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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACE Working Group S. Gerdes 3 Internet-Draft O. Bergmann 4 Intended status: Standards Track C. Bormann 5 Expires: 9 September 2021 Universität Bremen TZI 6 G. Selander 7 Ericsson AB 8 L. Seitz 9 Combitech 10 8 March 2021 12 Datagram Transport Layer Security (DTLS) Profile for Authentication and 13 Authorization for Constrained Environments (ACE) 14 draft-ietf-ace-dtls-authorize-16 16 Abstract 18 This specification defines a profile of the ACE framework that allows 19 constrained servers to delegate client authentication and 20 authorization. The protocol relies on DTLS version 1.2 for 21 communication security between entities in a constrained network 22 using either raw public keys or pre-shared keys. A resource- 23 constrained server can use this protocol to delegate management of 24 authorization information to a trusted host with less severe 25 limitations regarding processing power and memory. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on 9 September 2021. 44 Copyright Notice 46 Copyright (c) 2021 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 51 license-info) in effect on the date of publication of this document. 52 Please review these documents carefully, as they describe your rights 53 and restrictions with respect to this document. Code Components 54 extracted from this document must include Simplified BSD License text 55 as described in Section 4.e of the Trust Legal Provisions and are 56 provided without warranty as described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 62 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4 63 3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 6 64 3.1. Communication Between the Client and the Authorization 65 Server . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 3.2. RawPublicKey Mode . . . . . . . . . . . . . . . . . . . . 7 67 3.2.1. Access Token Retrieval from the Authorization 68 Server . . . . . . . . . . . . . . . . . . . . . . . 7 69 3.2.2. DTLS Channel Setup Between Client and Resource 70 Server . . . . . . . . . . . . . . . . . . . . . . . 9 71 3.3. PreSharedKey Mode . . . . . . . . . . . . . . . . . . . . 10 72 3.3.1. Access Token Retrieval from the Authorization 73 Server . . . . . . . . . . . . . . . . . . . . . . . 10 74 3.3.2. DTLS Channel Setup Between Client and Resource 75 Server . . . . . . . . . . . . . . . . . . . . . . . 14 76 3.4. Resource Access . . . . . . . . . . . . . . . . . . . . . 16 77 4. Dynamic Update of Authorization Information . . . . . . . . . 18 78 5. Token Expiration . . . . . . . . . . . . . . . . . . . . . . 19 79 6. Secure Communication with an Authorization Server . . . . . . 20 80 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 81 7.1. Reuse of Existing Sessions . . . . . . . . . . . . . . . 21 82 7.2. Multiple Access Tokens . . . . . . . . . . . . . . . . . 22 83 7.3. Out-of-Band Configuration . . . . . . . . . . . . . . . . 22 84 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 85 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 86 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 87 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 88 11.1. Normative References . . . . . . . . . . . . . . . . . . 24 89 11.2. Informative References . . . . . . . . . . . . . . . . . 26 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 92 1. Introduction 94 This specification defines a profile of the ACE framework 95 [I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource 96 server use CoAP [RFC7252] over DTLS version 1.2 [RFC6347] to 97 communicate. The client obtains an access token, bound to a key (the 98 proof-of-possession key), from an authorization server to prove its 99 authorization to access protected resources hosted by the resource 100 server. Also, the client and the resource server are provided by the 101 authorization server with the necessary keying material to establish 102 a DTLS session. The communication between client and authorization 103 server may also be secured with DTLS. This specification supports 104 DTLS with Raw Public Keys (RPK) [RFC7250] and with Pre-Shared Keys 105 (PSK) [RFC4279]. 107 The ACE framework requires that client and server mutually 108 authenticate each other before any application data is exchanged. 109 DTLS enables mutual authentication if both client and server prove 110 their ability to use certain keying material in the DTLS handshake. 111 The authorization server assists in this process on the server side 112 by incorporating keying material (or information about keying 113 material) into the access token, which is considered a "proof of 114 possession" token. 116 In the RPK mode, the client proves that it can use the RPK bound to 117 the token and the server shows that it can use a certain RPK. 119 The resource server needs access to the token in order to complete 120 this exchange. For the RPK mode, the client must upload the access 121 token to the resource server before initiating the handshake, as 122 described in Section 5.8.1 of the ACE framework 123 [I-D.ietf-ace-oauth-authz]. 125 In the PSK mode, client and server show with the DTLS handshake that 126 they can use the keying material that is bound to the access token. 127 To transfer the access token from the client to the resource server, 128 the "psk_identity" parameter in the DTLS PSK handshake may be used 129 instead of uploading the token prior to the handshake. 131 As recommended in Section 5.8 of [I-D.ietf-ace-oauth-authz], this 132 specification uses CBOR web tokens to convey claims within an access 133 token issued by the server. While other formats could be used as 134 well, those are out of scope for this document. 136 1.1. Terminology 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 140 "OPTIONAL" in this document are to be interpreted as described in BCP 141 14 [RFC2119] [RFC8174] when, and only when, they appear in all 142 capitals, as shown here. 144 Readers are expected to be familiar with the terms and concepts 145 described in [I-D.ietf-ace-oauth-authz] and in 146 [I-D.ietf-ace-oauth-params]. 148 The authorization information (authz-info) resource refers to the 149 authorization information endpoint as specified in 150 [I-D.ietf-ace-oauth-authz]. The term "claim" is used in this 151 document with the same semantics as in [I-D.ietf-ace-oauth-authz], 152 i.e., it denotes information carried in the access token or returned 153 from introspection. 155 2. Protocol Overview 157 The CoAP-DTLS profile for ACE specifies the transfer of 158 authentication information and, if necessary, authorization 159 information between the client (C) and the resource server (RS) 160 during setup of a DTLS session for CoAP messaging. It also specifies 161 how the client can use CoAP over DTLS to retrieve an access token 162 from the authorization server (AS) for a protected resource hosted on 163 the resource server. As specified in Section 6.7 of 164 [I-D.ietf-ace-oauth-authz], use of DTLS for one or both of these 165 interactions is completely independent 167 This profile requires the client to retrieve an access token for 168 protected resource(s) it wants to access on the resource server as 169 specified in [I-D.ietf-ace-oauth-authz]. Figure 1 shows the typical 170 message flow in this scenario (messages in square brackets are 171 optional): 173 C RS AS 174 | [---- Resource Request ------>]| | 175 | | | 176 | [<-AS Request Creation Hints-] | | 177 | | | 178 | ------- Token Request ----------------------------> | 179 | | | 180 | <---------------------------- Access Token --------- | 181 | + Access Information | 183 Figure 1: Retrieving an Access Token 185 To determine the authorization server in charge of a resource hosted 186 at the resource server, the client can send an initial Unauthorized 187 Resource Request message to the resource server. The resource server 188 then denies the request and sends an AS Request Creation Hints 189 message containing the address of its authorization server back to 190 the client as specified in Section 5.1.2 of 191 [I-D.ietf-ace-oauth-authz]. 193 Once the client knows the authorization server's address, it can send 194 an access token request to the token endpoint at the authorization 195 server as specified in [I-D.ietf-ace-oauth-authz]. As the access 196 token request as well as the response may contain confidential data, 197 the communication between the client and the authorization server 198 must be confidentiality-protected and ensure authenticity. The 199 client may have been registered at the authorization server via the 200 OAuth 2.0 client registration mechanism as outlined in Section 5.3 of 201 [I-D.ietf-ace-oauth-authz]. 203 The access token returned by the authorization server can then be 204 used by the client to establish a new DTLS session with the resource 205 server. When the client intends to use an asymmetric proof-of- 206 possession key in the DTLS handshake with the resource server, the 207 client MUST upload the access token to the authz-info resource, i.e. 208 the authz-info endpoint, on the resource server before starting the 209 DTLS handshake, as described in Section 5.8.1 of 210 [I-D.ietf-ace-oauth-authz]. In case the client uses a symmetric 211 proof-of-possession key in the DTLS handshake, the procedure as above 212 MAY be used, or alternatively, the access token MAY instead be 213 transferred in the DTLS ClientKeyExchange message (see 214 Section 3.3.2). In any case, DTLS MUST be used in a mode that 215 provides replay protection. 217 Figure 2 depicts the common protocol flow for the DTLS profile after 218 the client has retrieved the access token from the authorization 219 server, AS. 221 C RS AS 222 | [--- Access Token ------>] | | 223 | | | 224 | <== DTLS channel setup ==> | | 225 | | | 226 | == Authorized Request ===> | | 227 | | | 228 | <=== Protected Resource == | | 230 Figure 2: Protocol overview 232 3. Protocol Flow 234 The following sections specify how CoAP is used to interchange 235 access-related data between the resource server, the client and the 236 authorization server so that the authorization server can provide the 237 client and the resource server with sufficient information to 238 establish a secure channel, and convey authorization information 239 specific for this communication relationship to the resource server. 241 Section 3.1 describes how the communication between the client (C) 242 and the authorization server (AS) must be secured. Depending on the 243 used CoAP security mode (see also Section 9 of [RFC7252], the Client- 244 to-AS request, AS-to-Client response (see Section 5.6 of 245 [I-D.ietf-ace-oauth-authz]) and DTLS session establishment carry 246 slightly different information. Section 3.2 addresses the use of raw 247 public keys while Section 3.3 defines how pre-shared keys are used in 248 this profile. 250 3.1. Communication Between the Client and the Authorization Server 252 To retrieve an access token for the resource that the client wants to 253 access, the client requests an access token from the authorization 254 server. Before the client can request the access token, the client 255 and the authorization server MUST establish a secure communication 256 channel. This profile assumes that the keying material to secure 257 this communication channel has securely been obtained either by 258 manual configuration or in an automated provisioning process. The 259 following requirements in alignment with Section 6.5 of 260 [I-D.ietf-ace-oauth-authz] therefore must be met: 262 * The client MUST securely have obtained keying material to 263 communicate with the authorization server. 265 * Furthermore, the client MUST verify that the authorization server 266 is authorized to provide access tokens (including authorization 267 information) about the resource server to the client, and that 268 this authorization information about the authorization server is 269 still valid. 271 * Also, the authorization server MUST securely have obtained keying 272 material for the client, and obtained authorization rules approved 273 by the resource owner (RO) concerning the client and the resource 274 server that relate to this keying material. 276 The client and the authorization server MUST use their respective 277 keying material for all exchanged messages. How the security 278 association between the client and the authorization server is 279 bootstrapped is not part of this document. The client and the 280 authorization server must ensure the confidentiality, integrity and 281 authenticity of all exchanged messages within the ACE protocol. 283 Section 6 specifies how communication with the authorization server 284 is secured. 286 3.2. RawPublicKey Mode 288 When the client uses RawPublicKey authentication, the procedure is as 289 described in the following. 291 3.2.1. Access Token Retrieval from the Authorization Server 293 After the client and the authorization server mutually authenticated 294 each other and validated each other's authorization, the client sends 295 a token request to the authorization server's token endpoint. The 296 client MUST add a "req_cnf" object carrying either its raw public key 297 or a unique identifier for a public key that it has previously made 298 known to the authorization server. It is RECOMMENDED that the client 299 uses DTLS with the same keying material to secure the communication 300 with the authorization server, proving possession of the key as part 301 of the token request. Other mechanisms for proving possession of the 302 key may be defined in the future. 304 An example access token request from the client to the authorization 305 server is depicted in Figure 3. 307 POST coaps://as.example.com/token 308 Content-Format: application/ace+cbor 309 Payload: 310 { 311 grant_type : client_credentials, 312 req_aud : "tempSensor4711", 313 req_cnf : { 314 COSE_Key : { 315 kty : EC2, 316 crv : P-256, 317 x : h'e866c35f4c3c81bb96a1...', 318 y : h'2e25556be097c8778a20...' 319 } 320 } 321 } 323 Figure 3: Access Token Request Example for RPK Mode 325 The example shows an access token request for the resource identified 326 by the string "tempSensor4711" on the authorization server using a 327 raw public key. 329 The authorization server MUST check if the client that it 330 communicates with is associated with the RPK in the "req_cnf" 331 parameter before issuing an access token to it. If the authorization 332 server determines that the request is to be authorized according to 333 the respective authorization rules, it generates an access token 334 response for the client. The access token MUST be bound to the RPK 335 of the client by means of the "cnf" claim. 337 The response MAY contain a "profile" parameter with the value 338 "coap_dtls" to indicate that this profile MUST be used for 339 communication between the client and the resource server. The 340 "profile" may be specified out-of-band, in which case it does not 341 have to be sent. The response also contains an access token with 342 information for the resource server about the client's public key. 343 The authorization server MUST return in its response the parameter 344 "rs_cnf" unless it is certain that the client already knows the 345 public key of the resource server. The authorization server MUST 346 ascertain that the RPK specified in "rs_cnf" belongs to the resource 347 server that the client wants to communicate with. The authorization 348 server MUST protect the integrity of the access token such that the 349 resource server can detect unauthorized changes. If the access token 350 contains confidential data, the authorization server MUST also 351 protect the confidentiality of the access token. 353 The client MUST ascertain that the access token response belongs to a 354 certain previously sent access token request, as the request may 355 specify the resource server with which the client wants to 356 communicate. 358 An example access token response from the authorization server to the 359 client is depicted in Figure 4. Here, the contents of the 360 "access_token" claim have been truncated to improve readability. 361 Caching proxies process the Max-Age option in the CoAP response which 362 has a default value of 60 seconds (Section 5.6.1 of [RFC7252]). The 363 authorization server SHOULD adjust the Max-Age option such that it 364 does not exceed the "expires_in" parameter to avoid stale responses. 366 2.01 Created 367 Content-Format: application/ace+cbor 368 Max-Age: 3560 369 Payload: 370 { 371 access_token : b64'SlAV32hkKG... 372 (remainder of CWT omitted for brevity; 373 CWT contains the client's RPK in the cnf claim)', 374 expires_in : 3600, 375 rs_cnf : { 376 COSE_Key : { 377 kty : EC2, 378 crv : P-256, 379 x : h'd7cc072de2205bdc1537...', 380 y : h'f95e1d4b851a2cc80fff...' 381 } 382 } 383 } 385 Figure 4: Access Token Response Example for RPK Mode 387 3.2.2. DTLS Channel Setup Between Client and Resource Server 389 Before the client initiates the DTLS handshake with the resource 390 server, the client MUST send a "POST" request containing the obtained 391 access token to the authz-info resource hosted by the resource 392 server. After the client receives a confirmation that the resource 393 server has accepted the access token, it SHOULD proceed to establish 394 a new DTLS channel with the resource server. The client MUST use its 395 correct public key in the DTLS handshake. If the authorization 396 server has specified a "cnf" field in the access token response, the 397 client MUST use this key. Otherwise, the client MUST use the public 398 key that it specified in the "req_cnf" of the access token request. 399 The client MUST specify this public key in the SubjectPublicKeyInfo 400 structure of the DTLS handshake as described in [RFC7250]. 402 To be consistent with [RFC7252] which allows for shortened MAC tags 403 in constrained environments, an implementation that supports the RPK 404 mode of this profile MUST at least support the ciphersuite 405 TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. As discussed in 406 [RFC7748], new ECC curves have been defined recently that are 407 considered superior to the so-called NIST curves. This specification 408 therefore mandates implementation support for curve25519 (cf. 409 [RFC8032], [RFC8422]) as this curve said to be efficient and less 410 dangerous regarding implementation errors than the secp256r1 curve 411 mandated in [RFC7252]. 413 The resource server MUST check if the access token is still valid, if 414 the resource server is the intended destination (i.e., the audience) 415 of the token, and if the token was issued by an authorized 416 authorization server. The access token is constructed by the 417 authorization server such that the resource server can associate the 418 access token with the Client's public key. The "cnf" claim MUST 419 contain either the client's RPK or, if the key is already known by 420 the resource server (e.g., from previous communication), a reference 421 to this key. If the authorization server has no certain knowledge 422 that the Client's key is already known to the resource server, the 423 Client's public key MUST be included in the access token's "cnf" 424 parameter. If CBOR web tokens [RFC8392] are used (as recommended in 425 [I-D.ietf-ace-oauth-authz]), keys MUST be encoded as specified in 426 [RFC8747]. A resource server MUST have the capacity to store one 427 access token for every proof-of-possession key of every authorized 428 client. 430 The raw public key used in the DTLS handshake with the client MUST 431 belong to the resource server. If the resource server has several 432 raw public keys, it needs to determine which key to use. The 433 authorization server can help with this decision by including a "cnf" 434 parameter in the access token that is associated with this 435 communication. In this case, the resource server MUST use the 436 information from the "cnf" field to select the proper keying 437 material. 439 Thus, the handshake only finishes if the client and the resource 440 server are able to use their respective keying material. 442 3.3. PreSharedKey Mode 444 When the client uses pre-shared key authentication, the procedure is 445 as described in the following. 447 3.3.1. Access Token Retrieval from the Authorization Server 449 To retrieve an access token for the resource that the client wants to 450 access, the client MAY include a "cnf" object carrying an identifier 451 for a symmetric key in its access token request to the authorization 452 server. This identifier can be used by the authorization server to 453 determine the shared secret to construct the proof-of-possession 454 token. The authorization server MUST check if the identifier refers 455 to a symmetric key that was previously generated by the authorization 456 server as a shared secret for the communication between this client 457 and the resource server. If no such symmetric key was found, the 458 authorization server MUST generate a new symmetric key that is 459 returned in its response to the client. 461 The authorization server MUST determine the authorization rules for 462 the client it communicates with as defined by the resource owner and 463 generate the access token accordingly. If the authorization server 464 authorizes the client, it returns an AS-to-Client response. If the 465 profile parameter is present, it is set to "coap_dtls". The 466 authorization server MUST ascertain that the access token is 467 generated for the resource server that the client wants to 468 communicate with. Also, the authorization server MUST protect the 469 integrity of the access token to ensure that the resource server can 470 detect unauthorized changes. If the token contains confidential data 471 such as the symmetric key, the confidentiality of the token MUST also 472 be protected. Depending on the requested token type and algorithm in 473 the access token request, the authorization server adds access 474 Information to the response that provides the client with sufficient 475 information to setup a DTLS channel with the resource server. The 476 authorization server adds a "cnf" parameter to the access information 477 carrying a "COSE_Key" object that informs the client about the shared 478 secret that is to be used between the client and the resource server. 479 To convey the same secret to the resource server, the authorization 480 server can include it directly in the access token by means of the 481 "cnf" claim or provide sufficient information to enable the resource 482 server to derive the shared secret from the access token. As an 483 alternative, the resource server MAY use token introspection to 484 retrieve the keying material for this access token directly from the 485 authorization server. 487 An example access token request for an access token with a symmetric 488 proof-of-possession key is illustrated in Figure 5. 490 POST coaps://as.example.com/token 491 Content-Format: application/ace+cbor 492 Payload: 493 { 494 audience : "smokeSensor1807", 495 } 497 Figure 5: Example Access Token Request, (implicit) symmetric PoP-key 499 A corresponding example access token response is illustrated in 500 Figure 6. In this example, the authorization server returns a 2.01 501 response containing a new access token (truncated to improve 502 readability) and information for the client, including the symmetric 503 key in the cnf claim. The information is transferred as a CBOR data 504 structure as specified in [I-D.ietf-ace-oauth-authz]. 506 2.01 Created 507 Content-Format: application/ace+cbor 508 Max-Age: 85800 509 Payload: 510 { 511 access_token : h'd08343a10... 512 (remainder of CWT omitted for brevity) 513 token_type : PoP, 514 expires_in : 86400, 515 profile : coap_dtls, 516 cnf : { 517 COSE_Key : { 518 kty : symmetric, 519 kid : h'3d027833fc6267ce', 520 k : h'73657373696f6e6b6579' 521 } 522 } 523 } 525 Figure 6: Example Access Token Response, symmetric PoP-key 527 The access token also comprises a "cnf" claim. This claim usually 528 contains a "COSE_Key" object that carries either the symmetric key 529 itself or a key identifier that can be used by the resource server to 530 determine the secret key it shares with the client. If the access 531 token carries a symmetric key, the access token MUST be encrypted 532 using a "COSE_Encrypt0" structure. The authorization server MUST use 533 the keying material shared with the resource server to encrypt the 534 token. 536 The "cnf" structure in the access token is provided in Figure 7. 538 cnf : { 539 COSE_Key : { 540 kty : symmetric, 541 kid : h'3d027833fc6267ce' 542 } 543 } 545 Figure 7: Access Token without Keying Material 547 A response that declines any operation on the requested resource is 548 constructed according to Section 5.2 of [RFC6749], (cf. 549 Section 5.6.3. of [I-D.ietf-ace-oauth-authz]). Figure 8 shows an 550 example for a request that has been rejected due to invalid request 551 parameters. 553 4.00 Bad Request 554 Content-Format: application/ace+cbor 555 Payload: 556 { 557 error : invalid_request 558 } 560 Figure 8: Example Access Token Response With Reject 562 The method for how the resource server determines the symmetric key 563 from an access token containing only a key identifier is application- 564 specific; the remainder of this section provides one example. 566 The authorization server and the resource server are assumed to share 567 a key derivation key used to derive the symmetric key shared with the 568 client from the key identifier in the access token. The key 569 derivation key may be derived from some other secret key shared 570 between the authorization server and the resource server. This key 571 needs to be securely stored and processed in the same way as the key 572 used to protect the communication between the authorization server 573 and the resource server. 575 Knowledge of the symmetric key shared with the client must not reveal 576 any information about the key derivation key or other secret keys 577 shared between the authorization server and resource server. 579 In order to generate a new symmetric key to be used by client and 580 resource server, the authorization server generates a new key 581 identifier which MUST be unique among all key identifiers used by the 582 authorization server for this resource server. The authorization 583 server then uses the key derivation key shared with the resource 584 server to derive the symmetric key as specified below. Instead of 585 providing the keying material in the access token, the authorization 586 server includes the key identifier in the "kid" parameter, see 587 Figure 7. This key identifier enables the resource server to 588 calculate the symmetric key used for the communication with the 589 client using the key derivation key and a KDF to be defined by the 590 application, for example HKDF-SHA-256. The key identifier picked by 591 the authorization server MUST be unique for each access token where a 592 unique symmetric key is required. 594 In this example, HKDF consists of the composition of the HKDF-Extract 595 and HKDF-Expand steps [RFC5869]. The symmetric key is derived from 596 the key identifier, the key derivation key and other data: 598 OKM = HKDF(salt, IKM, info, L), 600 where: 602 * OKM, the output keying material, is the derived symmetric key 604 * salt is the empty byte string 606 * IKM, the input keying material, is the key derivation key as 607 defined above 609 * info is the serialization of a CBOR array consisting of 610 ([RFC8610]): 612 info = [ 613 type : tstr, 614 L : uint, 615 access_token: bytes 616 ] 618 where: 620 * type is set to the constant text string "ACE-CoAP-DTLS-key- 621 derivation", 623 * L is the size of the symmetric key in bytes, 625 * access_token is the content of the "access_token" field as 626 transferred from the authorization server to the resource server. 628 All CBOR data types are encoded in CBOR using preferred serialization 629 and deterministic encoding as specified in Section 4 of [RFC8949]. 630 This implies in particular that the "type" and "L" components use the 631 minimum length encoding. The content of the "access_token" field is 632 treated as opaque data for the purpose of key derivation. 634 Use of a unique (per resource server) "kid" and the use of a key 635 derivation IKM that MUST be unique per authorization server/resource 636 server pair as specified above will ensure that the derived key is 637 not shared across multiple clients. However, to additionally provide 638 variation in the derived key across different tokens used by the same 639 client, it is additionally RECOMMENDED to include the "iat" claim and 640 either the "exp" or "exi" claims in the access token. 642 3.3.2. DTLS Channel Setup Between Client and Resource Server 644 When a client receives an access token response from an authorization 645 server, the client MUST check if the access token response is bound 646 to a certain previously sent access token request, as the request may 647 specify the resource server with which the client wants to 648 communicate. 650 The client checks if the payload of the access token response 651 contains an "access_token" parameter and a "cnf" parameter. With 652 this information the client can initiate the establishment of a new 653 DTLS channel with a resource server. To use DTLS with pre-shared 654 keys, the client follows the PSK key exchange algorithm specified in 655 Section 2 of [RFC4279] using the key conveyed in the "cnf" parameter 656 of the AS response as PSK when constructing the premaster secret. To 657 be consistent with the recommendations in [RFC7252] a client is 658 expected to offer at least the ciphersuite TLS_PSK_WITH_AES_128_CCM_8 659 [RFC6655] to the resource server. 661 In PreSharedKey mode, the knowledge of the shared secret by the 662 client and the resource server is used for mutual authentication 663 between both peers. Therefore, the resource server must be able to 664 determine the shared secret from the access token. Following the 665 general ACE authorization framework, the client can upload the access 666 token to the resource server's authz-info resource before starting 667 the DTLS handshake. The client then needs to indicate during the 668 DTLS handshake which previously uploaded access token it intends to 669 use. To do so, it MUST create a "COSE_Key" structure with the "kid" 670 that was conveyed in the "rs_cnf" claim in the token response from 671 the authorization server and the key type "symmetric". This 672 structure then is included as the only element in the "cnf" structure 673 that is used as value for "psk_identity" as shown in Figure 9. 675 { cnf : { 676 COSE_Key : { 677 kty: symmetric, 678 kid : h'3d027833fc6267ce' 679 } 680 } 681 } 683 Figure 9: Access token containing a single kid parameter 685 As an alternative to the access token upload, the client can provide 686 the most recent access token in the "psk_identity" field of the 687 ClientKeyExchange message. To do so, the client MUST treat the 688 contents of the "access_token" field from the AS-to-Client response 689 as opaque data as specified in Section 4.2 of [RFC7925] and not 690 perform any re-coding. This allows the resource server to retrieve 691 the shared secret directly from the "cnf" claim of the access token. 693 If a resource server receives a ClientKeyExchange message that 694 contains a "psk_identity" with a length greater than zero, it MUST 695 parse the contents of the "psk_identity" field as CBOR data structure 696 and process the contents as following: 698 * If the data contains a "cnf" field with a "COSE_Key" structure 699 with a "kid", the resource server continues the DTLS handshake 700 with the associated key that corresponds to this kid. 702 * If the data comprises additional CWT information, this information 703 must be stored as an access token for this DTLS association before 704 continuing with the DTLS handshake. 706 If the contents of the "psk_identity" do not yield sufficient 707 information to select a valid access token for the requesting client, 708 the resource server aborts the DTLS handshake with an 709 "illegal_parameter" alert. 711 When the resource server receives an access token, it MUST check if 712 the access token is still valid, if the resource server is the 713 intended destination (i.e., the audience of the token), and if the 714 token was issued by an authorized authorization server. This 715 specification implements access tokens as proof-of-possession tokens. 716 Therefore, the access token is bound to a symmetric PoP key that is 717 used as shared secret between the client and the resource server. A 718 resource server MUST have the capacity to store one access token for 719 every proof-of-possession key of every authorized client. The 720 resource server may use token introspection [RFC7662] on the access 721 token to retrieve more information about the specific token. The use 722 of introspection is out of scope for this specification. 724 While the client can retrieve the shared secret from the contents of 725 the "cnf" parameter in the AS-to-Client response, the resource server 726 uses the information contained in the "cnf" claim of the access token 727 to determine the actual secret when no explicit "kid" was provided in 728 the "psk_identity" field. If key derivation is used, the resource 729 server uses the "COSE_KDF_Context" information as described above. 731 3.4. Resource Access 733 Once a DTLS channel has been established as described in Section 3.2 734 or Section 3.3, respectively, the client is authorized to access 735 resources covered by the access token it has uploaded to the authz- 736 info resource hosted by the resource server. 738 With the successful establishment of the DTLS channel, the client and 739 the resource server have proven that they can use their respective 740 keying material. An access token that is bound to the client's 741 keying material is associated with the channel. According to 742 Section 5.8.1 of [I-D.ietf-ace-oauth-authz], there should be only one 743 access token for each client. New access tokens issued by the 744 authorization server SHOULD replace previously issued access tokens 745 for the respective client. The resource server therefore needs a 746 common understanding with the authorization server how access tokens 747 are ordered. The authorization server may, e.g., specify a "cti" 748 claim for the access token (see Section 5.8.3 of 749 [I-D.ietf-ace-oauth-authz]) to employ a strict order. 751 Any request that the resource server receives on a DTLS channel that 752 is tied to an access token via its keying material MUST be checked 753 against the authorization rules that can be determined with the 754 access token. The resource server MUST check for every request if 755 the access token is still valid. If the token has expired, the 756 resource server MUST remove it. Incoming CoAP requests that are not 757 authorized with respect to any access token that is associated with 758 the client MUST be rejected by the resource server with 4.01 759 response. The response SHOULD include AS Request Creation Hints as 760 described in Section 5.1.1 of [I-D.ietf-ace-oauth-authz]. 762 The resource server MUST only accept an incoming CoAP request as 763 authorized if the following holds: 765 1. The message was received on a secure channel that has been 766 established using the procedure defined in this document. 768 2. The authorization information tied to the sending client is 769 valid. 771 3. The request is destined for the resource server. 773 4. The resource URI specified in the request is covered by the 774 authorization information. 776 5. The request method is an authorized action on the resource with 777 respect to the authorization information. 779 Incoming CoAP requests received on a secure DTLS channel that are not 780 thus authorized MUST be rejected according to Section 5.8.2 of 781 [I-D.ietf-ace-oauth-authz] 783 1. with response code 4.03 (Forbidden) when the resource URI 784 specified in the request is not covered by the authorization 785 information, and 787 2. with response code 4.05 (Method Not Allowed) when the resource 788 URI specified in the request covered by the authorization 789 information but not the requested action. 791 The client MUST ascertain that its keying material is still valid 792 before sending a request or processing a response. If the client 793 recently has updated the access token (see Section 4), it must be 794 prepared that its request is still handled according to the previous 795 authorization rules as there is no strict ordering between access 796 token uploads and resource access messages. See also Section 7.2 for 797 a discussion of access token processing. 799 If the client gets an error response containing AS Request Creation 800 Hints (cf. Section 5.1.2 of [I-D.ietf-ace-oauth-authz] as response 801 to its requests, it SHOULD request a new access token from the 802 authorization server in order to continue communication with the 803 resource server. 805 Unauthorized requests that have been received over a DTLS session 806 SHOULD be treated as non-fatal by the resource server, i.e., the DTLS 807 session SHOULD be kept alive until the associated access token has 808 expired. 810 4. Dynamic Update of Authorization Information 812 Resource servers must only use a new access token to update the 813 authorization information for a DTLS session if the keying material 814 that is bound to the token is the same that was used in the DTLS 815 handshake. By associating the access tokens with the identifier of 816 an existing DTLS session, the authorization information can be 817 updated without changing the cryptographic keys for the DTLS 818 communication between the client and the resource server, i.e. an 819 existing session can be used with updated permissions. 821 The client can therefore update the authorization information stored 822 at the resource server at any time without changing an established 823 DTLS session. To do so, the client requests a new access token from 824 the authorization server for the intended action on the respective 825 resource and uploads this access token to the authz-info resource on 826 the resource server. 828 Figure 10 depicts the message flow where the client requests a new 829 access token after a security association between the client and the 830 resource server has been established using this protocol. If the 831 client wants to update the authorization information, the token 832 request MUST specify the key identifier of the proof-of-possession 833 key used for the existing DTLS channel between the client and the 834 resource server in the "kid" parameter of the Client-to-AS request. 835 The authorization server MUST verify that the specified "kid" denotes 836 a valid verifier for a proof-of-possession token that has previously 837 been issued to the requesting client. Otherwise, the Client-to-AS 838 request MUST be declined with the error code "unsupported_pop_key" as 839 defined in Section 5.6.3 of [I-D.ietf-ace-oauth-authz]. 841 When the authorization server issues a new access token to update 842 existing authorization information, it MUST include the specified 843 "kid" parameter in this access token. A resource server MUST replace 844 the authorization information of any existing DTLS session that is 845 identified by this key identifier with the updated authorization 846 information. 848 C RS AS 849 | <===== DTLS channel =====> | | 850 | + Access Token | | 851 | | | 852 | --- Token Request ----------------------------> | 853 | | | 854 | <---------------------------- New Access Token - | 855 | + Access Information | 856 | | | 857 | --- Update /authz-info --> | | 858 | New Access Token | | 859 | | | 860 | == Authorized Request ===> | | 861 | | | 862 | <=== Protected Resource == | | 864 Figure 10: Overview of Dynamic Update Operation 866 5. Token Expiration 868 The resource server MUST delete access tokens that are no longer 869 valid. DTLS associations that have been setup in accordance with 870 this profile are always tied to specific tokens (which may be 871 exchanged with a dynamic update as described in Section 4). As 872 tokens may become invalid at any time (e.g., because they have 873 expired), the association may become useless at some point. A 874 resource server therefore MUST terminate existing DTLS association 875 after the last access token associated with this association has 876 expired. 878 As specified in Section 5.8.3 of [I-D.ietf-ace-oauth-authz], the 879 resource server MUST notify the client with an error response with 880 code 4.01 (Unauthorized) for any long running request before 881 terminating the association. 883 6. Secure Communication with an Authorization Server 885 As specified in the ACE framework (Sections 5.6 and 5.7 of 886 [I-D.ietf-ace-oauth-authz]), the requesting entity (the resource 887 server and/or the client) and the authorization server communicate 888 via the token endpoint or introspection endpoint. The use of CoAP 889 and DTLS for this communication is RECOMMENDED in this profile. 890 Other protocols fulfilling the security requirements defined in 891 Section 5 of [I-D.ietf-ace-oauth-authz] MAY be used instead. 893 How credentials (e.g., PSK, RPK, X.509 cert) for using DTLS with the 894 authorization server are established is out of scope for this 895 profile. 897 If other means of securing the communication with the authorization 898 server are used, the communication security requirements from 899 Section 6.2 of [I-D.ietf-ace-oauth-authz] remain applicable. 901 7. Security Considerations 903 This document specifies a profile for the Authentication and 904 Authorization for Constrained Environments (ACE) framework 905 [I-D.ietf-ace-oauth-authz]. As it follows this framework's general 906 approach, the general security considerations from Section 6 of 907 [I-D.ietf-ace-oauth-authz] also apply to this profile. 909 The authorization server must ascertain that the keying material for 910 the client that it provides to the resource server actually is 911 associated with this client. Malicious clients may hand over access 912 tokens containing their own access permissions to other entities. 913 This problem cannot be completely eliminated. Nevertheless, in RPK 914 mode it should not be possible for clients to request access tokens 915 for arbitrary public keys: if the client can cause the authorization 916 server to issue a token for a public key without proving possession 917 of the corresponding private key, this allows for identity misbinding 918 attacks where the issued token is usable by an entity other than the 919 intended one. The authorization server therefore at some point needs 920 to validate that the client can actually use the private key 921 corresponding to the client's public key. 923 When using pre-shared keys provisioned by the authorization server, 924 the security level depends on the randomness of PSK, and the security 925 of the TLS cipher suite and key exchange algorithm. As this 926 specification targets at constrained environments, message payloads 927 exchanged between the client and the resource server are expected to 928 be small and rare. CoAP [RFC7252] mandates the implementation of 929 cipher suites with abbreviated, 8-byte tags for message integrity 930 protection. For consistency, this profile requires implementation of 931 the same cipher suites. For application scenarios where the cost of 932 full-width authentication tags is low compared to the overall amount 933 of data being transmitted, the use of cipher suites with 16-byte 934 integrity protection tags is preferred. 936 The PSK mode of this profile offers a distribution mechanism to 937 convey authorization tokens together with a shared secret to a client 938 and a server. As this specification aims at constrained devices and 939 uses CoAP [RFC7252] as transfer protocol, at least the ciphersuite 940 TLS_PSK_WITH_AES_128_CCM_8 [RFC6655] should be supported. The access 941 tokens and the corresponding shared secrets generated by the 942 authorization server are expected to be sufficiently short-lived to 943 provide similar forward-secrecy properties to using ephemeral Diffie- 944 Hellman (DHE) key exchange mechanisms. For longer-lived access 945 tokens, DHE ciphersuites should be used. 947 Constrained devices that use DTLS [RFC6347] are inherently vulnerable 948 to Denial of Service (DoS) attacks as the handshake protocol requires 949 creation of internal state within the device. This is specifically 950 of concern where an adversary is able to intercept the initial cookie 951 exchange and interject forged messages with a valid cookie to 952 continue with the handshake. A similar issue exists with the 953 unprotected authorization information endpoint when the resource 954 server needs to keep valid access tokens for a long time. 955 Adversaries could fill up the constrained resource server's internal 956 storage for a very long time with interjected or otherwise retrieved 957 valid access tokens. To mitigate against this, the resource server 958 should set a time boundary until an access token that has not been 959 used until then will be deleted. 961 The protection of access tokens that are stored in the authorization 962 information endpoint depends on the keying material that is used 963 between the authorization server and the resource server: The 964 resource server must ensure that it processes only access tokens that 965 are (encrypted and) integrity-protected by an authorization server 966 that is authorized to provide access tokens for the resource server. 968 7.1. Reuse of Existing Sessions 970 To avoid the overhead of a repeated DTLS handshake, [RFC7925] 971 recommends session resumption [RFC5077] to reuse session state from 972 an earlier DTLS association and thus requires client side 973 implementation. In this specification, the DTLS session is subject 974 to the authorization rules denoted by the access token that was used 975 for the initial setup of the DTLS association. Enabling session 976 resumption would require the server to transfer the authorization 977 information with the session state in an encrypted SessionTicket to 978 the client. Assuming that the server uses long-lived keying 979 material, this could open up attacks due to the lack of forward 980 secrecy. Moreover, using this mechanism, a client can resume a DTLS 981 session without proving the possession of the PoP key again. 982 Therefore, the use of session resumption is NOT RECOMMENDED for 983 resource servers. 985 Since renegotiation of DTLS associations is prone to attacks as well, 986 [RFC7925] requires clients to decline any renogiation attempt. A 987 server that wants to initiate re-keying therefore SHOULD periodically 988 force a full handshake. 990 7.2. Multiple Access Tokens 992 The use of multiple access tokens for a single client increases the 993 strain on the resource server as it must consider every access token 994 and calculate the actual permissions of the client. Also, tokens may 995 contradict each other which may lead the server to enforce wrong 996 permissions. If one of the access tokens expires earlier than 997 others, the resulting permissions may offer insufficient protection. 998 Developers SHOULD avoid using multiple access tokens for a client. 1000 Even when a single access token per client is used, an attacker could 1001 compromise the dynamic update mechanism for existing DTLS connections 1002 by delaying or reordering packets destined for the authz-info 1003 endpoint. Thus, the order in which operations occur at the resource 1004 server (and thus which authorization info is used to process a given 1005 client request) cannot be guaranteed. Especially in the presence of 1006 later-issued access tokens that reduce the client's permissions from 1007 the initial access token, it is impossible to guarantee that the 1008 reduction in authorization will take effect prior to the expiration 1009 of the original token. 1011 7.3. Out-of-Band Configuration 1013 To communicate securely, the authorization server, the client and the 1014 resource server require certain information that must be exchanged 1015 outside the protocol flow described in this document. The 1016 authorization server must have obtained authorization information 1017 concerning the client and the resource server that is approved by the 1018 resource owner as well as corresponding keying material. The 1019 resource server must have received authorization information approved 1020 by the resource owner concerning its authorization managers and the 1021 respective keying material. The client must have obtained 1022 authorization information concerning the authorization server 1023 approved by its owner as well as the corresponding keying material. 1024 Also, the client's owner must have approved of the client's 1025 communication with the resource server. The client and the 1026 authorization server must have obtained a common understanding how 1027 this resource server is identified to ensure that the client obtains 1028 access token and keying material for the correct resource server. If 1029 the client is provided with a raw public key for the resource server, 1030 it must be ascertained to which resource server (which identifier and 1031 authorization information) the key is associated. All authorization 1032 information and keying material must be kept up to date. 1034 8. Privacy Considerations 1036 This privacy considerations from Section 7 of the 1037 [I-D.ietf-ace-oauth-authz] apply also to this profile. 1039 An unprotected response to an unauthorized request may disclose 1040 information about the resource server and/or its existing 1041 relationship with the client. It is advisable to include as little 1042 information as possible in an unencrypted response. When a DTLS 1043 session between an authenticated client and the resource server 1044 already exists, more detailed information MAY be included with an 1045 error response to provide the client with sufficient information to 1046 react on that particular error. 1048 Also, unprotected requests to the resource server may reveal 1049 information about the client, e.g., which resources the client 1050 attempts to request or the data that the client wants to provide to 1051 the resource server. The client SHOULD NOT send confidential data in 1052 an unprotected request. 1054 Note that some information might still leak after DTLS session is 1055 established, due to observable message sizes, the source, and the 1056 destination addresses. 1058 9. IANA Considerations 1060 The following registrations are done for the ACE OAuth Profile 1061 Registry following the procedure specified in 1062 [I-D.ietf-ace-oauth-authz]. 1064 Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]" 1065 with the RFC number of this specification and delete this paragraph. 1067 Profile name: coap_dtls 1069 Profile Description: Profile for delegating client authentication and 1070 authorization in a constrained environment by establishing a Datagram 1071 Transport Layer Security (DTLS) channel between resource-constrained 1072 nodes. 1074 Profile ID: TBD (suggested: 1) 1075 Change Controller: IESG 1077 Reference: [RFC-XXXX] 1079 10. Acknowledgments 1081 Special thanks to Jim Schaad for his contributions and reviews of 1082 this document and to Ben Kaduk for his thorough reviews of this 1083 document. Thanks also to Paul Kyzivat for his review. 1085 Ludwig Seitz worked on this document as part of the CelticNext 1086 projects CyberWI, and CRITISEC with funding from Vinnova. 1088 11. References 1090 11.1. Normative References 1092 [I-D.ietf-ace-oauth-authz] 1093 Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and 1094 H. Tschofenig, "Authentication and Authorization for 1095 Constrained Environments (ACE) using the OAuth 2.0 1096 Framework (ACE-OAuth)", Work in Progress, Internet-Draft, 1097 draft-ietf-ace-oauth-authz-36, 16 November 2020, 1098 . 1101 [I-D.ietf-ace-oauth-params] 1102 Seitz, L., "Additional OAuth Parameters for Authorization 1103 in Constrained Environments (ACE)", Work in Progress, 1104 Internet-Draft, draft-ietf-ace-oauth-params-13, 28 April 1105 2020, . 1108 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1109 Requirement Levels", BCP 14, RFC 2119, 1110 DOI 10.17487/RFC2119, March 1997, 1111 . 1113 [RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key 1114 Ciphersuites for Transport Layer Security (TLS)", 1115 RFC 4279, DOI 10.17487/RFC4279, December 2005, 1116 . 1118 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1119 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1120 January 2012, . 1122 [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", 1123 RFC 6749, DOI 10.17487/RFC6749, October 2012, 1124 . 1126 [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., 1127 Weiler, S., and T. Kivinen, "Using Raw Public Keys in 1128 Transport Layer Security (TLS) and Datagram Transport 1129 Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, 1130 June 2014, . 1132 [RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES- 1133 CCM Elliptic Curve Cryptography (ECC) Cipher Suites for 1134 TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014, 1135 . 1137 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1138 Application Protocol (CoAP)", RFC 7252, 1139 DOI 10.17487/RFC7252, June 2014, 1140 . 1142 [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer 1143 Security (TLS) / Datagram Transport Layer Security (DTLS) 1144 Profiles for the Internet of Things", RFC 7925, 1145 DOI 10.17487/RFC7925, July 2016, 1146 . 1148 [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", 1149 RFC 8152, DOI 10.17487/RFC8152, July 2017, 1150 . 1152 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1153 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1154 May 2017, . 1156 [RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic 1157 Curve Cryptography (ECC) Cipher Suites for Transport Layer 1158 Security (TLS) Versions 1.2 and Earlier", RFC 8422, 1159 DOI 10.17487/RFC8422, August 2018, 1160 . 1162 [RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. 1163 Tschofenig, "Proof-of-Possession Key Semantics for CBOR 1164 Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March 1165 2020, . 1167 [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object 1168 Representation (CBOR)", STD 94, RFC 8949, 1169 DOI 10.17487/RFC8949, December 2020, 1170 . 1172 11.2. Informative References 1174 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 1175 "Transport Layer Security (TLS) Session Resumption without 1176 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 1177 January 2008, . 1179 [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand 1180 Key Derivation Function (HKDF)", RFC 5869, 1181 DOI 10.17487/RFC5869, May 2010, 1182 . 1184 [RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for 1185 Transport Layer Security (TLS)", RFC 6655, 1186 DOI 10.17487/RFC6655, July 2012, 1187 . 1189 [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", 1190 RFC 7662, DOI 10.17487/RFC7662, October 2015, 1191 . 1193 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 1194 for Security", RFC 7748, DOI 10.17487/RFC7748, January 1195 2016, . 1197 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 1198 Signature Algorithm (EdDSA)", RFC 8032, 1199 DOI 10.17487/RFC8032, January 2017, 1200 . 1202 [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, 1203 "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, 1204 May 2018, . 1206 [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data 1207 Definition Language (CDDL): A Notational Convention to 1208 Express Concise Binary Object Representation (CBOR) and 1209 JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, 1210 June 2019, . 1212 [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 1213 "Object Security for Constrained RESTful Environments 1214 (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, 1215 . 1217 Authors' Addresses 1219 Stefanie Gerdes 1220 Universität Bremen TZI 1221 Postfach 330440 1222 D-28359 Bremen 1223 Germany 1225 Phone: +49-421-218-63906 1226 Email: gerdes@tzi.org 1228 Olaf Bergmann 1229 Universität Bremen TZI 1230 Postfach 330440 1231 D-28359 Bremen 1232 Germany 1234 Phone: +49-421-218-63904 1235 Email: bergmann@tzi.org 1237 Carsten Bormann 1238 Universität Bremen TZI 1239 Postfach 330440 1240 D-28359 Bremen 1241 Germany 1243 Phone: +49-421-218-63921 1244 Email: cabo@tzi.org 1246 Göran Selander 1247 Ericsson AB 1249 Email: goran.selander@ericsson.com 1250 Ludwig Seitz 1251 Combitech 1252 Djäknegatan 31 1253 SE-211 35 Malmö 1254 Sweden 1256 Email: ludwig.seitz@combitech.se