Internet Engineering Task Force (IETF) M. Jones
Request for Comments: 8392 Microsoft
Category: Standards Track E. Wahlstroem
ISSN: 2070-1721
S. Erdtman
Spotify AB
H. Tschofenig
ARM Ltd.
May 2018
CBOR Web Token (CWT)
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 is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8392.
Copyright Notice
Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. CBOR-Related Terminology . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Registered Claims . . . . . . . . . . . . . . . . . . . . 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 Claim Names, Keys, and Value Types . . . . . . 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 . . . . . . . . . . . . . . . . . 13
9.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 13
9.3. CoAP Content-Formats Registration . . . . . . . . . . . . 13
9.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 13
9.4. CBOR Tag registration . . . . . . . . . . . . . . . . . . 14
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 16
A.2. Example Keys . . . . . . . . . . . . . . . . . . . . . . 16
A.2.1. 128-Bit Symmetric Key . . . . . . . . . . . . . . . . 16
A.2.2. 256-Bit Symmetric Key . . . . . . . . . . . . . . . . 16 17
A.2.3. Elliptic Curve Digital Signature Algorithm (ECDSA)
P-256 256-Bit COSE Key . . . . . . . . . . . . . . . 17
A.3. Example Signed CWT . . . . . . . . . . . . . . . . . . . 17 18
A.4. Example MACed CWT . . . . . . . . . . . . . . . . . . . . 18 19
A.5. Example Encrypted CWT . . . . . . . . . . . . . . . . . . 19
A.6. Example Nested CWT . . . . . . . . . . . . . . . . . . . 20
A.7. Example MACed CWT with a Floating-Point Value . . . . . . 21
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 22
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 (the suggested pronunciation of CWT is the same as
the English word "cot"). To protect the claims contained in CWTs,
the CBOR Object Signing and Encryption (COSE) [RFC8152] specification
is used.
1.1. CBOR-Related Terminology
In JSON, maps are called objects and only have one kind of map key: a
string. CBOR uses 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.
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document reuses terminology from JWT [RFC7519] and COSE
[RFC8152].
StringOrURI
The "StringOrURI" term in this specification has the same meaning
and processing rules as the JWT "StringOrURI" term defined in
Section 2 of [RFC7519], except that it is represented as a CBOR
text string instead of a JSON text string.
NumericDate
The "NumericDate" term in this specification has the same meaning
and processing rules as the JWT "NumericDate" term defined in
Section 2 of [RFC7519], except that it is represented as a CBOR
numeric date (from Section 2.4.1 of [RFC7049]) instead of a JSON
number. The encoding is modified so that the leading tag 1
(epoch-based date/time) MUST be omitted.
Claim Name
The human-readable name used to identify a claim.
Claim Key
The CBOR map key used to identify a claim.
Claim Value
The CBOR map value representing the value of the claim.
CWT Claims Set
The 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 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. Registered Claims
None of the claims defined below are intended to be mandatory to use
or implement. Rather, they 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 and processing rules as
the "iss" claim defined in Section 4.1.1 of [RFC7519], except that
the value is a StringOrURI, as defined in Section 2 of this
specification. The Claim Key 1 is used to identify this claim.
3.1.2. sub (Subject) Claim
The "sub" (subject) claim has the same meaning and processing rules
as the "sub" claim defined in Section 4.1.2 of [RFC7519], except that
the value is a StringOrURI, as defined in Section 2 of this
specification. The Claim Key 2 is used to identify this claim.
3.1.3. aud (Audience) Claim
The "aud" (audience) claim has the same meaning and processing rules
as the "aud" claim defined in Section 4.1.3 of [RFC7519], except that
the value of the audience claim is a StringOrURI when it is not an
array or each of the audience array element values is a StringOrURI
when the audience claim value is an array. (StringOrURI is defined
in Section 2 of this specification.) The Claim Key 3 is used to
identify this claim.
3.1.4. exp (Expiration Time) Claim
The "exp" (expiration time) claim has the same meaning and processing
rules as the "exp" claim defined in Section 4.1.4 of [RFC7519],
except that the value is a NumericDate, as defined in Section 2 of
this specification. The Claim Key 4 is used to identify this claim.
3.1.5. nbf (Not Before) Claim
The "nbf" (not before) claim has the same meaning and processing
rules as the "nbf" claim defined in Section 4.1.5 of [RFC7519],
except that the value is a NumericDate, as defined in Section 2 of
this specification. The Claim Key 5 is used to identify this claim.
3.1.6. iat (Issued At) Claim
The "iat" (issued at) claim has the same meaning and processing rules
as the "iat" claim defined in Section 4.1.6 of [RFC7519], except that
the value is a NumericDate, as defined in Section 2 of this
specification. The Claim Key 6 is used to identify this claim.
3.1.7. cti (CWT ID) Claim
The "cti" (CWT ID) claim has the same meaning and processing rules as
the "jti" claim defined in Section 4.1.7 of [RFC7519], except that
the value is a byte string. The Claim Key 7 is used to identify this
claim.
4. Summary of the Claim Names, Keys, and Value Types
+------+-----+----------------------------------+
| Name | Key | Value type 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 | byte string |
+------+-----+----------------------------------+
Table 1: Summary of the Claim Names, Keys, and Value Types
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 1 (epoch-based date/
time) 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.
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 1: Example of 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 [RFC8152]
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 [RFC8152] 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 [RFC8152] 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 [RFC8152] 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 tagged COSE_Sign/COSE_Sign1,
COSE_Mac/COSE_Mac0, or COSE_Encrypt/COSE_Encrypt0, and return to
Step 3.
6. If needed by the application, prepend the COSE object with the
appropriate COSE CBOR tag to indicate the type of the COSE
object. If needed by the application, prepend the COSE object
with 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 Section 4 of [RFC8152] ("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 Section 6 of [RFC8152] ("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 Section 5 of [RFC8152]
("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 map; let the CWT Claims
Set be this CBOR map.
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
Syntactically, the signing and encryption operations for Nested CWTs
may be applied in any order, order; however, if both signing and encryption
are necessary, normally producers normally 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
IANA has created the "CBOR Web Token (CWT) Claims" registry. registry
[IANA.CWT.Claims].
Registration requests are evaluated using the criteria described in
the Claim Key instructions in the registration template below after a
three-week review period on the cwt-reg-review@ietf.org mailing list,
on the advice of one or more Designated Experts [RFC8126]. 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.
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. Registrations for the limited set
of values between -256 and 255 and strings of length 1 are to be
restricted to claims with general applicability.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.
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.
Since a high degree of overlap is expected between the contents of
the "CBOR Web Token (CWT) Claims" registry and the "JSON Web Token
Claims" registry, overlap in the corresponding pools of Designated
Experts would be useful to help ensure that an appropriate level of
coordination between the registries is maintained.
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".
Claim Key:
CBOR map key for the claim. Different ranges of values use
different registration policies [RFC8126]. Integer values from
-256 to 255 and strings of length 1 are designated as Standards
Action. Integer values from -65536 to -257 and from 256 to 65535
along with strings of length 2 are designated as Specification
Required. Integer values greater than 65535 and strings of length
greater than 2 are designated as Expert Review. Integer values
less than -65536 are marked as Private Use.
Claim Value Type(s):
CBOR types that can be used for the claim value.
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: (RESERVED)
o Claim Description: This registration reserves the key value 0.
o JWT Claim Name: N/A
o Claim Key: 0
o Claim Value Type(s): N/A
o Change Controller: IESG
o Specification Document(s): [RFC8392]
o Claim Name: "iss" iss
o Claim Description: Issuer
o JWT Claim Name: "iss" iss
o Claim Key: 1
o Claim Value Type(s): text string
o Change Controller: IESG
o Specification Document(s): Section 3.1.1 of [RFC8392]
o Claim Name: "sub" sub
o Claim Description: Subject
o JWT Claim Name: "sub" sub
o Claim Key: 2
o Claim Value Type(s): text string
o Change Controller: IESG
o Specification Document(s): Section 3.1.2 of [RFC8392]
o Claim Name: "aud" aud
o Claim Description: Audience
o JWT Claim Name: "aud" aud
o Claim Key: 3
o Claim Value Type(s): text string
o Change Controller: IESG
o Specification Document(s): Section 3.1.3 of [RFC8392]
o Claim Name: "exp" exp
o Claim Description: Expiration Time
o JWT Claim Name: "exp" exp
o Claim Key: 4
o Claim Value Type(s): integer or floating-point number
o Change Controller: IESG
o Specification Document(s): Section 3.1.4 of [RFC8392]
o Claim Name: "nbf" nbf
o Claim Description: Not Before
o JWT Claim Name: "nbf" nbf
o Claim Key: 5
o Claim Value Type(s): integer or floating-point number
o Change Controller: IESG
o Specification Document(s): Section 3.1.5 of [RFC8392]
o Claim Name: "iat" iat
o Claim Description: Issued At
o JWT Claim Name: "iat" iat
o Claim Key: 6
o Claim Value Type(s): integer or floating-point number
o Change Controller: IESG
o Specification Document(s): Section 3.1.6 of [RFC8392]
o Claim Name: "cti" cti
o Claim Description: CWT ID
o JWT Claim Name: "jti" jti
o Claim Key: 7
o Claim Value Type(s): byte string
o Change Controller: IESG
o Specification Document(s): Section 3.1.7 of [RFC8392]
9.2. Media Type Registration
IANA has registered 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.
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 [RFC8392]
o Interoperability considerations: N/A
o Published specification: [RFC8392]
o Applications that use this media type: IoT applications sending
security tokens over HTTP(S), CoAP(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
IANA has registered 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: 61
o Reference: [RFC8392]
9.4. CBOR Tag registration
IANA has registered the CWT CBOR tag in the "CBOR Tags" registry
[IANA.CBOR.Tags].
9.4.1. Registry Contents
o CBOR Tag: 61
o Data Item: CBOR Web Token (CWT)
o Semantics: CBOR Web Token (CWT), as defined in [RFC8392]
o Reference: [RFC8392]
o Point of Contact: Michael B. Jones, mbj@microsoft.com
10. References
10.1. Normative References
[IANA.CBOR.Tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
<http://www.iana.org/assignments/cbor-tags/>.
[IANA.CoAP.Content-Formats]
IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/>.
[IANA.CWT.Claims]
IANA, "CBOR Web Token (CWT) Claims",
<http://www.iana.org/assignments/cwt>.
[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,
<https://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, <https://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,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[IANA.JWT.Claims]
IANA, "JSON Web Token Claims",
<http://www.iana.org/assignments/jwt>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://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, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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].
Where a byte string is to carry an embedded CBOR-encoded item, the
diagnostic notation for this CBOR data item can be enclosed in '<<'
and '>>' to notate the byte string resulting from encoding the data
item, e.g., h'63666F6F' translates to <<"foo">>.
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 byte string.
a70175636f61703a2f2f61732e6578616d706c652e636f6d02656572696b7703
7818636f61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0
051a5610d9f0061a5610d9f007420b71
Figure 2: Example CWT Claims Set as Hex String
{
/ 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 3: 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
a42050231f4c4d4d3051fdc2ec0a3851d5b3830104024c53796d6d6574726963
313238030a
Figure 4: 128-bit symmetric COSE_Key as hex string
{
/ k / -1: h'231f4c4d4d3051fdc2ec0a3851d5b383'
/ kty / 1: 4 / Symmetric /,
/ kid / 2: h'53796d6d6574726963313238' / 'Symmetric128' /,
/ alg / 3: 10 / AES-CCM-16-64-128 /
}
Figure 5: 128-Bit Symmetric COSE_Key in CBOR Diagnostic Notation
A.2.2. 256-Bit Symmetric Key
a4205820403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1ec99192d
795693880104024c53796d6d6574726963323536030a
Figure 6: 256-Bit Symmetric COSE_Key as Hex String
{
/ k / -1: h'403697de87af64611c1d32a05dab0fe1fcb715a86ab435f1
ec99192d79569388'
/ kty / 1: 4 / Symmetric /,
/ kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /,
/ alg / 3: 4 / HMAC 256/64 /
}
Figure 7: 256-Bit Symmetric COSE_Key in CBOR Diagnostic Notation
A.2.3. Elliptic Curve Digital Signature Algorithm (ECDSA) P-256 256-Bit
COSE Key
a72358206c1382765aec5358f117733d281c1c7bdc39884d04a45a1e6c67c858
bc206c1922582060f7f1a780d8a783bfb7a2dd6b2796e8128dbbcef9d3d168db
9529971a36e7b9215820143329cce7868e416927599cf65a34f3ce2ffda55a7e
ca69ed8919a394d42f0f2001010202524173796d6d6574726963454344534132
35360326
Figure 8: 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 /,
/ kid / 2: h'4173796d6d657472696345434453413
23536' / 'AsymmetricECDSA256' /,
/ alg / 3: -7 / ECDSA 256 /
}
Figure 9: ECDSA 256-Bit COSE Key in CBOR Diagnostic Notation
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.
d28443a10126a104524173796d6d657472696345434453413235365850a701756
36f61703a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f
61703a2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d
9f0061a5610d9f007420b7158405427c1ff28d23fbad1f29c4c7c6a555e601d6f
a29f9179bc3d7438bacaca5acd08c8d4d4f96131680c429a01f85951ecee743a5
2b9b63632c57209120e1c9e30
Figure 10: Signed CWT as Hex String
18(
[
/ protected / << {
/ alg / 1: -7 / ECDSA 256 /
} >>,
/ unprotected / {
/ kid / 4: h'4173796d6d657472696345434453413
23536' / 'AsymmetricECDSA256' /
},
/ payload / << {
/ 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'5427c1ff28d23fbad1f29c4c7c6a555e601d6fa29f
9179bc3d7438bacaca5acd08c8d4d4f96131680c42
9a01f85951ecee743a52b9b63632c57209120e1c9e
30'
]
)
Figure 11: Signed CWT in CBOR Diagnostic Notation
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.
d83dd18443a10104a1044c53796d6d65747269633235365850a70175636f6170
3a2f2f61732e6578616d706c652e636f6d02656572696b77037818636f61703a
2f2f6c696768742e6578616d706c652e636f6d041a5612aeb0051a5610d9f006
1a5610d9f007420b7148093101ef6d789200
Figure 12: MACed CWT with CWT Tag as Hex String
61(
17(
[
/ protected / << {
/ alg / 1: 4 / HMAC-256-64 /
} >>,
/ unprotected / {
/ kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /
},
/ payload / << {
/ 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 13: 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.
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.
d08343a1010aa2044c53796d6d6574726963313238054d99a0d7846e762c49ff
e8a63e0b5858b918a11fd81e438b7f973d9e2e119bcb22424ba0f38a80f27562
f400ee1d0d6c0fdb559c02421fd384fc2ebe22d7071378b0ea7428fff157444d
45f7e6afcda1aae5f6495830c58627087fc5b4974f319a8707a635dd643b
Figure 14: Encrypted CWT as Hex String
16(
[
/ protected / << {
/ alg / 1: 10 / AES-CCM-16-64-128 /
} >>,
/ unprotected / {
/ kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /,
/ iv / 5: h'99a0d7846e762c49ffe8a63e0b'
},
/ ciphertext / h'b918a11fd81e438b7f973d9e2e119bcb22424ba0f38
a80f27562f400ee1d0d6c0fdb559c02421fd384fc2e
be22d7071378b0ea7428fff157444d45f7e6afcda1a
ae5f6495830c58627087fc5b4974f319a8707a635dd
643b'
]
)
Figure 15: 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.
d08343a1010aa2044c53796d6d6574726963313238054d4a0694c0e69ee6b595
6655c7b258b7f6b0914f993de822cc47e5e57a188d7960b528a747446fe12f0e
7de05650dec74724366763f167a29c002dfd15b34d8993391cf49bc91127f545
dba8703d66f5b7f1ae91237503d371e6333df9708d78c4fb8a8386c8ff09dc49
af768b23179deab78d96490a66d5724fb33900c60799d9872fac6da3bdb89043
d67c2a05414ce331b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bff142631
610a7e0f677b7e9b0bc73adefdcee16d9d5d284c616abeab5d8c291ce0
Figure 16: Signed and Encrypted CWT as Hex String
16(
[
/ protected / << {
/ alg / 1: 10 / AES-CCM-16-64-128 /
} >>,
/ unprotected / {
/ kid / 4: h'53796d6d6574726963313238' / 'Symmetric128' /,
/ iv / 5: h'4a0694c0e69ee6b5956655c7b2'
},
/ ciphertext / h'f6b0914f993de822cc47e5e57a188d7960b528a7474
46fe12f0e7de05650dec74724366763f167a29c002d
fd15b34d8993391cf49bc91127f545dba8703d66f5b
7f1ae91237503d371e6333df9708d78c4fb8a8386c8
ff09dc49af768b23179deab78d96490a66d5724fb33
900c60799d9872fac6da3bdb89043d67c2a05414ce3
31b5b8f1ed8ff7138f45905db2c4d5bc8045ab372bf
f142631610a7e0f677b7e9b0bc73adefdcee16d9d5d
284c616abeab5d8c291ce0'
]
)
Figure 17: 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.
d18443a10104a1044c53796d6d65747269633235364ba106fb41d584367c2000
0048b8816f34c0542892
Figure 18: MACed CWT with a Floating-Point Value as Hex String
17(
[
/ protected / << {
/ alg / 1: 4 / HMAC-256-64 /
} >>,
/ unprotected / {
/ kid / 4: h'53796d6d6574726963323536' / 'Symmetric256' /,
},
/ payload / << {
/ iat / 6: 1443944944.5
} >>,
/ tag / h'b8816f34c0542892'
]
)
Figure 19: MACed CWT with a Floating-Point Value in CBOR Diagnostic
Notation
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, including Carsten
Bormann, Alissa Cooper, Esko Dijk, Benjamin Kaduk, Warren Kumari,
Carlos Martinez, Alexey Melnikov, Kathleen Moriarty, Eric Rescorla,
Dan Romascanu, Adam Roach, Kyle Rose, Jim Schaad, Ludwig Seitz, and
Goeran Selander.
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
Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria
Email: Hannes.Tschofenig@arm.com