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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) == Missing Reference: 'Realm' is mentioned on line 1185, but not defined == Missing Reference: 'ServerInfo' is mentioned on line 1185, but not defined -- Possible downref: Non-RFC (?) normative reference: ref. 'NIST-DH' ** Downref: Normative reference to an Informational RFC: RFC 2104 ** Downref: Normative reference to an Informational RFC: RFC 6234 ** Downref: Normative reference to an Informational RFC: RFC 7748 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Aura 3 Internet-Draft Aalto University 4 Intended status: Standards Track M. Sethi 5 Expires: September 10, 2020 Ericsson 6 March 9, 2020 8 Nimble out-of-band authentication for EAP (EAP-NOOB) 9 draft-aura-eap-noob-08 11 Abstract 13 Extensible Authentication Protocol (EAP) provides support for 14 multiple authentication methods. This document defines the EAP-NOOB 15 authentication method for nimble out-of-band (OOB) authentication and 16 key derivation. The EAP method is intended for bootstrapping all 17 kinds of Internet-of-Things (IoT) devices that have no pre-configured 18 authentication credentials. The method makes use of a user-assisted 19 one-directional OOB message between the peer device and 20 authentication server to authenticate the in-band key exchange. The 21 device must have an input or output interface, such as a display, 22 microphone, speakers or blinking light, which can send or receive 23 dynamically generated messages of tens of bytes in length. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 10, 2020. 42 Copyright Notice 44 Copyright (c) 2020 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3. EAP-NOOB protocol . . . . . . . . . . . . . . . . . . . . . . 5 62 3.1. Protocol overview . . . . . . . . . . . . . . . . . . . . 5 63 3.2. Protocol messages and sequences . . . . . . . . . . . . . 8 64 3.2.1. Common handshake in all EAP-NOOB exchanges . . . . . 8 65 3.2.2. Initial Exchange . . . . . . . . . . . . . . . . . . 10 66 3.2.3. OOB Step . . . . . . . . . . . . . . . . . . . . . . 11 67 3.2.4. Completion Exchange . . . . . . . . . . . . . . . . . 13 68 3.2.5. Waiting Exchange . . . . . . . . . . . . . . . . . . 15 69 3.3. Protocol data fields . . . . . . . . . . . . . . . . . . 16 70 3.3.1. Peer identifier, realm and NAI . . . . . . . . . . . 16 71 3.3.2. Message data fields . . . . . . . . . . . . . . . . . 18 72 3.4. Fast reconnect and rekeying . . . . . . . . . . . . . . . 23 73 3.4.1. Persistent EAP-NOOB association . . . . . . . . . . . 23 74 3.4.2. Reconnect Exchange . . . . . . . . . . . . . . . . . 24 75 3.4.3. User reset . . . . . . . . . . . . . . . . . . . . . 27 76 3.5. Key derivation . . . . . . . . . . . . . . . . . . . . . 28 77 3.6. Error handling . . . . . . . . . . . . . . . . . . . . . 31 78 3.6.1. Invalid messages . . . . . . . . . . . . . . . . . . 33 79 3.6.2. Unwanted peer . . . . . . . . . . . . . . . . . . . . 33 80 3.6.3. State mismatch . . . . . . . . . . . . . . . . . . . 33 81 3.6.4. Negotiation failure . . . . . . . . . . . . . . . . . 33 82 3.6.5. Cryptographic verification failure . . . . . . . . . 34 83 3.6.6. Application-specific failure . . . . . . . . . . . . 34 84 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 85 4.1. Cryptosuites . . . . . . . . . . . . . . . . . . . . . . 35 86 4.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 35 87 4.3. Error codes . . . . . . . . . . . . . . . . . . . . . . . 36 88 4.4. Domain name reservation considerations . . . . . . . . . 37 89 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 38 90 5.1. Implementation with wpa_supplicant and hostapd . . . . . 38 91 5.2. Implementation on Contiki . . . . . . . . . . . . . . . . 39 92 5.3. Protocol modeling . . . . . . . . . . . . . . . . . . . . 39 93 6. Security considerations . . . . . . . . . . . . . . . . . . . 39 94 6.1. Authentication principle . . . . . . . . . . . . . . . . 39 95 6.2. Identifying correct endpoints . . . . . . . . . . . . . . 41 96 6.3. Trusted path issues and misbinding attacks . . . . . . . 42 97 6.4. Peer identifiers and attributes . . . . . . . . . . . . . 43 98 6.5. Identity protection . . . . . . . . . . . . . . . . . . . 44 99 6.6. Downgrading threats . . . . . . . . . . . . . . . . . . . 44 100 6.7. Recovery from loss of last message . . . . . . . . . . . 45 101 6.8. EAP security claims . . . . . . . . . . . . . . . . . . . 46 102 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 103 7.1. Normative references . . . . . . . . . . . . . . . . . . 48 104 7.2. Informative references . . . . . . . . . . . . . . . . . 49 105 Appendix A. Exchanges and events per state . . . . . . . . . . . 51 106 Appendix B. Application-specific parameters . . . . . . . . . . 52 107 Appendix C. ServerInfo and PeerInfo contents . . . . . . . . . . 53 108 Appendix D. EAP-NOOB roaming . . . . . . . . . . . . . . . . . . 55 109 Appendix E. OOB message as URL . . . . . . . . . . . . . . . . . 56 110 Appendix F. Example messages . . . . . . . . . . . . . . . . . . 57 111 Appendix G. TODO list . . . . . . . . . . . . . . . . . . . . . 59 112 Appendix H. Version history . . . . . . . . . . . . . . . . . . 59 113 Appendix I. Acknowledgments . . . . . . . . . . . . . . . . . . 62 114 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 62 116 1. Introduction 118 This document describes a method for registration, authentication and 119 key derivation for network-connected ubiquitous computing devices, 120 such as consumer and enterprise appliances that are part of the 121 Internet of Things (IoT). These devices may be off-the-shelf 122 hardware that is sold and distributed without any prior registration 123 or credential-provisioning process, or they may be recycled devices 124 after a hard reset. Thus, the device registration in a server 125 database, ownership of the device, and the authentication credentials 126 for both network access and application-level security must all be 127 established at the time of the device deployment. Furthermore, many 128 such devices have only limited user interfaces that could be used for 129 their configuration. Often, the interfaces are limited to either 130 only input (e.g. camera) or output (e.g. display screen). The device 131 configuration is made more challenging by the fact that the devices 132 may exist in large numbers and may have to be deployed or re- 133 configured nimbly based on user needs. 135 To summarize, devices may have the following characteristics: 137 o no pre-established relation with the intended server or user, 139 o no pre-provisioned device identifier or authentication 140 credentials, 142 o input or output interface that may be capable of only one- 143 directional communication. 145 Many proprietary OOB configuration methods exits for specific IoT 146 devices. The goal of this specification is to provide an open 147 standard and a generic protocol for bootstrapping the security of 148 network-connected appliances, such as displays, printers, speakers, 149 and cameras. The security bootstrapping in this specification makes 150 use of a user-assisted out-of-band (OOB) channel. The device 151 authentication relies on user having physical access to the device, 152 and the of the key exchange security is based on the assumption that 153 attackers are not able to observe or modify the messages conveyed 154 through the OOB channel. We follow the common approach taken in 155 pairing protocols: performing a Diffie-Hellman key exchange over the 156 insecure network and authenticating the established key with the help 157 of the OOB channel in order to prevent impersonation and man-in-the- 158 middle (MitM) attacks. 160 The solution presented here is intended for devices that have either 161 an input or output interface, such as a camera, microphone, display 162 screen, speakers or blinking LED light, which is able to send or 163 receive dynamically generated messages of tens of bytes in length. 164 Naturally, this solution may not be appropriate for very small 165 sensors or actuators that have no user interface at all or for 166 devices that are inaccessible to the user. We also assume that the 167 OOB channel is at least partly automated (e.g. camera scanning a bar 168 code) and, thus, there is no need to absolutely minimize the length 169 of the data transferred through the OOB channel. This differs, for 170 example, from Bluetooth simple pairing [BluetoothPairing], where it 171 is critical to minimize the length of the manually transferred or 172 compared codes. Since the OOB messages are dynamically generated, we 173 do not support static printed registration codes. This also prevents 174 attacks where a static secret code would be leaked. 176 2. Terminology 178 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 179 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 180 document are to be interpreted as described in [RFC2119]. 182 In addition, this document frequently uses the following terms as 183 they have been defined in [RFC5216]: 185 authenticator The entity initiating EAP authentication. 187 peer The entity that responds to the authenticator. In 188 [IEEE-802.1X], this entity is known as the supplicant. (We use 189 the terms peer, device and peer device interchangeably.) 191 server The entity that terminates the EAP authentication method with 192 the peer. In the case where no backend authentication server 193 is used, the EAP server is part of the authenticator. In the 194 case where the authenticator operates in pass-through mode, the 195 EAP server is located on the backend authentication server. 197 3. EAP-NOOB protocol 199 This section defines the EAP-NOOB protocol. The protocol is a 200 generalized version of the original idea presented by Sethi et al. 201 [Sethi14]. 203 3.1. Protocol overview 205 One EAP-NOOB protocol execution spans two or more EAP conversations, 206 called Exchanges in this specification. Each Exchange consists of 207 several EAP request-response pairs. At least two separate EAP 208 conversations are needed to give the human user time to deliver the 209 OOB message between them. 211 The overall protocol starts with the Initial Exchange, which 212 comprises four EAP request-response pairs. In the Initial Exchange, 213 the server allocates an identifier to the peer, and the server and 214 peer negotiate the protocol version and cryptosuite (i.e. 215 cryptographic algorithm suite), exchange nonces and perform an 216 Ephemeral Elliptic Curve Diffie-Hellman (ECDHE) key exchange. The 217 user-assisted OOB Step then takes place. This step requires only one 218 out-of-band message either from the peer to the server or from the 219 server to the peer. While waiting for the OOB Step action, the peer 220 MAY probe the server by reconnecting to it with EAP-NOOB. If the OOB 221 Step has already taken place, the probe leads to the Completion 222 Exchange, which completes the mutual authentication and key 223 confirmation. On the other hand, if the OOB Step has not yet taken 224 place, the probe leads to the Waiting Exchange, and the peer will 225 perform another probe after a server-defined minimum waiting time. 226 The Initial Exchange and Waiting Exchange always end in EAP-Failure, 227 while the Completion Exchange may result in EAP-Success. Once the 228 peer and server have performed a successful Completion Exchange, both 229 endpoints store the created association in persistent storage, and 230 the OOB Step is not repeated. Thereafter, creation of new temporal 231 keys, ECDHE rekeying, and updates of cryptographic algorithms can be 232 achieved with the Reconnect Exchange. 234 OOB Output/Initial Exchange/ 235 Waiting Exchange 236 .-----. 237 | v 238 .------------------. Initial .------------------. 239 | | Exchange | | 240 .->| Unregistered (0) |---------------->|Waiting for OOB(1)| 241 | | | | | 242 | '------------------' '------------------' 243 | | | ^ 244 User Reset Completion | | | 245 | Exchange | OOB OOB 246 |<-------. .-------------------------' Input Reject/ 247 | | | | Initial 248 | | | | Exchange 249 | | v v | 250 | .------------------. Completion .------------------. 251 | | | Exchange | | 252 | | Registered (4) |<----------------| OOB Received (2) | 253 | | | | | 254 | '------------------' '------------------' 255 | | ^ 256 | Mobility/ | 257 | Timeout/ Reconnect 258 | Failure Exchange 259 | | | 260 | v | 261 | .-----------------. 262 | | | 263 '--| Reconnecting (3)| 264 | | 265 '-----------------' 267 Figure 1: EAP-NOOB server-peer association state machine 269 Figure 1 shows the association state machine, which is the same for 270 the server and for the peer. (For readability, only the main state 271 transitions are shown. The complete table of transitions can be 272 found in Appendix A.) When the peer initiates the EAP-NOOB method, 273 the server chooses the ensuing message exchange based on the 274 combination of the server and peer states. The EAP server and peer 275 are initially in the Unregistered state, in which no state 276 information needs to be stored. Before a successful Completion 277 Exchange, the server-peer association state is ephemeral in both the 278 server and peer (ephemeral states 0..2), and either endpoint may 279 cause the protocol to fall back to the Initial Exchange. After the 280 Completion Exchange has resulted in EAP-Success, the association 281 state becomes persistent (persistent states 3..4). Only user reset 282 or memory failure can cause the return of the server or the peer from 283 the persistent states to the ephemeral states and to the Initial 284 Exchange. 286 The server MUST NOT repeat a successful OOB Step with the same peer 287 except if the association with the peer is explicitly reset by the 288 user or lost due to failure of the persistent storage in the server. 289 More specifically, once the association has entered the Registered 290 state, the server MUST NOT delete the association or go back to 291 states 0..2 without explicit user approval. Similarly, the peer MUST 292 NOT repeat the OOB Step unless the user explicitly deletes from the 293 peer the association with the server or resets the peer to the 294 Unregistered state. The server and peer MAY implement user reset of 295 the association by deleting the state data from that endpoint. If an 296 endpoint continues to store data about the association after the user 297 reset, its behavior SHOULD be equivalent to having deleted the 298 association data. 300 It can happen that the peer accidentally or through user reset loses 301 its persistent state and reconnects to the server without a 302 previously allocated peer identifier. In that case, the server MUST 303 treat the peer as a new peer. The server MAY use auxiliary 304 information, such as the PeerInfo field received in the Initial 305 Exchange, to detect multiple associations with the same peer. 306 However, it MUST NOT delete or merge redundant associations without 307 user or application approval because EAP-NOOB internally has no 308 secure way of verifying that the two peers are the same physical 309 device. Similarly, the server might lose the association state 310 because of a memory failure or user reset. In that case, the only 311 way to recover is that the user resets also the peer. 313 A special feature of the EAP-NOOB method is that the server is not 314 assumed to have any a-priori knowledge of the peer. Therefore, the 315 peer initially uses the generic identity string "noob@eap-noob.net" 316 (.arpa domain TBA) as its network access identifier (NAI). The 317 server then allocates a server-specific identifier to the peer. The 318 generic NAI serves two purposes: firstly, it tells the server that 319 the peer supports and expects the EAP-NOOB method and, secondly, it 320 allows routing of the EAP-NOOB sessions to a specific authentication 321 server in the AAA architecture. 323 EAP-NOOB is an unusual EAP method in that the peer has to have 324 multiple EAP conversations with the server before it can receive EAP- 325 Success. The reason is that, while EAP allows delays between the 326 request-response pairs, e.g. for repeated password entry, the user 327 delays in OOB authentication can be much longer than in password 328 trials. In particular, EAP-NOOB supports also peers with no input 329 capability in the user interface. Since user cannot initiate the 330 protocol in these devices, they have to perform the Initial Exchange 331 opportunistically and hope for the OOB Step to take place within a 332 timeout period (NoobTimeout), which is why the timeout needs to be 333 several minutes rather than seconds. For example, consider a printer 334 (peer) that outputs the OOB message on paper, which is then scanned 335 for the server. To support such high-latency OOB channels, the peer 336 and server perform the Initial Exchange in one EAP conversation, then 337 allow time for the OOB message to be delivered, and later perform the 338 Waiting and Completion Exchanges in different EAP conversations. 340 3.2. Protocol messages and sequences 342 This section defines the EAP-NOOB exchanges, which correspond to EAP 343 conversations. The exchanges start with a common handshake, which 344 determines the type of the following exchange. The common handshake 345 messages and the subsequent messages for each exchange type are 346 listed in the diagrams below. The diagrams also specify the data 347 members present in each message. Each exchange comprises multiple 348 EAP requests-response pairs and ends in either EAP-Failure, 349 indicating that authentication is not (yet) successful, or in EAP- 350 Success. 352 3.2.1. Common handshake in all EAP-NOOB exchanges 354 All EAP-NOOB exchanges start with common handshake messages. The 355 handshake starts with the identity request and response that are 356 common to all EAP methods. Their purpose is to enable the AAA 357 architecture to route the EAP conversation to the EAP server and to 358 enable the EAP server to select the EAP method. The handshake then 359 continues with one EAP-NOOB request-response pair in which the server 360 discovers the peer identifier used in EAP-NOOB and the peer state. 362 In more detail, each EAP-NOOB exchange begins with the authenticator 363 sending an EAP-Request/Identity packet to the peer. From this point 364 on, the EAP conversation occurs between the server and the peer, and 365 the authenticator acts as a pass-through device. The peer responds 366 to the authenticator with an EAP-Response/Identity packet, which 367 contains the network access identifier (NAI). The authenticator, 368 acting as a pass-through device, forwards this response and the 369 following EAP conversation between the peer and the AAA architecture. 370 The AAA architecture routes the conversation to a specific AAA server 371 (called "EAP server" or simply "server" in this specification) based 372 on the realm part of the NAI. The server selects the EAP-NOOB method 373 based on the user part of the NAI, as defined in Section 3.3.1. 375 After receiving the EAP-Response/Identity message, the server sends 376 the first EAP-NOOB request (Type=9) to the peer, which responds with 377 the peer identifier (PeerId) and state (PeerState) in the range 0..3. 378 However, the peer SHOULD omit the PeerId from the response (Type=9) 379 when PeerState=0. The server then chooses the EAP-NOOB exchange, 380 i.e. the ensuing message sequence, as explained below. The peer 381 recognizes the exchange based on the message type field (Type) of the 382 next EAP-NOOB request received from the server. 384 The server MUST determine the exchange type based on the combination 385 of the peer and server states as follows (also summarized in 386 Figure 11). If one of the peer and server is in the Unregistered (0) 387 state and the other is in one of the ephemeral states (0..2), the 388 server chooses the Initial Exchange. If one of the peer or server is 389 in the OOB Received (2) state and the other is either in the Waiting 390 for OOB (1) or OOB Received (2) state, the OOB Step has taken place 391 and the server chooses the Completion Exchange. If both the server 392 and peer are in the Waiting for OOB (1) state, the server chooses the 393 Waiting Exchange. If the peer is in the Reconnecting (3) state and 394 the server is in the Registered (4) or Reconnecting (3) state, the 395 server chooses the Reconnect Exchange. All other state combinations 396 are error situations where user action is required, and the server 397 SHOULD indicate such errors to the peer with the error code 2002 (see 398 Section 3.6.3). Note also that the peer MUST NOT initiate EAP-NOOB 399 when the peer is in Registered (4) state. 401 EAP Peer EAP Server 402 | | 403 |<----------- EAP-Request/Identity -| | 404 | | 405 | | 406 |------------ EAP-Response/Identity -------------->| 407 | (NAI=noob@eap-noob.net) | 408 | | 409 | | 410 |<----------- EAP-Request/EAP-NOOB ----------------| 411 | (Type=9) | 412 | | 413 | | 414 |------------ EAP-Response/EAP-NOOB -------------->| 415 | (Type=9,[PeerId],PeerState=1) | 416 | | 417 | continuing with exchange-specific messages... | 419 Figure 2: Common handshake in all EAP-NOOB exchanges 421 3.2.2. Initial Exchange 423 The Initial Exchange comprises the common handshake and two further 424 EAP-NOOB request-response pairs, one for version, cryptosuite and 425 parameter negotiation and the other for the ECDHE key exchange. The 426 first EAP-NOOB request (Type=1) from the server contains a newly 427 allocated PeerId for the peer and an optional Realm. The server 428 allocates a new PeerId in the Initial Exchange regardless of any old 429 PeerId in the username part of the received NAI. The server also 430 sends in the request a list of the protocol versions (Vers) and 431 cryptosuites (Cryptosuites) it supports, an indicator of the OOB 432 channel directions it supports (Dirs), and a ServerInfo object. The 433 peer chooses one of the versions and cryptosuites. The peer sends a 434 response (Type=1) with the selected protocol version (Verp), the 435 received PeerId, the selected cryptosuite (Cryptosuitep), an 436 indicator of the OOB channel directions selected by the peer (Dirp), 437 and a PeerInfo object. In the second EAP-NOOB request and response 438 (Type=2), the server and peer exchange the public components of their 439 ECDHE keys and nonces (PKs,Ns,PKp,Np). The ECDHE keys MUST be based 440 on the negotiated cryptosuite i.e. Cryptosuitep. The Initial 441 Exchange always ends with EAP-Failure from the server because the 442 authentication cannot yet be completed. 444 EAP Peer EAP Server 445 | ...continuing from common handshake | 446 | | 447 |<----------- EAP-Request/EAP-NOOB ----------------| 448 | (Type=1,Vers,PeerId,[Realm], | 449 | Cryptosuites,Dirs,ServerInfo) | 450 | | 451 | | 452 |------------ EAP-Response/EAP-NOOB -------------->| 453 | (Type=1,Verp,PeerId,Cryptosuitep, | 454 | Dirp,PeerInfo) | 455 | | 456 | | 457 |<----------- EAP-Request/EAP-NOOB ----------------| 458 | (Type=2,PeerId,PKs,Ns,[SleepTime]) | 459 | | 460 | | 461 |------------ EAP-Response/EAP-NOOB -------------->| 462 | (Type=2,PeerId,PKp,Np) | 463 | | 464 | | 465 |<----------- EAP-Failure -------------------------| 466 | | 468 Figure 3: Initial Exchange 470 At the conclusion of the Initial Exchange, both the server and the 471 peer move to the Waiting for OOB (1) state. 473 3.2.3. OOB Step 475 The OOB Step, labeled as OOB Output and OOB Input in Figure 1, takes 476 place after the Initial Exchange. Depending on the negotiated OOB 477 channel direction, the peer or the server outputs the OOB message 478 shown in Figure 4 or Figure 5, respectively. The data fields are the 479 PeerId, the secret nonce Noob, and the cryptographic fingerprint 480 Hoob. The contents of the data fields are defined in Section 3.3.2. 481 The OOB message is delivered to the other endpoint via a user- 482 assisted OOB channel. 484 For brevity, we will use the terms OOB sender and OOB receiver in 485 addition to the already familiar EAP server and EAP peer. If the OOB 486 message is sent in in the server-to-peer direction, the OOB sender is 487 the server and the OOB receiver is the peer. On the other hand, if 488 the OOB message is sent in the peer-to-server direction, the OOB 489 sender is the peer and the OOB receiver is the server. 491 EAP Peer EAP Server 492 | | 493 |=================OOB=============================>| 494 | (PeerId,Noob,Hoob) | 495 | | 497 Figure 4: OOB Step, from peer to EAP server 499 EAP Peer EAP Server 500 | | 501 |<================OOB==============================| 502 | (PeerId,Noob,Hoob) | 503 | | 505 Figure 5: OOB Step, from EAP server to peer 507 The OOB receiver MUST compare the received value of the fingerprint 508 Hoob (see Section 3.3.2) with a value that it computes locally. This 509 integrity check ensures that the endpoints agree on contents of the 510 Initial Exchange. If the values are equal, the receiver moves to the 511 OOB Received (2) state. Otherwise, the receiver MUST reject the OOB 512 message. For usability reasons, the OOB receiver SHOULD indicate the 513 acceptance or rejection of the OOB message to the user. The receiver 514 SHOULD reject invalid OOB messages without changing its state, until 515 an application-specific number of invalid messages (OobRetries) has 516 been reached, after which the receiver SHOULD consider it an error 517 and go back to the Unregistered (0) state. 519 The server or peer MAY send multiple OOB messages with different Noob 520 values while in the Waiting for OOB (1) state. The OOB sender SHOULD 521 remember the Noob values until they expire and accept any one of them 522 in the following Completion Exchange. The Noob values sent by the 523 server expire after an application-dependent timeout (NoobTimeout), 524 and the server MUST NOT accept Noob values older than that in the 525 Completion Exchange. The RECOMMENDED value for NoobTimeout is 3600 526 seconds if there are no application-specific reasons for making it 527 shorter or longer. The Noob values sent by the peer expire as 528 defined in Section 3.2.5. 530 The OOB receiver does not accept further OOB messages after it has 531 accepted one and moved to the OOB Received (2) state. However, the 532 receiver MAY buffer redundant OOB messages in case OOB message expiry 533 or similar error detected in the Completion Exchange causes it to 534 return to the Waiting for OOB (1) state. It is RECOMMENDED that the 535 OOB receiver notifies the user about redundant OOB messages, but it 536 MAY also discard them silently. 538 The sender will typically generate a new Noob, and therefore a new 539 OOB message, at constant time intervals (NoobInterval). The 540 RECOMMENDED interval is NoobInterval = NoobTimeout / 2, in which case 541 the receiver of the OOB will at any given time accept either of the 542 two latest Noob values. However, the timing of the Noob generation 543 may also be based on user interaction or on implementation 544 considerations. 546 Even though not recommended (see Section 3.3), this specification 547 allows both directions to be negotiated (Dirp=3) for the OOB channel. 548 In that case, both sides SHOULD output the OOB message, and it is up 549 to the user to deliver one of them. 551 The details of the OOB channel implementation including the message 552 encoding are defined by the application. Appendix E gives an example 553 of how the OOB message can be encoded as a URL that may be embedded 554 in a QR code and NFC tag. 556 3.2.4. Completion Exchange 558 After the Initial Exchange, if both the server and the peer support 559 the peer-to-server direction for the OOB channel, the peer SHOULD 560 initiate the EAP-NOOB method again after an applications-specific 561 waiting time in order to probe for completion of the OOB Step. Also, 562 if both sides support the server-to-peer direction of the OOB 563 exchange and the peer receives the OOB message, it SHOULD initiate 564 the EAP-NOOB method immediately. Depending on the combination of the 565 peer and server states, the server continues with with the Completion 566 Exchange or Waiting Exchange (see Section 3.2.1 on how the server 567 makes this decision). 569 The Completion Exchange comprises the common handshake and one or two 570 further EAP-NOOB request-response pairs. If the peer is in the 571 Waiting for OOB (1) state, the OOB message has been sent in the peer- 572 to-server direction. In that case, only one request-response pair 573 (Type=4) takes place. In the request, the server sends the NoobId 574 value, which the peer uses to identify the exact OOB message received 575 by the server. On the other hand, if the peer is in the OOB Received 576 (2) state, the direction of the OOB message is from server to peer. 577 In that case, two request-response pairs (Type=8 and Type=4) are 578 needed. The purpose of the first request-response pair (Type=8) is 579 that it enables the server to discover NoobId, which identifies the 580 exact OOB message received by the peer. The server returns the same 581 NoobId to the peer in the latter request. 583 In the last and sometimes only request-response pair (Type=4) of the 584 Completion Exchange, the server and peer exchange message 585 authentication codes. Both sides MUST compute the keys Kms and Kmp 586 as defined in Section 3.5 and the message authentication codes MACs 587 and MACp as defined in Section 3.3.2. Both sides MUST compare the 588 received message authentication code with a locally computed value. 589 If the peer finds that it has received the correct value of MACs and 590 the server finds that it has received the correct value of MACp, the 591 Completion Exchange ends in EAP-Success. Otherwise, the endpoint 592 where the comparison fails indicates this with an error message 593 (error code 4001, see Section 3.6.1) and the Completion Exchange ends 594 in EAP-Failure. 596 After successful Completion Exchange, both the server and the peer 597 move to the Registered (4) state. They also derive the output keying 598 material and store the persistent EAP-NOOB association state as 599 defined in Section 3.4 and Section 3.5. 601 It is possible that the OOB message expires before it is received. 602 In that case, the sender of the OOB message no longer recognizes the 603 NoobId that it receives in the Completion Exchange. Another reason 604 why the OOB sender might not recognize the NoobId is if the received 605 OOB message was spoofed and contained an attacker-generated Noob 606 value. The recipient of an unrecognized NoobId indicates this with 607 an error message (error code 2003, see Section 3.6.1) and the 608 Completion Exchange ends in EAP-Failure. The recipient of the error 609 message 2003 moves back to the Waiting for OOB (1) state. This state 610 transition is shown as OOB Reject in Figure 1 (even though it really 611 is a specific type of failed Completion Exchange). The sender of the 612 error message, on the other hand, stays in its previous state. 614 Although it is not expected to occur in practice, poor user interface 615 design could lead to two OOB messages delivered simultaneously, one 616 from the peer to the server and the other from the server to the 617 peer. The server detects this event in the beginning of the 618 Completion Exchange by observing that both the server and peer are in 619 the OOB Received state (2). In that case, as a tiebreaker, the 620 server MUST behave as if only the server-to-peer message had been 621 delivered. 623 EAP Peer EAP Server 624 | ...continuing from common handshake | 625 | | 626 |<----------- [ EAP-Request/EAP-NOOB ] ------------| 627 | (Type=8,PeerId) | 628 | | 629 | | 630 |------------ [ EAP-Response/EAP-NOOB ] ---------->| 631 | (Type=8,PeerId,NoobId) | 632 | | 633 | | 634 |<----------- EAP-Request/EAP-NOOB ----------------| 635 | (Type=4,PeerId,NoobId,MACs) | 636 | | 637 | | 638 |------------ EAP-Response/EAP-NOOB -------------->| 639 | (Type=4,PeerId,MACp) | 640 | | 641 | | 642 |<----------- EAP-Success -------------------------| 643 | | 645 Figure 6: Completion Exchange 647 3.2.5. Waiting Exchange 649 As explained in Section 3.2.4, the peer SHOULD probe the server for 650 completion of the OOB Step. When the combination of the peer and 651 server states indicates that the OOB message has not yet been 652 delivered, the server chooses the Waiting Exchange (see Section 3.2.1 653 on how the server makes this decision). The Waiting Exchange 654 comprises the common handshake and one further request-response pair, 655 and it ends always in EAP-Failure. 657 In order to limit the rate at which peers probe the server, the 658 server MAY send to the peer either in the Initial Exchange or in the 659 Waiting Exchange a minimum time to wait before probing the server 660 again. A peer that has not received an OOB message MUST wait at 661 least the server-specified minimum waiting time in seconds 662 (SleepTime) before initiating EAP again with the same server. The 663 peer uses the latest SleepTime value that it has received in or after 664 the Initial Exchange. If the server has not sent any SleepTime 665 value, the peer SHOULD wait for an application-specified minimum time 666 (SleepTimeDefault). 668 After the Waiting Exchange, the peer MUST discard (from its local 669 ephemeral storage) Noob values that it has sent to the server in OOB 670 messages that are older than the application-defined timeout 671 NoobTimeout (see Section 3.2.3). The peer SHOULD discard such 672 expired Noob values even if the probing failed, e.g. because of 673 failure to connect to the EAP server or incorrect HMAC. The timeout 674 of peer-generated Noob values is defined like this in order to allow 675 the peer to probe the server once after it has waited for the server- 676 specified SleepTime. 678 If the server and peer have negotiated to use only the server-to-peer 679 direction for the OOB channel (Dirp=2), the peer SHOULD nevertheless 680 probe the server. The purpose of this is to keep the server informed 681 about the peers that are still waiting for OOB messages. The server 682 MAY set SleepTime to a high number (3600) to prevent the peer from 683 probing the server frequently. 685 EAP Peer EAP Server 686 | ...continuing from common handshake | 687 | | 688 |<----------- EAP-Request/EAP-NOOB ----------------| 689 | (Type=3,PeerId,[SleepTime]) | 690 | | 691 | | 692 |------------ EAP-Response/EAP-NOOB -------------->| 693 | (Type=3,PeerId) | 694 | | 695 | | 696 |<----------- EAP-Failure -------------------------| 697 | | 699 Figure 7: Waiting Exchange 701 3.3. Protocol data fields 703 This section defines the various identifiers and data fields used in 704 the EAP-NOOB protocol. 706 3.3.1. Peer identifier, realm and NAI 708 The server allocates a new peer identifier (PeerId) for the peer in 709 the Initial Exchange. The peer identifier MUST follow the syntax of 710 the utf8-username specified in [RFC7542]. The server MUST generate 711 the identifiers in such a way that they do not repeat and cannot be 712 guessed by the peer or third parties before the server sends them to 713 the peer in the Initial Exchange. One way to generate the 714 identifiers is to choose a random 16-byte identifier and to base64url 715 encode it without padding [RFC4648] into a 22-character string. 717 Another way to generate the identifiers is to choose a random 718 22-character alphanumeric string. It is RECOMMENDED to not use 719 identifiers longer than this because they result in longer OOB 720 messages. 722 The peer uses the allocated PeerId to identify itself to the server 723 in the subsequent exchanges. It sets the PeerId value in response 724 type 9 as follows. When the peer is in the Unregistered (0) state, 725 it SHOULD omit the PeerId from response type 9. When the peer is in 726 one of the states 1..2, it MUST use the PeerId that the server 727 assigned to it in the latest Initial Exchange. When the peer is in 728 one of the persistent states 3..4, it MUST use the PeerId from its 729 persistent EAP-NOOB association. (The PeerId is written to the 730 association when the peer moves to the Registered (4) state after a 731 Completion Exchange.) 733 The default realm for the peer is "eap-noob.net" (.arpa domain TBA). 734 However, the user or application MAY provide a different default 735 realm to the peer. Furthermore, the server MAY assign a new realm to 736 the peer in the Initial Exchange or Reconnect Exchange, in the Realm 737 field of response types 1 and 5. The Realm value MUST follow the 738 syntax of the utf8-realm specified in [RFC7542]. When the peer is in 739 the Unregistered (0) state, or when the peer is in one of the states 740 1..2 and the server did not send a Realm in the latest Initial 741 Exchange, the peer MUST use the default realm. When the peer is in 742 one of the states 1..2 and the server sent a Realm in the latest 743 Initial Exchange, the peer MUST use that realm. Finally, when the 744 peer is in one of the persistent states 3..4, it MUST use the Realm 745 from its persistent EAP-NOOB association. (The Realm is written to 746 the association when the peer moves to the Registered (4) state after 747 a Completion Exchange or Reconnect Exchange.) 749 To compose its NAI [RFC7542], the peer concatenates the string 750 "noob@" and the server-assigned realm. When no server-assigned realm 751 is available, the default value is used instead. 753 The purpose of the server-assigned realm is to enable more flexible 754 routing of the EAP sessions over the AAA infrastructure, including 755 roaming scenarios (see Appendix D). Moreover, some Authenticators or 756 AAA servers use the assigned Realm to determine peer-specific 757 connection parameters, such as isolating the peer to a specific VLAN. 758 The possibility to configure a different default realm enables 759 registration of new devices while roaming. It also enables 760 manufacturers to set up their own AAA servers for bootstrapping of 761 new peer devices. 763 The peer's PeerId and Realm are ephemeral until a successful 764 Completion Exchange takes place. Thereafter, the values become parts 765 of the persistent EAP-NOOB association, until the user resets the 766 peer and the server or until a new Realm is assigned in the Reconnect 767 Exchange. 769 3.3.2. Message data fields 771 Table 1 defines the data fields in the protocol messages. The in- 772 band messages are formatted as JSON objects [RFC8259] in UTF-8 773 encoding. The JSON member names are in the left-hand column of the 774 table. 776 +------------------+------------------------------------------------+ 777 | Data field | Description | 778 +------------------+------------------------------------------------+ 779 | Vers, Verp | EAP-NOOB protocol versions supported by the | 780 | | EAP server, and the protocol version chosen by | 781 | | the peer. Vers is a JSON array of unsigned | 782 | | integers, and Verp is an unsigned integer. | 783 | | Example values are "[1]" and "1", | 784 | | respectively. | 785 | | | 786 | PeerId | Peer identifier as defined in Section 3.3.1. | 787 | | | 788 | Realm | Peer realm as defined in Section 3.3.1. | 789 | | | 790 | PeerState | Peer state is an integer in the range 0..4 | 791 | | (see Figure 1). However, only values 0..3 are | 792 | | ever sent in the protocol messages. | 793 | | | 794 | Type | EAP-NOOB message type. The type is an integer | 795 | | in the range 0..9. EAP-NOOB requests and the | 796 | | corresponding responses share the same type | 797 | | value. | 798 | | | 799 | PKs, PKp | The public components of the ECDHE keys of the | 800 | | server and peer. PKs and PKp are sent in the | 801 | | JSON Web Key (JWK) format [RFC7517]. Detailed | 802 | | format of the JWK object is defined by the | 803 | | cryptosuite. | 804 | | | 805 | Cryptosuites, | The identifiers of cryptosuites supported by | 806 | Cryptosuitep | the server and of the cryptosuite selected by | 807 | | the peer. The server-supported cryptosuites in | 808 | | Cryptosuites are formatted as a JSON array of | 809 | | the identifier integers. The server MUST send | 810 | | a nonempty array with no repeating elements, | 811 | | ordered by decreasing priority. The peer MUST | 812 | | respond with exactly one suite in the | 813 | | Cryptosuitep value, formatted as an identifier | 814 | | integer. The registration of cryptosuites is | 815 | | specified in Section 4.1. Example values are | 816 | | "[1]" and "1", respectively. | 817 | | | 818 | Dirs, Dirp | The OOB channel directions supported by the | 819 | | server and the directions selected by the | 820 | | peer. The possible values are 1=peer-to- | 821 | | server, 2=server-to-peer, 3=both directions. | 822 | | | 823 | Dir | The actual direction of the OOB message | 824 | | (1=peer-to-server, 2=server-to-peer). This | 825 | | value is not sent over any communication | 826 | | channel but it is included in the computation | 827 | | of the cryptographic fingerprint Hoob. | 828 | | | 829 | Ns, Np | 32-byte nonces for the Initial Exchange. | 830 | | | 831 | ServerInfo | This field contains information about the | 832 | | server to be passed from the EAP method to the | 833 | | application layer in the peer. The information | 834 | | is specific to the application or to the OOB | 835 | | channel and it is encoded as a JSON object of | 836 | | at most 500 bytes. It could include, for | 837 | | example, the access-network name and server | 838 | | name or a Uniform Resource Locator (URL) | 839 | | [RFC4266] or some other information that helps | 840 | | the user to deliver the OOB message to the | 841 | | server through the out-of-band channel. | 842 | | | 843 | PeerInfo | This field contains information about the peer | 844 | | to be passed from the EAP method to the | 845 | | application layer in the server. The | 846 | | information is specific to the application or | 847 | | to the OOB channel and it is encoded as a JSON | 848 | | object of at most 500 bytes. It could include, | 849 | | for example, the peer brand, model and serial | 850 | | number, which help the user to distinguish | 851 | | between devices and to deliver the OOB message | 852 | | to the correct peer through the out-of-band | 853 | | channel. | 854 | | | 855 | SleepTime | The number of seconds for which peer MUST NOT | 856 | | start a new execution of the EAP-NOOB method | 857 | | with the authenticator, unless the peer | 858 | | receives the OOB message or the peer is reset | 859 | | by the user. The server can use this field to | 860 | | limit the rate at which peers probe it. | 861 | | SleepTime is an unsigned integer in the range | 862 | | 0..3600. | 863 | | | 864 | Noob | 16-byte secret nonce sent through the OOB | 865 | | channel and used for the session key | 866 | | derivation. The endpoint that received the OOB | 867 | | message uses this secret in the Completion | 868 | | Exchange to authenticate the exchanged key to | 869 | | the endpoint that sent the OOB message. | 870 | | | 871 | Hoob | 16-byte cryptographic fingerprint (i.e. hash | 872 | | value) computed from all the parameters | 873 | | exchanged in the Initial Exchange and in the | 874 | | OOB message. Receiving this fingerprint over | 875 | | the OOB channel guarantees the integrity of | 876 | | the key exchange and parameter negotiation. | 877 | | Hence, it authenticates the exchanged key to | 878 | | the endpoint that receives the OOB message. | 879 | | | 880 | NoobId | 16-byte identifier for the OOB message, | 881 | | computed with a one-way function from the | 882 | | nonce Noob in the message. | 883 | | | 884 | MACs, MACp | Message authentication codes (HMAC) for mutual | 885 | | authentication, key confirmation, and | 886 | | integrity check on the exchanged information. | 887 | | The input to the HMAC is defined below, and | 888 | | the key for the HMAC is defined in | 889 | | Section 3.5. | 890 | | | 891 | Ns2, Np2 | 32-byte Nonces for the Reconnect Exchange. | 892 | | | 893 | KeyingMode | Integer indicating the key derivation method. | 894 | | 0 in the Completion Exchange, and 1..3 in the | 895 | | Reconnect Exchange. | 896 | | | 897 | PKs2, PKp2 | The public components of the ECDHE keys of the | 898 | | server and peer for the Reconnect Exchange. | 899 | | PKp2 and PKs2 are sent in the JSON Web Key | 900 | | (JWK) format [RFC7517]. Detailed format of the | 901 | | JWK object is defined by the cryptosuite. | 902 | | | 903 | MACs2, MACp2 | Message authentication codes (HMAC) for mutual | 904 | | authentication, key confirmation, and | 905 | | integrity check on the Reconnect Exchange. The | 906 | | input to the HMAC is defined below, and the | 907 | | key for the HMAC is defined in Section 3.5. | 908 | | | 909 | ErrorCode | Integer indicating an error condition. Defined | 910 | | in Section 4.3. | 911 | | | 912 | ErrorInfo | Textual error message for logging and | 913 | | debugging purposes. UTF-8 string of at most | 914 | | 500 bytes. | 915 | | | 916 +------------------+------------------------------------------------+ 918 Table 1: Message data fields 920 It is RECOMMENDED for servers to support both OOB channel directions 921 (Dirs=3), unless the type of the OOB channel limits them to one 922 direction (Dirs=1 or Dirs=2). On the other hand, it is RECOMMENDED 923 that the peer selects only one direction (Dirp=1 or Dirp=2) even when 924 both directions (Dirp=3) would be technically possible. The reason 925 is that, if value 3 is negotiated, the user may be presented with two 926 OOB messages, one for each direction, even though only one of them 927 needs to be delivered. This can be confusing to the user. 928 Nevertheless, the EAP-NOOB protocol is designed to cope also with 929 selected value 3, in which case it uses the first delivered OOB 930 message. In the unlikely case of simultaneously delivered OOB 931 messages, the protocol prioritizes the server-to-peer direction. 933 The nonces in the in-band messages (Ns, Np, Ns2, Np2) are 32-byte 934 fresh random byte strings, and the secret nonce Noob is a 16-byte 935 fresh random byte string. All the nonces are generated by the 936 endpoint that sends the message. 938 The fingerprint Hoob and the identifier NoobId are computed with the 939 cryptographic hash function specified in the negotiated cryptosuite 940 and truncated to the 16 leftmost bytes of the output. The message 941 authentication codes (MACs, MACp, MACs2, MACp2) are computed with the 942 HMAC function [RFC2104] based on the same cryptographic hash function 943 and truncated to the 32 leftmost bytes of the output. 945 The inputs to the hash function for computing the fingerprint Hoob 946 and to the HMAC for computing MACs, MACp, MACs2 and MACp2 are JSON 947 arrays containing a fixed number (17) of elements. The array 948 elements MUST be copied to the array verbatim from the sent and 949 received in-band messages. When the element is a JSON object, its 950 members MUST NOT be reordered or re-encoded. Whitespace MUST NOT be 951 added anywhere in the JSON structure. Implementers should check that 952 their JSON library copies the elements as UTF-8 strings and does not 953 modify then in any way, and that it does not add whitespace to the 954 HMAC input. 956 The inputs for computing the fingerprint and message authentication 957 codes are the following: 959 Hoob = H(Dir,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,Cryptos 960 uitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 962 NoobId = H("NoobId",Noob). 964 MACs = HMAC(Kms; 2,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C 965 ryptosuitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 967 MACp = HMAC(Kmp; 1,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C 968 ryptosuitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 970 MACs2 = HMAC(Kms2; 2,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo] 971 ,Cryptosuitep,"",[Realm],[PeerInfo],KeyingMode,[PKs2],Ns2,[PKp2],N 972 p2,"") 974 MACp2 = HMAC(Kmp2; 1,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo] 975 ,Cryptosuitep,"",[Realm],[PeerInfo],KeyingMode,[PKs2],Ns2,[PKp2],N 976 p2,"") 978 The inputs denoted with "" above are not present, and the values in 979 brackets [] are optional. Both kinds of missing input values are are 980 represented by empty strings "" in the HMAC input (JSON array). 981 Realm is included in the computation of MACs and MACp if it was sent 982 or received in the preceding Initial Exchange. Each of the values in 983 brackets for the computation of Macs2 and Macp2 MUST be included if 984 it was sent or received in the same Reconnect Exchange; otherwise the 985 value is replaced by an empty string "". 987 The parameter Dir indicates the direction in which the OOB message 988 containing the Noob value is being sent (1=peer-to-server, 2=server- 989 to-peer). This field is included in the Hoob input to prevent the 990 user from accidentally delivering the OOB message back to its 991 originator in the rare cases where both OOB directions have been 992 negotiated. The keys (Kms, Kmp, Kms2, Kmp2) for the HMACs are 993 defined in Section 3.5. 995 The nonces (Ns, Np, Ns2, Np2, Noob) and the hash value (NoobId) MUST 996 be base64url encoded [RFC4648] when they are used as input to the 997 cryptographic functions H or HMAC. These values and the message 998 authentication codes (MACs, MACp, MACs2, MACp2) MUST also be 999 base64url encoded when they are sent in the in-band messages. The 1000 values Noob and Hoob in the OOB channel MAY be base64url encoded if 1001 that is appropriate for the application and the OOB channel. All 1002 base64url encoding is done without padding. The base64url encoded 1003 values will naturally consume more space than the number of bytes 1004 specified above (22-character string for a 16-byte nonce and 1005 43-character string for a 32-byte nonce or message authentication 1006 code). In the key derivation in Section 3.5, on the other hand, the 1007 unencoded nonces (raw bytes) are used as input to the key derivation 1008 function. 1010 The ServerInfo and PeerInfo are JSON objects with UTF-8 encoding. 1011 The length of either encoded object as a byte array MUST NOT exceed 1012 500 bytes. The format and semantics of these objects MUST be defined 1013 by the application that uses the EAP-NOOB method. 1015 3.4. Fast reconnect and rekeying 1017 EAP-NOOB implements Fast Reconnect ([RFC3748], section 7.2.1) that 1018 avoids repeated use of the user-assisted OOB channel. 1020 The rekeying and the Reconnect Exchange may be needed for several 1021 reasons. New EAP output values MSK and EMSK may be needed because of 1022 mobility or timeout of session keys. Software or hardware failure or 1023 user action may also cause the authenticator, EAP server or peer to 1024 lose its non-persistent state data. The failure would typically be 1025 detected by the peer or authenticator when session keys no longer are 1026 accepted by the other endpoint. Change in the supported cryptosuites 1027 in the EAP server or peer may also cause the need for a new key 1028 exchange. When the EAP server or peer detects any one of these 1029 events, it MUST change from the Registered to Reconnecting state. 1030 These state transitions are labeled Mobility/Timeout/Failure in 1031 Figure 1. The EAP-NOOB method will then perform the Reconnect 1032 Exchange next time when EAP is triggered. 1034 3.4.1. Persistent EAP-NOOB association 1036 To enable rekeying, the EAP server and peer store the session state 1037 in persistent memory after a successful Completion Exchange. This 1038 state data, called "persistent EAP-NOOB association", MUST include at 1039 least the data fields shown in Table 2. They are used for 1040 identifying and authenticating the peer in the Reconnect Exchange. 1041 When a persistent EAP-NOOB association exists, the EAP server and 1042 peer are in the Registered state (4) or Reconnecting state (3), as 1043 shown in Figure 1. 1045 +------------------+--------------------------------+---------------+ 1046 | Data field | Value | Type | 1047 +------------------+--------------------------------+---------------+ 1048 | PeerId | Peer identifier allocated by | UTF-8 string | 1049 | | server | (typically 22 | 1050 | | | bytes) | 1051 | | | | 1052 | Verp | Negotiated protocol version | integer | 1053 | | | | 1054 | Cryptosuitep | Negotiated cryptosuite | integer | 1055 | | | | 1056 | CryptosuitepPrev | Previous cryptosuite | integer | 1057 | (at peer only) | | | 1058 | | | | 1059 | Realm | Optional realm assigned by | UTF-8 string | 1060 | | server (default value is "eap- | | 1061 | | noob.net" (.arpa domain TBA)) | | 1062 | | | | 1063 | Kz | Persistent key material | 32 bytes | 1064 | | | | 1065 | KzPrev (at | Previous Kz value | 32 bytes | 1066 | peer only) | | | 1067 +------------------+--------------------------------+---------------+ 1069 Table 2: Persistent EAP-NOOB association 1071 3.4.2. Reconnect Exchange 1073 The server chooses the Reconnect Exchange when both the peer and the 1074 server are in a persistent state and fast reconnection is needed (see 1075 Section 3.2.1 for details). 1077 The Reconnect Exchange comprises the common handshake and three 1078 further EAP-NOOB request-response pairs, one for cryptosuite and 1079 parameter negotiation, another for the nonce and ECDHE key exchange, 1080 and the last one for exchanging message authentication codes. In the 1081 first request and response (Type=5) the server and peer negotiate a 1082 protocol version and cryptosuite in the same way as in the Initial 1083 Exchange. The server SHOULD NOT offer and the peer MUST NOT accept 1084 protocol versions or cryptosuites that it knows to be weaker than the 1085 one currently in the Cryptosuitep field of the persistent EAP-NOOB 1086 association. The server SHOULD NOT needlessly change the 1087 cryptosuites it offers to the same peer because peer devices may have 1088 limited ability to update their persistent storage. However, if the 1089 peer has different values in the Cryptosuitep and CryptosuitepPrev 1090 fields, it SHOULD also accept offers that are not weaker than 1091 CryptosuitepPrev. Note that Cryptosuitep and CryptosuitePrev from 1092 the persistent EAP-NOOB association are only used to support the 1093 negotiation as described above; all actual cryptographic operations 1094 use the negotiated cryptosuite. The request and response (Type=5) 1095 MAY additionally contain PeerInfo and ServerInfo objects. 1097 The server then determines the KeyingMode (defined in Section 3.5) 1098 based on changes in the negotiated cryptosuite and whether it desires 1099 to achieve forward secrecy or not. The server SHOULD only select 1100 KeyingMode 3 when the negotiated cryptosuite differs from the 1101 Cryptosuitep in the server's persistent EAP-NOOB association, 1102 although it is technically possible to select this values without 1103 changing the cryptosuite. In the second request and response 1104 (Type=6), the server informs the peer about the KeyingMode, and the 1105 server and peer exchange nonces (Ns2, Np2). When KeyingMode is 2 or 1106 3 (rekeying with ECDHE), they also exchange public components of 1107 ECDHE keys (PKs2, PKp2). The server ECDHE key MUST be fresh, i.e. 1108 not previously used with the same peer, and the peer ECDHE key SHOULD 1109 be fresh, i.e. not previously used. 1111 In the third and final request and response (Type=7), the server and 1112 peer exchange message authentication codes. Both sides MUST compute 1113 the keys Kms2 and Kmp2 as defined in Section 3.5 and the message 1114 authentication codes MACs2 and MACp2 as defined in Section 3.3.2. 1115 Both sides MUST compare the received message authentication code with 1116 a locally computed value. 1118 The rules by which the peer compares the received MACs2 are non- 1119 trivial because, in addition to authenticating the current exchange, 1120 MACs2 may confirm the success or failure of a recent cryptosuite 1121 upgrade. The peer processes the final request (Type=7) as follows: 1123 1. The peer first compares the received MACs2 value with one it 1124 computed using the Kz stored in the persistent EAP-NOOB 1125 association. If the received and computed values match, the peer 1126 deletes any data stored in the CryptosuitepPrev and KzPrev fields 1127 of the persistent EAP-NOOB association. It does this because the 1128 received MACs2 confirms that the peer and server share the same 1129 Cryptosuitep and Kz, and any previous values must no longer be 1130 accepted. 1132 2. If, on the other hand, the peer finds that the received MACs2 1133 value does not match the one it computed locally with Kz, the 1134 peer checks whether the KzPrev field in the persistent EAP-NOOB 1135 association stores a key. If it does, the peer repeats the key 1136 derivation (Section 3.5) and local MACs2 computation 1137 (Section 3.3.2) using KzPrev in place of Kz. If this second 1138 computed MACs2 matches the received value, the match indicates 1139 synchronization failure caused by the loss of the last response 1140 (Type=7) in a previously attempted cryptosuite upgrade. In this 1141 case, the peer rolls back that upgrade by overwriting 1142 Cryptosuitep with CryptosuitepPrev and Kz with KzPrev in the 1143 persistent EAP-NOOB association. It also clears the 1144 CryptosuitepPrev and KzPrev fields. 1146 3. If the received MACs2 matched one of the locally computed values, 1147 the peer proceeds to send the final response (Type=7). The peer 1148 also moves to the Registered (4) state. When KeyingMode is 1 or 1149 2, the peer stops here. When KeyingMode is 3, the peer also 1150 updates the persistent EAP-NOOB association with the negotiated 1151 Cryptosuitep and the newly-derived Kz value. To prepare for 1152 possible synchronization failure caused by the loss of the final 1153 response (Type=7) during cryptosuite upgrade, the peer copies the 1154 old Cryptosuitep and Kz values in the persistent EAP-NOOB 1155 association to the CryptosuitepPrev and KzPrev fields. 1157 4. Finally, if the peer finds that the received MACs2 does not match 1158 either of the two values that it computed locally (or one value 1159 if no KzPrev was stored), the peer sends an error message (error 1160 code 4001, see Section 3.6.1), which causes the the Reconnect 1161 Exchange to end in EAP-Failure. 1163 The server rules for processing the final message are simpler than 1164 the peer rules because the server does not store previous keys and it 1165 never rolls back a cryptosuite upgrade. Upon receiving the final 1166 response (Type=7), the server compares the received value of MACp2 1167 with one it computes locally. If the values match, the Reconnect 1168 Exchange ends in EAP-Success. When KeyingMode is 3, the server also 1169 updates Cryptosuitep and Kz in the persistent EAP-NOOB association. 1170 On the other hand, if the server finds that the values do not match, 1171 it sends an error message (error code 4001), and the Reconnect 1172 Exchange ends in EAP-Failure. 1174 The endpoints MAY send updated Realm, ServerInfo and PeerInfo objects 1175 in the Reconnect Exchange. When there is no update to the values, 1176 they SHOULD omit this information from the messages. If the Realm 1177 was sent, each side updates Realm in the persistent EAP-NOOB 1178 association when moving to the Registered (4) state. 1180 EAP Peer EAP Server 1181 | ...continuing from common handshake | 1182 | | 1183 |<----------- EAP-Request/EAP-NOOB ----------------| 1184 | (Type=5,Vers,PeerId,Cryptosuites, | 1185 | [Realm],[ServerInfo]) | 1186 | | 1187 | | 1188 |------------ EAP-Response/EAP-NOOB -------------->| 1189 | (Type=5,Verp,PeerId,Cryptosuitep,[PeerInfo])| 1190 | | 1191 | | 1192 |<----------- EAP-Request/EAP-NOOB ----------------| 1193 | (Type=6,PeerId,KeyingMode,[PKs2],Ns2) | 1194 | | 1195 | | 1196 |------------ EAP-Response/EAP-NOOB -------------->| 1197 | (Type=6,PeerId,[PKp2],Np2) | 1198 | | 1199 | | 1200 |<----------- EAP-Request/EAP-NOOB ----------------| 1201 | (Type=7,PeerId,MACs2) | 1202 | | 1203 | | 1204 |------------ EAP-Response/EAP-NOOB -------------->| 1205 | (Type=7,PeerId,MACp2) | 1206 | | 1207 | | 1208 |<----------- EAP-Success -------------------------| 1209 | | 1211 Figure 8: Reconnect Exchange 1213 3.4.3. User reset 1215 As shown in the association state machine in Figure 1, the only 1216 specified way for the association to return from the Registered state 1217 (4) to the Unregistered state (0) is through user-initiated reset. 1218 After the reset, a new OOB message will be needed to establish a new 1219 association between the EAP server and peer. Typical situations in 1220 which the user reset is required are when the other side has 1221 accidentally lost the persistent EAP-NOOB association data, or when 1222 the peer device is decommissioned. 1224 The server could detect that the peer is in the Registered or 1225 Reconnecting state but the server itself is in one of the ephemeral 1226 states 0..2 (including situations where the server does not recognize 1227 the PeerId). In this case, effort should be made to recover the 1228 persistent server state, for example, from a backup storage - 1229 especially if many peer devices are similarly affected. If that is 1230 not possible, the EAP server SHOULD log the error or notify an 1231 administrator. The only way to continue from such a situation is by 1232 having the user reset the peer device. 1234 On the other hand, if the peer is in any of the ephemeral states 1235 0..2, including the Unregistered state, the server will treat the 1236 peer as a new peer device and allocate a new PeerId to it. The 1237 PeerInfo can be used by the user as a clue to which physical device 1238 has lost its state. However, there is no secure way of matching the 1239 "new" peer with the old PeerId without repeating the OOB Step. This 1240 situation will be resolved when the user performs the OOB Step and, 1241 thus, identifies the physical peer device. The server user interface 1242 MAY support situations where the "new" peer is actually a previously 1243 registered peer that has been reset by a user or otherwise lost its 1244 persistent data. In those cases, the user could choose to merge new 1245 peer identity with the old one in the server. The alternative is to 1246 treat the device just like a new peer. 1248 3.5. Key derivation 1250 EAP-NOOB derives the EAP output values MSK and EMSK and other secret 1251 keying material from the output of an Ephemeral Elliptic Curve 1252 Diffie-Hellman (ECDHE) algorithm following the NIST specification 1253 [NIST-DH]. In NIST terminology, we use a C(2, 0, ECC CDH) scheme, 1254 i.e. two ephemeral keys and no static keys. In the Initial and 1255 Reconnect Exchanges, the server and peer compute the ECDHE shared 1256 secret Z as defined in section 6.1.2.2 of the NIST specification 1257 [NIST-DH]. In the Completion and Reconnect Exchanges, the server and 1258 peer compute the secret keying material from Z with the single-step 1259 key derivation function (KDF) defined in section 5.8.1 of the NIST 1260 specification. The hash function H for KDF is taken from the 1261 negotiated cryptosuite. 1263 +------------+------------------------------------------------------+ 1264 | KeyingMode | Description | 1265 +------------+------------------------------------------------------+ 1266 | 0 | Completion Exchange (always with ECDHE) | 1267 | | | 1268 | 1 | Reconnect Exchange, rekeying without ECDHE | 1269 | | | 1270 | 2 | Reconnect Exchange, rekeying with ECHDE, no change | 1271 | | in cryptosuite | 1272 | | | 1273 | 3 | Reconnect Exchange, rekeying with ECDHE, new | 1274 | | cryptosuite negotiated | 1275 +------------+------------------------------------------------------+ 1277 Table 3: Keying modes 1279 The key derivation has four different modes (KeyingMode), which are 1280 specified in Table 3. Table 4 defines the inputs to KDF in each 1281 KeyingMode. 1283 In the Completion Exchange (KeyingMode=0), the input Z comes from the 1284 preceding Initial exchange. KDF takes some additional inputs 1285 (OtherInfo), for which we use the concatenation format defined in 1286 section 5.8.1.2.1 of the NIST specification [NIST-DH]. OtherInfo 1287 consists of the AlgorithmId, PartyUInfo, PartyVInfo, and SuppPrivInfo 1288 fields. The first three fields are fixed-length bit strings, and 1289 SuppPrivInfo is a variable-length string with a one-byte Datalength 1290 counter. AlgorithmId is the fixed-length 8-byte ASCII string "EAP- 1291 NOOB". The other input values are the server and peer nonces. In 1292 the Completion Exchange, the inputs also include the secret nonce 1293 Noob from the OOB message. 1295 In the simplest form of the Reconnect Exchange (KeyingMode=1), fresh 1296 nonces are exchanged but no ECDHE keys are sent. In this case, input 1297 Z to the KDF is replaced with the shared key Kz from the persistent 1298 EAP-NOOB association. The result is rekeying without the 1299 computational cost of the ECDHE exchange, but also without forward 1300 secrecy. 1302 When forward secrecy is desired in the Reconnect Exchange 1303 (KeyingMode=2 or KeyingMode=3), both nonces and ECDHE keys are 1304 exchanged. Input Z is the fresh shared secret from the ECDHE 1305 exchange with PKs2 and PKp2. The inputs also include the shared 1306 secret Kz from the persistent EAP-NOOB association. This binds the 1307 rekeying output to the previously authenticated keys. 1309 +--------------+--------------+------------------------+------------+ 1310 | KeyingMode | KDF input | Value | Length | 1311 | | field | | (bytes) | 1312 +--------------+--------------+------------------------+------------+ 1313 | 0 | Z | ECDHE shared secret | variable | 1314 | Completion | | from PKs and PKp | | 1315 | | AlgorithmId | "EAP-NOOB" | 8 | 1316 | | PartyUInfo | Np | 32 | 1317 | | PartyVInfo | Ns | 32 | 1318 | | SuppPubInfo | (not allowed) | | 1319 | | SuppPrivInfo | Noob | 16 | 1320 | | | | | 1321 | 1 | Z | Kz | 32 | 1322 | Reconnect, | AlgorithmId | "EAP-NOOB" | 8 | 1323 | rekeying | PartyUInfo | Np2 | 32 | 1324 | without | PartyVInfo | Ns2 | 32 | 1325 | ECDHE | SuppPubInfo | (not allowed) | | 1326 | | SuppPrivInfo | (null) | 0 | 1327 | | | | | 1328 | 2 or 3 | Z | ECDHE shared secret | variable | 1329 | Reconnect, | | from PKs2 and PKp2 | | 1330 | rekeying, | AlgorithmId | "EAP-NOOB" | 8 | 1331 | with ECDHE, | PartyUInfo | Np2 | 32 | 1332 | same or new | PartyVInfo | Ns2 | 32 | 1333 | cryptosuite | SuppPubInfo | (not allowed) | | 1334 | | SuppPrivInfo | Kz | 32 | 1335 +--------------+--------------+------------------------+------------+ 1337 Table 4: Key derivation input 1339 Table 5 defines how the output bytes of KDF are used. In addition to 1340 the EAP output values MSK and EMSK, the server and peer derive 1341 another shared secret key AMSK, which MAY be used for application- 1342 layer security. Further output bytes are used internally by EAP-NOOB 1343 for the message authentication keys (Kms, Kmp, Kms2, Kmp2). 1345 The Completion Exchange (KeyingMode=0) produces the shared secret Kz, 1346 which the server and peer store in the persistent EAP-NOOB 1347 association. When a new cryptosuite is negotiated in the Reconnect 1348 Exchange (KeyingMode=3), it similarly produces a new Kz. In that 1349 case, the server and peer update both the cryptosuite and Kz in the 1350 persistent EAP-NOOB association. Additionally, the peer stores the 1351 previous Cryptosuitep and Kz values in the CryptosuitepPrev and 1352 KzPrev fields of the persistent EAP-NOOB association. 1354 +-----------------+------------------+----------+----------------+ 1355 | KeyingMode | KDF output bytes | Used as | Length (bytes) | 1356 +-----------------+------------------+----------+----------------+ 1357 | 0 | 0..63 | MSK | 64 | 1358 | Completion | 64..127 | EMSK | 64 | 1359 | | 128..191 | AMSK | 64 | 1360 | | 192..223 | MethodId | 32 | 1361 | | 224..255 | Kms | 32 | 1362 | | 256..287 | Kmp | 32 | 1363 | | 288..319 | Kz | 32 | 1364 | | | | | 1365 | 1 or 2 | 0..63 | MSK | 64 | 1366 | Reconnect, | 64..127 | EMSK | 64 | 1367 | rekeying | 128..191 | AMSK | 64 | 1368 | without ECDHE, | 192..223 | MethodId | 32 | 1369 | or with ECDHE | 224..255 | Kms2 | 32 | 1370 | and unchanged | 256..287 | Kmp2 | 32 | 1371 | cryptosuite | | | | 1372 | | | | | 1373 | | | | | 1374 | 3 Reconnect, | 0..63 | MSK | 64 | 1375 | rekeying | 64..127 | EMSK | 64 | 1376 | with ECDHE, | 128..191 | AMSK | 64 | 1377 | new cryptosuite | 192..223 | MethodId | 32 | 1378 | | 224..255 | Kms2 | 32 | 1379 | | 256..287 | Kmp2 | 32 | 1380 | | 288..319 | Kz | 32 | 1381 +-----------------+------------------+----------+----------------+ 1383 Table 5: Key derivation output 1385 Finally, every EAP method must export a Server-Id, Peer-Id and 1386 Session-Id [RFC5247]. In EAP-NOOB, the exported Peer-Id is the 1387 PeerId which the server has assigned to the peer. The exported 1388 Server-Id is a zero-length string (i.e. null string) because EAP-NOOB 1389 neither knows nor assigns any server identifier. The exported 1390 Session-Id is created by concatenating the Type-Code xxx (TBA) with 1391 the MethodId, which is obtained from the KDF output as shown in 1392 Table 5. 1394 3.6. Error handling 1396 Various error conditions in EAP-NOOB are handled by sending an error 1397 notification message (Type=0) instead of the expected next EAP 1398 request or response message. Both the EAP server and the peer may 1399 send the error notification, as shown in Figure 9 and Figure 10. 1400 After sending or receiving an error notification, the server MUST 1401 send an EAP-Failure (as required by [RFC3748] section 4.2). The 1402 notification MAY contain an ErrorInfo field, which is a UTF-8 encoded 1403 text string with a maximum length of 500 bytes. It is used for 1404 sending descriptive information about the error for logging and 1405 debugging purposes. 1407 EAP Peer EAP Server 1408 ... ... 1409 | | 1410 |<----------- EAP-Request/EAP-NOOB ----------------| 1411 | (Type=0,[PeerId],ErrorCode,[ErrorInfo]) | 1412 | | 1413 | | 1414 |<----------- EAP-Failure -------------------------| 1415 | | 1417 Figure 9: Error notification from server to peer 1419 EAP Peer EAP Server 1420 ... ... 1421 | | 1422 |------------ EAP-Response/EAP-NOOB -------------->| 1423 | (Type=0,[PeerId],ErrorCode,[ErrorInfo]) | 1424 | | 1425 | | 1426 |<----------- EAP-Failure -------------------------| 1427 | | 1429 Figure 10: Error notification from peer to server 1431 After the exchange fails due to an error notification, the server and 1432 peer set the association state as follows. In the Initial Exchange, 1433 both the sender and recipient of the error notification MUST set the 1434 association state to the Unregistered (0) state. In the Waiting and 1435 Completion Exchanges, each side MUST remain in its old state as if 1436 the failed exchange had not taken place, with the exception that the 1437 recipient of error code 2003 processes it as specified in 1438 Section 3.2.4. In the Reconnect Exchange, both sides MUST set the 1439 association state to the Reconnecting (3) state. 1441 Errors that occur in the OOB channel are not explicitly notified in- 1442 band. 1444 3.6.1. Invalid messages 1446 If the NAI structure is invalid, the server SHOULD send the error 1447 code 1001 to the peer. The recipient of an EAP-NOOB request or 1448 response SHOULD send the following error codes back to the sender: 1449 1002 if it cannot parse the message as a JSON object or the top-level 1450 JSON object has missing or unrecognized members; 1003 if a data field 1451 has an invalid value, such as an integer out of range, and there is 1452 no more specific error code available; 1004 if the received message 1453 type was unexpected in the current state; 2004 if the PeerId has an 1454 unexpected value; 2003 if the NoobId is not recognized; and 1007 if 1455 the ECDHE key is invalid. 1457 3.6.2. Unwanted peer 1459 The preferred way for the EAP server to rate limit EAP-NOOB 1460 connections from a peer is to use the SleepTime parameter in the 1461 Waiting Exchange. However, if the EAP server receives repeated EAP- 1462 NOOB connections from a peer which apparently should not connect to 1463 this server, the server MAY indicate that the connections are 1464 unwanted by sending the error code 2001. After receiving this error 1465 message, the peer MAY refrain from reconnecting to the same EAP 1466 server and, if possible, both the EAP server and peer SHOULD indicate 1467 this error condition to the user or server administrator. However, 1468 in order to avoid persistent denial of service, the peer is not 1469 required to stop entirely from reconnecting to the server. 1471 3.6.3. State mismatch 1473 In the states indicated by "-" in Figure 11 in Appendix A, user 1474 action is required to reset the association state or to recover it, 1475 for example, from backup storage. In those cases, the server sends 1476 the error code 2002 to the peer. If possible, both the EAP server 1477 and peer SHOULD indicate this error condition to the user or server 1478 administrator. 1480 3.6.4. Negotiation failure 1482 If there is no matching protocol version, the peer sends the error 1483 code 3001 to the server. If there is no matching cryptosuite, the 1484 peer sends the error code 3002 to the server. If there is no 1485 matching OOB direction, the peer sends the error code 3003 to the 1486 server. 1488 In practice, there is no way of recovering from these errors without 1489 software or hardware changes. If possible, both the EAP server and 1490 peer SHOULD indicate these error conditions to the user. 1492 3.6.5. Cryptographic verification failure 1494 If the receiver of the OOB message detects an unrecognized PeerId or 1495 incorrect fingerprint (Hoob) in the OOB message, the receiver MUST 1496 remain in the Waiting for OOB state (1) as if no OOB message was 1497 received. The receiver SHOULD indicate the failure to accept the OOB 1498 message to the user. No in-band error message is sent. 1500 Note that if the OOB message was delivered from the server to the 1501 peer and the peer does not recognize the PeerId, the likely cause is 1502 that the user has unintentionally delivered the OOB message to the 1503 wrong peer device. If possible, the peer SHOULD indicate this to the 1504 user; however, the peer device may not have the capability for many 1505 different error indications to the user and it MAY use the same 1506 indication as in the case of an incorrect fingerprint. 1508 The rationale for the above is that the invalid OOB message could 1509 have been presented to the receiver by mistake or intentionally by a 1510 malicious party and, thus, it should be ignored in the hope that the 1511 honest user will soon deliver a correct OOB message. 1513 If the EAP server or peer detects an incorrect message authentication 1514 code (MACs, MACp, MACs2, MACp2), it sends the error code 4001 to the 1515 other side. As specified in the beginning of Section 3.6, the failed 1516 Completion Exchange will not result in server or peer state changes 1517 while error in the Reconnect Exchange will put both sides to the 1518 Reconnecting (3) state and thus lead to another reconnect attempt. 1520 The rationale for this is that the invalid cryptographic message may 1521 have been spoofed by a malicious party and, thus, it should be 1522 ignored. In particular, a spoofed message on the in-band channel 1523 should not force the honest user to perform the OOB Step again. In 1524 practice, however, the error may be caused by other failures, such as 1525 a software bug. For this reason, the EAP server MAY limit the rate 1526 of peer connections with SleepTime after the above error. Also, 1527 there SHOULD be a way for the user to reset the peer to the 1528 Unregistered state (0), so that the OOB Step can be repeated at the 1529 last resort. 1531 3.6.6. Application-specific failure 1533 Applications MAY define new error messages for failures that are 1534 specific to the application or to one type of OOB channel. They MAY 1535 also use the generic application-specific error code 5001, or the 1536 error codes 5002 and 5004, which have been reserved for indicating 1537 invalid data in the ServerInfo and PeerInfo fields, respectively. 1538 Additionally, anticipating OOB channels that make use of a URL, the 1539 error code 5003 has been reserved for indicating invalid server URL. 1541 4. IANA Considerations 1543 This section provides guidance to the Internet Assigned Numbers 1544 Authority (IANA) regarding registration of values related to the EAP- 1545 NOOB protocol, in accordance with [RFC8126]. 1547 The EAP Method Type number for EAP-NOOB needs to be assigned. 1549 This memo also requires IANA to create new registries as defined in 1550 the following subsections. 1552 4.1. Cryptosuites 1554 Cryptosuites are identified by an integer. Each cryptosuite MUST 1555 specify an ECDHE curve for the key exchange, encoding of the ECDHE 1556 public key as a JWK object, and a cryptographic hash function for the 1557 fingerprint and HMAC computation and key derivation. The hash value 1558 output by the cryptographic hash function MUST be at least 32 bytes 1559 in length. The following suites are defined by EAP-NOOB: 1561 +-------------+-----------------------------------------------------+ 1562 | Cryptosuite | Algorithms | 1563 +-------------+-----------------------------------------------------+ 1564 | 1 | ECDHE curve Curve25519 [RFC7748], public-key format | 1565 | | [RFC7518] Section 6.2.1, hash function SHA-256 | 1566 | | [RFC6234] | 1567 +-------------+-----------------------------------------------------+ 1569 Table 6: EAP-NOOB cryptosuites 1571 An example of Cryptosuite 1 public-key encoded as a JWK object is 1572 given below (line breaks are for readability only). 1574 "jwk":{"kty":"EC","crv":"Curve25519","x":"3p7bfXt9wbTTW2HC7OQ1Nz- 1575 DQ8hbeGdNrfx-FG-IK08"} 1577 Assignment of new values for new cryptosuites MUST be done through 1578 IANA with "Specification Required" and "IESG Approval" as defined in 1579 [RFC8126]. 1581 4.2. Message Types 1583 EAP-NOOB request and response pairs are identified by an integer 1584 Message Type. The following Message Types are defined by EAP-NOOB: 1586 +----------+------------+-------------------------------------------+ 1587 | Message | Used in | Purpose | 1588 | Type | Exchange | | 1589 +----------+------------+-------------------------------------------+ 1590 | 1 | Initial | Version, cryptosuite and parameter | 1591 | | | negotiation | 1592 | | | | 1593 | 2 | Initial | Exchange of ECDHE keys and nonces | 1594 | | | | 1595 | 3 | Waiting | Indication to peer that the server has | 1596 | | | not yet received an OOB message | 1597 | | | | 1598 | 4 | Completion | Authentication and key confirmation with | 1599 | | | HMAC | 1600 | | | | 1601 | 5 | Reconnect | Version, cryptosuite, and parameter | 1602 | | | negotiation | 1603 | | | | 1604 | 6 | Reconnect | Exchange of ECDHE keys and nonces | 1605 | | | | 1606 | 7 | Reconnect | Authentication and key confirmation with | 1607 | | | HMAC | 1608 | | | | 1609 | 8 | Completion | NoobId discovery | 1610 | | | | 1611 | 9 | All | PeerId and PeerState discovery | 1612 | | exchanges | | 1613 | | | | 1614 | 0 | Error | Error notification | 1615 | | | | 1616 +----------+------------+-------------------------------------------+ 1618 Table 7: EAP-NOOB 1620 Assignment of new values for new Message Types MUST be done through 1621 IANA with "Expert Review" as defined in [RFC8126]. 1623 4.3. Error codes 1625 The error codes defined by EAP-NOOB are listed in Table 8. 1627 +------------+----------------------------------------+ 1628 | Error code | Purpose | 1629 +------------+----------------------------------------+ 1630 | 1001 | Invalid NAI | 1631 | 1002 | Invalid message structure | 1632 | 1003 | Invalid data | 1633 | 1004 | Unexpected message type | 1634 | 1007 | Invalid ECDHE key | 1635 | 2001 | Unwanted peer | 1636 | 2002 | State mismatch, user action required | 1637 | 2003 | Unrecognized OOB message identifier | 1638 | 2004 | Unexpected peer identifier | 1639 | 3001 | No mutually supported protocol version | 1640 | 3002 | No mutually supported cryptosuite | 1641 | 3003 | No mutually supported OOB direction | 1642 | 4001 | HMAC verification failure | 1643 | 5001 | Application-specific error | 1644 | 5002 | Invalid server info | 1645 | 5003 | Invalid server URL | 1646 | 5004 | Invalid peer info | 1647 | 6001-6999 | Private and experimental use | 1648 +------------+----------------------------------------+ 1650 Table 8: EAP-NOOB error codes 1652 Assignment of new error codes MUST be done through IANA with 1653 "Specification Required" and "IESG Approval" as defined in [RFC8126], 1654 with the exception of the range 6001-6999, which is reserved for 1655 "Private Use" and "Experimental Use". 1657 4.4. Domain name reservation considerations 1659 A special-use domain (.arpa) should be registered to replace the 1660 temporary domain "eap-noob.net" used in this draft. The 1661 considerations required by [RFC6761] for registering this special-use 1662 domain name are the following: 1664 o Users: Non-admin users are not expected to encounter this name or 1665 recognize it as special. AAA administrators may need to recognize 1666 the name. 1668 o Application Software: Application software is not expected to 1669 recognize this domain name as special. 1671 o Name Resolution APIs and Libraries: Name resolution APIs and 1672 libraries are not expected to recognize this domain name as 1673 special. 1675 o Caching DNS Servers: Caching servers are not expected to recognize 1676 this domain name as special. 1678 o Authoritative DNS Servers: Authoritative DNS servers MUST respond 1679 to queries for eap-noob.net (.arpa domain TBA) with NXDOMAIN. 1681 o DNS Server Operators: Except for the authoritative DNS server, 1682 there are no special requirements for the operators. 1684 o DNS Registries/Registrars: There are no special requirements for 1685 DNS registrars. 1687 5. Implementation Status 1689 This section records the status of known implementations of the 1690 protocol defined by this specification at the time of posting of this 1691 Internet-Draft, and is based on a proposal described in [RFC7942]. 1692 The description of implementations in this section is intended to 1693 assist the IETF in its decision processes in progressing drafts to 1694 RFCs. Please note that the listing of any individual implementation 1695 here does not imply endorsement by the IETF. Furthermore, no effort 1696 has been spent to verify the information presented here that was 1697 supplied by IETF contributors. This is not intended as, and must not 1698 be construed to be, a catalog of available implementations or their 1699 features. Readers are advised to note that other implementations may 1700 exist. 1702 5.1. Implementation with wpa_supplicant and hostapd 1704 o Responsible Organization: Aalto University 1706 o Location: 1708 o Coverage: This implementation includes all of the features 1709 described in the current specification. The implementation 1710 supports two dimensional QR codes and NFC as example out-of-band 1711 (OOB) channels 1713 o Level of Maturity: Alpha 1715 o Version compatibility: Version 06 of the draft implemented 1717 o Licensing: BSD 1719 o Contact Information: Tuomas Aura, tuomas.aura@aalto.fi 1721 5.2. Implementation on Contiki 1723 o Responsible Organization: University of Murcia and Aalto 1724 University 1726 o Location: 1728 o Coverage: This implementation includes all of the features 1729 described in the current specification. The implementation uses a 1730 blinking LED light as the out-of-band (OOB) channel 1732 o Level of Maturity: Alpha 1734 o Version compatibility: Version 05 of the draft implemented 1736 o Licensing: BSD 1738 o Contact Information: Eduardo Ingles, eduardo.ingles@um.es 1740 5.3. Protocol modeling 1742 The current EAP-NOOB specification has been modeled with the mCRL2 1743 formal specification language [mcrl2]. The model 1744 was used mainly for simulating the protocol behavior and for 1746 verifying basic safety and liveness properties as part of the 1747 specification process. For example, we verified the correctness of 1748 the tiebreaking mechanism when two OOB messages are received 1749 simultaneously, one in each direction. We also verified that a man- 1750 in-the-middle attacker cannot cause persistent failure by spoofing a 1751 finite number of messages in the Reconnect Exchange. Additionally, 1752 the protocol has been modeled with the ProVerif [proverif] tool. 1753 This model was used to verify security 1755 properties such as mutual authentication. 1757 6. Security considerations 1759 EAP-NOOB is an authentication and key derivation protocol and, thus, 1760 security considerations can be found in most sections of this 1761 specification. In the following, we explain the protocol design and 1762 highlight some other special considerations. 1764 6.1. Authentication principle 1766 EAP-NOOB establishes a shared secret with an authenticated ECDHE key 1767 exchange. The mutual authentication in EAP-NOOB is based on two 1768 separate features, both conveyed in the OOB message. The first 1769 authentication feature is the secret nonce Noob. The peer and server 1770 use this secret in the Completion Exchange to mutually authenticate 1771 the session key previously created with ECDHE. The message 1772 authentication codes computed with the secret nonce Noob are alone 1773 sufficient for authenticating the key exchange. The second 1774 authentication feature is the integrity-protecting fingerprint Hoob. 1775 Its purpose is to prevent impersonation and man-in-the-middle attacks 1776 even in situations where the attacker is able to eavesdrop the OOB 1777 channel and the nonce Noob is compromised. In some human-assisted 1778 OOB channels, such as human-perceptible audio or user-typed URL, it 1779 may be easier to detect tampering than spying of the OOB message, and 1780 such applications benefit from the second authentication feature. 1782 The additional security provided by the cryptographic fingerprint 1783 Hoob is somewhat intricate to understand. The endpoint that receives 1784 the OOB message uses Hoob to verify the integrity of the ECDHE 1785 exchange. Thus, the OOB receiver can detect impersonation and man- 1786 in-the-middle attacks that may have happened on the in-band channel. 1787 The other endpoint, however, is not equally protected because the OOB 1788 message and fingerprint are sent only in one direction. Some 1789 protection to the OOB sender is afforded by the fact that the user 1790 may notice the failure of the association at the OOB receiver and 1791 therefore reset the OOB sender. Other device-pairing protocols have 1792 solved similar situations by requiring the user to confirm to the OOB 1793 sender that the association was accepted by the OOB receiver, e.g. 1794 with a button press on the sender side. Applications MAY implement 1795 EAP-NOOB in this way. Nevertheless, since EAP-NOOB was designed to 1796 work with strictly one-directional OOB communication and the 1797 fingerprint is only the second authentication feature, the EAP-NOOB 1798 specification does not mandate such explicit confirmation to the OOB 1799 sender. 1801 To summarize, EAP-NOOB uses the combined protection of the secret 1802 nonce Noob and the cryptographic fingerprint Hoob, both conveyed in 1803 the OOB message. The secret nonce Noob alone is sufficient for 1804 mutual authentication, unless the attacker can eavesdrop it from the 1805 OOB channel. Even if an attacker is able to eavesdrop the secret 1806 nonce Noob, it nevertheless cannot perform a full man-in-the-middle 1807 attack on the in-band channel because a mismatching fingerprint would 1808 alert the OOB receiver, which would reject the OOB message. The 1809 attacker that eavesdropped the secret nonce can impersonate the OOB 1810 receiver to the OOB sender. If it does, the association will appear 1811 to be complete only on the OOB sender side, and such situations have 1812 to be resolved by the user by resetting the OOB sender to the initial 1813 state. 1815 The expected use cases for EAP-NOOB are ones where it replaces a 1816 user-entered access credential in IoT appliances. In wireless 1817 network access without EAP, the user-entered credential is often a 1818 passphrase that is shared by all the network stations. The advantage 1819 of an EAP-based solution, including EAP-NOOB, is that it establishes 1820 a different master secret for each peer device, which makes the 1821 system more resilient against device compromise. Another advantage 1822 is that it is possible to revoke the security association for an 1823 individual device on the server side. 1825 Forward secrecy in EAP-NOOB is optional. The Reconnect Exchange in 1826 EAP-NOOB provides forward secrecy only if both the server and peer 1827 send their fresh ECDHE keys. This allows both the server and the 1828 peer to limit the frequency of the costly computation that is 1829 required for forward secrecy. The server MAY adjust the frequency of 1830 its attempts at ECDHE rekeying based on what it knows about the 1831 peer's computational capabilities. 1833 The users delivering the OOB messages will often authenticate 1834 themselves to the EAP server, e.g. by logging into a secure web page 1835 or API. In this case, the server can reliably associate the peer 1836 device with the user account. Applications that make use of EAP-NOOB 1837 can use this information for configuring the initial owner of the 1838 freshly-registered device. 1840 6.2. Identifying correct endpoints 1842 Potential weaknesses in EAP-NOOB arise from the fact that the user 1843 must identify physically the correct peer device. If the attacker is 1844 able to trick the user into delivering the OOB message to or from the 1845 wrong peer device, the server may create an association with the 1846 wrong peer. This reliance on user in identifying the correct 1847 endpoints is an inherent property of user-assisted out-of-band 1848 authentication. 1850 It is, however, not possible to exploit accidental delivery of the 1851 OOB message to the wrong device when the user makes an unexpected 1852 mistake. This is because the wrong peer device would not have 1853 prepared for the attack by performing the Initial Exchange with the 1854 server. In comparison, simpler security bootstrapping solutions 1855 where the master key is transferred to the device via the OOB channel 1856 are vulnerable to opportunistic attacks if the user mistakenly 1857 delivers the master key to the wrong device or to more than one 1858 device. 1860 One mechanism that can mitigate user mistakes is certification of 1861 peer devices. The certificate can convey to the server authentic 1862 identifiers and attributes, such as model and serial number, of the 1863 peer device. Compared to a fully certificate-based authentication, 1864 however, EAP-NOOB can be used without trusted third parties and does 1865 not require the user to know any identifier of the peer device; 1866 physical access to the device is sufficient for bootstrapping with 1867 EAP-NOOB. 1869 Similarly, the attacker can try to trick the user into delivering the 1870 OOB message to the wrong server, so that the peer device becomes 1871 associated with the wrong server. If the EAP server is accessed 1872 through a web user interface, the attack is akin to phishing attacks 1873 where the user is tricked into accessing the wrong URL and wrong web 1874 page. OOB implementation with a dedicated app on a mobile device, 1875 which communicates with a server API at a pre-configured URL, can 1876 protect against such attacks. 1878 6.3. Trusted path issues and misbinding attacks 1880 Another potential threat is spoofed user input or output on the peer 1881 device. When the user is delivering the OOB message to or from the 1882 correct peer device, a trusted path between the user and the peer 1883 device is needed. That is, the user must communicate directly with 1884 an authentic operating system and EAP-NOOB implementation in the peer 1885 device and not with a spoofed user interface. Otherwise, a 1886 Registered device that is under the control of the attacker could 1887 emulate the behavior of an unregistered device. The secure path can 1888 be implemented, for example, by having the user press a reset button 1889 to return the device to the Unregistered state and to invoke a 1890 trusted UI. The problem with such trusted paths is that they are not 1891 standardized across devices. 1893 Another potential consequence of a spoofed UI is the misbinding 1894 attack where the user tries to register a correct but compromised 1895 device, which tricks the user into registering another 1896 (uncompromised) device instead. For example, the compromised device 1897 might have a malicious full-screen app running, which presents to the 1898 user QR codes copied, in real time, from another device's screen. If 1899 the unwitting user scans the QR code and delivers the OOB message in 1900 it to the server, the wrong device may become registered in the 1901 server. Such misbinding vulnerabilities arise because the user does 1902 not have any secure way of verifying that the in-band cryptographic 1903 handshake and the out-of-band physical access are terminated at the 1904 same physical device. Sethi et al. [Sethi19] analyze the misbinding 1905 threat against device-pairing protocols and also EAP-NOOB. 1906 Essentially, all protocols where the authentication relies on the 1907 user's physical access to the device are vulnerable to misbinding, 1908 including EAP-NOOB. 1910 A standardized trusted path for communicating directly with the 1911 trusted computing base in a physical device would mitigate the 1912 misbinding threat, but such paths rarely exist in practice. Careful 1913 asset tracking on the server side can also prevent most misbinding 1914 attacks if the peer device sends its identifers or attributes in the 1915 PeerInfo field and the server compares them with the expected values. 1916 The wrong but uncompomised device's PeerInfo will not match the 1917 expected values. Device certification by the manufacturer can 1918 further strengthen the asset tracking. 1920 6.4. Peer identifiers and attributes 1922 The PeerId value in the protocol is a server-allocated identifier for 1923 its association with the peer and SHOULD NOT be shown to the user 1924 because its value is initially ephemeral. Since the PeerId is 1925 allocated by the server and the scope of the identifier is the single 1926 server, the so-called identifier squatting attacks, where a malicious 1927 peer could reserve another peer's identifier, are not possible in 1928 EAP-NOOB. The server SHOULD assign a random or pseudo-random PeerId 1929 to each new peer. It SHOULD NOT select the PeerId based on any peer 1930 characteristics that it may know, such as the peer's link-layer 1931 network address. 1933 User reset or failure in the OOB Step can cause the peer to perform 1934 many Initial Exchanges with the server, to allocate many PeerId 1935 values, and to store the ephemeral protocol state for them. The peer 1936 will typically only remember the latest one. EAP-NOOB leaves it to 1937 the implementation to decide when to delete these ephemeral 1938 associations. There is no security reason to delete them early, and 1939 the server does not have any way to verify that the peers are 1940 actually the same one. Thus, it is safest to store the ephemeral 1941 states for at least one day. If the OOB messages are sent only in 1942 the server-to-peer direction, the server SHOULD NOT delete the 1943 ephemeral state before all the related Noob values have expired. 1945 After completion of EAP-NOOB, the server may store the PeerInfo data, 1946 and the user may use it to identify the peer and its attributes, such 1947 as the make and model or serial number. A compromised peer could lie 1948 in the PeerInfo that it sends to the server. If the server stores 1949 any information about the peer, it is important that this information 1950 is approved by the user during or after the OOB Step. Without 1951 verification by the user or authentication with vendor certificates 1952 on the application level, the PeerInfo is not authenticated 1953 information and should not be relied on. 1955 One possible use for the PeerInfo field is EAP channel binding 1956 ([RFC3748] Section 7.15). That is, the peer MAY include in PeerInfo 1957 any data items that it wants to bind to the the EAP-NOOB association 1958 and to the exported keys. These can be properties of the 1959 authenticator or the access link, such as the SSID and BSSID of the 1960 wireless network (see Appendix C). 1962 6.5. Identity protection 1964 The PeerInfo field contains identifiers and other information about 1965 the peer device (see Appendix C), and the peer sends this information 1966 in plaintext to the EAP server before the server authentication in 1967 EAP-NOOB has been completed. While the information refers to the 1968 peer device and not directly to the user, it may be better for user 1969 privacy to avoid sending unnecessary information. In the Reconnect 1970 Exchange, the optional PeerInfo SHOULD be omitted unless some 1971 critical data has changed. 1973 Peer devices that randomize their layer-2 address to prevent tracking 1974 can do this whenever the user resets the EAP-NOOB association. 1975 During the lifetime of the association, the PeerId is a unique 1976 identifier that can be used to track the peer in the access network. 1977 Later versions of this specification may consider updating the PeerId 1978 at each Reconnect Exchange. In that case, it is necessary to 1979 consider how the authenticator and access-network administrators can 1980 recognize and blacklist misbehaving peer devices and how to avoid 1981 loss of synchronization between the server and the peer if messages 1982 are lost during the identifier update. 1984 6.6. Downgrading threats 1986 The fingerprint Hoob protects all the information exchanged in the 1987 Initial Exchange, including the cryptosuite negotiation. The message 1988 authentication codes MACs and MACp also protect the same information. 1989 The message authentication codes MACs2 and MACp2 protect information 1990 exchanged during key renegotiation in the Reconnect Exchange. This 1991 prevents downgrading attacks to weaker cryptosuites as long as the 1992 possible attacks take more time than the maximum time allowed for the 1993 EAP-NOOB completion. This is typically the case for recently 1994 discovered cryptanalytic attacks. 1996 As an additional precaution, the EAP server and peer MUST check for 1997 downgrading attacks in the Reconnect Exchange af follows. As long as 1998 the server or peer saves any information about the other endpoint, it 1999 MUST also remember the previously negotiated cryptosuite and MUST NOT 2000 accept renegotiation of any cryptosuite that is known to be weaker 2001 than the previous one, such as a deprecated cryptosuite. 2003 Integrity of the direction negotiation cannot be verified in the same 2004 way as the integrity of the cryptosuite negotiation. That is, if the 2005 OOB channel used in an application is critically insecure in one 2006 direction, a man-in-the-middle attacker could modify the negotiation 2007 messages and thereby cause that direction to be used. Applications 2008 that support OOB messages in both directions SHOULD therefore ensure 2009 that the OOB channel has sufficiently strong security in both 2010 directions. While this is a theoretical vulnerability, it could 2011 arise in practice if EAP-NOOB is deployed in new applications. 2012 Currently, we expect most peer devices to support only one OOB 2013 direction, in which case interfering with the direction negotiation 2014 can only prevent the completion of the protocol. 2016 The long-term shared key material Kz in the persistent EAP-NOOB 2017 association is established with an ECDHE key exchange when the peer 2018 and server are first associated. It is a weaker secret than a 2019 manually configured random shared key because advances in 2020 cryptanalysis against the used ECDHE curve could eventually enable 2021 the attacker to recover Kz. EAP-NOOB protects against such attacks 2022 by allowing cryptosuite upgrades in the Reconnect Exchange and by 2023 updating the shared key material Kz whenever the cryptosuite is 2024 upgraded. We do not expect the cryptosuite upgrades to be frequent, 2025 but if an upgrade becomes necessary, it can be done without manual 2026 reset and reassociation of the peer devices. 2028 6.7. Recovery from loss of last message 2030 The EAP-NOOB Completion Exchange, as well as the Reconnect Exchange 2031 with cryptosuite update, result in a persistent state change that 2032 should take place either on both endpoints or on neither; otherwise, 2033 the result is a state mismatch that requires user action to resolve. 2034 The state mismatch can occur if the final EAP response of the 2035 exchanges is lost. In the Completion Exchange, the loss of the final 2036 response (Type=4) results in the peer moving to Registered (4) state 2037 and creating a persistent EAP-NOOB association while the server stays 2038 in an ephemeral state (1 or 2). In the Reconnect Exchange, the loss 2039 of the final response (Type=7) results in the peer moving to the 2040 Registered (4) state and updating its persistent key material Kz 2041 while the server stays in the Reconnecting (3) state and keeps the 2042 old key material. 2044 The state mismatch is an example of a unavoidable problem in 2045 distributed systems: it is theoretically impossible to guarantee 2046 synchronous state changes in endpoints that communicate 2047 asynchronously. The protocol will always have one critical message 2048 that may get lost, so that one side commits to the state change and 2049 the other side does not. In EAP, the critical message is the final 2050 response from the peer to the server. While the final response is 2051 normally followed by EAP-Success, [RFC3748] section 4.2 states that 2052 the peer MAY assume that the EAP-Success was lost and the 2053 authentication was successful. Furthermore, EAP method 2054 implementations in the peer do not receive notification of the EAP- 2055 Success message from the parent EAP state machine [RFC4137]. For 2056 these reasons, EAP-NOOB on the peer side commits to a state change 2057 already when it sends the final response. 2059 The best available solution to the loss of the critical message is to 2060 keep trying. EAP retransmission behavior defined in Section 4.3 of 2061 [RFC3748] suggests 3-5 retransmissions. In the absence of an 2062 attacker, this would be sufficient to reduce the probability of 2063 failure to an acceptable level. However, a determined attacker on 2064 the in-band channel can drop the final EAP-Response message and all 2065 subsequent retransmissions. In the Completion Exchange 2066 (KeyingMode=0) and in the Reconnect Exchange with cryptosuite upgrade 2067 (KeyingMode=3), this could result in a state mismatch and persistent 2068 denial of service until user resets the peer state. 2070 EAP-NOOB implements its own recovery mechanism that allows unlimited 2071 retries of the Reconnect Exchange. When the DoS attacker eventually 2072 stops dropping packets on the in-band channel, the protocol will 2073 recover. The logic for this recovery mechanism is specified in 2074 Section 3.4.2. 2076 EAP-NOOB does not implement the same kind of retry mechanism in the 2077 Completion Exchange. The reason is that there is always a user 2078 involved in the initial association process, and the user can repeat 2079 the OOB Step to complete the association after the DoS attacker has 2080 left. On the other hand, Reconnect Exchange needs to work without 2081 user involvement. 2083 6.8. EAP security claims 2085 EAP security claims are defined in section 7.2.1 of [RFC3748]. The 2086 security claims for EAP-NOOB are listed in Table 9. 2088 +----------------+--------------------------------------------------+ 2089 | Security | EAP-NOOB claim | 2090 | property | | 2091 +----------------+--------------------------------------------------+ 2092 | Authentication | ECDHE key exchange with out-of-band | 2093 | mechanism | authentication | 2094 | | | 2095 | Protected | yes | 2096 | cryptosuite | | 2097 | negotiation | | 2098 | | | 2099 | Mutual | yes | 2100 | authentication | | 2101 | | | 2102 | Integrity | yes | 2103 | protection | | 2104 | | | 2105 | Replay | yes | 2106 | protection | | 2107 | | | 2108 | Key derivation | yes | 2109 | | | 2110 | Key strength | The specified cryptosuites provide key strength | 2111 | | of at least 128 bits. | 2112 | | | 2113 | Dictionary | yes | 2114 | attack | | 2115 | protection | | 2116 | | | 2117 | Fast reconnect | yes | 2118 | | | 2119 | Cryptographic | not applicable | 2120 | binding | | 2121 | | | 2122 | Session | yes | 2123 | independence | | 2124 | | | 2125 | Fragmentation | no | 2126 | | | 2127 | Channel | yes (The ServerInfo and PeerInfo can be used to | 2128 | binding | convey integrity-protected channel properties | 2129 | | such as network SSID or peer MAC address.) | 2130 +----------------+--------------------------------------------------+ 2132 Table 9: EAP security claims 2134 7. References 2136 7.1. Normative references 2138 [NIST-DH] Barker, E., Chen, L., Roginsky, A., and M. Smid, 2139 "Recommendation for Pair-Wise Key Establishment Schemes 2140 Using Discrete Logarithm Cryptography", NIST Special 2141 Publication 800-56A Revision 2 , May 2013, 2142 . 2145 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 2146 Hashing for Message Authentication", RFC 2104, 2147 DOI 10.17487/RFC2104, February 1997, 2148 . 2150 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2151 Requirement Levels", BCP 14, RFC 2119, 2152 DOI 10.17487/RFC2119, March 1997, 2153 . 2155 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 2156 Levkowetz, Ed., "Extensible Authentication Protocol 2157 (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004, 2158 . 2160 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 2161 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 2162 . 2164 [RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible 2165 Authentication Protocol (EAP) Key Management Framework", 2166 RFC 5247, DOI 10.17487/RFC5247, August 2008, 2167 . 2169 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 2170 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 2171 DOI 10.17487/RFC6234, May 2011, 2172 . 2174 [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", 2175 RFC 6761, DOI 10.17487/RFC6761, February 2013, 2176 . 2178 [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, 2179 DOI 10.17487/RFC7517, May 2015, 2180 . 2182 [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, 2183 DOI 10.17487/RFC7518, May 2015, 2184 . 2186 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2187 DOI 10.17487/RFC7542, May 2015, 2188 . 2190 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 2191 for Security", RFC 7748, DOI 10.17487/RFC7748, January 2192 2016, . 2194 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2195 Writing an IANA Considerations Section in RFCs", BCP 26, 2196 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2197 . 2199 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 2200 Interchange Format", STD 90, RFC 8259, 2201 DOI 10.17487/RFC8259, December 2017, 2202 . 2204 7.2. Informative references 2206 [BluetoothPairing] 2207 Bluetooth, SIG, "Simple pairing whitepaper", Technical 2208 report , 2007. 2210 [EUI-48] Institute of Electrical and Electronics Engineers, 2211 "802-2014 IEEE Standard for Local and Metropolitan Area 2212 Networks: Overview and Architecture.", IEEE Standard 2213 802-2014. , June 2014. 2215 [IEEE-802.1X] 2216 Institute of Electrical and Electronics Engineers, "Local 2217 and Metropolitan Area Networks: Port-Based Network Access 2218 Control", IEEE Standard 802.1X-2004. , December 2004. 2220 [mcrl2] Groote, J. and M. Mousavi, "Modeling and analysis of 2221 communicating systems", The MIT press , 2014, 2222 . 2225 [proverif] 2226 Blanchet, B., Smyth, B., Cheval, V., and M. Sylvestre, 2227 "ProVerif 2.00: Automatic Cryptographic Protocol Verifier, 2228 User Manual and Tutorial", The MIT press , 2018, 2229 . 2232 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 2233 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 2234 D. Spence, "AAA Authorization Framework", RFC 2904, 2235 DOI 10.17487/RFC2904, August 2000, 2236 . 2238 [RFC4137] Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba, 2239 "State Machines for Extensible Authentication Protocol 2240 (EAP) Peer and Authenticator", RFC 4137, 2241 DOI 10.17487/RFC4137, August 2005, 2242 . 2244 [RFC4266] Hoffman, P., "The gopher URI Scheme", RFC 4266, 2245 DOI 10.17487/RFC4266, November 2005, 2246 . 2248 [RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS 2249 Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216, 2250 March 2008, . 2252 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 2253 Code: The Implementation Status Section", BCP 205, 2254 RFC 7942, DOI 10.17487/RFC7942, July 2016, 2255 . 2257 [Sethi14] Sethi, M., Oat, E., Di Francesco, M., and T. Aura, "Secure 2258 Bootstrapping of Cloud-Managed Ubiquitous Displays", 2259 Proceedings of ACM International Joint Conference on 2260 Pervasive and Ubiquitous Computing (UbiComp 2014), pp. 2261 739-750, Seattle, USA , September 2014, 2262 . 2264 [Sethi19] Sethi, M., Peltonen, A., and T. Aura, "Misbinding Attacks 2265 on Secure Device Pairing", 2019, 2266 . 2268 Appendix A. Exchanges and events per state 2270 Figure 11 shows how the EAP server chooses the exchange type 2271 depending on the server and peer states. In the state combinations 2272 marked with hyphen "-", there is no possible exchange and user action 2273 is required to make progress. Note that peer state 4 is omitted from 2274 the table because the peer never connects to the server when the peer 2275 is in that state. The table also shows the handling of errors in 2276 each exchange. A notable detail is that the recipient of error code 2277 2003 moves to state 1. 2279 +--------+---------------------------+------------------------------+ 2280 | peer | exchange chosen by | next peer and | 2281 | states | server | server states | 2282 +========+===========================+==============================+ 2283 | server state: Unregistered (0) | 2284 +--------+---------------------------+------------------------------+ 2285 | 0..2 | Initial Exchange | both 1 (0 on error) | 2286 | 3 | - | no change, notify user | 2287 +--------+---------------------------+------------------------------+ 2288 | server state: Waiting for OOB (1) | 2289 +--------+---------------------------+------------------------------+ 2290 | 0 | Initial Exchange | both 1 (0 on error) | 2291 | 1 | Waiting Exchange | both 1 (no change on error) | 2292 | 2 | Completion Exchange | both 4 (A) | 2293 | 3 | - | no change, notify user | 2294 +--------+---------------------------+------------------------------+ 2295 | server state: OOB Received (2) | 2296 +--------+---------------------------+------------------------------+ 2297 | 0 | Initial Exchange | both 1 (0 on error) | 2298 | 1 | Completion Exchange | both 4 (B) | 2299 | 2 | Completion Exchange | both 4 (A) | 2300 | 3 | - | no change, notify user | 2301 +--------+---------------------------+------------------------------+ 2302 | server state: Reconnecting (3) or Registered (4) | 2303 +--------+---------------------------+------------------------------+ 2304 | 0..2 | - | no change, notify user | 2305 | 3 | Reconnect Exchange | both 4 (3 on error) | 2306 +--------+---------------------------+------------------------------+ 2307 (A) peer to 1 on error 2003, no other changes on error 2308 (B) server to 1 on error 2003, no other changes on error 2310 Figure 11: How server chooses the exchange type 2312 Figure 12 lists the local events that can take place in the server or 2313 peer. Both the server and peer output and accept OOB messages in 2314 association state 1, leading the receiver to state 2. Communication 2315 errors and timeouts in states 0..2 lead back to state 0, while 2316 similar errors in states 3..4 lead to state 3. Application request 2317 for rekeying (e.g. to refresh session keys or to upgrade cryptosuite) 2318 also takes the association from state 3..4 to state 3. User can 2319 always reset the association state to 0. Recovering association 2320 data, e.g. from a backup, leads to state 3. 2322 +--------+---------------------------+------------------------------+ 2323 | server/| possible local events | next state | 2324 | peer | on server and peer | | 2325 | state | | | 2326 +========+===========================+==============================+ 2327 | 1 | OOB Output* | 1 | 2328 | 1 | OOB Input* | 2 (1 on error) | 2329 | 0..2 | Timeout/network failure | 0 | 2330 | 3..4 | Timeout/network failure | 3 | 2331 | 3..4 | Rekeying request | 3 | 2332 | 0..4 | User resets peer state | 0 | 2333 | 0..4 | Association state recovery| 3 | 2334 +--------+---------------------------+------------------------------+ 2336 Figure 12: Local events on server and peer 2338 Appendix B. Application-specific parameters 2340 Table 10 lists OOB channel parameters that need to be specified in 2341 each application that makes use of EAP-NOOB. The list is not 2342 exhaustive and is included for the convenience of implementors only. 2344 +--------------------+----------------------------------------------+ 2345 | Parameter | Description | 2346 +--------------------+----------------------------------------------+ 2347 | OobDirs | Allowed directions of the OOB channel | 2348 | | | 2349 | OobMessageEncoding | How the OOB message data fields are encoded | 2350 | | for the OOB channel | 2351 | | | 2352 | SleepTimeDefault | Default minimum time in seconds that the | 2353 | | peer should sleep before the next Waiting | 2354 | | Exchange | 2355 | | | 2356 | OobRetries | Number of received OOB messages with invalid | 2357 | | Hoob after which the receiver moves to | 2358 | | Unregistered (0) state | 2359 | | | 2360 | NoobTimeout | How many seconds the sender of the OOB | 2361 | | message remembers the sent Noob value. The | 2362 | | RECOMMENDED value is 3600 seconds. | 2363 | | | 2364 | ServerInfoMembers | Required members in ServerInfo | 2365 | | | 2366 | PeerInfoMembers | Required members in PeerInfo | 2367 +--------------------+----------------------------------------------+ 2369 Table 10: OOB channel characteristics 2371 Appendix C. ServerInfo and PeerInfo contents 2373 The ServerInfo and PeerInfo fields in the Initial Exchange and 2374 Reconnect Exchange enable the server and peer, respectively, send 2375 information about themselves to the other endpoint. They contain 2376 JSON objects whose structure may be specified separately for each 2377 application and each type of OOB channel. ServerInfo and PeerInfo 2378 MAY contain auxiliary data needed for the OOB channel messaging and 2379 for EAP channel binding. Table 11 lists some suggested data fields 2380 for ServerInfo. 2382 +----------------+--------------------------------------------------+ 2383 | Data field | Description | 2384 +----------------+--------------------------------------------------+ 2385 | ServerName | String that may be used to aid human | 2386 | | identification of the server. | 2387 | | | 2388 | ServerURL | Prefix string when the OOB message is formatted | 2389 | | as URL, as suggested in Appendix E. | 2390 | | | 2391 | SSIDList | List of wireless network identifier (SSID) | 2392 | | strings used for roaming support, as suggested | 2393 | | in Appendix D. JSON array of UTF-8 encoded SSID | 2394 | | strings. | 2395 | | | 2396 | Base64SSIDList | List of wireless network identifier (SSID) | 2397 | | strings used for roaming support, as suggested | 2398 | | in Appendix D. JSON array of SSIDs, each of | 2399 | | which is base64url encoded without padding. Peer | 2400 | | SHOULD send at most one of the fields SSIDList | 2401 | | and Base64SSIDList in PeerInfo, and the server | 2402 | | SHOULD ignore SSIDList if Base64SSIDList is | 2403 | | included. | 2404 +----------------+--------------------------------------------------+ 2406 Table 11: Suggested ServerInfo data fields 2408 PeerInfo typically contains auxiliary information for identifying and 2409 managing peers on the application level at the server end. Table 12 2410 lists some suggested data fields for PeerInfo. 2412 +--------------+----------------------------------------------------+ 2413 | Data field | Description | 2414 +--------------+----------------------------------------------------+ 2415 | PeerName | String that may be used to aid human | 2416 | | identification of the peer. | 2417 | | | 2418 | Manufacturer | Manufacturer or brand string. | 2419 | | | 2420 | Model | Manufacturer-specified model string. | 2421 | | | 2422 | SerialNumber | Manufacturer-assigned serial number. | 2423 | | | 2424 | MACAddress | Peer link-layer identifier (EUI-48) in the | 2425 | | 12-digit base-16 form [EUI-48]. The string MAY | 2426 | | include additional colon ':' or dash '-' | 2427 | | characters that MUST be ignored by the server. | 2428 | | | 2429 | SSID | Wireless network SSID for channel binding. The | 2430 | | SSID is a UTF-8 string. | 2431 | | | 2432 | Base64SSID | Wireless network SSID for channel binding. The | 2433 | | SSID is base64url encoded. Peer SHOULD send at | 2434 | | most one of the fields SSID and Base64SSID in | 2435 | | PeerInfo, and the server SHOULD ignore SSID if | 2436 | | Base64SSID is included. | 2437 | | | 2438 | BSSID | Wireless network BSSID (EUI-48) in the 12-digit | 2439 | | base-16 form [EUI-48]. The string MAY include | 2440 | | additional colon ':' or dash '-' characters that | 2441 | | MUST be ignored by the server. | 2442 | | | 2443 +--------------+----------------------------------------------------+ 2445 Table 12: Suggested PeerInfo data fields 2447 Appendix D. EAP-NOOB roaming 2449 AAA architectures [RFC2904] allow for roaming of network-connected 2450 appliances that are authenticated over EAP. While the peer is 2451 roaming in a visited network, authentication still takes place 2452 between the peer and an authentication server at its home network. 2453 EAP-NOOB supports such roaming by assigning a Realm to the peer. 2454 After the Realm has been assigned, the peer's NAI enables the visited 2455 network to route the EAP session to the peer's home AAA server. 2457 A peer device that is new or has gone through a hard reset should be 2458 connected first to the home network and establish an EAP-NOOB 2459 association with its home AAA server before it is able to roam. 2461 After that, it can perform the Reconnect Exchange from the visited 2462 network. 2464 Alternatively, the device may provide some method for the user to 2465 configure the Realm of the home network. In that case, the EAP-NOOB 2466 association can be created while roaming. The device will use the 2467 user-assigned Realm in the Initial Exchange, which enables the EAP 2468 messages to be routed correctly to the home AAA server. 2470 While roaming, the device needs to identify the networks where the 2471 EAP-NOOB association can be used to gain network access. For 802.11 2472 access networks, the server MAY send a list of SSID strings in the 2473 ServerInfo JSON object in a member called either SSIDList or 2474 Base64SSIDList. The list is formated as explained in Table 11. If 2475 present, the peer MAY use this list as a hint to determine the 2476 networks where the EAP-NOOB association can be used for access 2477 authorization, in addition to the access network where the Initial 2478 Exchange took place. 2480 Appendix E. OOB message as URL 2482 While EAP-NOOB does not mandate any particular OOB communication 2483 channel, typical OOB channels include graphical displays and emulated 2484 NFC tags. In the peer-to-server direction, it may be convenient to 2485 encode the OOB message as a URL, which is then encoded as a QR code 2486 for displays and printers or as an NDEF record for NFC tags. A user 2487 can then simply scan the QR code or NFC tag and open the URL, which 2488 causes the OOB message to be delivered to the authentication server. 2489 The URL MUST specify the https protocol i.e. secure connection to the 2490 server, so that the man-in-the-middle attacker cannot read or modify 2491 the OOB message. 2493 The ServerInfo in this case includes a JSON member called ServerUrl 2494 of the following format with maximum length of 60 characters: 2496 https://[:]/[] 2498 To this, the peer appends the OOB message fields (PeerId, Noob, Hoob) 2499 as a query string. PeerId is provided to the peer by the server and 2500 might be a 22-character string. The peer base64url encodes, without 2501 padding, the 16-byte values Noob and Hoob into 22-character strings. 2502 The query parameters MAY be in any order. The resulting URL is of 2503 the following format: 2505 https://[:]/[]?P=&N=&H= 2507 The following is an example of a well-formed URL encoding the OOB 2508 message (without line breaks): 2510 https://example.com/Noob?P=ZrD7qkczNoHGbGcN2bN0&N=rMinS0-F4EfCU8D9ljx 2511 X_A&H=QvnMp4UGxuQVFaXPW_14UW 2513 Appendix F. Example messages 2515 The message examples in this section are generated with Curve25519 2516 ECDHE test vectors specified in section 6.1 of [RFC7748] 2517 (server=Alice, peer=Bob). The direction of the OOB channel 2518 negotiated is 2 (server-to-peer). The JSON messages are as follows 2519 (line breaks are for readability only). 2521 ====== Initial Exchange ====== 2523 Identity response: 2524 noob@eap-noob.net 2526 EAP request (type 9): 2527 {"Type":9} 2529 EAP response (type 9): 2530 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":0} 2532 EAP request (type 1): 2533 {"Type":1,"Vers":[1],"PeerId":"07KRU6OgqX0HIeRFldnbSW","Realm":"no 2534 ob.example.com","Cryptosuites":[1],"Dirs":3,"ServerInfo":{"Name":" 2535 Example","Url":"https://noob.example.com/sendOOB"}} 2537 EAP response (type 1): 2538 {"Type":1,"Verp":1,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuitep 2539 ":1,"Dirp":2,"PeerInfo":{"Make":"Acme","Type":"None","Serial":"DU- 2540 9999","SSID":"Noob1","BSSID":"6c:19:8f:83:c2:80"}} 2542 EAP request (type 2): 2543 {"Type":2,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PKs":{"kty":"EC","crv 2544 ":"Curve25519","x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"}, 2545 "Ns":"PYO7NVd9Af3BxEri1MI6hL8Ck49YxwCjSRPqlC1SPbw","SleepTime":60} 2547 EAP response (type 2): 2548 {"Type":2,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PKp":{"kty":"EC","crv 2549 ":"Curve25519","x":"3p7bfXt9wbTTW2HC7OQ1Nz-DQ8hbeGdNrfx-FG- 2550 IK08"},"Np":"HIvB6g0n2btpxEcU7YXnWB-451ED6L6veQQd6ugiPFU"} 2552 ====== Waiting Exchange ====== 2554 Identity response: 2555 noob@eap-noob.net 2557 EAP request (type 9): 2559 {"Type":9} 2561 EAP response (type 9): 2562 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":1} 2564 EAP request (type 3): 2565 {"Type":3,"PeerId":"07KRU6OgqX0HIeRFldnbSW","SleepTime":60} 2567 EAP response (type 3): 2568 {"Type":3,"PeerId":"07KRU6OgqX0HIeRFldnbSW"} 2570 ====== OOB Step ====== 2572 OOB message: 2573 P=07KRU6OgqX0HIeRFldnbSW&N=x3JlolaPciK4Wa6XlMJxtQ&H=WJ6Covspd50NT2 2574 RxkLHSeA 2576 ====== Completion Exchange ====== 2578 Identity response: 2579 noob@eap-noob.net 2581 EAP request (type 9): 2582 {"Type":9} 2584 EAP response (type 9): 2585 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":2} 2587 EAP request (type 8): 2588 {"Type":8,"PeerId":"07KRU6OgqX0HIeRFldnbSW"} 2590 EAP response (type 8): 2591 {"Type":8,"PeerId":"07KRU6OgqX0HIeRFldnbSW","NoobId":"U0OHwYGCS4nE 2592 kzk2TPIE6g"} 2594 EAP request (type 4): 2595 {"Type":4,"PeerId":"07KRU6OgqX0HIeRFldnbSW","NoobId":"U0OHwYGCS4nE 2596 kzk2TPIE6g","MACs":"APpnhlFLWS2pfJPH5S7N3yr6FJWocuaAiuVrhgh8Xko"} 2598 EAP response (type 4): 2599 {"Type":4,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACp":"hihGS4v8w4cDy_ 2600 yokNlOyQa87GRBLvMfmF9JFwJ6RrQ"} 2602 ====== Reconnect Exchange ====== 2604 Identity response: 2605 noob@eap-noob.net 2607 EAP request (type 9): 2608 {"Type":9} 2610 EAP response (type 9): 2611 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":3} 2613 EAP request (type 5): 2614 {"Type":5,"Vers":[1],"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuit 2615 es":[1],"Realm":"noob.example.com","ServerInfo":{"Name":"Example", 2616 "Url":"https://noob.example.com/sendOOB"}} 2618 EAP response (type 5): 2619 {"Type":5,"Verp":1,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuitep 2620 ":1,"PeerInfo":{"Make":"Acme","Type":"None","Serial":"DU- 2621 9999","SSID":"Noob1","BSSID":"6c:19:8f:83:c2:80"}} 2623 EAP request (type 6): 2624 {"Type":6,"PeerId":"07KRU6OgqX0HIeRFldnbSW","KeyingMode":2,"Ns2":" 2625 RDLahHBlIgnmL_F_xcynrHurLPkCsrp3G3B_S82WUF4"} 2627 EAP response (type 6): 2628 {"Type":6,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Np2":"jN0_V4P0JoTqwI9 2629 VHHQKd9ozUh7tQdc9ABd-j6oTy_4"} 2631 EAP request (type 7): 2632 {"Type":7,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACs2":"TT_B9w- 2633 o86C1c1O_rhNxzcf9gJa0_8SiIhyxQecdM70"} 2635 EAP response (type 7): 2636 {"Type":7,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACp2":"GS9f8Mw3mUFvj 2637 IDKS54U27xPt6umIrnVXOGLl-iFRKk"} 2639 Appendix G. TODO list 2641 o 2643 Appendix H. Version history 2645 o Version 01: 2647 * Fixed Reconnection Exchange. 2649 * URL examples. 2651 * Message examples. 2653 * Improved state transition (event) tables. 2655 o Version 02: 2657 * Reworked the rekeying and key derivation. 2659 * Increased internal key lengths and in-band nonce and HMAC 2660 lengths to 32 bytes. 2662 * Less data in the persistent EAP-NOOB association. 2664 * Updated reference [NIST-DH] to Revision 2 (2013). 2666 * Shorter suggested PeerId format. 2668 * Optimized the example of encoding OOB message as URL. 2670 * NoobId in Completion Exchange to differentiate between multiple 2671 valid Noob values. 2673 * List of application-specific parameters in appendix. 2675 * Clarified the equivalence of Unregistered state and no state. 2677 * Peer SHOULD probe the server regardless of the OOB channel 2678 direction. 2680 * Added new error messages. 2682 * Realm is part of the persistent association and can be updated. 2684 * Clarified error handling. 2686 * Updated message examples. 2688 * Explained roaming in appendix. 2690 * More accurate definition of timeout for the Noob nonce. 2692 * Additions to security considerations. 2694 o Version 03: 2696 * Clarified reasons for going to Reconnecting state. 2698 * Included Verp in persistent state. 2700 * Added appendix on suggested ServerInfo and PeerInfo fields. 2702 * Exporting PeerId and SessionId. 2704 * Explicitly specified next state after OOB Step. 2706 * Clarified the processing of an expired OOB message and 2707 unrecognized NoobId. 2709 * Enabled protocol version upgrade in Reconnect Exchange. 2711 * Explained handling of redundant received OOB messages. 2713 * Clarified where raw and base64url encoded values are used. 2715 * Cryptosuite must specify the detailed format of the JWK object. 2717 * Base64url encoding in JSON strings is done without padding. 2719 * Simplified explanation of PeerId, Realm and NAI. 2721 * Added error codes for private and experimental use. 2723 * Updated the security considerations. 2725 o Version 04: 2727 * Recovery from synchronization failure due to lost last 2728 response. 2730 o Version 05: 2732 * Kz identifier added to help recovery from lost last messages. 2734 * Error message codes changed for better structure. 2736 * Improved security considerations section. 2738 o Version 06: 2740 * Kz identifier removed to enable PeerId anonymization in the 2741 future. 2743 * Clarified text on when to use server-assigned realm. 2745 * Send PeerId and PeerState in a separate request-reponse pair, 2746 not in NAI. 2748 * New subsection for the common handshake in all exchanges to 2749 avoid repetition. 2751 o Version 07: 2753 * Updated example messages. 2755 * Added pointers to new implementation in Contiki. 2757 o Version 08: 2759 * Editorial improvements and corrections. 2761 Appendix I. Acknowledgments 2763 Aleksi Peltonen modeled the protocol specification with the mCRL2 2764 formal specification language. Shiva Prasad TP and Raghavendra MS 2765 implemented parts of the protocol with wpa_supplicant and hostapd. 2766 Their inputs helped us in improving the specification. 2768 The authors would also like to thank Rhys Smith and Josh Howlett for 2769 providing valuable feedback as well as new use cases and requirements 2770 for the protocol. Thanks to Eric Rescorla, Darshak Thakore, Stefan 2771 Winter, Hannes Tschofenig, and Daniel Migault for interesting 2772 discussions in this problem space. 2774 Authors' Addresses 2776 Tuomas Aura 2777 Aalto University 2778 Aalto 00076 2779 Finland 2781 EMail: tuomas.aura@aalto.fi 2783 Mohit Sethi 2784 Ericsson 2785 Jorvas 02420 2786 Finland 2788 EMail: mohit@piuha.net