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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 5296 (Obsoleted by RFC 6696) -- Obsolete informational reference (is this intentional?): RFC 3588 (Obsoleted by RFC 6733) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Hoeper, Ed. 3 Internet-Draft M. Nakhjiri 4 Intended status: Standards Track Motorola 5 Expires: June 6, 2010 Y. Ohba, Ed. 6 Toshiba 7 December 3, 2009 9 Distribution of EAP based keys for handover and re-authentication 10 draft-ietf-hokey-key-mgm-13 12 Abstract 14 This document describes an abstract mechanism for delivering root 15 keys from an Extensible Authentication Protocol (EAP) server to 16 another network server that requires the keys for offering security 17 protected services, such as re-authentication, to an EAP peer. The 18 distributed root key can be either a usage-specific root key (USRK), 19 a domain-specific root key (DSRK) or a domain-specific usage-specific 20 root key (DSUSRK) that has been derived from an Extended Master 21 Session Key (EMSK) hierarchy previously established between the EAP 22 server and an EAP peer. The document defines a template for a key 23 distribution exchange (KDE) protocol that can distribute these 24 different types of root keys using an AAA (Authentication, 25 Authorization and Accounting) protocol and discusses its security 26 requirements. The described protocol template does not specify 27 message formats, data encoding, or other implementation details. It 28 thus needs to be instantiated with a specific protocol (e.g. RADIUS 29 or Diameter) before it can be used. 31 Status of this Memo 33 This Internet-Draft is submitted to IETF in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF), its areas, and its working groups. Note that 38 other groups may also distribute working documents as Internet- 39 Drafts. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 The list of current Internet-Drafts can be accessed at 47 http://www.ietf.org/ietf/1id-abstracts.txt. 49 The list of Internet-Draft Shadow Directories can be accessed at 50 http://www.ietf.org/shadow.html. 52 This Internet-Draft will expire on June 6, 2010. 54 Copyright Notice 56 Copyright (c) 2009 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 BSD License. 69 This document may contain material from IETF Documents or IETF 70 Contributions published or made publicly available before November 71 10, 2008. The person(s) controlling the copyright in some of this 72 material may not have granted the IETF Trust the right to allow 73 modifications of such material outside the IETF Standards Process. 74 Without obtaining an adequate license from the person(s) controlling 75 the copyright in such materials, this document may not be modified 76 outside the IETF Standards Process, and derivative works of it may 77 not be created outside the IETF Standards Process, except to format 78 it for publication as an RFC or to translate it into languages other 79 than English. 81 Table of Contents 83 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 84 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 85 3. Key Delivery Architecture . . . . . . . . . . . . . . . . . . 6 86 4. Key Distribution Exchange (KDE) . . . . . . . . . . . . . . . 7 87 4.1. Context and Scope for Distributed Keys . . . . . . . . . . 8 88 4.2. Key Distribution Exchange Scenarios . . . . . . . . . . . 9 89 5. KDE used in the EAP Re-authentication Protocol (ERP) . . . . . 9 90 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 91 6.1. Requirements on AAA Key Transport Protocols . . . . . . . 10 92 6.2. Distributing RK without Peer Consent . . . . . . . . . . . 11 93 7. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 11 94 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 95 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11 96 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 97 10.1. Normative References . . . . . . . . . . . . . . . . . . . 11 98 10.2. Informative references . . . . . . . . . . . . . . . . . . 12 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 101 1. Introduction 103 The Extensible Authentication Protocol (EAP) [RFC3748] is an 104 authentication framework supporting authentication methods that are 105 specified in EAP methods. By definition, any key-generating EAP 106 method derives a Master Session Key (MSK) and an Extended Master 107 Session Key (EMSK). [RFC5295] reserves the EMSK for the sole purpose 108 of deriving root keys that can be used for specific purposes called 109 usages. In particular, [RFC5295] defines how to create a usage- 110 specific root key (USRK) for bootstrapping security in a specific 111 application, a domain-specific root key (DSRK) for bootstrapping 112 security of a set of services within a domain, and a usage-specific 113 DSRK (DSUSRK) for a specific application within a domain. [RFC5296] 114 defines a re-authentication root key (rRK) that is a USRK designated 115 for re-authentication. 117 The MSK and EMSK may be used to derive further keying material for a 118 variety of security mechanisms [RFC5247]. For example, the MSK has 119 been widely used for bootstrapping the wireless link security 120 associations between the peer and the network attachment points. 121 However, performance as well as security issues arise when using the 122 MSK and the current bootstrapping methods in mobile scenarios that 123 require handovers, as described in [RFC5169]. To address handover 124 latencies and other shortcomings, [RFC5296] specifies an EAP re- 125 authentication protocol (ERP) that uses keys derived from the EMSK or 126 DSRK to enable efficient re-authentications in handover scenarios. 127 [RFC5295] and [RFC5296] both do not specify how root keys are 128 delivered to the network server requiring the key. Such a key 129 delivery mechanism is essential because the EMSK cannot leave the EAP 130 server ([RFC5295]) but root keys are needed by other network servers 131 disjoint with the EAP server. For example, in order to enable an EAP 132 peer to re-authenticate to a network during a handover, certain root 133 keys need to be made available by the EAP server to the server 134 carrying out the re-authentication. 136 This document specifies an abstract mechanism for the delivery of the 137 EMSK child keys from the server holding the EMSK or a root key to 138 another network server that requests a root key for providing 139 protected services (such as re-authentication and other usage and 140 domain-specific services) to EAP peers. In the remainder of this 141 document, a server delivering root keys is referred to as Key 142 Delivering Server (KDS) and a server authorized to request and 143 receive root keys from a KDS is referred to as Key Requesting Server 144 (KRS). The Key Distribution Exchange (KDE) mechanism defined in this 145 document runs over an AAA (Authentication, Authorization and 146 Accounting) protocol, e.g., RADIUS [RFC2865], [RFC3579] or Diameter 147 [RFC3588], and has several variants depending on the type of key that 148 is requested and delivered (i.e., DRSK, USRK, and DSUSRK). The 149 presented KDE mechanism is a protocol template that must be 150 instantiated for a particular protocol, such as RADIUS or Diameter, 151 to specify the format and encoding of the abstract protocol messages. 152 Only after such an instantiation can the KDE mechanism described in 153 this document be implemented. The document also describes security 154 requirements for the secure key delivery over AAA. 156 2. Terminology 158 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 159 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 160 document are to be interpreted as described in [RFC2119]. 162 AAA 163 Authentication, Authorization and Accounting. AAA protocols with 164 EAP support include RADIUS [RFC2865], [RFC3579] and Diameter 165 [RFC3588]. 167 USRK 168 Usage-Specific Root Key. A root key that is derived from the EMSK, 169 see [RFC5295]. 171 USR-KH 172 USRK Holder. A network server that is authorized to request and 173 receive a USRK from the EAP server. The USR-KH can be an AAA 174 server or dedicated service server. 176 DSRK 177 Domain-Specific Root Key. A root key that is derived from the 178 EMSK, see [RFC5295]. 180 DSR-KH 181 DSRK Holder. A network server that is authorized to request and 182 receive a DSRK from the EAP server. The most likely 183 implementation of a DSR-KH is an AAA server in a domain, enforcing 184 the policies for the usage of the DSRK within this domain. 186 DSUSRK 187 Domain-Specific Usage-Specific Root Key. A root key that is 188 derived from the DSRK, see [RFC5295]. 190 DSUSR-KH 191 DSUSRK holder. A network server authorized to request and receive 192 a DSUSRK from the DSR-KH. The most likely implementation of a 193 DSUSR-KH is an AAA server in a domain, responsible for a 194 particular service offered within this domain. 196 RK 197 Root Key. An EMSK child key, i.e., a USRK, DSRK, or DSUSRK. 199 KDS 200 Key Delivering Server. A network server that holds an EMSK or 201 DSRK and delivers root keys to KRS requesting root keys. The EAP 202 server together with the AAA server it exports the keys to for 203 delivery and the DSR-KH can both act as KDS. 205 KRS 206 Key Requesting Server. A network server that shares an interface 207 with a KDS and is authorized to request root keys from the KDS. 208 USR-KH, DSR-KH, and DSUSR-KH can all act as KRS. 210 3. Key Delivery Architecture 212 An EAP server carries out normal EAP authentications with EAP peers 213 but is typically not involved in potential handovers and re- 214 authentication attempts by the same EAP peer. Other servers are 215 typically in place to offer these requested services. These servers 216 can be AAA servers or other service network servers. Whenever EAP- 217 based keying material is used to protect a requested service, the 218 respective keying material has to be available to the server 219 providing the requested service. For example, the first time a peer 220 requests a service from a network server, this server acts as a KRS. 221 The KRS requests the root keys needed to derive the keys for 222 protecting the requested service from the respective KDS. In 223 subsequent requests from the same peer and as long as the root key 224 has not expired, the KRS can use the same root keys to derive fresh 225 keying material to protect the requested service. These kinds of key 226 requests and distributions are necessary because an EMSK cannot leave 227 the EAP server ([RFC5295]). Hence, any root key that is directly 228 derived from an EMSK can only be derived by the EAP server itself. 229 The EAP server then exports these keys to a server that can 230 distribute the keys to the KRS. In the remainder of this document, 231 the KDS consisting of the EAP server that derives the root keys 232 together with the AAA server that distributes these keys is denoted 233 EAP/AAA server. Root keys derived from EMSK child keys, such as a 234 DSUSRK, can be requested from the respective root key holder. Hence, 235 a KDS can be either the EAP/AAA server or a DSRK holder (DSR-KH), 236 whereas a KRS can be either a USRK holder (USR-KH), a DSR-KH or a 237 DSUSRK holder (DSUSR-KH). 239 The KRS needs to share an interface with the KDS to be able to send 240 all necessary input data to derive the requested key and to receive 241 the requested key. The provided data includes the Key Derivation 242 Function (KDF) that should be used to derive the requested key. The 243 KRS uses the received root key to derive further keying material in 244 order to secure its offered services. Every KDS is responsible for 245 storing and protecting the received root key as well as the 246 derivation and distribution of any child key derived from the root 247 key. An example of a key delivery architecture is illustrated in 248 Figure 1 showing the different types of KRS and their interfaces to 249 the KDS. 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | EAP/AAA server | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 / | | \ 255 / | | \ 256 / | | \ 257 +-+-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ 258 | USR-KH1 | | USR-KH2 | | DSR-KH1 | | DSR-KH2 | 259 | HOKEY server| | XYZ server| |Domain 1 | | Domain 2| 260 +-+-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+ 261 / | 262 / | 263 / | 264 +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ 265 | DSUSR-KH | | DSUSR-KH2 | 266 | Domain 1 | | Domain 2 | 267 |Home domain | |Visited domain | 268 |HOKEY server | |HOKEY server | 269 +-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ 271 Figure 1: Example Key Delivery Architecture for the Different KRS and 272 KDS 274 4. Key Distribution Exchange (KDE) 276 In this section, a generic mechanism for a key distribution exchange 277 (KDE) over AAA is described in which a root key (RK) is distributed 278 from a KDS to a KRS. It is required that the communication path 279 between the KDS and the KRS is protected by the use of an appropriate 280 AAA transport security mechanism (see Section 6 for security 281 requirements). Here, it is assumed that the KRS and the KDS are 282 separate entities, logically if not physically, and the delivery of 283 the requested RK is specified accordingly. 285 The key distribution exchange consists of one round-trip, i.e., two 286 messages between the KRS and the KDS, as illustrated in Figure 2. 287 First, the KRS sends a KDE-Request carrying a Key Request Token 288 (KRT). As a response, the KDS sends a KDE-Response carrying a Key 289 Delivery Token (KDT). Both tokens are encapsulated in AAA messages. 290 The definition of the AAA attributes depends on the implemented AAA 291 protocol and is out of scope of this document. However, the security 292 requirements for AAA messages carrying KDE messages are discussed in 293 Section 6. The contents of KRT and KDT are defined in the following. 295 KRS KDS 296 -------- ------- 297 | | 298 | KDE-Request: AAA{KRT} | 299 |----------------------------------------->| 300 | KDE-Response: AAA{KDT} | 301 |<-----------------------------------------| 303 Figure 2: KDE Message Flow 305 KRT : (PID, KT, KL) 307 KRT carries the identifiers of the peer (PID), the key type (KT) 308 and the key label (KL). The key type specifies which type of root 309 key is requested, e.g., DSRK, USRK and DSUSRK. The encoding rules 310 for each key type are left to the protocol developers who define 311 the instantiation of the KDE mechanism for a particular protocol. 312 For the specification of key labels and the associated IANA 313 registries, please refer to [RFC5295] which specifies key labels 314 for USRKs and establishes an IANA registry for them. The same 315 specifications can be applied to other root keys. 317 KDT : (KT, KL, RK, KN_RK, LT_RK) 319 KDT carries the root key (RK) to be distributed to the KRS, as 320 well as the key type (KT) of the key, the key label (KL), the key 321 name (KN_RK) and the lifetime of RK (LT_RK). The key lifetime of 322 each distributed key MUST NOT be greater than that of its parent 323 key. 325 4.1. Context and Scope for Distributed Keys 327 The key context of each distributed key is determined by the sequence 328 of KTs in the key hierarchy. The key scope of each distributed key 329 is determined by the sequence of (PID, KT, KL)-tuples in the key 330 hierarchy and the identifier of the KRS. The KDF used to generate 331 the requested keys includes context and scope information, thus, 332 binding the key to the specific channel [RFC5295]. 334 4.2. Key Distribution Exchange Scenarios 336 Given the three types of KRS, there are three scenarios for the 337 distribution of the EMSK child keys. For all scenarios, the trigger 338 and mechanism for key delivery may involve a specific request from an 339 EAP peer and/or another intermediary (such as an authenticator). For 340 simplicity, it is assumed that USR-KHs reside in the same domain as 341 the EAP server. 343 Scenario 1: EAP/AAA server to USR-KH: In this scenario, the EAP/AAA 344 server delivers a USRK to a USR-KH. 346 Scenario 2: EAP/AAA server to DSR-KH: In this scenario, the EAP/AAA 347 server delivers a DSRK to a DSR-KH. 349 Scenario 3: DSR-KH to DSUSR-KH: In this scenario, a DSR-KH in a 350 specific domain delivers keying material to a DSUSR-KH in the same 351 domain. 353 The key distribution exchanges for Scenario 3 can be combined with 354 the key distribution exchanges for Scenario 2 into a single round- 355 trip exchange as shown in Figure 3. Here, KDE-Request and KDE- 356 Response are messages for Scenarios 2, whereas KDE-Request' and KDE- 357 Response' are messages for Scenarios 3. 359 DSUSR-KH DSR-KH EAP/AAA Server 360 -------- ------ ------------ 361 | KDE-Request'(KRT') | KDE-Request(KRT) | 362 |------------------------>|-------------------------->| 363 | KDE-Response'(KDT') | KDE-Response(KDT) | 364 |<----------------------- |<--------------------------| 365 | | | 367 Figure 3: Combined Message Exchange 369 5. KDE used in the EAP Re-authentication Protocol (ERP) 371 This section describes how the presented KDE mechanism should be used 372 to request and deliver the root keys used for re-authentication in 373 the EAP Re-authentication Protocol (ERP) defined in [RFC5296]. ERP 374 supports two forms of bootstrapping, implicit as well as explicit 375 bootstrapping, and KDE is discussed for both cases in the remainder 376 of this section. 378 In implicit bootstrapping the local EAP Re-authentication (ER) server 379 requests the DSRK from the home AAA server during the initial EAP 380 exchange. Here, the local ER server acts as the KRS and the home AAA 381 server as the KDS. In this case, the local ER server requesting the 382 DSRK includes a KDE-Request in the AAA packet encapsulating the first 383 EAP-Response message from the peer. Here, an AAA User-Name attribute 384 is used as the PID. If the EAP exchange is successful, the home AAA 385 server includes a KDE-Response in the AAA message that carries the 386 EAP-Success message. 388 Explicit bootstrapping is initiated by peers that do not know the 389 domain. Here, the peer sends an EAP-Initiate message with the 390 bootstrapping flag turned on. The local ER server (acting as KRS) 391 includes a KDE-Request message in the AAA message that carries the 392 peer's EAP-Initiate message and sends it to the peer's home AAA 393 server. Here, an AAA User-Name attribute is used as the PID. In its 394 response, the home AAA server (acting as KDS) includes a KDE-Response 395 in the AAA message that carries the EAP-Finish message with the 396 bootstrapping flag set. 398 6. Security Considerations 400 This section provides security requirements and a discussion of 401 distributing RK without peer consent. 403 6.1. Requirements on AAA Key Transport Protocols 405 Any KDE attribute that is exchanged as part of a KDE-Request or KDE- 406 Response MUST be integrity-protected and replay-protected by the 407 underlying AAA protocol that is used to encapsulate the attributes. 408 Additionally, a secure key wrap algorithm MUST be used by the AAA 409 protocol to protect the RK in a KDE-Response. Other confidential 410 information as part of the KDE messages (e.g., identifiers if privacy 411 is a requirement) SHOULD be encrypted by the underlying AAA protocol. 413 When there is an intermediary, such as an AAA proxy, on the path 414 between the KRS and the KDS, there will be a series of hop-by-hop 415 security associations along the path. The use of hop-by-hop security 416 associations implies that the intermediary on each hop can access the 417 distributed keying material. Hence the use of hop-by-hop security 418 SHOULD be limited to an environment where an intermediary is trusted 419 not to abuse the distributed key material. If such a trusted AAA 420 infrastructure does not exist, other means must be applied at a 421 different layer to ensure the end-to-end security (i.e., between KRS 422 and KDS) of the exchanged KDE messages. The security requirements 423 for such a protocol are the same as previously outlined for AAA 424 protocols and MUST hold when encapsulated in AAA messages. 426 6.2. Distributing RK without Peer Consent 428 When a KDE-Request is sent as a result of explicit ERP bootstrapping 429 [RFC5296], cryptographic verification of peer consent on distributing 430 an RK is provided by the integrity checksum of the EAP-Initiate 431 message with the bootstrapping flag turned on. 433 On the other hand, when a KDE-Request is sent as a result of implicit 434 ERP bootstrapping [RFC5296], cryptographic verification of peer 435 consent on distributing an RK is not provided. A peer is not 436 involved in the process and, thus, not aware of a key delivery 437 requests for root keys derived from its established EAP keying 438 material. Hence, a peer has no control where keys derived from its 439 established EAP keying material are distributed to. A possible 440 consequence of this is that a KRS may request and obtain an RK from 441 the home server even if the peer does not support ERP. EAP-Initiate/ 442 Re-auth-Start messages send to the peer will be silently dropped by 443 the peer causing further waste of resources. 445 7. IANA consideration 447 This document contains no IANA considerations. 449 8. Acknowledgments 451 The editors would like to thank Dan Harkins, Chunqiang Li, Rafael 452 Marin Lopez and Charles Clancy for their valuable comments. 454 9. Contributors 456 The following people contributed to this document: Kedar Gaonkar, 457 Lakshminath Dondeti, Vidya Narayanan, and Glen Zorn. 459 10. References 461 10.1. Normative References 463 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 464 Requirement Levels", BCP 14, RFC 2119, March 1997. 466 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 467 Levkowetz, "Extensible Authentication Protocol (EAP)", 468 RFC 3748, June 2004. 470 [RFC5295] Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, 471 "Specification for the Derivation of Root Keys from an 472 Extended Master Session Key (EMSK)", RFC 5295, 473 August 2008. 475 [RFC5296] Narayanan, V. and L. Dondeti, "EAP Extensions for EAP Re- 476 authentication Protocol (ERP)", RFC 5296, August 2008. 478 10.2. Informative references 480 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 481 "Remote Authentication Dial In User Service (RADIUS)", 482 RFC 2865, June 2000. 484 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 485 Dial In User Service) Support For Extensible 486 Authentication Protocol (EAP)", RFC 3579, September 2003. 488 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 489 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 491 [RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible 492 Authentication Protocol (EAP) Key Management Framework", 493 RFC 5247, August 2008. 495 [RFC5169] Clancy, T., Nakhjiri, M., Narayanan, V., and L. Dondeti, 496 "Handover Key Management and Re-Authentication Problem 497 Statement", RFC 5169, March 2008. 499 Authors' Addresses 501 Katrin Hoeper (editor) 502 Motorola, Inc. 503 1301 E Algonquin Road 504 Schaumburg, IL 60196 505 USA 507 Phone: +1 847 576 4714 508 Email: khoeper@motorola.com 509 Madjid F Nakhjiri 510 Motorola, Inc. 511 6450 Sequence Drive 512 San Diego, CA 92121 513 USA 515 Email: madjid.nakhjiri@motorola.com 517 Yoshihiro Ohba (editor) 518 Toshiba America Research, Inc. 519 1 Telcordia Drive 520 Piscataway, NJ 08854 521 USA 523 Phone: +1 732 699 5305 524 Email: yohba@tari.toshiba.com