idnits 2.17.1 draft-ietf-ace-actors-02.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 (October 19, 2015) is 3083 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-14) exists of draft-hardjono-oauth-umacore-13 == Outdated reference: A later version (-10) exists of draft-ietf-ace-usecases-09 == Outdated reference: A later version (-05) exists of draft-koster-core-coap-pubsub-02 == Outdated reference: A later version (-06) exists of draft-selander-ace-object-security-02 -- Obsolete informational reference (is this intentional?): RFC 5246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 (~~), 5 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: April 21, 2016 SICS Swedish ICT AB 6 G. Selander 7 Ericsson 8 C. Bormann, Ed. 9 Universitaet Bremen TZI 10 October 19, 2015 12 An architecture for authorization in constrained environments 13 draft-ietf-ace-actors-02 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 April 21, 2016. 42 Copyright Notice 44 Copyright (c) 2015 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 . . . . . . . . 5 62 2.1. Elements of an Architecture . . . . . . . . . . . . . . . 5 63 2.2. Architecture Variants . . . . . . . . . . . . . . . . . . 8 64 2.3. Problem statement . . . . . . . . . . . . . . . . . . . . 11 65 3. Security Objectives . . . . . . . . . . . . . . . . . . . . . 12 66 3.1. End-to-End Security Objectives in Multi-Hop Scenarios . . 13 67 4. Authentication and Authorization . . . . . . . . . . . . . . 13 68 5. Actors and their Tasks . . . . . . . . . . . . . . . . . . . 15 69 5.1. Constrained Level Actors . . . . . . . . . . . . . . . . 16 70 5.2. Principal Level Actors . . . . . . . . . . . . . . . . . 17 71 5.3. Less-Constrained Level Actors . . . . . . . . . . . . . . 17 72 6. Kinds of Protocols . . . . . . . . . . . . . . . . . . . . . 18 73 6.1. Constrained Level Protocols . . . . . . . . . . . . . . . 18 74 6.1.1. Cross Level Support Protocols . . . . . . . . . . . . 19 75 6.2. Less-Constrained Level Protocols . . . . . . . . . . . . 19 76 7. Elements of a Solution . . . . . . . . . . . . . . . . . . . 19 77 7.1. Authorization . . . . . . . . . . . . . . . . . . . . . . 19 78 7.2. Authentication . . . . . . . . . . . . . . . . . . . . . 20 79 7.3. Communication Security . . . . . . . . . . . . . . . . . 21 80 7.4. Cryptographic Keys . . . . . . . . . . . . . . . . . . . 21 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 . . . . . . . . . . 24 87 8.6. Server-side Authorization Information . . . . . . . . . . 25 88 8.7. Resource Access . . . . . . . . . . . . . . . . . . . . . 25 89 8.8. Keys and Cipher Suites . . . . . . . . . . . . . . . . . 26 90 8.9. Network Considerations . . . . . . . . . . . . . . . . . 26 91 8.10. Legacy Considerations . . . . . . . . . . . . . . . . . . 26 92 9. Security Considerations . . . . . . . . . . . . . . . . . . . 27 93 9.1. Physical Attacks on Sensor and Actuator Networks . . . . 27 94 9.2. Time Measurements . . . . . . . . . . . . . . . . . . . . 28 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. 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. 191 Constrained node: a constrained device in the sense of [RFC7228]. 193 Actor: A logical functional entity that performs one or more tasks. 194 Multiple actors may be present within a single device or a single 195 piece of software. 197 Resource Server (RS): An entity which hosts and represents a 198 Resource. 200 Client (C): An entity which attempts to access a resource on an RS. 202 Principal: (Used in its English sense here, and specifically as:) An 203 individual that is either RqP or RO or both. 205 Resource Owner (RO): The principal that is in charge of the resource 206 and controls its access permissions. 208 Requesting Party (RqP): The principal that is in charge of the 209 Client and controls the requests a Client makes and its acceptance 210 of responses. 212 Authorization Server (AS): An entity that prepares and endorses 213 authentication and authorization data for a Resource Server. 215 Client Authorization Server (CAS): An entity that prepares and 216 endorses authentication and authorization data for a Client. 218 Authenticated Authorization: A synthesis of mechanisms for 219 authentication and authorization. 221 Note that other authorization architectures such as OAuth [RFC6749] 222 or UMA [I-D.hardjono-oauth-umacore] focus on the authorization 223 problems on the RS side, in particular what accesses to resources the 224 RS is to allow. In this document the term authorization includes 225 this aspect, but is also used for the client-side aspect of 226 authorization, i.e., more generally to describe allowed interactions 227 with other endpoints. 229 2. Architecture and High-level Problem Statement 231 2.1. Elements of an Architecture 233 This document deals with how to control and protect resource-based 234 interaction between potentially constrained endpoints. The following 235 setting is assumed: 237 o An endpoint may host functionality of one or more actors. 239 o C in one endpoint requests to access R on a RS in another 240 endpoint. 242 o A priori, the endpoints do not necessarily have a pre-existing 243 security relationship to each other. 245 o Either of the endpoints, or both, may be constrained. 247 Without loss of generality, we focus on the C functionality in one 248 endpoint, which we therefore also call C, accessing the RS 249 functionality in another endpoint, which we therefore also call RS. 251 The constrained level and its security objectives are detailed in 252 Section 5.1. 254 -------------- -------------- 255 | ------- | | ------- | 256 | | C | ------ requests resource -----> | RS | | 257 | ------- <----- provides resource ------ ------- | 258 | Endpoint | | Endpoint | 259 -------------- -------------- 261 Figure 1: Constrained Level 263 The authorization decisions at the endpoints are made on behalf of 264 the principals that control the endpoints. To reuse OAuth and UMA 265 terminology, the present document calls C's controlling principal the 266 Requesting Party (RqP), and calls RS's controlling principal the 267 Resource Owner (RO). Each principal makes authorization decisions 268 (possibly encapsulating them into security policies) which the 269 endpoint it controls then enforces. 271 The specific security objectives will vary, but for any specific 272 version of this scenario will include one or more of: 274 o Objectives of type 1: No entity not authorized by the RO has 275 access to (or otherwise gains knowledge of) R. 277 o Objectives of type 2: C is exchanging information with (sending a 278 request to, accepting a response from) a resource only where it 279 can ascertain that RqP has authorized the exchange with R. 281 Objectives of type 1 require performing authorization on the Resource 282 Server side while objectives of type 2 require performing 283 authorization on the Client side. 285 More on the security objectives of the principal level in 286 Section 5.2. 288 ------- ------- 289 | RqP | | RO | Principal Level 290 ------- ------- 291 | | 292 in charge of in charge of 293 | | 294 V V 295 ------- ------- 296 | C | -- requests resource --> | RS | Constrained Level 297 ------- <-- provides resource-- ------- 299 Figure 2: Constrained Level and Principal Level 301 The use cases defined in [I-D.ietf-ace-usecases] demonstrate that 302 constrained devices are often used for scenarios where their 303 principals are not present at the time of the communication, are not 304 able to communicate directly with the device because of a lack of 305 user interfaces or displays, or may prefer the device to communicate 306 autonomously. 308 Moreover, constrained endpoints may need support with tasks requiring 309 heavy processing, large memory or storage, or interfacing to humans, 310 such as management of security policies defined by a principal. The 311 principal, in turn, requires some agent maintaining the policies 312 governing how its endpoints will interact. 314 For these reasons, another level of nodes is introduced in the 315 architecture, the less-constrained level. Using OAuth terminology, 316 AS acts on behalf of the RO to control and support the RS in handling 317 access requests, employing a pre-existing security relationship with 318 RS. We complement this with CAS acting on behalf of RqP to control 319 and support the C in making resource requests and acting on the 320 responses received, employing a pre-existing security relationship 321 with C. To further relieve the constrained level, authorization (and 322 related authentication) mechanisms may be employed between CAS and AS 323 (Section 6.2). (Again, both CAS and AS are conceptual entities 324 controlled by their respective principals. Many of these entities, 325 often acting for different principals, can be combined into a single 326 server implementation; this of course requires proper segregation of 327 the control information provided by each principal.) 328 ------- ------- 329 | RqP | | RO | Principal Level 330 ------- ------- 331 | | 332 controls controls 333 | | 334 V V 335 -------- ------- 336 | CAS | <- AuthN and AuthZ -> | AS | Less-Constrained Level 337 -------- ------- 338 | | 339 controls and supports controls and supports 340 authentication authentication 341 and authorization and authorization 342 | | 343 V V 344 ------- ------- 345 | C | -- requests resource --> | RS | Constrained Level 346 ------- <-- provides resource-- ------- 348 Figure 3: Overall architecture 350 Figure 3 shows all three levels considered in this document. Note 351 that the vertical arrows point down to illustrate exerting control 352 and providing support; this is complemented by information flows that 353 often are bidirectional. Note also that not all entities need to be 354 ready to communicate at any point in time; for instance, RqP may have 355 provided enough information to CAS that CAS can autonomously 356 negotiate access to RS with AS for C based on this information. 358 2.2. Architecture Variants 360 The elements of the architecture described above are architectural. 361 In a specific scenario, several elements can share a single device or 362 even be combined in a single piece of software. If C is located on a 363 more powerful device, it can be combined with CAS: 365 ------- -------- 366 | RqP | | RO | Principal Level 367 ------- -------- 368 | | 369 in charge of in charge of 370 | | 371 V V 372 ------------ -------- 373 | CAS + C | <- AuthN and AuthZ -> | AS | Less-Constrained Level 374 ------------ -------- 375 ^ | 376 \__ | 377 \___ authentication 378 \___ and authorization 379 requests resource/ \___ support 380 provides resource \___ | 381 \___ | 382 V V 383 ------- 384 | RS | Constrained Level 385 ------- 387 Figure 4: Combined C and CAS 389 If RS is located on a more powerful device, it can be combined with 390 AS: 392 ------- ------- 393 | RqP | | RO | Principal Level 394 ------- ------- 395 | | 396 in charge of in charge of 397 | | 398 V V 399 ---------- ----------- 400 | CAS | <- AuthN and AuthZ -> | RS + AS | Less-Constrained Level 401 ---------- ----------- 402 | ^ 403 authentication ___/ 404 and authorization ___/ 405 support ___/ request resource / provides resource 406 | ___/ 407 V ___/ 408 ------- / 409 | C | <- 410 ------- 412 Figure 5: Combined AS and RS 414 If C and RS have the same principal, CAS and AS can be combined. 416 ------------ 417 | RqP = RO | Principal Level 418 ------------ 419 | 420 in charge of 421 | 422 V 423 -------------- 424 | CAS + AS | Less-Constrained Level 425 -------------- 426 / \ 427 / \ 428 authentication authentication 429 and authorization and authorization 430 support support 431 / \ 432 V V 433 ------- ------- 434 | C | -- requests resource --> | RS | Constrained Level 435 ------- <-- provides resource -- ------- 437 Figure 6: CAS combined with AS 439 2.3. Problem statement 441 We now formulate the problem statement in terms of the information 442 flows the architecture focuses on. 444 The interaction with the nodes on the principal level, RO and RqP, is 445 not involving constrained nodes and therefore can employ an existing 446 mechanism. The less-constrained nodes, CAS and AS, support the 447 constrained nodes, C and RS, with control information, for example 448 permissions of clients, conditions on resources, attributes of client 449 and resource servers, keys and credentials. This control information 450 may be rather different for C and RS, reflecting the intrinsic 451 asymmetry with C initiating the request for access to a resource, and 452 RS acting on a received request, and C finally acting on the received 453 response. 455 The potential information flows are shown in Figure 7. The direction 456 of the vertical arrows expresses the exertion of control; actual 457 information flow is bidirectional. 459 The message flow may pass unprotected paths and thus need to be 460 protected, potentially beyond a single REST hop (Section 3.1): 462 ------- ------- 463 | CAS | | AS | 464 ------- ------- 465 a ^ | b a = requests for control info a ^ | b 466 | | b = control information | | 467 | v | v 468 ------- ------- 469 | C | ------ request -------------------> | RS | 470 | | <----- response ------------------- | | 471 ------- ------- 473 Figure 7: Information flows that need to be protected 475 o We assume that the necessary keys/credentials for protecting the 476 control information between the potentially constrained nodes and 477 their associated less-constrained nodes are pre-established, for 478 example as part of the commissioning procedure. 480 o Any necessary keys/credentials for protecting the interaction 481 between the potentially constrained nodes will need to be 482 established and maintained as part of a solution. 484 The problem statement for authorization in constrained environments 485 can be summarized as follows: 487 o The interaction between potentially constrained endpoints is 488 controlled by control information provided by less-constrained 489 nodes on behalf of the principals of the endpoints. 491 o The interaction between the endpoints needs to be secured, as well 492 as the establishment of the necessary keys for securing the 493 interaction, potentially end-to-end through intermediary nodes. 495 o The mechanism for transferring control information needs to be 496 secured, potentially end-to-end through intermediary nodes. Pre- 497 established keying material may need to be employed for 498 establishing the keys used to protect these information flows. 500 3. Security Objectives 502 The security objectives that are addressed by an authorization 503 solution include confidentiality and integrity. Additionally, 504 allowing only selected entities limits the burden on system 505 resources, thus helping to achieve availability. Misconfigured or 506 wrongly designed authorization solutions can result in availability 507 breaches: Users might no longer be able to use data and services as 508 they are supposed to. 510 Authentication mechanisms can achieve additional security objectives 511 such as accountability and third-party verifiability. These 512 additional objectives are not directly related to authorization and 513 thus are not in scope of this draft, but may nevertheless be 514 relevant. Accountability and third-party verifiability may require 515 authentication on a device level, if it is necessary to determine 516 which device performed an action. In other cases it may be more 517 important to find out who is responsible for the device's actions. 518 See also Section 4 for more discussion about authentication and 519 authorization. 521 The security objectives and their relative importance differ for the 522 various constrained environment applications and use cases 523 [I-D.ietf-ace-usecases]. 525 In many cases, one participating party has different security 526 objectives than another. To achieve a security objective of one 527 party, another party may be required to provide a service. For 528 example, if RqP requires the integrity of representations of a 529 resource R that RS is hosting, both C and RS need to partake in 530 integrity-protecting the transmitted data. Moreover, RS needs to 531 protect any write access to this resource as well as to relevant 532 other resources (such as configuration information, firmware update 533 resources) to prevent unauthorized users from manipulating R. 535 3.1. End-to-End Security Objectives in Multi-Hop Scenarios 537 In many cases, the information flows described in Section 2.3 cross 538 multiple client-server pairings but still need to be protected end- 539 to-end. For example, AS may not be connected to RS (or may not want 540 to exercise such a connection), relying on C for transferring 541 authorization information. As the authorization information is 542 related to the permissions granted to C, C must not be in a position 543 to manipulate this information, which therefore requires integrity 544 protection on the way between AS and RS. 546 As another example, resource representations sent between endpoints 547 may be stored in intermediary nodes, such as caching proxies or pub- 548 sub brokers. Where these intermediaries cannot be relied on to 549 fulfill the security objectives of the endpoints, these will need to 550 protect the exchanges beyond a single client-server exchange. 552 Note that there may also be cases of intermediary nodes that very 553 much partake in the security objectives to be achieved. The question 554 what are the pairs of endpoints between which the communication needs 555 end-to-end protection (and which aspect of protection) is defined by 556 the use case. Two examples of intermediary nodes executing security 557 functionality: 559 o To enable a trustworthy publication service, a pub-sub broker may 560 be untrusted with the plaintext content of a publication 561 (confidentiality), but required to verify that the publication is 562 performed by claimed publisher and is not a replay of an old 563 publication (authenticity/integrity). 565 o To comply with requirements of transparency, a gateway may be 566 allowed to read, verify (authenticity) but not modify (integrity) 567 a resource representation which therefore also is end-to-end 568 integrity protected from the server towards a client behind the 569 gateway. 571 In order to support the required communication and application 572 security, keying material needs to be established between the 573 relevant nodes in the architecture. 575 4. Authentication and Authorization 577 Server-side authorization solutions aim at protecting the access to 578 items of interest, for instance hardware or software resources or 579 data: They enable the resource owner to control who can access it and 580 how. 582 To determine if an entity is authorized to access a resource, an 583 authentication mechanism is needed. According to the Internet 584 Security Glossary [RFC4949], authentication is "the process of 585 verifying a claim that a system entity or system resource has a 586 certain attribute value." Examples for attribute values are the ID 587 of a device, the type of the device or the name of its owner. 589 The security objectives the authorization mechanism aims at can only 590 be achieved if the authentication and the authorization mechanism 591 work together correctly. We speak of authenticated authorization to 592 refer to the required synthesis of mechanism for authentication and 593 authorization. 595 Where used for authorization, the set of authenticated attributes 596 must be meaningful for this purpose, i.e., authorization decisions 597 must be possible based on these attributes. If the authorization 598 policy assigns permissions to an individual entity, the set of 599 authenticated attributes must be suitable to uniquely identify this 600 entity. 602 In scenarios where devices are communicating autonomously there is 603 often less need to uniquely identify an individual device: For a 604 principal, the fact that a device belongs to a certain company or 605 that it has a specific type (such as a light bulb) or location may be 606 more important than that it has a unique identifier. 608 (As a special case for the authorization of read access to a 609 resource, RS may simply make an encrypted representation available to 610 anyone [OSCAR]. In this case, controlling read access to that 611 resource can be reduced to controlling read access to the key; 612 partially removing access also requires a timely update of the key 613 for RS and all participants still authorized.) 615 Principals (RqP and RO) need to decide about the required level of 616 granularity for the authorization. For example, we distinguish 617 device authorization from owner authorization, and flat authorization 618 from unrestricted authorization. In the first case different access 619 permissions are granted to individual devices while in the second 620 case individual owners are authorized. If flat authorization is 621 used, all authenticated entities are implicitly authorized and have 622 the same access permissions. Unrestricted authorization for an item 623 of interest means that no authorization mechanism is used for 624 accessing this resource (not even by authentication) and all entities 625 are able to access the item as they see fit (note that an 626 authorization mechanism may still be used to arrive at the decision 627 to employ unrestricted authorization). 629 More fine-grained authorization does not necessarily provide more 630 security but can be more flexible. Principals need to consider that 631 an entity should only be granted the permissions it really needs 632 (principle of least privilege), to ensure the confidentiality and 633 integrity of resources. 635 For all cases where an authorization solution is needed (all but 636 Unrestricted Authorization), the enforcing party needs to be able to 637 authenticate the party that is to be authorized. Authentication is 638 therefore required for messages that contain (or otherwise update) 639 representations of an accessed item. More precisely: The enforcing 640 party needs to make sure that the receiver of a message containing a 641 representation is authorized to receive it, both in the case of a 642 client sending a representation to a server and vice versa. In 643 addition, it needs to ensure that the actual sender of a message 644 containing a representation is indeed the one authorized to send this 645 message, again for both the client-to-server and server-to-client 646 case. To achieve this, integrity protection of these messages is 647 required: Authenticity cannot be assured if it is possible for an 648 attacker to modify the message during transmission. 650 In some cases, only one side (client or server side) requires the 651 integrity and / or confidentiality of a resource value. Principals 652 may decide to omit authentication (unrestricted authorization), or 653 use flat authorization (just employing an authentication mechanism). 654 However, as indicated in Section 3, the security objectives of both 655 sides must be considered, which can often only be achieved when the 656 the other side can be relied on to perform some security service. 658 5. Actors and their Tasks 660 This and the following section look at the resulting architecture 661 from two different perspectives: This section provides a more 662 detailed description of the various "actors" in the architecture, the 663 logical functional entities performing the tasks required. The 664 following section then will focus on the protocols run between these 665 functional entities. 667 For the purposes of this document, an actor consists of a set of 668 tasks and additionally has a security domain (client domain or server 669 domain) and a level (constrained, principal, less-constrained). 670 Tasks are assigned to actors according to their security domain and 671 required level. 673 Note that actors are a concept to understand the security 674 requirements for constrained devices. The architecture of an actual 675 solution might differ as long as the security requirements that 676 derive from the relationship between the identified actors are 677 considered. Several actors might share a single device or even be 678 combined in a single piece of software. Interfaces between actors 679 may be realized as protocols or be internal to such a piece of 680 software. 682 A more detailed discussion of the tasks the actors have to perform in 683 order to achieve specific security objectives is provided in 684 [I-D.gerdes-ace-tasks]. 686 5.1. Constrained Level Actors 688 As described in the problem statement (see Section 2), either C or RS 689 or both of them may be located on a constrained node. We therefore 690 define that C and RS must be able to perform their tasks even if they 691 are located on a constrained node. Thus, C and RS are considered to 692 be Constrained Level Actors. 694 C performs the following tasks: 696 o Communicate in a secure way (provide for confidentiality and 697 integrity of messages), including access requests. 699 o Validate that an entity is an authorized server for R. 701 RS performs the following tasks: 703 o Communicate in a secure way (provide for confidentiality and 704 integrity of messages), including responses to access requests. 706 o Validate the authorization of the requester to access the 707 requested resource as requested. 709 R is an item of interest such as a sensor or actuator value. R is 710 considered to be part of RS and not a separate actor. The device on 711 which RS is located might contain several resources of different ROs. 712 For simplicity of exposition, these resources are described as if 713 they had separate RS. 715 As C and RS do not necessarily know each other they might belong to 716 different security domains. 718 (See Figure 8.) 719 ------- -------- 720 | C | -- requests resource ---> | RS | Constrained Level 721 ------- <-- provides resource--- -------- 723 Figure 8: Constrained Level Actors 725 5.2. Principal Level Actors 727 Our objective is that C and RS are under control of principals in the 728 physical world, the Requesting Party (RqP) and the Resource Owner 729 (RO) respectively. The principals decide about the security policies 730 of their respective endpoints and belong to the same security domain. 732 RqP is in charge of C, i.e. RqP specifies security policies for C, 733 such as with whom C is allowed to communicate. By definition, C and 734 RqP belong to the same security domain. 736 RqP must fulfill the following task: 738 o Configure for C authorization information for sources for R. 740 RO is in charge of R and RS. RO specifies authorization policies for 741 R and decides with whom RS is allowed to communicate. By definition, 742 R, RS and RO belong to the same security domain. 744 RO must fulfill the following task: 746 o Configure for RS authorization information for accessing R. 748 (See Figure 2.) 750 5.3. Less-Constrained Level Actors 752 Constrained level actors can only fulfill a limited number of tasks 753 and may not have network connectivity all the time. To relieve them 754 from having to manage keys for numerous endpoints and conducting 755 computationally intensive tasks, another complexity level for actors 756 is introduced. An actor on the less-constrained level belongs to the 757 same security domain as its respective constrained level actor. They 758 also have the same principal. 760 The Client Authorization Server (CAS) belongs to the same security 761 domain as C and RqP. CAS acts on behalf of RqP. It assists C in 762 authenticating RS and determining if RS is an authorized server for 763 R. CAS can do that because for C, CAS is the authority for claims 764 about RS. 766 CAS performs the following tasks: 768 o Validate on the client side that an entity has certain attributes. 770 o Obtain authorization information about an entity from C's 771 principal (RqP) and provide it to C. 773 o Negotiate means for secure communication to communicate with C. 775 The Authorization Server (AS) belongs to the same security domain as 776 R, RS and RO. AS acts on behalf of RO. It supports RS by 777 authenticating C and determining C's permissions on R. AS can do 778 that because for RS, AS is the authority for claims about C. 780 AS performs the following tasks: 782 o Validate on the server side that an entity has certain attributes. 784 o Obtain authorization information about an entity from RS' 785 principal (RO) and provide it to RS. 787 o Negotiate means for secure communication to communicate with RS. 789 6. Kinds of Protocols 791 Devices on the less-constrained level potentially are more powerful 792 than constrained level devices in terms of processing power, memory, 793 non-volatile storage. This results in different characteristics for 794 the protocols used on these levels. 796 6.1. Constrained Level Protocols 798 A protocol is considered to be on the constrained level if it is used 799 between the actors C and RS which are considered to be constrained 800 (see Section 5.1). C and RS might not belong to the same security 801 domain. Therefore, constrained level protocols need to work between 802 different security domains. 804 Commonly used Internet protocols can not in every case be applied to 805 constrained environments. In some cases, tweaking and profiling is 806 required. In other cases it is beneficial to define new protocols 807 which were designed with the special characteristics of constrained 808 environments in mind. 810 On the constrained level, protocols need to address the specific 811 requirements of constrained environments. Examples for protocols 812 that consider these requirements is the transfer protocol CoAP 813 (Constrained Application Protocol) [RFC7252] and the Datagram 814 Transport Layer Security Protocol (DTLS) [RFC6347] which can be used 815 for channel security. 817 Constrained devices have only limited storage space and thus cannot 818 store large numbers of keys. This is especially important because 819 constrained networks are expected to consist of thousands of nodes. 820 Protocols on the constrained level should keep this limitation in 821 mind. 823 6.1.1. Cross Level Support Protocols 825 Protocols which operate between a constrained device on one side and 826 the corresponding less-constrained device on the other are considered 827 to be (cross level) support protocols. Protocols used between C and 828 CAS or RS and AS are therefore support protocols. 830 Support protocols must consider the limitations of their constrained 831 endpoint and therefore belong to the constrained level protocols. 833 6.2. Less-Constrained Level Protocols 835 A protocol is considered to be on the less-constrained level if it is 836 used between the actors CAS and AS. CAS and AS might belong to 837 different security domains. 839 On the less-constrained level, HTTP [RFC7230] and Transport Layer 840 Security (TLS) [RFC5246] can be used alongside or instead of CoAP and 841 DTLS. Moreover, existing security solutions for authentication and 842 authorization such as the OAuth web authorization framework [RFC6749] 843 and Kerberos [RFC4120] can likely be used without modifications and 844 there are no limitations for the use of a Public Key Infrastructure 845 (PKI). 847 7. Elements of a Solution 849 Without anticipating specific solutions, the following considerations 850 may be helpful in discussing them. 852 7.1. Authorization 854 The core problem we are trying to solve is authorization. The 855 following problems related to authorization need to be addressed: 857 o AS needs to transfer authorization information to RS and CAS needs 858 to transfer authorization information to C. 860 o The transferred authorization information needs to follow a 861 defined format and encoding, which must be efficient for 862 constrained devices, considering size of authorization information 863 and parser complexity. 865 o C and RS need to be able to verify the authenticity of the 866 authorization information they receive. Here as well, there is a 867 trade-off between processing complexity and deployment complexity. 869 o The RS needs to enforce the authorization decisions of the AS, 870 while C needs to abide with the authorization decisions of the 871 CAS. The authorization information might require additional 872 policy evaluation (such as matching against local access control 873 lists, evaluating local conditions). The required "policy 874 evaluation" at the constrained actors needs to be adapted to the 875 capabilities of the devices implementing them. 877 o Finally, as is indicated in the previous bullet, for a particular 878 authorization decision there may be different kinds of 879 authorization information needed, and these pieces of information 880 may be transferred to C and RS at different times and in different 881 ways prior to or during the client request. 883 7.2. Authentication 885 The following problems need to be addressed, when considering 886 authentication: 888 o RS needs to authenticate AS, and C needs to authenticate CAS, to 889 ensure that the authorization information and related data comes 890 from the correct source. 892 o CAS and AS may need to to authenticate each other, both to perform 893 the required business logic and to ensure that CAS gets security 894 information related to the resources from the right source. 896 o In some use cases RS needs to authenticate some property of C, in 897 order to map it to the relevant authorization information. In 898 other use cases, authentication and authorization of C may be 899 implicit, for example by encrypting the resource representation 900 the RS only providing access to those who possess the key to 901 decrypt. 903 o C may need to authenticate RS, in order to ensure that it is 904 interacting with the right resources. Alternatively C may just 905 verify the integrity of a received resource representation. 907 o CAS and AS need to authenticate their communication partner (C or 908 RS), in order to ensure it serves the correct device. 910 7.3. Communication Security 912 There are different alternatives to provide communication security, 913 and the problem here is to choose the optimal one for each scenario. 914 We list the available alternatives: 916 o Session-based security at transport layer such as DTLS [RFC6347] 917 offers security, including integrity and confidentiality 918 protection, for the whole application layer exchange. However, 919 DTLS may not provide end-to-end security over multiple hops. 920 Another problem with DTLS is the cost of the handshake protocol, 921 which may be too expensive for constrained devices especially in 922 terms of memory and power consumption for message transmissions. 924 o An alternative is object security at application layer, for 925 instance using [I-D.selander-ace-object-security]. Secure objects 926 can be stored or cached in network nodes and provide security for 927 a more flexible communication model such as publish/subscribe 928 (compare e.g. CoRE Mirror Server [I-D.koster-core-coap-pubsub]). 929 A problem with object security is that it can not provide 930 confidentiality for the message headers. 932 o Hybrid solutions using both session-based and object security are 933 also possible. An example of a hybrid is where authorization 934 information and cryptographic keys are provided by AS in the 935 format of secure data objects, but where the resource access is 936 protected by session-based security. 938 7.4. Cryptographic Keys 940 With respect to cryptographic keys, we see the following problems 941 that need to be addressed: 943 Symmetric vs Asymmetric Keys 944 We need keys both for protection of resource access and for 945 protection of transport of authentication and authorization 946 information. Do we want to support solutions based on asymmetric 947 keys or symmetric keys in both cases? There are classes of 948 devices that can easily perform symmetric cryptography, but 949 consume considerably more time/battery for asymmetric operations. 950 On the other hand asymmetric cryptography has benefits such as in 951 terms of deployment. 953 Key Establishment 954 How are the corresponding cryptographic keys established? 955 Considering Section 7.1 there must be a mapping between these keys 956 and the authorization information, at least in the sense that AS 957 must be able to specify a unique client identifier which RS can 958 verify (using an associated key). One of the use cases of 959 [I-D.ietf-ace-usecases] describes spontaneous change of access 960 policies - such as giving a hitherto unknown client the right to 961 temporarily unlock your house door. In this case C is not 962 previously known to RS and a key must be provisioned by AS. 964 Revocation and Expiration 965 How are keys replaced and how is a key that has been compromised 966 revoked in a manner that reaches all affected parties, also 967 keeping in mind scenarios with intermittent connectivity? 969 8. Assumptions and Requirements 971 In this section we list a set of candidate assumptions and 972 requirements to make the problem description in the previous sections 973 more concise and precise. 975 8.1. Architecture 977 The architecture consists of at least the following types of nodes: 979 o RS hosting resources, and responding to access requests 981 o C requesting access to resources 983 o AS supporting the access request/response procedure by providing 984 authorization information to RS 986 * AS may support this by aiding RS in authenticating C, or 987 providing cryptographic keys or credentials to C and/or RS to 988 secure the request/response procedure. 990 o CAS supporting the access request/response procedure by providing 991 authorization information to C 993 * CAS may support this by aiding C in authenticating RS, 994 forwarding information between AS and C (possibly ultimately 995 for RS), or providing cryptographic keys or credentials to C 996 and/or RS to secure the request/response procedure. 998 o The architecture allows for intermediary nodes between any pair of 999 C, RS, AS, and CAS, such as forward or reverse proxies in the CoRE 1000 architecture. (Solutions may or may not support all 1001 combinations.) 1003 * The architecture does not make a choice between session based 1004 security and data object security. 1006 8.2. Constrained Devices 1008 o C and/or RS may be constrained in terms of power, processing, 1009 communication bandwidth, memory and storage space, and moreover: 1011 * unable to manage complex authorization policies 1013 * unable to manage a large number of secure connections 1015 * without user interface 1017 * without constant network connectivity 1019 * unable to precisely measure time 1021 * required to save on wireless communication due to high power 1022 consumption 1024 o CAS and AS are not assumed to be constrained devices. 1026 o All devices under consideration can process symmetric cryptography 1027 without incurring an excessive performance penalty. 1029 * We assume the use of a standardized symmetric key algorithm, 1030 such as AES. 1032 * Except for the most constrained devices we assume the use of a 1033 standardized cryptographic hash function such as SHA-256. 1035 o Public key cryptography requires additional resources (such as 1036 RAM, ROM, power, specialized hardware). 1038 o A DTLS handshake involves significant computation, communication, 1039 and memory overheads in the context of constrained devices. 1041 * The RAM requirements of DTLS handshakes with public key 1042 cryptography are prohibitive for certain constrained devices. 1044 * Certificate-based DTLS handshakes require significant volumes 1045 of communication, RAM (message buffers) and computation. 1047 o A solution will need to consider support for a simple scheme for 1048 expiring authentication and authorization information on devices 1049 which are unable to measure time (cf. section Section 9.2). 1051 8.3. Authentication 1053 o RS needs to authenticate AS to ensure that the authorization 1054 information and related data comes from the correct source. 1056 o Similary, C needs to authenticate CAS to ensure that the 1057 authorization information and related data comes from the correct 1058 source. 1060 o Depending on use case and authorization requirements, C, RS, CAS, 1061 or AS may need to authenticate messages from each other. 1063 8.4. Server-side Authorization 1065 o RS enforces authorization for access to a resource based on 1066 credentials presented by C, the requested resource, the REST 1067 method, and local context in RS at the time of the request, or on 1068 any subset of this information. 1070 o The credentials presented by C may have been provided by CAS. 1072 o The underlying authorization decision is taken either by AS or RS. 1074 o The authorization decision is enforced by RS. 1076 * RS needs to have authorization information in order to verify 1077 that C is allowed to access the resource as requested. 1079 * RS needs to make sure that it provides resource access only to 1080 authorized clients. 1082 o Apart from authorization for access to a resource, authorization 1083 may also be required for access to information about a resource 1084 (for instance, resource descriptions). 1086 o The solution may need to be able to support the delegation of 1087 access rights. 1089 8.5. Client-side Authorization Information 1091 o C enforces client-side authorization by protecting its requests to 1092 RS and by authenticating results from RS, making use of decisions 1093 and policies as well as keying material provided by CAS. 1095 8.6. Server-side Authorization Information 1097 o Authorization information is transferred from AS to RS using 1098 Agent, Push or Pull mechanisms [RFC2904]. 1100 o RS needs to authenticate that the authorization information is 1101 coming from AS (integrity). 1103 o The authorization information may also be encrypted end-to-end 1104 between AS and RS (confidentiality). 1106 o The architecture supports the case where RS may not be able to 1107 communicate with AS at the time of the request from C. 1109 o RS may store or cache authorization information. 1111 o Authorization information may be pre-configured in RS. 1113 o Authorization information stored or cached in RS needs to be 1114 possible to change. The change of such information needs to be 1115 subject to authorization. 1117 o Authorization policies stored on RS may be handled as a resource, 1118 i.e. information located at a particular URI, accessed with 1119 RESTful methods, and the access being subject to the same 1120 authorization mechanics. AS may have special privileges when 1121 requesting access to the authorization policy resources on RS. 1123 o There may be mechanisms for C to look up the AS which provides 1124 authorization information about a particular resource. 1126 8.7. Resource Access 1128 o Resources are accessed in a RESTful manner using GET, PUT, POST, 1129 DELETE. 1131 o By default, the resource request needs to be integrity protected 1132 and may be encrypted end-to-end from C to RS. It needs to be 1133 possible for RS to detect a replayed request. 1135 o By default, the response to a request needs to be integrity 1136 protected and encrypted end-to-end from RS to C. It needs to be 1137 possible for C to detect a replayed response. 1139 o RS needs to be able to verify that the request comes from an 1140 authorized client 1142 o C needs to be able to verify that the response to a request comes 1143 from the intended RS. 1145 o There may be resources whose access need not be protected (e.g. 1146 for discovery of the responsible AS). 1148 8.8. Keys and Cipher Suites 1150 o A constrained node and its authorization manager (i.e., RS and AS, 1151 and C and CAS) have established cryptographic keys. For example, 1152 they share a secret key or each have the other's public key. 1154 o The transfer of authorization information is protected with 1155 symmetric and/or asymmetric keys. 1157 o The access request/response can be protected with symmetric and/or 1158 asymmetric keys. 1160 o There must be a mechanism for RS to establish the necessary key(s) 1161 to verify and decrypt the request and to protect the response. 1163 o There must be a mechanism for C to establish the necessary key(s) 1164 to protect the request and to verify and decrypt the response. 1166 o There must be a mechanism for C to obtain the supported cipher 1167 suites of a RS. 1169 8.9. Network Considerations 1171 o A solution will need to consider network overload due to avoidable 1172 communication of a constrained node with its authorization manager 1173 (C with CAS, RS with AS). 1175 o A solution will need to consider network overload by compact 1176 authorization information representation. 1178 o A solution may want to optimize the case where authorization 1179 information does not change often. 1181 o A solution may consider support for an efficient mechanism for 1182 providing authorization information to multiple RSs, for example 1183 when multiple entities need to be configured or change state. 1185 8.10. Legacy Considerations 1187 o A solution may consider interworking with existing infrastructure. 1189 o A solution may consider supporting authorization of access to 1190 legacy devices. 1192 9. Security Considerations 1194 This document discusses authorization-related tasks for constrained 1195 environments and describes how these tasks can be mapped to actors in 1196 the architecture. 1198 The entire document is about security. Security considerations 1199 applicable to authentication and authorization in RESTful 1200 environments are provided in e.g. OAuth 2.0 [RFC6749]. 1202 In this section we focus on specific security aspects related to 1203 authorization in constrained-node networks. Section 11.6 of 1204 [RFC7252], "Constrained node considerations", discusses implications 1205 of specific constraints on the security mechanisms employed. A wider 1206 view of security in constrained-node networks is provided in 1207 [I-D.garcia-core-security]. 1209 9.1. Physical Attacks on Sensor and Actuator Networks 1211 The focus of this work is on constrained-node networks consisting of 1212 connected sensors and actuators. The main function of such devices 1213 is to interact with the physical world by gathering information or 1214 performing an action. We now discuss attacks performed with physical 1215 access to such devices. 1217 The main threats to sensors and actuator networks are: 1219 o Unauthorized access to data to and from sensors and actuators, 1220 including eavesdropping and manipulation of data. 1222 o Denial-of-service making the sensor/actuator unable to perform its 1223 intended task correctly. 1225 A number of attacks can be made with physical access to a device 1226 including probing attacks, timing attacks, power attacks, etc. 1227 However, with physical access to a sensor or actuator device it is 1228 possible to directly perform attacks equivalent of eavesdropping, 1229 manipulating data or denial of service. For example: 1231 o Instead of eavesdropping the sensor data or attacking the 1232 authorization system to gain access to the data, the attacker 1233 could make its own measurements on the physical object. 1235 o Instead of manipulating the sensor data the attacker could change 1236 the physical object which the sensor is measuring, thereby 1237 changing the payload data which is being sent. 1239 o Instead of manipulating data for an actuator or attacking the 1240 authorization system, the attacker could perform an unauthorized 1241 action directly on the physical object. 1243 o A denial-of-service attack could be performed physically on the 1244 object or device. 1246 All these attacks are possible by having physical access to the 1247 device, since the assets are related to the physical world. 1248 Moreover, this kind of attacks are in many cases straightforward 1249 (requires no special competence or tools, low cost given physical 1250 access, etc.) 1252 As a conclusion, if an attacker has full physical access to a 1253 sensor or actuator device, then much of the security functionality 1254 elaborated in this draft is not effective to protect the asset 1255 during the physical attack. 1257 Since it does not make sense to design a solution for a situation 1258 that cannot be protected against we assume there is no need to 1259 protect assets which are exposed during a physical attack. In 1260 other words, either an attacker does not have physical access to 1261 the sensor or actuator device, or if it has, the attack shall only 1262 have effect during the period of physical attack, and shall be 1263 limited in extent to the physical control the attacker exerts 1264 (e.g., must not affect the security of other devices.) 1266 9.2. Time Measurements 1268 Measuring time with certain accuracy is important to achieve certain 1269 security properties, for example to determine whether a public key 1270 certificate, access token or some other assertion is valid. 1272 Dynamic authorization in itself requires the ability to handle expiry 1273 or revocation of authorization decisions or to distinguish new 1274 authorization decisions from old. 1276 For certain categories of devices we can assume that there is an 1277 internal clock which is sufficiently accurate to handle the time 1278 measurement requirements. If RS can connect directly to AS it could 1279 get updated in terms of time as well as revocation information. 1281 If RS continuously measures time but can't connect to AS or other 1282 trusted source, time drift may have to be accepted and it may not be 1283 able to manage revocation. However, it may still be able to handle 1284 short lived access rights within some margins, by measuring the time 1285 since arrival of authorization information or request. 1287 Some categories of devices in scope may be unable measure time with 1288 any accuracy (e.g. because of sleep cycles). This category of 1289 devices is not suitable for the use cases which require measuring 1290 validity of assertions and authorizations in terms of absolute time. 1292 10. IANA Considerations 1294 This document has no actions for IANA. 1296 11. Acknowledgements 1298 The authors would like to thank Olaf Bergmann, Robert Cragie, Klaus 1299 Hartke, Sandeep Kumar, John Mattson, Corinna Schmitt, Mohit Sethi, 1300 Hannes Tschofenig, Vlasios Tsiatsis and Erik Wahlstroem for 1301 contributing to the discussion, giving helpful input and commenting 1302 on previous forms of this draft. The authors would also like to 1303 specifically acknowledge input provided by Hummen and others 1304 [HUM14delegation]. 1306 12. Informative References 1308 [HUM14delegation] 1309 Hummen, R., Shafagh, H., Raza, S., Voigt, T., and K. 1310 Wehrle, "Delegation-based Authentication and Authorization 1311 for the IP-based Internet of Things", 11th IEEE 1312 International Conference on Sensing, Communication, and 1313 Networking (SECON'14), June 30 - July 3, 2014. 1315 [I-D.garcia-core-security] 1316 Garcia-Morchon, O., Kumar, S., Keoh, S., Hummen, R., and 1317 R. Struik, "Security Considerations in the IP-based 1318 Internet of Things", draft-garcia-core-security-06 (work 1319 in progress), September 2013. 1321 [I-D.gerdes-ace-tasks] 1322 Gerdes, S., "Authorization-Related Tasks in Constrained 1323 Environments", draft-gerdes-ace-tasks-00 (work in 1324 progress), September 2015. 1326 [I-D.hardjono-oauth-umacore] 1327 Hardjono, T., Maler, E., Machulak, M., and D. Catalano, 1328 "User-Managed Access (UMA) Profile of OAuth 2.0", draft- 1329 hardjono-oauth-umacore-13 (work in progress), April 2015. 1331 [I-D.ietf-ace-usecases] 1332 Seitz, L., Gerdes, S., Selander, G., Mani, M., and S. 1333 Kumar, "ACE use cases", draft-ietf-ace-usecases-09 (work 1334 in progress), October 2015. 1336 [I-D.koster-core-coap-pubsub] 1337 Koster, M., Keranen, A., and J. Jimenez, "Publish- 1338 Subscribe Broker for the Constrained Application Protocol 1339 (CoAP)", draft-koster-core-coap-pubsub-02 (work in 1340 progress), July 2015. 1342 [I-D.selander-ace-object-security] 1343 Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 1344 "June 29, 2015", draft-selander-ace-object-security-02 1345 (work in progress), June 2015. 1347 [OSCAR] Vucinic, M., Tourancheau, B., Rousseau, F., Duda, A., 1348 Damon, L., and R. Guizzetti, "OSCAR: Object Security 1349 Architecture for the Internet of Things", CoRR vol. 1350 abs/1404.7799, 2014. 1352 [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., 1353 Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and 1354 D. Spence, "AAA Authorization Framework", RFC 2904, DOI 1355 10.17487/RFC2904, August 2000, 1356 . 1358 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The 1359 Kerberos Network Authentication Service (V5)", RFC 4120, 1360 DOI 10.17487/RFC4120, July 2005, 1361 . 1363 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 1364 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 1365 . 1367 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1368 (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ 1369 RFC5246, August 2008, 1370 . 1372 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1373 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1374 January 2012, . 1376 [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", 1377 RFC 6749, DOI 10.17487/RFC6749, October 2012, 1378 . 1380 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1381 Constrained-Node Networks", RFC 7228, DOI 10.17487/ 1382 RFC7228, May 2014, 1383 . 1385 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1386 Protocol (HTTP/1.1): Message Syntax and Routing", RFC 1387 7230, DOI 10.17487/RFC7230, June 2014, 1388 . 1390 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1391 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 1392 10.17487/RFC7231, June 2014, 1393 . 1395 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1396 Application Protocol (CoAP)", RFC 7252, DOI 10.17487/ 1397 RFC7252, June 2014, 1398 . 1400 Authors' Addresses 1402 Stefanie Gerdes 1403 Universitaet Bremen TZI 1404 Postfach 330440 1405 Bremen D-28359 1406 Germany 1408 Phone: +49-421-218-63906 1409 Email: gerdes@tzi.org 1411 Ludwig Seitz 1412 SICS Swedish ICT AB 1413 Scheelevaegen 17 1414 Lund 223 70 1415 Sweden 1417 Email: ludwig@sics.se 1419 Goeran Selander 1420 Ericsson 1421 Faroegatan 6 1422 Kista 164 80 1423 Sweden 1425 Email: goran.selander@ericsson.com 1426 Carsten Bormann (editor) 1427 Universitaet Bremen TZI 1428 Postfach 330440 1429 Bremen D-28359 1430 Germany 1432 Phone: +49-421-218-63921 1433 Email: cabo@tzi.org