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