idnits 2.17.1 draft-ietf-ace-actors-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 01, 2016) is 2978 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-05) exists of draft-koster-core-coap-pubsub-04 == Outdated reference: A later version (-06) exists of draft-selander-ace-object-security-03 -- Obsolete informational reference (is this intentional?): RFC 5246 (Obsoleted by RFC 8446) -- Obsolete informational reference (is this intentional?): RFC 6347 (Obsoleted by RFC 9147) -- Obsolete informational reference (is this intentional?): RFC 7230 (Obsoleted by RFC 9110, RFC 9112) -- Obsolete informational reference (is this intentional?): RFC 7231 (Obsoleted by RFC 9110) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACE Working Group S. Gerdes 3 Internet-Draft Universitaet Bremen TZI 4 Intended status: Informational L. Seitz 5 Expires: September 2, 2016 SICS Swedish ICT AB 6 G. Selander 7 Ericsson 8 C. Bormann, Ed. 9 Universitaet Bremen TZI 10 March 01, 2016 12 An architecture for authorization in constrained environments 13 draft-ietf-ace-actors-03 15 Abstract 17 Constrained-node networks are networks where some nodes have severe 18 constraints on code size, state memory, processing capabilities, user 19 interface, power and communication bandwidth (RFC 7228). 21 This document provides terminology, and identifies the elements that 22 an architecture needs to address, providing a problem statement, for 23 authentication and authorization in these networks. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 2, 2016. 42 Copyright Notice 44 Copyright (c) 2016 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 61 2. Architecture and High-level Problem Statement . . . . . . . . 6 62 2.1. Elements of an Architecture . . . . . . . . . . . . . . . 6 63 2.2. Architecture Variants . . . . . . . . . . . . . . . . . . 8 64 2.3. Information Flows . . . . . . . . . . . . . . . . . . . . 11 65 3. Security Objectives . . . . . . . . . . . . . . . . . . . . . 12 66 3.1. End-to-End Security Objectives in Multi-Hop Scenarios . . 13 67 4. Authentication and Authorization . . . . . . . . . . . . . . 14 68 5. Actors and their Tasks . . . . . . . . . . . . . . . . . . . 16 69 5.1. Constrained Level Actors . . . . . . . . . . . . . . . . 16 70 5.2. Principal Level Actors . . . . . . . . . . . . . . . . . 17 71 5.3. Less-Constrained Level Actors . . . . . . . . . . . . . . 18 72 6. Kinds of Protocols . . . . . . . . . . . . . . . . . . . . . 18 73 6.1. Constrained Level Protocols . . . . . . . . . . . . . . . 19 74 6.1.1. Cross Level Support Protocols . . . . . . . . . . . . 19 75 6.2. Less-Constrained Level Protocols . . . . . . . . . . . . 19 76 7. Elements of a Solution . . . . . . . . . . . . . . . . . . . 20 77 7.1. Authorization . . . . . . . . . . . . . . . . . . . . . . 20 78 7.2. Authentication . . . . . . . . . . . . . . . . . . . . . 20 79 7.3. Communication Security . . . . . . . . . . . . . . . . . 21 80 7.4. Cryptographic Keys . . . . . . . . . . . . . . . . . . . 22 81 8. Assumptions and Requirements . . . . . . . . . . . . . . . . 22 82 8.1. Architecture . . . . . . . . . . . . . . . . . . . . . . 22 83 8.2. Constrained Devices . . . . . . . . . . . . . . . . . . . 23 84 8.3. Authentication . . . . . . . . . . . . . . . . . . . . . 24 85 8.4. Server-side Authorization . . . . . . . . . . . . . . . . 24 86 8.5. Client-side Authorization Information . . . . . . . . . . 25 87 8.6. Server-side Authorization Information . . . . . . . . . . 25 88 8.7. Resource Access . . . . . . . . . . . . . . . . . . . . . 26 89 8.8. Keys and Cipher Suites . . . . . . . . . . . . . . . . . 26 90 8.9. Network Considerations . . . . . . . . . . . . . . . . . 26 91 8.10. Legacy Considerations . . . . . . . . . . . . . . . . . . 27 92 9. Security Considerations . . . . . . . . . . . . . . . . . . . 27 93 9.1. Physical Attacks on Sensor and Actuator Networks . . . . 27 94 9.2. Time Measurements . . . . . . . . . . . . . . . . . . . . 29 95 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 96 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 97 12. Informative References . . . . . . . . . . . . . . . . . . . 29 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 100 1. Introduction 102 Constrained nodes are small devices with limited abilities which in 103 many cases are made to fulfill a specific simple task. They have 104 limited hardware resources such as processing power, memory, non- 105 volatile storage and transmission capacity and additionally in most 106 cases do not have user interfaces and displays. Due to these 107 constraints, commonly used security protocols are not always easily 108 applicable. 110 Constrained nodes are expected to be integrated in all aspects of 111 everyday life and thus will be entrusted with vast amounts of data. 112 Without appropriate security mechanisms attackers might gain control 113 over things relevant to our lives. Authentication and authorization 114 mechanisms are therefore prerequisites for a secure Internet of 115 Things. 117 Authorization is about who can do what to which objects. 118 Authentication specifically addresses the who, but is often specific 119 to the authorization that is required (for example, it may be 120 sufficient to authenticate the age of an actor, so no identifier is 121 needed or even desired). Authentication often involves credentials, 122 only some of which need to be long-lived and generic; others may be 123 directed towards specific authorizations (but still possibly long- 124 lived). Authorization then makes use of these credentials, as well 125 as other information (such as the time of day). This means that the 126 application-induced complexity of authenticated authorization can 127 often be moved back and forth between these two aspects. 129 In some cases authentication and authorization can be addressed by 130 static configuration provisioned during manufacturing or deployment 131 by means of fixed trust anchors and static access control lists. 132 This is particularly applicable to siloed, fixed-purpose deployments. 134 However, as the need for flexible access to assets already deployed 135 increases, the legitimate set of authorized entities as well as their 136 specific privileges cannot be conclusively defined during deployment, 137 without any need for change during the lifetime of the device. 138 Moreover, several use cases illustrate the need for fine-grained 139 access control policies, for which for instance a basic access 140 control list concept may not be sufficiently powerful [RFC7744]. 142 The limitations of the constrained nodes ask for security mechanisms 143 which take the special characteristics of constrained environments 144 into account; not all constituents may be able to perform all 145 necessary tasks by themselves. In order to meet the security 146 requirements in constrained scenarios, the necessary tasks need to be 147 assigned to logical functional entities. 149 In order to be able to achieve complex security objectives between 150 actors some of which are hosted on simple ("constrained") devices, 151 some of the actors will make use of help from other, less constrained 152 actors. (This offloading is not specific to networks with 153 constrained nodes, but their constrainedness as the main motivation 154 is.) 156 We therefore group the logical functional entities by whether they 157 can be assigned to a constrained device ("constrained level") or need 158 higher function platforms ("less-constrained level"); the latter does 159 not necessarily mean high-function, "server" or "cloud" platforms. 160 Note that assigning a logical functional entity to the constrained 161 level does not mean that the specific implementation needs to be 162 constrained, only that it _can_ be. 164 This document provides some terminology, and identifies the elements 165 an architecture needs to address, representing the relationships 166 between the logical functional entities involved; on this basis, a 167 problem description for authentication and authorization in 168 constrained-node networks is provided. 170 1.1. Terminology 172 Readers are required to be familiar with the terms and concepts 173 defined in [RFC4949], including "authentication", "authorization", 174 "confidentiality", "(data) integrity", "message authentication code", 175 and "verify". 177 REST terms including "resource", "representation", etc. are to be 178 understood as used in HTTP [RFC7231] and CoAP [RFC7252]; the latter 179 also defines additional terms such as "endpoint". 181 Terminology for constrained environments including "constrained 182 device", "constrained-node network", "class 1", etc. is defined in 183 [RFC7228]. 185 In addition, this document uses the following terminology: 187 Resource (R): an item of interest which is represented through an 188 interface. It might contain sensor or actuator values or other 189 information. (Intended to coincide with the definitions of 190 [RFC7252] and [RFC7231].) 192 Constrained node: a constrained device in the sense of [RFC7228]. 194 Actor: A logical functional entity that performs one or more tasks. 195 Multiple actors may be present within a single device or a single 196 piece of software. 198 Resource Server (RS): An entity which hosts and represents a 199 Resource. (Used here to discuss the server that provides a 200 resource that is the end, not the means, of the authenticated 201 authorization process - i.e., not CAS or AS.) 203 Client (C): An entity which attempts to access a resource on a RS. 204 (Used to discuss the client whose access to a resource is the end, 205 not the means, of the authenticated authorization process.) 207 Principal: (Used in its English sense here, and specifically as:) An 208 individual that is either RqP or RO or both. 210 Resource Owner (RO): The principal that is in charge of the resource 211 and controls its access permissions. 213 Requesting Party (RqP): The principal that is in charge of the 214 Client and controls the requests a Client makes and its acceptance 215 of responses. 217 Authorization Server (AS): An entity that prepares and endorses 218 authentication and authorization data for a Resource Server. 220 Client Authorization Server (CAS): An entity that prepares and 221 endorses authentication and authorization data for a Client. 223 Authorization Manager: An entity that prepares and endorses 224 authentication and authorization data for a constrained node. 225 Used in constructions such as "a constrained node's authorization 226 manager" to denote AS for RS and CAS for C. 228 Authenticated Authorization: The confluence of mechanisms for 229 authentication and authorization, ensuring that authorization is 230 applied to and made available for authenticated entities and that 231 entities providing authentication services are authorized to do so 232 for the specific authorization process at hand. 234 Note that other authorization architectures such as OAuth [RFC6749] 235 or UMA [I-D.hardjono-oauth-umacore] focus on the authorization 236 problems on the RS side, in particular what accesses to resources the 237 RS is to allow. In this document the term authorization includes 238 this aspect, but is also used for the client-side aspect of 239 authorization, i.e., more generally allowing RqPs to decide what 240 interactions clients may perform with other endpoints. 242 2. Architecture and High-level Problem Statement 244 This document deals with how to control and protect resource-based 245 interaction between potentially constrained endpoints. The following 246 setting is assumed as a high-level problem statement: 248 o An endpoint may host functionality of one or more actors. 250 o C in one endpoint requests to access R on a RS in another 251 endpoint. 253 o A priori, the endpoints do not necessarily have a pre-existing 254 security relationship to each other. 256 o Either of the endpoints, or both, may be constrained. 258 2.1. Elements of an Architecture 260 Without loss of generality, we focus on the C functionality in one 261 endpoint, which we therefore also call C, accessing the RS 262 functionality in another endpoint, which we therefore also call RS. 264 The constrained level and its security objectives are detailed in 265 Section 5.1. 267 -------------- -------------- 268 | ------- | | ------- | 269 | | C | ------ requests resource -----> | RS | | 270 | ------- <----- provides resource ------ ------- | 271 | Endpoint | | Endpoint | 272 -------------- -------------- 274 Figure 1: Constrained Level 276 The authorization decisions at the endpoints are made on behalf of 277 the principals that control the endpoints. To reuse OAuth and UMA 278 terminology, the present document calls the principal that is 279 controlling C the Requesting Party (RqP), and calls the principal 280 that is controlling RS the Resource Owner (RO). Each principal makes 281 authorization decisions (possibly encapsulating them into security 282 policies) which the endpoint it controls then enforces. 284 The specific security objectives will vary, but for any specific 285 version of this scenario will include one or more of: 287 o Objectives of type 1: No entity not authorized by the RO has 288 access to (or otherwise gains knowledge of) R. 290 o Objectives of type 2: C is exchanging information with (sending a 291 request to, accepting a response from) a resource only where it 292 can ascertain that RqP has authorized the exchange with R. 294 Objectives of type 1 require performing authorization on the Resource 295 Server side while objectives of type 2 require performing 296 authorization on the Client side. 298 More on the security objectives of the principal level in 299 Section 5.2. 301 ------- ------- 302 | RqP | | RO | Principal Level 303 ------- ------- 304 | | 305 in charge of in charge of 306 | | 307 V V 308 ------- ------- 309 | C | -- requests resource --> | RS | Constrained Level 310 ------- <-- provides resource-- ------- 312 Figure 2: Constrained Level and Principal Level 314 The use cases defined in [RFC7744] demonstrate that constrained 315 devices are often used for scenarios where their principals are not 316 present at the time of the communication, are not able to communicate 317 directly with the device because of a lack of user interfaces or 318 displays, or may prefer the device to communicate autonomously. 320 Moreover, constrained endpoints may need support with tasks requiring 321 heavy processing, large memory or storage, or interfacing to humans, 322 such as management of security policies defined by a principal. The 323 principal, in turn, requires some agent maintaining the policies 324 governing how its endpoints will interact. 326 For these reasons, another level of nodes is introduced in the 327 architecture, the less-constrained level. Using OAuth terminology, 328 AS acts on behalf of the RO to control and support the RS in handling 329 access requests, employing a pre-existing security relationship with 330 RS. We complement this with CAS acting on behalf of RqP to control 331 and support the C in making resource requests and acting on the 332 responses received, employing a pre-existing security relationship 333 with C. To further relieve the constrained level, authorization (and 334 related authentication) mechanisms may be employed between CAS and AS 335 (Section 6.2). (Again, both CAS and AS are conceptual entities 336 controlled by their respective principals. Many of these entities, 337 often acting for different principals, can be combined into a single 338 server implementation; this of course requires proper segregation of 339 the control information provided by each principal.) 341 ------- ------- 342 | RqP | | RO | Principal Level 343 ------- ------- 344 | | 345 controls controls 346 | | 347 V V 348 -------- ------- 349 | CAS | <- AuthN and AuthZ -> | AS | Less-Constrained Level 350 -------- ------- 351 | | 352 controls and supports controls and supports 353 authentication authentication 354 and authorization and authorization 355 | | 356 V V 357 ------- ------- 358 | C | -- requests resource --> | RS | Constrained Level 359 ------- <-- provides resource-- ------- 361 Figure 3: Overall architecture 363 Figure 3 shows all three levels considered in this document. Note 364 that the vertical arrows point down to illustrate exerting control 365 and providing support; this is complemented by information flows that 366 often are bidirectional. Note also that not all entities need to be 367 ready to communicate at any point in time; for instance, RqP may have 368 provided enough information to CAS that CAS can autonomously 369 negotiate access to RS with AS for C based on this information. 371 2.2. Architecture Variants 373 The elements of the architecture described above are architectural. 374 In a specific scenario, several elements can share a single device or 375 even be combined in a single piece of software. If C is located on a 376 more powerful device, it can be combined with CAS: 378 ------- -------- 379 | RqP | | RO | Principal Level 380 ------- -------- 381 | | 382 in charge of in charge of 383 | | 384 V V 385 ------------ -------- 386 | CAS + C | <- AuthN and AuthZ -> | AS | Less-Constrained Level 387 ------------ -------- 388 ^ | 389 \__ | 390 \___ authentication 391 \___ and authorization 392 requests resource/ \___ support 393 provides resource \___ | 394 \___ | 395 V V 396 ------- 397 | RS | Constrained Level 398 ------- 400 Figure 4: Combined C and CAS 402 If RS is located on a more powerful device, it can be combined with 403 AS: 405 ------- ------- 406 | RqP | | RO | Principal Level 407 ------- ------- 408 | | 409 in charge of in charge of 410 | | 411 V V 412 ---------- ----------- 413 | CAS | <- AuthN and AuthZ -> | RS + AS | Less-Constrained Level 414 ---------- ----------- 415 | ^ 416 authentication ___/ 417 and authorization ___/ 418 support ___/ request resource / provides resource 419 | ___/ 420 V ___/ 421 ------- / 422 | C | <- 423 ------- 425 Figure 5: Combined AS and RS 427 If C and RS have the same principal, CAS and AS can be combined. 429 ------------ 430 | RqP = RO | Principal Level 431 ------------ 432 | 433 in charge of 434 | 435 V 436 -------------- 437 | CAS + AS | Less-Constrained Level 438 -------------- 439 / \ 440 / \ 441 authentication authentication 442 and authorization and authorization 443 support support 444 / \ 445 V V 446 ------- ------- 447 | C | -- requests resource --> | RS | Constrained Level 448 ------- <-- provides resource -- ------- 450 Figure 6: CAS combined with AS 452 2.3. Information Flows 454 We now formulate the problem statement in terms of the information 455 flows the architecture focuses on. 457 The interaction with the nodes on the principal level, RO and RqP, is 458 not involving constrained nodes and therefore can employ an existing 459 mechanism. The less-constrained nodes, CAS and AS, support the 460 constrained nodes, C and RS, with control information, for example 461 permissions of clients, conditions on resources, attributes of client 462 and resource servers, keys and credentials. This control information 463 may be rather different for C and RS, reflecting the intrinsic 464 asymmetry with C initiating the request for access to a resource, and 465 RS acting on a received request, and C finally acting on the received 466 response. 468 The potential information flows are shown in Figure 7. The direction 469 of the vertical arrows expresses the exertion of control; actual 470 information flow is bidirectional. 472 The message flow may pass unprotected paths and thus need to be 473 protected, potentially beyond a single REST hop (Section 3.1): 475 ------- ------- 476 | CAS | | AS | 477 ------- ------- 478 a ^ | b a = requests for control info a ^ | b 479 | | b = control information | | 480 | v | v 481 ------- ------- 482 | C | ------ request -------------------> | RS | 483 | | <----- response ------------------- | | 484 ------- ------- 486 Figure 7: Information flows that need to be protected 488 o We assume that the necessary keys/credentials for protecting the 489 control information between the potentially constrained nodes and 490 their associated less-constrained nodes are pre-established, for 491 example as part of the commissioning procedure. 493 o Any necessary keys/credentials for protecting the interaction 494 between the potentially constrained nodes will need to be 495 established and maintained as part of a solution. 497 In terms of the elements of the architecture laid out above, this 498 document's problem statement for authorization in constrained 499 environments can then be summarized as follows: 501 o The interaction between potentially constrained endpoints is 502 controlled by control information provided by less-constrained 503 nodes on behalf of the principals of the endpoints. 505 o The interaction between the endpoints needs to be secured, as well 506 as the establishment of the necessary keys for securing the 507 interaction, potentially end-to-end through intermediary nodes. 509 o The mechanism for transferring control information needs to be 510 secured, potentially end-to-end through intermediary nodes. Pre- 511 established keying material may need to be employed for 512 establishing the keys used to protect these information flows. 514 (Note that other aspects relevant to secure constrained node 515 communication such as secure bootstrap or group communication are not 516 specifically addressed by the present document.) 518 3. Security Objectives 520 The security objectives that are addressed by an authorization 521 solution include confidentiality and integrity. Additionally, 522 allowing only selected entities limits the burden on system 523 resources, thus helping to achieve availability. Misconfigured or 524 wrongly designed authorization solutions can result in availability 525 breaches (denial of service): Users might no longer be able to use 526 data and services as they are supposed to. 528 Authentication mechanisms can achieve additional security objectives 529 such as accountability and third-party verifiability. These 530 additional objectives are not directly related to authorization and 531 thus are not in scope of this draft, but may nevertheless be 532 relevant. Accountability and third-party verifiability may require 533 authentication on a device level, if it is necessary to determine 534 which device performed an action. In other cases it may be more 535 important to find out who is responsible for the device's actions. 536 See also Section 4 for more discussion about authentication and 537 authorization. 539 The security objectives and their relative importance differ for the 540 various constrained environment applications and use cases [RFC7744]. 542 In many cases, one participating party has different security 543 objectives than another. To achieve a security objective of one 544 party, another party may be required to provide a service. For 545 example, if RqP requires the integrity of representations of a 546 resource R that RS is hosting, both C and RS need to partake in 547 integrity-protecting the transmitted data. Moreover, RS needs to 548 protect any write access to this resource as well as to relevant 549 other resources (such as configuration information, firmware update 550 resources) to prevent unauthorized users from manipulating R. 552 3.1. End-to-End Security Objectives in Multi-Hop Scenarios 554 In many cases, the information flows described in Section 2.3 cross 555 multiple client-server pairings but still need to be protected end- 556 to-end. For example, AS may not be connected to RS (or may not want 557 to exercise such a connection), relying on C for transferring 558 authorization information. As the authorization information is 559 related to the permissions granted to C, C must not be in a position 560 to manipulate this information, which therefore requires integrity 561 protection on the way between AS and RS. 563 As another example, resource representations sent between endpoints 564 may be stored in intermediary nodes, such as caching proxies or pub- 565 sub brokers. Where these intermediaries cannot be relied on to 566 fulfill the security objectives of the endpoints, these will need to 567 protect the exchanges beyond a single client-server exchange. 569 Note that there may also be cases of intermediary nodes that very 570 much partake in the security objectives to be achieved. The question 571 what are the pairs of endpoints between which the communication needs 572 end-to-end protection (and which aspect of protection) is defined by 573 the specific use case. Two examples of intermediary nodes executing 574 security functionality: 576 o To enable a trustworthy publication service, a pub-sub broker may 577 be untrusted with the plaintext content of a publication 578 (confidentiality), but required to verify that the publication is 579 performed by claimed publisher and is not a replay of an old 580 publication (authenticity/integrity). 582 o To comply with requirements of transparency, a gateway may be 583 allowed to read, verify (authenticity) but not modify (integrity) 584 a resource representation which therefore also is end-to-end 585 integrity protected from the server towards a client behind the 586 gateway. 588 In order to support the required communication and application 589 security, keying material needs to be established between the 590 relevant nodes in the architecture. 592 4. Authentication and Authorization 594 Server-side authorization solutions aim at protecting the access to 595 items of interest, for instance hardware or software resources or 596 data: They enable the resource owner to control who can access it and 597 how. 599 To determine if an entity is authorized to access a resource, an 600 authentication mechanism is needed. According to the Internet 601 Security Glossary [RFC4949], authentication is "the process of 602 verifying a claim that a system entity or system resource has a 603 certain attribute value." Examples for attribute values are the ID 604 of a device, the type of the device or the name of its owner. 606 The security objectives the authorization mechanism aims at can only 607 be achieved if the authentication and the authorization mechanism 608 work together correctly. We speak of authenticated authorization to 609 refer to the required synthesis of mechanism for authentication and 610 authorization. 612 Where used for authorization, the set of authenticated attributes 613 must be meaningful for this purpose, i.e., authorization decisions 614 must be possible based on these attributes. If the authorization 615 policy assigns permissions to an individual entity, the set of 616 authenticated attributes must be suitable to uniquely identify this 617 entity. 619 In scenarios where devices are communicating autonomously there is 620 often less need to uniquely identify an individual device: For a 621 principal, the fact that a device belongs to a certain company or 622 that it has a specific type (such as a light bulb) or location may be 623 more important than that it has a unique identifier. 625 (As a special case for the authorization of read access to a 626 resource, RS may simply make an encrypted representation available to 627 anyone [OSCAR]. In this case, controlling read access to that 628 resource can be reduced to controlling read access to the key; 629 partially removing access also requires a timely update of the key 630 for RS and all participants still authorized.) 632 Principals (RqP and RO) need to decide about the required level of 633 granularity for the authorization. For example, we distinguish 634 device authorization from owner authorization, and flat authorization 635 from unrestricted authorization. In the first case different access 636 permissions are granted to individual devices while in the second 637 case individual owners are authorized. If flat authorization is 638 used, all authenticated entities are implicitly authorized and have 639 the same access permissions. Unrestricted authorization for an item 640 of interest means that no authorization mechanism is used for 641 accessing this resource (not even by authentication) and all entities 642 are able to access the item as they see fit (note that an 643 authorization mechanism may still be used to arrive at the decision 644 to employ unrestricted authorization). 646 More fine-grained authorization does not necessarily provide more 647 security but can be more flexible. Principals need to consider that 648 an entity should only be granted the permissions it really needs 649 (principle of least privilege), to ensure the confidentiality and 650 integrity of resources. 652 Client-side authorization solutions aim at protecting the client from 653 disclosing information to or ingesting information from resource 654 servers RqP does not want it to interact with in the given way. 655 Again, flat authorization (the server can be authenticated) may be 656 sufficient, or more fine-grained authorization may be required. The 657 client-side authorization also pertains to the level of protection 658 required for the exchanges with the server (e.g., confidentiality). 659 In the browser web, client-side authorization is often left to the 660 human user; a constrained client may not have that available all the 661 time but still needs to implement the wishes of the principal 662 controlling it, the RqP. 664 For all cases where an authorization solution is needed (all but 665 unrestricted authorization), the enforcing party needs to be able to 666 authenticate the party that is to be authorized. Authentication is 667 therefore required for messages that contain (or otherwise update) 668 representations of an accessed item. More precisely: The enforcing 669 party needs to make sure that the receiver of a message containing a 670 representation is authorized to receive it, both in the case of a 671 client sending a representation to a server and vice versa. In 672 addition, it needs to ensure that the actual sender of a message 673 containing a representation is indeed the one authorized to send this 674 message, again for both the client-to-server and server-to-client 675 case. To achieve this, integrity protection of these messages is 676 required: Authenticity cannot be assured if it is possible for an 677 attacker to modify the message during transmission. 679 In some cases, only one side (client or server side) requires the 680 integrity and / or confidentiality of a resource value. Principals 681 may decide to omit authentication (unrestricted authorization), or 682 use flat authorization (just employing an authentication mechanism). 683 However, as indicated in Section 3, the security objectives of both 684 sides must be considered, which can often only be achieved when the 685 other side can be relied on to perform some security service. 687 5. Actors and their Tasks 689 This and the following section look at the resulting architecture 690 from two different perspectives: This section provides a more 691 detailed description of the various "actors" in the architecture, the 692 logical functional entities performing the tasks required. The 693 following section then will focus on the protocols run between these 694 functional entities. 696 For the purposes of this document, an actor consists of a set of 697 tasks and additionally has a security domain (client domain or server 698 domain) and a level (constrained, principal, less-constrained). 699 Tasks are assigned to actors according to their security domain and 700 required level. 702 Note that actors are a concept to understand the security 703 requirements for constrained devices. The architecture of an actual 704 solution might differ as long as the security requirements that 705 derive from the relationship between the identified actors are 706 considered. Several actors might share a single device or even be 707 combined in a single piece of software. Interfaces between actors 708 may be realized as protocols or be internal to such a piece of 709 software. 711 A more detailed discussion of the tasks the actors have to perform in 712 order to achieve specific security objectives is provided in 713 [I-D.gerdes-ace-tasks]. 715 5.1. Constrained Level Actors 717 As described in the problem statement (see Section 2), either C or RS 718 or both of them may be located on a constrained node. We therefore 719 define that C and RS must be able to perform their tasks even if they 720 are located on a constrained node. Thus, C and RS are considered to 721 be Constrained Level Actors. 723 C performs the following tasks: 725 o Communicate in a secure way (provide for confidentiality and 726 integrity of messages), including access requests. 728 o Validate that the RqP ("client-side") authorization information 729 allows C to communicate with RS as a server for R (i.e., from C's 730 point of view, RS is authorized as a server for the specific 731 access to R). 733 RS performs the following tasks: 735 o Communicate in a secure way (provide for confidentiality and 736 integrity of messages), including responses to access requests. 738 o Validate that the RO ("server-side") authorization information 739 allows RS to grant C access to the requested resource as requested 740 (i.e., from RS' point of view, C is authorized as a client for the 741 specific access to R). 743 R is an item of interest such as a sensor or actuator value. R is 744 considered to be part of RS and not a separate actor. The device on 745 which RS is located might contain several resources controlled by 746 different ROs. For simplicity of exposition, these resources are 747 described as if they had separate RS. 749 As C and RS do not necessarily know each other they might belong to 750 different security domains. 752 (See Figure 8.) 754 ------- -------- 755 | C | -- requests resource ---> | RS | Constrained Level 756 ------- <-- provides resource--- -------- 758 Figure 8: Constrained Level Actors 760 5.2. Principal Level Actors 762 Our objective is that C and RS are under control of principals in the 763 physical world, the Requesting Party (RqP) and the Resource Owner 764 (RO) respectively. The principals decide about the security policies 765 of their respective endpoints and belong to the same security domain. 767 RqP is in charge of C, i.e. RqP specifies security policies for C, 768 such as with whom C is allowed to communicate. By definition, C and 769 RqP belong to the same security domain. 771 RqP must fulfill the following task: 773 o Configure for C authorization information for sources for R. 775 RO is in charge of R and RS. RO specifies authorization policies for 776 R and decides with whom RS is allowed to communicate. By definition, 777 R, RS and RO belong to the same security domain. 779 RO must fulfill the following task: 781 o Configure for RS authorization information for accessing R. 783 (See Figure 2.) 785 5.3. Less-Constrained Level Actors 787 Constrained level actors can only fulfill a limited number of tasks 788 and may not have network connectivity all the time. To relieve them 789 from having to manage keys for numerous endpoints and conducting 790 computationally intensive tasks, another complexity level for actors 791 is introduced. An actor on the less-constrained level belongs to the 792 same security domain as its respective constrained level actor. They 793 also have the same principal. 795 The Client Authorization Server (CAS) belongs to the same security 796 domain as C and RqP. CAS acts on behalf of RqP. It assists C in 797 authenticating RS and determining if RS is an authorized server for 798 R. CAS can do that because for C, CAS is the authority for claims 799 about RS. 801 CAS performs the following tasks: 803 o Validate on the client side that an entity has certain attributes. 805 o Obtain authorization information about an entity from C's 806 principal (RqP) and provide it to C. 808 o Negotiate means for secure communication to communicate with C. 810 The Authorization Server (AS) belongs to the same security domain as 811 R, RS and RO. AS acts on behalf of RO. It supports RS by 812 authenticating C and determining C's permissions on R. AS can do 813 that because for RS, AS is the authority for claims about C. 815 AS performs the following tasks: 817 o Validate on the server side that an entity has certain attributes. 819 o Obtain authorization information about an entity from RS' 820 principal (RO) and provide it to RS. 822 o Negotiate means for secure communication to communicate with RS. 824 6. Kinds of Protocols 826 Devices on the less-constrained level potentially are more powerful 827 than constrained level devices in terms of processing power, memory, 828 non-volatile storage. This results in different characteristics for 829 the protocols used on these levels. 831 6.1. Constrained Level Protocols 833 A protocol is considered to be on the constrained level if it is used 834 between the actors C and RS which are considered to be constrained 835 (see Section 5.1). C and RS might not belong to the same security 836 domain. Therefore, constrained level protocols need to work between 837 different security domains. 839 Commonly used Internet protocols can not in every case be applied to 840 constrained environments. In some cases, tweaking and profiling is 841 required. In other cases it is beneficial to define new protocols 842 which were designed with the special characteristics of constrained 843 environments in mind. 845 On the constrained level, protocols need to address the specific 846 requirements of constrained environments. Examples for protocols 847 that consider these requirements is the transfer protocol CoAP 848 (Constrained Application Protocol) [RFC7252] and the Datagram 849 Transport Layer Security Protocol (DTLS) [RFC6347] which can be used 850 for channel security. 852 Constrained devices have only limited storage space and thus cannot 853 store large numbers of keys. This is especially important because 854 constrained networks are expected to consist of thousands of nodes. 855 Protocols on the constrained level should keep this limitation in 856 mind. 858 6.1.1. Cross Level Support Protocols 860 Protocols which operate between a constrained device on one side and 861 the corresponding less-constrained device on the other are considered 862 to be (cross level) support protocols. Protocols used between C and 863 CAS or RS and AS are therefore support protocols. 865 Support protocols must consider the limitations of their constrained 866 endpoint and therefore belong to the constrained level protocols. 868 6.2. Less-Constrained Level Protocols 870 A protocol is considered to be on the less-constrained level if it is 871 used between the actors CAS and AS. CAS and AS might belong to 872 different security domains. 874 On the less-constrained level, HTTP [RFC7230] and Transport Layer 875 Security (TLS) [RFC5246] can be used alongside or instead of CoAP and 876 DTLS. Moreover, existing security solutions for authentication and 877 authorization such as the OAuth web authorization framework [RFC6749] 878 and Kerberos [RFC4120] can likely be used without modifications and 879 there are no limitations for the use of a Public Key Infrastructure 880 (PKI). 882 7. Elements of a Solution 884 Without anticipating specific solutions, the following considerations 885 may be helpful in discussing them. 887 7.1. Authorization 889 The core problem we are trying to solve is authorization. The 890 following problems related to authorization need to be addressed: 892 o AS needs to transfer authorization information to RS and CAS needs 893 to transfer authorization information to C. 895 o The transferred authorization information needs to follow a 896 defined format and encoding, which must be efficient for 897 constrained devices, considering size of authorization information 898 and parser complexity. 900 o C and RS need to be able to verify the authenticity of the 901 authorization information they receive. Here as well, there is a 902 trade-off between processing complexity and deployment complexity. 904 o The RS needs to enforce the authorization decisions of the AS, 905 while C needs to abide with the authorization decisions of the 906 CAS. The authorization information might require additional 907 policy evaluation (such as matching against local access control 908 lists, evaluating local conditions). The required "policy 909 evaluation" at the constrained actors needs to be adapted to the 910 capabilities of the devices implementing them. 912 o Finally, as is indicated in the previous bullet, for a particular 913 authorization decision there may be different kinds of 914 authorization information needed, and these pieces of information 915 may be transferred to C and RS at different times and in different 916 ways prior to or during the client request. 918 7.2. Authentication 920 The following problems need to be addressed, when considering 921 authentication: 923 o RS needs to authenticate AS, and C needs to authenticate CAS, to 924 ensure that the authorization information and related data comes 925 from the correct source. 927 o CAS and AS may need to authenticate each other, both to perform 928 the required business logic and to ensure that CAS gets security 929 information related to the resources from the right source. 931 o In some use cases RS needs to authenticate some property of C, in 932 order to map it to the relevant authorization information. In 933 other use cases, authentication and authorization of C may be 934 implicit, for example by encrypting the resource representation 935 the RS only providing access to those who possess the key to 936 decrypt. 938 o C may need to authenticate RS, in order to ensure that it is 939 interacting with the right resources. Alternatively C may just 940 verify the integrity of a received resource representation. 942 o CAS and AS need to authenticate their communication partner (C or 943 RS), in order to ensure it serves the correct device. 945 7.3. Communication Security 947 There are different alternatives to provide communication security, 948 and the problem here is to choose the optimal one for each scenario. 949 We list the available alternatives: 951 o Session-based security at transport layer such as DTLS [RFC6347] 952 offers security, including integrity and confidentiality 953 protection, for the whole application layer exchange. However, 954 DTLS may not provide end-to-end security over multiple hops. 955 Another problem with DTLS is the cost of the handshake protocol, 956 which may be too expensive for constrained devices especially in 957 terms of memory and power consumption for message transmissions. 959 o An alternative is object security at application layer, for 960 instance using [I-D.selander-ace-object-security]. Secure objects 961 can be stored or cached in network nodes and provide security for 962 a more flexible communication model such as publish/subscribe 963 (compare e.g. CoRE Mirror Server [I-D.koster-core-coap-pubsub]). 964 A problem with object security is that it can not provide 965 confidentiality for the message headers. 967 o Hybrid solutions using both session-based and object security are 968 also possible. An example of a hybrid is where authorization 969 information and cryptographic keys are provided by AS in the 970 format of secure data objects, but where the resource access is 971 protected by session-based security. 973 7.4. Cryptographic Keys 975 With respect to cryptographic keys, we see the following problems 976 that need to be addressed: 978 Symmetric vs Asymmetric Keys 979 We need keys both for protection of resource access and for 980 protection of transport of authentication and authorization 981 information. Do we want to support solutions based on asymmetric 982 keys or symmetric keys in both cases? There are classes of 983 devices that can easily perform symmetric cryptography, but 984 consume considerably more time/battery for asymmetric operations. 985 On the other hand asymmetric cryptography has benefits such as in 986 terms of deployment. 988 Key Establishment 989 How are the corresponding cryptographic keys established? 990 Considering Section 7.1 there must be a mapping between these keys 991 and the authorization information, at least in the sense that AS 992 must be able to specify a unique client identifier which RS can 993 verify (using an associated key). One of the use cases of 994 [RFC7744] describes spontaneous change of access policies - such 995 as giving a hitherto unknown client the right to temporarily 996 unlock your house door. In this case C is not previously known to 997 RS and a key must be provisioned by AS. 999 Revocation and Expiration 1000 How are keys replaced and how is a key that has been compromised 1001 revoked in a manner that reaches all affected parties, also 1002 keeping in mind scenarios with intermittent connectivity? 1004 8. Assumptions and Requirements 1006 In this section we list a set of candidate assumptions and 1007 requirements to make the problem description in the previous sections 1008 more concise and precise. 1010 8.1. Architecture 1012 The architecture consists of at least the following types of nodes: 1014 o RS hosting resources, and responding to access requests 1016 o C requesting access to resources 1018 o AS supporting the access request/response procedure by providing 1019 authorization information to RS 1020 * AS may support this by aiding RS in authenticating C, or 1021 providing cryptographic keys or credentials to C and/or RS to 1022 secure the request/response procedure. 1024 o CAS supporting the access request/response procedure by providing 1025 authorization information to C 1027 * CAS may support this by aiding C in authenticating RS, 1028 forwarding information between AS and C (possibly ultimately 1029 for RS), or providing cryptographic keys or credentials to C 1030 and/or RS to secure the request/response procedure. 1032 o The architecture allows for intermediary nodes between any pair of 1033 C, RS, AS, and CAS, such as forward or reverse proxies in the CoRE 1034 architecture. (Solutions may or may not support all 1035 combinations.) 1037 * The architecture does not make a choice between session based 1038 security and data object security. 1040 8.2. Constrained Devices 1042 o C and/or RS may be constrained in terms of power, processing, 1043 communication bandwidth, memory and storage space, and moreover: 1045 * unable to manage complex authorization policies 1047 * unable to manage a large number of secure connections 1049 * without user interface 1051 * without constant network connectivity 1053 * unable to precisely measure time 1055 * required to save on wireless communication due to high power 1056 consumption 1058 o CAS and AS are not assumed to be constrained devices. 1060 o All devices under consideration can process symmetric cryptography 1061 without incurring an excessive performance penalty. 1063 * We assume the use of a standardized symmetric key algorithm, 1064 such as AES. 1066 * Except for the most constrained devices we assume the use of a 1067 standardized cryptographic hash function such as SHA-256 (which 1068 can be used with the HMAC construction for integrity 1069 protection). 1071 o Public key cryptography requires additional resources (such as 1072 RAM, ROM, power, specialized hardware). 1074 o A DTLS handshake involves significant computation, communication, 1075 and memory overheads in the context of constrained devices. 1077 * The RAM requirements of DTLS handshakes with public key 1078 cryptography are prohibitive for certain constrained devices. 1080 * Certificate-based DTLS handshakes require significant volumes 1081 of communication, RAM (message buffers) and computation. 1083 o A solution will need to consider support for a simple scheme for 1084 expiring authentication and authorization information on devices 1085 which are unable to measure time (cf. section Section 9.2). 1087 8.3. Authentication 1089 o RS needs to authenticate AS to ensure that the authorization 1090 information and related data comes from the correct source. 1092 o Similarly, C needs to authenticate CAS to ensure that the 1093 authorization information and related data comes from the correct 1094 source. 1096 o Depending on use case and authorization requirements, C, RS, CAS, 1097 or AS may need to authenticate messages from each other. 1099 8.4. Server-side Authorization 1101 o RS enforces authorization for access to a resource based on 1102 credentials presented by C, the requested resource, the REST 1103 method, and local context in RS at the time of the request, or on 1104 any subset of this information. 1106 o The credentials presented by C may have been provided by CAS. 1108 o The underlying authorization decision is taken either by AS or RS. 1110 o The authorization decision is enforced by RS. 1112 * RS needs to have authorization information in order to verify 1113 that C is allowed to access the resource as requested. 1115 * RS needs to make sure that it provides resource access only to 1116 authorized clients. 1118 o Apart from authorization for access to a resource, authorization 1119 may also be required for access to information about a resource 1120 (for instance, resource descriptions). 1122 o The solution may need to be able to support the delegation of 1123 access rights. 1125 8.5. Client-side Authorization Information 1127 o C enforces client-side authorization by protecting its requests to 1128 RS and by authenticating results from RS, making use of decisions 1129 and policies as well as keying material provided by CAS. 1131 8.6. Server-side Authorization Information 1133 o Authorization information is transferred from AS to RS using 1134 Agent, Push or Pull mechanisms [RFC2904]. 1136 o RS needs to authenticate that the authorization information is 1137 coming from AS (integrity). 1139 o The authorization information may also be encrypted end-to-end 1140 between AS and RS (confidentiality). 1142 o The architecture supports the case where RS may not be able to 1143 communicate with AS at the time of the request from C. 1145 o RS may store or cache authorization information. 1147 o Authorization information may be pre-configured in RS. 1149 o Authorization information stored or cached in RS needs to be 1150 possible to change. The change of such information needs to be 1151 subject to authorization. 1153 o Authorization policies stored on RS may be handled as a resource, 1154 i.e. information located at a particular URI, accessed with 1155 RESTful methods, and the access being subject to the same 1156 authorization mechanics. AS may have special privileges when 1157 requesting access to the authorization policy resources on RS. 1159 o There may be mechanisms for C to look up the AS which provides 1160 authorization information about a particular resource. 1162 8.7. Resource Access 1164 o Resources are accessed in a RESTful manner using methods such as 1165 GET, PUT, POST, DELETE. 1167 o By default, the resource request needs to be integrity protected 1168 and may be encrypted end-to-end from C to RS. It needs to be 1169 possible for RS to detect a replayed request. 1171 o By default, the response to a request needs to be integrity 1172 protected and may be encrypted end-to-end from RS to C. It needs 1173 to be possible for C to detect a replayed response. 1175 o RS needs to be able to verify that the request comes from an 1176 authorized client. 1178 o C needs to be able to verify that the response to a request comes 1179 from the intended RS. 1181 o There may be resources whose access need not be protected (e.g. 1182 for discovery of the responsible AS). 1184 8.8. Keys and Cipher Suites 1186 o A constrained node and its authorization manager (i.e., RS and AS, 1187 and C and CAS) have established cryptographic keys. For example, 1188 they share a secret key or each have the other's public key. 1190 o The transfer of authorization information is protected with 1191 symmetric and/or asymmetric keys. 1193 o The access request/response can be protected with symmetric and/or 1194 asymmetric keys. 1196 o There must be a mechanism for RS to establish the necessary key(s) 1197 to verify and decrypt the request and to protect the response. 1199 o There must be a mechanism for C to establish the necessary key(s) 1200 to protect the request and to verify and decrypt the response. 1202 o There must be a mechanism for C to obtain the supported cipher 1203 suites of a RS. 1205 8.9. Network Considerations 1207 o A solution will need to consider network overload due to avoidable 1208 communication of a constrained node with its authorization manager 1209 (C with CAS, RS with AS). 1211 o A solution will need to consider network overload by compact 1212 authorization information representation. 1214 o A solution may want to optimize the case where authorization 1215 information does not change often. 1217 o A solution may consider support for an efficient mechanism for 1218 providing authorization information to multiple RSs, for example 1219 when multiple entities need to be configured or change state. 1221 8.10. Legacy Considerations 1223 o A solution may consider interworking with existing infrastructure. 1225 o A solution may consider supporting authorization of access to 1226 legacy devices. 1228 9. Security Considerations 1230 This document discusses authorization-related tasks for constrained 1231 environments and describes how these tasks can be mapped to actors in 1232 the architecture. 1234 The entire document is about security. Security considerations 1235 applicable to authentication and authorization in RESTful 1236 environments are provided in e.g. OAuth 2.0 [RFC6749]. 1238 In this section we focus on specific security aspects related to 1239 authorization in constrained-node networks. Section 11.6 of 1240 [RFC7252], "Constrained node considerations", discusses implications 1241 of specific constraints on the security mechanisms employed. A wider 1242 view of security in constrained-node networks is provided in 1243 [I-D.garcia-core-security]. 1245 9.1. Physical Attacks on Sensor and Actuator Networks 1247 The focus of this work is on constrained-node networks consisting of 1248 connected sensors and actuators. The main function of such devices 1249 is to interact with the physical world by gathering information or 1250 performing an action. We now discuss attacks performed with physical 1251 access to such devices. 1253 The main threats to sensors and actuator networks are: 1255 o Unauthorized access to data to and from sensors and actuators, 1256 including eavesdropping and manipulation of data. 1258 o Denial-of-service making the sensor/actuator unable to perform its 1259 intended task correctly. 1261 A number of attacks can be made with physical access to a device 1262 including probing attacks, timing attacks, power attacks, etc. 1263 However, with physical access to a sensor or actuator device it is 1264 possible to directly perform attacks equivalent of eavesdropping, 1265 manipulating data or denial of service. For example: 1267 o Instead of eavesdropping the sensor data or attacking the 1268 authorization system to gain access to the data, the attacker 1269 could make its own measurements on the physical object. 1271 o Instead of manipulating the sensor data the attacker could change 1272 the physical object which the sensor is measuring, thereby 1273 changing the payload data which is being sent. 1275 o Instead of manipulating data for an actuator or attacking the 1276 authorization system, the attacker could perform an unauthorized 1277 action directly on the physical object. 1279 o A denial-of-service attack could be performed physically on the 1280 object or device. 1282 All these attacks are possible by having physical access to the 1283 device, since the assets are related to the physical world. 1284 Moreover, this kind of attacks are in many cases straightforward 1285 (requires no special competence or tools, low cost given physical 1286 access, etc.) 1288 As a conclusion, if an attacker has full physical access to a 1289 sensor or actuator device, then much of the security functionality 1290 elaborated in this draft is not effective to protect the asset 1291 during the physical attack. 1293 Since it does not make sense to design a solution for a situation 1294 that cannot be protected against we assume there is no need to 1295 protect assets which are exposed during a physical attack. In 1296 other words, either an attacker does not have physical access to 1297 the sensor or actuator device, or if it has, the attack shall only 1298 have effect during the period of physical attack, and shall be 1299 limited in extent to the physical control the attacker exerts 1300 (e.g., must not affect the security of other devices.) 1302 9.2. Time Measurements 1304 Measuring time with certain accuracy is important to achieve certain 1305 security properties, for example to determine whether a public key 1306 certificate, access token or some other assertion is valid. 1308 Dynamic authorization in itself requires the ability to handle expiry 1309 or revocation of authorization decisions or to distinguish new 1310 authorization decisions from old. 1312 For certain categories of devices we can assume that there is an 1313 internal clock which is sufficiently accurate to handle the time 1314 measurement requirements. If RS can connect directly to AS it could 1315 get updated in terms of time as well as revocation information. 1317 If RS continuously measures time but can't connect to AS or other 1318 trusted source, time drift may have to be accepted and it may not be 1319 able to manage revocation. However, it may still be able to handle 1320 short lived access rights within some margins, by measuring the time 1321 since arrival of authorization information or request. 1323 Some categories of devices in scope may be unable measure time with 1324 any accuracy (e.g. because of sleep cycles). This category of 1325 devices is not suitable for the use cases which require measuring 1326 validity of assertions and authorizations in terms of absolute time. 1328 10. IANA Considerations 1330 This document has no actions for IANA. 1332 11. Acknowledgements 1334 The authors would like to thank Olaf Bergmann, Robert Cragie, Samuel 1335 Erdtman, Klaus Hartke, Sandeep Kumar, John Mattson, Corinna Schmitt, 1336 Mohit Sethi, Abhinav Somaraju, Hannes Tschofenig, Vlasios Tsiatsis 1337 and Erik Wahlstroem for contributing to the discussion, giving 1338 helpful input and commenting on previous forms of this draft. The 1339 authors would also like to specifically acknowledge input provided by 1340 Hummen and others [HUM14delegation]. 1342 12. Informative References 1344 [HUM14delegation] 1345 Hummen, R., Shafagh, H., Raza, S., Voigt, T., and K. 1346 Wehrle, "Delegation-based Authentication and Authorization 1347 for the IP-based Internet of Things", 11th IEEE 1348 International Conference on Sensing, Communication, and 1349 Networking (SECON'14), June 30 - July 3, 2014. 1351 [I-D.garcia-core-security] 1352 Garcia-Morchon, O., Kumar, S., Keoh, S., Hummen, R., and 1353 R. Struik, "Security Considerations in the IP-based 1354 Internet of Things", draft-garcia-core-security-06 (work 1355 in progress), September 2013. 1357 [I-D.gerdes-ace-tasks] 1358 Gerdes, S., "Authorization-Related Tasks in Constrained 1359 Environments", draft-gerdes-ace-tasks-00 (work in 1360 progress), September 2015. 1362 [I-D.hardjono-oauth-umacore] 1363 Hardjono, T., Maler, E., Machulak, M., and D. Catalano, 1364 "User-Managed Access (UMA) Profile of OAuth 2.0", draft- 1365 hardjono-oauth-umacore-14 (work in progress), January 1366 2016. 1368 [I-D.koster-core-coap-pubsub] 1369 Koster, M., Keranen, A., and J. Jimenez, "Publish- 1370 Subscribe Broker for the Constrained Application Protocol 1371 (CoAP)", draft-koster-core-coap-pubsub-04 (work in 1372 progress), November 2015. 1374 [I-D.selander-ace-object-security] 1375 Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 1376 "Object Security of CoAP (OSCOAP)", draft-selander-ace- 1377 object-security-03 (work in progress), October 2015. 1379 [OSCAR] Vucinic, M., Tourancheau, B., Rousseau, F., Duda, A., 1380 Damon, L., and R. Guizzetti, "OSCAR: Object Security 1381 Architecture for the Internet of Things", CoRR vol. 1382 abs/1404.7799, 2014. 1384 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 1385 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 1386 D. Spence, "AAA Authorization Framework", RFC 2904, DOI 1387 10.17487/RFC2904, August 2000, 1388 . 1390 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The 1391 Kerberos Network Authentication Service (V5)", RFC 4120, 1392 DOI 10.17487/RFC4120, July 2005, 1393 . 1395 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 1396 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 1397 . 1399 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1400 (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ 1401 RFC5246, August 2008, 1402 . 1404 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1405 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1406 January 2012, . 1408 [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", 1409 RFC 6749, DOI 10.17487/RFC6749, October 2012, 1410 . 1412 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1413 Constrained-Node Networks", RFC 7228, DOI 10.17487/ 1414 RFC7228, May 2014, 1415 . 1417 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1418 Protocol (HTTP/1.1): Message Syntax and Routing", RFC 1419 7230, DOI 10.17487/RFC7230, June 2014, 1420 . 1422 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1423 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 1424 10.17487/RFC7231, June 2014, 1425 . 1427 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1428 Application Protocol (CoAP)", RFC 7252, DOI 10.17487/ 1429 RFC7252, June 2014, 1430 . 1432 [RFC7744] Seitz, L., Ed., Gerdes, S., Ed., Selander, G., Mani, M., 1433 and S. Kumar, "Use Cases for Authentication and 1434 Authorization in Constrained Environments", RFC 7744, DOI 1435 10.17487/RFC7744, January 2016, 1436 . 1438 Authors' Addresses 1439 Stefanie Gerdes 1440 Universitaet Bremen TZI 1441 Postfach 330440 1442 Bremen D-28359 1443 Germany 1445 Phone: +49-421-218-63906 1446 Email: gerdes@tzi.org 1448 Ludwig Seitz 1449 SICS Swedish ICT AB 1450 Scheelevaegen 17 1451 Lund 223 70 1452 Sweden 1454 Email: ludwig@sics.se 1456 Goeran Selander 1457 Ericsson 1458 Faroegatan 6 1459 Kista 164 80 1460 Sweden 1462 Email: goran.selander@ericsson.com 1464 Carsten Bormann (editor) 1465 Universitaet Bremen TZI 1466 Postfach 330440 1467 Bremen D-28359 1468 Germany 1470 Phone: +49-421-218-63921 1471 Email: cabo@tzi.org