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Bormann 3 Internet-Draft Universitaet Bremen TZI 4 Intended status: Informational March 29, 2019 5 Expires: September 30, 2019 7 An Authorization Information Format (AIF) for ACE 8 draft-bormann-core-ace-aif-06 10 Abstract 12 Constrained Devices as they are used in the "Internet of Things" need 13 security. One important element of this security is that devices in 14 the Internet of Things need to be able to decide which operations 15 requested of them should be considered authorized, need to ascertain 16 that the authorization to request the operation does apply to the 17 actual requester, and need to ascertain that other devices they place 18 requests on are the ones they intended. 20 On the ACE mailing list, an activity to create specifications for 21 such authenticated authorization for constrained devices is 22 contemplated, leading to protocol proposals such as 23 [I-D.ietf-ace-dtls-authorize] or [I-D.seitz-ace-oscoap-profile]. 25 One potential work item complementing this protocol work is an 26 Authorization Information Format (AIF). 28 This document provides a strawman for such a format that should 29 enable further discussion of the objectives for its development. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on September 30, 2019. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Information Model . . . . . . . . . . . . . . . . . . . . . . 3 68 2.1. Limitations . . . . . . . . . . . . . . . . . . . . . . . 3 69 3. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 71 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 72 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 73 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 74 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 75 7.2. Informative References . . . . . . . . . . . . . . . . . 6 76 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 78 1. Introduction 80 (See Abstract.) 82 1.1. Terminology 84 This memo uses terms from [RFC7252] and [RFC4949]. 86 (Note that this document is itself informational, but it is 87 discussing normative statements.) 89 The term "byte", abbreviated by "B", is used in its now customary 90 sense as a synonym for "octet". 92 2. Information Model 94 Authorizations are generally expressed through some data structures 95 that are cryptographically secured (or transmitted in a secure way). 96 This section discusses the information model underlying the payload 97 of that data (as opposed to the cryptographic armor around it). 99 For the purposes of this strawman, the underlying access control 100 model will be that of an access matrix, which gives a set of 101 permissions for each possible combination of a subject and on object. 103 For the objects, we simply use the URI of a resource on a CoAP 104 server. More specifically, the parts of the URI that identify the 105 server ("authority" in [RFC3986]) are considered the realm of the 106 authentication mechanism (which are handled in the cryptographic 107 armor); we therefore focus on the "path-absolute" and "query" parts 108 of the URI (URI "local-part" in this specification, as expressed by 109 the Uri-Path and Uri-Query options in CoAP). Similarly, we do not 110 concern the AIF format with the subject for which the AIF object is 111 issued, focusing the AIF object on a single row in the access matrix 112 (such a row traditionally is also called a capability list). 114 At the information model level, this leaves a set of pairs of local 115 URIs and related permissions. We simplify the model for the 116 permissions to simply giving the subset of the CoAP methods 117 permitted. This model is summarized in Table 1. 119 +------------+----------------+ 120 | local-part | Permission Set | 121 +------------+----------------+ 122 | /s/light | GET | 123 | | | 124 | /a/led | PUT, GET | 125 | | | 126 | /dtls | POST | 127 +------------+----------------+ 129 Table 1: An authorization instance in the AIF Information Model 131 2.1. Limitations 133 This simple information model only allows granting permissions for 134 static URIs. It is probably necessary to extend the model towards 135 URI templates [RFC6570], however, that requires some considerations 136 of the ease and unambiguity of matching a given URI against a set of 137 templates in an AIF object. 139 This simple information model also doesn't allow conditionalizing 140 access (e.g., "opening a door is allowed if that isn't locked"). 142 Finally, the model does not provide any special access for a set of 143 resources that are specific to a subject, e.g. that the subject 144 created itself by previous operations (PUT, POST) or that were 145 specifically created for the subject by others. 147 3. Data Model 149 For representing the AIF object discussion in Section 2, the 150 permission set is reduced to a single number by the following steps: 152 o The entries in the table that specify the same local-part are 153 merged into a single entry that specifies the union of the 154 permission sets 156 o The methods in the permission sets are converted into their CoAP 157 method numbers, minus 1 159 o The set of numbers is converted into a single number by taking 160 each number to the power of two and computing the inclusive OR of 161 the binary representations of all the numbers. 163 This strawman data model could be interchanged in the JSON [RFC8259] 164 representation given in Figure 1 (more extensible/more compact 165 representations are possible). 167 [["/s/light", 1], ["/a/led", 5], ["/dtls", 2]] 169 Figure 1: An authorization instance encoded in JSON (46 bytes) 171 In CDDL [I-D.greevenbosch-appsawg-cbor-cddl], a straightforward 172 specification of the data model (including both the methods from 173 [RFC7252] and the new ones from [RFC8132], identified by the method 174 code minus 1) is: 176 authorization-info = [* authorization] 177 authorization = [ 178 path: tstr, 179 permissions: uint .bits methods, 180 ] 181 methods = &( 182 GET: 0 183 POST: 1 184 PUT: 2 185 DELETE: 3 186 FETCH: 4 187 PATCH: 5 188 iPATCH: 6 189 ) 191 Figure 2: AIF in CDDL 193 A representation of this information in CBOR [RFC7049] is given in 194 Figure 3; again, several optimizations/improvements are possible. 196 83 # array(3) 197 82 # array(2) 198 68 # text(8) 199 2f732f6c69676874 # "/s/light" 200 01 # unsigned(1) 201 82 # array(2) 202 66 # text(6) 203 2f612f6c6564 # "/a/led" 204 05 # unsigned(5) 205 82 # array(2) 206 65 # text(5) 207 2f64746c73 # "/dtls" 208 02 # unsigned(2) 210 Figure 3: An authorization instance encoded in CBOR (29 bytes) 212 4. IANA Considerations 214 This document makes no requirements on IANA. (This section to be 215 removed by RFC editor.) 217 5. Security Considerations 219 (TBD. Some issues are already discussed in the security 220 considerations of [RFC7252] and in [I-D.irtf-t2trg-iot-seccons].) 222 6. Acknowledgements 224 TBD 226 7. References 228 7.1. Normative References 230 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 231 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 232 . 234 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 235 Application Protocol (CoAP)", RFC 7252, 236 DOI 10.17487/RFC7252, June 2014, 237 . 239 7.2. Informative References 241 [I-D.greevenbosch-appsawg-cbor-cddl] 242 Birkholz, H., Vigano, C., and C. Bormann, "Concise data 243 definition language (CDDL): a notational convention to 244 express CBOR data structures", draft-greevenbosch-appsawg- 245 cbor-cddl-11 (work in progress), July 2017. 247 [I-D.ietf-ace-dtls-authorize] 248 Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and 249 L. Seitz, "Datagram Transport Layer Security (DTLS) 250 Profile for Authentication and Authorization for 251 Constrained Environments (ACE)", draft-ietf-ace-dtls- 252 authorize-07 (work in progress), March 2019. 254 [I-D.irtf-t2trg-iot-seccons] 255 Garcia-Morchon, O., Kumar, S., and M. Sethi, "State-of- 256 the-Art and Challenges for the Internet of Things 257 Security", draft-irtf-t2trg-iot-seccons-16 (work in 258 progress), December 2018. 260 [I-D.seitz-ace-oscoap-profile] 261 Seitz, L., Palombini, F., and M. Gunnarsson, "OSCORE 262 profile of the Authentication and Authorization for 263 Constrained Environments Framework", draft-seitz-ace- 264 oscoap-profile-06 (work in progress), October 2017. 266 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 267 Resource Identifier (URI): Generic Syntax", STD 66, 268 RFC 3986, DOI 10.17487/RFC3986, January 2005, 269 . 271 [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., 272 and D. Orchard, "URI Template", RFC 6570, 273 DOI 10.17487/RFC6570, March 2012, 274 . 276 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 277 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 278 October 2013, . 280 [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and 281 FETCH Methods for the Constrained Application Protocol 282 (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, 283 . 285 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 286 Interchange Format", STD 90, RFC 8259, 287 DOI 10.17487/RFC8259, December 2017, 288 . 290 Author's Address 292 Carsten Bormann 293 Universitaet Bremen TZI 294 Postfach 330440 295 Bremen D-28359 296 Germany 298 Phone: +49-421-218-63921 299 Email: cabo@tzi.org