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'I-D.ietf-cbor-7049bis' ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Downref: Normative reference to an Informational RFC: RFC 7251 ** Obsolete normative reference: RFC 8152 (Obsoleted by RFC 9052, RFC 9053) -- Obsolete informational reference (is this intentional?): RFC 5077 (Obsoleted by RFC 8446) Summary: 3 errors (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). 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: March 12, 2021 Universitaet Bremen TZI 6 G. Selander 7 Ericsson AB 8 L. Seitz 9 Combitech 10 September 08, 2020 12 Datagram Transport Layer Security (DTLS) Profile for Authentication and 13 Authorization for Constrained Environments (ACE) 14 draft-ietf-ace-dtls-authorize-13 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 March 12, 2021. 44 Copyright Notice 46 Copyright (c) 2020 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 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . . 5 65 3.1. Communication Between the Client and the Authorization 66 Server . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 3.2. RawPublicKey Mode . . . . . . . . . . . . . . . . . . . . 7 68 3.2.1. Access Token Retrieval from the Authorization Server 7 69 3.2.2. DTLS Channel Setup Between Client and Resource Server 9 70 3.3. PreSharedKey Mode . . . . . . . . . . . . . . . . . . . . 10 71 3.3.1. Access Token Retrieval from the Authorization Server 10 72 3.3.2. DTLS Channel Setup Between Client and Resource Server 14 73 3.4. Resource Access . . . . . . . . . . . . . . . . . . . . . 16 74 4. Dynamic Update of Authorization Information . . . . . . . . . 18 75 5. Token Expiration . . . . . . . . . . . . . . . . . . . . . . 19 76 6. Secure Communication with an Authorization Server . . . . . . 19 77 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 78 7.1. Reuse of Existing Sessions . . . . . . . . . . . . . . . 21 79 7.2. Multiple Access Tokens . . . . . . . . . . . . . . . . . 22 80 7.3. Out-of-Band Configuration . . . . . . . . . . . . . . . . 22 81 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 82 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 83 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 84 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 85 11.1. Normative References . . . . . . . . . . . . . . . . . . 24 86 11.2. Informative References . . . . . . . . . . . . . . . . . 25 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 89 1. Introduction 91 This specification defines a profile of the ACE framework 92 [I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource 93 server use CoAP [RFC7252] over DTLS version 1.2 [RFC6347] to 94 communicate. The client obtains an access token, bound to a key (the 95 proof-of-possession key), from an authorization server to prove its 96 authorization to access protected resources hosted by the resource 97 server. Also, the client and the resource server are provided by the 98 authorization server with the necessary keying material to establish 99 a DTLS session. The communication between client and authorization 100 server may also be secured with DTLS. This specification supports 101 DTLS with Raw Public Keys (RPK) [RFC7250] and with Pre-Shared Keys 102 (PSK) [RFC4279]. 104 The ACE framework requires that client and server mutually 105 authenticate each other before any application data is exchanged. 106 DTLS enables mutual authentication if both client and server prove 107 their ability to use certain keying material in the DTLS handshake. 108 The authorization server assists in this process on the server side 109 by incorporating keying material (or information about keying 110 material) into the access token, which is considered a "proof of 111 possession" token. 113 In the RPK mode, the client proves that it can use the RPK bound to 114 the token and the server shows that it can use a certain RPK. 116 The resource server needs access to the token in order to complete 117 this exchange. For the RPK mode, the client must upload the access 118 token to the resource server before initiating the handshake, as 119 described in Section 5.8.1 of the ACE framework 120 [I-D.ietf-ace-oauth-authz]. 122 In the PSK mode, client and server show with the DTLS handshake that 123 they can use the keying material that is bound to the access token. 124 To transfer the access token from the client to the resource server, 125 the "psk_identity" parameter in the DTLS PSK handshake may be used 126 instead of uploading the token prior to the handshake. 128 As recommended in Section 5.8 of [I-D.ietf-ace-oauth-authz], this 129 specification uses CBOR web tokens to convey claims within an access 130 token issued by the server. While other formats could be used as 131 well, those are out of scope for this document. 133 1.1. Terminology 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 137 "OPTIONAL" in this document are to be interpreted as described in BCP 138 14 [RFC2119] [RFC8174] when, and only when, they appear in all 139 capitals, as shown here. 141 Readers are expected to be familiar with the terms and concepts 142 described in [I-D.ietf-ace-oauth-authz] and in 143 [I-D.ietf-ace-oauth-params]. 145 The authorization information (authz-info) resource refers to the 146 authorization information endpoint as specified in 147 [I-D.ietf-ace-oauth-authz]. The term "claim" is used in this 148 document with the same semantics as in [I-D.ietf-ace-oauth-authz], 149 i.e., it denotes information carried in the access token or returned 150 from introspection. 152 2. Protocol Overview 154 The CoAP-DTLS profile for ACE specifies the transfer of 155 authentication information and, if necessary, authorization 156 information between the client (C) and the resource server (RS) 157 during setup of a DTLS session for CoAP messaging. It also specifies 158 how the client can use CoAP over DTLS to retrieve an access token 159 from the authorization server (AS) for a protected resource hosted on 160 the resource server. As specified in Section 6.7 of 161 [I-D.ietf-ace-oauth-authz], use of DTLS for one or both of these 162 interactions is completely independent 164 This profile requires the client to retrieve an access token for 165 protected resource(s) it wants to access on the resource server as 166 specified in [I-D.ietf-ace-oauth-authz]. Figure 1 shows the typical 167 message flow in this scenario (messages in square brackets are 168 optional): 170 C RS AS 171 | [---- Resource Request ------>]| | 172 | | | 173 | [<-AS Request Creation Hints-] | | 174 | | | 175 | ------- Token Request ----------------------------> | 176 | | | 177 | <---------------------------- Access Token --------- | 178 | + Access Information | 180 Figure 1: Retrieving an Access Token 182 To determine the authorization server in charge of a resource hosted 183 at the resource server, the client can send an initial Unauthorized 184 Resource Request message to the resource server. The resource server 185 then denies the request and sends an AS Request Creation Hints 186 message containing the address of its authorization server back to 187 the client as specified in Section 5.1.2 of 188 [I-D.ietf-ace-oauth-authz]. 190 Once the client knows the authorization server's address, it can send 191 an access token request to the token endpoint at the authorization 192 server as specified in [I-D.ietf-ace-oauth-authz]. As the access 193 token request as well as the response may contain confidential data, 194 the communication between the client and the authorization server 195 must be confidentiality-protected and ensure authenticity. The 196 client may have been registered at the authorization server via the 197 OAuth 2.0 client registration mechanism as outlined in Section 5.3 of 198 [I-D.ietf-ace-oauth-authz]. 200 The access token returned by the authorization server can then be 201 used by the client to establish a new DTLS session with the resource 202 server. When the client intends to use an asymmetric proof-of- 203 possession key in the DTLS handshake with the resource server, the 204 client MUST upload the access token to the authz-info resource, i.e. 205 the authz-info endpoint, on the resource server before starting the 206 DTLS handshake, as described in Section 5.8.1 of 207 [I-D.ietf-ace-oauth-authz]. In case the client uses a symmetric 208 proof-of-possession key in the DTLS handshake, the procedure as above 209 MAY be used, or alternatively, the access token MAY instead be 210 transferred in the DTLS ClientKeyExchange message (see 211 Section 3.3.2). In any case, DTLS MUST be used in a mode that 212 provides replay protection. 214 Figure 2 depicts the common protocol flow for the DTLS profile after 215 the client has retrieved the access token from the authorization 216 server, AS. 218 C RS AS 219 | [--- Access Token ------>] | | 220 | | | 221 | <== DTLS channel setup ==> | | 222 | | | 223 | == Authorized Request ===> | | 224 | | | 225 | <=== Protected Resource == | | 227 Figure 2: Protocol overview 229 3. Protocol Flow 231 The following sections specify how CoAP is used to interchange 232 access-related data between the resource server, the client and the 233 authorization server so that the authorization server can provide the 234 client and the resource server with sufficient information to 235 establish a secure channel, and convey authorization information 236 specific for this communication relationship to the resource server. 238 Section 3.1 describes how the communication between the client (C) 239 and the authorization server (AS) must be secured. Depending on the 240 used CoAP security mode (see also Section 9 of [RFC7252], the Client- 241 to-AS request, AS-to-Client response (see Section 5.6 of 242 [I-D.ietf-ace-oauth-authz]) and DTLS session establishment carry 243 slightly different information. Section 3.2 addresses the use of raw 244 public keys while Section 3.3 defines how pre-shared keys are used in 245 this profile. 247 3.1. Communication Between the Client and the Authorization Server 249 To retrieve an access token for the resource that the client wants to 250 access, the client requests an access token from the authorization 251 server. Before the client can request the access token, the client 252 and the authorization server MUST establish a secure communication 253 channel. This profile assumes that the keying material to secure 254 this communication channel has securely been obtained either by 255 manual configuration or in an automated provisioning process. The 256 following requirements in alignment with Section 6.5 of 257 [I-D.ietf-ace-oauth-authz] therefore must be met: 259 o The client MUST securely have obtained keying material to 260 communicate with the authorization server. 262 o Furthermore, the client MUST verify that the authorization server 263 is authorized to provide access tokens (including authorization 264 information) about the resource server to the client, and that 265 this authorization information about the authorization server is 266 still valid. 268 o Also, the authorization server MUST securely have obtained keying 269 material for the client, and obtained authorization rules approved 270 by the resource owner (RO) concerning the client and the resource 271 server that relate to this keying material. 273 The client and the authorization server MUST use their respective 274 keying material for all exchanged messages. How the security 275 association between the client and the authorization server is 276 bootstrapped is not part of this document. The client and the 277 authorization server must ensure the confidentiality, integrity and 278 authenticity of all exchanged messages within the ACE protocol. 280 Section 6 specifies how communication with the authorization server 281 is secured. 283 3.2. RawPublicKey Mode 285 When the client uses RawPublicKey authentication, the procedure is as 286 described in the following. 288 3.2.1. Access Token Retrieval from the Authorization Server 290 After the client and the authorization server mutually authenticated 291 each other and validated each other's authorization, the client sends 292 a token request to the authorization server's token endpoint. The 293 client MUST add a "req_cnf" object carrying either its raw public key 294 or a unique identifier for a public key that it has previously made 295 known to the authorization server. It is RECOMMENDED that the client 296 uses DTLS with the same keying material to secure the communication 297 with the authorization server, proving possession of the key as part 298 of the token request. Other mechanisms for proving possession of the 299 key may be defined in the future. 301 An example access token request from the client to the authorization 302 server is depicted in Figure 3. 304 POST coaps://as.example.com/token 305 Content-Format: application/ace+cbor 306 Payload: 307 { 308 grant_type : client_credentials, 309 req_aud : "tempSensor4711", 310 req_cnf : { 311 COSE_Key : { 312 kty : EC2, 313 crv : P-256, 314 x : h'e866c35f4c3c81bb96a1...', 315 y : h'2e25556be097c8778a20...' 316 } 317 } 318 } 320 Figure 3: Access Token Request Example for RPK Mode 322 The example shows an access token request for the resource identified 323 by the string "tempSensor4711" on the authorization server using a 324 raw public key. 326 The authorization server MUST check if the client that it 327 communicates with is associated with the RPK in the "req_cnf" 328 parameter before issuing an access token to it. If the authorization 329 server determines that the request is to be authorized according to 330 the respective authorization rules, it generates an access token 331 response for the client. The access token MUST be bound to the RPK 332 of the client by means of the "cnf" claim. 334 The response MAY contain a "profile" parameter with the value 335 "coap_dtls" to indicate that this profile MUST be used for 336 communication between the client and the resource server. The 337 "profile" may be specified out-of-band, in which case it does not 338 have to be sent. The response also contains an access token with 339 information for the resource server about the client's public key. 340 The authorization server MUST return in its response the parameter 341 "rs_cnf" unless it is certain that the client already knows the 342 public key of the resource server. The authorization server MUST 343 ascertain that the RPK specified in "rs_cnf" belongs to the resource 344 server that the client wants to communicate with. The authorization 345 server MUST protect the integrity of the access token such that the 346 resource server can detect unauthorized changes. If the access token 347 contains confidential data, the authorization server MUST also 348 protect the confidentiality of the access token. 350 The client MUST ascertain that the access token response belongs to a 351 certain previously sent access token request, as the request may 352 specify the resource server with which the client wants to 353 communicate. 355 An example access token response from the authorization server to the 356 client is depicted in Figure 4. Here, the contents of the 357 "access_token" claim have been truncated to improve readability. 358 Caching proxies process the Max-Age option in the CoAP response which 359 has a default value of 60 seconds (Section 5.6.1 of [RFC7252]). The 360 authorization server SHOULD adjust the Max-Age option such that it 361 does not exceed the "expires_in" parameter to avoid stale responses. 363 2.01 Created 364 Content-Format: application/ace+cbor 365 Max-Age: 3560 366 Payload: 367 { 368 access_token : b64'SlAV32hkKG... 369 (remainder of CWT omitted for brevity; 370 CWT contains the client's RPK in the cnf claim)', 371 expires_in : 3600, 372 rs_cnf : { 373 COSE_Key : { 374 kty : EC2, 375 crv : P-256, 376 x : h'd7cc072de2205bdc1537...', 377 y : h'f95e1d4b851a2cc80fff...' 378 } 379 } 380 } 382 Figure 4: Access Token Response Example for RPK Mode 384 3.2.2. DTLS Channel Setup Between Client and Resource Server 386 Before the client initiates the DTLS handshake with the resource 387 server, the client MUST send a "POST" request containing the obtained 388 access token to the authz-info resource hosted by the resource 389 server. After the client receives a confirmation that the resource 390 server has accepted the access token, it SHOULD proceed to establish 391 a new DTLS channel with the resource server. The client MUST use its 392 correct public key in the DTLS handshake. If the authorization 393 server has specified a "cnf" field in the access token response, the 394 client MUST use this key. Otherwise, the client MUST use the public 395 key that it specified in the "req_cnf" of the access token request. 396 The client MUST specify this public key in the SubjectPublicKeyInfo 397 structure of the DTLS handshake as described in [RFC7250]. 399 To be consistent with [RFC7252] which allows for shortened MAC tags 400 in constrained environments, an implementation that supports the RPK 401 mode of this profile MUST at least support the ciphersuite 402 TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. As discussed in 403 [RFC7748], new ECC curves have been defined recently that are 404 considered superior to the so-called NIST curves. This specification 405 therefore mandates implementation support for curve25519 (cf. 406 [RFC8032], [RFC8422]) as this curve said to be efficient and less 407 dangerous regarding implementation errors than the secp256r1 curve 408 mandated in [RFC7252]. 410 The resource server MUST check if the access token is still valid, if 411 the resource server is the intended destination (i.e., the audience) 412 of the token, and if the token was issued by an authorized 413 authorization server. The access token is constructed by the 414 authorization server such that the resource server can associate the 415 access token with the Client's public key. The "cnf" claim MUST 416 contain either the client's RPK or, if the key is already known by 417 the resource server (e.g., from previous communication), a reference 418 to this key. If the authorization server has no certain knowledge 419 that the Client's key is already known to the resource server, the 420 Client's public key MUST be included in the access token's "cnf" 421 parameter. If CBOR web tokens [RFC8392] are used (as recommended in 422 [I-D.ietf-ace-oauth-authz]), keys MUST be encoded as specified in 423 [RFC8747]. A resource server MUST have the capacity to store one 424 access token for every proof-of-possession key of every authorized 425 client. 427 The raw public key used in the DTLS handshake with the client MUST 428 belong to the resource server. If the resource server has several 429 raw public keys, it needs to determine which key to use. The 430 authorization server can help with this decision by including a "cnf" 431 parameter in the access token that is associated with this 432 communication. In this case, the resource server MUST use the 433 information from the "cnf" field to select the proper keying 434 material. 436 Thus, the handshake only finishes if the client and the resource 437 server are able to use their respective keying material. 439 3.3. PreSharedKey Mode 441 When the client uses pre-shared key authentication, the procedure is 442 as described in the following. 444 3.3.1. Access Token Retrieval from the Authorization Server 446 To retrieve an access token for the resource that the client wants to 447 access, the client MAY include a "cnf" object carrying an identifier 448 for a symmetric key in its access token request to the authorization 449 server. This identifier can be used by the authorization server to 450 determine the shared secret to construct the proof-of-possession 451 token. The authorization server MUST check if the identifier refers 452 to a symmetric key that was previously generated by the authorization 453 server as a shared secret for the communication between this client 454 and the resource server. If no such symmetric key was found, the 455 authorization server MUST generate a new symmetric key that is 456 returned in its response to the client. 458 The authorization server MUST determine the authorization rules for 459 the client it communicates with as defined by the resource owner and 460 generate the access token accordingly. If the authorization server 461 authorizes the client, it returns an AS-to-Client response. If the 462 profile parameter is present, it is set to "coap_dtls". The 463 authorization server MUST ascertain that the access token is 464 generated for the resource server that the client wants to 465 communicate with. Also, the authorization server MUST protect the 466 integrity of the access token to ensure that the resource server can 467 detect unauthorized changes. If the token contains confidential data 468 such as the symmetric key, the confidentiality of the token MUST also 469 be protected. Depending on the requested token type and algorithm in 470 the access token request, the authorization server adds access 471 Information to the response that provides the client with sufficient 472 information to setup a DTLS channel with the resource server. The 473 authorization server adds a "cnf" parameter to the access information 474 carrying a "COSE_Key" object that informs the client about the shared 475 secret that is to be used between the client and the resource server. 476 To convey the same secret to the resource server, the authorization 477 server can include it directly in the access token by means of the 478 "cnf" claim or provide sufficient information to enable the resource 479 server to derive the shared secret from the access token. As an 480 alternative, the resource server MAY use token introspection to 481 retrieve the keying material for this access token directly from the 482 authorization server. 484 An example access token request for an access token with a symmetric 485 proof-of-possession key is illustrated in Figure 5. 487 POST coaps://as.example.com/token 488 Content-Format: application/ace+cbor 489 Payload: 490 { 491 audience : "smokeSensor1807", 492 } 494 Figure 5: Example Access Token Request, (implicit) symmetric PoP-key 496 A corresponding example access token response is illustrated in 497 Figure 6. In this example, the authorization server returns a 2.01 498 response containing a new access token (truncated to improve 499 readability) and information for the client, including the symmetric 500 key in the cnf claim. The information is transferred as a CBOR data 501 structure as specified in [I-D.ietf-ace-oauth-authz]. 503 2.01 Created 504 Content-Format: application/ace+cbor 505 Max-Age: 85800 506 Payload: 507 { 508 access_token : h'd08343a10... 509 (remainder of CWT omitted for brevity) 510 token_type : PoP, 511 expires_in : 86400, 512 profile : coap_dtls, 513 cnf : { 514 COSE_Key : { 515 kty : symmetric, 516 kid : h'3d027833fc6267ce', 517 k : h'73657373696f6e6b6579' 518 } 519 } 520 } 522 Figure 6: Example Access Token Response, symmetric PoP-key 524 The access token also comprises a "cnf" claim. This claim usually 525 contains a "COSE_Key" object that carries either the symmetric key 526 itself or a key identifier that can be used by the resource server to 527 determine the secret key it shares with the client. If the access 528 token carries a symmetric key, the access token MUST be encrypted 529 using a "COSE_Encrypt0" structure. The authorization server MUST use 530 the keying material shared with the resource server to encrypt the 531 token. 533 The "cnf" structure in the access token is provided in Figure 7. 535 cnf : { 536 COSE_Key : { 537 kty : symmetric, 538 kid : h'3d027833fc6267ce' 539 } 540 } 542 Figure 7: Access Token without Keying Material 544 A response that declines any operation on the requested resource is 545 constructed according to Section 5.2 of [RFC6749], (cf. 546 Section 5.6.3. of [I-D.ietf-ace-oauth-authz]). Figure 8 shows an 547 example for a request that has been rejected due to invalid request 548 parameters. 550 4.00 Bad Request 551 Content-Format: application/ace+cbor 552 Payload: 553 { 554 error : invalid_request 555 } 557 Figure 8: Example Access Token Response With Reject 559 The method for how the resource server determines the symmetric key 560 from an access token containing only a key identifier is application- 561 specific; the remainder of this section provides one example. 563 The authorization server and the resource server are assumed to share 564 a key derivation key used to derive the symmetric key shared with the 565 client from the key identifier in the access token. The key 566 derivation key may be derived from some other secret key shared 567 between the authorization server and the resource server. This key 568 needs to be securely stored and processed in the same way as the key 569 used to protect the communication between the authorization server 570 and the resource server. 572 Knowledge of the symmetric key shared with the client must not reveal 573 any information about the key derivation key or other secret keys 574 shared between the authorization server and resource server. 576 In order to generate a new symmetric key to be used by client and 577 resource server, the authorization server generates a new key 578 identifier which MUST be unique among all key identifiers used by the 579 authorization server for this resource server. The authorization 580 server then uses the key derivation key shared with the resource 581 server to derive the symmetric key as specified below. Instead of 582 providing the keying material in the access token, the authorization 583 server includes the key identifier in the "kid" parameter, see 584 Figure 7. This key identifier enables the resource server to 585 calculate the symmetric key used for the communication with the 586 client using the key derivation key and a KDF to be defined by the 587 application, for example HKDF-SHA-256. The key identifier picked by 588 the authorization server MUST be unique for each access token where a 589 unique symmetric key is required. 591 In this example, HKDF consists of the composition of the HKDF-Extract 592 and HKDF-Expand steps [RFC5869]. The symmetric key is derived from 593 the key identifier, the key derivation key and other data: 595 OKM = HKDF(salt, IKM, info, L), 597 where: 599 o OKM, the output keying material, is the derived symmetric key 601 o salt is the empty byte string 603 o IKM, the input keying material, is the key derivation key as 604 defined above 606 o info is the serialization of a CBOR array consisting of 607 ([RFC8610]): 609 info = [ 610 type : tstr, 611 L : uint, 612 access_token: bytes 613 ] 615 where: 617 o type is set to the constant text string "ACE-CoAP-DTLS-key- 618 derivation", 620 o L is the size of the symmetric key in bytes, 622 o access_token is the content of the "access_token" field as 623 transferred from the authorization server to the resource server. 625 All CBOR data types are encoded in CBOR using preferred serialization 626 and deterministic encoding as specified in Section 4 of 627 [I-D.ietf-cbor-7049bis]. This implies in particular that the "type" 628 and "L" components use the minimum length encoding. The content of 629 the "access_token" field is treated as opaque data for the purpose of 630 key derivation. 632 Use of a unique (per resource server) "kid" and the use of a key 633 derivation IKM that MUST be unique per authorization server/resource 634 server pair as specified above will ensure that the derived key is 635 not shared across multiple clients. However, to additionally provide 636 variation in the derived key across different tokens used by the same 637 client, it is additionally RECOMMENDED to include the "iat" claim and 638 either the "exp" or "exi" claims in the access token. 640 3.3.2. DTLS Channel Setup Between Client and Resource Server 642 When a client receives an access token response from an authorization 643 server, the client MUST check if the access token response is bound 644 to a certain previously sent access token request, as the request may 645 specify the resource server with which the client wants to 646 communicate. 648 The client checks if the payload of the access token response 649 contains an "access_token" parameter and a "cnf" parameter. With 650 this information the client can initiate the establishment of a new 651 DTLS channel with a resource server. To use DTLS with pre-shared 652 keys, the client follows the PSK key exchange algorithm specified in 653 Section 2 of [RFC4279] using the key conveyed in the "cnf" parameter 654 of the AS response as PSK when constructing the premaster secret. To 655 be consistent with the recommendations in [RFC7252] a client is 656 expected to offer at least the ciphersuite TLS_PSK_WITH_AES_128_CCM_8 657 [RFC6655] to the resource server. 659 In PreSharedKey mode, the knowledge of the shared secret by the 660 client and the resource server is used for mutual authentication 661 between both peers. Therefore, the resource server must be able to 662 determine the shared secret from the access token. Following the 663 general ACE authorization framework, the client can upload the access 664 token to the resource server's authz-info resource before starting 665 the DTLS handshake. The client then needs to indicate during the 666 DTLS handshake which previously uploaded access token it intends to 667 use. To do so, it MUST create a "COSE_Key" structure with the "kid" 668 that was conveyed in the "rs_cnf" claim in the token response from 669 the authorization server and the key type "symmetric". This 670 structure then is included as the only element in the "cnf" structure 671 that is used as value for "psk_identity" as shown in Figure 9. 673 { cnf : { 674 COSE_Key : { 675 kty: symmetric, 676 kid : h'3d027833fc6267ce' 677 } 678 } 679 } 681 Figure 9: Access token containing a single kid parameter 683 As an alternative to the access token upload, the client can provide 684 the most recent access token in the "psk_identity" field of the 685 ClientKeyExchange message. To do so, the client MUST treat the 686 contents of the "access_token" field from the AS-to-Client response 687 as opaque data as specified in Section 4.2 of [RFC7925] and not 688 perform any re-coding. This allows the resource server to retrieve 689 the shared secret directly from the "cnf" claim of the access token. 691 If a resource server receives a ClientKeyExchange message that 692 contains a "psk_identity" with a length greater than zero, it MUST 693 parse the contents of the "psk_identity" field as CBOR data structure 694 and process the contents as following: 696 o If the data contains a "cnf" field with a "COSE_Key" structure 697 with a "kid", the resource server continues the DTLS handshake 698 with the associated key that corresponds to this kid. 700 o If the data comprises additional CWT information, this information 701 must be stored as an access token for this DTLS association before 702 continuing with the DTLS handshake. 704 If the contents of the "psk_identity" do not yield sufficient 705 information to select a valid access token for the requesting client, 706 the resource server aborts the DTLS handshake with an 707 "illegal_parameter" alert. 709 When the resource server receives an access token, it MUST check if 710 the access token is still valid, if the resource server is the 711 intended destination (i.e., the audience of the token), and if the 712 token was issued by an authorized authorization server. This 713 specification implements access tokens as proof-of-possession tokens. 714 Therefore, the access token is bound to a symmetric PoP key that is 715 used as shared secret between the client and the resource server. A 716 resource server MUST have the capacity to store one access token for 717 every proof-of-possession key of every authorized client. The 718 resource server may use token introspection [RFC7662] on the access 719 token to retrieve more information about the specific token. The use 720 of introspection is out of scope for this specification. 722 While the client can retrieve the shared secret from the contents of 723 the "cnf" parameter in the AS-to-Client response, the resource server 724 uses the information contained in the "cnf" claim of the access token 725 to determine the actual secret when no explicit "kid" was provided in 726 the "psk_identity" field. If key derivation is used, the resource 727 server uses the "COSE_KDF_Context" information as described above. 729 3.4. Resource Access 731 Once a DTLS channel has been established as described in Section 3.2 732 or Section 3.3, respectively, the client is authorized to access 733 resources covered by the access token it has uploaded to the authz- 734 info resource hosted by the resource server. 736 With the successful establishment of the DTLS channel, the client and 737 the resource server have proven that they can use their respective 738 keying material. An access token that is bound to the client's 739 keying material is associated with the channel. According to 740 Section 5.8.1 of [I-D.ietf-ace-oauth-authz], there should be only one 741 access token for each client. New access tokens issued by the 742 authorization server replace previously issued access tokens for the 743 respective client. The resource server therefore must have a common 744 understanding with the authorization server how access tokens are 745 ordered. The authorization server may, e.g., specify a "cti" claim 746 for the access token (see Section 5.8.3 of 747 [I-D.ietf-ace-oauth-authz]) to employ a strict order. 749 Any request that the resource server receives on a DTLS channel that 750 is tied to an access token via its keying material MUST be checked 751 against the authorization rules that can be determined with the 752 access token. The resource server MUST check for every request if 753 the access token is still valid. If the token has expired, the 754 resource server MUST remove it. Incoming CoAP requests that are not 755 authorized with respect to any access token that is associated with 756 the client MUST be rejected by the resource server with 4.01 757 response. The response SHOULD include AS Request Creation Hints as 758 described in Section 5.1.1 of [I-D.ietf-ace-oauth-authz]. 760 The resource server MUST only accept an incoming CoAP request as 761 authorized if the following holds: 763 1. The message was received on a secure channel that has been 764 established using the procedure defined in this document. 766 2. The authorization information tied to the sending client is 767 valid. 769 3. The request is destined for the resource server. 771 4. The resource URI specified in the request is covered by the 772 authorization information. 774 5. The request method is an authorized action on the resource with 775 respect to the authorization information. 777 Incoming CoAP requests received on a secure DTLS channel that are not 778 thus authorized MUST be rejected according to Section 5.8.2 of 779 [I-D.ietf-ace-oauth-authz] 781 1. with response code 4.03 (Forbidden) when the resource URI 782 specified in the request is not covered by the authorization 783 information, and 785 2. with response code 4.05 (Method Not Allowed) when the resource 786 URI specified in the request covered by the authorization 787 information but not the requested action. 789 The client MUST ascertain that its keying material is still valid 790 before sending a request or processing a response. If the client 791 recently has updated the access token (see Section 4), it must be 792 prepared that its request is still handled according to the previous 793 authorization rules as there is no strict ordering between access 794 token uploads and resource access messages. See also Section 7.2 for 795 a discussion of access token processing. 797 If the client gets an error response containing AS Request Creation 798 Hints (cf. Section 5.1.2 of [I-D.ietf-ace-oauth-authz] as response 799 to its requests, it SHOULD request a new access token from the 800 authorization server in order to continue communication with the 801 resource server. 803 Unauthorized requests that have been received over a DTLS session 804 SHOULD be treated as non-fatal by the resource server, i.e., the DTLS 805 session SHOULD be kept alive until the associated access token has 806 expired. 808 4. Dynamic Update of Authorization Information 810 Resource servers must only use a new access token to update the 811 authorization information for a DTLS session if the keying material 812 that is bound to the token is the same that was used in the DTLS 813 handshake. By associating the access tokens with the identifier of 814 an existing DTLS session, the authorization information can be 815 updated without changing the cryptographic keys for the DTLS 816 communication between the client and the resource server, i.e. an 817 existing session can be used with updated permissions. 819 The client can therefore update the authorization information stored 820 at the resource server at any time without changing an established 821 DTLS session. To do so, the client requests a new access token from 822 the authorization server for the intended action on the respective 823 resource and uploads this access token to the authz-info resource on 824 the resource server. 826 Figure 10 depicts the message flow where the client requests a new 827 access token after a security association between the client and the 828 resource server has been established using this protocol. If the 829 client wants to update the authorization information, the token 830 request MUST specify the key identifier of the proof-of-possession 831 key used for the existing DTLS channel between the client and the 832 resource server in the "kid" parameter of the Client-to-AS request. 833 The authorization server MUST verify that the specified "kid" denotes 834 a valid verifier for a proof-of-possession token that has previously 835 been issued to the requesting client. Otherwise, the Client-to-AS 836 request MUST be declined with the error code "unsupported_pop_key" as 837 defined in Section 5.6.3 of [I-D.ietf-ace-oauth-authz]. 839 When the authorization server issues a new access token to update 840 existing authorization information, it MUST include the specified 841 "kid" parameter in this access token. A resource server MUST replace 842 the authorization information of any existing DTLS session that is 843 identified by this key identifier with the updated authorization 844 information. 846 C RS AS 847 | <===== DTLS channel =====> | | 848 | + Access Token | | 849 | | | 850 | --- Token Request ----------------------------> | 851 | | | 852 | <---------------------------- New Access Token - | 853 | + Access Information | 854 | | | 855 | --- Update /authz-info --> | | 856 | New Access Token | | 857 | | | 858 | == Authorized Request ===> | | 859 | | | 860 | <=== Protected Resource == | | 862 Figure 10: Overview of Dynamic Update Operation 864 5. Token Expiration 866 The resource server MUST delete access tokens that are no longer 867 valid. DTLS associations that have been setup in accordance with 868 this profile are always tied to specific tokens (which may be 869 exchanged with a dynamic update as described in Section 4). As 870 tokens may become invalid at any time (e.g., because they have 871 expired), the association may become useless at some point. A 872 resource server therefore MUST terminate existing DTLS association 873 after the last access token associated with this association has 874 expired. 876 As specified in Section 5.8.3 of [I-D.ietf-ace-oauth-authz], the 877 resource server MUST notify the client with an error response with 878 code 4.01 (Unauthorized) for any long running request before 879 terminating the association. 881 6. Secure Communication with an Authorization Server 883 As specified in the ACE framework (Sections 5.6 and 5.7 of 884 [I-D.ietf-ace-oauth-authz]), the requesting entity (the resource 885 server and/or the client) and the authorization server communicate 886 via the token endpoint or introspection endpoint. The use of CoAP 887 and DTLS for this communication is RECOMMENDED in this profile, other 888 protocols (such as HTTP and TLS, or CoAP and OSCORE [RFC8613]) MAY be 889 used instead. 891 How credentials (e.g., PSK, RPK, X.509 cert) for using DTLS with the 892 authorization server are established is out of scope for this 893 profile. 895 If other means of securing the communication with the authorization 896 server are used, the communication security requirements from 897 Section 6.2 of [I-D.ietf-ace-oauth-authz] remain applicable. 899 7. Security Considerations 901 This document specifies a profile for the Authentication and 902 Authorization for Constrained Environments (ACE) framework 903 [I-D.ietf-ace-oauth-authz]. As it follows this framework's general 904 approach, the general security considerations from Section 6 of 905 [I-D.ietf-ace-oauth-authz] also apply to this profile. 907 The authorization server must ascertain that the keying material for 908 the client that it provides to the resource server actually is 909 associated with this client. Malicious clients may hand over access 910 tokens containing their own access permissions to other entities. 911 This problem cannot be completely eliminated. Nevertheless, in RPK 912 mode it should not be possible for clients to request access tokens 913 for arbitrary public keys: if the client can cause the authorization 914 server to issue a token for a public key without proving possession 915 of the corresponding private key, this allows for identity misbinding 916 attacks where the issued token is usable by an entity other than the 917 intended one. The authorization server therefore at some point needs 918 to validate that the client can actually use the private key 919 corresponding to the client's public key. 921 When using pre-shared keys provisioned by the authorization server, 922 the security level depends on the randomness of PSK, and the security 923 of the TLS cipher suite and key exchange algorithm. As this 924 specification targets at constrained environments, message payloads 925 exchanged between the client and the resource server are expected to 926 be small and rare. CoAP [RFC7252] mandates the implementation of 927 cipher suites with abbreviated, 8-byte tags for message integrity 928 protection. For consistency, this profile requires implementation of 929 the same cipher suites. For application scenarios where the cost of 930 full-width authentication tags is low compared to the overall amount 931 of data being transmitted, the use of cipher suites with 16-byte 932 integrity protection tags is preferred. 934 The PSK mode of this profile offers a distribution mechanism to 935 convey authorization tokens together with a shared secret to a client 936 and a server. As this specification aims at constrained devices and 937 uses CoAP [RFC7252] as transfer protocol, at least the ciphersuite 938 TLS_PSK_WITH_AES_128_CCM_8 [RFC6655] should be supported. The access 939 tokens and the corresponding shared secrets generated by the 940 authorization server are expected to be sufficiently short-lived to 941 provide similar forward-secrecy properties to using ephemeral Diffie- 942 Hellman (DHE) key exchange mechanisms. For longer-lived access 943 tokens, DHE ciphersuites should be used. 945 Constrained devices that use DTLS [RFC6347] are inherently vulnerable 946 to Denial of Service (DoS) attacks as the handshake protocol requires 947 creation of internal state within the device. This is specifically 948 of concern where an adversary is able to intercept the initial cookie 949 exchange and interject forged messages with a valid cookie to 950 continue with the handshake. A similar issue exists with the 951 unprotected authorization information endpoint when the resource 952 server needs to keep valid access tokens for a long time. 953 Adversaries could fill up the constrained resource server's internal 954 storage for a very long time with interjected or otherwise retrieved 955 valid access tokens. To mitigate against this, the resource server 956 should set a time boundary until an access token that has not been 957 used until then will be deleted. 959 The protection of access tokens that are stored in the authorization 960 information endpoint depends on the keying material that is used 961 between the authorization server and the resource server: The 962 resource server must ensure that it processes only access tokens that 963 are (encrypted and) integrity-protected by an authorization server 964 that is authorized to provide access tokens for the resource server. 966 7.1. Reuse of Existing Sessions 968 To avoid the overhead of a repeated DTLS handshake, [RFC7925] 969 recommends session resumption [RFC5077] to reuse session state from 970 an earlier DTLS association and thus requires client side 971 implementation. In this specification, the DTLS session is subject 972 to the authorization rules denoted by the access token that was used 973 for the initial setup of the DTLS association. Enabling session 974 resumption would require the server to transfer the authorization 975 information with the session state in an encrypted SessionTicket to 976 the client. Assuming that the server uses long-lived keying 977 material, this could open up attacks due to the lack of forward 978 secrecy. Moreover, using this mechanism, a client can resume a DTLS 979 session without proving the possession of the PoP key again. 980 Therefore, the use of session resumption is NOT RECOMMENDED for 981 resource servers. 983 Since renegotiation of DTLS associations is prone to attacks as well, 984 [RFC7925] requires clients to decline any renogiation attempt. A 985 server that wants to initiate re-keying therefore SHOULD periodically 986 force a full handshake. 988 7.2. Multiple Access Tokens 990 The use of multiple access tokens for a single client increases the 991 strain on the resource server as it must consider every access token 992 and calculate the actual permissions of the client. Also, tokens may 993 contradict each other which may lead the server to enforce wrong 994 permissions. If one of the access tokens expires earlier than 995 others, the resulting permissions may offer insufficient protection. 996 Developers SHOULD avoid using multiple access tokens for a client. 998 Even when a single access token per client is used, an attacker could 999 compromise the dynamic update mechanism for existing DTLS connections 1000 by delaying or reordering packets destined for the authz-info 1001 endpoint. Thus, the order in which operations occur at the resource 1002 server (and thus which authorization info is used to process a given 1003 client request) cannot be guaranteed. Especially in the presence of 1004 later-issued access tokens that reduce the client's permissions from 1005 the initial access token, it is impossible to guarantee that the 1006 reduction in authorization will take effect prior to the expiration 1007 of the original token. 1009 7.3. Out-of-Band Configuration 1011 To communicate securely, the authorization server, the client and the 1012 resource server require certain information that must be exchanged 1013 outside the protocol flow described in this document. The 1014 authorization server must have obtained authorization information 1015 concerning the client and the resource server that is approved by the 1016 resource owner as well as corresponding keying material. The 1017 resource server must have received authorization information approved 1018 by the resource owner concerning its authorization managers and the 1019 respective keying material. The client must have obtained 1020 authorization information concerning the authorization server 1021 approved by its owner as well as the corresponding keying material. 1022 Also, the client's owner must have approved of the client's 1023 communication with the resource server. The client and the 1024 authorization server must have obtained a common understanding how 1025 this resource server is identified to ensure that the client obtains 1026 access token and keying material for the correct resource server. If 1027 the client is provided with a raw public key for the resource server, 1028 it must be ascertained to which resource server (which identifier and 1029 authorization information) the key is associated. All authorization 1030 information and keying material must be kept up to date. 1032 8. Privacy Considerations 1034 This privacy considerations from Section 7 of the 1035 [I-D.ietf-ace-oauth-authz] apply also to this profile. 1037 An unprotected response to an unauthorized request may disclose 1038 information about the resource server and/or its existing 1039 relationship with the client. It is advisable to include as little 1040 information as possible in an unencrypted response. When a DTLS 1041 session between an authenticated client and the resource server 1042 already exists, more detailed information MAY be included with an 1043 error response to provide the client with sufficient information to 1044 react on that particular error. 1046 Also, unprotected requests to the resource server may reveal 1047 information about the client, e.g., which resources the client 1048 attempts to request or the data that the client wants to provide to 1049 the resource server. The client SHOULD NOT send confidential data in 1050 an unprotected request. 1052 Note that some information might still leak after DTLS session is 1053 established, due to observable message sizes, the source, and the 1054 destination addresses. 1056 9. IANA Considerations 1058 The following registrations are done for the ACE OAuth Profile 1059 Registry following the procedure specified in 1060 [I-D.ietf-ace-oauth-authz]. 1062 Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]" 1063 with the RFC number of this specification and delete this paragraph. 1065 Profile name: coap_dtls 1067 Profile Description: Profile for delegating client authentication and 1068 authorization in a constrained environment by establishing a Datagram 1069 Transport Layer Security (DTLS) channel between resource-constrained 1070 nodes. 1072 Profile ID: TBD (suggested: 1) 1074 Change Controller: IESG 1076 Reference: [RFC-XXXX] 1078 10. Acknowledgments 1080 Thanks to Jim Schaad for his contributions and reviews of this 1081 document. Special thanks to Ben Kaduk for his thorough reviews of 1082 this document. 1084 Ludwig Seitz worked on this document as part of the CelticNext 1085 projects CyberWI, and CRITISEC with funding from Vinnova. 1087 11. References 1089 11.1. Normative References 1091 [I-D.ietf-ace-oauth-authz] 1092 Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and 1093 H. Tschofenig, "Authentication and Authorization for 1094 Constrained Environments (ACE) using the OAuth 2.0 1095 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-35 1096 (work in progress), June 2020. 1098 [I-D.ietf-ace-oauth-params] 1099 Seitz, L., "Additional OAuth Parameters for Authorization 1100 in Constrained Environments (ACE)", draft-ietf-ace-oauth- 1101 params-13 (work in progress), April 2020. 1103 [I-D.ietf-cbor-7049bis] 1104 Bormann, C. and P. Hoffman, "Concise Binary Object 1105 Representation (CBOR)", draft-ietf-cbor-7049bis-14 (work 1106 in progress), June 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 11.2. Informative References 1169 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 1170 "Transport Layer Security (TLS) Session Resumption without 1171 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 1172 January 2008, . 1174 [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand 1175 Key Derivation Function (HKDF)", RFC 5869, 1176 DOI 10.17487/RFC5869, May 2010, 1177 . 1179 [RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for 1180 Transport Layer Security (TLS)", RFC 6655, 1181 DOI 10.17487/RFC6655, July 2012, 1182 . 1184 [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", 1185 RFC 7662, DOI 10.17487/RFC7662, October 2015, 1186 . 1188 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 1189 for Security", RFC 7748, DOI 10.17487/RFC7748, January 1190 2016, . 1192 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 1193 Signature Algorithm (EdDSA)", RFC 8032, 1194 DOI 10.17487/RFC8032, January 2017, 1195 . 1197 [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, 1198 "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, 1199 May 2018, . 1201 [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data 1202 Definition Language (CDDL): A Notational Convention to 1203 Express Concise Binary Object Representation (CBOR) and 1204 JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, 1205 June 2019, . 1207 [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 1208 "Object Security for Constrained RESTful Environments 1209 (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, 1210 . 1212 Authors' Addresses 1214 Stefanie Gerdes 1215 Universitaet Bremen TZI 1216 Postfach 330440 1217 Bremen D-28359 1218 Germany 1220 Phone: +49-421-218-63906 1221 Email: gerdes@tzi.org 1222 Olaf Bergmann 1223 Universitaet Bremen TZI 1224 Postfach 330440 1225 Bremen D-28359 1226 Germany 1228 Phone: +49-421-218-63904 1229 Email: bergmann@tzi.org 1231 Carsten Bormann 1232 Universitaet Bremen TZI 1233 Postfach 330440 1234 Bremen D-28359 1235 Germany 1237 Phone: +49-421-218-63921 1238 Email: cabo@tzi.org 1240 Goeran Selander 1241 Ericsson AB 1243 Email: goran.selander@ericsson.com 1245 Ludwig Seitz 1246 Combitech 1247 Djaeknegatan 31 1248 Malmoe 211 35 1249 Sweden 1251 Email: ludwig.seitz@combitech.se