idnits 2.17.1 draft-ietf-nea-pt-eap-06.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 : ---------------------------------------------------------------------------- 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 date (December 27, 2012) is 4138 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) == Unused Reference: 'RFC5792' is defined on line 834, but no explicit reference was found in the text ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) == Outdated reference: A later version (-10) exists of draft-ietf-emu-eap-tunnel-method-04 Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NEA N. Cam-Winget 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track P. Sangster 5 Expires: June 30, 2013 Symantec Corporation 6 December 27, 2012 8 PT-EAP: Posture Transport (PT) Protocol For EAP Tunnel Methods 9 draft-ietf-nea-pt-eap-06 11 Abstract 13 This document specifies PT-EAP, an Extensible Authentication Protocol 14 (EAP) based Posture Transport (PT) protocol designed to be used only 15 inside a TLS protected EAP tunnel method. The document also 16 describes the intended applicability of PT-EAP. 18 Status of this Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on June 30, 2013. 35 Copyright Notice 37 Copyright (c) 2012 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 1.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 3 54 1.2. Message Diagram Conventions . . . . . . . . . . . . . . . 3 55 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 56 1.4. Conventions used in this document . . . . . . . . . . . . 4 57 1.5. Compatibility with other Specifications . . . . . . . . . 4 58 2. Use of PT-EAP . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Definition of PT-EAP . . . . . . . . . . . . . . . . . . . . . 5 60 3.1. Protocol Overview . . . . . . . . . . . . . . . . . . . . 5 61 3.2. Version Negotiation . . . . . . . . . . . . . . . . . . . 6 62 3.3. PT-EAP Message Format . . . . . . . . . . . . . . . . . . 6 63 3.4. Preventing MITM Attacks with Channel Bindings . . . . . . 8 64 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 65 4.1. Trust Relationships . . . . . . . . . . . . . . . . . . . 9 66 4.1.1. Posture Transport Client . . . . . . . . . . . . . . . 9 67 4.1.2. Posture Transport Server . . . . . . . . . . . . . . . 10 68 4.2. Threats and Countermeasures . . . . . . . . . . . . . . . 11 69 4.2.1. Message Confidentiality . . . . . . . . . . . . . . . 11 70 4.2.2. Message Fabrication . . . . . . . . . . . . . . . . . 12 71 4.2.3. Message Modification . . . . . . . . . . . . . . . . . 12 72 4.2.4. Denial of Service . . . . . . . . . . . . . . . . . . 13 73 4.2.5. NEA Asokan Attacks . . . . . . . . . . . . . . . . . . 13 74 4.3. Candidate EAP Tunnel Method Protections . . . . . . . . . 14 75 4.4. Security Claims for PT-EAP as per RFC3748 . . . . . . . . 14 76 5. Requirements for EAP Tunnel Methods . . . . . . . . . . . . . 15 77 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 16 78 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 79 7.1. Registry for PT-EAP Versions . . . . . . . . . . . . . . . 17 80 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 81 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 82 9.1. Normative References . . . . . . . . . . . . . . . . . . . 18 83 9.2. Informative References . . . . . . . . . . . . . . . . . . 19 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 86 1. Introduction 88 This document specifies PT-EAP, a Posture Transport (PT) protocol 89 protected by a TLS protected EAP tunnel method. The PT protocol in 90 the NEA architecture is responsible for transporting Posture Broker 91 (PB-TNC [RFC5793]) batches (often containing Posture Attributes [PA- 92 TNC [RFC5792]] attributes) across the network between the NEA Client 93 and NEA Server. The PT-EAP protocol MUST be protected by an outer 94 TLS-based EAP tunnel method to ensure the exchanged messages are 95 protected from a variety of threats from hostile intermediaries. 97 NEA protocols are intended to be used both for pre-admission 98 assessment of endpoints joining the network and to assess endpoints 99 already present on the network. In order to support both usage 100 models, two types of PT protocols are needed. One type of PT, PT-TLS 101 [I-D.ietf-nea-pt-tls], operates after the endpoint has an assigned IP 102 address, layering on top of the IP protocol to carry a NEA exchange. 103 The other type of PT operates before the endpoint gains any access to 104 the IP network. This specification defines PT-EAP, the PT protocol 105 used to assess endpoints before they gain access to the network. 107 PT-EAP is an inner EAP [RFC3748] method designed to be used inside a 108 protected tunnel such as TEAP [I-D.ietf-emu-eap-tunnel-method], EAP- 109 FAST [RFC4851] or EAP-TTLS [RFC5281]. That is, an outer EAP method 110 is typically a TLS-based EAP method that first establishes a 111 protected tunnel by which other conversations, such as other EAP 112 methods (e.g. "inner" EAP methods) can ensue under the tunnel 113 protection. 115 1.1. Prerequisites 117 This document does not define an architecture or reference model. 118 Instead, it defines a protocol that works within the reference model 119 described in the NEA Requirements specification [RFC5209]. The 120 reader is assumed to be thoroughly familiar with that document. 122 1.2. Message Diagram Conventions 124 This specification defines the syntax of PT-EAP messages using 125 diagrams. Each diagram depicts the format and size of each field in 126 bits. Implementations MUST send the bits in each diagram as they are 127 shown, traversing the diagram from top to bottom and then from left 128 to right within each line (which represents a 32-bit quantity). 129 Multi-byte fields representing numeric values MUST be sent in network 130 (big endian) byte order. 132 Descriptions of bit field (e.g. flag) values are described referring 133 to the position of the bit within the field. These bit positions are 134 numbered from the most significant bit through the least significant 135 bit so a one octet field with only bit 0 set has the value 0x80. 137 1.3. Terminology 139 This document reuses many terms defined in the NEA Requirements 140 document [RFC5209], such as Posture Transport Client and Posture 141 Transport Server. The reader is assumed to have read that document 142 and understood it. 144 When defining the PT-EAP method, this specification does not use the 145 terms "EAP peer" and "EAP authenticator". Instead, it uses the terms 146 "NEA Client" and "NEA Server" since those are considered to be more 147 familiar to NEA WG participants. However, these terms are equivalent 148 for the purposes of these specifications. The part of the NEA Client 149 that terminates PT-EAP (generally in the Posture Transport Client) is 150 the EAP peer for PT-EAP. The part of the NEA Server that terminates 151 PT-EAP (generally in the Posture Transport Server) is the EAP 152 authenticator for PT-EAP. 154 1.4. Conventions used in this document 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 158 document are to be interpreted as described in RFC 2119 [RFC2119]. 160 1.5. Compatibility with other Specifications 162 One of the goals of the NEA effort is to deliver a single set of 163 endpoint assessment standards, agreed upon by all parties. For this 164 reason, the authors understand that the Trusted Computing Group (TCG) 165 will be replacing its existing posture transport protocols with new 166 versions that are equivalent to and interoperable with the NEA 167 specifications. 169 2. Use of PT-EAP 171 PT-EAP is designed to encapsulate PB-TNC batches in a simple EAP 172 method that can be carried within EAP tunnel methods. The EAP tunnel 173 methods provide confidentiality and message integrity, so PT-EAP does 174 not have to do so. Therefore, PT-EAP MUST be used inside a TLS-based 175 EAP tunnel method that provides strong cryptographic authentication 176 (possibly server only), message integrity and confidentiality 177 services. 179 3. Definition of PT-EAP 181 The PT-EAP protocol operates between a Posture Transport Client and a 182 Posture Transport Server, allowing them to send PB-TNC batches to 183 each other over an EAP tunnel method. When PT-EAP is used, the 184 Posture Transport Client in the NEA reference model acts as an EAP 185 peer (terminating the PT-EAP method on the endpoint) and the Posture 186 Transport Server acts as an EAP authenticator (terminating the PT-EAP 187 method on the NEA Server). 189 This section describes and defines the PT-EAP method. First, it 190 provides a protocol overview. Second, it describes specific features 191 like version negotiation. Third, it gives a detailed packet 192 description. Finally, it describes how the tls-unique channel 193 binding [RFC5929] may be used to bind PA-TNC exchanges to the EAP 194 tunnel method, defeating MITM attacks such as the Asokan attack 195 [Asokan]. 197 3.1. Protocol Overview 199 PT-EAP has two phases that follow each other in strict sequence: 200 negotiation and data transport. 202 The PT-EAP method begins with the negotiation phase. The NEA Server 203 starts this phase by sending a PT-EAP Start message: an EAP Request 204 message of type PT-EAP with the S (Start) flag set. The NEA Server 205 also sets the Version field as described in Section 3.2. This is the 206 only message in the negotiation phase. 208 The data transport phase is the only phase of PT-EAP where PB-TNC 209 batches are allowed to be exchanged. This phase always starts with 210 the NEA Client sending a PB-TNC batch to the NEA Server. The NEA 211 Client and NEA Server then take turns sending a PB-TNC batch. The 212 data transport phase always ends with an EAP Response message from 213 the NEA Client to the NEA Server. The Data field of this message may 214 have zero length if the NEA Server has just sent the last PB-TNC 215 batch in the PB-TNC exchange. 217 Note that the success of PT-EAP does not mean the overall 218 authentication (using the outer EAP tunnel method) will succeed. 219 Neither does the failure of PT-EAP mean that the overall 220 authentication will fail. Success of the overall authentication 221 depends on the policy configured by the administrator. 223 At the end of the PT-EAP method, the NEA Server will indicate success 224 or failure to the EAP tunnel method. Some EAP tunnel methods may 225 provide explicit confirmation of inner method success; others may 226 not. This is out of scope for the PT-EAP method specification. 228 Successful completion of PT-EAP does not imply successful completion 229 of the overall authentication nor does PT-EAP failure imply overall 230 failure. This depends on the administrative policy in place. 232 The NEA Server and NEA Client may engage in an abnormal termination 233 of the PT-EAP exchange at any time by simply stopping the exchange. 234 This may also require terminating the EAP tunnel method, depending on 235 the capabilities of the EAP tunnel method. 237 3.2. Version Negotiation 239 PT-EAP version negotiation takes place in the first PT-EAP message 240 sent by the NEA Server (the Start message) and the first PT-EAP 241 message sent by the NEA Client (the response to the Start message). 242 The NEA Server MUST set the Version field in the Start message to the 243 maximum PT-EAP version that the NEA Server supports and is willing to 244 accept. 246 The NEA Client chooses the PT-EAP version to be used for the exchange 247 and places this value in the Version field in its response to the 248 Start message. The NEA Client SHOULD choose the value sent by the 249 NEA Server if the NEA Client supports it. However, the NEA Client 250 MAY set the Version field to a value less than the value sent by the 251 NEA Server (for example, if the NEA Client only supports lesser PT- 252 EAP versions). If the NEA Client only supports PT-EAP versions 253 greater than the value sent by the NEA Server, the NEA Client MUST 254 abnormally terminate the EAP negotiation. 256 If the version sent by the NEA Client is not acceptable to the NEA 257 Server, the NEA Server MUST terminate the PT-EAP session immediately. 258 Otherwise, the version sent by the NEA Client is the version of PT- 259 EAP that MUST be used. Both the NEA Client and the NEA Server MUST 260 set the Version field to the chosen version number in all subsequent 261 PT-EAP messages in this exchange. 263 This specification defines version 1 of PT-EAP. Version 0 is 264 reserved and MUST never be sent. New versions of PT-EAP (values 2-7) 265 may be defined by Standards Action, as defined in [RFC5226]. 267 3.3. PT-EAP Message Format 269 This section provides a detailed description of the fields in a PT- 270 EAP message. For a description of the diagram conventions used here, 271 see Section 1.2. Since PT-EAP is an EAP method, the first four 272 fields (e.g. Code, Identifier, Length and Type as shown in Figure 1) 273 in each message are mandated by and defined in EAP. The other 274 fields, e.g. Flags, Version and Data are specific to PT-EAP. 276 0 1 2 3 277 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | Code | Identifier | Length | 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 | Type | Flags | Ver | Data ... | 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 284 Figure 1: PT-EAP Message Format 286 Code 288 The Code field is one octet and identifies the type of the EAP 289 message. The only values used for PT-EAP are: 291 1 Request 293 2 Response 295 Identifier 297 The Identifier field is one octet and aids in matching Responses 298 with Requests. 300 Length 302 The Length field is two octets and indicates the length in octets 303 of this PT-EAP message, starting from the Code field. 305 Type 307 TBD EAP Method Type [RFC3748] assignment for PT-EAP. 309 Flags 311 +-+-+-+-+-+ 312 |S R R R R| 313 +-+-+-+-+-+ 315 S: Start 317 Indicates the beginning of a PT-EAP exchange. This flag MUST be 318 set only for the first message from the NEA Server. If the S flag 319 is set, the EAP message MUST NOT contain Data. 321 R: Reserved 323 This flag MUST be set to 0 and ignored upon receipt. 325 Version 327 This field is used for version negotiation, as described in 328 Section 3.2. 330 Data 332 Variable length data. This field is processed by the PB layer and 333 MUST include PB-TNC messages. For more information see PB-TNC 334 [RFC5793]. 336 The length of the Data field in a particular PT-EAP message may be 337 determined by subtracting the length of the PT-EAP header fields 338 from the value of the two octet Length field. 340 3.4. Preventing MITM Attacks with Channel Bindings 342 As described in the NEA Asokan Attack Analysis [I-D.ietf-nea-asokan], 343 a sophisticated MITM attack can be mounted against NEA systems. The 344 attacker forwards PA-TNC messages from a healthy machine through an 345 unhealthy one so that the unhealthy machine can gain network access. 346 Because there are easier attacks on NEA systems, like having the 347 unhealthy machine lie about its configuration, this attack is 348 generally only mounted against machines with an External Measurement 349 Agent (EMA). The EMA is a separate entity, difficult to compromise, 350 which measures and attests to the configuration of the endpoint. 352 To protect against NEA Asokan attacks, it is necessary for the 353 Posture Broker on an EMA-equipped endpoint to pass the tls-unique 354 channel binding [RFC5929] for PT-EAP's tunnel method to the EMA. 355 This value can then be included in the EMA's attestation so that the 356 Posture Validator responsible may then confirm that the value matches 357 the tls-unique channel binding for its end of the tunnel. If the 358 tls-unique values of the NEA Client and NEA Server match and this is 359 confirmed by the EMA, then the posture sent by a trustworthy EMA (and 360 thus the NEA Client) is from the same endpoint as the client side of 361 the TLS connection (since the endpoint knows the tls-unique value) so 362 no man-in-the-middle is forwarding posture. If they differ, an 363 attack has been detected and the Posture Validator SHOULD fail its 364 verification. 366 Note that tls-unique, as opposed to invoking a mutual cryptographic 367 binding, is used as there is no keying material being generated by 368 PT-EAP (the method is defined to facilitate the transport of posture 369 data and is not an authentication method). However, the NEA Client 370 may host an EMA which can be used as the means to cryptographically 371 bind the tls-unique content that may be validated by the Posture 372 Validator interfacing with the EAP Server. The binding of the tls- 373 unique to the client authentication prevents the client's message 374 from being used in another context. This prevents a poorly 375 configured client from unintentionally compromising the NEA system. 376 Strong mutual authentication of the NEA server and client is still 377 REQUIRED to prevent the disclosure of possibly sensitive NEA client 378 information to an attacker. 380 4. Security Considerations 382 This section discusses the major threats and countermeasures provided 383 by PT-EAP. As discussed throughout the document, the PT-EAP method 384 is designed to run inside an EAP tunnel method which is capable of 385 protecting the PT-EAP protocol from many threats. Since the EAP 386 tunnel method will be specified separately, this section describes 387 the considerations on the EAP tunnel method but does not evaluate its 388 ability to meet those requirements. The security considerations and 389 requirements for NEA can be found in [RFC5209]. 391 4.1. Trust Relationships 393 In order to understand where security countermeasures are necessary, 394 this section starts with a discussion of where the NEA architecture 395 envisions some trust relationships between the processing elements of 396 the PT-EAP protocol. The following sub-sections discuss the trust 397 properties associated with each portion of the NEA reference model 398 directly involved with the processing of the PT-EAP protocol flowing 399 inside an EAP tunnel. 401 4.1.1. Posture Transport Client 403 The Posture Transport Client is trusted by the Posture Broker Client 404 to: 406 o Not disclose to unauthorized parties, fabricate or alter the 407 contents of the PB-TNC batches received from the network 409 o Not observe, fabricate or alter the PB-TNC batches passed down 410 from the Posture Broker Client for transmission on the network 412 o Transmit on the network any PB-TNC batches passed down from the 413 Posture Broker Client 415 o Provide configured security protections (e.g. authentication, 416 integrity and confidentiality) for the Posture Broker Client's PB- 417 TNC batches sent on the network 419 o Expose the authenticated identity of the Posture Transport Server 420 to the Posture Broker Client. 422 o Verify the security protections placed upon messages received from 423 the network to ensure the messages are authentic and protected 424 from attacks on the network 426 o Deliver to the Posture Broker Client the PB-TNC batches received 427 from the network so long as they are properly security protected 429 o Provide a secure, reliable, in order delivery, full duplex 430 transport for the Posture Broker Client's messages 432 Since the Posture Transport Server can not validate the 433 trustworthiness of the Posture Transport Client; the Posture 434 Transport Server should protect itself appropriately. 436 4.1.2. Posture Transport Server 438 The Posture Transport Server is trusted by the Posture Broker Server 439 to: 441 o Not observe, fabricate or alter the contents of the PB-TNC batches 442 received from the network 444 o Not observe, fabricate or alter the PB-TNC batches passed down 445 from the Posture Broker Server for transmission on the network 447 o Transmit on the network any PB-TNC batches passed down from the 448 Posture Broker Server 450 o Ensure PB-TNC batches received from the network is properly 451 protected from a security perspective 453 o Provide configured security protections (e.g. authentication, 454 integrity and confidentiality) for the Posture Broker Server's 455 messages sent on the network 457 o Expose the authenticated identity of the Posture Transport Client 458 to the Posture Broker Server 460 o Verify the security protections placed upon messages received from 461 the network to ensure the messages are authentic and protected 462 from attacks on the network 464 Since the Posture Transport Client can not validate the 465 trustworthiness of the Posture Transport Server; the Posture 466 Transport Client should protect itself appropriately 468 4.2. Threats and Countermeasures 470 Beyond the trusted relationships assumed in Section 4.1, the PT-EAP 471 EAP method faces a number of potential security attacks that could 472 require security countermeasures. 474 Generally, the PT protocol is responsible for providing strong 475 security protections for all of the NEA protocols so any threats to 476 PT's ability to protect NEA protocol messages could be very damaging 477 to deployments. For the PT-EAP method, most of the cryptographic 478 security is provided by the outer EAP tunnel method and PT-EAP is 479 encapsulated within the protected tunnel. Therefore, this section 480 highlights the cryptographic requirements that need to be met by the 481 EAP tunnel method carrying PT-EAP in order to meet the NEA PT 482 requirements. 484 Once the message is delivered to the Posture Broker Client or Posture 485 Broker Server, the posture brokers are trusted to properly safely 486 process the messages. 488 4.2.1. Message Confidentiality 490 When PT-EAP messages are sent over unprotected network links or 491 spanning local software stacks that are not trusted, the contents of 492 the messages may be subject to information theft by an intermediary 493 party. This theft could result in information being recorded for 494 future use or analysis by an adversary. Messages observed by 495 eavesdroppers could contain information that exposes potential 496 weaknesses in the security of the endpoint, or system fingerprinting 497 information easing the ability of the attacker to employ attacks more 498 likely to be successful against the endpoint. The eavesdropper might 499 also learn information about the endpoint or network policies that 500 either singularly or collectively is considered sensitive 501 information. For example, if PT-EAP is carried by an EAP tunnel 502 method that does not provide confidentiality protection, an adversary 503 could observe the PA-TNC attributes included in the PB-TNC batch and 504 determine that the endpoint is lacking patches, or particular sub- 505 networks have more lenient policies. 507 In order to protect against NEA assessment message theft, the EAP 508 tunnel method carrying PT-EAP must provide strong cryptographic 509 authentication, integrity and confidentiality protection. The use of 510 bi-directional authentication in the EAP tunnel method carrying PT- 511 EAP ensures that only properly authenticated and authorized parties 512 may be involved in an assessment message exchange. When PT-EAP is 513 carried within a cryptographically protected EAP tunnel method like 514 EAP-FAST or EAP-TTLS, all of the PB-TNC and PA-TNC protocol messages 515 contents are hidden from potential theft by intermediaries lurking on 516 the network. 518 4.2.2. Message Fabrication 520 Attackers on the network or present within the NEA system could 521 introduce fabricated PT-EAP messages intending to trick or create a 522 denial of service against aspects of an assessment. For example, an 523 adversary could attempt to insert a PT-EAP message to tell a NEA 524 Server that the endpoint is totally infected. This could cause the 525 device to be blocked from accessing a critical resource, which would 526 be a denial of service. 528 The EAP tunnel method carrying a PT-EAP method needs to provide 529 strong security protections for the complete message exchange over 530 the network. These security protections prevent an intermediary from 531 being able to insert fake messages into the assessment. See 532 Section 5 for more details on the EAP tunnel requirements. 534 4.2.3. Message Modification 536 This attack could allow an active attacker capable of intercepting a 537 message to modify a PT-EAP message or transported PA-TNC attribute to 538 a desired value to ease the compromise of an endpoint. Without the 539 ability for message recipients to detect whether a received message 540 contains the same content as what was originally sent, active 541 attackers can stealthily modify the attribute exchange. 543 PT-EAP leverages the EAP tunnel method (e.g. TEAP, EAP-FAST or EAP- 544 TTLS) to provide strong authentication and integrity protections as a 545 countermeasure to this threat. The bi-directional authentication 546 prevents the attacker from acting as an active man-in-the-middle to 547 the protocol that could be used to modify the message exchange. The 548 strong integrity protections offered by the TLS-based EAP tunnel 549 method allows the PT-EAP message recipients to detect message 550 alterations by other types of network based adversaries. Because PT- 551 EAP does not itself provide explicit integrity protection for the PT- 552 EAP payload, an EAP tunnel method that offers strong integrity 553 protection is needed to mitigate this threat. 555 4.2.4. Denial of Service 557 A variety of types of denial of service attacks are possible against 558 PT-EAP if the message exchange is left unprotected while traveling 559 over the network. The Posture Transport Client and Posture Transport 560 Server are trusted not to participate in the denial of service of the 561 assessment session, leaving the threats to come from the network. 563 The PT-EAP method primarily relies on the outer EAP tunnel method to 564 provide strong authentication (at least of one party) and deployers 565 are expected to leverage other EAP methods to authenticate the other 566 party (typically the client) within the protected tunnel. The use of 567 a protected bi-directional authentication will prevent unauthorized 568 parties from participating in a PT-EAP exchange. 570 After the cryptographic authentication by the EAP tunnel method, the 571 session can be protected cryptographically to provide confidentiality 572 and source authenticity. Such protection prevents undetected 573 modification that could create a denial of service situation. 574 However it is possible for an adversary to alter the message flows 575 causing each message to be rejected by the recipient because it fails 576 the integrity checking. 578 4.2.5. NEA Asokan Attacks 580 As described in Section 3.4 and in the NEA Asokan Attack Analysis 581 [I-D.ietf-nea-asokan], a sophisticated MITM attack can be mounted 582 against NEA systems. The attacker forwards PA-TNC messages from a 583 healthy machine through an unhealthy one so that the unhealthy 584 machine can gain network access. Section 3.4 and the NEA Asokan 585 Attack Analysis provide a detailed description of this attack and of 586 the countermeasures that can be employed against it. 588 Because lying endpoint attacks are much easier than Asokan attacks 589 and an effective countermeasure against lying endpoint attacks is the 590 use of an External Measurement Agent (EMA), countermeasures against 591 an Asokan attack are not necessary unless an EMA is in use. However, 592 PT-EAP implementers may not know whether an EMA will be used with 593 their implementation. Therefore, PT-EAP implementers SHOULD support 594 these countermeasures by providing the value of the tls-unique 595 channel binding to higher layers in the NEA reference model: Posture 596 Broker Clients, Posture Broker Servers, Posture Collectors, and 597 Posture Validators. 599 4.3. Candidate EAP Tunnel Method Protections 601 This section discusses how PT-EAP is used within various EAP tunnel 602 methods to meet the PT requirements from Section 5. 604 TEAP [I-D.ietf-emu-eap-tunnel-method], EAP-FAST [RFC4851] and EAP- 605 TTLS [RFC5281] make use of TLS [RFC5246] to protect the transport of 606 information between the NEA Client and NEA Server. Each of these EAP 607 tunnel methods has two phases. In the first phase, a TLS tunnel is 608 established between NEA Client and NEA Server. In the second phase, 609 the tunnel is used to pass other information. PT-EAP requires that 610 establishing this tunnel include at least an authentication of the 611 NEA Server by the NEA Client. 613 The phase two dialog may include authentication of the user by doing 614 other EAP methods or in the case of EAP-TTLS by using EAP or non-EAP 615 authentication dialogs. PT-EAP is also carried by the phase two 616 tunnel allowing the NEA assessment to be within an encrypted and 617 integrity protected transport. 619 With all these methods (e.g. TEAP [I-D.ietf-emu-eap-tunnel-method], 620 EAP-FAST [RFC4851] and EAP-TTLS [RFC5281]), a cryptographic key is 621 derived from the authentication that may be used to secure later 622 transmissions. Each of these methods employs at least a NEA Server 623 authentication using an X.509 certificate. Within each EAP tunnel 624 method will exist a set of inner EAP methods. These inner methods 625 may perform additional security handshakes including more granular 626 authentications or exchanges of integrity information (such as PT- 627 EAP.) At some point after the conclusion of each inner EAP method, 628 some of the methods will export the established secret keys to the 629 outer tunnel method. It's expected that the outer method will 630 cryptographically mix these keys into any keys it is currently using 631 to protect the session and perform a final operation to determine 632 whether both parties have arrived at the same mixed key. This 633 cryptographic binding of the inner method results to the outer 634 method's keys is essential for detection of conventional (non-NEA) 635 Asokan attacks. 637 TEAP [I-D.ietf-emu-eap-tunnel-method] is the mandatory to implement 638 EAP tunnel method. 640 4.4. Security Claims for PT-EAP as per RFC3748 642 This section summarizes the security claims for this specification, 643 as required by RFC3748 Section 7.2: 645 Auth. mechanism: None 646 Ciphersuite negotiation: No 647 Mutual authentication: No 648 Integrity protection: No 649 Replay protection: No 650 Confidentiality: No 651 Key derivation: No 652 Key strength: N/A 653 Dictionary attack resistant: N/A 654 Fast reconnect: No 655 Crypt. binding: N/A 656 Session independence: N/A 657 Fragmentation: No 658 Channel binding: No 660 5. Requirements for EAP Tunnel Methods 662 Because the PT-EAP inner method described in this specification 663 relies on the outer EAP tunnel method for a majority of its security 664 protections, this section reiterates the PT requirements that MUST be 665 met by the IETF standard EAP tunnel method for use with PT-EAP. 667 There is no mandatory to implement EAP tunnel based method defined in 668 this draft since there exists no such standard method. At the time 669 of this writing, the IETF EAP Method Update (EMU) working group is 670 working on standardizing on TEAP [I-D.ietf-emu-eap-tunnel-method] as 671 a Standards Track EAP tunnel method that will satisfy NEA's 672 requirements. 674 The security requirements described in this specification MUST be 675 implemented in any product claiming to be PT-EAP compliant. The 676 decision of whether a particular deployment chooses to use these 677 protections is a deployment issue. A customer may choose to avoid 678 potential deployment issues or performance penalties associated with 679 the use of cryptography when the required protection has been 680 achieved through other mechanisms (e.g. physical isolation). If 681 security mechanisms may be deactivated by policy, an implementation 682 SHOULD offer an interface to query how a message will be (or was) 683 protected by PT so higher layer NEA protocols can factor this into 684 their decisions. 686 RFC 5209 [RFC5209] includes the following requirement that is to be 687 applied during the selection of the EAP tunnel method(s) used in 688 conjunction with PT-EAP: 690 PT-2: The PT protocol MUST be capable of supporting mutual 691 authentication, integrity, confidentiality, and replay protection 692 of the PB messages between the Posture Transport Client and the 693 Posture Transport Server. 695 Note that mutual authentication could be achieved by a combination of 696 a strong authentication of one party (e.g. server authentication 697 while establishing the TLS-based tunnel) by the EAP tunnel method in 698 conjunction with a second authentication of the other party (e.g. 699 client authentication inside the protected tunnel) by another EAP 700 method running prior to PT-EAP. 702 Having the Posture Transport Client always authenticate the Posture 703 Transport Server provides assurance to the NEA Client that the NEA 704 Server is authentic (not a rogue or MiTM) prior to disclosing secret 705 or potentially privacy sensitive information about what is running or 706 configured on the endpoint. However the NEA Server's policy may 707 allow for the delay of the authentication of the NEA Client until a 708 suitable protected channel has been established allowing for non- 709 cryptographic NEA Client credentials (e.g. username/password) to be 710 used. Whether the communication channel is established with mutual 711 or server-side only authentication, the resulting channel needs to 712 provide strong integrity and confidentiality protection to its 713 contents. These protections are to be bound to at least the 714 authentication of the NEA Server by the NEA Client, so the session is 715 cryptographically bound to a particular authentication event. 717 The EAP tunnel method carrying PT-EAP MUST provide strong 718 cryptographic authentication, integrity and confidentiality 719 protection to protect against NEA assessment message theft as 720 described in Section 4.2.1. The cryptographically protected EAP 721 tunnel ensures that all of the PA-TNC and PB-TNC protocol messages 722 are hidden from intermediaries wanting to steal NEA data. 724 To support countermeasures against NEA Asokan attacks as described in 725 Section 3.4, the EAP Tunnel Method used with PT-EAP will need to 726 support the tls-unique channel binding. This should not be a high 727 bar since all EAP tunnel methods currently support this but not all 728 implementations of those methods may do so. 730 6. Privacy Considerations 732 The role of PT-EAP is to act as a secure transport for PB-TNC over a 733 network before the endpoint has been admitted to the network. As a 734 transport protocol, PT-EAP does not directly utilize or require 735 direct knowledge of any personally identifiable information (PII). 736 PT-EAP will typically be used in conjunction with other EAP methods 737 that provide for the user authentication (if bi-directional 738 authentication is used), so the user's credentials are not directly 739 seen by the PT-EAP inner method. 741 While PT-EAP does not provide cryptographic protection for the PB-TNC 742 batches, it is designed to operate within an EAP tunnel method that 743 provides strong authentication, integrity and confidentiality 744 services. Therefore, it is important for deployers to leverage these 745 protections in order to prevent disclosure of PII potentially 746 contained within PA-TNC or PB-TNC within the PT-EAP payload. 748 7. IANA Considerations 750 This section provides guidance to the Internet Assigned numbers 751 Authority (IANA) regarding registration of values related to the PT- 752 EAP protocol, in accordance with BCP 26 [RFC5226]. 754 The EAP Method type for PT-EAP needs to be assigned; e.g. the 755 assignment for TYPE in Section 3.3. 757 +-------+--------------------------+--------------------------------+ 758 | Value | Description | Reference | 759 +-------+--------------------------+--------------------------------+ 760 | TBD | EAP Method Type for | RFC number assigned to this | 761 | | PT-EAP | draft | 762 +-------+--------------------------+--------------------------------+ 764 [TO BE REMOVED PRIOR TO PUBLICATION: This registration should take 765 place at the following location: http://www.iana.org/assignments/ 766 eap-numbers/eap-numbers.xml#eap-numbers-3 ] 768 This document also defines one new IANA top-level registry: PT-EAP 769 Versions. This section explains how this registry works. Because 770 only eight (8) values are available in this registry, a high bar is 771 set for new assignments. The only way to register new values in this 772 registry is through Standards Action (via an approved Standards Track 773 RFC). 775 7.1. Registry for PT-EAP Versions 777 The name for this registry is "PT-EAP Versions". Each entry in this 778 registry includes a decimal integer value between 1 and 7 identifying 779 the version, and a reference to the RFC where the version is defined. 781 The following entries for this registry are defined in this document. 782 Once this document becomes an RFC, they will become the initial 783 entries in the registry for PT-EAP Versions. Additional entries to 784 this registry are added by Standards Action, as defined in RFC 5226 785 [RFC5226]. 787 +-------+----------------------------+ 788 | Value | Defining Specification | 789 +-------+----------------------------+ 790 | 0 | Reserved | 791 | 1 | RFC # Assigned to this I-D | 792 +-------+----------------------------+ 794 8. Acknowledgements 796 Thanks to the Trusted Computing Group for contributing the initial 797 text upon which this document was based. 799 The authors of this draft would like to acknowledge the following 800 people who have contributed to or provided substantial input on the 801 preparation of this document or predecessors to it: Amit Agarwal, 802 Morteza Ansari, Diana Arroyo, Stuart Bailey, Boris Balacheff, Uri 803 Blumenthal, Gene Chang, Scott Cochrane, Pasi Eronen, Aman Garg, 804 Sandilya Garimella, David Grawrock, Stephen Hanna, Thomas Hardjono, 805 Chris Hessing, Ryan Hurst, Hidenobu Ito, John Jerrim, Meenakshi 806 Kaushik, Greg Kazmierczak, Scott Kelly, Bryan Kingsford, PJ Kirner, 807 Sung Lee, Lisa Lorenzin, Mahalingam Mani, Bipin Mistry, Seiji 808 Munetoh, Rod Murchison, Barbara Nelson, Kazuaki Nimura, Ron Pon, Ivan 809 Pulleyn, Alex Romanyuk, Ravi Sahita, Chris Salter, Mauricio Sanchez, 810 Joseph Salowey, Dean Sheffield, Curtis Simonson, Jeff Six, Ned Smith, 811 Michelle Sommerstad, Joseph Tardo, Lee Terrell, Susan Thomson, Chris 812 Trytten, and John Vollbrecht. 814 This document was prepared using template-bare-05.xml. 816 9. References 818 9.1. Normative References 820 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 821 Requirement Levels", BCP 14, RFC 2119, March 1997. 823 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 824 Levkowetz, "Extensible Authentication Protocol (EAP)", 825 RFC 3748, June 2004. 827 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 828 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 829 May 2008. 831 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 832 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 834 [RFC5792] Sangster, P. and K. Narayan, "PA-TNC: A Posture Attribute 835 (PA) Protocol Compatible with Trusted Network Connect 836 (TNC)", RFC 5792, March 2010. 838 [RFC5793] Sahita, R., Hanna, S., Hurst, R., and K. Narayan, "PB-TNC: 839 A Posture Broker (PB) Protocol Compatible with Trusted 840 Network Connect (TNC)", RFC 5793, March 2010. 842 9.2. Informative References 844 [Asokan] Asokan, N., Niemi, V., Nyberg, K., and Nokia Research 845 Center, Finland, ""Man in the Middle Attacks in Tunneled 846 Authentication Protocols"", Nov 2002, 847 . 849 [I-D.ietf-emu-eap-tunnel-method] 850 Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna, 851 "Tunnel EAP Method (TEAP) Version 1", 852 draft-ietf-emu-eap-tunnel-method-04 (work in progress), 853 October 2012. 855 [I-D.ietf-nea-asokan] 856 Salowey, J. and S. Hanna, "NEA Asokan Attack Analysis", 857 draft-ietf-nea-asokan-02 (work in progress), October 2012. 859 [I-D.ietf-nea-pt-tls] 860 Sangster, P., Cam-Winget, N., and J. Salowey, "PT-TLS: A 861 TLS-based Posture Transport (PT) Protocol", 862 draft-ietf-nea-pt-tls-08 (work in progress), October 2012. 864 [RFC4851] Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "The 865 Flexible Authentication via Secure Tunneling Extensible 866 Authentication Protocol Method (EAP-FAST)", RFC 4851, 867 May 2007. 869 [RFC5209] Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J. 870 Tardo, "Network Endpoint Assessment (NEA): Overview and 871 Requirements", RFC 5209, June 2008. 873 [RFC5281] Funk, P. and S. Blake-Wilson, "Extensible Authentication 874 Protocol Tunneled Transport Layer Security Authenticated 875 Protocol Version 0 (EAP-TTLSv0)", RFC 5281, August 2008. 877 [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings 878 for TLS", RFC 5929, July 2010. 880 Authors' Addresses 882 Nancy Cam-Winget 883 Cisco Systems 884 80 West Tasman Drive 885 San Jose, CA 95134 887 Email: ncamwing@cisco.com 889 Paul Sangster 890 Symantec Corporation 891 6825 Citrine Drive 892 Carlsbad, CA 92009 893 USA 895 Email: paul_sangster@symantec.com