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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 1174, but not defined == Missing Reference: 'ServerInfo' is mentioned on line 1174, 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: May 1, 2020 Ericsson 6 October 29, 2019 8 Nimble out-of-band authentication for EAP (EAP-NOOB) 9 draft-aura-eap-noob-07 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. This EAP method is intended for bootstrapping all 17 kinds of Internet-of-Things (IoT) devices that have a minimal user 18 interface and no pre-configured authentication credentials. The 19 method makes use of a user-assisted one-directional OOB channel 20 between the peer device and authentication server. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on May 1, 2020. 39 Copyright Notice 41 Copyright (c) 2019 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 3. EAP-NOOB protocol . . . . . . . . . . . . . . . . . . . . . . 5 59 3.1. Protocol overview . . . . . . . . . . . . . . . . . . . . 5 60 3.2. Protocol messages and sequences . . . . . . . . . . . . . 8 61 3.2.1. Common handshake in all EAP exchanges . . . . . . . . 8 62 3.2.2. Initial Exchange . . . . . . . . . . . . . . . . . . 10 63 3.2.3. OOB Step . . . . . . . . . . . . . . . . . . . . . . 11 64 3.2.4. Completion Exchange . . . . . . . . . . . . . . . . . 13 65 3.2.5. Waiting Exchange . . . . . . . . . . . . . . . . . . 15 66 3.3. Protocol data fields . . . . . . . . . . . . . . . . . . 16 67 3.3.1. Peer identifier, realm and NAI . . . . . . . . . . . 16 68 3.3.2. Message data fields . . . . . . . . . . . . . . . . . 18 69 3.4. Fast reconnect and rekeying . . . . . . . . . . . . . . . 23 70 3.4.1. Persistent EAP-NOOB association . . . . . . . . . . . 23 71 3.4.2. Reconnect Exchange . . . . . . . . . . . . . . . . . 24 72 3.4.3. User reset . . . . . . . . . . . . . . . . . . . . . 27 73 3.5. Key derivation . . . . . . . . . . . . . . . . . . . . . 28 74 3.6. Error handling . . . . . . . . . . . . . . . . . . . . . 31 75 3.6.1. Invalid messages . . . . . . . . . . . . . . . . . . 33 76 3.6.2. Unwanted peer . . . . . . . . . . . . . . . . . . . . 33 77 3.6.3. State mismatch . . . . . . . . . . . . . . . . . . . 33 78 3.6.4. Negotiation failure . . . . . . . . . . . . . . . . . 33 79 3.6.5. Cryptographic verification failure . . . . . . . . . 34 80 3.6.6. Application-specific failure . . . . . . . . . . . . 34 81 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 82 4.1. Cryptosuites . . . . . . . . . . . . . . . . . . . . . . 35 83 4.2. Message Types . . . . . . . . . . . . . . . . . . . . . . 35 84 4.3. Error codes . . . . . . . . . . . . . . . . . . . . . . . 36 85 4.4. Domain name reservation considerations . . . . . . . . . 37 86 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 38 87 5.1. Implementation with wpa_supplicant and hostapd . . . . . 38 88 5.2. Implementation on Contiki . . . . . . . . . . . . . . . . 39 89 5.3. Protocol modeling . . . . . . . . . . . . . . . . . . . . 39 90 6. Security considerations . . . . . . . . . . . . . . . . . . . 39 91 6.1. Authentication principle . . . . . . . . . . . . . . . . 39 92 6.2. Identifying correct endpoints . . . . . . . . . . . . . . 41 93 6.3. Trusted path issues and misbinding attacks . . . . . . . 42 94 6.4. Peer identifiers and attributes . . . . . . . . . . . . . 43 95 6.5. Identity protection . . . . . . . . . . . . . . . . . . . 43 96 6.6. Downgrading threats . . . . . . . . . . . . . . . . . . . 44 97 6.7. Recovery from loss of last message . . . . . . . . . . . 45 98 6.8. EAP security claims . . . . . . . . . . . . . . . . . . . 46 99 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 100 7.1. Normative references . . . . . . . . . . . . . . . . . . 48 101 7.2. Informative references . . . . . . . . . . . . . . . . . 49 102 Appendix A. Exchanges and events per state . . . . . . . . . . . 51 103 Appendix B. Application-specific parameters . . . . . . . . . . 52 104 Appendix C. ServerInfo and PeerInfo contents . . . . . . . . . . 53 105 Appendix D. EAP-NOOB roaming . . . . . . . . . . . . . . . . . . 55 106 Appendix E. OOB message as URL . . . . . . . . . . . . . . . . . 56 107 Appendix F. Example messages . . . . . . . . . . . . . . . . . . 57 108 Appendix G. TODO list . . . . . . . . . . . . . . . . . . . . . 59 109 Appendix H. Version history . . . . . . . . . . . . . . . . . . 59 110 Appendix I. Acknowledgments . . . . . . . . . . . . . . . . . . 62 111 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 62 113 1. Introduction 115 This document describes a method for registration, authentication and 116 key derivation for network-connected ubiquitous computing devices, 117 such as consumer and enterprise appliances that are part of the 118 Internet of Things (IoT). These devices may be off-the-shelf 119 hardware that is sold and distributed without any prior registration 120 or credential-provisioning process. Thus, the device registration in 121 a server database, ownership of the device, and the authentication 122 credentials for both network access and application-level security 123 must all be established at the time of the device deployment. 124 Furthermore, many such devices have only limited user interfaces that 125 could be used for their configuration. Often, the interfaces are 126 limited to either only input (e.g. camera) or output (e.g. display 127 screen). The device configuration is made more challenging by the 128 fact that the devices may exist in large numbers and may have to be 129 deployed or re-configured nimbly based on user needs. 131 More specifically, the devices may have the following 132 characteristics: 134 o no pre-established relation with a specific server or user, 136 o no pre-provisioned device identifier or authentication 137 credentials, 139 o limited user interface and configuration capabilities. 141 Many proprietary OOB configuration methods exits for specific IoT 142 devices. The goal of this specification is to provide an open 143 standard and a generic protocol for bootstrapping the security of 144 network-connected appliances, such as displays, printers, speakers, 145 and cameras. The security bootstrapping in this specification makes 146 use of a user-assisted out-of-band (OOB) channel. The device 147 authentication relies on user having physical access to the device, 148 and the of the key exchange security is based on the assumption that 149 attackers are not able to observe or modify the messages conveyed 150 through the OOB channel. We follow the common approach taken in 151 pairing protocols: performing a Diffie-Hellman key exchange over the 152 insecure network and authenticating the established key with the help 153 of the OOB channel in order to prevent impersonation and man-in-the- 154 middle (MitM) attacks. 156 The solution presented here is intended for devices that have either 157 an input or output interface, such as a camera, microphone, display 158 screen, speakers or blinking LED light, which is able to send or 159 receive dynamically generated messages of tens of bytes in length. 160 Naturally, this solution may not be appropriate for very small 161 sensors or actuators that have no user interface at all or for 162 devices that are inaccessible to the user. We also assume that the 163 OOB channel is at least partly automated (e.g. camera scanning a bar 164 code) and, thus, there is no need to absolutely minimize the length 165 of the data transferred through the OOB channel. This differs, for 166 example, from Bluetooth simple pairing [BluetoothPairing], where it 167 is critical to minimize the length of the manually transferred or 168 compared codes. Since the OOB messages are dynamically generated, we 169 do not support static printed registration codes. This also prevents 170 attacks where a static secret code would be leaked. 172 2. Terminology 174 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 175 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 176 document are to be interpreted as described in [RFC2119]. 178 In addition, this document frequently uses the following terms as 179 they have been defined in [RFC5216]: 181 authenticator The entity initiating EAP authentication. 183 peer The entity that responds to the authenticator. In 184 [IEEE-802.1X], this entity is known as the supplicant. 186 server The entity that terminates the EAP authentication method with 187 the peer. In the case where no backend authentication server 188 is used, the EAP server is part of the authenticator. In the 189 case where the authenticator operates in pass-through mode, the 190 EAP server is located on the backend authentication server. 192 3. EAP-NOOB protocol 194 This section defines the EAP-NOOB protocol. The protocol is a 195 generalized version of the original idea presented by Sethi et al. 196 [Sethi14]. 198 3.1. Protocol overview 200 One EAP-NOOB protocol execution spans multiple EAP conversations, 201 called Exchanges. This is necessary to leave time for the OOB 202 message to be delivered, as will be explained below. 204 The overall protocol starts with the Initial Exchange, in which the 205 server allocates an identifier to the peer, and the server and peer 206 negotiate the protocol version and cryptosuite (i.e. cryptographic 207 algorithm suite), exchange nonces and perform an Ephemeral Elliptic 208 Curve Diffie-Hellman (ECDHE) key exchange. The user-assisted OOB 209 Step then takes place. This step requires only one out-of-band 210 message either from the peer to the server or from the server to the 211 peer. While waiting for the OOB Step action, the peer MAY probe the 212 server by reconnecting to it with EAP-NOOB. If the OOB Step has 213 already taken place, the probe leads to the Completion Exchange, 214 which completes the mutual authentication and key confirmation. On 215 the other hand, if the OOB Step has not yet taken place, the probe 216 leads to the Waiting Exchange, and the peer will perform another 217 probe after a server-defined minimum waiting time. The Initial 218 Exchange and Waiting Exchange always end in EAP-Failure, while the 219 Completion Exchange may result in EAP-Success. Once the peer and 220 server have performed a successful Completion Exchange, both 221 endpoints store the created association in persistent storage, and 222 the OOB Step is not repeated. Thereafter, creation of new temporal 223 keys, ECDHE rekeying, and updates of cryptographic algorithms can be 224 achieved with the Reconnect Exchange. 226 OOB Output/Initial Exchange/ 227 Waiting Exchange 228 .-----. 229 | v 230 .------------------. Initial .------------------. 231 | | Exchange | | 232 .->| 0. Unregistered |---------------->|1. Waiting for OOB| 233 | | | | | 234 | '------------------' '------------------' 235 | | | ^ 236 User Reset Completion | | | 237 | Exchange | OOB OOB 238 |<-------. .-------------------------' Input Reject/ 239 | | | | Initial 240 | | | | Exchange 241 | | v v | 242 | .------------------. Completion .------------------. 243 | | | Exchange | | 244 | | 4. Registered |<----------------| 2. OOB Received | 245 | | | | | 246 | '------------------' '------------------' 247 | | ^ 248 | Mobility/ | 249 | Timeout/ Reconnect 250 | Failure Exchange 251 | | | 252 | v | 253 | .-----------------. 254 | | | 255 '--| 3. Reconnecting | 256 | | 257 '-----------------' 259 Figure 1: EAP-NOOB server-peer association state machine 261 Figure 1 shows the association state machine, which is the same for 262 the server and for the peer. (For readability, only the main state 263 transitions are shown. The complete table of transitions can be 264 found in Appendix A.) When the peer initiates the EAP-NOOB method, 265 the server chooses the ensuing message exchange based on the 266 combination of the server and peer states. The EAP server and peer 267 are initially in the Unregistered state, in which no state 268 information needs to be stored. Before a successful Completion 269 Exchange, the server-peer association state is ephemeral in both the 270 server and peer (ephemeral states 0..2), and either endpoint may 271 cause the protocol to fall back to the Initial Exchange. After the 272 Completion Exchange has resulted in EAP-Success, the association 273 state becomes persistent (persistent states 3..4). Only user reset 274 or memory failure can cause the return of the server or the peer from 275 the persistent states to the ephemeral states and to the Initial 276 Exchange. 278 The server MUST NOT repeat a successful OOB Step with the same peer 279 except if the association with the peer is explicitly reset by the 280 user or lost due to failure of the persistent storage in the server. 281 More specifically, once the association has entered the Registered 282 state, the server MUST NOT delete the association or go back to 283 states 0..2 without explicit user approval. Similarly, the peer MUST 284 NOT repeat the OOB Step unless the user explicitly deletes from the 285 peer the association with the server or resets the peer to the 286 Unregistered state. The server and peer MAY implement user reset of 287 the association by deleting the state data from that endpoint. If an 288 endpoint continues to store data about the association after the user 289 reset, its behavior SHOULD be equivalent to having deleted the 290 association data. 292 It can happen that the peer accidentally or through user reset loses 293 its persistent state and reconnects to the server without a 294 previously allocated peer identifier. In that case, the server MUST 295 treat the peer as a new peer. The server MAY use auxiliary 296 information, such as the PeerInfo field received in the Initial 297 Exchange, to detect multiple associations with the same peer. 298 However, it MUST NOT delete or merge redundant associations without 299 user or application approval because EAP-NOOB internally has no 300 secure way of verifying that the two peers are the same physical 301 device. Similarly, the server might lose the association state 302 because of a memory failure or user reset. In that case, the only 303 way to recover is that the user resets also the peer. 305 A special feature of the EAP-NOOB method is that the server is not 306 assumed to have any a-priori knowledge of the peer. Therefore, the 307 peer initially uses the generic identity string "noob@eap-noob.net" 308 as its network access identifier (NAI). The server then allocates a 309 server-specific identifier to the peer. The generic NAI serves two 310 purposes: firstly, it tells the server that the peer supports and 311 expects the EAP-NOOB method and, secondly, it allows routing of the 312 EAP-NOOB sessions to a specific authentication server in the AAA 313 architecture. 315 EAP-NOOB is an unusual EAP method in that the peer has to have 316 multiple EAP conversations with the server before it can receive EAP- 317 Success. The reason is that, while EAP allows delays between the 318 request-response pairs, e.g. for repeated password entry, the user 319 delays in OOB authentication can be much longer than in password 320 trials. In particular, EAP-NOOB supports also peers with no input 321 capability in the user interface. Since user cannot initiate the 322 protocol in these devices, they have to perform the Initial Exchange 323 opportunistically and hope for the OOB Step to take place within a 324 timeout period (NoobTimeout), which is why the timeout needs to be 325 several minutes rather than seconds. For example, consider a printer 326 (peer) that outputs the OOB message on paper, which is then scanned 327 for the server. To support such high-latency OOB channels, the peer 328 and server perform the Initial Exchange in one EAP conversation, then 329 allow time for the OOB message to be delivered, and later perform the 330 Waiting and Completion Exchanges in different EAP conversations. 332 3.2. Protocol messages and sequences 334 This section defines the EAP-NOOB exchanges, which correspond to EAP 335 conversations. The exchanges start with a common handshake, which 336 determines the type of the following exchange. The common handshake 337 messages and the subsequent messages for each exchange type are 338 listed in the diagrams below. The diagrams also specify the data 339 members present in each message. Each exchange comprises multiple 340 EAP requests-response pairs and ends in either EAP-Failure, 341 indicating that authentication is not (yet) successful, or in EAP- 342 Success. 344 3.2.1. Common handshake in all EAP exchanges 346 All EAP-NOOB exchanges start with common handshake messages. The 347 handshake starts with the identity request and response that are 348 common to all EAP methods. Their purpose is to enable the AAA 349 architecture to route the EAP conversation to the EAP server and to 350 enable the EAP server to select the EAP method. The handshake then 351 continues with one EAP-NOOB request-response pair in which the server 352 discovers the peer identifier used in EAP-NOOB and the peer state. 354 In more detail, each EAP-NOOB exchanges begin with the authenticator 355 sending an EAP-Request/Identity packet to the peer. From this point 356 on, the EAP conversation occurs between the server and the peer, and 357 the authenticator acts as a pass-through device. The peer responds 358 to the authenticator with an EAP-Response/Identity packet, which 359 contains the network access identifier (NAI). The authenticator, 360 acting as a pass-through device, forwards this response and the 361 following EAP conversation between the peer and the AAA architecture. 362 The AAA architecture routes the conversation to a specific AAA server 363 (called "EAP server" or simply "server" in this specification) based 364 on the realm part of the NAI. The server selects the EAP-NOOB method 365 based on the user part of the NAI, as defined in Section 3.3.1. 367 After receiving the EAP-Response/Identity message, the server sends 368 the first EAP-NOOB request (Type=9) to the peer, which responds with 369 the peer identifier (PeerId) and state (PeerState) in the range 0..3. 370 However, the peer SHOULD omit the PeerId from the response (Type=9) 371 when PeerState=0. The server then chooses the EAP-NOOB exchange, 372 i.e. the ensuing message sequence, as explained below. The peer 373 recognizes the exchange based on the message type field (Type) of the 374 next EAP-NOOB request received from the server. 376 The server determines the exchange type based on the combination of 377 the peer and server states as follows (also summarized in Figure 11). 378 If one of the peer and server is in the Unregistered (0) state and 379 the other is in one of the ephemeral states (0..2), the server 380 chooses the Initial Exchange. If one of the peer or server is in the 381 OOB Received (2) state and the other is either in the Waiting for OOB 382 (1) or OOB Received (2) state, the OOB Step has taken place and the 383 server chooses the Completion Exchange. If both the server and peer 384 are in the Waiting for OOB (1) state, the server chooses the Waiting 385 Exchange. If the peer is in the Reconnecting (3) state and the 386 server is in the Registered (4) or Reconnecting (3) state, the server 387 chooses the Reconnect Exchange. All other state combinations are 388 error situations where user action is required, and the server 389 indicates such errors to the peer with the error code 2002 (see 390 Section 3.6.3). Note also that the peer MUST NOT initiate EAP-NOOB 391 when the peer is in Registered (4) state. 393 EAP Peer EAP Server 394 | | 395 |<----------- EAP-Request/Identity -| | 396 | | 397 | | 398 |------------ EAP-Response/Identity -------------->| 399 | (NAI=noob@eap-noob.net) | 400 | | 401 | | 402 |<----------- EAP-Request/EAP-NOOB ----------------| 403 | (Type=9) | 404 | | 405 | | 406 |------------ EAP-Response/EAP-NOOB -------------->| 407 | (Type=9,[PeerId],PeerState=1) | 408 | | 409 | continuing with exchange-specific messages... | 411 Figure 2: Common handshake in all EAP-NOOB exchanges 413 3.2.2. Initial Exchange 415 The Initial Exchange comprises the common handshake and two further 416 EAP-NOOB request-response pairs, one for version, cryptosuite and 417 parameter negotiation and the other for the ECDHE key exchange. The 418 first EAP-NOOB request (Type=1) from the server contains a newly 419 allocated PeerId for the peer and an optional Realm. The server 420 allocates a new PeerId in the Initial Exchange regardless of any old 421 PeerId in the username part of the received NAI. The server also 422 sends in the request a list of the protocol versions (Vers) and 423 cryptosuites (Cryptosuites) it supports, an indicator of the OOB 424 channel directions it supports (Dirs), and a ServerInfo object. The 425 peer chooses one of the versions and cryptosuites. The peer sends a 426 response (Type=1) with the selected protocol version (Verp), the 427 received PeerId, the selected cryptosuite (Cryptosuitep), an 428 indicator of the OOB channel directions selected by the peer (Dirp), 429 and a PeerInfo object. In the second EAP-NOOB request and response 430 (Type=2), the server and peer exchange the public components of their 431 ECDHE keys and nonces (PKs,Ns,PKp,Np). The ECDHE keys MUST be based 432 on the negotiated cryptosuite i.e. Cryptosuitep. The Initial 433 Exchange always ends with EAP-Failure from the server because the 434 authentication cannot yet be completed. 436 EAP Peer EAP Server 437 | ...continuing from common handshake | 438 | | 439 |<----------- EAP-Request/EAP-NOOB ----------------| 440 | (Type=1,Vers,PeerId,[Realm], | 441 | Cryptosuites,Dirs,ServerInfo) | 442 | | 443 | | 444 |------------ EAP-Response/EAP-NOOB -------------->| 445 | (Type=1,Verp,PeerId,Cryptosuitep, | 446 | Dirp,PeerInfo) | 447 | | 448 | | 449 |<----------- EAP-Request/EAP-NOOB ----------------| 450 | (Type=2,PeerId,PKs,Ns,[SleepTime]) | 451 | | 452 | | 453 |------------ EAP-Response/EAP-NOOB -------------->| 454 | (Type=2,PeerId,PKp,Np) | 455 | | 456 | | 457 |<----------- EAP-Failure -------------------------| 458 | | 460 Figure 3: Initial Exchange 462 At the conclusion of the Initial Exchange, both the server and the 463 peer move to the Waiting for OOB (1) state. 465 3.2.3. OOB Step 467 The OOB Step, labeled as OOB Output and OOB Input in Figure 1, takes 468 place after the Initial Exchange. Depending on the negotiated OOB 469 channel direction, the peer or the server outputs the OOB message 470 shown in Figure 4 or Figure 5, respectively. The data fields are the 471 PeerId, the secret nonce Noob, and the cryptographic fingerprint 472 Hoob. The contents of the data fields are defined in Section 3.3.2. 473 The OOB message is delivered to the other endpoint via a user- 474 assisted OOB channel. 476 For brevity, we will use the terms OOB sender and OOB receiver in 477 addition to the already familiar EAP server and EAP peer. If the OOB 478 message is sent in in the server-to-peer direction, the OOB sender is 479 the server and the OOB receiver is the peer. On the other hand, if 480 the OOB message is sent in the peer-to-server direction, the OOB 481 sender is the peer and the OOB receiver is the server. 483 EAP Peer EAP Server 484 | | 485 |=================OOB=============================>| 486 | (PeerId,Noob,Hoob) | 487 | | 489 Figure 4: OOB Step, from peer to EAP server 491 EAP Peer EAP Server 492 | | 493 |<================OOB==============================| 494 | (PeerId,Noob,Hoob) | 495 | | 497 Figure 5: OOB Step, from EAP server to peer 499 The OOB receiver MUST compare the received value of the fingerprint 500 Hoob with a value that it computes locally. If the values are equal, 501 the receiver moves to the OOB Received (2) state. Otherwise, the 502 receiver MUST reject the OOB message. For usability reasons, the OOB 503 receiver SHOULD indicate the acceptance or rejection of the OOB 504 message to the user. The receiver SHOULD reject invalid OOB messages 505 without changing its state, until an application-specific number of 506 invalid messages (OobRetries) has been reached, after which the 507 receiver SHOULD consider it an error and go back to the Unregistered 508 (0) state. 510 The server or peer MAY send multiple OOB messages with different Noob 511 values while in the Waiting for OOB (1) state. The OOB sender SHOULD 512 remember the Noob values until they expire and accept any one of them 513 in the following Completion Exchange. The Noob values sent by the 514 server expire after an application-dependent timeout (NoobTimeout), 515 and the server MUST NOT accept Noob values older than that in the 516 Completion Exchange. The RECOMMENDED value for NoobTimeout is 3600 517 seconds if there are no application-specific reasons for making it 518 shorter or longer. The Noob values sent by the peer expire as 519 defined in Section 3.2.5. 521 The OOB receiver does not accept further OOB messages after it has 522 accepted one and moved to the OOB Received (2) state. However, the 523 receiver MAY buffer redundant OOB messages in case OOB message expiry 524 or similar error detected in the Completion Exchange causes it to 525 return to the Waiting for OOB (1) state. It is RECOMMENED that the 526 OOB receiver notifies the user about redundant OOB messages, but it 527 MAY also discard them silently. 529 The sender will typically generate a new Noob, and therefore a new 530 OOB message, at constant time intervals (NoobInterval). The 531 RECOMMENDED interval is NoobInterval = NoobTimeout / 2, so that the 532 two latest values are always accepted. However, the timing of the 533 Noob generation may also be based on user interaction or on 534 implementation considerations. 536 Even though not recommended (see Section 3.3), this specification 537 allows both directions to be negotiated (Dirp=3) for the OOB channel. 538 In that case, both sides SHOULD output the OOB message, and it is up 539 to the user to deliver one of them. 541 The details of the OOB channel implementation including the message 542 encoding are defined by the application. Appendix E gives an example 543 of how the OOB message can be encoded as a URL that may be embedded 544 in a QR code and NFC tag. 546 3.2.4. Completion Exchange 548 After the Initial Exchange, if both the server and the peer support 549 the peer-to-server direction for the OOB channel, the peer SHOULD 550 initiate the EAP-NOOB method again after an applications-specific 551 waiting time in order to probe for completion of the OOB Step. Also, 552 if both sides support the server-to-peer direction of the OOB 553 exchange and the peer receives the OOB message, it SHOULD initiate 554 the EAP-NOOB method immediately. Depending on the combination of the 555 peer and server states, the server continues with with the Completion 556 Exchange or Waiting Exchange (see Section 3.2.1 on how the server 557 makes this decision). 559 The Completion Exchange comprises the common handshake and one or two 560 further EAP-NOOB request-response pairs. If the peer is in the 561 Waiting for OOB (1) state, the OOB message has been sent in the peer- 562 to-server direction. In that case, only one request-response pair 563 (Type=4) takes place. In the request, the server sends the NoobId 564 value, which the peer uses to identify the exact OOB message received 565 by the server. On the other hand, if the peer is in the OOB Received 566 (2) state, the direction of the OOB message is from server to peer. 567 In that case, two request-response pairs (Type=8 and Type=4) are 568 needed. The purpose of the first request-response pair (Type=8) is 569 that it enables the server to discover NoobId, which identifies the 570 exact OOB message received by the peer. The server returns the same 571 NoobId to the peer in the latter request. 573 In the last and sometimes only request-response pair (Type=4) of the 574 Completion Exchange, the server and peer exchange message 575 authentication codes. Both sides MUST compute the keys Kms and Kmp 576 as defined in Section 3.5 and the message authentication codes MACs 577 and MACp as defined in Section 3.3.2. Both sides MUST compare the 578 received message authentication code with a locally computed value. 579 If the peer finds that it has received the correct value of MACs and 580 the server finds that it has received the correct value of MACp, the 581 Completion Exchange ends in EAP-Success. Otherwise, the endpoint 582 where the comparison fails indicates this with an error message 583 (error code 4001, see Section 3.6.1) and the Completion Exchange ends 584 in EAP-Failure. 586 After successful Completion Exchange, both the server and the peer 587 move to the Registered (4) state. They also derive the output keying 588 material and store the persistent EAP-NOOB association state as 589 defined in Section 3.4 and Section 3.5. 591 It is possible that the OOB message expires before it is received. 592 In that case, the sender of the OOB message no longer recognizes the 593 NoobId that it receives in the Completion Exchange. Another reason 594 why the OOB sender might not recognize the NoobId is if the received 595 OOB message was spoofed and contained an attacker-generated Noob 596 value. The recipient of an unrecognized NoobId indicates this with 597 an error message (error code 2003, see Section 3.6.1) and the 598 Completion Exchange ends in EAP-Failure. The recipient of the error 599 message 2003 moves back to the Waiting for OOB (1) state. This state 600 transition is shown as OOB Reject in Figure 1 (even though it really 601 is a specific type of failed Completion Exchange). The sender of the 602 error message, on the other hand, stays in its previous state. 604 Although it is not expected to occur in practice, poor user interface 605 design could lead to two OOB messages delivered simultaneously, one 606 from the peer to the server and the other from the server to the 607 peer. The server detects this event in the beginning of the 608 Completion Exchange by observing that both the server and peer are in 609 the OOB Received state (2). In that case, as a tiebreaker, the 610 server MUST behave as if only the server-to-peer message had been 611 delivered. 613 EAP Peer EAP Server 614 | ...continuing from common handshake | 615 | | 616 |<----------- [ EAP-Request/EAP-NOOB ] ------------| 617 | (Type=8,PeerId) | 618 | | 619 | | 620 |------------ [ EAP-Response/EAP-NOOB ] ---------->| 621 | (Type=8,PeerId,NoobId) | 622 | | 623 | | 624 |<----------- EAP-Request/EAP-NOOB ----------------| 625 | (Type=4,PeerId,NoobId,MACs) | 626 | | 627 | | 628 |------------ EAP-Response/EAP-NOOB -------------->| 629 | (Type=4,PeerId,MACp) | 630 | | 631 | | 632 |<----------- EAP-Success -------------------------| 633 | | 635 Figure 6: Completion Exchange 637 3.2.5. Waiting Exchange 639 As explained in Section 3.2.4, the peer SHOULD probe the server for 640 completion of the OOB Step. When the combination of the peer and 641 server states indicates that the OOB message has not yet been 642 delivered, the server chooses the Waiting Exchange (see Section 3.2.1 643 on how the server makes this decision). The Waiting Exchange 644 comprises the common handshake and one further request-response pair, 645 and it ends always in EAP-Failure. 647 In order to limit the rate at which peers probe the server, the 648 server MAY send to the peer either in the Initial Exchange or in the 649 Waiting Exchange a minimum time to wait before probing the server 650 again. A peer that has not received an OOB message MUST wait at 651 least the server-specified minimum waiting time in seconds 652 (SleepTime) before initiating EAP again with the same server. The 653 peer uses the latest SleepTime value that it has received in or after 654 the Initial Exchange. If the server has not sent any SleepTime 655 value, the peer SHOULD wait for an application-specified minimum time 656 (SleepTimeDefault). 658 After the Waiting Exchange, the peer MUST discard (from its local 659 ephemeral storage) Noob values that it has sent to the server in OOB 660 messages that are older than the application-defined timeout 661 NoobTimeout (see Section 3.2.3). The peer SHOULD discard such 662 expired Noob values even if the probing failed, e.g. because of 663 failure to connect to the EAP server or incorrect HMAC. The timeout 664 of peer-generated Noob values is defined like this in order to allow 665 the peer to probe the server once after it has waited for the server- 666 specified SleepTime. 668 If the server and peer have negotiated to use only the server-to-peer 669 direction for the OOB channel (Dirp=2), the peer SHOULD nevertheless 670 probe the server. The purpose of this is to keep the server informed 671 about the peers that are still waiting for OOB messages. The server 672 MAY set SleepTime to a high number (3600) to prevent the peer from 673 probing the server frequently. 675 EAP Peer EAP Server 676 | ...continuing from common handshake | 677 | | 678 |<----------- EAP-Request/EAP-NOOB ----------------| 679 | (Type=3,PeerId,[SleepTime]) | 680 | | 681 | | 682 |------------ EAP-Response/EAP-NOOB -------------->| 683 | (Type=3,PeerId) | 684 | | 685 | | 686 |<----------- EAP-Failure -------------------------| 687 | | 689 Figure 7: Waiting Exchange 691 3.3. Protocol data fields 693 This section defines the various identifiers and data fields used in 694 the EAP-NOOB protocol. 696 3.3.1. Peer identifier, realm and NAI 698 The server allocates a new peer identifier (PeerId) for the peer in 699 the Initial Exchange. The peer identifier MUST follow the syntax of 700 the utf8-username specified in [RFC7542]. The server MUST generate 701 the identifiers in such a way that they do not repeat and cannot be 702 guessed by the peer or third parties before the server sends them to 703 the peer in the Initial Exchange. One way to generate the 704 identifiers is to choose a random 16-byte identifier and to base64url 705 encode it without padding [RFC4648] into a 22-character string. 707 Another way to generate the identifiers is to choose a random 708 22-character alphanumeric string. It is RECOMMENDED to not use 709 identifiers longer than this because they result in longer OOB 710 messages. 712 The peer uses the allocated PeerId to identify itself to the server 713 in the subsequent exchanges. It sets the PeerId value in response 714 type 9 as follows. When the peer is in the Unregistered (0) state, 715 it SHOULD omit the PeerId from response type 9. When the peer is in 716 one of the states 1..2, it MUST use the PeerId that the server 717 assigned to it in the latest Initial Exchange. When the peer is in 718 one of the persistent states 3..4, it MUST use the PeerId from its 719 persistent EAP-NOOB association. (The PeerId is written to the 720 association when the peer moves to the Registered (4) state after a 721 Completion Exchange.) 723 The default realm for the peer is "eap-noob.net". However, the user 724 or application MAY provide a different default realm to the peer. 725 Furthermore, the server MAY assign a new realm to the peer in the 726 Initial Exchange or Reconnect Exchange, in the Realm field of 727 response types 1 and 5. The Realm value MUST follow the syntax of 728 the utf8-realm specified in [RFC7542]. When the peer is in the 729 Unregistered (0) state, or when the peer is in one of the states 1..2 730 and the server did not send a Realm in the latest Initial Exchange, 731 the peer MUST use the default realm. When the peer is in one of the 732 states 1..2 and the server sent a Realm in the latest Initial 733 Exchange, the peer MUST use that realm. Finally, when the peer is in 734 one of the persistent states 3..4, it MUST use the Realm from its 735 persistent EAP-NOOB association. (The Realm is written to the 736 association when the peer moves to the Registered (4) state after a 737 Completion Exchange or Reconnect Exchange.) 739 To compose its NAI [RFC7542], the peer concatenates the string 740 "noob@" and the server-assigned realm. When no server-assigned realm 741 is available, the default value is used instead. 743 The purpose of the server-assigned realm is to enable more flexible 744 routing of the EAP sessions over the AAA infrastructure, including 745 roaming scenarios (see Appendix D). Moreover, some Authenticators or 746 AAA servers use the assigned Realm to determine peer-specific 747 connection parameters, such as isolating the peer to a specific VLAN. 748 The possibility to configure a different default realm enables 749 registration of new devices while roaming. It also enables 750 manufacturers to set up their own AAA servers for bootstrapping of 751 new peer devices. 753 The peer's PeerId and Realm are ephemeral until a successful 754 Completion Exchange takes place. Thereafter, the values become parts 755 of the persistent EAP-NOOB association, until the user resets the 756 peer and the server or until a new Realm is assigned in the Reconnect 757 Exchange. 759 3.3.2. Message data fields 761 Table 1 defines the data fields in the protocol messages. The in- 762 band messages are formatted as JSON objects [RFC8259] in UTF-8 763 encoding. The JSON member names are in the left-hand column of the 764 table. 766 +------------------+------------------------------------------------+ 767 | Data field | Description | 768 +------------------+------------------------------------------------+ 769 | Vers, Verp | EAP-NOOB protocol versions supported by the | 770 | | EAP server, and the protocol version chosen by | 771 | | the peer. Vers is a JSON array of unsigned | 772 | | integers, and Verp is an unsigned integer. | 773 | | Example values are "[1]" and "1", | 774 | | respectively. | 775 | | | 776 | PeerId | Peer identifier as defined in Section 3.3.1. | 777 | | | 778 | Realm | Peer realm as defined in Section 3.3.1. | 779 | | | 780 | PeerState | Peer state is an integer in the range 0..4 | 781 | | (see Figure 1). However, only values 0..3 are | 782 | | ever sent in the protocol messages. | 783 | | | 784 | Type | EAP-NOOB message type. The type is an integer | 785 | | in the range 0..9. EAP-NOOB requests and the | 786 | | corresponding responses share the same type | 787 | | value. | 788 | | | 789 | PKs, PKp | The public components of the ECDHE keys of the | 790 | | server and peer. PKs and PKp are sent in the | 791 | | JSON Web Key (JWK) format [RFC7517]. Detailed | 792 | | format of the JWK object is defined by the | 793 | | cryptosuite. | 794 | | | 795 | Cryptosuites, | The identifiers of cryptosuites supported by | 796 | Cryptosuitep | the server and of the cryptosuite selected by | 797 | | the peer. The server-supported cryptosuites in | 798 | | Cryptosuites are formatted as a JSON array of | 799 | | the identifier integers. The server MUST send | 800 | | a nonempty array with no repeating elements, | 801 | | ordered by decreasing priority. The peer MUST | 802 | | respond with exactly one suite in the | 803 | | Cryptosuitep value, formatted as an identifier | 804 | | integer. The registration of cryptosuites is | 805 | | specified in Section 4.1. Example values are | 806 | | "[1]" and "1", respectively. | 807 | | | 808 | Dirs, Dirp | The OOB channel directions supported by the | 809 | | server and the directions selected by the | 810 | | peer. The possible values are 1=peer-to- | 811 | | server, 2=server-to-peer, 3=both directions. | 812 | | | 813 | Dir | The actual direction of the OOB message (1 | 814 | | =peer-to-server, 2=server-to-peer). This value | 815 | | is not sent over any communication channel but | 816 | | it is included in the computation of the | 817 | | cryptographic fingerprint Hoob. | 818 | | | 819 | Ns, Np | 32-byte nonces for the Initial Exchange. | 820 | | | 821 | ServerInfo | This field contains information about the | 822 | | server to be passed from the EAP method to the | 823 | | application layer in the peer. The information | 824 | | is specific to the application or to the OOB | 825 | | channel and it is encoded as a JSON object of | 826 | | at most 500 bytes. It could include, for | 827 | | example, the access-network name and server | 828 | | name or a Uniform Resource Locator (URL) | 829 | | [RFC4266] or some other information that helps | 830 | | the user to deliver the OOB message to the | 831 | | server through the out-of-band channel. | 832 | | | 833 | PeerInfo | This field contains information about the peer | 834 | | to be passed from the EAP method to the | 835 | | application layer in the server. The | 836 | | information is specific to the application or | 837 | | to the OOB channel and it is encoded as a JSON | 838 | | object of at most 500 bytes. It could include, | 839 | | for example, the peer brand, model and serial | 840 | | number, which help the user to distinguish | 841 | | between devices and to deliver the OOB message | 842 | | to the correct peer through the out-of-band | 843 | | channel. | 844 | | | 845 | SleepTime | The number of seconds for which peer MUST NOT | 846 | | start a new execution of the EAP-NOOB method | 847 | | with the authenticator, unless the peer | 848 | | receives the OOB message or the peer is reset | 849 | | by the user. The server can use this field to | 850 | | limit the rate at which peers probe it. | 851 | | SleepTime is an unsigned integer in the range | 852 | | 0..3600. | 853 | | | 854 | Noob | 16-byte secret nonce sent through the OOB | 855 | | channel and used for the session key | 856 | | derivation. The endpoint that received the OOB | 857 | | message uses this secret in the Completion | 858 | | Exchange to authenticate the exchanged key to | 859 | | the endpoint that sent the OOB message. | 860 | | | 861 | Hoob | 16-byte cryptographic fingerprint (i.e. hash | 862 | | value) computed from all the parameters | 863 | | exchanged in the Initial Exchange and in the | 864 | | OOB message. Receiving this fingerprint over | 865 | | the OOB channel guarantees the integrity of | 866 | | the key exchange and parameter negotiation. | 867 | | Hence, it authenticates the exchanged key to | 868 | | the endpoint that receives the OOB message. | 869 | | | 870 | NoobId | 16-byte identifier for the OOB message, | 871 | | computed with a one-way function from the | 872 | | nonce Noob in the message. | 873 | | | 874 | MACs, MACp | Message authentication codes (HMAC) for mutual | 875 | | authentication, key confirmation, and | 876 | | integrity check on the exchanged information. | 877 | | The input to the HMAC is defined below, and | 878 | | the key for the HMAC is defined in Section | 879 | | 3.5. | 880 | | | 881 | Ns2, Np2 | 32-byte Nonces for the Reconnect Exchange. | 882 | | | 883 | KeyingMode | Integer indicating the key derivation method. | 884 | | 0 in the Completion Exchange, and 1..3 in the | 885 | | Reconnect Exchange. | 886 | | | 887 | PKs2, PKp2 | The public components of the ECDHE keys of the | 888 | | server and peer for the Reconnect Exchange. | 889 | | PKp2 and PKs2 are sent in the JSON Web Key | 890 | | (JWK) format [RFC7517]. Detailed format of the | 891 | | JWK object is defined by the cryptosuite. | 892 | | | 893 | MACs2, MACp2 | Message authentication codes (HMAC) for mutual | 894 | | authentication, key confirmation, and | 895 | | integrity check on the Reconnect Exchange. The | 896 | | input to the HMAC is defined below, and the | 897 | | key for the HMAC is defined in Section 3.5. | 898 | | | 899 | ErrorCode | Integer indicating an error condition. Defined | 900 | | in Section 4.3. | 901 | | | 902 | ErrorInfo | Textual error message for logging and | 903 | | debugging purposes. UTF-8 string of at most | 904 | | 500 bytes. | 905 | | | 906 +------------------+------------------------------------------------+ 908 Table 1: Message data fields 910 It is RECOMMENDED for servers to support both OOB channel directions 911 (Dirs=3), unless the type of the OOB channel limits them to one 912 direction (Dirs=1 or Dirs=2). On the other hand, it is RECOMMENDED 913 that the peer selects only one direction (Dirp=1 or Dirp=2) even when 914 both directions (Dirp=3) would be technically possible. The reason 915 is that, if value 3 is negotiated, the user may be presented with two 916 OOB messages, one for each direction, even though only one of them 917 needs to be delivered. This can be confusing to the user. 918 Nevertheless, the EAP-NOOB protocol is designed to cope also with 919 selected value 3, in which case it uses the first delivered OOB 920 message. In the unlikely case of simultaneously delivered OOB 921 messages, the protocol prioritizes the server-to-peer direction. 923 The nonces in the in-band messages (Ns, Np, Ns2, Np2) are 32-byte 924 fresh random byte strings, and the secret nonce Noob is a 16-byte 925 fresh random byte string. All the nonces are generated by the 926 endpoint that sends the message. 928 The fingerprint Hoob and the identifier NoobId are computed with the 929 cryptographic hash function specified in the negotiated cryptosuite 930 and truncated to the 16 leftmost bytes of the output. The message 931 authentication codes (MACs, MACp, MACs2, MACp2) are computed with the 932 HMAC function [RFC2104] based on the same cryptographic hash function 933 and truncated to the 32 leftmost bytes of the output. 935 The inputs to the hash function for computing the fingerprint Hoob 936 and to the HMAC for computing MACs, MACp, MACs2 and MACp2 are JSON 937 arrays containing a fixed number (17) of elements. The array 938 elements MUST be copied to the array verbatim from the sent and 939 received in-band messages. When the element is a JSON object, its 940 members MUST NOT be reordered or re-encoded. Whitespace MUST NOT be 941 added anywhere in the JSON structure. Implementers should check that 942 their JSON library copies the elements as UTF-8 strings and does not 943 modify then in any way, and that it does not add whitespace to the 944 HMAC input. 946 The inputs for computing the fingerprint and message authentication 947 codes are the following: 949 Hoob = H(Dir,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,Cryptos 950 uitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 952 NoobId = H("NoobId",Noob). 954 MACs = HMAC(Kms; 2,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C 955 ryptosuitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 957 MACp = HMAC(Kmp; 1,Vers,Verp,PeerId,Cryptosuites,Dirs,ServerInfo,C 958 ryptosuitep,Dirp,[Realm],PeerInfo,0,PKs,Ns,PKp,Np,Noob). 960 MACs2 = HMAC(Kms2; 2,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo] 961 ,Cryptosuitep,"",[Realm],[PeerInfo],KeyingMode,[PKs2],Ns2,[PKp2],N 962 p2,"") 964 MACp2 = HMAC(Kmp2; 1,Vers,Verp,PeerId,Cryptosuites,"",[ServerInfo] 965 ,Cryptosuitep,"",[Realm],[PeerInfo],KeyingMode,[PKs2],Ns2,[PKp2],N 966 p2,"") 968 Missing input values are represented by empty strings "" in the 969 array. The values indicated with "" above are always empty strings. 970 Realm is included in the computation of MACs and MACp if it was sent 971 or received in the preceding Initial Exchange. Each of the values in 972 brackets for the computation of Macs2 and Macp2 MUST be included if 973 it was sent or received in the same Reconnect Exchange; otherwise the 974 value is replaced by an empty string "". 976 The parameter Dir indicates the direction in which the OOB message 977 containing the Noob value is being sent (1=peer-to-server, 2=server- 978 to-peer). This field is included in the Hoob input to prevent the 979 user from accidentally delivering the OOB message back to its 980 originator in the rare cases where both OOB directions have been 981 negotiated. The keys (Kms, Kmp, Kms2, Kmp2) for the HMACs are 982 defined in Section 3.5. 984 The nonces (Ns, Np, Ns2, Np2, Noob) and the hash value (NoobId) MUST 985 be base64url encoded [RFC4648] when they are used as input to the 986 cryptograhic functions H or HMAC. These values and the message 987 authentication codes (MACs, MACp, MACs2, MACp2) MUST also be 988 base64url encoded when they are sent in the in-band messages. The 989 values Noob and Hoob in the OOB channel MAY be base64url encoded if 990 that is appropriate for the application and the OOB channel. All 991 base64url encoding is done without padding. The base64url encoded 992 values will naturally consume more space than the number of bytes 993 specified above (22-character string for a 16-byte nonce and 994 43-character string for a 32-byte nonce or message authentication 995 code). In the key derivation in Section 3.5, on the other hand, the 996 unencoded nonces (raw bytes) are used as input to the key derivation 997 function. 999 The ServerInfo and PeerInfo are JSON objects with UTF-8 encoding. 1000 The length of either encoded object as a byte array MUST NOT exceed 1001 500 bytes. The format and semantics of these objects MUST be defined 1002 by the application that uses the EAP-NOOB method. 1004 3.4. Fast reconnect and rekeying 1006 EAP-NOOB implements Fast Reconnect ([RFC3748], section 7.2.1) that 1007 avoids repeated use of the user-assisted OOB channel. 1009 The rekeying and the Reconnect Exchange may be needed for several 1010 reasons. New EAP output values MSK and EMSK may be needed because of 1011 mobility or timeout of session keys. Software or hardware failure or 1012 user action may also cause the authenticator, EAP server or peer to 1013 lose its non-persistent state data. The failure would typically be 1014 detected by the peer or authenticator when session keys no longer are 1015 accepted by the other endpoint. Change in the supported cryptosuites 1016 in the EAP server or peer may also cause the need for a new key 1017 exchange. When the EAP server or peer detects any one of these 1018 events, it MUST change from the Registered to Reconnecting state. 1019 These state transitions are labeled Mobility/Timeout/Failure in 1020 Figure 1. The EAP-NOOB method will then perform the Reconnect 1021 Exchange next time when EAP is triggered. 1023 3.4.1. Persistent EAP-NOOB association 1025 To enable rekeying, the EAP server and peer store the session state 1026 in persistent memory after a successful Completion Exchange. This 1027 state data, called "persistent EAP-NOOB association", MUST include at 1028 least the data fields shown in Table 2. They are used for 1029 identifying and authenticating the peer in the Reconnect Exchange. 1030 When a persistent EAP-NOOB association exists, the EAP server and 1031 peer are in the Registered state (4) or Reconnecting state (3), as 1032 shown in Figure 1. 1034 +------------------+------------------------------+-----------------+ 1035 | Data field | Value | Type | 1036 +------------------+------------------------------+-----------------+ 1037 | PeerId | Peer identifier allocated by | UTF-8 string | 1038 | | server | (typically 22 | 1039 | | | bytes) | 1040 | | | | 1041 | Verp | Negotiated protocol version | integer | 1042 | | | | 1043 | Cryptosuitep | Negotiated cryptosuite | integer | 1044 | | | | 1045 | CryptosuitepPrev | Previous cryptosuite | integer | 1046 | (at peer only) | | | 1047 | | | | 1048 | Realm | Optional realm assigned by | UTF-8 string | 1049 | | server (default value is | | 1050 | | "eap-noob.net") | | 1051 | | | | 1052 | Kz | Persistent key material | 32 bytes | 1053 | | | | 1054 | KzPrev (at | Previous Kz value | 32 bytes | 1055 | peer only) | | | 1056 +------------------+------------------------------+-----------------+ 1058 Table 2: Persistent EAP-NOOB association 1060 3.4.2. Reconnect Exchange 1062 The server chooses the Reconnect Exchange when both the peer and the 1063 server are in a persistent state and fast reconnection is needed (see 1064 Section 3.2.1 for details). 1066 The Reconnect Exchange comprises the common handshake and three 1067 further EAP-NOOB request-response pairs, one for cryptosuite and 1068 parameter negotiation, another for the nonce and ECDHE key exchange, 1069 and the last one for exchanging message authentication codes. In the 1070 first request and response (Type=5) the server and peer negotiate a 1071 protocol version and cryptosuite in the same way as in the Initial 1072 Exchange. The server SHOULD NOT offer and the peer MUST NOT accept 1073 protocol versions or cryptosuites that it knows to be weaker than the 1074 one currently in the Cryptosuitep field of the persistent EAP-NOOB 1075 association. The server SHOULD NOT needlessly change the 1076 cryptosuites it offers to the same peer because peer devices may have 1077 limited ability to update their persistent storage. However, if the 1078 peer has different values in the Cryptosuitep and CryptosuitepPrev 1079 fields, it SHOULD also accept offers that are not weaker than 1080 CryptosuitepPrev. Note that Cryptosuitep and CryptosuitePrev from 1081 the persistent EAP-NOOB association are only used to support the 1082 negotiation as described above; all actual cryptographic operations 1083 use the negotiated cryptosuite. The request and response (Type=5) 1084 MAY additionally contain PeerInfo and ServerInfo objects. 1086 The server then determines the KeyingMode (defined in Section 3.5) 1087 based on changes in the negotiated cryptosuite and whether it desires 1088 to achieve forward secrecy or not. The server SHOULD only select 1089 KeyingMode 3 when the negotiated cryptosuite differs from the 1090 Cryptosuitep in the server's persistent EAP-NOOB association, 1091 although it is technically possible to select this values without 1092 changing the cryptosuite. In the second request and response 1093 (Type=6), the server informs the peer about the KeyingMode, and the 1094 server and peer exchange nonces (Ns2, Np2). When KeyingMode is 2 or 1095 3 (rekeying with ECDHE), they also exchange public components of 1096 ECDHE keys (PKs2, PKp2). The server ECDHE key MUST be fresh, i.e. 1097 not previously used with the same peer, and the peer ECDHE key SHOULD 1098 be fresh, i.e. not previously used. 1100 In the third and final request and response (Type=7), the server and 1101 peer exchange message authentication codes. Both sides MUST compute 1102 the keys Kms2 and Kmp2 as defined in Section 3.5 and the message 1103 authentication codes MACs2 and MACp2 as defined in Section 3.3.2. 1104 Both sides MUST compare the received message authentication code with 1105 a locally computed value. 1107 The rules by which the peer compares the received MACs2 are non- 1108 trivial because, in addition to authenticating the current exchange, 1109 MACs2 may confirm the success or failure of a recent cryptosuite 1110 upgrade. The peer processes the final request (Type=7) as follows: 1112 1. The peer first compares the received MACs2 value with one it 1113 computed using the Kz stored in the persistent EAP-NOOB 1114 association. If the received and computed values match, the peer 1115 deletes any data stored in the CryptosuitepPrev and KzPrev fields 1116 of the persistent EAP-NOOB association. It does this because the 1117 received MACs2 confirms that the peer and server share the same 1118 Cryptosuitep and Kz, and any previous values must no longer be 1119 accepted. 1121 2. If, on the other hand, the peer finds that the received MACs2 1122 value does not match the one it computed locally with Kz, the 1123 peer checks whether the KzPrev field in the persistent EAP-NOOB 1124 association stores a key. If it does, the peer repeats the key 1125 derivation (Section 3.5) and local MACs2 computation 1126 (Section 3.3.2) using KzPrev in place of Kz. If this second 1127 computed MACs2 matches the received value, the match indicates 1128 synchronization failure caused by the loss of the last response 1129 (Type=7) in a previously attempted cryptosuite upgrade. In this 1130 case, the peer rolls back that upgrade by overwriting 1131 Cryptosuitep with CryptosuitepPrev and Kz with KzPrev in the 1132 persistent EAP-NOOB association. It also clears the 1133 CryptosuitepPrev and KzPrev fields. 1135 3. If the received MACs2 matched one of the locally computed values, 1136 the peer proceeds to send the final response (Type=7). The peer 1137 also moves to the Registered (4) state. When KeyingMode is 1 or 1138 2, the peer stops here. When KeyingMode is 3, the peer also 1139 updates the persistent EAP-NOOB association with the negotiated 1140 Cryptosuitep and the newly-derived Kz value. To prepare for 1141 possible synchronization failure caused by the loss of the final 1142 response (Type=7) during cryptosuite upgrade, the peer copies the 1143 old Cryptosuitep and Kz values in the persistent EAP-NOOB 1144 association to the CryptosuitepPrev and KzPrev fields. 1146 4. Finally, if the peer finds that the received MACs2 does not match 1147 either of the two values that it computed locally (or one value 1148 if no KzPrev was stored), the peer sends an error message (error 1149 code 4001, see Section 3.6.1), which causes the the Reconnect 1150 Exchange to end in EAP-Failure. 1152 The server rules for processing the final message are simpler than 1153 the peer rules because the server does not store previous keys and it 1154 never rolls back a cryptosuite upgrade. Upon receiving the final 1155 response (Type=7), the server compares the received value of MACp2 1156 with one it computes locally. If the values match, the Reconnect 1157 Exchange ends in EAP-Success. When KeyingMode is 3, the server also 1158 updates Cryptosuitep and Kz in the persistent EAP-NOOB association. 1159 On the other hand, if the server finds that the values do not match, 1160 it sends an error message (error code 4001), and the Reconnect 1161 Exchange ends in EAP-Failure. 1163 The endpoints MAY send updated Realm, ServerInfo and PeerInfo objects 1164 in the Reconnect Exchange. When there is no update to the values, 1165 they SHOULD omit this information from the messages. If the Realm 1166 was sent, each side updates Realm in the persistent EAP-NOOB 1167 association when moving to the Registered (4) state. 1169 EAP Peer EAP Server 1170 | ...continuing from common handshake | 1171 | | 1172 |<----------- EAP-Request/EAP-NOOB ----------------| 1173 | (Type=5,Vers,PeerId,Cryptosuites, | 1174 | [Realm],[ServerInfo]) | 1175 | | 1176 | | 1177 |------------ EAP-Response/EAP-NOOB -------------->| 1178 | (Type=5,Verp,PeerId,Cryptosuitep,[PeerInfo])| 1179 | | 1180 | | 1181 |<----------- EAP-Request/EAP-NOOB ----------------| 1182 | (Type=6,PeerId,KeyingMode,[PKs2],Ns2) | 1183 | | 1184 | | 1185 |------------ EAP-Response/EAP-NOOB -------------->| 1186 | (Type=6,PeerId,[PKp2],Np2) | 1187 | | 1188 | | 1189 |<----------- EAP-Request/EAP-NOOB ----------------| 1190 | (Type=7,PeerId,MACs2) | 1191 | | 1192 | | 1193 |------------ EAP-Response/EAP-NOOB -------------->| 1194 | (Type=7,PeerId,MACp2) | 1195 | | 1196 | | 1197 |<----------- EAP-Success -------------------------| 1198 | | 1200 Figure 8: Reconnect Exchange 1202 3.4.3. User reset 1204 As shown in the association state machine in Figure 1, the only 1205 specified way for the association to return from the Registered state 1206 (4) to the Unregistered state (0) is through user-initiated reset. 1207 After the reset, a new OOB message will be needed to establish a new 1208 association between the EAP server and peer. Typical situations in 1209 which the user reset is required are when the other side has 1210 accidentally lost the persistent EAP-NOOB association data, or when 1211 the peer device is decommissioned. 1213 The server could detect that the peer is in the Registered or 1214 Reconnecting state but the server itself is in one of the ephemeral 1215 states 0..2 (including situations where the server does not recognize 1216 the PeerId). In this case, effort should be made to recover the 1217 persistent server state, for example, from a backup storage - 1218 especially if many peer devices are similarly affected. If that is 1219 not possible, the EAP server SHOULD log the error or notify an 1220 administrator. The only way to continue from such a situation is by 1221 having the user reset the peer device. 1223 On the other hand, if the peer is in any of the ephemeral states 1224 0..2, including the Unregistered state, the server will treat the 1225 peer as a new peer device and allocate a new PeerId to it. The 1226 PeerInfo can be used by the user as a clue to which physical device 1227 has lost its state. However, there is no secure way of matching the 1228 "new" peer with the old PeerId without repeating the OOB Step. This 1229 situation will be resolved when the user performs the OOB Step and, 1230 thus, identifies the physical peer device. The server user interface 1231 MAY support situations where the "new" peer is actually a previously 1232 registered peer that has been reset by a user or otherwise lost its 1233 persistent data. In those cases, the user could choose to merge new 1234 peer identity with the old one in the server. The alternative is to 1235 treat the device just like a new peer. 1237 3.5. Key derivation 1239 EAP-NOOB derives the EAP output values MSK and EMSK and other secret 1240 keying material from the output of an Ephemeral Elliptic Curve 1241 Diffie-Hellman (ECDHE) algorithm following the NIST specification 1242 [NIST-DH]. In NIST terminology, we use a C(2, 0, ECC CDH) scheme, 1243 i.e. two ephemeral keys and no static keys. In the Initial and 1244 Reconnect Exchanges, the server and peer compute the ECDHE shared 1245 secret Z as defined in section 6.1.2.2 of the NIST specification 1246 [NIST-DH]. In the Completion and Reconnect Exchanges, the server and 1247 peer compute the secret keying material from Z with the single-step 1248 key derivation function (KDF) defined in section 5.8.1 of the NIST 1249 specification. The hash function H for KDF is taken from the 1250 negotiated cryptosuite. 1252 +------------+------------------------------------------------------+ 1253 | KeyingMode | Description | 1254 +------------+------------------------------------------------------+ 1255 | 0 | Completion Exchange (always with ECDHE) | 1256 | | | 1257 | 1 | Reconnect Exchange, rekeying without ECDHE | 1258 | | | 1259 | 2 | Reconnect Exchange, rekeying with ECHDE, no change | 1260 | | in cryptosuite | 1261 | | | 1262 | 3 | Reconnect Exchange, rekeying with ECDHE, new | 1263 | | cryptosuite negotiated | 1264 +------------+------------------------------------------------------+ 1266 Table 3: Keying modes 1268 The key derivation has three different modes (KeyingMode), which are 1269 specified in Table 3. Table 4 defines the inputs to KDF in each 1270 KeyingMode. 1272 In the Completion Exchange (KeyingMode=0), the input Z comes from the 1273 preceding Initial exchange. KDF takes some additional inputs 1274 (OtherInfo), for which we use the concatenation format defined in 1275 section 5.8.1.2.1 of the NIST specification [NIST-DH]. OtherInfo 1276 consists of the AlgorithmId, PartyUInfo, PartyVInfo, and SuppPrivInfo 1277 fields. The first three fields are fixed-length bit strings, and 1278 SuppPrivInfo is a variable-length string with a one-byte Datalength 1279 counter. AlgorithmId is the fixed-length 8-byte ASCII string "EAP- 1280 NOOB". The other input values are the server and peer nonces. In 1281 the Completion Exchange, the inputs also include the secret nonce 1282 Noob from the OOB message. 1284 In the simplest form of the Reconnect Exchange (KeyingMode=1), fresh 1285 nonces are exchanged but no ECDHE keys are sent. In this case, input 1286 Z to the KDF is replaced with the shared key Kz from the persistent 1287 EAP-NOOB association. The result is rekeying without the 1288 computational cost of the ECDHE exchange, but also without forward 1289 secrecy. 1291 When forward secrecy is desired in the Reconnect Exchange 1292 (KeyingMode=2 or KeyingMode=3), both nonces and ECDHE keys are 1293 exchanged. Input Z is the fresh shared secret from the ECDHE 1294 exchange with PKs2 and PKp2. The inputs also include the shared 1295 secret Kz from the persistent EAP-NOOB association. This binds the 1296 rekeying output to the previously authenticated keys. 1298 +--------------+--------------+------------------------+------------+ 1299 | KeyingMode | KDF input | Value | Length | 1300 | | field | | (bytes) | 1301 +--------------+--------------+------------------------+------------+ 1302 | 0 | Z | ECDHE shared secret | variable | 1303 | Completion | | from PKs and PKp | | 1304 | | AlgorithmId | "EAP-NOOB" | 8 | 1305 | | PartyUInfo | Np | 32 | 1306 | | PartyVInfo | Ns | 32 | 1307 | | SuppPubInfo | (not allowed) | | 1308 | | SuppPrivInfo | Noob | 16 | 1309 | | | | | 1310 | 1 | Z | Kz | 32 | 1311 | Reconnect, | AlgorithmId | "EAP-NOOB" | 8 | 1312 | rekeying | PartyUInfo | Np2 | 32 | 1313 | without | PartyVInfo | Ns2 | 32 | 1314 | ECDHE | SuppPubInfo | (not allowed) | | 1315 | | SuppPrivInfo | (null) | 0 | 1316 | | | | | 1317 | 2 or 3 | Z | ECDHE shared secret | variable | 1318 | Reconnect, | | from PKs2 and PKp2 | | 1319 | rekeying, | AlgorithmId | "EAP-NOOB" | 8 | 1320 | with ECDHE, | PartyUInfo | Np2 | 32 | 1321 | same or new | PartyVInfo | Ns2 | 32 | 1322 | cryptosuite | SuppPubInfo | (not allowed) | | 1323 | | SuppPrivInfo | Kz | 32 | 1324 +--------------+--------------+------------------------+------------+ 1326 Table 4: Key derivation input 1328 Table 5 defines how the output bytes of KDF are used. In addition to 1329 the EAP output values MSK and EMSK, the server and peer derive 1330 another shared secret key AMSK, which MAY be used for application- 1331 layer security. Further output bytes are used internally by EAP-NOOB 1332 for the message authentication keys (Kms, Kmp, Kms2, Kmp2). 1334 The Completion Exchange (KeyingMode=0) produces the shared secret Kz, 1335 which the server and peer store in the persistent EAP-NOOB 1336 association. When a new cryptosuite is negotiated in the Reconnect 1337 Exchange (KeyingMode=3), it similarly produces a new Kz. In that 1338 case, the server and peer update both the cryptosuite and Kz in the 1339 persistent EAP-NOOB association. Additionally, the peer stores the 1340 previous Cryptosuitep and Kz values in the CryptosuitepPrev and 1341 KzPrev fields of the persistent EAP-NOOB association. 1343 +-----------------+------------------+----------+----------------+ 1344 | KeyingMode | KDF output bytes | Used as | Length (bytes) | 1345 +-----------------+------------------+----------+----------------+ 1346 | 0 | 0..63 | MSK | 64 | 1347 | Completion | 64..127 | EMSK | 64 | 1348 | | 128..191 | AMSK | 64 | 1349 | | 192..223 | MethodId | 32 | 1350 | | 224..255 | Kms | 32 | 1351 | | 256..287 | Kmp | 32 | 1352 | | 288..319 | Kz | 32 | 1353 | | | | | 1354 | 1 or 2 | 0..63 | MSK | 64 | 1355 | Reconnect, | 64..127 | EMSK | 64 | 1356 | rekeying | 128..191 | AMSK | 64 | 1357 | without ECDHE, | 192..223 | MethodId | 32 | 1358 | or with ECDHE | 224..255 | Kms2 | 32 | 1359 | and unchanged | 256..287 | Kmp2 | 32 | 1360 | cryptosuite | | | | 1361 | | | | | 1362 | | | | | 1363 | 3 Reconnect, | 0..63 | MSK | 64 | 1364 | rekeying | 64..127 | EMSK | 64 | 1365 | with ECDHE, | 128..191 | AMSK | 64 | 1366 | new cryptosuite | 192..223 | MethodId | 32 | 1367 | | 224..255 | Kms2 | 32 | 1368 | | 256..287 | Kmp2 | 32 | 1369 | | 288..319 | Kz | 32 | 1370 +-----------------+------------------+----------+----------------+ 1372 Table 5: Key derivation output 1374 Finally, every EAP method must export a Server-Id, Peer-Id and 1375 Session-Id [RFC5247]. In EAP-NOOB, the exported Peer-Id is the 1376 PeerId which the server has assigned to the peer. The exported 1377 Server-Id is a zero-length string (i.e. null string) because EAP-NOOB 1378 neither knows nor assigns any server identifier. The exported 1379 Session-Id is created by concatenating the Type-Code xxx (TBA) with 1380 the MethodId, which is obtained from the KDF output as shown in 1381 Table 5. 1383 3.6. Error handling 1385 Various error conditions in EAP-NOOB are handled by sending an error 1386 notification message (Type=0) instead of the expected next EAP 1387 request or response message. Both the EAP server and the peer may 1388 send the error notification, as shown in Figure 9 and Figure 10. 1389 After sending or receiving an error notification, the server MUST 1390 send an EAP-Failure (as required by [RFC3748] section 4.2). The 1391 notification MAY contain an ErrorInfo field, which is a UTF-8 encoded 1392 text string with a maximum length of 500 bytes. It is used for 1393 sending descriptive information about the error for logging and 1394 debugging purposes. 1396 EAP Peer EAP Server 1397 ... ... 1398 | | 1399 |<----------- EAP-Request/EAP-NOOB ----------------| 1400 | (Type=0,[PeerId],ErrorCode,[ErrorInfo]) | 1401 | | 1402 | | 1403 |<----------- EAP-Failure -------------------------| 1404 | | 1406 Figure 9: Error notification from server to peer 1408 EAP Peer EAP Server 1409 ... ... 1410 | | 1411 |------------ EAP-Response/EAP-NOOB -------------->| 1412 | (Type=0,[PeerId],ErrorCode,[ErrorInfo]) | 1413 | | 1414 | | 1415 |<----------- EAP-Failure -------------------------| 1416 | | 1418 Figure 10: Error notification from peer to server 1420 After the exchange fails due to an error notification, the server and 1421 peer set the association state as follows. In the Initial Exchange, 1422 both the sender and recipient of the error notification MUST set the 1423 association state to the Unregistered (0) state. In the Waiting and 1424 Completion Exchanges, each side MUST remain in its old state as if 1425 the failed exchange had not taken place, with the exception that the 1426 recipient of error code 2003 processes it as specified in 1427 Section 3.2.4. In the Reconnect Exchange, both sides MUST set the 1428 association state to the Reconnecting (3) state. 1430 Errors that occur in the OOB channel are not explicitly notified in- 1431 band. 1433 3.6.1. Invalid messages 1435 If the NAI structure is invalid, the server SHOULD send the error 1436 code 1001 to the peer. The recipient of an EAP-NOOB request or 1437 response SHOULD send the following error codes back to the sender: 1438 1002 if it cannot parse the message as a JSON object or the top-level 1439 JSON object has missing or unrecognized members; 1003 if a data field 1440 has an invalid value, such as an integer out of range, and there is 1441 no more specific error code available; 1004 if the received message 1442 type was unexpected in the current state; 2004 if the PeerId has an 1443 unexpected value; 2003 if the NoobId is not recognized; and 1007 if 1444 the ECDHE key is invalid. 1446 3.6.2. Unwanted peer 1448 The preferred way for the EAP server to rate limit EAP-NOOB 1449 connections from a peer is to use the SleepTime parameter in the 1450 Waiting Exchange. However, if the EAP server receives repeated EAP- 1451 NOOB connections from a peer which apparently should not connect to 1452 this server, the server MAY indicate that the connections are 1453 unwanted by sending the error code 2001. After receiving this error 1454 message, the peer MAY refrain from reconnecting to the same EAP 1455 server and, if possible, both the EAP server and peer SHOULD indicate 1456 this error condition to the user or server administrator. However, 1457 in order to avoid persistent denial of service, the peer is not 1458 required to stop entirely from reconnecting to the server. 1460 3.6.3. State mismatch 1462 In the states indicated by "-" in Figure 11 in Appendix A, user 1463 action is required to reset the association state or to recover it, 1464 for example, from backup storage. In those cases, the server sends 1465 the error code 2002 to the peer. If possible, both the EAP server 1466 and peer SHOULD indicate this error condition to the user or server 1467 administrator. 1469 3.6.4. Negotiation failure 1471 If there is no matching protocol version, the peer sends the error 1472 code 3001 to the server. If there is no matching cryptosuite, the 1473 peer sends the error code 3002 to the server. If there is no 1474 matching OOB direction, the peer sends the error code 3003 to the 1475 server. 1477 In practice, there is no way of recovering from these errors without 1478 software or hardware changes. If possible, both the EAP server and 1479 peer SHOULD indicate these error conditions to the user. 1481 3.6.5. Cryptographic verification failure 1483 If the receiver of the OOB message detects an unrecognized PeerId or 1484 incorrect fingerprint (Hoob) in the OOB message, the receiver MUST 1485 remain in the Waiting for OOB state (1) as if no OOB message was 1486 received. The receiver SHOULD indicate the failure to accept the OOB 1487 message to the user. No in-band error message is sent. 1489 Note that if the OOB message was delivered from the server to the 1490 peer and the peer does not recognize the PeerId, the likely cause is 1491 that the user has unintentionally delivered the OOB message to the 1492 wrong peer device. If possible, the peer SHOULD indicate this to the 1493 user; however, the peer device may not have the capability for many 1494 different error indications to the user and it MAY use the same 1495 indication as in the case of an incorrect fingerprint. 1497 The rationale for the above is that the invalid OOB message could 1498 have been presented to the receiver by mistake or intentionally by a 1499 malicious party and, thus, it should be ignored in the hope that the 1500 honest user will soon deliver a correct OOB message. 1502 If the EAP server or peer detects an incorrect message authentication 1503 code (MACs, MACp, MACs2, MACp2), it sends the error code 4001 to the 1504 other side. As specified in the beginning of Section 3.6, the failed 1505 Completion Exchange will not result in server or peer state changes 1506 while error in the Reconnect Exchange will put both sides to the 1507 Reconnecting (3) state and thus lead to another reconnect attempt. 1509 The rationale for this is that the invalid cryptographic message may 1510 have been spoofed by a malicious party and, thus, it should be 1511 ignored. In particular, a spoofed message on the in-band channel 1512 should not force the honest user to perform the OOB Step again. In 1513 practice, however, the error may be caused by other failures, such as 1514 a software bug. For this reason, the EAP server MAY limit the rate 1515 of peer connections with SleepTime after the above error. Also, 1516 there SHOULD be a way for the user to reset the peer to the 1517 Unregistered state (0), so that the OOB Step can be repeated at the 1518 last resort. 1520 3.6.6. Application-specific failure 1522 Applications MAY define new error messages for failures that are 1523 specific to the application or to one type of OOB channel. They MAY 1524 also use the generic application-specific error code 5001, or the 1525 error codes 5002 and 5004, which have been reserved for indicating 1526 invalid data in the ServerInfo and PeerInfo fields, respectively. 1527 Additionally, anticipating OOB channels that make use of a URL, the 1528 error code 5003 has been reserved for indicating invalid server URL. 1530 4. IANA Considerations 1532 This section provides guidance to the Internet Assigned Numbers 1533 Authority (IANA) regarding registration of values related to the EAP- 1534 NOOB protocol, in accordance with [RFC8126]. 1536 The EAP Method Type number for EAP-NOOB needs to be assigned. 1538 This memo also requires IANA to create new registries as defined in 1539 the following subsections. 1541 4.1. Cryptosuites 1543 Cryptosuites are identified by an integer. Each cryptosuite MUST 1544 specify an ECDHE curve for the key exchange, encoding of the ECDHE 1545 public key as a JWK object, and a cryptographic hash function for the 1546 fingerprint and HMAC computation and key derivation. The hash value 1547 output by the cryptographic hash function MUST be at least 32 bytes 1548 in length. The following suites are defined by EAP-NOOB: 1550 +-------------+-----------------------------------------------------+ 1551 | Cryptosuite | Algorithms | 1552 +-------------+-----------------------------------------------------+ 1553 | 1 | ECDHE curve Curve25519 [RFC7748], public-key format | 1554 | | [RFC7518] Section 6.2.1, hash function SHA-256 | 1555 | | [RFC6234] | 1556 +-------------+-----------------------------------------------------+ 1558 Table 6: EAP-NOOB cryptosuites 1560 An example of Cryptosuite 1 public-key encoded as a JWK object is 1561 given below (line breaks are for readability only). 1563 "jwk":{"kty":"EC","crv":"Curve25519","x":"3p7bfXt9wbTTW2HC7OQ1Nz- 1564 DQ8hbeGdNrfx-FG-IK08"} 1566 Assignment of new values for new cryptosuites MUST be done through 1567 IANA with "Specification Required" and "IESG Approval" as defined in 1568 [RFC8126]. 1570 4.2. Message Types 1572 EAP-NOOB request and response pairs are identified by an integer 1573 Message Type. The following Message Types are defined by EAP-NOOB: 1575 +----------+------------+-------------------------------------------+ 1576 | Message | Used in | Purpose | 1577 | Type | Exchange | | 1578 +----------+------------+-------------------------------------------+ 1579 | 1 | Initial | Version, cryptosuite and parameter | 1580 | | | negotiation | 1581 | | | | 1582 | 2 | Initial | Exchange of ECDHE keys and nonces | 1583 | | | | 1584 | 3 | Waiting | Indication to peer that the server has | 1585 | | | not yet received an OOB message | 1586 | | | | 1587 | 4 | Completion | Authentication and key confirmation with | 1588 | | | HMAC | 1589 | | | | 1590 | 5 | Reconnect | Version, cryptosuite, and parameter | 1591 | | | negotiation | 1592 | | | | 1593 | 6 | Reconnect | Exchange of ECDHE keys and nonces | 1594 | | | | 1595 | 7 | Reconnect | Authentication and key confirmation with | 1596 | | | HMAC | 1597 | | | | 1598 | 8 | Completion | NoobId discovery | 1599 | | | | 1600 | 9 | All | PeerId and PeerState discovery | 1601 | | exchanges | | 1602 | | | | 1603 | 0 | Error | Error notification | 1604 | | | | 1605 +----------+------------+-------------------------------------------+ 1607 Table 7: EAP-NOOB 1609 Assignment of new values for new Message Types MUST be done through 1610 IANA with "Expert Review" as defined in [RFC8126]. 1612 4.3. Error codes 1614 The error codes defined by EAP-NOOB are listed in Table 8. 1616 +------------+----------------------------------------+ 1617 | Error code | Purpose | 1618 +------------+----------------------------------------+ 1619 | 1001 | Invalid NAI | 1620 | 1002 | Invalid message structure | 1621 | 1003 | Invalid data | 1622 | 1004 | Unexpected message type | 1623 | 1007 | Invalid ECDHE key | 1624 | 2001 | Unwanted peer | 1625 | 2002 | State mismatch, user action required | 1626 | 2003 | Unrecognized OOB message identifier | 1627 | 2004 | Unexpected peer identifier | 1628 | 3001 | No mutually supported protocol version | 1629 | 3002 | No mutually supported cryptosuite | 1630 | 3003 | No mutually supported OOB direction | 1631 | 4001 | HMAC verification failure | 1632 | 5001 | Application-specific error | 1633 | 5002 | Invalid server info | 1634 | 5003 | Invalid server URL | 1635 | 5004 | Invalid peer info | 1636 | 6001-6999 | Private and experimental use | 1637 +------------+----------------------------------------+ 1639 Table 8: EAP-NOOB error codes 1641 Assignment of new error codes MUST be done through IANA with 1642 "Specification Required" and "IESG Approval" as defined in [RFC8126], 1643 with the exception of the range 6001-6999, which is reserved for 1644 "Private Use" and "Experimental Use". 1646 4.4. Domain name reservation considerations 1648 "eap-noob.net" should be registered as a special-use domain. The 1649 considerations required by [RFC6761] for registering this special-use 1650 domain name are the following: 1652 o Users: Non-admin users are not expected to encounter this name or 1653 recognize it as special. AAA administrators may need to recognize 1654 the name. 1656 o Application Software: Application software is not expected to 1657 recognize this domain name as special. 1659 o Name Resolution APIs and Libraries: Name resolution APIs and 1660 libraries are not expected to recognize this domain name as 1661 special. 1663 o Caching DNS Servers: Caching servers are not expected to recognize 1664 this domain name as special. 1666 o Authoritative DNS Servers: Authoritative DNS servers MUST respond 1667 to queries for eap-noob.net with NXDOMAIN. 1669 o DNS Server Operators: Except for the authoritative DNS server, 1670 there are no special requirements for the operators. 1672 o DNS Registries/Registrars: There are no special requirements for 1673 DNS registrars. 1675 5. Implementation Status 1677 This section records the status of known implementations of the 1678 protocol defined by this specification at the time of posting of this 1679 Internet-Draft, and is based on a proposal described in [RFC7942]. 1680 The description of implementations in this section is intended to 1681 assist the IETF in its decision processes in progressing drafts to 1682 RFCs. Please note that the listing of any individual implementation 1683 here does not imply endorsement by the IETF. Furthermore, no effort 1684 has been spent to verify the information presented here that was 1685 supplied by IETF contributors. This is not intended as, and must not 1686 be construed to be, a catalog of available implementations or their 1687 features. Readers are advised to note that other implementations may 1688 exist. 1690 5.1. Implementation with wpa_supplicant and hostapd 1692 o Responsible Organization: Aalto University 1694 o Location: 1696 o Coverage: This implementation includes all of the features 1697 described in the current specification. The implementation 1698 supports two dimensional QR codes and NFC as example out-of-band 1699 (OOB) channels 1701 o Level of Maturity: Alpha 1703 o Version compatibility: Version 06 of the draft implemented 1705 o Licensing: BSD 1707 o Contact Information: Tuomas Aura, tuomas.aura@aalto.fi 1709 5.2. Implementation on Contiki 1711 o Responsible Organization: University of Murcia and Aalto 1712 University 1714 o Location: 1716 o Coverage: This implementation includes all of the features 1717 described in the current specification. The implementation uses a 1718 blinking LED light as the out-of-band (OOB) channel 1720 o Level of Maturity: Alpha 1722 o Version compatibility: Version 05 of the draft implemented 1724 o Licensing: BSD 1726 o Contact Information: Eduardo Ingles, eduardo.ingles@um.es 1728 5.3. Protocol modeling 1730 The current EAP-NOOB specification has been modeled with the mCRL2 1731 formal specification language [mcrl2]. The model 1732 was used mainly for simulating the protocol behavior and for 1734 verifying basic safety and liveness properties as part of the 1735 specification process. For example, we verified the correctness of 1736 the tiebreaking mechanism when two OOB messages are received 1737 simultaneously, one in each direction. We also verified that a man- 1738 in-the-middle attacker cannot cause persistent failure by spoofing a 1739 finite number of messages in the Reconnect Exchange. Additionally, 1740 the protocol has been modeled with the ProVerif [proverif] tool. 1741 This model was used to verify security 1743 properties such as mutual authentication. 1745 6. Security considerations 1747 EAP-NOOB is an authentication and key derivation protocol and, thus, 1748 security considerations can be found in most sections of this 1749 specification. In the following, we explain the protocol design and 1750 highlight some other special considerations. 1752 6.1. Authentication principle 1754 EAP-NOOB establishes a shared secret with an authenticated ECDHE key 1755 exchange. The mutual authentication in EAP-NOOB is based on two 1756 separate features, both conveyed in the OOB message. The first 1757 authentication feature is the secret nonce Noob. The peer and server 1758 use this secret in the Completion Exchange to mutually authenticate 1759 the session key previously created with ECDHE. The message 1760 authentication codes computed with the secret nonce Noob are alone 1761 sufficient for authenticating the key exchange. The second 1762 authentication feature is the integrity-protecting fingerprint Hoob. 1763 Its purpose is to prevent impersonation and man-in-the-middle attacks 1764 even in situations where the attacker is able to eavesdrop the OOB 1765 channel and the nonce Noob is compromised. In some human-assisted 1766 OOB channels, such as sound burst or user-transferred URL, it may be 1767 easier to detect tampering than spying of the OOB message, and such 1768 applications benefit from the second authentication feature. 1770 The additional security provided by the cryptographic fingerprint 1771 Hoob is somewhat intricate to understand. The endpoint that receives 1772 the OOB message uses Hoob to verify the integrity of the ECDHE 1773 exchange. Thus, the OOB receiver can detect impersonation and man- 1774 in-the-middle attacks on the in-band channel. The other endpoint, 1775 however, is not equally protected because the OOB message and 1776 fingerprint are sent only in one direction. Some protection to the 1777 OOB sender is afforded by the fact that the user may notice the 1778 failure of the association at the OOB receiver and therefore reset 1779 the OOB sender. Other device-pairing protocols have solved similar 1780 situations by requiring the user to confirm to the OOB sender that 1781 the association was accepted by the OOB receiver, e.g. by pressing an 1782 "confirm" button on the sender side. Applications MAY implement EAP- 1783 NOOB in this way. Nevertheless, since EAP-NOOB was designed to work 1784 with strictly one-directional OOB communication and the fingerprint 1785 is only the second authentication feature, the EAP-NOOB specification 1786 does not mandate such explicit confirmation to the OOB sender. 1788 To summarize, EAP-NOOB uses the combined protection of the secret 1789 nonce Noob and the cryptographic fingerprint Hoob, both conveyed in 1790 the OOB message. The secret nonce Noob alone is sufficient for 1791 mutual authentication, unless the attacker can eavesdrop it from the 1792 OOB channel. Even if an attacker is able to eavesdrop the secret 1793 nonce Noob, it nevertheless cannot perform a full man-in-the-middle 1794 attack on the in-band channel because the mismatching fingerprint 1795 would alert the OOB receiver, which would reject the OOB message. 1796 The attacker that eavesdropped the secret nonce can impersonate the 1797 OOB receiver to the OOB sender. In this case, the association will 1798 appear to be complete only on the OOB sender side, and such 1799 situations have to be resolved by the user by resetting the OOB 1800 sender to the initial state. 1802 The expected use cases for EAP-NOOB are ones where it replaces a 1803 user-entered access credentials in IoT appliances. In wireless 1804 network access without EAP, the user-entered credential is often a 1805 passphrase that is shared by all the network stations. The advantage 1806 of an EAP-based solution, including EAP-NOOB, is that it establishes 1807 a different master secret for each peer device, which makes the 1808 system more resilient against device compromise than if there were a 1809 common master secret. Additionally, it is possible to revoke the 1810 security association for an individual device on the server side. 1812 Forward secrecy in EAP-NOOB is optional. The Reconnect Exchange in 1813 EAP-NOOB provides forward secrecy only if both the server and peer 1814 send their fresh ECDHE keys. This allows both the server and the 1815 peer to limit the frequency of the costly computation that is 1816 required for forward secrecy. The server MAY adjust the frequency of 1817 its attempts at ECDHE rekeying based on what it knows about the 1818 peer's computational capabilities. 1820 The users delivering the OOB messages will often authenticate 1821 themselves to the EAP server, e.g. by logging into a secure web page. 1822 In this case, the server can reliably associate the peer device with 1823 the user account. Applications that make use of EAP-NOOB can use 1824 this information for configuring the initial owner of the freshly- 1825 registered device. 1827 6.2. Identifying correct endpoints 1829 Potential weaknesses in EAP-NOOB arise from the fact that the user 1830 must identify physically the correct peer device. If the attacker is 1831 able to trick the user into delivering the OOB message to or from the 1832 wrong peer device, the server may create an association with the 1833 wrong peer. This reliance on user in identifying the correct 1834 endpoints is an inherent property of user-assisted out-of-band 1835 authentication. 1837 It is, however, not possible to exploit accidental delivery of the 1838 OOB message to the wrong device when the user makes a mistake. This 1839 is because the wrong peer device would not have prepared for the 1840 attack by performing the Initial Exchange with the server. In 1841 comparison, simpler solutions where the master key is transferred to 1842 the device via the OOB channel are vulnerable to opportunistic 1843 attacks if the user mistakenly delivers the master key to more than 1844 one device. 1846 One mechanism that can mitigate user mistakes is certification of 1847 peer devices. The certificate can convey to the server authentic 1848 identifiers and attributes of the peer device. Compared to a fully 1849 certificate-based authentication, however, EAP-NOOB can be used 1850 without trusted third parties and does not require the user to know 1851 any identifier of the peer device; physical access to the device is 1852 sufficient. 1854 Similarly, the attacker can try to trick the user to deliver the OOB 1855 message to the wrong server, so that the peer device becomes 1856 associated with the wrong server. Since the EAP server is typically 1857 online and accessed through a web user interface, the attack would be 1858 akin to phishing attacks where the user is tricked to accessing the 1859 wrong URL and wrong web page. 1861 6.3. Trusted path issues and misbinding attacks 1863 Another potential threat is spoofed user input or output on the peer 1864 device. When the user is delivering the OOB message to or from the 1865 correct peer device, a trusted path between the user and the peer 1866 device is needed. That is, the user must communicate directly with 1867 an authentic operating system and EAP-NOOB implementation in the peer 1868 device and not with a spoofed user interface. Otherwise, a 1869 Registered device that is under the control of the attacker could 1870 emulate the behavior of an unregistered device. The secure path can 1871 be implemented, for example, by having the user pressing a reset 1872 button to return the device to the Unregistered state and a trusted 1873 UI. The problem with such trusted paths is that they are not 1874 standardized across devices. 1876 Another potential consequence of spoofed UI is the misbinding attack 1877 where the user tries to register the correct but compromised device, 1878 and that device tricks the user into registering another device 1879 instead. For example, a compromised device might have a malicious 1880 full-screen app running, which presents to the user QR codes copied, 1881 in real time, from another device's screen. If the unwitting user 1882 scans the QR code and delivers the OOB message in it to the server, 1883 the wrong device may become registered in the server. Such 1884 misbinding vulnerabilities arise because the user does not have any 1885 secure way of verifying that the in-band cryptographic handshake and 1886 the out-of-band physical access are terminated at the same physical 1887 device. Sethi et al. [Sethi19] analyze the binding threat against 1888 device-pairing protocols and also EAP-NOOB. Essentially, all 1889 protocols where the authentication relies on the user's physical 1890 access to the device are vulnerable to misbinding, including EAP- 1891 NOOB. 1893 A standardized trusted path for communicating directly with the 1894 trusted computing base in a physical device would mitigate the 1895 misbinding threat, but such paths rarely exist in practice. Careful 1896 asset tracking can also prevent most misbinding attacks because the 1897 PeerInfo sent in-band by the wrong device will not match expected 1898 values. Device certification by the manufacturer can further 1899 strengthen the asset tracking. 1901 6.4. Peer identifiers and attributes 1903 The PeerId value in the protocol is a server-allocated identifier for 1904 its association with the peer and SHOULD NOT be shown to the user 1905 because its value is initially ephemeral. Since the PeerId is 1906 allocated by the server and the scope of the identifier is the single 1907 server, the so-called identifier squatting attacks, where a malicious 1908 peer could reserve another peer's identifier, are not possible in 1909 EAP-NOOB. The server SHOULD assign a random or pseudo-random PeerId 1910 to each new peer. It SHOULD NOT select the PeerId based on any peer 1911 characteristics that it may know, such as the peer's link-layer 1912 network address. 1914 User reset or failure in the OOB Step can cause the peer to perform 1915 many Initial Exchanges with the server and to allocate many PeerIds 1916 and to store the ephemeral protocol state for them. The peer will 1917 typically only remember the latest one. EAP-NOOB leaves it to the 1918 implementation to decide when to delete these ephemeral associations. 1919 There is no security reason to delete them early, and the server does 1920 not have any way to verify that the peers are actually the same one. 1921 Thus, it is safest to store the ephemeral states for at least one 1922 day. If the OOB messages are sent only in the server-to-peer 1923 direction, the server SHOULD NOT delete the ephemeral state before 1924 all the related Noob values have expired. 1926 After completion of EAP-NOOB, the server may store the PeerInfo data, 1927 and the user may use it to identify the peer and its properties, such 1928 as the make and model or serial number. A compromised peer could lie 1929 in the PeerInfo that it sends to the server. If the server stores 1930 any information about the peer, it is important that this information 1931 is approved by the user during or after the OOB Step. Without 1932 verification by the user or authentication with vendor certificates 1933 on the application level, the PeerInfo is not authenticated 1934 information and should not be relied on. 1936 One possible use for the PeerInfo field is EAP channel binding 1937 ([RFC3748] Section 7.15). That is, the PeerInfo may include data 1938 items that bind the EAP-NOOB association and exported keys to 1939 properties of the authenticator or the access link, such as the SSID 1940 and BSSID of the wireless network (see Appendix C). 1942 6.5. Identity protection 1944 The PeerInfo field contains identifiers and other information about 1945 the peer device (see Appendix C), and the peer sends this information 1946 in plaintext to the EAP server before the server authentication in 1947 EAP-NOOB has been completed. While the information refers to the 1948 peer device and not directly to the user, it may be better for user 1949 privacy to avoid sending unnecessary information. In the Reconnect 1950 Exchange, the optional PeerInfo SHOULD be omitted unless some 1951 critical data has changed. 1953 Peer devices that randomize their layer-2 address to prevent tracking 1954 can do this whenever the user resets the EAP-NOOB association. 1955 During the lifetime of the association, the PeerId is a unique 1956 identifier that can be used to track the peer in the access network. 1957 Later versions of this specification may consider updating the PeerId 1958 at each Reconnect Exchange. In that case, it is necessary to 1959 consider how the authenticator and access-network administrators can 1960 recognize and blacklist misbehaving peer devices and how to avoid 1961 loss of synchronization between the server and the peer if messages 1962 are lost during the identifier update. 1964 6.6. Downgrading threats 1966 The fingerprint Hoob protects all the information exchanged in the 1967 Initial Exchange, including the cryptosuite negotiation. The message 1968 authentication codes MACs and MACp also protect the same information. 1969 The message authentication codes MACs2 and MACp2 protect information 1970 exchanged during key renegotiation in the Reconnect Exchange. This 1971 prevents downgrading attacks to weaker cryptosuites as long as the 1972 possible attacks take more time than the maximum time allowed for the 1973 EAP-NOOB completion. This is typically the case for recently 1974 discovered cryptanalytic attacks. 1976 As an additional precaution, the EAP server and peer SHOULD check for 1977 downgrading attacks in the Reconnect Exchange. As long as the server 1978 or peer saves any information about the other endpoint, it MUST also 1979 remember the previously negotiated cryptosuite and MUST NOT accept 1980 renegotiation of any cryptosuite that is known to be weaker than the 1981 previous one, such as a deprecated cryptosuite. 1983 Integrity of the direction negotiation cannot be verified in the same 1984 way as the integrity of the cryptosuite negotiation. That is, if the 1985 OOB channel used in an application is critically insecure in one 1986 direction, a man-in-the-middle attacker could modify the negotiation 1987 messages and thereby cause that direction to be used. Applications 1988 that support OOB messages in both directions SHOULD therefore ensure 1989 that the OOB channel has sufficiently strong security in both 1990 directions. While this is a theoretical vulnerability, it could 1991 arise in practice if EAP-NOOB is deployed in unexpected applications. 1992 However, most devices acting as the peer are likely to support only 1993 one direction of exchange, in which case interfering with the 1994 direction negotiation can only prevent the completion of the 1995 protocol. 1997 The long-term shared key material Kz in the persistent EAP-NOOB 1998 association is established with an ECDHE key exchange when the peer 1999 and server are first associated. It is a weaker secret than a 2000 manually configured random shared key because advances in 2001 cryptanalysis against the used ECDHE curve could eventually enable 2002 the attacker to recover Kz. EAP-NOOB protects against such attacks 2003 by allowing cryptosuite upgrades in the Reconnect Exchange and by 2004 updating shared key material Kz whenever the cryptosuite is upgraded. 2005 We do not expect the cryptosuite upgrades to be frequent, but if one 2006 becomes necessary, the upgrade can be made without manual resetting 2007 and reassociation of the peer devices. 2009 6.7. Recovery from loss of last message 2011 The EAP-NOOB Completion Exchange, as well as the Reconnect Exchange 2012 with cryptosuite update, result in a persistent state change that 2013 should take place either on both endpoints or on neither; otherwise, 2014 the result is a state mismatch that requires user action to resolve. 2015 The state mismatch can occur if the final EAP response of the 2016 exchanges is lost. In the Completion Exchange, the loss of the final 2017 response (Type=4) results in the peer moving to Registered (4) state 2018 and creating a persistent EAP-NOOB association while the server stays 2019 in an ephemeral state (1 or 2). In the Reconnect Exchange, the loss 2020 of the final response (Type=7) results in the peer moving to the 2021 Registered (4) state and updating its persistent key material Kz 2022 while the server stays in the Reconnecting (3) state and keeps the 2023 old key material. 2025 The state mismatch is an example of a unavoidable problem in 2026 distributed systems: it is theoretically impossible to guarantee 2027 synchronous state changes in endpoints that communicate 2028 asynchronously. The protocol will always have one critical message 2029 that may get lost, so that one side commits to the state change and 2030 the other side does not. In EAP, the critical message is the final 2031 response from the peer to the server. While the final response is 2032 normally followed by EAP-Success, [RFC3748] section 4.2 states that 2033 the peer MAY assume that the EAP-Success was lost and the 2034 authentication was successful. Furthermore, EAP methods in the peer 2035 do not receive notification of the EAP-Success message from the 2036 parent EAP state machine [RFC4137]. For these reasons, EAP-NOOB on 2037 the peer side commits to a state change already when it sends the 2038 final response. 2040 The best available solution to the loss of the critical message is to 2041 keep trying. EAP retransmission behavior defined in Section 4.3 of 2042 [RFC3748] suggests 3-5 retransmissions. In the absence of an 2043 attacker, this would be sufficient to reduce the probability of 2044 failure to an acceptable level. However, a determined attacker on 2045 the in-band channel can drop the final EAP-Response message and all 2046 subsequent retransmissions. In the Completion Exchange 2047 (KeyingMode=0) and in the Reconnect Exchange with cryptosuite upgrade 2048 (KeyingMode=3), this could result in state mismatch and persistent 2049 denial of service until user resets the peer state. 2051 EAP-NOOB implements its own recovery mechanism that allows unlimited 2052 retries of the Reconnect Exchange. When the DoS attacker eventually 2053 stops dropping packets on the in-band channel, the protocol will 2054 recover. The logic for this recovery mechanism is specified in 2055 Section 3.4.2. 2057 EAP-NOOB does not implement the same kind of retry mechanism in the 2058 Completion Exchange. The reason is that there is always a user 2059 involved in the initial association process, and the user can repeat 2060 the OOB Step to complete the association after the DoS attacker has 2061 left. On the other hand, Reconnect Exchange needs to work without 2062 user involvement. 2064 6.8. EAP security claims 2066 EAP security claims are defined in section 7.2.1 of [RFC3748]. The 2067 security claims for EAP-NOOB are listed in Table 9. 2069 +----------------+--------------------------------------------------+ 2070 | Security | EAP-NOOB claim | 2071 | property | | 2072 +----------------+--------------------------------------------------+ 2073 | Authentication | ECDHE key exchange with out-of-band | 2074 | mechanism | authentication | 2075 | | | 2076 | Protected | yes | 2077 | cryptosuite | | 2078 | negotiation | | 2079 | | | 2080 | Mutual | yes | 2081 | authentication | | 2082 | | | 2083 | Integrity | yes | 2084 | protection | | 2085 | | | 2086 | Replay | yes | 2087 | protection | | 2088 | | | 2089 | Key derivation | yes | 2090 | | | 2091 | Key strength | The specified cryptosuites provide key strength | 2092 | | of at least 128 bits. | 2093 | | | 2094 | Dictionary | yes | 2095 | attack | | 2096 | protection | | 2097 | | | 2098 | Fast reconnect | yes | 2099 | | | 2100 | Cryptographic | not applicable | 2101 | binding | | 2102 | | | 2103 | Session | yes | 2104 | independence | | 2105 | | | 2106 | Fragmentation | no | 2107 | | | 2108 | Channel | yes (The ServerInfo and PeerInfo can be used to | 2109 | binding | convey integrity-protected channel properties | 2110 | | such as network SSID or peer MAC address.) | 2111 +----------------+--------------------------------------------------+ 2113 Table 9: EAP security claims 2115 7. References 2117 7.1. Normative references 2119 [NIST-DH] Barker, E., Chen, L., Roginsky, A., and M. Smid, 2120 "Recommendation for Pair-Wise Key Establishment Schemes 2121 Using Discrete Logarithm Cryptography", NIST Special 2122 Publication 800-56A Revision 2 , May 2013, 2123 . 2126 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 2127 Hashing for Message Authentication", RFC 2104, 2128 DOI 10.17487/RFC2104, February 1997, 2129 . 2131 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2132 Requirement Levels", BCP 14, RFC 2119, 2133 DOI 10.17487/RFC2119, March 1997, 2134 . 2136 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 2137 Levkowetz, Ed., "Extensible Authentication Protocol 2138 (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004, 2139 . 2141 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 2142 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 2143 . 2145 [RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible 2146 Authentication Protocol (EAP) Key Management Framework", 2147 RFC 5247, DOI 10.17487/RFC5247, August 2008, 2148 . 2150 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 2151 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 2152 DOI 10.17487/RFC6234, May 2011, 2153 . 2155 [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", 2156 RFC 6761, DOI 10.17487/RFC6761, February 2013, 2157 . 2159 [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, 2160 DOI 10.17487/RFC7517, May 2015, 2161 . 2163 [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, 2164 DOI 10.17487/RFC7518, May 2015, 2165 . 2167 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2168 DOI 10.17487/RFC7542, May 2015, 2169 . 2171 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 2172 for Security", RFC 7748, DOI 10.17487/RFC7748, January 2173 2016, . 2175 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2176 Writing an IANA Considerations Section in RFCs", BCP 26, 2177 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2178 . 2180 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 2181 Interchange Format", STD 90, RFC 8259, 2182 DOI 10.17487/RFC8259, December 2017, 2183 . 2185 7.2. Informative references 2187 [BluetoothPairing] 2188 Bluetooth, SIG, "Simple pairing whitepaper", Technical 2189 report , 2007. 2191 [EUI-48] Institute of Electrical and Electronics Engineers, 2192 "802-2014 IEEE Standard for Local and Metropolitan Area 2193 Networks: Overview and Architecture.", IEEE Standard 2194 802-2014. , June 2014. 2196 [IEEE-802.1X] 2197 Institute of Electrical and Electronics Engineers, "Local 2198 and Metropolitan Area Networks: Port-Based Network Access 2199 Control", IEEE Standard 802.1X-2004. , December 2004. 2201 [mcrl2] Groote, J. and M. Mousavi, "Modeling and analysis of 2202 communicating systems", The MIT press , 2014, 2203 . 2206 [proverif] 2207 Blanchet, B., Smyth, B., Cheval, V., and M. Sylvestre, 2208 "ProVerif 2.00: Automatic Cryptographic Protocol Verifier, 2209 User Manual and Tutorial", The MIT press , 2018, 2210 . 2213 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 2214 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 2215 D. Spence, "AAA Authorization Framework", RFC 2904, 2216 DOI 10.17487/RFC2904, August 2000, 2217 . 2219 [RFC4137] Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba, 2220 "State Machines for Extensible Authentication Protocol 2221 (EAP) Peer and Authenticator", RFC 4137, 2222 DOI 10.17487/RFC4137, August 2005, 2223 . 2225 [RFC4266] Hoffman, P., "The gopher URI Scheme", RFC 4266, 2226 DOI 10.17487/RFC4266, November 2005, 2227 . 2229 [RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS 2230 Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216, 2231 March 2008, . 2233 [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 2234 Code: The Implementation Status Section", BCP 205, 2235 RFC 7942, DOI 10.17487/RFC7942, July 2016, 2236 . 2238 [Sethi14] Sethi, M., Oat, E., Di Francesco, M., and T. Aura, "Secure 2239 Bootstrapping of Cloud-Managed Ubiquitous Displays", 2240 Proceedings of ACM International Joint Conference on 2241 Pervasive and Ubiquitous Computing (UbiComp 2014), pp. 2242 739-750, Seattle, USA , September 2014, 2243 . 2245 [Sethi19] Sethi, M., Peltonen, A., and T. Aura, "Misbinding Attacks 2246 on Secure Device Pairing", 2019, 2247 . 2249 Appendix A. Exchanges and events per state 2251 Figure 11 shows how the EAP server chooses the exchange type 2252 depending on the server and peer states. In the state combinations 2253 marked with hyphen "-", there is no possible exchange and user action 2254 is required to make progress. Note that peer state 4 is omitted from 2255 the table because the peer never connects to the server when the peer 2256 is in that state. The table also shows the handling of errors in 2257 each exchange. A notable detail is that the recipient of error code 2258 2003 moves to state 1. 2260 +--------+---------------------------+------------------------------+ 2261 | peer | exchange chosen by | next peer and | 2262 | states | server | server states | 2263 +========+===========================+==============================+ 2264 | server state: Unregistered (0) | 2265 +--------+---------------------------+------------------------------+ 2266 | 0..2 | Initial Exchange | both 1 (0 on error) | 2267 | 3 | - | no change, notify user | 2268 +--------+---------------------------+------------------------------+ 2269 | server state: Waiting for OOB (1) | 2270 +--------+---------------------------+------------------------------+ 2271 | 0 | Initial Exchange | both 1 (0 on error) | 2272 | 1 | Waiting Exchange | both 1 (no change on error) | 2273 | 2 | Completion Exchange | both 4 (A) | 2274 | 3 | - | no change, notify user | 2275 +--------+---------------------------+------------------------------+ 2276 | server state: OOB Received (2) | 2277 +--------+---------------------------+------------------------------+ 2278 | 0 | Initial Exchange | both 1 (0 on error) | 2279 | 1 | Completion Exchange | both 4 (B) | 2280 | 2 | Completion Exchange | both 4 (A) | 2281 | 3 | - | no change, notify user | 2282 +--------+---------------------------+------------------------------+ 2283 | server state: Reconnecting (3) or Registered (4) | 2284 +--------+---------------------------+------------------------------+ 2285 | 0..2 | - | no change, notify user | 2286 | 3 | Reconnect Exchange | both 4 (3 on error) | 2287 +--------+---------------------------+------------------------------+ 2288 (A) peer to 1 on error 2003, no other changes on error 2289 (B) server to 1 on error 2003, no other changes on error 2291 Figure 11: How server chooses the exchange type 2293 Figure 12 lists the local events that can take place in the server or 2294 peer. Both the server and peer output and accept OOB messages in 2295 association state 1, leading the receiver to state 2. Communication 2296 errors and timeouts in states 0..2 lead back to state 0, while 2297 similar errors in states 3..4 lead to state 3. Application request 2298 for rekeying (e.g. to refresh session keys or to upgrade cryptosuite) 2299 also takes the association from state 3..4 to state 3. User can 2300 always reset the association state to 0. Recovering association 2301 data, e.g. from a backup, leads to state 3. 2303 +--------+---------------------------+------------------------------+ 2304 | server/| possible local events | next state | 2305 | peer | on server and peer | | 2306 | state | | | 2307 +========+===========================+==============================+ 2308 | 1 | OOB Output* | 1 | 2309 | 1 | OOB Input* | 2 (1 on error) | 2310 | 0..2 | Timeout/network failure | 0 | 2311 | 3..4 | Timeout/network failure | 3 | 2312 | 3..4 | Rekeying request | 3 | 2313 | 0..4 | User resets peer state | 0 | 2314 | 0..4 | Association state recovery| 3 | 2315 +--------+---------------------------+------------------------------+ 2317 Figure 12: Local events on server and peer 2319 Appendix B. Application-specific parameters 2321 Table 10 lists OOB channel parameters that need to be specified in 2322 each application that makes use of EAP-NOOB. The list is not 2323 exhaustive and is included for the convenience of implementors only. 2325 +--------------------+----------------------------------------------+ 2326 | Parameter | Description | 2327 +--------------------+----------------------------------------------+ 2328 | OobDirs | Allowed directions of the OOB channel | 2329 | | | 2330 | OobMessageEncoding | How the OOB message data fields are encoded | 2331 | | for the OOB channel | 2332 | | | 2333 | SleepTimeDefault | Default minimum time in seconds that the | 2334 | | peer should sleep before the next Waiting | 2335 | | Exchange | 2336 | | | 2337 | OobRetries | Number of received OOB messages with invalid | 2338 | | Hoob after which the receiver moves to | 2339 | | Unregistered (0) state | 2340 | | | 2341 | NoobTimeout | How many seconds the sender of the OOB | 2342 | | message remembers the sent Noob value. The | 2343 | | RECOMMENDED value is 3600 seconds. | 2344 | | | 2345 | ServerInfoMembers | Required members in ServerInfo | 2346 | | | 2347 | PeerInfoMembers | Required members in PeerInfo | 2348 +--------------------+----------------------------------------------+ 2350 Table 10: OOB channel characteristics 2352 Appendix C. ServerInfo and PeerInfo contents 2354 The ServerInfo and PeerInfo fields in the Initial Exchange and 2355 Reconnect Exchange enable the server and peer, respectively, send 2356 information about themselves to the other endpoint. They contain 2357 JSON objects whose structure may be specified separately for each 2358 application and each type of OOB channel. ServerInfo and PeerInfo 2359 MAY contain auxiliary data needed for the OOB channel messaging and 2360 for EAP channel binding. Table 11 lists some suggested data fields 2361 for ServerInfo. 2363 +----------------+--------------------------------------------------+ 2364 | Data field | Description | 2365 +----------------+--------------------------------------------------+ 2366 | ServerName | String that may be used to aid human | 2367 | | identification of the server. | 2368 | | | 2369 | ServerURL | Prefix string when the OOB message is formatted | 2370 | | as URL, as suggested in Appendix E. | 2371 | | | 2372 | SSIDList | List of wireless network identifier (SSID) | 2373 | | strings used for roaming support, as suggested | 2374 | | in Appendix D. JSON array of UTF-8 encoded SSID | 2375 | | strings. | 2376 | | | 2377 | Base64SSIDList | List of wireless network identifier (SSID) | 2378 | | strings used for roaming support, as suggested | 2379 | | in Appendix D. JSON array of SSIDs, each of | 2380 | | which is base64url encoded without padding. Peer | 2381 | | SHOULD send at most one of the fields SSIDList | 2382 | | and Base64SSIDList in PeerInfo, and the server | 2383 | | SHOULD ignore SSIDList if Base64SSIDList is | 2384 | | included. | 2385 +----------------+--------------------------------------------------+ 2387 Table 11: Suggested ServerInfo data fields 2389 PeerInfo typically contains auxiliary information for identifying and 2390 managing peers on the application level at the server end. Table 12 2391 lists some suggested data fields for PeerInfo. 2393 +--------------+----------------------------------------------------+ 2394 | Data field | Description | 2395 +--------------+----------------------------------------------------+ 2396 | PeerName | String that may be used to aid human | 2397 | | identification of the peer. | 2398 | | | 2399 | Manufacturer | Manufacturer or brand string. | 2400 | | | 2401 | Model | Manufacturer-specified model string. | 2402 | | | 2403 | SerialNumber | Manufacturer-assigned serial number. | 2404 | | | 2405 | MACAddress | Peer link-layer identifier (EUI-48) in the | 2406 | | 12-digit base-16 form [EUI-48]. The string MAY | 2407 | | include additional colon ':' or dash '-' | 2408 | | characters that MUST be ignored by the server. | 2409 | | | 2410 | SSID | Wireless network SSID for channel binding. The | 2411 | | SSID is a UTF-8 string. | 2412 | | | 2413 | Base64SSID | Wireless network SSID for channel binding. The | 2414 | | SSID is base64url encoded. Peer SHOULD send at | 2415 | | most one of the fields SSID and Base64SSID in | 2416 | | PeerInfo, and the server SHOULD ignore SSID if | 2417 | | Base64SSID is included. | 2418 | | | 2419 | BSSID | Wireless network BSSID (EUI-48) in the 12-digit | 2420 | | base-16 form [EUI-48]. The string MAY include | 2421 | | additional colon ':' or dash '-' characters that | 2422 | | MUST be ignored by the server. | 2423 | | | 2424 +--------------+----------------------------------------------------+ 2426 Table 12: Suggested PeerInfo data fields 2428 Appendix D. EAP-NOOB roaming 2430 AAA architectures [RFC2904] allow for roaming of network-connected 2431 appliances that are authenticated over EAP. While the peer is 2432 roaming in a visited network, authentication still takes place 2433 between the peer and an authentication server at its home network. 2434 EAP-NOOB supports such roaming by assigning a Realm to the peer. 2435 After the Realm has been assigned, the peer's NAI enables the visited 2436 network to route the EAP session to the peer's home AAA server. 2438 A peer device that is new or has gone through a hard reset should be 2439 connected first to the home network and establish an EAP-NOOB 2440 association with its home AAA server before it is able to roam. 2442 After that, it can perform the Reconnect Exchange from the visited 2443 network. 2445 Alternatively, the device may provide some method for the user to 2446 configure the Realm of the home network. In that case, the EAP-NOOB 2447 association can be created while roaming. The device will use the 2448 user-assigned Realm in the Initial Exchange, which enables the EAP 2449 messages to be routed correctly to the home AAA server. 2451 While roaming, the device needs to identify the networks where the 2452 EAP-NOOB association can be used to gain network access. For 802.11 2453 access networks, the server MAY send a list of SSID strings in the 2454 ServerInfo JSON object in a member called either SSIDList or 2455 Base64SSIDList. The list is formated as explained in Table 11. If 2456 present, the peer MAY use this list as a hint to determine the 2457 networks where the EAP-NOOB association can be used for access 2458 authorization, in addition to the access network where the Initial 2459 Exchange took place. 2461 Appendix E. OOB message as URL 2463 While EAP-NOOB does not mandate any particular OOB communication 2464 channel, typical OOB channels include graphical displays and emulated 2465 NFC tags. In the peer-to-server direction, it may be convenient to 2466 encode the OOB message as a URL, which is then encoded as a QR code 2467 for displays and printers or as an NDEF record for NFC tags. A user 2468 can then simply scan the QR code or NFC tag and open the URL, which 2469 causes the OOB message to be delivered to the authentication server. 2470 The URL MUST specify the https protocol i.e. secure connection to the 2471 server, so that the man-in-the-middle attacker cannot read or modify 2472 the OOB message. 2474 The ServerInfo in this case includes a JSON member called ServerUrl 2475 of the following format with maximum length of 60 characters: 2477 https://[:]/[] 2479 To this, the peer appends the OOB message fields (PeerId, Noob, Hoob) 2480 as a query string. PeerId is provided to the peer by the server and 2481 might be a 22-character string. The peer base64url encodes, without 2482 padding, the 16-byte values Noob and Hoob into 22-character strings. 2483 The query parameters MAY be in any order. The resulting URL is of 2484 the following format: 2486 https://[:]/[]?P=&N=&H= 2488 The following is an example of a well-formed URL encoding the OOB 2489 message (without line breaks): 2491 https://example.com/Noob?P=ZrD7qkczNoHGbGcN2bN0&N=rMinS0-F4EfCU8D9ljx 2492 X_A&H=QvnMp4UGxuQVFaXPW_14UW 2494 Appendix F. Example messages 2496 The message examples in this section are generated with Curve25519 2497 ECDHE test vectors specified in section 6.1 of [RFC7748] 2498 (server=Alice, peer=Bob). The direction of the OOB channel 2499 negotiated is 2 (server-to-peer). The JSON messages are as follows 2500 (line breaks are for readability only). 2502 ====== Initial Exchange ====== 2504 Identity response: 2505 noob@eap-noob.net 2507 EAP request (type 9): 2508 {"Type":9} 2510 EAP response (type 9): 2511 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":0} 2513 EAP request (type 1): 2514 {"Type":1,"Vers":[1],"PeerId":"07KRU6OgqX0HIeRFldnbSW","Realm":"no 2515 ob.example.com","Cryptosuites":[1],"Dirs":3,"ServerInfo":{"Name":" 2516 Example","Url":"https://noob.example.com/sendOOB"}} 2518 EAP response (type 1): 2519 {"Type":1,"Verp":1,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuitep 2520 ":1,"Dirp":2,"PeerInfo":{"Make":"Acme","Type":"None","Serial":"DU- 2521 9999","SSID":"Noob1","BSSID":"6c:19:8f:83:c2:80"}} 2523 EAP request (type 2): 2524 {"Type":2,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PKs":{"kty":"EC","crv 2525 ":"Curve25519","x":"hSDwCYkwp1R0i33ctD73Wg2_Og0mOBr066SpjqqbTmo"}, 2526 "Ns":"PYO7NVd9Af3BxEri1MI6hL8Ck49YxwCjSRPqlC1SPbw","SleepTime":60} 2528 EAP response (type 2): 2529 {"Type":2,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PKp":{"kty":"EC","crv 2530 ":"Curve25519","x":"3p7bfXt9wbTTW2HC7OQ1Nz-DQ8hbeGdNrfx-FG- 2531 IK08"},"Np":"HIvB6g0n2btpxEcU7YXnWB-451ED6L6veQQd6ugiPFU"} 2533 ====== Waiting Exchange ====== 2535 Identity response: 2536 noob@eap-noob.net 2538 EAP request (type 9): 2540 {"Type":9} 2542 EAP response (type 9): 2543 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":1} 2545 EAP request (type 3): 2546 {"Type":3,"PeerId":"07KRU6OgqX0HIeRFldnbSW","SleepTime":60} 2548 EAP response (type 3): 2549 {"Type":3,"PeerId":"07KRU6OgqX0HIeRFldnbSW"} 2551 ====== OOB Step ====== 2553 OOB message: 2554 P=07KRU6OgqX0HIeRFldnbSW&N=x3JlolaPciK4Wa6XlMJxtQ&H=WJ6Covspd50NT2 2555 RxkLHSeA 2557 ====== Completion Exchange ====== 2559 Identity response: 2560 noob@eap-noob.net 2562 EAP request (type 9): 2563 {"Type":9} 2565 EAP response (type 9): 2566 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":2} 2568 EAP request (type 8): 2569 {"Type":8,"PeerId":"07KRU6OgqX0HIeRFldnbSW"} 2571 EAP response (type 8): 2572 {"Type":8,"PeerId":"07KRU6OgqX0HIeRFldnbSW","NoobId":"U0OHwYGCS4nE 2573 kzk2TPIE6g"} 2575 EAP request (type 4): 2576 {"Type":4,"PeerId":"07KRU6OgqX0HIeRFldnbSW","NoobId":"U0OHwYGCS4nE 2577 kzk2TPIE6g","MACs":"APpnhlFLWS2pfJPH5S7N3yr6FJWocuaAiuVrhgh8Xko"} 2579 EAP response (type 4): 2580 {"Type":4,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACp":"hihGS4v8w4cDy_ 2581 yokNlOyQa87GRBLvMfmF9JFwJ6RrQ"} 2583 ====== Reconnect Exchange ====== 2585 Identity response: 2586 noob@eap-noob.net 2588 EAP request (type 9): 2589 {"Type":9} 2591 EAP response (type 9): 2592 {"Type":9,"PeerId":"07KRU6OgqX0HIeRFldnbSW","PeerState":3} 2594 EAP request (type 5): 2595 {"Type":5,"Vers":[1],"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuit 2596 es":[1],"Realm":"noob.example.com","ServerInfo":{"Name":"Example", 2597 "Url":"https://noob.example.com/sendOOB"}} 2599 EAP response (type 5): 2600 {"Type":5,"Verp":1,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Cryptosuitep 2601 ":1,"PeerInfo":{"Make":"Acme","Type":"None","Serial":"DU- 2602 9999","SSID":"Noob1","BSSID":"6c:19:8f:83:c2:80"}} 2604 EAP request (type 6): 2605 {"Type":6,"PeerId":"07KRU6OgqX0HIeRFldnbSW","KeyingMode":2,"Ns2":" 2606 RDLahHBlIgnmL_F_xcynrHurLPkCsrp3G3B_S82WUF4"} 2608 EAP response (type 6): 2609 {"Type":6,"PeerId":"07KRU6OgqX0HIeRFldnbSW","Np2":"jN0_V4P0JoTqwI9 2610 VHHQKd9ozUh7tQdc9ABd-j6oTy_4"} 2612 EAP request (type 7): 2613 {"Type":7,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACs2":"TT_B9w- 2614 o86C1c1O_rhNxzcf9gJa0_8SiIhyxQecdM70"} 2616 EAP response (type 7): 2617 {"Type":7,"PeerId":"07KRU6OgqX0HIeRFldnbSW","MACp2":"GS9f8Mw3mUFvj 2618 IDKS54U27xPt6umIrnVXOGLl-iFRKk"} 2620 Appendix G. TODO list 2622 o 2624 Appendix H. Version history 2626 o Version 01: 2628 * Fixed Reconnection Exchange. 2630 * URL examples. 2632 * Message examples. 2634 * Improved state transition (event) tables. 2636 o Version 02: 2638 * Reworked the rekeying and key derivation. 2640 * Increased internal key lengths and in-band nonce and HMAC 2641 lengths to 32 bytes. 2643 * Less data in the persistent EAP-NOOB association. 2645 * Updated reference [NIST-DH] to Revision 2 (2013). 2647 * Shorter suggested PeerId format. 2649 * Optimized the example of encoding OOB message as URL. 2651 * NoobId in Completion Exchange to differentiate between multiple 2652 valid Noob values. 2654 * List of application-specific parameters in appendix. 2656 * Clarified the equivalence of Unregistered state and no state. 2658 * Peer SHOULD probe the server regardless of the OOB channel 2659 direction. 2661 * Added new error messages. 2663 * Realm is part of the persistent association and can be updated. 2665 * Clarified error handling. 2667 * Updated message examples. 2669 * Explained roaming in appendix. 2671 * More accurate definition of timeout for the Noob nonce. 2673 * Additions to security considerations. 2675 o Version 03: 2677 * Clarified reasons for going to Reconnecting state. 2679 * Included Verp in persistent state. 2681 * Added appendix on suggested ServerInfo and PeerInfo fields. 2683 * Exporting PeerId and SessionId. 2685 * Explicitly specified next state after OOB Step. 2687 * Clarified the processing of an expired OOB message and 2688 unrecognized NoobId. 2690 * Enabled protocol version upgrade in Reconnect Exchange. 2692 * Explained handling of redundant received OOB messages. 2694 * Clarified where raw and base64url encoded values are used. 2696 * Cryptosuite must specify the detailed format of the JWK object. 2698 * Base64url encoding in JSON strings is done without padding. 2700 * Simplified explanation of PeerId, Realm and NAI. 2702 * Added error codes for private and experimental use. 2704 * Updated the security considerations. 2706 o Version 04: 2708 * Recovery from synchronization failure due to lost last 2709 response. 2711 o Version 05: 2713 * Kz identifier added to help recovery from lost last messages. 2715 * Error message codes changed for better structure. 2717 * Improved security considerations section. 2719 o Version 06: 2721 * Kz identifier removed to enable PeerId anonymization in the 2722 future. 2724 * Clarified text on when to use server-assigned realm. 2726 * Send PeerId and PeerState in a separate request-reponse pair, 2727 not in NAI. 2729 * New subsection for the common handshake in all exchanges to 2730 avoid repetition. 2732 o Version 07: 2734 * Updated example messages. 2736 * Added pointers to new implementation in Contiki. 2738 Appendix I. Acknowledgments 2740 Aleksi Peltonen modeled the protocol specification with the mCRL2 2741 formal specification language. Shiva Prasad TP and Raghavendra MS 2742 implemented parts of the protocol with wpa_supplicant and hostapd. 2743 Their inputs helped us in improving the specification. 2745 The authors would also like to thank Rhys Smith and Josh Howlett for 2746 providing valuable feedback as well as new use cases and requirements 2747 for the protocol. Thanks to Eric Rescorla, Darshak Thakore, Stefan 2748 Winter, and Hannes Tschofenig for interesting discussions in this 2749 problem space. 2751 Authors' Addresses 2753 Tuomas Aura 2754 Aalto University 2755 Aalto 00076 2756 Finland 2758 EMail: tuomas.aura@aalto.fi 2760 Mohit Sethi 2761 Ericsson 2762 Jorvas 02420 2763 Finland 2765 EMail: mohit@piuha.net