ACE Working Group E. Wahlstroem Internet-Draft Nexus Technology Intended status: Informational M. Jones Expires: June 6, 2016 Microsoft H. Tschofenig ARM Ltd. December 4, 2015 CBOR Web Token (CWT) draft-wahlstroem-ace-cbor-web-token-00 Abstract CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. CWT is a profile of the JSON Web Token (JWT) that is optimized for constrained devices. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR) and CBOR Object Signing and Encryption (COSE) is used for added application layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/ value pair consisting of a claim name and a claim value. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on June 6, 2016. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Wahlstroem, et al. Expires June 6, 2016 [Page 1]
Internet-Draft CBOR Web Token December 2015 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Claim Names . . . . . . . . . . . . . . . . . . . . . . . 4 3.1.1. iss (Issuer) Claim . . . . . . . . . . . . . . . . . 4 3.1.2. sub (Subject) Claim . . . . . . . . . . . . . . . . . 4 3.1.3. aud (Audience) Claim . . . . . . . . . . . . . . . . 4 3.1.4. exp (Expiration Time) Claim . . . . . . . . . . . . . 4 3.1.5. nbf (Not Before) Claim . . . . . . . . . . . . . . . 4 3.1.6. iat (Issued At) Claim . . . . . . . . . . . . . . . . 5 3.1.7. cti (CWT ID) Claim . . . . . . . . . . . . . . . . . 5 4. Summary of the values, CBOR major types and encoded claim keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 6 A.1. CWT with "aud" and symmetric key . . . . . . . . . . . . 7 A.2. CWT with "aud" and EC key . . . . . . . . . . . . . . . . 8 A.3. Full CWT . . . . . . . . . . . . . . . . . . . . . . . . 10 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 12 Appendix C. Document History . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction The JSON Web Token (JWT) [5] is a standardized security token format that has found use in OAuth 2.0 and OpenID Connect deployments, among other applications. JWT uses JSON Web Signatures (JWS) [3] and JSON Web Encryption (JWE) [4] to secure the contents of the JWT, which is a set of claims represented in JSON [5]. The use of JSON for encoding information is popular for Web and native applications, but it is considered inefficient for some Internet of Things (IoT) systems that use low power radio technologies. In this document an alternative encoding of claims is defined. Instead of using JSON, as provided by JWTs, this specification uses CBOR [6] and calls this new structure "CBOR Web Token (CWT)", which is a compact means of representing secured claims to be transferred Wahlstroem, et al. Expires June 6, 2016 [Page 2]
Internet-Draft CBOR Web Token December 2015 between two parties. CWT is closely related to JWT. It references the JWT claims and both its name and pronunciation are derived from JWT. To protect the claims contained in CWTs, the CBOR Object Signing and Encryption (COSE) [7] specification is used. The suggested pronunciation of CWT is the same as the English word "cot". 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in "Key words for use in RFCs to Indicate Requirement Levels" [1]. This document reuses terminology from JWT [5] and COSE [7]. Type3StringOrURI: The "Type3StringOrURI" term has the same meaning, syntax, and processing rules as the "StringOrUri" term defined in Section 2 of JWT [5], except that Type3StringOrURI uses CBOR major type 3 instead of a JSON string value. FIXME: Use tag 32 for URIs? Type6NumericDate: The "Type6NumericDate" term has the same meaning, syntax, and processing rules as the "NumericDate" term defined in Section 2 of JWT [5], except that Type6NumericDate uses CBOR major type 6, with tag value 1, instead of a numeric JSON value. CBOR encoded claim key: The key used to identify a claim value. 3. Claims The set of claims that a CWT must contain to be considered valid is context dependent and is outside the scope of this specification. Specific applications of CWTs will require implementations to understand and process some claims in particular ways. However, in the absence of such requirements, all claims that are not understood by implementations MUST be ignored. Wahlstroem, et al. Expires June 6, 2016 [Page 3]
Internet-Draft CBOR Web Token December 2015 To keep CWTs as small as possible, the CBOR encoded claim keys are represented using CBOR major type 0. Section 4 summaries all keys used to identity the claims defined in this document. 3.1. Claim Names None of the claims defined below are intended to be mandatory to use or implement. They rather provide a starting point for a set of useful, interoperable claims. Applications using CWTs should define which specific claims they use and when they are required or optional. 3.1.1. iss (Issuer) Claim The "iss" (issuer) claim has the same meaning, syntax, and processing rules as the "iss" claim defined in Section 4.1.1 of JWT [5], except that the format MUST be a Type3StringOrURI. The CBOR encoded claim key 1 MUST be used to identify this claim. 3.1.2. sub (Subject) Claim The "sub" (subject) claim has the same meaning, syntax, and processing rules as the "sub" claim defined in Section 4.1.2 of JWT [5], except that the format MUST be a Type3StringOrURI. The CBOR encoded claim key 2 MUST be used to identify this claim. 3.1.3. aud (Audience) Claim The "aud" (audience) claim has the same meaning, syntax, and processing rules as the "aud" claim defined in Section 4.1.3 of JWT [5], except that the format MUST be a Type3StringOrURI. The CBOR encoded claim key 3 MUST be used to identify this claim. 3.1.4. exp (Expiration Time) Claim The "exp" (expiration time) claim has the same meaning, syntax, and processing rules as the "exp" claim defined in Section 4.1.4 of JWT [5], except that the format MUST be a Type6NumericDate. The CBOR encoded claim key 4 MUST be used to identify this claim. 3.1.5. nbf (Not Before) Claim The "nbf" (not before) claim has the same meaning, syntax, and processing rules as the "nbf" claim defined in Section 4.1.5 of JWT [5], except that the format MUST be a Type6NumericDate. The CBOR encoded claim key 5 MUST be used to identify this claim. Wahlstroem, et al. Expires June 6, 2016 [Page 4]
Internet-Draft CBOR Web Token December 2015 3.1.6. iat (Issued At) Claim The "iat" (issued at) claim has the same meaning, syntax, and processing rules as the "iat" claim defined in Section 4.1.6 of JWT [5], except that the format MUST be a Type6NumericDate. The CBOR encoded claim key 6 MUST be used to identify this claim. 3.1.7. cti (CWT ID) Claim The "cti" (CWT ID) claim has the same meaning, syntax, and processing rules as the "jti" claim defined in Section 4.1.7 of JWT [5], except that the format MUST be of major type 3 with a case-sensitive string value. The CBOR encoded claim key 7 MUST be used to identify this claim. 4. Summary of the values, CBOR major types and encoded claim keys /---------+------------------------+--------------------------\ | Claim | CBOR encoded claim key | CBOR major type of value | |---------+------------------------+--------------------------| | iss | 1 | 3 | | sub | 2 | 3 | | aud | 3 | 3 | | exp | 4 | 6 tag value 1 | | nbf | 5 | 6 tag value 1 | | iat | 6 | 6 tag value 1 | | cti | 7 | 3 | \---------+------------------------+--------------------------/ Figure 1: Summary of the values, CBOR major types and encoded claim keys. Note: Claims defined by the OpenID Foundation have not yet been included in the table above. 5. Security Considerations The security of the CWT is dependent on the protection offered by COSE. Without protecting the claims contained in a CWT an adversary is able to modify, add or remove claims. Since the claims conveyed in a CWT are used to make authorization decisions it is not only important to protect the CWT in transit but also to ensure that the recipient is able to authenticate the party that collected the claims and created the CWT. Without trust of the recipient in the party that created the CWT no sensible authorization decision can be made. Furthermore, the creator of the CWT needs to carefully evaluate each claim value prior to including it in the CWT so that the recipient can be assured about the correctness of the provided information. Wahlstroem, et al. Expires June 6, 2016 [Page 5]
Internet-Draft CBOR Web Token December 2015 6. IANA Considerations This section will create a registry for CWT claims, possibly relating them to the JWT Claims Registry. 7. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [2] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, <http://www.rfc-editor.org/info/rfc7159>. [3] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, <http://www.rfc-editor.org/info/rfc7515>. [4] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015, <http://www.rfc-editor.org/info/rfc7516>. [5] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, <http://www.rfc-editor.org/info/rfc7519>. [6] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, <http://www.rfc-editor.org/info/rfc7049>. [7] Schaad, J., "CBOR Encoded Message Syntax", draft-ietf- cose-msg-08 (work in progress), November 2015. [8] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "Authorization for the Internet of Things using OAuth 2.0", draft-seitz-ace-oauth-authz-00 (work in progress), October 2015. Appendix A. Examples Three examples of CWTs follow. Wahlstroem, et al. Expires June 6, 2016 [Page 6]
Internet-Draft CBOR Web Token December 2015 A.1. CWT with "aud" and symmetric key A CWT used in the context of ACE requires at least the "aud" and a "cks" claim (defined elsewhere). This means that "iss", "alg", "key_ops" and others are pre-established and assumed. This would look like this non-normative JSON. { "aud":"coap://light.example.com", "cks": [ // COSE_Key is a CBOR map with an array of keys { "kty":4, // symmetric key is indicated using kty 4 "k": "loremipsum" // the symmetric key } ] } Figure 2: "aud" claim and symmetric key in non-normative JSON Using the CBOR encoded claim keys according to Section 4 and COSE [7] makes a CWT with "aud" and a symmetric key look like this in CBOR diagnostic notation: { 3: "coap://light.example.com", 8: [ { 1: 4, -1: "loremipsum" } ] } Figure 3: CWT in CBOR diagnostic notation Defined in CBOR. Wahlstroem, et al. Expires June 6, 2016 [Page 7]
Internet-Draft CBOR Web Token December 2015 a2 # map(2) 03 # unsigned(3) 78 18 # text(24) 636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com" 08 # unsigned(8) 81 # array(1) a2 # map(2) 01 # unsigned(1) 04 # unsigned(4) 20 # negative(0) 6a # text(10) 6c6f72656d697073756d # "loremipsum" Figure 4: CWT with "aud" and symmetric key in CBOR Size of the CWT with a symmetric key of 10 bytes is 45 bytes. This is then packaged signed and encrypted using COSE. A.2. CWT with "aud" and EC key Token with "aud" set to "coap://light.example.com" and an EC key with "kid" set to "11". { "aud": "coap://light.example.com", "cks": [ // COSE_Key is a CBOR map with an array of keys { "kty": "EC", "kid": "11", "crv": 1, // using P-384 "x": h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', "y": h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e' } ] } Figure 5: "aud" claim and EC key in non-normative JSON Using the CBOR encoded claim keys according to Section 4 and COSE [7] makes a CWT with "aud" and an EC key look like this in CBOR diagnostic notation: Wahlstroem, et al. Expires June 6, 2016 [Page 8]
Internet-Draft CBOR Web Token December 2015 { 3: "coap://light.example.com", 8: [ { 1: 2, 2: "11", -1: 1, -2: h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', -3: h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e' } ] } Figure 6: CWT with EC key in CBOR diagnostic notation Defined in CBOR. a2 # map(2) 03 # unsigned(3) 78 18 # text(24) 636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com" 08 # unsigned(8) 81 # array(1) a5 # map(5) 01 # unsigned(1) 02 # unsigned(2) 02 # unsigned(2) 62 # text(2) 3131 # "11" 20 # negative(0) 01 # unsigned(1) 21 # negative(1) 58 20 # bytes(32) bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff # "\xBA\xC5\xB1\x1C\xAD\x8F\x99\xF9\xC7+\x05\xCFK\x9E&\xD2D\xDC\x18\x9FtR(%Z!\x9A\x86\xD6\xA0\x9E\xFF" 22 # negative(2) 58 20 # bytes(32) 20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e # "\x13\x8B\xF8-\xC1\xB6\xD5b\xBE\x0F\xA5J\xB7\x80J:d\xB6\xD7,\xCF\xEDko\xB6\xED(\xBB\xFC\x11~" Figure 7: CWT with EC in CBOR Size of the CWT with an EC key is 109 bytes. This is then packaged signed and encrypted using COSE. Wahlstroem, et al. Expires June 6, 2016 [Page 9]
Internet-Draft CBOR Web Token December 2015 A.3. Full CWT CWT using all claims defined by this specification, plus extensions for AIF and an EC key. { "iss": "coap://as.example.com", "aud": "coap://light.example.com", "sub": "erikw", "exp": 1444064944, "nbf": 1443944944, "iat": 1443944944, "cti": 2929, "cks": [ // COSE_Key is a CBOR map with an array of keys { "kty": "EC", "kid": "11", "crv": 1, // using P-384 "x": h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', "y": h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e' } ], "aif": [["/s/light", 1], ["/a/led", 5], ["/dtls", 2]] } Figure 8: All claims, "aif" and EC key in non-normative JSON Using the CBOR encoded claim keys according to Section 4 and COSE [7] makes a full CWT look like this in CBOR diagnostic notation: Wahlstroem, et al. Expires June 6, 2016 [Page 10]
Internet-Draft CBOR Web Token December 2015 { 1: "coap://as.example.com", 3: "coap://light.example.com", 2: "erikw", 4: 1(1444064944), 5: 1(1443944944), 6: 1(1443944944), 7: 2929, 8: [ { 1: 2, 2: "11", -1: 1, -2: h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff', -3: h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e' } ], 9: [["/s/light", 1], ["/a/led", 5], ["/dtls", 2]] } Figure 9: Full CWT with EC key in CBOR diagnostic notation Defined in CBOR. a9 # map(9) 01 # unsigned(1) 75 # text(21) 636f61703a2f2f61732e6578616d706c652e636f6d # "coap://as.example.com" 03 # unsigned(3) 78 18 # text(24) 636f61703a2f2f6c696768742e6578616d706c652e636f6d # "coap://light.example.com" 02 # unsigned(2) 65 # text(5) 6572696b77 # "erikw" 04 # unsigned(4) c1 # tag(1) 1a 5612aeb0 # unsigned(1444064944) 05 # unsigned(5) c1 # tag(1) 1a 5610d9f0 # unsigned(1443944944) 06 # unsigned(6) c1 # tag(1) 1a 5610d9f0 # unsigned(1443944944) 07 # unsigned(7) 19 0b71 # unsigned(2929) 08 # unsigned(8) Wahlstroem, et al. Expires June 6, 2016 [Page 11]
Internet-Draft CBOR Web Token December 2015 81 # array(1) a5 # map(5) 01 # unsigned(1) 02 # unsigned(2) 02 # unsigned(2) 62 # text(2) 3131 # "11" 20 # negative(0) 01 # unsigned(1) 21 # negative(1) 58 20 # bytes(32) bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a09eff # "\xBA\xC5\xB1\x1C\xAD\x8F\x99\xF9\xC7+\x05\xCFK\x9E&\xD2D\xDC\x18\x9FtR(%Z!\x9A\x86\xD6\xA0\x9E\xFF" 22 # negative(2) 58 20 # bytes(32) 20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbfc117e # "\x13\x8B\xF8-\xC1\xB6\xD5b\xBE\x0F\xA5J\xB7\x80J:d\xB6\xD7,\xCF\xEDko\xB6\xED(\xBB\xFC\x11~" 09 # unsigned(9) 83 # array(3) 82 # array(2) 68 # text(8) 2f732f6c69676874 # "/s/light" 01 # unsigned(1) 82 # array(2) 66 # text(6) 2f612f6c6564 # "/a/led" 05 # unsigned(5) 82 # array(2) 65 # text(5) 2f64746c73 # "/dtls" 02 # unsigned(2) Figure 10: Full CWT with EC in CBOR Size of the CWT with an EC key is 194 bytes. This is then packaged signed and encrypted using COSE. Appendix B. Acknowledgements A straw man proposal of CWT was written in the draft "Authorization for the Internet of Things using OAuth 2.0" [8] with the help of Ludwig Seitz, Goeran Selander, and Samuel Erdtman. Appendix C. Document History [[ to be removed by the RFC Editor before publication as an RFC ]] -00 Wahlstroem, et al. Expires June 6, 2016 [Page 12]
Internet-Draft CBOR Web Token December 2015 o Created the initial version based on draft-wahlstroem-oauth-cbor- web-token-00. o Now reference the JWT claim definitions, rather than repeating them. Authors' Addresses Erik Wahlstroem Nexus Technology Sweden Email: erik.wahlstrom@nexusgroup.com URI: https://www.nexusgroup.com Michael B. Jones Microsoft Email: mbj@microsoft.com URI: http://self-issued.info/ Hannes Tschofenig ARM Ltd. Hall in Tirol 6060 Austria Email: Hannes.Tschofenig@arm.com Wahlstroem, et al. Expires June 6, 2016 [Page 13]