idnits 2.17.00 (12 Aug 2021) /tmp/idnits49387/draft-nir-tls-eap-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** The document seems to lack a License Notice according IETF Trust Provisions of 28 Dec 2009, Section 6.b.ii or Provisions of 12 Sep 2009 Section 6.b -- however, there's a paragraph with a matching beginning. Boilerplate error? (You're using the IETF Trust Provisions' Section 6.b License Notice from 12 Feb 2009 rather than one of the newer Notices. See https://trustee.ietf.org/license-info/.) 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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 20, 2009) is 4779 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '12' on line 331 ** Obsolete normative reference: RFC 4346 (ref. 'TLS') (Obsoleted by RFC 5246) ** Obsolete normative reference: RFC 4366 (ref. 'TLS-EXT') (Obsoleted by RFC 5246, RFC 6066) -- Obsolete informational reference (is this intentional?): RFC 3588 (ref. 'Diameter') (Obsoleted by RFC 6733) == Outdated reference: draft-ietf-emu-eap-gpsk has been published as RFC 5433 == Outdated reference: draft-ietf-eap-keying has been published as RFC 5247 -- Obsolete informational reference (is this intentional?): RFC 4306 (Obsoleted by RFC 5996) Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TLS Working Group Y. Nir 3 Internet-Draft Y. Sheffer 4 Intended status: Standards Track Check Point 5 Expires: October 22, 2009 H. Tschofenig 6 NSN 7 P. Gutmann 8 University of Auckland 9 April 20, 2009 11 TLS using EAP Authentication 12 draft-nir-tls-eap-05.txt 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on October 22, 2009. 37 Copyright Notice 39 Copyright (c) 2009 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents in effect on the date of 44 publication of this document (http://trustee.ietf.org/license-info). 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. 48 Abstract 50 This document describes an extension to the TLS protocol to allow TLS 51 clients to authenticate with legacy credentials using the Extensible 52 Authentication Protocol (EAP). 54 This work follows the example of IKEv2, where EAP has been added to 55 the IKEv2 protocol to allow clients to use different credentials such 56 as passwords, token cards, and shared secrets. 58 When TLS is used with EAP, additional records are sent after the 59 ChangeCipherSpec protocol message and before the Finished message, 60 effectively creating an extended handshake before the application 61 layer data can be sent. Each EapMsg handshake record contains 62 exactly one EAP message. Using EAP for client authentication allows 63 TLS to be used with various AAA back-end servers such as RADIUS or 64 Diameter. 66 TLS with EAP may be used for securing a data connection such as HTTP 67 or POP3. We believe it has three main benefits: 68 o The ability of EAP to work with backend servers can remove that 69 burden from the application layer. 70 o Moving the user authentication into the TLS handshake protects the 71 presumably less secure application layer from attacks by 72 unauthenticated parties. 73 o Using mutual authentication methods within EAP can help thwart 74 certain classes of phishing attacks. 76 Table of Contents 78 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 79 1.1. EAP Applicability . . . . . . . . . . . . . . . . . . . . 5 80 1.2. Comparison with Design Alternatives . . . . . . . . . . . 5 81 1.3. Conventions Used in This Document . . . . . . . . . . . . 5 82 2. Operating Environment . . . . . . . . . . . . . . . . . . . . 6 83 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7 84 3.1. The tee_supported Extension . . . . . . . . . . . . . . . 8 85 3.2. The InterimAuth Handshake Message . . . . . . . . . . . . 8 86 3.3. The EapMsg Handshake Message . . . . . . . . . . . . . . . 8 87 3.4. Calculating the Finished message . . . . . . . . . . . . . 9 88 4. Security Considerations . . . . . . . . . . . . . . . . . . . 10 89 4.1. InterimAuth vs. Finished . . . . . . . . . . . . . . . . . 10 90 4.2. Identity Protection . . . . . . . . . . . . . . . . . . . 10 91 4.3. Mutual Authentication . . . . . . . . . . . . . . . . . . 11 92 5. Performance Considerations . . . . . . . . . . . . . . . . . . 12 93 6. Operational Considerations . . . . . . . . . . . . . . . . . . 13 94 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 95 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 96 9. Changes from Previous Versions . . . . . . . . . . . . . . . . 16 97 9.1. Changes in version -02 . . . . . . . . . . . . . . . . . . 16 98 9.2. Changes in version -01 . . . . . . . . . . . . . . . . . . 16 99 9.3. Changes from the protocol model draft . . . . . . . . . . 16 100 10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 17 101 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 102 11.1. Normative References . . . . . . . . . . . . . . . . . . . 18 103 11.2. Informative References . . . . . . . . . . . . . . . . . . 18 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 106 1. Introduction 108 This document describes a new extension to [TLS]. This extension 109 allows a TLS client to authenticate using [EAP] instead of performing 110 the authentication at the application level. The extension follows 111 [TLS-EXT]. For the remainder of this document we will refer to this 112 extension as TEE (TLS with EAP Extension). 114 TEE extends the TLS handshake beyond the regular setup, to allow the 115 EAP protocol to run between the TLS server (called an "authenticator" 116 in EAP) and the TLS client (called a "supplicant"). This allows the 117 TLS architecture to handle client authentication before exposing the 118 server application software to an unauthenticated client. In doing 119 this, we follow the approach taken for IKEv2 in [RFC4306]. However, 120 similar to regular TLS, we protect the user identity by only sending 121 the client identity after the server has authenticated. In this our 122 solution differs from that of IKEv2. 124 Currently used applications that rely on non-certificate user 125 credentials use TLS to authenticate the server only. After that, the 126 application takes over, and presents a login screen where the user is 127 expected to present their credentials. 129 This creates several problems. It allows a client to access the 130 application before authentication, thus creating a potential for 131 anonymous attacks on non-hardened applications. Additionally, web 132 pages are not particularly well suited for long shared secrets and 133 for interfacing with certain devices such as USB tokens. 135 TEE allows full mutual authentication to occur for all these 136 applications within the TLS exchange. The application receives 137 control only when the user is identified and authenticated. The 138 authentication can be built into the server infrastructure by 139 connecting to an AAA server. The client side can be integrated into 140 client software such as web browsers and mail clients. An EAP 141 infrastructure is already built into some operating systems providing 142 a user interface for each authentication method within EAP. 144 We intend TEE to be used for various protocols that use TLS such as 145 HTTPS, in cases where certificate based client authentication is not 146 practical. This includes web-based mail services, online banking, 147 premium content websites and mail clients. 149 Another class of applications that may see benefit from TEE are TLS 150 based VPN clients used as part of so-called "SSL VPN" products. No 151 such client protocols have so far been standardized. 153 1.1. EAP Applicability 155 Section 1.3 of [EAP] states that EAP is only applicable for network 156 access authentication, rather than for "bulk data transfer". It then 157 goes on to explain why the transport properties of EAP indeed make it 158 unsuitable for bulk data transfer, e.g. for large file transport. 159 Our proposed use of EAP falls squarely within the applicability as 160 defined, since we make no further use of EAP beyond access 161 authentication. 163 1.2. Comparison with Design Alternatives 165 It has been suggested to implement EAP authentication as part of the 166 protected application, rather than as part of the TLS handshake. A 167 BCP document could be used to describe a secure way of doing this. 168 The drawbacks we see in such an approach are listed below: 169 o EAP does not have a pre-defined transport method. Application 170 designers would need to specify an EAP transport for each 171 application. Making this a part of TLS has the benefit of a 172 single specification for all protected applications. 173 o The integration of EAP and TLS is security-sensitive and should be 174 standardized and interoperable. We do not believe that it should 175 be left to application designers to do this in a secure manner. 176 Specifically on the server-side, integration with AAA servers adds 177 complexity and is more naturally part of the underlying 178 infrastrcture. 179 o Our current proposal provides channel binding between TLS and EAP, 180 to counter the MITM attacks described in [MITM]. TLS does not 181 provide any standard way of extracting cryptographic material from 182 the TLS state, and in most implementations, the TLS state is not 183 exposed to the protected application. Because of this, it is 184 difficult for application designers to bind the user 185 authentication to the protected channel provided by TLS. 187 1.3. Conventions Used in This Document 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 191 document are to be interpreted as described in [RFC2119]. 193 2. Operating Environment 195 TEE will work between a client application and a server application, 196 performing either client authentication or mutual authentication 197 within the TLS exchange. 199 Client Server 200 +-------------------------+ +------------------------+ 201 | |GUI| | Client | |TLS+-+-----+-+TLS| |Server | | 202 | +-^-+ |Software| +-^-+ | +-+-^-+ |Application | | 203 | | +--------+ | | | | |Software | | 204 | | | | | | +------------+ | 205 | +-v----------------v-+ | | | | 206 | | EAP | | +---|--------------------+ 207 | | Infrastructure | | | 208 | +--------------------+ | | +--------+ 209 +-------------------------+ | | AAA | 210 | | Server | 211 +----- | 212 +--------+ 214 The above diagram shows the typical deployment. The client has 215 software that either includes a UI for some EAP methods, or else is 216 able to invoke some operating system EAP infrastructure that takes 217 care of the user interaction. The server is configured with the 218 address and protocol of the AAA server. Typically the AAA server 219 communicates using the RADIUS protocol with EAP ([RADIUS] and 220 [RAD-EAP]), or the Diameter protocol ([Diameter] and [Dia-EAP]). 222 As stated in the introduction, we expect TEE to be used in both 223 browsers and applications. Further uses may be authentication and 224 key generation for other protocols, and tunneling clients, which so 225 far have not been standardized. 227 3. Protocol Overview 229 The TEE extension defines the following: 230 o A new extension type called tee_supported, used to indicate that 231 the communicating application (either client or server) supports 232 this extension. 233 o A new message type for the handshake protocol, called InterimAuth, 234 which is used to sign previous messages. 235 o A new message type for the handshake protocol, called EapMsg, 236 which is used to carry a single EAP message. 238 The diagram below outlines the protocol structure. For illustration 239 purposes only, we use the GPSK EAP method [EAP-GPSK]. 241 Client Server 242 ------ ------ 244 ClientHello(*) --------> 245 ServerHello(*) 246 (Certificate) 247 ServerKeyExchange 248 EapMsg(Identity-Request) 249 <-------- ServerHelloDone 250 ClientKeyExchange 251 (CertificateVerify) 252 ChangeCipherSpec 253 InterimAuth 254 EapMsg(Identity-Reply) --------> 255 ChangeCipherSpec 256 InterimAuth 257 EapMsg(GPSK-Request) 258 <-------- 259 EapMsg(GPSK-Reply) --------> 260 EapMsg(GPSK-Request) 261 <-------- 262 EapMsg(GPSK-Reply) --------> 263 EapMsg(Success) 264 <-------- Finished 265 Finished --------> 267 (*) The ClientHello and ServerHello include the tee_supported 268 extension to indicate support for TEE 270 The client indicates in the first message its support for TEE. The 271 server sends an EAP identity request in the reply. The client sends 272 the identity reply after the handshake completion. The EAP request- 273 response sequence continues until the client is either authenticated 274 or rejected. 276 3.1. The tee_supported Extension 278 The tee_supported extension is a ClientHello and ServerHello 279 extension as defined in section 2.3 of [TLS-EXT]. The extension_type 280 field is TBA by IANA. The extension_data is zero-length. 282 3.2. The InterimAuth Handshake Message 284 The InterimAuth message is identical in syntax to the Finished 285 message described in section 7.4.9 of [TLS]. It is calculated in 286 exactly the same way. 288 The semantics, however, are somewhat different. The "Finished" 289 message indicates that application data may now be sent. The 290 "InterimAuth" message does not indicate this. Instead, further 291 handshake messages are needed. 293 The HandshakeType value for the InterimAuth handshake message is TBA 294 by IANA. 296 3.3. The EapMsg Handshake Message 298 The EapMsg handshake message carries exactly one EAP message as 299 defined in [EAP]. 301 The HandshakeType value for the EapMsg handshake message is TBA by 302 IANA. 304 The EapMsg message is used to tunnel EAP messages between the 305 authentication server, which may be co-located with the TLS server, 306 or else may be a separate AAA server, and the supplicant, which is 307 co-located with the TLS client. TLS on either side receives the EAP 308 data from the EAP infrastructure, and treats it as opaque. TLS does 309 not make any changes to the EAP payload or make any decisions based 310 on the contents of an EapMsg handshake message. 312 Note that it is expected that the authentication server notifies the 313 TLS server about authentication success or failure, and so TLS need 314 not inspect the eap_payload within the EapMsg to detect success or 315 failure. 317 struct { 318 opaque eap_payload[4..65535]; 319 } EapMsg; 321 eap_payload is defined in section 4 of RFC 3748. It includes 322 the Code, Identifier, Length and Data fields of the EAP 323 packet. 325 3.4. Calculating the Finished message 327 If the EAP method is key-generating (see [I-D.ietf-eap-keying]), the 328 Finished message is calculated as follows: 330 struct { 331 opaque verify_data[12]; 332 } Finished; 334 verify_data 335 PRF(MSK, finished_label, MD5(handshake_messages) + 336 SHA-1(handshake_messages)) [0..11]; 338 The finished_label and the PRF are as defined in section 7.4.9 of 339 [TLS]. 341 The handshake_messages field, unlike regular TLS, does not sign all 342 the data in the handshake. Instead it signs all the data that has 343 not been signed by the previous InterimAuth message. The 344 handshake_messages field includes all of the octets beginning with 345 and including the InterimAuth message, up to but not including this 346 Finished message. This is the concatenation of all the Handshake 347 structures exchanged thus far, and not yet signed, as defined in 348 section 7.4 of [TLS]and in this document. 350 The Master Session Key (MSK) is derived by the AAA server and by the 351 client if the EAP method is key-generating. On the server-side, it 352 is typically received from the AAA server over the RADIUS or Diameter 353 protocol. On the client-side, it is passed to TLS by some other 354 method. 356 If the EAP method is not key-generating, then the master_secret is 357 used to sign the messages instead of the MSK. For a discussion on 358 the use of such methods, see Section 4.1. 360 4. Security Considerations 362 4.1. InterimAuth vs. Finished 364 In regular TLS, the Finished message provides two functions: it signs 365 all preceding messages, and it signals that application data can now 366 be sent. In TEE, it only signs those messages that have not yet been 367 signed. 369 Some EAP methods, such as EAP-TLS, EAP-IKEv2 and EAP-SIM generate 370 keys in addition to authenticating clients. Such methods are said to 371 be resistant to man-in-the-middle (MITM) attacks as discussed in 372 [MITM]. Such methods are called key-generating methods. 374 To realize the benefit of such methods, we need to verify the key 375 that was generated within the EAP method. This is referred to as the 376 MSK in EAP. In TEE, the InterimAuth message signs all previous 377 messages with the master_secret, just like the Finished message in 378 regular TLS. The Finished message signs the rest of the messages 379 using the MSK if such exists. If not, then the messages are signed 380 with the master_secret as in regular TLS. 382 The need for signing twice arises from the fact that we need to use 383 both the master_secret and the MSK. It was possible to use just one 384 Finished record and blend the MSK into the master_secret. However, 385 this would needlessly complicate the protocol and make security 386 analysis more difficult. Instead, we have decided to follow the 387 example of IKEv2, where two AUTH payloads are exchanged. 389 It should be noted that using non-key-generating methods may expose 390 the client to a MITM attack if the same method and credentials are 391 used in some other situation, in which the EAP is done outside of a 392 protected tunnel with an authenticated server. Unless it can be 393 determined that the EAP method is never used in such a situation, 394 non-key-generating methods SHOULD NOT be used. This issue is 395 discussed extensively in [Compound-Authentication]. 397 4.2. Identity Protection 399 Unlike [TLS-PSK], TEE provides identity protection for the client. 400 The client's identity is hidden from a passive eavesdropper using TLS 401 encryption. Active attacks are discussed in Section 4.3. 403 We could save one round-trip by having the client send its identity 404 within the Client Hello message. This is similar to TLS-PSK. 405 However, we believe that identity protection is a worthy enough goal, 406 so as to justify the extra round-trip. 408 4.3. Mutual Authentication 410 In order to achieve our security goals, we need to have both the 411 server and the client authenticate. Client authentication is 412 obviously done using the EAP method. The server authentication can 413 be done in either of two ways: 414 1. The client can verify the server certificate. This may work well 415 depending on the scenario, but implies that the client or its 416 user can recognize the right DN or alternate name, and 417 distinguish it from plausible alternatives. The introduction to 418 [I.D.Webauth-phishing] shows that at least in HTTPS, this is not 419 always the case. 420 2. The client can use a mutually authenticated (MA) EAP method such 421 as GPSK. In this case, server certificate verification does not 422 matter, and the TLS handshake may as well be anonymous. Note 423 that in this case, the client identity is sent to the server 424 before server authentication. 426 To summarize: 427 o Clients MUST NOT propose anonymous ciphersuites, unless they 428 support MA EAP methods. 429 o Clients MUST NOT accept non-MA methods if the ciphersuite is 430 anonymous. 431 o Clients MUST NOT accept non-MA methods if they are not able to 432 verify the server credentials. Note that this document does not 433 define what verification involves. If the server DN is known and 434 stored on the client, verifying certificate signature and checking 435 revocation may be enough. For web browsers, the case is not as 436 clear cut, and MA methods SHOULD be used. 438 5. Performance Considerations 440 Regular TLS adds two round-trips to a TCP connection. However, 441 because of the stream nature of TCP, the client does not really need 442 to wait for the server's Finished message, and can begin sending 443 application data immediately after its own Finished message. In 444 practice, many clients do so, and TLS only adds one round-trip of 445 delay. 447 TEE adds as many round-trips as the EAP method requires. For 448 example, EAP-MD5 requires 1 round-trip, while EAP-GPSK requires 2 449 round-trips. Additionally, the client MUST wait for the EAP-Success 450 message before sending its own Finished message, so we need at least 451 3 round-trips for the entire handshake. The best a client can do is 452 two round-trips plus however many round-trips the EAP method 453 requires. 455 It should be noted, though, that these extra round-trips save 456 processing time at the application level. Two extra round-trips take 457 a lot less time than presenting a log-in web page and processing the 458 user's input. 460 It should also be noted, that TEE reverses the order of the Finished 461 messages. In regular TLS the client sends the Finished message 462 first. In TEE it is the server that sends the Finished message 463 first. This should not affect performance, and it is clear that the 464 client may send application data immediately after the Finished 465 message. 467 6. Operational Considerations 469 Section 4.3 defines a dependency between the TLS state and the EAP 470 state in that it mandates that certain EAP methods should not be used 471 with certain TLS ciphersuites. To avoid such dependencies, there are 472 two approaches that implementations can take. They can either not 473 use any anonymous ciphersuites, or else they can use only MA EAP 474 methods. 476 Where certificate validation is problematic, such as in browser-based 477 HTTPS, we recommend the latter approach. 479 In cases where the use of EAP within TLS is not known before opening 480 the connection, it is necessary to consider the implications of 481 requiring the user to type in credentials after the connection has 482 already started. TCP sessions may time out, because of security 483 considerations, and this may lead to session setup failure. 485 7. IANA Considerations 487 IANA is asked to assign an extension type value from the 488 "ExtensionType Values" registry for the tee_supported extension. 490 IANA is asked to assign two handshake message types from the "TLS 491 HandshakeType Registry", one for "EapMsg" and one for "InterimAuth". 493 8. Acknowledgments 495 The authors would like to thank Josh Howlett for his comments. 497 The TLS Inner Application Extension work ([TLS/IA]) has inspired the 498 authors to create this simplified work. TLS/IA provides a somewhat 499 different approach to integrating non-certificate credentials into 500 the TLS protocol, in addition to several other features available 501 from the RADIUS namespace. 503 The authors would also like to thank the various contributors to 504 [RFC4306] whose work inspired this one. 506 9. Changes from Previous Versions 508 9.1. Changes in version -02 510 o Added discussion of alternative designs. 512 9.2. Changes in version -01 514 o Changed the construction of the Finished message 515 o Replaced MS-CHAPv2 with GPSK in examples. 516 o Added open issues section. 517 o Added reference to [Compound-Authentication] 518 o Fixed reference to MITM attack 520 9.3. Changes from the protocol model draft 522 o Added diagram for EapMsg 523 o Added discussion of EAP applicability 524 o Added discussion of mutually-authenticated EAP methods vs other 525 methods in the security considerations. 526 o Added operational considerations. 527 o Other minor nits. 529 10. Open Issues 531 Some have suggested that since the protocol is identical to regular 532 TLS up to the InterimAuth message, we should call that the Finished 533 message, and call the last message in the extended handshake 534 something like "EapFinished". This has the advantage that the 535 construction of Finished is already well defined and will not change. 536 However, the Finished message has a specific meaning as indicated by 537 its name. It means that the handshake is over and that application 538 data can now be sent. This is not true of what is in this draft 539 called InterimAuth. We'd like the opinions of reviewrs about this 540 issue. 542 The MSK from the EAP exchange is only used to sign the Finished 543 message. It is not used again in the data encryption. In this we 544 followed the example of IKEv2. The reason is that TLS already has 545 perfectly good ways of exchanging keys, and we do not need this 546 capability from EAP methods. Also, using the MSK in keys would 547 require an additional ChangeCipherSpec and would complicate the 548 protocol. We'd like the opinions of reviewrs about this issue. 550 Another response we got was that we should have a MUST requirement 551 that only mutually authenticated and key-generating methods be used 552 in TEE. This would simplify the security considerations section. 553 While we agree that this is a good idea, most EAP methods in common 554 use are not compliant. Additionally, such requirements assume that 555 EAP packets are visible to a passive attacker. As EAP is used in 556 protected tunnels such as in L2TP, in IKEv2 and here, this assumption 557 may not be required. If we consider the server authenticated by its 558 certificate, it may be acceptable to use a non-MA method. 560 It has been suggested that identity protection is not important 561 enough to add a roundtrip, and so we should have the client send the 562 username in the ClientHello. We are not sure about how others feel 563 about this, and would like to solicit the reviewers opinion. Note 564 that if this is done, the client sends the user name before ever 565 receiving any indication that the server actually supports TEE. This 566 might be acceptable in an email client, where the server is 567 preconfigured, but it may be unacceptable in other uses, such as web 568 browsers. 570 11. References 572 11.1. Normative References 574 [EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 575 Levkowetz, "Extensible Authentication Protocol (EAP)", 576 RFC 3748, June 2004. 578 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 579 Requirement Levels", BCP 14, RFC 2119, March 1997. 581 [TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security 582 (TLS) Protocol Version 1.1", RFC 4346, April 2006. 584 [TLS-EXT] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., 585 and T. Wright, "Transport Layer Security (TLS) 586 Extensions", RFC 4366, April 2006. 588 11.2. Informative References 590 [Compound-Authentication] 591 Puthenkulam, J., Lortz, V., Palekar, A., and D. Simon, 592 "The Compound Authentication Binding Problem", 593 draft-puthenkulam-eap-binding-04 (work in progress), 594 October 2003. 596 [Dia-EAP] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 597 Authentication Protocol (EAP) Application", RFC 4072, 598 August 2005. 600 [Diameter] 601 Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 602 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 604 [EAP-GPSK] 605 Clancy, T. and H. Tschofenig, "EAP Generalized Pre-Shared 606 Key (EAP-GPSK)", draft-ietf-emu-eap-gpsk-05 (work in 607 progress), April 2007. 609 [I-D.ietf-eap-keying] 610 Aboba, B., "Extensible Authentication Protocol (EAP) Key 611 Management Framework", draft-ietf-eap-keying-18 (work in 612 progress), February 2007. 614 [I.D.Webauth-phishing] 615 Hartman, S., "Requirements for Web Authentication 616 Resistant to Phishing", draft-hartman-webauth-phishing-03 617 (work in progress), March 2007. 619 [MITM] Asokan, N., Niemi, V., and K. Nyberg, "Man-in-the-Middle 620 in Tunneled Authentication Protocols", IACR ePrint 621 Archive , October 2002. 623 [RAD-EAP] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 624 Dial In User Service) Support For Extensible 625 Authentication Protocol (EAP)", RFC 3579, September 2003. 627 [RADIUS] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 628 "Remote Authentication Dial In User Service (RADIUS)", 629 RFC 2865, June 2000. 631 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 632 RFC 4306, December 2005. 634 [TLS-PSK] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites 635 for Transport Layer Security (TLS)", RFC 4279, 636 December 2005. 638 [TLS/IA] Funk, P., Blake-Wilson, S., Smith, H., Tschofenig, N., and 639 T. Hardjono, "TLS Inner Application Extension (TLS/IA)", 640 draft-funk-tls-inner-application-extension-03 (work in 641 progress), June 2006. 643 Authors' Addresses 645 Yoav Nir 646 Check Point Software Technologies Ltd. 647 5 Hasolelim st. 648 Tel Aviv 67897 649 Israel 651 Email: ynir@checkpoint.com 653 Yaron Sheffer 654 Check Point Software Technologies Ltd. 655 5 Hasolelim st. 656 Tel Aviv 67897 657 Israel 659 Email: yaronf at checkpoint dot com 661 Hannes Tschofenig 662 Nokia Siemens Networks 663 Linnoitustie 6 664 Espoo 02600 665 Finland 667 Phone: +358 (50) 4871445 668 Email: Hannes.Tschofenig@gmx.net 669 URI: http://www.tschofenig.priv.at 671 Peter Gutmann 672 University of Auckland 673 Department of Computer Science 674 New Zealand 676 Email: pgut001@cs.auckland.ac.nz