ACE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Informational E. Wahlstroem
Expires: July 17, 2017
S. Erdtman
Spotify AB
H. Tschofenig
ARM Ltd.
January 13, 2017
CBOR Web Token (CWT)
draft-ietf-ace-cbor-web-token-02
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
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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 July 17, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . 5
3.1.5. nbf (Not Before) Claim . . . . . . . . . . . . . . . 5
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. Creating and Validating CWTs . . . . . . . . . . . . . . . . 6
5.1. Creating a CWT . . . . . . . . . . . . . . . . . . . . . 6
5.2. Validating a CWT . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7.1. CBOR Web Token (CWT) Claims Registry . . . . . . . . . . 8
7.1.1. Registration Template . . . . . . . . . . . . . . . . 8
7.1.2. Initial Registry Contents . . . . . . . . . . . . . . 9
7.2. Media Type Registration . . . . . . . . . . . . . . . . . 10
7.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 10
7.3. CoAP Content-Formats Registration . . . . . . . . . . . . 11
7.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13
A.1. CWT with "aud" and symmetric key . . . . . . . . . . . . 13
A.2. CWT with "aud" and EC key . . . . . . . . . . . . . . . . 14
A.3. Full CWT . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Appendix C. Document History . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The JSON Web Token (JWT) [RFC7519] 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) [RFC7515] and JSON Web Encryption (JWE) [RFC7516] to secure the
contents of the JWT, which is a set of claims represented in JSON
[RFC7519]. 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 [RFC7049] and calls this new structure "CBOR Web Token (CWT)",
which is a compact means of representing secured claims to be
transferred 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) [I-D.ietf-cose-msg]
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" [RFC2119].
This document reuses terminology from JWT [RFC7519] and COSE
[I-D.ietf-cose-msg].
Type3StringOrURI:
The "Type3StringOrURI" term has the same meaning, syntax, and
processing rules as the "StringOrUri" term defined in Section 2 of
JWT [RFC7519], except that Type3StringOrURI uses CBOR major type 3
instead of a JSON string value.
Type6NumericDate:
The "Type6NumericDate" term has the same meaning, syntax, and
processing rules as the "NumericDate" term defined in Section 2 of
JWT [RFC7519], except that Type6NumericDate uses CBOR major type
6, with tag value 1, instead of a numeric JSON value.
CBOR encoded claim key:
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The key used to identify a claim value.
CWT Claims Set
A CBOR map that contains the claims conveyed by the CWT.
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.
To keep CWTs as small as possible, the CBOR encoded claim keys are
represented using CBOR major type 0. Section 4 summarizes all keys
used to identify 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 [RFC7519],
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
[RFC7519], 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
[RFC7519], except that the format MUST be a Type3StringOrURI. The
CBOR encoded claim key 3 MUST be used to identify this claim.
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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
[RFC7519], 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
[RFC7519], except that the format MUST be a Type6NumericDate. The
CBOR encoded claim key 5 MUST be used to identify this claim.
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
[RFC7519], 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 [RFC7519],
except that the format MUST be of major type 2, binary string. 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 | 2 |
\---------+------------------------+--------------------------/
Figure 1: Summary of the values, CBOR major types and encoded claim
keys.
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5. Creating and Validating CWTs
5.1. Creating a CWT
To create a CWT, the following steps are performed. The order of the
steps is not significant in cases where there are no dependencies
between the inputs and outputs of the steps.
1. Create a CWT Claims Set containing the desired claims.
2. Let the Message be the binary representation of the CWT Claims
Set.
3. Create a COSE Header containing the desired set of Header
Parameters. The COSE Header MUST be valid according to the
[I-D.ietf-cose-msg] specification.
4. Depending upon whether the CWT is signed, MACed or encrypted,
there are three cases:
* If the CWT is signed, create a COSE_Sign/COSE_Sign1 object
using the Message as the COSE_Sign/COSE_Sign1 Payload; all
steps specified in [I-D.ietf-cose-msg] for creating a
COSE_Sign/COSE_Sign1 object MUST be followed.
* Else, if the CWT is MACed, create a COSE_Mac/COSE_Mac0 object
using the Message as the COSE_Mac/COSE_Mac0 Payload; all steps
specified in [I-D.ietf-cose-msg] for creating a COSE_Mac/
COSE_Mac0 object MUST be followed.
* Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object,
create a COSE_Encrypt/COSE_Encrypt0 using the Message as the
plaintext for the COSE_Encrypt/COSE_Encrypt0 object; all steps
specified in [I-D.ietf-cose-msg] for creating a COSE_Encrypt/
COSE_Encrypt0 object MUST be followed.
5. If a nested signing, MACing or encryption operation will be
performed, let the Message be the COSE_Sign/COSE_Sign1, COSE_Mac/
COSE_Mac0 or COSE_Encrypt/COSE_Encrypt0, and return to Step 3,
using a "content type" header value corresponding to the media
type "application/cwt" in the new COSE Header created in that
step.
Note: If integrity (signing/MACing) and confidentiality
(encryption) protection are needed, it is recommended to use an
authenticated encryption algorithm to save space and processing.
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5.2. Validating a CWT
When validating a CWT, the following steps are performed. The order
of the steps is not significant in cases where there are no
dependencies between the inputs and outputs of the steps. If any of
the listed steps fail, then the CWT MUST be rejected -- that is,
treated by the application as an invalid input.
1. Verify that the CWT is a valid CBOR object.
2. Verify that the resulting COSE Header includes only parameters
and values whose syntax and semantics are both understood and
supported or that are specified as being ignored when not
understood.
3. Use the CBOR tag to determine the type of the CWT, COSE_Sign/
COSE_Sign1, COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0.
4. Depending upon whether the CWT is a COSE_Sign/COSE_Sign1,
COSE_Mac/COSE_Mac0 or COSE_Encrypt/COSE_Encrypt0, there are three
cases:
* If the CWT is a COSE_Sign/COSE_Sign1, follow the steps
specified in [I-D.ietf-cose-msg] Section 4 (Signing Objects)
for validating a COSE_Sign/COSE_Sign1 object. Let the Message
be the COSE_Sign/COSE_Sign1 payload.
* Else, if the CWT is a COSE_Mac/COSE_Mac0, follow the steps
specified in [I-D.ietf-cose-msg] Section 6 (MAC Objects) for
validating a COSE_Mac/COSE_Mac0 object. Let the Message be
the COSE_Mac/COSE_Mac0 payload.
* Else, if the CWT is a COSE_Encrypt/COSE_Encrypt0 object,
follow the steps specified in [I-D.ietf-cose-msg] Section 5
(Encryption Objects) for validating a COSE_Encrypt/
COSE_Encrypt0 object. Let the Message be the resulting
plaintext.
5. If the COSE Header contains a "content type" header value
corresponding to the media type "application/cwt", then the
Message is a CWT that was the subject of nested signing or
encryption operations. In this case, return to Step 1, using the
Message as the CWT.
6. Verify that the Message is a valid CBOR object; let the CWT
Claims Set be this CBOR object.
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6. 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.
7. IANA Considerations
7.1. CBOR Web Token (CWT) Claims Registry
This section establishes the IANA "CBOR Web Token (CWT) Claims"
registry.
Values are registered on a Specification Required [RFC5226] basis, on
the advice of one or more Designated Experts. However, to allow for
the allocation of values prior to publication, the Designated Experts
may approve registration once they are satisfied that such a
specification will be published.
Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability or
whether it is useful only for a single application, and whether the
registration description is clear.
7.1.1. Registration Template
Claim Name:
The human-readable name requested (e.g., "iss").
Claim Description:
Brief description of the claim (e.g., "Issuer").
JWT Claim Name:
Claim Name of the equivalent JWT claim as registered in
[IANA.JWT.Claims]. CWT claims should normally have a
corresponding JWT claim. If a corresponding JWT claim would not
make sense, the Designated Experts can choose to accept
registrations for which the JWT Claim Name is listed as "N/A".
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CBOR Key Value:
Key value for the claim. The key value MUST be an integer in the
range of 1 to 65536.
CBOR Major Type:
CBOR major type and optional tag for the claim.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the parameter,
preferably including URIs that can be used to retrieve copies of
the documents. An indication of the relevant sections may also be
included but is not required.
7.1.2. Initial Registry Contents
o Claim Name: "iss"
o Claim Description: Issuer
o JWT Claim Name: "iss"
o CBOR Key Value: 1
o CBOR Major Type: 3
o Change Controller: IESG
o Specification Document(s): Section 3.1.1 of [[ this specification
]]
o Claim Name: "sub"
o Claim Description: Subject
o JWT Claim Name: "sub"
o CBOR Key Value: 2
o CBOR Major Type: 3
o Change Controller: IESG
o Specification Document(s): Section 3.1.2 of [[ this specification
]]
o Claim Name: "aud"
o Claim Description: Audience
o JWT Claim Name: "aud"
o CBOR Key Value: 3
o CBOR Major Type: 3
o Change Controller: IESG
o Specification Document(s): Section 3.1.3 of [[ this specification
]]
o Claim Name: "exp"
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o Claim Description: Expiration Time
o JWT Claim Name: "exp"
o CBOR Key Value: 4
o CBOR Major Type: 6, tag value 1
o Change Controller: IESG
o Specification Document(s): Section 3.1.4 of [[ this specification
]]
o Claim Name: "nbf"
o Claim Description: Not Before
o JWT Claim Name: "nbf"
o CBOR Key Value: 5
o CBOR Major Type: 6, tag value 1
o Change Controller: IESG
o Specification Document(s): Section 3.1.5 of [[ this specification
]]
o Claim Name: "iat"
o Claim Description: Issued At
o JWT Claim Name: "iat"
o CBOR Key Value: 6
o CBOR Major Type: 6, tag value 1
o Change Controller: IESG
o Specification Document(s): Section 3.1.6 of [[ this specification
]]
o Claim Name: "cti"
o Claim Description: CWT ID
o JWT Claim Name: "jti"
o CBOR Key Value: 7
o CBOR Major Type: 2
o Change Controller: IESG
o Specification Document(s): Section 3.1.7 of [[ this specification
]]
7.2. Media Type Registration
This section registers the "application/cwt" media type [RFC2046] in
the "Media Types" registry [IANA.MediaTypes] in the manner described
in RFC 6838 [RFC6838], which can be used to indicate that the content
is a CWT.
7.2.1. Registry Contents
o Type name: application
o Subtype name: cwt
o Required parameters: N/A
o Optional parameters: N/A
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o Encoding considerations: binary
o Security considerations: See the Security Considerations section
of [[ this specification ]]
o Interoperability considerations: N/A
o Published specification: [[ this specification ]]
o Applications that use this media type: IoT applications sending
security tokens over HTTP(S) and other transports.
o Fragment identifier considerations: N/A
o Additional information:
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
o Person & email address to contact for further information:
IESG, iesg@ietf.org
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Michael B. Jones, mbj@microsoft.com
o Change controller: IESG
o Provisional registration? No
7.3. CoAP Content-Formats Registration
This section registers the CoAP Content-Format ID for the
"application/cwt" media type in the "CoAP Content-Formats" registry
[IANA.CoAP.Content-Formats] established by [RFC7252].
7.3.1. Registry Contents
o Media Type: application/cwt
o Encoding: -
o Id: TBD (maybe 61)
o Reference: [[ this specification ]]
8. References
8.1. Normative References
[I-D.ietf-cose-msg]
Schaad, J., "CBOR Object Signing and Encryption (COSE)",
draft-ietf-cose-msg-24 (work in progress), November 2016.
[IANA.CoAP.Content-Formats]
IANA, "CoAP Content-Formats",
<http://www.iana.org/assignments/core-parameters/
core-parameters.xhtml#content-formats>.
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[IANA.JWT.Claims]
IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>.
[IANA.MediaTypes]
IANA, "Media Types",
<http://www.iana.org/assignments/media-types>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<http://www.rfc-editor.org/info/rfc2046>.
[RFC2119] 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>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC7049] 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>.
[RFC7159] 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>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7515] 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>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<http://www.rfc-editor.org/info/rfc7516>.
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[RFC7519] 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>.
8.2. Informative References
[I-D.seitz-ace-oauth-authz]
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.
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
[I-D.ietf-cose-msg] makes a CWT with "aud" and a symmetric key look
like this in CBOR diagnostic notation:
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{
3: "coap://light.example.com",
8:
[
{
1: 4,
-1: "loremipsum"
}
]
}
Figure 3: CWT 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)
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".
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{
"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
[I-D.ietf-cose-msg] makes a CWT with "aud" and an EC key look like
this in CBOR diagnostic notation:
{
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.
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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.
A.3. Full CWT
CWT using all claims defined by this specification, plus extensions
for AIF and an EC key.
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{
"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
[I-D.ietf-cose-msg] makes a full CWT look like this in CBOR
diagnostic notation:
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{
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)
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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
This specification is based on JSON Web Token (JWT) [RFC7519], the
authors of which also include Nat Sakimura and John Bradley. A straw
man proposal of CWT was written in the draft "Authorization for the
Internet of Things using OAuth 2.0" [I-D.seitz-ace-oauth-authz] with
the help of Ludwig Seitz and Goeran Selander.
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Appendix C. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-02
o Added IANA registration for the application/cwt media type.
o Clarified the nested CWT language.
o Corrected nits identified by Ludwig Seitz.
-01
o Added IANA registration for CWT Claims.
o Added IANA registration for the application/cwt CoAP content-
format type.
o Added Samuel Erdtman as an editor.
o Changed Erik's e-mail address.
-00
o Created the initial working group version based on draft-
wahlstroem-ace-cbor-web-token-00.
Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
Erik Wahlstroem
Sweden
Email: erik@wahlstromstekniska.se
Samuel Erdtman
Spotify AB
Birger Jarlsgatan 61, 4tr
Stockholm 113 56
Sweden
Phone: +46702691499
Email: erdtman@spotify.com
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Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria
Email: Hannes.Tschofenig@arm.com
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