ACE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track E. Wahlstroem
Expires: December 7, 2017
S. Erdtman
Spotify AB
H. Tschofenig
ARM Ltd.
June 5, 2017
CBOR Web Token (CWT)
draft-ietf-ace-cbor-web-token-05
Abstract
CBOR Web Token (CWT) is a compact means of representing claims to be
transferred between two parties. 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. CWT is derived from JSON Web Token
(JWT), but uses CBOR rather than JSON.
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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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on December 7, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. CBOR Related Terminology . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Claim Names . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. iss (Issuer) Claim . . . . . . . . . . . . . . . . . 5
3.1.2. sub (Subject) Claim . . . . . . . . . . . . . . . . . 5
3.1.3. aud (Audience) Claim . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . 6
4. Summary of the values, value types, and encoded claim keys . 6
5. CBOR Tags and Claim Values . . . . . . . . . . . . . . . . . 6
6. CWT CBOR Tag . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Creating and Validating CWTs . . . . . . . . . . . . . . . . 7
7.1. Creating a CWT . . . . . . . . . . . . . . . . . . . . . 7
7.2. Validating a CWT . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9.1. CBOR Web Token (CWT) Claims Registry . . . . . . . . . . 9
9.1.1. Registration Template . . . . . . . . . . . . . . . . 10
9.1.2. Initial Registry Contents . . . . . . . . . . . . . . 11
9.2. Media Type Registration . . . . . . . . . . . . . . . . . 12
9.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 13
9.3. CoAP Content-Formats Registration . . . . . . . . . . . . 13
9.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 13
9.4. CBOR Tag registration . . . . . . . . . . . . . . . . . . 13
9.4.1. Registry Contents . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 15
A.1. Example CWT Claims Set . . . . . . . . . . . . . . . . . 15
A.2. Example keys . . . . . . . . . . . . . . . . . . . . . . 16
A.2.1. 128-bit Symmetric Key as Hex Encoded String . . . . . 16
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A.2.2. 256-bit Symmetric Key as Hex Encoded String . . . . . 16
A.2.3. ECDSA P-256 256-bit COSE Key . . . . . . . . . . . . 16
A.3. Example Signed CWT . . . . . . . . . . . . . . . . . . . 17
A.4. Example MACed CWT . . . . . . . . . . . . . . . . . . . . 18
A.5. Example Encrypted CWT . . . . . . . . . . . . . . . . . . 18
A.6. Example Nested CWT . . . . . . . . . . . . . . . . . . . 19
A.7. Example MACed CWT with a floating-point value . . . . . . 20
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 21
Appendix C. Document History . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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 Signature
(JWS) [RFC7515] and JSON Web Encryption (JWE) [RFC7516] to secure the
contents of the JWT, which is a set of claims represented in JSON.
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.
An alternative encoding of claims is defined in this document.
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".
1.1. CBOR Related Terminology
In JSON, maps are called objects and only have one kind of map key: a
string. In COSE, we use strings, negative integers, and unsigned
integers as map keys. The integers are used for compactness of
encoding and easy comparison. The inclusion of strings allows for an
additional range of short encoded values to be used as well.
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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].
StringOrURI:
The "StringOrURI" term has the same meaning, syntax, and
processing rules as the "StringOrUri" term defined in Section 2 of
JWT [RFC7519], except that it uses a CBOR text string instead of a
JSON string value.
NumericDate:
The "NumericDate" term has the same meaning, syntax, and
processing rules as the "NumericDate" term defined in Section 2 of
JWT [RFC7519], except that the CBOR numeric date representation
(from Section 2.4.1 of [RFC7049]) is used. The encoding is
modified so that the leading tag (6.1 or 0xC1) MUST be omitted.
CBOR encoded claim key:
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 integers or text strings. 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
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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 StringOrURI. 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 StringOrURI. 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 StringOrURI. 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
[RFC7519], except that the format MUST be a NumericDate. 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 NumericDate. 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 NumericDate. The CBOR
encoded claim key 6 MUST be used to identify this claim.
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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 binary string. The CBOR encoded claim
key 7 MUST be used to identify this claim.
4. Summary of the values, value types, and encoded claim keys
/---------+-----+----------------------------------\
| Name | Key | Value type |
|---------+-----+----------------------------------|
| iss | 1 | text string |
| sub | 2 | text string |
| aud | 3 | text string |
| exp | 4 | integer or floating-point number |
| nbf | 5 | integer or floating-point number |
| iat | 6 | integer or floating-point number |
| cti | 7 | binary string |
\---------+-----+----------------------------------/
Figure 1: Summary of the values, value types, and encoded claim keys
5. CBOR Tags and Claim Values
The claim values defined in this specification MUST NOT be prefixed
with any CBOR tag. For instance, while CBOR tag 6.1 (seconds-since-
the-epoch) could logically be prefixed to values of the "exp", "nbf",
and "iat" claims, this is unnecessary, since the representation of
the claim values is already specified by the claim definitions.
Tagging claim values would only take up extra space without adding
information. However, this does not prohibit future claim
definitions from requiring the use of CBOR tags for those specific
claims.
6. CWT CBOR Tag
How to determine that a CBOR data structure is a CWT is application-
dependent. In some cases, this information is known from the
application context, such as from the position of the CWT in a data
structure at which the value must be a CWT. One method of indicating
that a CBOR object is a CWT is the use of the "application/cwt"
content type by a transport protocol.
This section defines the CWT CBOR tag as another means for
applications to declare that a CBOR data structure is a CWT. Its use
is optional, and is intended for use in cases in which this
information would not otherwise be known.
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If present, the CWT tag MUST prefix a tagged object using one of the
COSE CBOR tags. In this example, the COSE_Mac0 tag is used. The
actual COSE_Mac0 object has been excluded from this example.
/ CWT CBOR tag / 61(
/ COSE_Mac0 CBOR tag / 17(
/ COSE_Mac0 object /
)
)
Figure 2: Example of a CWT tag usage
7. Creating and Validating CWTs
7.1. 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 per 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.
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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, add the matching COSE
CBOR tag, and return to Step 3.
6. If needed by the application, add the appropriate COSE CBOR tag
to the COSE object to indicate the type of the COSE object. If
needed by the application, add the CWT CBOR tag to indicate that
the COSE object is a CWT.
7.2. 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 invalid input.
1. Verify that the CWT is a valid CBOR object.
2. If the object begins with the CWT CBOR tag, remove it and verify
that one of the COSE CBOR tags follows it.
3. If the object is tagged with one of the COSE CBOR tags, remove it
and use it to determine the type of the CWT, COSE_Sign/
COSE_Sign1, COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0.
If the object does not have a COSE CBOR tag, the COSE message
type is determined from the application context.
4. 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.
5. Depending upon whether the CWT is a signed, MACed, or encrypted,
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.
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* 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.
6. If the Message begins with a COSE CBOR tag, then the Message is a
CWT that was the subject of nested signing, MACing, or encryption
operations. In this case, return to Step 1, using the Message as
the CWT.
7. Verify that the Message is a valid CBOR object; let the CWT
Claims Set be this CBOR object.
8. Security Considerations
The security of the CWT relies upon on the protections offered by
COSE. Unless the claims in a CWT are protected, an adversary can
modify, add, or remove claims.
Since the claims conveyed in a CWT may be used to make authorization
decisions, it is not only important to protect the CWT in transit but
also to ensure that the recipient can authenticate the party that
assembled 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 of the validity of
the information provided.
While syntactically, the signing and encryption operations for Nested
CWTs may be applied in any order, if both signing and encryption are
necessary, normally producers should sign the message and then
encrypt the result (thus encrypting the signature). This prevents
attacks in which the signature is stripped, leaving just an encrypted
message, as well as providing privacy for the signer. Furthermore,
signatures over encrypted text are not considered valid in many
jurisdictions.
9. IANA Considerations
9.1. 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
after a three-week review period on the cwt-reg-review@ietf.org
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mailing list, 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. [[ Note to
the RFC Editor: The name of the mailing list should be determined in
consultation with the IESG and IANA. Suggested name: cwt-reg-
review@ietf.org. ]]
Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register claim: example").
Registration requests that are undetermined for a period longer than
21 days can be brought to the IESG's attention (using the
iesg@ietf.org mailing list) for resolution.
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.
It is suggested that multiple Designated Experts be appointed who are
able to represent the perspectives of different applications using
this specification in order to enable broadly informed review of
registration decisions. In cases where a registration decision could
be perceived as creating a conflict of interest for a particular
Expert, that Expert should defer to the judgment of the other
Experts.
9.1.1. 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".
CBOR Key Value:
Integer values between -256 and 255 and strings of length 1 are
designated as Standards Track Document required. Integer values
from -65536 to 65535 and strings of length 2 are designated as
Specification Required. Integer values of greater than 65535 and
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strings of length greater than 2 are designated as expert review.
Integer values less than -65536 are marked as private use.
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.
9.1.2. Initial Registry Contents
o Claim Name: N/A
o Claim Description: This registration reserves the key value 0.
o JWT Claim Name: N/A
o CBOR Key Value: 0
o CBOR Major Type: N/A
o Change Controller: IESG
o Specification Document(s): [[ this specification ]]
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"
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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"
o Claim Description: Expiration Time
o JWT Claim Name: "exp"
o CBOR Key Value: 4
o CBOR Major Type: 0, 1, or 7 with subtypes 25, 26, or 27
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: 0, 1, or 7 with subtypes 25, 26, or 27
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: 0, 1, or 7 with subtypes 25, 26, or 27
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
]]
9.2. Media Type Registration
This section registers the "application/cwt" media type 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.
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9.2.1. Registry Contents
o Type name: application
o Subtype name: cwt
o Required parameters: N/A
o Optional parameters: N/A
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
9.3. 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].
9.3.1. Registry Contents
o Media Type: application/cwt
o Encoding: -
o Id: TBD (maybe 61)
o Reference: [[ this specification ]]
9.4. CBOR Tag registration
This section registers the CWT CBOR tag in the "CBOR Tags" registry
[IANA.CBOR.Tags].
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9.4.1. Registry Contents
o CBOR Tag: TBD (maybe 61 to use the same value as the Content-
Format)
o Data Item: CBOR Web Token (CWT)
o Semantics: CBOR Web Token (CWT), as defined in [[ this
specification ]]
o Reference: [[ this specification ]]
o Point of Contact: Michael B. Jones, mbj@microsoft.com
10. References
10.1. 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.CBOR.Tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
<http://www.iana.org/assignments/cbor-tags/
cbor-tags.xhtml>.
[IANA.CoAP.Content-Formats]
IANA, "CoAP Content-Formats",
<http://www.iana.org/assignments/core-parameters/
core-parameters.xhtml#content-formats>.
[IANA.MediaTypes]
IANA, "Media Types",
<http://www.iana.org/assignments/media-types>.
[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>.
[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>.
[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>.
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10.2. Informative References
[IANA.JWT.Claims]
IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>.
[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>.
[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>.
Appendix A. Examples
This appendix includes a set of CWT examples that show how the CWT
Claims Set can be protected. There are examples that are signed,
MACed, encrypted, and that use nested signing and encryption. To
make the examples easier to read, they are presented both as hex
strings and in the extended CBOR diagnostic notation described in
Section 6 of [RFC7049].
A.1. Example CWT Claims Set
The CWT Claims Set used for the different examples displays usage of
all the defined claims. For signed and MACed examples, the CWT
Claims Set is the CBOR encoding as a binary string.
a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703
7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0
051a5610d9f0061a5610d9f007420b71
Figure 3: Example CWT Claims Set as hex string
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{
/ iss / 1: "coap://as.example.com",
/ sub / 2: "erikw",
/ aud / 3: "coap://light.example.com",
/ exp / 4: 1444064944,
/ nbf / 5: 1443944944,
/ iat / 6: 1443944944,
/ cti / 7: h'0b71'
}
Figure 4: Example CWT Claims Set in CBOR diagnostic notation
A.2. Example keys
This section contains the keys used to sign, MAC, and encrypt the
messages in this appendix. Line breaks are for display purposes
only.
A.2.1. 128-bit Symmetric Key as Hex Encoded String
231f4c4d4d3051fdc2ec0a3851d5b383
A.2.2. 256-bit Symmetric Key as Hex Encoded String
403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d79569388
A.2.3. ECDSA P-256 256-bit COSE Key
a622582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db952997
1a36e7b92358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c
67c858bc206c1903260102215820143329cce7868e416927599cf65a34f3ce2f
fda55a7eca69ed8919a394d42f0f2001
Figure 5: ECDSA 256-bit COSE Key as hex string
{
/ d / -4: h'6c1382765aec5358f117733d281c1c7bdc39884d04a45a1e
6c67c858bc206c19',
/ y / -3: h'60f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168
db9529971a36e7b9',
/ x / -2: h'143329cce7868e416927599cf65a34f3ce2ffda55a7eca69
ed8919a394d42f0f',
/ crv / -1: 1 / P-256 / ,
/ kty / 1: 2 / EC2 / ,
/ alg / 3: -7 / ECDSA 256 /
}
Figure 6: ECDSA 256-bit COSE Key in CBOR diagnostic notation
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A.3. Example Signed CWT
This section shows a signed CWT with a single recipient and a full
CWT Claims Set.
The signature is generated using the private key listed in
Appendix A.2.3 and it can be validated using the public key from
Appendix A.2.3. Line breaks are for display purposes only.
d28443a10126a05850a70175636f61703a2f2f61732e6578616d706c652e636f6
d02656572696b77037818636f61703a2f2f6c696768742e6578616d706c652e63
6f6d041a5612aeb0051a5610d9f0061a5610d9f007420b715840b9b2821b6b2c2
f9d1d984b11854dcfcee1f219746800ce76112c21f58c45dea1d7f01cec1ab394
0f75c459305365210a23a9ed463b4f6fc984c2f1c08e504d90
Figure 7: Signed CWT as hex string
18(
[
/ protected / h'a10126' / {
/ alg / 1: -7 / ECDSA 256 /
} / ,
/ unprotected / {},
/ payload / h'a70175636f61703a2f2f61732e6578616d706c652e63
6f6d02656572696b77037818636f61703a2f2f6c6967
68742e6578616d706c652e636f6d041a5612aeb0051a
5610d9f0061a5610d9f007420b71' / {
/ iss / 1: "coap://as.example.com",
/ sub / 2: "erikw",
/ aud / 3: "coap://light.example.com",
/ exp / 4: 1444064944,
/ nbf / 5: 1443944944,
/ iat / 6: 1443944944,
/ cti / 7: h'0b71'
} / ,
/ signature / h'b9b2821b6b2c2f9d1d984b11854dcfcee1f2197468
00ce76112c21f58c45dea1d7f01cec1ab3940f75c4
59305365210a23a9ed463b4f6fc984c2f1c08e504d
90'
]
)
Figure 8: Signed CWT in CBOR diagnostic notation
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A.4. Example MACed CWT
This section shows a MACed CWT with a single recipient, a full CWT
Claims Set, and a CWT tag.
The MAC is generated using the 256-bit symmetric key from
Appendix A.2.2 with a 64-bit truncation. Line breaks are for display
purposes only.
d83dd18443a10104a05850a70175636f61703a2f2f61732e6578616d706c652e
636f6d02656572696b77037818636f61703a2f2f6c696768742e6578616d706c
652e636f6d041a5612aeb0051a5610d9f0061a5610d9f007420b7148093101ef
6d789200
Figure 9: MACed CWT with CWT tag as hex string
61(
17(
[
/ protected / h'a10104' / {
/ alg / 1: 4 / HMAC 256/64 /
} / ,
/ unprotected / {},
/ payload / h'a70175636f61703a2f2f61732e6578616d706c652e636f
6d02656572696b77037818636f61703a2f2f6c69676874
2e6578616d706c652e636f6d041a5612aeb0051a5610d9
f0061a5610d9f007420b71' / {
/ iss / 1: "coap://as.example.com",
/ sub / 2: "erikw",
/ aud / 3: "coap://light.example.com",
/ exp / 4: 1444064944,
/ nbf / 5: 1443944944,
/ iat / 6: 1443944944,
/ cti / 7: h'0b71'
} / ,
/ tag / h'093101ef6d789200'
]
)
)
Figure 10: MACed CWT with CWT tag in CBOR diagnostic notation
A.5. Example Encrypted CWT
This section shows an encrypted CWT with a single recipient and a
full CWT Claims Set.
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The encryption is done with AES-CCM mode using the 128-bit symmetric
key from Appendix A.2.1 with a 64-bit tag and 13-byte nonce, i.e.,
COSE AES-CCM-16-64-128. Line breaks are for display purposes only.
d08343a1010aa1054d3d9624bfb90a612bdcfc5077c45858e06d4b57cf3b3c9d
a3a16325dadcb9d2a0748f00ecd728f4b79030b56a292ee9cc8cc75349c120fc
1ba5d67ee29affde28df75a20f344812453ff68270ad5f46295660558168e1d1
85cb308226cdad0a50417dcd4a8d4b47
Figure 11: Encrypted CWT as hex string
16(
[
/ protected / h'a1010a' / {
/ alg / 1: 10 / AES-CCM-16-64-128 /
} /,
/ unprotected / {
/ iv / 5: h'3d9624bfb90a612bdcfc5077c4'
},
/ ciphertext / h'e06d4b57cf3b3c9da3a16325dadcb9d2a0748f00ecd
728f4b79030b56a292ee9cc8cc75349c120fc1ba5d6
7ee29affde28df75a20f344812453ff68270ad5f462
95660558168e1d185cb308226cdad0a50417dcd4a8d
4b47'
]
)
Figure 12: Encrypted CWT in CBOR diagnostic notation
A.6. Example Nested CWT
This section shows a Nested CWT, signed and then encrypted, with a
single recipient and a full CWT Claims Set.
The signature is generated using the private ECDSA key from
Appendix A.2.3 and it can be validated using the public ECDSA parts
from Appendix A.2.3. The encryption is done with AES-CCM mode using
the 128-bit symmetric key from Appendix A.2.1 with a 64-bit tag and
13-byte nonce, i.e., COSE AES-CCM-16-64-128. The content type is set
to CWT to indicate that there are multiple layers of COSE protection
before finding the CWT Claims Set. The decrypted ciphertext will be a
COSE_sign1 structure. In this example, it is the same one as in
Appendix A.3, i.e., a Signed CWT Claims Set. Note that there is no
limitation to the number of layers; this is an example with two
layers. Line breaks are for display purposes only.
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d08343a1010aa1054dd3bdeeb4daaa50625a5b576cc458a3318af5c80a11e081
91ca790b0793156451afc144e0f9f892679dff1d01cd52d7fe1e43ac8dabace0
f74af095f918197da1550a76d59c2a89db6331e12451fc87fef56f2ff179fb33
d6132ca34eb7fa8de0960d5f02a2b625792ccc8e5b3d59c0bede9d7438dc5c4f
e0c403c8fc32e874fbb7516c52edddfc09d4444a762dcd0cd486895131c343ae
040620cdd4448c6ce0b7803022ff3d7877a83c345c05a57b36105a
Figure 13: Signed and Encrypted CWT as hex string
16(
[
/ protected / h'a203183d010a' / {
/ alg / 1: 10 / AES-CCM-16-64-128 /
} / ,
/ unprotected / {
/ iv / 5: h'd3bdeeb4daaa50625a5b576cc4'
},
/ ciphertext / h'318af5c80a11e08191ca790b0793156451afc144e0f
9f892679dff1d01cd52d7fe1e43ac8dabace0f74af0
95f918197da1550a76d59c2a89db6331e12451fc87f
ef56f2ff179fb33d6132ca34eb7fa8de0960d5f02a2
b625792ccc8e5b3d59c0bede9d7438dc5c4fe0c403c
8fc32e874fbb7516c52edddfc09d4444a762dcd0cd4
86895131c343ae040620cdd4448c6ce0b7803022ff3
d7877a83c345c05a57b36105a'
]
)
Figure 14: Signed and Encrypted CWT in CBOR diagnostic notation
A.7. Example MACed CWT with a floating-point value
This section shows a MACed CWT with a single recipient and a simple
CWT Claims Set. The CWT Claims Set with a floating-point 'iat' value.
The MAC is generated using the 256-bit symmetric key from
Appendix A.2.2 with a 64-bit truncation. Line breaks are for display
purposes only.
d18443a10104a04ba106fb41d584367c20000048b8816f34c0542892
Figure 15: MACed CWT with a floating-point value as hex string
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17(
[
/ protected / h'a10104' / {
/ alg / 1: 4 / HMAC 256/64 /
} / ,
/ unprotected / {},
/ payload / h'a106fb41d584367c200000' / {
/ iat / 6: 1443944944.5
} / ,
/ tag / h'b8816f34c0542892'
]
)
Figure 16: MACed CWT with a floating-point value in CBOR diagnostic
notation
Appendix B. Acknowledgements
This specification is based on JSON Web Token (JWT) [RFC7519], the
authors of which also include Nat Sakimura and John Bradley. It also
incorporates suggestions made by many people, notably Carsten
Bormann, Jim Schaad, Ludwig Seitz, and Goeran Selander.
Appendix C. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-05
o Addressed working group last call comments with the following
changes:
o Say that CWT is derived from JWT, rather than CWT is a profile of
JWT.
o Used CBOR type names in descriptions, rather than major/minor type
numbers.
o Clarified the NumericDate and StringOrURI descriptions.
o Changed to allow CWT claim names to use values of any legal CBOR
map key type.
o Changed to use the CWT tag to identify nested CWTs instead of the
CWT content type.
o Added an example using a floating-point date value.
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o Acknowledged reviewers.
-04
o Specified that the use of CBOR tags to prefix any of the claim
values defined in this specification is NOT RECOMMENDED.
-03
o Reworked the examples to include signed, MACed, encrypted, and
nested CWTs.
o Defined the CWT CBOR tag and explained its usage.
-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/
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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
Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria
Email: Hannes.Tschofenig@arm.com
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