will check configuration and policy to determine if the 172 attributes are to be released. There is currently no direct 173 client participation in this decision. 175 Provisioning 177 Sometimes a Relying Party needs, or would like, to know more about 178 a subject than an affiliation or a pseudonym. For example, a 179 Relying Party may want the Subject's email address or name. Some 180 federated access management technologies provide the ability for 181 the IdP to supply this information, either on request by the RP or 182 unsolicited. 184 This memo describes the Application Bridging for Federated Access 185 Beyond the Web (ABFAB) architecture. This architecture makes use of 186 extensions to the commonly used security mechanisms for both 187 federated and non-federated access management, including the RADIUS 188 and the Diameter protocols, the Generic Security Service (GSS), the 189 GS2 family, the Extensible Authentication Protocol (EAP) and SAML. 190 The architecture addresses the problem of federated access management 191 primarily for non-web-based services. It does so in a manner that 192 will scale to large numbers of identity providers, relying parties, 193 and federations. 195 1.1. Terminology 197 This document uses identity management and privacy terminology from 198 [I-D.iab-privacy-considerations]. In particular, this document uses 199 the terms identity provider, relying party, identifier, pseudonymity, 200 unlinkability, and anonymity. 202 In this architecture the IdP consists of the following components: an 203 EAP server, a RADIUS or a Diameter server, and optionally a SAML 204 Assertion service. 206 This document uses the term Network Access Identifier (NAI), as 207 defined in [RFC4282]. An NAI consists of a realm identifier, which 208 is associated with an IdP and a username which is associated with a 209 specific client of the IdP. 211 One of the problems people will find with reading this document is 212 that the terminology sometimes appears to be inconsistent. This is 213 due the fact that the terms used by the different standards we are 214 picking up don't use the same terms. In general the document uses 215 either a consistent term or the term associated with the standard 216 under discussion as appropriate. For reference we include this table 217 which maps the different terms into a single table. 219 +----------+-----------+--------------------+-----------------------+ 220 | Protocol | Subject | Relying Party | Identity Provider | 221 +----------+-----------+--------------------+-----------------------+ 222 | ABFAB | Client | Relying Party (RP) | Identity Provider | 223 | | | | (IdP) | 224 | | | | | 225 | | Initiator | Acceptor | | 226 | | | | | 227 | | | Server | | 228 | | | | | 229 | SAML | Subject | Service Provider | Issuer | 230 | | | | | 231 | GSS-API | Initiator | Acceptor | | 232 | | | | | 233 | EAP | EAP peer | | EAP server | 234 | | | | | 235 | AAA | | AAA Client | AAA server | 236 | | | | | 237 | RADIUS | user | NAS | RADIUS server | 238 | | | | | 239 | | | RADIUS client | | 240 +----------+-----------+--------------------+-----------------------+ 242 Note that in some cases a cell has been left empty, in these cases 243 there is no direct name that represents this concept. 245 Note to reviewers - I have most likely missed some entries in the 246 table. Please provide me with both correct names from the protocol 247 and missing names that are used in the text below. 249 1.1.1. Channel Binding 251 This document uses the term channel binding with two different 252 meanings. 254 EAP channel binding, also called channel binding, is used to provide 255 GSS-API naming semantics. Channel binding sends a set of attributes 256 from the peer to the EAP server either as part of the EAP 257 converstaion or as part of a secure association protocol. In 258 addition, attributes are sent in the baackend protocol from the 259 authenticator to the EAP server. The EAP server confirms the 260 consistency of these attributes and provides the confirmation back to 261 the peer. 263 GSS-API channel binding provides protection against man-in-the-middle 264 attacks when GSS-API is used for authentication inside of some 265 tunnel; it is similar to a facility called cryptographic binding in 266 EAP. The binding works by each side deriving a cryptographic value 267 from the tunnel itself and then using that cyrptographic value to 268 prove to the otherside that it knows the value. 270 See [RFC5056] for a discussion of the differences between these two 271 facilities. 273 Typically when considering channel binding, people think of channel 274 binding in combination with mutual authentication. This is 275 sufficiently common that without additional qualification channel 276 binding should be assumed to imply mutual authentication. Without 277 mutual authentication, only one party knows that the endpoints are 278 correct. That's sometimes useful. Consider for example a user who 279 wishes to access a protected resource from a shared whiteboard in a 280 conference room. The whiteboard is the initiator; it does not need 281 to actually authenticate that it is talking to the correct resource 282 because the user will be able to recognize whether the displayed 283 content is correct. If channel binding were used without mutual 284 authentication, it would in effect be a request to only disclose the 285 resource in the context of a particular channel. Such an 286 authentication would be similar in concept to a holder-of-key SAML 287 assertion. However, also note that while it is not happening in the 288 protocol, mutual authentication is happening in the overall system: 289 the user is able to visually authenticate the content. This is 290 consistent with all uses of channel binding without protocol level 291 mutual authentication found so far. 293 1.2. An Overview of Federation 295 In the previous section we introduced the following actors: 297 o the Client, 299 o the Identity Provider, and 301 o the Relying Party. 303 One additional actor in can be an Individual. An individual is a 304 human being that is using a client. Individuals may or may not exist 305 in any given deployment. The client may be either a front end on an 306 individual or an independent automated entity. 308 These entities and their relationships are illustrated graphically in 309 Figure 1. 311 ,----------\ ,---------\ 312 | Identity | Federation | Relying | 313 | Provider + <-------------------> + Party | 314 `----------' '---------' 315 < 316 \ 317 \ Authentication 318 \ 319 \ 320 \ 321 \ 322 \ +---------+ 323 \ | | O 324 v| Client | \|/ Individual 325 | | | 326 +---------+ / \ 328 Figure 1: Entities and their Relationships 330 The relationships between the entities in Figure 1 are: 332 Federation 334 The Identity Provider and the Relying Parties are part of a 335 Federation. The relationship may be direct (they have an explicit 336 trust relationship) or transitive (the trust releationship is 337 mediated by one or more entities). The federation relationship is 338 governed by a federation agreement. Within a single federation, 339 there may be multiple Identity Providers as well as multiple 340 Relying Parties. A federation is governed by a federation 341 agreement. 343 Authentication 345 There is a direct relationship between the Client and the Identity 346 Provider by which the entities trust and can securely authenticate 347 each other. 349 A federation agreement typically encompasses operational 350 specifications and legal rules: 352 Operational Specifications: 354 These includes the technical specifications (e.g. protocols used 355 to communicate between the three parties), process standards, 356 policies, identity proofing, credential and authentication 357 algorithm requirements, performance requirements, assessment and 358 audit criteria, etc. The goal of operational specifications is to 359 provide enough definition that the system works and 360 interoperability is possible. 362 Legal Rules: 364 The legal rules take the legal framework into consideration and 365 provides contractual obligations for each entity. The rules 366 define the responsibilities of each party and provide further 367 clarification of the operational specifications. These legal 368 rules regulate the operational specifications, make operational 369 specifications legally binding to the participants, define and 370 govern the rights and responsibilities of the participants. The 371 legal rules may, for example, describe liability for losses, 372 termination rights, enforcement mechanisms, measures of damage, 373 dispute resolution, warranties, etc. 375 The Operational Specifications can demand the usage of a 376 sophisticated technical infrastructure, including requirements on the 377 message routing intermediaries, to offer the required technical 378 functionality. In other environments, the Operational Specifications 379 require fewer technical components in order to meet the required 380 technical functionality. 382 The Legal Rules include many non-technical aspects of federation, 383 such as business practices and legal arrangements, which are outside 384 the scope of the IETF. The Legal Rules can still have an impact the 385 architectural setup or on how to ensure the dynamic establishment of 386 trust. 388 While a federation agreement is often discussed within the context of 389 formal relationships, such as between an enterprise and an employee 390 or a government and a citizen, a federation agreement does not have 391 to require any particular level of formality. For an IdP and a 392 Client, it is sufficient for a relationship to be established by 393 something as simple as using a web form and confirmation email. For 394 an IdP and an RP, it is sufficient for the IdP to publish contact 395 information along with a public key and for the RP to use that data. 396 With in the framework of ABFAB, it will generally be required that a 397 mechanism exists for the IdP to be able to trust the identity of the 398 RP, if this is not present then the IdP cannot provide the assurances 399 to the client that the identity of the RP has been established. 401 The nature of federation dictates that there is some form of 402 relationship between the identity provider and the relying party. 403 This is particularly important when the relying party wants to use 404 information obtained from the identity provider for access management 405 decisions and when the identity provider does not want to release 406 information to every relying party (or only under certain 407 conditions). 409 While it is possible to have a bilateral agreement between every IdP 410 and every RP; on an Internet scale this setup requires the 411 introduction of the multi-lateral federation concept, as the 412 management of such pair-wise relationships would otherwise prove 413 burdensome. 415 The IdP will typically have a long-term relationship with the Client. 416 This relationship typically involves the IdP positively identifying 417 and credentialing the Client (for example, at time of employment 418 within an organization). When dealing with individuals, this process 419 is called identity proofing [NIST-SP.800-63]. The relationship will 420 often be instantiated within an agreement between the IdP and the 421 Client (for example, within an employment contract or terms of use 422 that stipulates the appropriate use of credentials and so forth). 424 The nature and quality of the relationship between the Subject and 425 the IdP is an important contributor to the level of trust that an RP 426 may attribute to an assertion describing a Client made by an IdP. 427 This is sometimes described as the Level of Assurance 428 [NIST-SP.800-63]. 430 Federation does not require an a priori relationship or a long-term 431 relationship between the RP and the Client; it is this property of 432 federation that yields many of its benefits. However, federation 433 does not preclude the possibility of a pre-existing relationship 434 between the RP and the Client, nor that they may use the introduction 435 to create a new long-term relationship independent of the federation. 437 Finally, it is important to reiterate that in some scenarios there 438 might indeed be an Individual behind the Client and in other cases 439 the Client may be autonomous. 441 1.3. Challenges for Contemporary Federation 443 As the number of federated services has proliferated, the role of the 444 individual can become ambiguous in certain circumstances. For 445 example, a school might provide online access for a student's grades 446 to their parents for review, and to the student's teacher for 447 modification. A teacher who is also a parent must clearly 448 distinguish her role upon access. 450 Similarly, as the number of federations proliferates, it becomes 451 increasingly difficult to discover which identity provider(s) a user 452 is associated with. This is true for both the web and non-web case, 453 but is particularly acute for the latter as many non-web 454 authentication systems are not semantically rich enough on their own 455 to allow for such ambiguities. For instance, in the case of an email 456 provider, the use of SMTP and IMAP protocols do not have the ability 457 for the server to get additional information, beyond the clients NAI, 458 in order to provide additional input to decide between multiple 459 federations it may be associated with. However, the building blocks 460 do exist to add this functionality. 462 1.4. An Overview of ABFAB-based Federation 464 The previous section described the general model of federation, and 465 its the application of federated access management. This section 466 provides a brief overview of ABFAB in the context of this model. 468 In this example, a client is attempting to connect to a server in 469 order to either get access to some data or perform some type of 470 transaction. In order for the client to mutually authenticate with 471 the server, the following steps are taken in an ABFAB federated 472 architecture: 474 1. Client Configuration: The Client Application is configured with 475 an NAI assigned by the IdP. It is also configured with any 476 keys, certificates, passwords or other secret and public 477 information needed to run the EAP protocols between it and the 478 IdP. 480 2. Authentication mechanism selection: The GSS-EAP GSS-API 481 mechanism is selected for authentication/authorization. 483 3. Client provides an NAI to RP: The client application sets up a 484 transport to the RP and begins the GSS-EAP authentication. In 485 response, the RP sends an EAP request message (nested in the 486 GSS-EAP protocol) asking for the Client's name. The Client 487 sends an EAP response with an NAI name form that at a minimum, 488 contains the realm portion of it's full NAI. 490 4. Discovery of federated IdP: The RP uses pre-configured 491 information or a federation proxy to determine what IdP to use 492 based on policy and the realm portion of the provided Client 493 NAI. This is discussed in detail below (Section 2.1.2). 495 5. Request from Relying Party to IdP: Once the RP knows who the IdP 496 is, it (or its agent) will send a RADIUS/Diameter request to the 497 IdP. The RADIUS/Diameter access request encapsulates the EAP 498 response. At this stage, the RP will likely have no idea who 499 the client is. The RP sends its identity to the IdP in AAA 500 attributes, and it may send a SAML Attribute Requests in a AAA 501 attribute. The AAA network checks that the identity claimed by 502 the RP is valid. 504 6. IdP begins EAP with the client: The IdP sends an EAP message to 505 the client with an EAP method to be run. The IdP may re-request 506 the clients name in this message, but this is unexpected 507 behavior. The available and appropriate methods are discussed 508 below in this memo (Section 2.2.1). 510 7. The EAP protocol is run: A bunch of EAP messages are passed 511 between the client (EAP peer) and the IdP (EAP server), until 512 the result of the authentication protocol is determined. The 513 number and content of those messages depends on the EAP method 514 selected. If the IdP is unable to authenticate the client, the 515 IdP sends a EAP failure message to the RP. As part of the EAP 516 protocol, the client sends a channel bindings EAP message to the 517 IdP (Section 2.2.2). In the channel binding message the client 518 identifies, among other things, the RP to which it is attempting 519 to authenticate. The IdP checks the channel binding data from 520 the client with that provided by the RP via the AAA protocol. 521 If the bindings do not match the IdP sends an EAP failure 522 message to the RP. 524 8. Successful EAP Authentication: At this point, the IdP (EAP 525 server) and client (EAP peer) have mutually authenticated each 526 other. As a result, the subject and the IdP hold two 527 cryptographic keys: a Master Session Key (MSK), and an Extended 528 MSK (EMSK). At this point the client has a level of assurance 529 about the identity of the RP based on the name checking the IdP 530 has done using the RP naming information from the AAA framework 531 and from the client (by the channel binding data). 533 9. Local IdP Policy Check: At this stage, the IdP checks local 534 policy to determine whether the RP and client are authorized for 535 a given transaction/service, and if so, what if any, attributes 536 will be released to the RP. If the IdP gets a policy failure, 537 it sends an EAP failure message to the RP.[anchor4] (The RP will 538 have done its policy checks during the discovery process.) 540 10. IdP provide the RP with the MSK: The IdP sends a positive result 541 EAP to the RP, along with an optional set of AAA attributes 542 associated with the client (usually as one or more SAML 543 assertions). In addition, the EAP MSK is returned to the RP. 545 11. RP Processes Results: When the RP receives the result from the 546 IdP, it should have enough information to either grant or refuse 547 a resource access request. It may have information that 548 associates the client with specific authorization identities. 549 If additional attributes are needed from the IdP the RP may make 550 a new SAML Request to the IdP. It will apply these results in 551 an application-specific way. 553 12. RP returns results to client: Once the RP has a response it must 554 inform the client application of the result. If all has gone 555 well, all are authenticated, and the application proceeds with 556 appropriate authorization levels. The client can now complete 557 the authentication of the RP by the use of the EAP MSK value. 559 An example communication flow is given below: 561 Relying Client Identity 562 Party App Provider 564 | (1) | Client Configuration 565 | | | 566 |<-----(2)----->| | Mechanism Selection 567 | | | 568 |<-----(3)-----<| | NAI transmitted to RP 569 | | | 570 |<=====(4)====================>| Discovery 571 | | | 572 |>=====(5)====================>| Access request from RP to IdP 573 | | | 574 | |< - - (6) - -<| EAP method to Client 575 | | | 576 | |< - - (7) - ->| EAP Exchange to authenticate 577 | | | Client 578 | | | 579 | | (8 & 9) Local Policy Check 580 | | | 581 |<====(10)====================<| IdP Assertion to RP 582 | | | 583 (11) | | RP processes results 584 | | | 585 |>----(12)----->| | Results to client app. 587 ----- = Between Client App and RP 588 ===== = Between RP and IdP 589 - - - = Between Client App and IdP 591 1.5. Design Goals 593 Our key design goals are as follows: 595 o Each party of a transaction will be authenticated, although 596 perhaps not identified, and the client will be authorized for 597 access to a specific resource. 599 o Means of authentication is decoupled so as to allow for multiple 600 authentication methods. 602 o Hence, the architecture requires no sharing of long term private 603 keys between clients and servers. 605 o The system will scale to large numbers of identity providers, 606 relying parties, and users. 608 o The system will be designed primarily for non-Web-based 609 authentication. 611 o The system will build upon existing standards, components, and 612 operational practices. 614 Designing new three party authentication and authorization protocols 615 is hard and fraught with risk of cryptographic flaws. Achieving 616 widespead deployment is even more difficult. A lot of attention on 617 federated access has been devoted to the Web. This document instead 618 focuses on a non-Web-based environment and focuses on those protocols 619 where HTTP is not used. Despite the increased excitement for 620 layering every protocol on top of HTTP there are still a number of 621 protocols available that do not use HTTP-based transports. Many of 622 these protocols are lacking a native authentication and authorization 623 framework of the style shown in Figure 1. 625 2. Architecture 627 We have already introduced the federated access architecture, with 628 the illustration of the different actors that need to interact, but 629 did not expand on the specifics of providing support for non-Web 630 based applications. This section details this aspect and motivates 631 design decisions. The main theme of the work described in this 632 document is focused on re-using existing building blocks that have 633 been deployed already and to re-arrange them in a novel way. 635 Although this architecture assumes updates to the relying party, the 636 client application, and the Identity Provider, those changes are kept 637 at a minimum. A mechanism that can demonstrate deployment benefits 638 (based on ease of update of existing software, low implementation 639 effort, etc.) is preferred and there may be a need to specify 640 multiple mechanisms to support the range of different deployment 641 scenarios. 643 There are a number of ways for encapsulating EAP into an application 644 protocol. For ease of integration with a wide range of non-Web based 645 application protocols the usage of the GSS-API was chosen. A 646 description of the technical specification can be found in 647 [I-D.ietf-abfab-gss-eap]. Other alternatives exist as well and may 648 be considered later, such as "TLS using EAP Authentication" 649 [I-D.nir-tls-eap]. [anchor7] 651 The architecture consists of several building blocks, which is shown 652 graphically in Figure 2. In the following sections, we discuss the 653 data flow between each of the entities, the protocols used for that 654 data flow and some of the trade-offs made in choosing the protocols. 656 +--------------+ 657 | Identity | 658 | Provider | 659 | (IdP) | 660 +-^----------^-+ 661 * EAP o RADIUS/ 662 * o Diameter 663 --v----------v-- 664 /// \\\ 665 // \\ 666 | Federation | 667 | Substrate | 668 \\ // 669 \\\ /// 670 --^----------^-- 671 * EAP o RADIUS/ 672 * o Diameter 673 +-------------+ +-v----------v--+ 674 | | | | 675 | Client | EAP/EAP Method | Relying Party | 676 | Application |<****************>| (RP) | 677 | | GSS-API | | 678 | |<---------------->| | 679 | | Application | | 680 | | Protocol | | 681 | |<================>| | 682 +-------------+ +---------------+ 684 Legend: 686 <****>: Client-to-IdP Exchange 687 <---->: Client-to-RP Exchange 688 : RP-to-IdP Exchange 689 <====>: Protocol through which GSS-API/GS2 exchanges are tunneled 691 Figure 2: ABFAB Protocol Instantiation 693 2.1. Relying Party to Identity Provider 695 Communications between the Relying Party and the Identity Provider is 696 done by the federation substrate. This communication channel is 697 responsible for: 699 o Establishing the trust relationship between the RP and the IdP. 701 o Determining the rules governing the relationship. 703 o Conveying authentication packets from the client to the IdP and 704 back. 706 o Providing the means of establishing a trust relationship between 707 the RP and the client. 709 o Providing a means for the RP to obtain attributes about the client 710 from the IdP. 712 The ABFAB working group has chosen the AAA framework for the messages 713 transported between the RP and IdP. The AAA framework supports the 714 requirements stated above as follows: 716 o The AAA backbone supplies the trust relationship between the RP 717 and the IdP. 719 o The agreements governing a specific AAA backbone contains the 720 rules governing the relationships within the AAA federation. 722 o A method exists for carrying EAP packets within RADIUS [RFC3579] 723 and Diameter [RFC4072]. 725 o The use of EAP channel binding [RFC6677] along with the core ABFAB 726 protocol provide the pieces necessary to establish the identities 727 of the RP and the client, while EAP provides the cryptographic 728 methods for the RP and the client to validate they are talking to 729 each other. 731 o A method exists for carrying SAML packets within RADIUS 732 [I-D.ietf-abfab-aaa-saml] and Diameter (work in progress) which 733 allows the RP to query attributes about the client from the IdP. 735 Future protocols that support the same framework but do different 736 routing may be used in the future. Once such effort is to setup a 737 framework that creates a trusted point-to-point channel on the fly. 739 2.1.1. AAA, RADIUS and Diameter 741 Interestingly, for network access authentication the usage of the AAA 742 framework with RADIUS [RFC2865] and Diameter [RFC3588] was quite 743 successful from a deployment point of view. To map the terminology 744 used in Figure 1 to the AAA framework the IdP corresponds to the AAA 745 server, the RP corresponds to the AAA client, and the technical 746 building blocks of a federation are AAA proxies, relays and redirect 747 agents (particularly if they are operated by third parties, such as 748 AAA brokers and clearing houses). The front-end, i.e. the end host 749 to AAA client communication, is in case of network access 750 authentication offered by link layer protocols that forward 751 authentication protocol exchanges back-and-forth. An example of a 752 large scale RADIUS-based federation is EDUROAM [2]. 754 By using the AAA framework, ABFAB gets a lot of mileage as many of 755 the federation agreements already exist and merely need to be 756 expanded to cover the ABFAB additions. The AAA framework has already 757 addressed some of the problems outlined above. For example, 759 o It already has a method for routing requests based on a domain. 761 o It already has an extensible architecture allowing for new 762 attributes to be defined and transported. 764 o Pre-existing relationships can be re-used. 766 The astute reader will notice that RADIUS and Diameter have 767 substantially similar characteristics. Why not pick one? RADIUS and 768 Diameter are deployed in different environments. RADIUS can often be 769 found in enterprise and university networks, and is also in use by 770 fixed network operators. Diameter, on the other hand, is deployed by 771 mobile operators. Another key difference is that today RADIUS is 772 largely transported upon UDP. We leave as a deployment decision, 773 which protocol will be appropriate. The protocol defines all the 774 necessary new AAA attributes as RADIUS attributes. A future document 775 would defined the same AAA attributes for a Diameter environment. We 776 also note that there exist proxies which convert from RADIUS to 777 Diameter and back. This makes it possible for both to be deployed in 778 a single federation substrate. 780 Through the integrity protection mechanisms in the AAA framework, the 781 identity provider can establish technical trust that messages are 782 being sent by the appropriate relying party. Any given interaction 783 will be associated with one federation at the policy level. The 784 legal or business relationship defines what statements the identity 785 provider is trusted to make and how these statements are interpreted 786 by the relying party. The AAA framework also permits the relying 787 party or elements between the relying party and identity provider to 788 make statements about the relying party. 790 The AAA framework provides transport for attributes. Statements made 791 about the subject by the identity provider, statements made about the 792 relying party and other information are transported as attributes. 794 One demand that the AAA substrate makes of the upper layers is that 795 they must properly identify the end points of the communication. It 796 must be possible for the AAA client at the RP to determine where to 797 send each RADIUS or Diameter message. Without this requirement, it 798 would be the RP's responsibility to determine the identity of the 799 client on its own, without the assistance of an IdP. This 800 architecture makes use of the Network Access Identifier (NAI), where 801 the IdP is indicated by the realm component [RFC4282]. The NAI is 802 represented and consumed by the GSS-API layer as GSS_C_NT_USER_NAME 803 as specified in [RFC2743]. The GSS-API EAP mechanism includes the 804 NAI in the EAP Response/Identity message. 806 2.1.2. Discovery and Rules Determination 808 While we are using the AAA protocols to communicate with the IdP, the 809 RP may have multiple federation substrates to select from. The RP 810 has a number of criteria that it will use in selecting which of the 811 different federations to use: 813 o The federation selected must be able to communicate with the IdP. 815 o The federation selected must match the business rules and 816 technical policies required for the RP security requirements. 818 The RP needs to discover which federation will be used to contact the 819 IdP. The first selection criteria in discovery is going to be the 820 name of the IdP to be contacted. The second selection criteria in 821 discovery is going to be the set of business rules and technical 822 policies governing the relationship; this is called rules 823 determination. The RP also needs to establish technical trust in the 824 communications with the IdP. 826 Rules determination covers a broad range of decisions about the 827 exchange. One of these is whether the given RP is permitted to talk 828 to the IdP using a given federation at all, so rules determination 829 encompasses the basic authorization decision. Other factors are 830 included, such as what policies govern release of information about 831 the principal to the RP and what policies govern the RP's use of this 832 information. While rules determination is ultimately a business 833 function, it has significant impact on the technical exchanges. The 834 protocols need to communicate the result of authorization. When 835 multiple sets of rules are possible, the protocol must disambiguate 836 which set of rules are in play. Some rules have technical 837 enforcement mechanisms; for example in some federations 838 intermediaries validate information that is being communicated within 839 the federation. 841 At the time of writing no protocol mechanism has been specified to 842 allow a AAA client to determine whether a AAA proxy will indeed be 843 able to route AAA requests to a specific IdP. The AAA routing is 844 impacted by business rules and technical policies that may be quite 845 complex and atpresent time, the route selection is based on manual 846 configuration. 848 2.1.3. Routing and Technical Trust 850 Several approaches to having messages routed through the federation 851 substrate are possible. These routing methods can most easily be 852 classified based on the mechanism for technical trust that is used. 853 The choice of technical trust mechanism constrains how rules 854 determination is implemented. Regardless of what deployment strategy 855 is chosen, it is important that the technical trust mechanism be able 856 to validate the names of both parties to the exchange. The trust 857 mechanism must to ensure that the entity acting as IdP for a given 858 NAI is permitted to be the IdP for that realm, and that any service 859 name claimed by the RP is permitted to be claimed by that entity. 860 Here are the categories of technical trust determination: 862 AAA Proxy: 863 The simplest model is that an RP supports a request directly to an 864 AAA proxy. The hop-by-hop integrity protection of the AAA fabric 865 provides technical trust. An RP can submit a request directly to 866 a federation. Alternatively, a federation disambiguation fabric 867 can be used. Such a fabric takes information about what 868 federations the RP is part of and what federations the IdP is part 869 of and routes a message to the appropriate federation. The 870 routing of messages across the fabric plus attributes added to 871 requests and responses provides rules determination. For example, 872 when a disambiguation fabric routes a message to a given 873 federation, that federation's rules are chosen. Name validation 874 is enforced as messages travel across the fabric. The entities 875 near the RP confirm its identity and validate names it claims. 876 The fabric routes the message towards the appropriate IdP, 877 validating the IdP's name in the process. The routing can be 878 statically configured. Alternatively a routing protocol could be 879 developed to exchange reachability information about given IdPs 880 and to apply policy across the AAA fabric. Such a routing 881 protocol could flood naming constraints to the appropriate points 882 in the fabric. 884 Trust Broker: 885 Instead of routing messages through AAA proxies, some trust broker 886 could establish keys between entities near the RP and entities 887 near the IdP. The advantage of this approach is efficiency of 888 message handling. Fewer entities are needed to be involved for 889 each message. Security may be improved by sending individual 890 messages over fewer hops. Rules determination involves decisions 891 made by trust brokers about what keys to grant. Also, associated 892 with each credential is context about rules and about other 893 aspects of technical trust including names that may be claimed. A 894 routing protocol similar to the one for AAA proxies is likely to 895 be useful to trust brokers in flooding rules and naming 896 constraints. 898 Global Credential: 899 A global credential such as a public key and certificate in a 900 public key infrastructure can be used to establish technical 901 trust. A directory or distributed database such as the Domain 902 Name System is used by the RP to discover the endpoint to contact 903 for a given NAI. Either the database or certificates can provide 904 a place to store information about rules determination and naming 905 constraints. Provided that no intermediates are required (or 906 appear to be required) and that the RP and IdP are sufficient to 907 enforce and determine rules, rules determination is reasonably 908 simple. However applying certain rules is likely to be quite 909 complex. For example if multiple sets of rules are possible 910 between an IdP and RP, confirming the correct set is used may be 911 difficult. This is particularly true if intermediates are 912 involved in making the decision. Also, to the extent that 913 directory information needs to be trusted, rules determination may 914 be more complex. 916 Real-world deployments are likely to be mixtures of these basic 917 approaches. For example, it will be quite common for an RP to route 918 traffic to a AAA proxy within an organization. That proxy could then 919 use any of the three methods to get closer to the IdP. It is also 920 likely that rather than being directly reachable, the IdP may have a 921 proxy on the edge of its organization. Federations will likely 922 provide a traditional AAA proxy interface even if they also provide 923 another mechanism for increased efficiency or security. 925 2.1.4. AAA Security 927 For the AAA framework there are two different places where security 928 needs to be examined. The first is the security that is in place for 929 the links in the AAA backbone being used. The second is the nodes 930 that the backbone consists of. 932 The default link security for RADIUS is showing it's age as it uses 933 MD5 and a shared secret to both obfuscate passwords and to provide 934 integrity on the RADIUS messages. In many environments this is 935 considered to be insufficient, especially as not all attributes are 936 obfuscated and can thus leak information to a passive eavesdropper. 937 The use of RADIUS with TLS [RFC6614] and/or DTLS 938 [I-D.ietf-radext-dtls] addresses these attacks. The same level of 939 security is included in the base Diameter specifications. 941 TBD - Put in text - Not all nodes can be eliminated - proxy nodes may 942 be required Trust router looks for a way to shorten the list of inner 943 nodes. Reference DYNAMIC and say that it does or does not help and 944 why. Talk about Diameter in the same context - does it have the same 945 set of issues or not? 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 IdPs 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 will obviously remove any signatures on the 1000 SAML assertions as they would no longer validate. In this case the 1001 technical trust is the required mechanism for validating the 1002 integrity of the assertion. Finally, the attributes may still be in 1003 the namespace of the originating IdP. When this occurs the RP will 1004 need to get the required mapping operations from the federation 1005 agreements and do the appropriate mappings itself. 1007 As of this writing, no one has defined a SAML name format that 1008 corresponds to the NAI structure defined by RFC 4282 [RFC4282]. This 1009 means that there is no method to directly place the same NAI used in 1010 RADIUS or Diameter as the subject name of a SAML assertion. It is a 1011 requirement on the EAP server that it validate that the subject of 1012 the SAML name, if any, is equivalent to the subject identified by the 1013 NAI used in the RADIUS or Diameter session. 1015 RADIUS has the ability to deal with multiple SAML queries for those 1016 EAP Servers which follow RFC 5080 [RFC5080]. In this case a State 1017 attribute will always been returned with the Access-Accept. The EAP 1018 client can then send a new Access-Request with the State attribute 1019 and the new SAML request Multiple SAML queries can them be done by 1020 making a new Access-Request using the State attribute returned in the 1021 last Access-Accept to link together the different RADIUS sessions. 1023 Some RPs need to ensure that specfic criteria are met during the 1024 authentication process. This need is met by using Levels of 1025 Assurance. The way a Level of Assurance is communicated to from the 1026 RP to the EAP server is by the use of a SAML Authentication Request 1027 using the Authentication Profile from RFC XXX 1028 [I-D.ietf-abfab-aaa-saml] When crossing boundaries between different 1029 federations, either the policy specfied will need to be shared 1030 between the two federations, the policy will need to be mapped by the 1031 proxy server on the boundary or the proxy server on the boundary will 1032 need to supply infomration the EAP server so that it can do the 1033 required mapping. If this mapping is not done, then the EAP server 1034 will not be able to enforce the desired Level of Assurance as it will 1035 not understand the policy requirements. 1037 2.2. Client To Identity Provider 1039 Looking at the communications between the client and the IdP, the 1040 following items need to be dealt with: 1042 o The client and the IdP need to mutually authenticate each other. 1044 o The client and the IdP need to mutually agree on the identity of 1045 the RP. 1047 ABFAB selected EAP for the purposes of mutual authentication and 1048 assisted in creating some new EAP channel binding documents for 1049 dealing with determining the identity of the RP. A framework for the 1050 channel binding mechanism has been defined in RFC 6677 [RFC6677] that 1051 allows the IdP to check the identity of the RP provided by the AAA 1052 framework with that provided by the client. 1054 2.2.1. Extensible Authentication Protocol (EAP) 1056 Traditional web federation does not describe how a subject interacts 1057 with an identity provider for authentication. As a result, this 1058 communication is not standardized. There are several disadvantages 1059 to this approach. Since the communication is not standardized, it is 1060 difficult for machines to correctly enter their credentials with 1061 different authentications, where Individuals can correctly identify 1062 the entyr mechanism on the fly. The use of browsers for 1063 authentication restricts the deployment of more secure forms of 1064 authentication beyond plaintext username and password known by the 1065 server. In a number of cases the authentication interface may be 1066 presented before the subject has adequately validated they are 1067 talking to the intended server. By giving control of the 1068 authentication interface to a potential attacker, then the security 1069 of the system may be reduced and phishing opportunities introduced. 1071 As a result, it is desirable to choose some standardized approach for 1072 communication between the subject's end-host and the identity 1073 provider. There are a number of requirements this approach must 1074 meet. 1076 Experience has taught us one key security and scalability 1077 requirement: it is important that the relying party not get 1078 possession of the long-term secret of the client. Aside from a 1079 valuable secret being exposed, a synchronization problem can develop 1080 when the client changes keys with the IdP. 1082 Since there is no single authentication mechanism that will be used 1083 everywhere there is another associated requirement: The 1084 authentication framework must allow for the flexible integration of 1085 authentication mechanisms. For instance, some IdPs require hardware 1086 tokens while others use passwords. A service provider wants to 1087 provide support for both authentication methods, and other methods 1088 from IdPs not yet seen. 1090 Fortunately, these requirements can be met by utilizing standardized 1091 and successfully deployed technology, namely by the Extensible 1092 Authentication Protocol (EAP) framework [RFC3748]. Figure 2 1093 illustrates the integration graphically. 1095 EAP is an end-to-end framework; it provides for two-way communication 1096 between a peer (i.e,service client or principal) through the 1097 authenticator (i.e., service provider) to the back-end (i.e., 1098 identity provider). Conveniently, this is precisely the 1099 communication path that is needed for federated identity. Although 1100 EAP support is already integrated in AAA systems (see [RFC3579] and 1101 [RFC4072]) several challenges remain: 1103 o The first is how to carry EAP payloads from the end host to the 1104 relying party. 1106 o Another is to verify statements the relying party has made to the 1107 subject, confirm these statements are consistent with statements 1108 made to the identity provider and confirm all the above are 1109 consistent with the federation and any federation-specific policy 1110 or configuration. 1112 o Another challenge is choosing which identity provider to use for 1113 which service. 1115 The EAP method used for ABFAB needs to meet the following 1116 requirements: 1118 o It needs to provide mutual authentication of the client and IdP. 1120 o It needs to support channel binding. 1122 As of this writing, the only EAP method that meets these criteria is 1123 TEAP [I-D.ietf-emu-eap-tunnel-method] either alone (if client 1124 certificates are used) or with an inner EAP method that does mutual 1125 authentication. 1127 2.2.2. EAP Channel Binding 1129 EAP channel binding is easily confused with a facility in GSS-API 1130 also called channel binding. GSS-API channel binding provides 1131 protection against man-in-the-middle attacks when GSS-API is used as 1132 authentication inside some tunnel; it is similar to a facility called 1133 cryptographic binding in EAP. See [RFC5056] for a discussion of the 1134 differences between these two facilities and Section 6.1 for how GSS- 1135 API channel binding is handled in this mechanism. 1137 The client knows, in theory, the name of the RP that it attempted to 1138 connect to, however in the event that an attacker has intercepted the 1139 protocol, the client and the IdP need to be able to detect this 1140 situation. A general overview of the problem along with a 1141 recommended way to deal with the channel binding issues can be found 1142 in RFC 6677 [RFC6677]. 1144 Since that document was published, a number of possible attacks were 1145 found and methods to address these attacks have been outlined in 1146 [I-D.ietf-emu-crypto-bind]. 1148 2.3. Client to Relying Party 1150 The final set of interactions between parties to consider are those 1151 between the client and the RP. In some ways this is the most complex 1152 set since at least part of it is outside the scope of the ABFAB work. 1153 The interactions between these parties include: 1155 o Running the protocol that implements the service that is provided 1156 by the RP and desired by the client. 1158 o Authenticating the client to the RP and the RP to the client. 1160 o Providing the necessary security services to the service protocol 1161 that it needs beyond authentication. 1163 o Deal with client re-authentication where desired. 1165 2.3.1. GSS-API 1167 One of the remaining layers is responsible for integration of 1168 federated authentication into the application. There are a number of 1169 approaches that applications have adopted for security. So, there 1170 may need to be multiple strategies for integration of federated 1171 authentication into applications. However, we have started with a 1172 strategy that provides integration to a large number of application 1173 protocols. 1175 Many applications such as SSH [RFC4462], NFS [RFC2203], DNS [RFC3645] 1176 and several non-IETF applications support the Generic Security 1177 Services Application Programming Interface [RFC2743]. Many 1178 applications such as IMAP, SMTP, XMPP and LDAP support the Simple 1179 Authentication and Security Layer (SASL) [RFC4422] framework. These 1180 two approaches work together nicely: by creating a GSS-API mechanism, 1181 SASL integration is also addressed. In effect, using a GSS-API 1182 mechanism with SASL simply requires placing some headers on the front 1183 of the mechanism and constraining certain GSS-API options. 1185 GSS-API is specified in terms of an abstract set of operations which 1186 can be mapped into a programming language to form an API. When 1187 people are first introduced to GSS-API, they focus on it as an API. 1188 However, from the prospective of authentication for non-web 1189 applications, GSS-API should be thought of as a protocol not an API. 1190 It consists of some abstract operations such as the initial context 1191 exchange, which includes two sub-operations (gss_init_sec_context and 1192 gss_accept_sec_context). An application defines which abstract 1193 operations it is going to use and where messages produced by these 1194 operations fit into the application architecture. A GSS-API 1195 mechanism will define what actual protocol messages result from that 1196 abstract message for a given abstract operation. So, since this work 1197 is focusing on a particular GSS-API mechanism, we generally focus on 1198 protocol elements rather than the API view of GSS-API. 1200 The API view has significant value. Since the abstract operations 1201 are well defined, the set of information that a mechanism gets from 1202 the application is well defined. Also, the set of assumptions the 1203 application is permitted to make is generally well defined. As a 1204 result, an application protocol that supports GSS-API or SASL is very 1205 likely to be usable with a new approach to authentication including 1206 this one with no required modifications. In some cases, support for 1207 a new authentication mechanism has been added using plugin interfaces 1208 to applications without the application being modified at all. Even 1209 when modifications are required, they can often be limited to 1210 supporting a new naming and authorization model. For example, this 1211 work focuses on privacy; an application that assumes it will always 1212 obtain an identifier for the principal will need to be modified to 1213 support anonymity, unlinkability or pseudonymity. 1215 So, we use GSS-API and SASL because a number of the application 1216 protocols we wish to federate support these strategies for security 1217 integration. What does this mean from a protocol standpoint and how 1218 does this relate to other layers? This means we need to design a 1219 concrete GSS-API mechanism. We have chosen to use a GSS-API 1220 mechanism that encapsulates EAP authentication. So, GSS-API (and 1221 SASL) encapsulate EAP between the end-host and the service. The AAA 1222 framework encapsulates EAP between the relying party and the identity 1223 provider. The GSS-API mechanism includes rules about how principals 1224 and services are named as well as per-message security and other 1225 facilities required by the applications we wish to support. 1227 2.3.2. Protocol Transport 1229 The transport of data between the client and the relying party is not 1230 provided by GSS-API. GSS-API creates and consumes messages, but it 1231 does not provide the transport itself, instead the protocol using 1232 GSS-API needs to provide the transport. In many cases HTTP or HTTPS 1233 is used for this transport, but other transports are perfectly 1234 acceptable. The core GSS-API document [RFC2743] provides some 1235 details on what requirements exist. 1237 In addition we highlight the following: 1239 o The transport does not need to provide either privacy or 1240 integrity. After GSS-EAP has finished negotiation, GSS-API can be 1241 used to provide both services. If the negotiation process itself 1242 needs protection from eavesdroppers then the transport would need 1243 to provide the necessary services. 1245 o The transport needs to provide reliable transport of the messages. 1247 o The transport needs to ensure that tokens are delivered in order 1248 during the negotiation process. 1250 o GSS-API messages need to be delivered atomically. If the 1251 transport breaks up a message it must also reassemble the message 1252 before delivery. 1254 2.3.3. Reauthentication 1256 TBD. 1258 3. Application Security Services 1260 One of the key goals is to integrate federated authentication into 1261 existing application protocols and where possible, existing 1262 implementations of these protocols. Another goal is to perform this 1263 integration while meeting the best security practices of the 1264 technologies used to perform the integration. This section describes 1265 security services and properties required by the EAP GSS-API 1266 mechanism in order to meet these goals. This information could be 1267 viewed as specific to that mechanism. However, other future 1268 application integration strategies are very likely to need similar 1269 services. So, it is likely that these services will be expanded 1270 across application integration strategies if new application 1271 integration strategies are adopted. 1273 3.1. Authentication 1275 GSS-API provides an optional security service called mutual 1276 authentication. This service means that in addition to the initiator 1277 providing (potentially anonymous or pseudonymous) identity to the 1278 acceptor, the acceptor confirms its identity to the initiator. 1279 Especially for the ABFAB context, this service is confusingly named. 1280 We still say that mutual authentication is provided when the identity 1281 of an acceptor is strongly authenticated to an anonymous initiator. 1283 RFC 2743, unfortunately, does not explicitly talk about what mutual 1284 authentication means. Within this document we therefore define it 1285 as: 1287 o If a target name is configured for the initiator, then the 1288 initiator trusts that the supplied target name describes the 1289 acceptor. This implies both that appropriate cryptographic 1290 exchanges took place for the initiator to make such a trust 1291 decision, and that after evaluating the results of these 1292 exchanges, the initiator's policy trusts that the target name is 1293 accurate. 1295 o If no target name is configured for the initiator, then the 1296 initiator trusts that the acceptor name, supplied by the acceptor, 1297 correctly names the entity it is communicating with. 1299 o Both the initiator and acceptor have the same key material for 1300 per-message keys and both parties have confirmed they actually 1301 have the key material. In EAP terms, there is a protected 1302 indication of success. 1304 Mutual authentication is an important defense against certain aspects 1305 of phishing. Intuitively, clients would like to assume that if some 1306 party asks for their credentials as part of authentication, 1307 successfully gaining access to the resource means that they are 1308 talking to the expected party. Without mutual authentication, the 1309 server could "grant access" regardless of what credentials are 1310 supplied. Mutual authentication better matches this user intuition. 1312 It is important, therefore, that the GSS-EAP mechanism implement 1313 mutual authentication. That is, an initiator needs to be able to 1314 request mutual authentication. When mutual authentication is 1315 requested, only EAP methods capable of providing the necessary 1316 service can be used, and appropriate steps need to be taken to 1317 provide mutual authentication. While a broader set of EAP methods 1318 could be supported by not requiring mutual authentication, it was 1319 decided that the client needs to always have the ability to request 1320 it. In some cases the IdP and the RP will not support mutual 1321 authentication, however the client will always be able to detect this 1322 and make an appropriate security decision. 1324 The AAA infrastructure MAY hide the initiator's identity from the 1325 GSS-API acceptor, providing anonymity between the initiator and the 1326 acceptor. At this time, whether the identity is disclosed is 1327 determined by EAP server policy rather than by an indication from the 1328 initiator. Also, initiators are unlikely to be able to determine 1329 whether anonymous communication will be provided. For this reason, 1330 initiators are unlikely to set the anonymous return flag from 1331 GSS_Init_Sec_context. 1333 3.2. GSS-API Channel Binding 1335 [RFC5056] defines a concept of channel binding to which is used 1336 prevent man-in-the-middle attacks. The channel binding works by 1337 taking a cryptographic value from the transport security and checks 1338 that both sides of the GSS-API conversation know this value. 1339 Transport Layer Security (TLS) is the most common transport security 1340 layer used for this purpose. 1342 It needs to be stressed that RFC 5056 channel binding (also called 1343 GSS-API channel binding when GSS-API is involved) is not the same 1344 thing as EAP channel binding. GSS-API channel binding is used for 1345 detecting Man-In-The-Middle attacks. EAP channel binding is used for 1346 mututal authentication and acceptor naming checks. Details are 1347 discussed in the mechanisms specification [I-D.ietf-abfab-gss-eap]. 1348 A fuller discription of the differences between the factilities cn be 1349 found in RFC 5056 [RFC5056]. 1351 The use of TLS can provide both encryption and integrity on the 1352 channel. It is common to provide SASL and GSS-API with these other 1353 security services. 1355 On of the benifits that the use of TLS provides, is that client has 1356 the ability to validate the name of the server. However this 1357 validation is predicated on on a couple of things. The TLS sessions 1358 needs to be using certificates and not be an anonymous session. The 1359 client and the TLS need to share a common trust point for the 1360 certificate used in validating the server. TLS provides its own 1361 server authentication. However there are a variety of situations 1362 where this authentication is not checked for policy or usability 1363 reasons. Even when it is checked, if the trust infrastructure behind 1364 the TLS authentication is different from the trust infrastructure 1365 behind the GSS-API mutual authentication then confirming the end- 1366 points using both trust infrastructures is likely to enhance 1367 security. If the endpoints of the GSS-API authentication are 1368 different than the endpoints of the lower layer, this is a strong 1369 indication of a problem such as a man-in-the-middle attack. Channel 1370 binding provides a facility to determine whether these endpoints are 1371 the same. 1373 The GSS-EAP mechanism needs to support channel binding. When an 1374 application provides channel binding data, the mechanism needs to 1375 confirm this is the same on both sides consistent with the GSS-API 1376 specification. 1378 3.3. Host-Based Service Names 1380 IETF security mechanisms typically take a host name and perhaps a 1381 service, entered by a user, and make some trust decision about 1382 whether the remote party in the interaction is the intended party. 1383 This decision can be made by the use of certificates, pre-configured 1384 key information or a previous leap of trust. GSS-API has defined a 1385 relatively flexible name convention, however most of the IETF 1386 applications that use GSS-API (including SSH, NFS, IMAP, LDAP and 1387 XMPP) have chosen to use a more restricted naming convention based on 1388 the host name. The GSS-EAP mechanism needs to support host-based 1389 service names in order to work with existing IETF protocols. 1391 The use of host-based service names leads to a challenging trust 1392 delegation problem. Who is allowed to decide whether a particular 1393 host name maps to a specific entity. Possible solutions to this 1394 problem have been looked at. 1396 The public-key infrastructure (PKI) used by the web has chosen to 1397 have a number of trust anchors (root certificate authorities) each 1398 of which can map any host name to a public key. 1400 A number of GSS-API mechanisms, such as Kerberos [RFC1964], have 1401 split the problem into two parts. A new concept called a realm is 1402 introduced, the realm is responsible for host mapping within that 1403 realm. The mechanism then decides what realm is responsible for a 1404 given name. This is the approach adopted by ABFAB. 1406 GSS-EAP defines a host naming convention that takes into account the 1407 host name, the realm, the service and the service parameters. An 1408 example of GSS-API service name is "xmpp/foo@example.com". This 1409 identifies the XMPP service on the host foo in the realm example.com. 1410 Any of the components, except for the service name may be omitted 1411 from a name. When omitted, then a local default would be used for 1412 that component of the name. 1414 While there is no requirement that realm names map to Fully Qualified 1415 Domain Names (FQDN) within DNS, in practice this is normally true. 1416 Doing so allows for the realm portion of service names and the 1417 portion of NAIs to be the same. It also allows for the use of DNS in 1418 locating the host of a service while establishing the transport 1419 channel between the client and the relying party. 1421 It is the responsibility of the application to determine the server 1422 that it is going to communicate with, GSS-API has the ability to help 1423 confirm that the server is the desired server but not to determine 1424 the name of the server to use. It is also the responsibility of the 1425 application to determine how much of the information identifying the 1426 service needs to be validated by the ABFAB system. The information 1427 that needs to be validated is used to build up the service name 1428 passed into the GSS-EAP mechanism. What information is to be 1429 validated will depend on both what information was provided by the 1430 client, and what information is considered significant. If the 1431 client only cares about getting a specific service, then the host and 1432 realm that provides the service does not need to be validated. 1434 In many cases applications may retrieve information about providers 1435 of services from DNS. When Service Records (SRV) and Naming 1436 Authority Pointer (NAPTR) records are used to help find a host that 1437 provides a service, the security requirements on the referrals is 1438 going to interact with the information used in the service name. If 1439 the a host name is returned from the DNS referrals, and the host name 1440 is to be validated by GS-EAP, then it makes sense that the referrals 1441 themselves should be secure. On the other hand, if the host name 1442 returned is not validated, i.e. only the service is passed in, then 1443 it is less important that the host name be obtained in a secure 1444 manner. 1446 Another issue that needs to be addressed for host-based service names 1447 is that they do not work ideally when different instances of a 1448 service are running on different ports. If the services are 1449 equivalent, then it does not matter. However if there are 1450 substantial differences in the quality of the service that 1451 information needs to be part of the validation process. If one has 1452 just a host name and not a port in the information being validated, 1453 then this is not going to be a successful strategy. 1455 3.4. Additional GSS-API Services 1457 GSS-API provides per-message security services that can provide 1458 confidentiality and/or integrity. Some IETF protocols such as NFS 1459 and SSH take advantage of these services. As a result GSS-EAP needs 1460 to support these services. As with mutual authentication, per- 1461 message services will limit the set of EAP methods that can be used 1462 to those that generate a Master Session Key (MSK). Any EAP method 1463 that produces an MSK is able to support per-message security services 1464 described in [RFC2743]. 1466 GSS-API provides a pseudo-random function. This function generates a 1467 pseudo-random sequence using the shared private key as the seed for 1468 the bytes generated. This provides an algorithm that both the 1469 initiator and acceptor can run in order to arrive at the same key 1470 value. The use of this feature allows for an application to generate 1471 keys or other shared secrets for use in other places in the protocol. 1472 In this regards, it is similar in concept to the TLS extractor (RFC 1473 5705 [RFC5705].). While no current IETF protocols require this, non- 1474 IETF protocols are expected to take advantage of this in the near 1475 future. Additionally, a number of protocols have found the TLS 1476 extractor to be useful in this regards so it is highly probably that 1477 IETF protocols may also start using this feature. 1479 4. Privacy Considerations 1481 ABFAB, as an architecture designed to enable federated authentication 1482 and allow for the secure transmission of identity information between 1483 entities, obviously requires careful consideration around privacy and 1484 the potential for privacy violations. 1486 This section examines the privacy related information presented in 1487 this document, summarising the entities that are involved in ABFAB 1488 communications and what exposure they have to identity information. 1489 In discussing these privacy considerations in this section, we use 1490 terminology and ideas from [I-D.iab-privacy-considerations]. 1492 Note that the ABFAB architecture uses at its core several existing 1493 technologies and protocols; detailed privacy discussion around these 1494 is not examined. This section instead focuses on privacy 1495 considerations specifically related to overall architecture and usage 1496 of ABFAB. 1498 4.1. Entities and their roles 1500 In an ABFAB environment, there are four distinct types of entities 1501 involved in communication paths. Figure 2 shows the ABFAB 1502 architecture with these entity types. We have: 1504 o The client application: usually a piece of software running on a 1505 user's device. This communicates with a service (the Relying 1506 Party) that the user wishes to interact with. 1508 o The Identity Provider: The home AAA server for the user. 1510 o The Relying Party: The service the user wishes to connect to. 1512 o The federation substrate: A set of entities through which messages 1513 pass on their path between RP and AAA server. 1515 As described in detail earlier in this document, when a user wishes 1516 to access a Relying Party, a secure tunnel is set up between their 1517 client application and their Identity Provider (via the Relying Party 1518 and the federation substrate) through which credentials are 1519 exchanged. An indication of success or failure, alongside a set of 1520 AAA attributes about a principal is then passed from the Identity 1521 Provider to the Relying Party (usually in the form of a SAML 1522 assertion). 1524 4.2. Relationship between user and entities 1526 o Between User and Identity Provider - the identity Provider is an 1527 entity the user will have a direct relationship with, created when 1528 the organisation that operates the entity provisioned and 1529 exchanged the user's credentials. Privacy and data protection 1530 guarantees may form a part of this relationship. 1532 o Between User and Relying Party - the Relying Party is an entity 1533 the user may or may not have a direct relationship with, depending 1534 on the service in question. Some services may only be offered to 1535 those users where such a direct relationship exists (for 1536 particularly sensitive services, for example), while some may not 1537 require this and would instead be satisfied with basic federation 1538 trust guarantees between themselves and the Identity Provider). 1539 This may well include the option that the user stays anonymous 1540 with respect to the Relying Party (though obviously not to the 1541 Identity Provider). If attempting to preserve privacy through the 1542 mitigation of data minimisation, then the only attribute 1543 information about individuals exposed to the Relying Party should 1544 be that which is strictly necessary for the operation of the 1545 service. 1547 o Between User and Federation substrate - the user is highly likely 1548 to have no knowledge of, or relationship with, any entities 1549 involved with the federation substrate (not that the Identity 1550 Provider and/or Relying Party may, however). Knowledge of 1551 attribute information about individuals for these entities is not 1552 necessary, and thus such information should be protected in such a 1553 way as to prevent access to this information from being possible. 1555 4.3. Data and Identifiers in use 1557 In the ABFAB architecture, there are a few different types of data 1558 and identifiers in use. 1560 4.3.1. NAI 1562 In order for the Relying Party to be able to route messages to enable 1563 an EAP transaction to occur between client application and the 1564 correct identity Provider, it is necessary for the client application 1565 to provide enough information to the Relying Party to enable the 1566 identification of the correct Identity Provider. This takes the form 1567 of an Network Access Identifier (NAI) (as specified in [RFC4282]). 1568 Note that an NAI can have inner and outer forms in a AAA 1569 architecture. 1571 o The outer part of NAI is exposed to the Relying Party; this can 1572 simply contain realm information. Doing so (i.e. not including 1573 user identification details such as a username) minimises the data 1574 given to the Relying Part to that which is purely necessary to 1575 support the necessary routing decision. 1577 o The inner part of NAI is sent through the secure tunnel as 1578 established by the EAP protocol; this form of the NAI will contain 1579 credentials for the user suitable for authenticating them 1580 successfully (e.g. a username and password). Since the entire 1581 purpose of the secure tunnel is to protect communications between 1582 client application (EAP client) and Identity Provider (EAP 1583 server), then it is considered secure from eavesdroppers or 1584 malicious intermediaries and no further privacy discussion is 1585 necessary. 1587 4.3.2. Identity Information 1589 As a part of the ABFAB process, after a successful authentication has 1590 occurred between client application and Identity Provider, an 1591 indication of this success is sent to the Relying Party. Alongside 1592 this message, information about the user may be returned through AAA 1593 attributes, usually in form of a SAML assertion. This information is 1594 arbitrary and may include either only attributes that prevent an 1595 individual from being identified by the Relying Party (thus enabling 1596 anonymous or pseudonymous access) or attributes that contain 1597 personally identifiable information. 1599 Depending on the method used, this information carried through AAA 1600 attributes may or may not be accessible to intermediaries involved in 1601 communications - e.g. in the case of RADIUS and unencrypted SAML, 1602 these headers are plain text and could be seen by any observer, 1603 whereas if using RADSEC or encrypted SAML, these headers are 1604 protected from observers. Obviously, where the protection of the 1605 privacy of an individual is required then this information needs to 1606 be protected by some appropriate means. 1608 4.3.3. Accounting Information 1610 Alongside the core authentication and authorization that occurs in 1611 AAA communications, accounting information about resource consumption 1612 may be delivered as part of the accounting exchange during the 1613 lifetime of the granted application session. 1615 4.3.4. Collection and retention of data and identifiers 1617 In cases where Relying Parties do not require to identify a 1618 particular individual when an individual wishes to make use of their 1619 service, the ABFAB architecture enable anonymous or pseudonymous 1620 access. Thus data and identifiers other than pseudonyms and 1621 unlinkable attribute information need not be stored and retained. 1623 However, in cases where Relying Parties require the ability to 1624 identify a particular individual (e.g. so they can link this identity 1625 information to a particular account in their service, or where 1626 identity information is required for audit purposes), the service 1627 will need to collect and store such information, and to retain it for 1628 as long as they require. Deprovisioning of such accounts and 1629 information is out of scope for ABFAB, but obviously for privacy 1630 protection any identifiers collected should be deleted when they are 1631 no longer needed. 1633 4.4. User Participation 1635 In the ABFAB architecture, by its very nature users are active 1636 participants in the sharing of their identifiers as they initiate the 1637 communications exchange every time they wish to access a server. 1638 They are, however, not involved in control of the set of information 1639 related to them that transmitted from Identity Provider to Relying 1640 Party for authorisation purposes. 1642 5. Deployment Considerations 1644 5.1. EAP Channel Binding 1646 Discuss the implications of needing EAP channel binding. 1648 5.2. AAA Proxy Behavior 1650 Discuss deployment implications of our proxy requirements. 1652 6. Security Considerations 1654 This document describes the architecture for Application Bridging for 1655 Federated Access Beyond Web (ABFAB) and security is therefore the 1656 main focus. This section highlights the main communication channels 1657 and their security properties: 1659 Client-to-RP Channel: 1661 The channel binding material is provided by any certificates and 1662 the final message (i.e., a cryptographic token for the channel). 1663 Authentication may be provided by the RP to the client but a 1664 deployment without authentication at the TLS layer is possible as 1665 well. In addition, there is a channel between the GSS requestor 1666 and the GSS acceptor, but the keying material is provided by a 1667 "third party" to both entities. The client can derive keying 1668 material locally, but the RP gets the material from the IdP. In 1669 the absence of a transport that provides encryption and/or 1670 integrity, the channel between the client and the RP has no 1671 ability to have any cryptographic protection until the EAP 1672 authentication has been completed and the MSK is transfered from 1673 the IdP to the RP. 1675 RP-to-IdP Channel: 1677 The security of this communication channel is mainly provided by 1678 the functionality offered via RADIUS and Diameter. At the time of 1679 writing there are no end-to-end security mechanisms standardized 1680 and thereby the architecture has to rely on hop-by-hop security 1681 with trusted AAA entities or, as an alternative but possible 1682 deployment variant, direct communication between the AAA client to 1683 the AAA server. Note that the authorization result the IdP 1684 provides to the RP in the form of a SAML assertion may, however, 1685 be protected such that the SAML related components are secured 1686 end-to-end. 1688 The MSK is transported from the IdP to the RP over this channel. 1689 As no end-to-end security is provided by AAA, all AAA entities on 1690 the path between the RP and IdP have the ability to eavesdrop if 1691 no additional security measures are taken. One such measure is to 1692 use a transport between the client and the IdP that provides 1693 confidentiality. 1695 Client-to-IdP Channel: 1697 This communication interaction is accomplished with the help of 1698 EAP and EAP methods. The offered security protection will depend 1699 on the EAP method that is chosen but a minimum requirement is to 1700 offer mutual authentication, and key derivation. The IdP is 1701 responsible during this process to determine that the RP that is 1702 communication to the client over the RP-to-IdP channel is the same 1703 one talking to the IdP. This is accomplished via the EAP channel 1704 binding. 1706 Partial list of issues to be addressed in this section: Privacy, 1707 SAML, Trust Anchors, EAP Algorithm Selection, Diameter/RADIUS/AAA 1708 Issues, Naming of Entities, Protection of passwords, Channel Binding, 1709 End-point-connections (TLS), Proxy problems 1711 When a psuedonym is generated as a unique long term identifier for a 1712 Subject by an IdP, care MUST be taken in the algorithm that it cannot 1713 easily be reverse engineered by the service provider. If it can be 1714 reversed then the service provider can consult an oracle to determine 1715 if a given unique long term identifier is associated with a different 1716 known identifier. 1718 7. IANA Considerations 1720 This document does not require actions by IANA. 1722 8. Acknowledgments 1724 We would like to thank Mayutan Arumaithurai and Klaas Wierenga for 1725 their feedback. Additionally, we would like to thank Eve Maler, 1726 Nicolas Williams, Bob Morgan, Scott Cantor, Jim Fenton, Paul Leach, 1727 and Luke Howard for their feedback on the federation terminology 1728 question. 1730 Furthermore, we would like to thank Klaas Wierenga for his review of 1731 the pre-00 draft version. 1733 9. References 1735 9.1. Normative References 1737 [RFC2743] Linn, J., "Generic Security Service Application Program 1738 Interface Version 2, Update 1", RFC 2743, January 2000. 1740 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 1741 "Remote Authentication Dial In User Service (RADIUS)", 1742 RFC 2865, June 2000. 1744 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 1745 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 1747 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 1748 Levkowetz, "Extensible Authentication Protocol (EAP)", 1749 RFC 3748, June 2004. 1751 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 1752 Dial In User Service) Support For Extensible 1753 Authentication Protocol (EAP)", RFC 3579, September 2003. 1755 [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 1756 Authentication Protocol (EAP) Application", RFC 4072, 1757 August 2005. 1759 [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The 1760 Network Access Identifier", RFC 4282, December 2005. 1762 [I-D.ietf-abfab-gss-eap] 1763 Hartman, S. and J. Howlett, "A GSS-API Mechanism for the 1764 Extensible Authentication Protocol", 1765 draft-ietf-abfab-gss-eap-09 (work in progress), 1766 August 2012. 1768 [I-D.ietf-abfab-aaa-saml] 1769 Howlett, J. and S. Hartman, "A RADIUS Attribute, Binding 1770 and Profiles for SAML", draft-ietf-abfab-aaa-saml-04 (work 1771 in progress), October 2012. 1773 [RFC6677] Hartman, S., Clancy, T., and K. Hoeper, "Channel-Binding 1774 Support for Extensible Authentication Protocol (EAP) 1775 Methods", RFC 6677, July 2012. 1777 9.2. Informative References 1779 [RFC2903] de Laat, C., Gross, G., Gommans, L., Vollbrecht, J., and 1780 D. Spence, "Generic AAA Architecture", RFC 2903, 1781 August 2000. 1783 [I-D.nir-tls-eap] 1784 Nir, Y., Sheffer, Y., Tschofenig, H., and P. Gutmann, "A 1785 Flexible Authentication Framework for the Transport Layer 1786 Security (TLS) Protocol using the Extensible 1787 Authentication Protocol (EAP)", draft-nir-tls-eap-13 (work 1788 in progress), December 2011. 1790 [I-D.ietf-oauth-v2] 1791 Hardt, D., "The OAuth 2.0 Authorization Framework", 1792 draft-ietf-oauth-v2-31 (work in progress), August 2012. 1794 [I-D.iab-privacy-considerations] 1795 Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1796 Morris, J., Hansen, M., and R. Smith, "Privacy 1797 Considerations for Internet Protocols", 1798 draft-iab-privacy-considerations-03 (work in progress), 1799 July 2012. 1801 [I-D.perez-radext-radius-fragmentation] 1802 Perez-Mendez, A., Lopez, R., Pereniguez-Garcia, F., Lopez- 1803 Millan, G., Lopez, D., and A. DeKok, "Support of 1804 fragmentation of RADIUS packets", 1805 draft-perez-radext-radius-fragmentation-05 (work in 1806 progress), February 2013. 1808 [RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible 1809 Authentication Protocol (EAP) Method Requirements for 1810 Wireless LANs", RFC 4017, March 2005. 1812 [RFC5106] Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y., 1813 and F. Bersani, "The Extensible Authentication Protocol- 1814 Internet Key Exchange Protocol version 2 (EAP-IKEv2) 1815 Method", RFC 5106, February 2008. 1817 [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", 1818 RFC 1964, June 1996. 1820 [RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol 1821 Specification", RFC 2203, September 1997. 1823 [RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J., 1824 and R. Hall, "Generic Security Service Algorithm for 1825 Secret Key Transaction Authentication for DNS (GSS-TSIG)", 1826 RFC 3645, October 2003. 1828 [RFC2138] Rigney, C., Rigney, C., Rubens, A., Simpson, W., and S. 1830 Willens, "Remote Authentication Dial In User Service 1831 (RADIUS)", RFC 2138, April 1997. 1833 [RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch, 1834 "Generic Security Service Application Program Interface 1835 (GSS-API) Authentication and Key Exchange for the Secure 1836 Shell (SSH) Protocol", RFC 4462, May 2006. 1838 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 1839 Security Layer (SASL)", RFC 4422, June 2006. 1841 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 1842 Channels", RFC 5056, November 2007. 1844 [RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication 1845 Dial In User Service (RADIUS) Implementation Issues and 1846 Suggested Fixes", RFC 5080, December 2007. 1848 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 1849 Layer Security (TLS)", RFC 5705, March 2010. 1851 [RFC5801] Josefsson, S. and N. Williams, "Using Generic Security 1852 Service Application Program Interface (GSS-API) Mechanisms 1853 in Simple Authentication and Security Layer (SASL): The 1854 GS2 Mechanism Family", RFC 5801, July 2010. 1856 [RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849, 1857 April 2010. 1859 [RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga, 1860 "Transport Layer Security (TLS) Encryption for RADIUS", 1861 RFC 6614, May 2012. 1863 [OASIS.saml-core-2.0-os] 1864 Cantor, S., Kemp, J., Philpott, R., and E. Maler, 1865 "Assertions and Protocol for the OASIS Security Assertion 1866 Markup Language (SAML) V2.0", OASIS Standard saml-core- 1867 2.0-os, March 2005. 1869 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 1870 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 1871 D. Spence, "AAA Authorization Framework", RFC 2904, 1872 August 2000. 1874 [I-D.ietf-emu-crypto-bind] 1875 Hartman, S., Wasserman, M., and D. Zhang, "EAP Mutual 1876 Cryptographic Binding", draft-ietf-emu-crypto-bind-02 1877 (work in progress), February 2013. 1879 [I-D.ietf-emu-eap-tunnel-method] 1880 Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna, 1881 "Tunnel EAP Method (TEAP) Version 1", 1882 draft-ietf-emu-eap-tunnel-method-05 (work in progress), 1883 February 2013. 1885 [I-D.ietf-radext-dtls] 1886 DeKok, A., "DTLS as a Transport Layer for RADIUS", 1887 draft-ietf-radext-dtls-03 (work in progress), 1888 January 2013. 1890 [WS-TRUST] 1891 Lawrence, K., Kaler, C., Nadalin, A., Goodner, M., Gudgin, 1892 M., Barbir, A., and H. Granqvist, "WS-Trust 1.4", OASIS 1893 Standard ws-trust-200902, February 2009, . 1896 [NIST-SP.800-63] 1897 Burr, W., Dodson, D., and W. Polk, "Electronic 1898 Authentication Guideline", NIST Special 1899 Publication 800-63, April 2006. 1901 URIs 1903 [1] 1905 [2] 1907 Editorial Comments 1909 [anchor4] JLS: Should this be an EAP failure to the client as well? 1911 [anchor7] JLS: I don't believe this is a true statement - check it 1912 with Josh and Sam. 1914 Authors' Addresses 1916 Josh Howlett 1917 JANET(UK) 1918 Lumen House, Library Avenue, Harwell 1919 Oxford OX11 0SG 1920 UK 1922 Phone: +44 1235 822363 1923 Email: Josh.Howlett@ja.net 1925 Sam Hartman 1926 Painless Security 1928 Phone: 1929 Email: hartmans-ietf@mit.edu 1931 Hannes Tschofenig 1932 Nokia Siemens Networks 1933 Linnoitustie 6 1934 Espoo 02600 1935 Finland 1937 Phone: +358 (50) 4871445 1938 Email: Hannes.Tschofenig@gmx.net 1939 URI: http://www.tschofenig.priv.at 1941 Eliot Lear 1942 Cisco Systems GmbH 1943 Richtistrasse 7 1944 Wallisellen, ZH CH-8304 1945 Switzerland 1947 Phone: +41 44 878 9200 1948 Email: lear@cisco.com 1950 Jim Schaad 1951 Soaring Hawk Consulting 1953 Email: ietf@augustcellars.com