Secure Patterns for Internet CrEdentials M. Prorock
Internet-Draft mesur.io
Updates: RFC8392 (if approved) O. Steele
Intended status: Standards Track Transmute
Expires: 4 September 2025 H. Birkholz
Fraunhofer SIT
R. Mahy
Rohan Mahy Consulting Services
3 March 2025
SPICE SD-CWT
draft-ietf-spice-sd-cwt-03
Abstract
This document describes a data minimization technique for use with
CBOR Web Token (CWT). The approach is based on Selective Disclosure
JSON Web Token (SD-JWT), with changes to align with CBOR Object
Signing and Encryption (COSE).
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://ietf-wg-
spice.github.io/draft-ietf-spice-sd-cwt/draft-ietf-spice-sd-cwt.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-spice-sd-cwt/.
Discussion of this document takes place on the Secure Patterns for
Internet CrEdentials Working Group mailing list
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Source for this draft and an issue tracker can be found at
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. High level flow . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of Selective Disclosure CWT . . . . . . . . . . . . 7
3.1. A CWT without Selective Disclosure . . . . . . . . . . . 7
3.2. Holder gets an SD-CWT from the Issuer . . . . . . . . . . 8
4. Holder prepares an SD-CWT for a Verifier . . . . . . . . . . 11
5. Update to the CBOR Web Token Specification . . . . . . . . . 12
6. SD-CWT definition . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Types of blinded claims . . . . . . . . . . . . . . . . . 14
7. SD-CWT Issuance . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Issuer generation . . . . . . . . . . . . . . . . . . . . 15
7.2. Holder validation . . . . . . . . . . . . . . . . . . . . 15
8. SD-CWT Presentation . . . . . . . . . . . . . . . . . . . . . 17
8.1. Creating a Key Binding Token . . . . . . . . . . . . . . 18
9. SD-KBT and SD-CWT Verifier Validation . . . . . . . . . . . . 19
10. Decoy Digests . . . . . . . . . . . . . . . . . . . . . . . . 20
11. Encrypted Disclosures . . . . . . . . . . . . . . . . . . . . 20
12. Credential Types . . . . . . . . . . . . . . . . . . . . . . 22
13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 22
13.1. Minimal spanning example . . . . . . . . . . . . . . . . 23
13.2. Nested example . . . . . . . . . . . . . . . . . . . . . 25
14. Implementation Status . . . . . . . . . . . . . . . . . . . . 29
14.1. Transmute Prototype . . . . . . . . . . . . . . . . . . 30
15. Security Considerations . . . . . . . . . . . . . . . . . . . 30
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15.1. Transparency . . . . . . . . . . . . . . . . . . . . . . 30
15.2. Traceability . . . . . . . . . . . . . . . . . . . . . . 31
15.3. Credential Types . . . . . . . . . . . . . . . . . . . . 31
15.4. Determinism & Augmentation . . . . . . . . . . . . . . . 31
15.5. Threat Model . . . . . . . . . . . . . . . . . . . . . . 31
15.6. Random Numbers . . . . . . . . . . . . . . . . . . . . . 32
15.7. Binding the KBT and the CWT . . . . . . . . . . . . . . 32
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
16.1. COSE Header Parameters . . . . . . . . . . . . . . . . . 33
16.1.1. sd_claims . . . . . . . . . . . . . . . . . . . . . 33
16.1.2. sd_alg . . . . . . . . . . . . . . . . . . . . . . . 34
16.1.3. sd_encrypted_claims . . . . . . . . . . . . . . . . 34
16.2. CBOR Tags . . . . . . . . . . . . . . . . . . . . . . . 34
16.2.1. To be redacted tag . . . . . . . . . . . . . . . . . 34
16.2.2. Redacted claim keys tag . . . . . . . . . . . . . . 35
16.2.3. Redacted claim element tag . . . . . . . . . . . . . 35
16.3. CBOR Web Token (CWT) Claims . . . . . . . . . . . . . . 35
16.3.1. vct . . . . . . . . . . . . . . . . . . . . . . . . 35
16.4. Media Types . . . . . . . . . . . . . . . . . . . . . . 36
16.4.1. application/sd+cwt . . . . . . . . . . . . . . . . . 36
16.4.2. application/kb+cwt . . . . . . . . . . . . . . . . . 37
16.5. Content-Formats . . . . . . . . . . . . . . . . . . . . 38
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
17.1. Normative References . . . . . . . . . . . . . . . . . . 38
17.2. Informative References . . . . . . . . . . . . . . . . . 40
Appendix A. Complete CDDL Schema . . . . . . . . . . . . . . . . 42
Appendix B. Comparison to SD-JWT . . . . . . . . . . . . . . . . 44
B.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 44
B.2. Redaction Claims . . . . . . . . . . . . . . . . . . . . 44
B.3. Issuance . . . . . . . . . . . . . . . . . . . . . . . . 44
B.4. Presentation . . . . . . . . . . . . . . . . . . . . . . 44
B.5. Validation . . . . . . . . . . . . . . . . . . . . . . . 44
Appendix C. Keys used in the examples . . . . . . . . . . . . . 44
C.1. Subject / Holder . . . . . . . . . . . . . . . . . . . . 45
C.2. Issuer . . . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix D. Document History . . . . . . . . . . . . . . . . . . 48
D.1. draft-ietf-spice-sd-cwt-03 . . . . . . . . . . . . . . . 49
D.2. draft-ietf-spice-sd-cwt-02 . . . . . . . . . . . . . . . 49
D.3. draft-ietf-spice-sd-cwt-01 . . . . . . . . . . . . . . . 50
D.4. draft-ietf-spice-sd-cwt-00 . . . . . . . . . . . . . . . 50
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
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1. Introduction
This document updates the CBOR Web Token (CWT) specification
[RFC8392], enabling the holder of a CWT to disclose or redact special
claims marked disclosable by the issuer of a CWT. The approach is
modeled after SD-JWT [I-D.draft-ietf-oauth-selective-disclosure-jwt],
with changes to align with conventions from CBOR Object Signing and
Encryption (COSE) [RFC9052]. This specification enables Holders of
CWT based credentials to prove the integrity and authenticity of
selected attributes asserted by an Issuer about a Subject to a
Verifier. Although techniques such as one time use and batch
issuance can improve the confidentiality and security characteristics
of CWT based credential protocols, CWTs remain traceable. Selective
Disclosure CBOR Web Tokens (SD-CWTs) are CWTs and can be deployed in
protocols that are already using CWTs, even if they contain no
optional to disclose claims. Credential types are distinguished by
their attributes, for example a license to operate a vehicle and a
license to import a product will contain different attributes. The
specification of credential types is out of scope for this document,
and the examples used in this document are informative. SD-CWT
operates on CWT Claims Sets as described in [RFC8392]. CWT Claims
Sets contain Claim Keys and Claim Values. SD-CWT enables Issuers to
mark certain Claim Keys or Claim Values mandatory or optional for a
holder of a CWT to disclose. A holder cannot send redacted claim
keys to a verifier who does not understand selective disclosure at
all. However, Claim Keys and Claim Values which are not understood
remain ignored as described in Section 3 of [RFC8392].
1.1. High level flow
Figure 1: High level SD-CWT Issuance and Presentation Flow
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Issuer Holder Verifier
| | |
| +---+ |
| | | Key Gen |
| Request SD-CWT |<--+ |
|<-------------------------------| |
| | |
+------------------------------->| Request Nonce |
| Receive SD-CWT +-------------------------------->|
| | |
| |<--------------------------------+
| | Receive Nonce |
| +---+ |
| | | Redact Claims |
| |<--+ |
| | |
| +---+ |
| | | Demonstrate |
| |<--+ Posession |
| | |
| | Present SD-CWT |
| +-------------------------------->|
| | |
This diagram captures the essential details necessary to issue and
present an SD-CWT. The parameters necessary to support these
processes can be obtained using transports or protocols which are out
of scope for this specification. However the following guidance is
generally recommended, regardless of protocol or transport.
1. The issuer SHOULD confirm the holder controls all confirmation
material before issuing credentials using the cnf claim.
2. To protect against replay attacks, the verifier SHOULD provide a
nonce, and reject requests that do not include an acceptable an
nonce (cnonce). This guidance can be ignored in cases where
replay attacks are mitigated at another layer.
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 uses terms from CWT [RFC8392], and COSE [RFC9052]
[RFC9053].
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The terms Claim Name, Claim Key and Claim Value are defined in
[RFC8392].
This document defines the following new terms:
Selective Disclosure CBOR Web Token (SD-CWT): A CWT with claims
enabling selective disclosure with key binding.
Selective Disclosure Key Binding Token (SD-CWT-KBT): A CWT used to
demonstrate possession of a confirmation method, associated to an
SD-CWT.
Issuer: An entity that produces a Selective Disclosure CBOR Web
Token.
Holder: An entity that presents a Selective Disclosure CBOR Web
Token which includes a Selective Disclosure Key Binding Token.
Verifier: An entity that validates a Partial or Full Disclosure by a
holder.
Partial Disclosure: When a subset of the original claims protected
by the Issuer, are disclosed by the Holder.
Full Disclosure: When the full set of claims protected by the
Issuer, is disclosed by the Holder. An SD-CWT with no blinded
claims (all claims are marked mandatory to disclose by the Issuer)
is considered a Full Disclosure.
Salted Disclosed Claim: A salted claim disclosed in the unprotected
header of an SD-CWT.
Digested Salted Disclosed Claim / Blinded Claim Hash: A hash digest
of a Salted Disclosed Claim.
Blinded Claim: Any Redacted Claim Key or Redacted Claim Element
which has been replaced in the CWT payload by a Blinded Claim
Hash.
Redacted Claim Key: The hash of a claim redacted from a map data
structure.
Redacted Claim Element: The hash of an element redacted from an
array data structure.
Presented Disclosed Claims Set: The CBOR map containing zero or more
Redacted Claim Keys or Redacted Claim Elements.
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Validated Disclosed Claims Set: The CBOR map containing all
mandatory to disclose claims signed by the issuer, all selectively
disclosed claims presented by the holder, and omitting all
undisclosed instances of Redacted Claim Keys and Redacted Claim
Element claims that are present in the original SD-CWT.
3. Overview of Selective Disclosure CWT
3.1. A CWT without Selective Disclosure
Below is the payload of a standard CWT without selective disclosure.
It consists of standard CWT claims, the holder confirmation key, and
five specific custom claims. The payload is shown below in CBOR
Extended Diagnostic Notation (EDN) [I-D.ietf-cbor-edn-literals].
Note that some of the CWT claim map keys shown in the examples have
been invented for this example and do not have registered integer
keys.
{
/ iss / 1 : "https://issuer.example",
/ sub / 2 : "https://device.example",
/ exp / 4 : 1725330600, /2024-09-02T19:30:00Z/
/ nbf / 5 : 1725243840, /2024-09-01T19:25:00Z/
/ iat / 6 : 1725244200, /2024-09-01T19:30:00Z/
/ cnf / 8 : {
/ cose key / 1 : {
/ kty / 1: 2, / EC2 /
/ crv / -1: 1, / P-256 /
/ x / -2: h'8554eb275dcd6fbd1c7ac641aa2c90d9
2022fd0d3024b5af18c7cc61ad527a2d',
/ y / -3: h'4dc7ae2c677e96d0cc82597655ce92d5
503f54293d87875d1e79ce4770194343'
}
},
/most_recent_inspection_passed/ 500: true,
/inspector_license_number/ 501: "ABCD-123456",
/inspection_dates/ 502 : [
1549560720, / 2019-02-07T17:32:00 /
1612498440, / 2021-02-04T20:14:00 /
1674004740, / 2023-01-17T17:19:00 /
],
/inspection_location/ 503: {
"country": "us", / United States /
"region": "ca", / California /
"postal_code": "94188"
}
}
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The custom claims deal with attributes of an inspection of the
subject: the pass/fail result, the inspection location, the license
number of the inspector, and a list of date when the subject was
inspected.
3.2. Holder gets an SD-CWT from the Issuer
Alice would like to selectively disclose some of these (custom)
claims to different verifiers. Note that some of the claims may not
be selectively disclosable. In our next example the pass/fail status
of the inspection, the most recent inspection date, and the country
of the inspection will be fixed claims (always present in the SD-
CWT). After the Holder requests an SD-CWT from the issuer, the
issuer generates an SD-CWT as follows:
/ cose-sign1 / 18([ / issuer SD-CWT /
/ CWT protected / << {
/ alg / 1 : -35, / ES384 /
/ typ / 16 : "application/sd+cwt",
/ kid / 4 : 'https://issuer.example/cwt-key3',
/ sd_alg / 18 : -16 / SHA256 /
} >>,
/ CWT unprotected / {
/ sd_claims / 17 : [ / these are all the disclosures /
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'7af7084b50badeb57d49ea34627c7a52',
/value/ 1612560720 / inspected 4-Feb-2021 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/claim/ "region", / region=California /
/value/ "ca"
]>>,
<<[
/salt/ h'37c23d4ec4db0806601e6b6dc6670df9',
/claim/ "postal_code",
/value/ "94188"
]>>,
]
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}
/ CWT payload / << {
/ iss / 1 : "https://issuer.example",
/ sub / 2 : "https://device.example",
/ exp / 4 : 1725330600, /2024-09-03T02:30:00+00:00Z/
/ nbf / 5 : 1725243900, /2024-09-02T02:25:00+00:00Z/
/ iat / 6 : 1725244200, /2024-09-02T02:30:00+00:00Z/
/ cnf / 8 : {
/ cose key / 1 : {
/ kty / 1: 2, / EC2 /
/ crv / -1: 1, / P-256 /
/ x / -2: h'8554eb275dcd6fbd1c7ac641aa2c90d9
2022fd0d3024b5af18c7cc61ad527a2d',
/ y / -3: h'4dc7ae2c677e96d0cc82597655ce92d5
503f54293d87875d1e79ce4770194343'
}
},
/most_recent_inspection_passed/ 500: true,
/ redacted_claim_keys / 59(0) : [
/ redacted inspector_license_number /
h'0ad0f76dcb7fd812ca64c3ada3f543be
96d0e351e1e576fbab5cb659b49e599e'
],
/inspection_dates/ 502 : [
/ redacted inspection date 7-Feb-2019 /
60(h'f468b68dd7432030d7f33a8783acb3a4
d6afc215bbc184dce8831c64b539f335'),
/ redacted inspection date 4-Feb-2021 /
60(h'0839dcbdd9ed55c8aac3e573ccf59c81
0fa8d9f6ec551cb9737621faf3584e1f'),
1674004740, / 2023-01-17T17:19:00 /
],
/ inspection_location / 503 : {
"country" : "us", / United States /
/ redacted_claim_keys / 59(0) : [
/ redacted region /
h'dff0cb7a6ff555544554c527d5e32eed
ee6a9d80a1dae2e0ac611796674ce281'
/ redacted postal_code /
h'5f5e6bfc2de598c80df58ff84090125a
f8bb1ada795a37e5cfcf8f480e445755'
]
}
} >>,
/ CWT signature / h'd6b1f5143a3f6b2e54a1ea29ed98e9ed
7abb2927b34ba100fe91ed493d66062b
d71716eed6b209b9d6c6861a6886ad47
5716220bcb3a0276a205002c3f6d3e86
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a52d3e990f869bd38c5a476f73ee3319
64dee2cb51321b7bf2e64e62811a9b22'
])
Figure 1: Issued SD-CWT with all disclosures
Some of the claims are _redacted_ in the payload. The corresponding
_disclosure_ is communicated in the unprotected header in the
sd_claims key. For example, the inspector_license_number claim is a
Salted Disclosed Claim, consisting of a per-disclosure random salt,
the claim name, and claim value.
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>,
Figure 2: CBOR extended diagnostic notation representation of
inspector_license_number disclosure
This is represented in CBOR pretty printed formal as follows (end of
line comments and spaces inserted for clarity):
83 # array(3)
50 # bytes(16)
18d27ca1148990c3c999ed914a1b73c6 # 16-byte salt
19 01f5 # unsigned(501)
6b # text(11)
414243442d313233343536 # "ABCD-123456"
Figure 3: CBOR encoding of inspector_license_number disclosure
The SHA-256 hash (the hash algorithm identified in the sd_alg
protected header field) of that bytes string is the Digested Salted
Disclosed Claim (in hex). The digest value is included in the
payload in a redacted_claim_keys field for a Redacted Claim Key (in
this example), or in a named array for a Redacted Claim Element (ex:
for a redacted claim element of inspection_dates).
e7d2ca13738de42ebfe3d72af06756314940ac1b129e5ecf0ed08af379ae98f8
Figure 4: SHA-256 hash of inspector_license_number disclosure
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Finally, since this redacted claim is a map key and value, the
Digested Salted Disclosed Claim is placed in a redacted_claim_keys
array in the SD-CWT payload at the same level of hierarchy as the
original claim. Redacted claims which are array elements are handled
slightly differently, as described in Section 6.1.
/ redacted_claim_keys / 59(0) : [
/ redacted inspector_license_number /
h'e7d2ca13738de42ebfe3d72af0675631
4940ac1b129e5ecf0ed08af379ae98f8',
/ ... next redacted claim at the same level would go here / ],
Figure 5: redacted inspector_license_number claim in the issued
CWT payload
4. Holder prepares an SD-CWT for a Verifier
When the Holder wants to send an SD-CWT and disclose none, some, or
all of the redacted values, it makes a list of the values to disclose
and puts them in sd_claims in the unprotected header.
For example, Alice decides to disclose to a verifier the
inspector_license_number claim (ABCD-123456), the region claim
(California), and the earliest date element in the inspection_dates
array (7-Feb-2019).
/ sd_claims / 17 : [ / these are the disclosures /
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/claim/ "region", / region=California /
/value/ "ca"
]>>,
]
The Holder MAY fetch a nonce from the Verifier to prevent replay, or
obtain a nonce acceptable to the verifier through a process similar
to the method described in [I-D.ietf-httpbis-unprompted-auth].
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Finally, the Holder generates a Selective Disclosure Key Binding
Token (SD-KBT) that ties together the SD-CWT generated by the Issuer
(with the disclosures the Holder chose for the Verifier in its
unprotected header), the Verifier target audience and optional
nonces, and proof of possession of the Holder's private key.
The issued SD-CWT is placed in the kcwt (Confirmation Key CWT)
protected header field (defined in [RFC9528]).
/ cose-sign1 / 18( / sd_kbt / [
/ KBT protected / << {
/ alg / 1: -7, / ES256 /
/ typ / 16: "application/kb+cwt",
/ kcwt / 13: ...
/ *** SD-CWT from Issuer goes here /
/ with Holder's choice of disclosures /
/ in the SD-CWT unprotected header *** /
/ end of issuer SD-CWT /
} >>, / end of KBT protected header /
/ KBT unprotected / {},
/ KBT payload / << {
/ cnonce / 39 : h'8c0f5f523b95bea44a9a48c649240803',
/ aud / 3 : "https://verifier.example/app",
/ iat / 6 : 1725244237, / 2024-09-02T02:30:37+00:00Z /
} >>, / end of KBT payload /
/ KBT signature / h'feb37bac837b25d3510962ac706297cd
2ef1ace1b47a382e911124c9a4c32287
280f48931c2988d71b297d57dd9d392f
5792d8f87a95166c5ea5110a81c1bfc7'
]) / end of kbt /
Together the digests in protected parts of the issued SD-CWT, and the
disclosures hashed in unprotected header of the issuer_sd_cwt are
used by the Verifier to confirm the disclosed claims. Since the
unprotected header of the included SD-CWT is covered by the signature
in the SW-KBT, the Verifier has assurance the Holder included the
sent list of disclosures.
5. Update to the CBOR Web Token Specification
The CBOR Web Token Specification (Section 1.1 of [RFC8392]), uses
strings, negative integers, and unsigned integers as map keys. This
specification relaxes that requirement, by also allowing CBOR tagged
integers and text strings as map keys. CBOR maps used in a CWT
cannot have duplicate keys. (An integer or string map key is
distinct key from a tagged map key which wraps the corresponding
integer or string value).
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When sorted, map keys in CBOR are arranged in bytewise
lexicographic order of the key's deterministic encodings (see
Section 4.2.1 of [RFC8949]). So an integer key of 3 is
represented in hex as 03, an integer key of -2 is represented in
hex as 21, and a tag of 60 wrapping a 3 is represented in hex as
D8 3C 03
Note that holders presenting to a verifier that does not support this
specification would need to present a CWT without tagged map keys.
Tagged keys are not registered in the CBOR Web Token Claims IANA
registry. Instead the tag provides additional information about the
tagged claim key and the corresponding (untagged) value. Multiple
levels of tags in a key are not permitted.
Variability in serialization requirements impacts privacy.
See the security considerations section for more details on the
privacy impact of serialization and profiling.
6. SD-CWT definition
SD-CWT is modeled after SD-JWT, with adjustments to align with
conventions in CBOR and COSE. An SD-CWT MUST include the protected
header parameter typ [RFC9596] with either a text value "application/
sd-cwt" or an uint value of "C-F-TBD" in the SD-CWT.
An SD-CWT is a CWT that can contain blinded claims (each expressed as
a Blinded Claim Hash) in the CWT payload, at the root level or in any
arrays or maps inside that payload. It is not required to contain
any blinded claims.
Optionally the salted claim values (and often claim names) for the
corresponding Blinded Claim Hash are actually disclosed in the
sd_claims field in the unprotected header of the CWT (the
disclosures). If there are no disclosures (and when no Blinded
Claims Hash is present in the payload) the sd_claims field in the
unprotected header is an empty array.
Any party with a Salted Disclosed Claim can generate its hash, find
that hash in the CWT payload, and unblind the content. However a
Verifier with the hash cannot reconstruct the corresponding blinded
claim without disclosure of the Salted Disclosed Claim.
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6.1. Types of blinded claims
Salted Disclosed Claims for named claims are structured as a 128-bit
salt, the name of the redacted element, and the disclosed value. For
Salted Disclosed Claims of items in an array, the name is omitted.
salted = salted-claim / salted-element / decoy
salted-claim = [
bstr .size 16, ; 128-bit salt
(int / text), ; claim name
any ; claim value
]
salted-element = [
bstr .size 16, ; 128-bit salt
any ; claim value
]
decoy = [
bstr .size 16, ; 128-bit salt
]
; a collection of Salted Disclosed Claims
salted-array = [ +bstr .cbor salted ]
When a blinded claim is a key in a map, its blinded claim hash is
added to a redacted_claim_keys array claim in the CWT payload that is
at the same level of hierarchy as the key being blinded. The
redacted_claim_keys key is the integer 0 (which is reserved for top-
level CWT claim keys), wrapped with a CBOR tag (requested tag number
59).
When blinding an individual item in an array, the value of the item
is replaced with the digested salted hash as a CBOR binary string,
wrapped with a CBOR tag (requested tag number 60).
redacted_claim_element = #6.60( bstr .size 16 )
Blinded claims can be nested. For example, both individual keys in
the inspection_location claim, and the entire inspection_location
element can be separately blinded. An example nested claim is shown
in Section 13.2.
Finally, an issuer may create "decoy digests" which look like a
blinded claim hash but have only a salt. Decoy digests are discussed
in Section 10.
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7. SD-CWT Issuance
How the Holder communicates to the Issuer to request a CWT or an SD-
CWT is out-of-scope of this specification. Likewise, how the Holder
determines which claims to blind or to always disclose is a policy
matter which is not discussed in this specification. This
specification defines the format of an SD-CWT communicated between an
Issuer and a Holder in this section, and describes the format of a
Key Binding Token containing that SD-CWT communicated between a
Holder and a Verifier in Section 8.
The protected header MUST contain the sd_alg field identifying the
algorithm (from the COSE Algorithms registry) used to hash the Salted
Disclosed Claims. The unprotected header MUST contain an sd_claims
section with a Salted Disclosed Claim for _every_ blinded claim hash
present anywhere in the payload, and any decoys (see Section 10). If
there are no disclosures, the sd_claims header is an empty array.
The payload MUST also include a key confirmation element (cnf)
[RFC8747] for the Holder's public key.
In an SD-CWT, either the subject sub/ 2 claim is present, or the
redacted form of the subject is present. The issuer iss / 1 standard
claim SHOULD be present, unless the protected header contains a
certificate or certificate-like entity which fully identifies the
issuer. All other standard CWT claims (aud/ 3, exp / 4, nbf / 5, iat
/ 6, and cti / 7) are OPTIONAL. The cnonce / 39 claim is OPTIONAL.
The cnf claim, the cnonce claim, and the standard claims other than
the subject MUST NOT be redacted. Any other claims are OPTIONAL and
MAY be redacted.
7.1. Issuer generation
The Issuer follows all the requirements of generating a valid CWT as
updated by Section 5. The Issuer MUST implement COSE_Sign1 using an
appropriate asymmetric signature algorithm / curve combination (for
example ES256/P-256 or EdDSA/Ed25519)
The Issuer MUST generate a unique cryptographically random salt with
at least 128-bits of entropy for each Salted Disclosed Claim. If the
client communicates a client-generated nonce (cnonce) when requesting
the SD-CWT, the Issuer SHOULD include it in the payload.
7.2. Holder validation
Upon receiving an SD-CWT from the Issuer with the Holder as the
subject, the Holder verifies the following:
* the issuer (iss) and subject (sub) are correct;
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* if an audience (aud) is present, it is acceptable;
* the CWT is valid according to the nbf and exp claims, if present;
* a public key under the control of the Holder is present in the cnf
claim;
* the hash algorithm in the sd_alg protected header is supported by
the Holder;
* if a cnonce is present, it was provided by the Holder to this
Issuer and is still "fresh";
* there are no unblinded claims about the subject which violate its
privacy policies;
* every blinded claim hash (some of which may be nested as in
Section 13.2) has a corresponding Salted Disclosed Claim, and vice
versa;
* all the Salted Disclosed Claims are correct in their unblinded
context in the payload.
The following informative CDDL is provided to describe the syntax for
an SD-CWT issuance. A complete CDDL schema is in Appendix A.
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sd-cwt-issued = #6.18([
protected: bstr .cbor sd-protected,
sd-unprotected,
payload: bstr .cbor sd-payload,
signature: bstr
])
sd-protected = {
&(typ: 16) ^ => "application/sd+cwt" / TBD1,
&(alg: 1) ^ => int,
&(sd_alg: 18) ^= int, ; -16 for sha-256
* key => any
}
sd-unprotected = {
? &(sd_claims: 17) ^ => salted-array,
* key => any
}
sd-payload = {
; standard claims
&(iss: 1) ^ => tstr, ; "https://issuer.example"
? &(sub: 2) ^ => tstr, ; "https://device.example"
? &(aud: 3) ^ => tstr, ; "https://verifier.example/app"
? &(exp: 4) ^ => int, ; 1883000000
? &(nbf: 5) ^ => int, ; 1683000000
? &(iat: 6) ^ => int, ; 1683000000
? &(cti: 7) ^ => bstr,
&(cnf: 8) ^ => { * key => any }, ; key confirmation
? &(cnonce: 39) ^ => bstr,
;
? &(redacted_keys: #6.59(0)) ^ => [ * bstr ],
* key => any
}
8. SD-CWT Presentation
When a Holder presents an SD-CWT to a Verifier, it can disclose none,
some, or all of its blinded claims. If the Holder wishes to disclose
any claims, it includes that subset of its Salted Disclosed Claims in
the sd_claims claim of the unprotected header.
An SD-CWT presentation to a Verifier has the same syntax as an SD-CWT
issued to a Holder, except the Holder choses the subset of
disclosures included in the sd_claims claim. Since the unprotected
header is not included in the signature, it will contain all the
Salted Disclosed Claims when sent from the Issuer to the Holder.
When sent from the Holder to the Verifier, the unprotected header
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will contain none, some, or all of these Claims. Finally, the SD-CWT
used for presentation to a Verifier is included in a key binding
token, as discsused in the next section.
8.1. Creating a Key Binding Token
Regardless if it discloses any claims, the Holder sends the Verifier
a unique Holder key binding (SD-KBT) Section 8.1 for every
presentation of an SD-CWT to a different Verifier.
An SD-KBT is itself a type of CWT, signed using the private key
corresponding to the key in the cnf claim in the presented SD-CWT.
The SD-KBT contains the SD-CWT, including the Holder's choice of
presented disclosures, in the kcwt protected header field in the SD-
KBT.
The Holder is conceptually both the subject and the issuer of the Key
Binding Token. Therefore the sub and iss of an SD-KBT are implied
from the cnf claim in the included SD-CWT, and are ignored for
validation purposes if they are present. (A profile may define
additional semantics.)
The aud claim MUST be included and relevant to the Verifier. The SD-
KBT payload MUST contain the issued_at (iat) claims. The protected
header of the SD-KBT MUST include the typ header parameter with the
value application/sd-kbt.
The SD-KBT provides the following assurances to the Verifier:
* the Holder of the SD-CWT controls the confirmation method chosen
by the Issuer;
* the Holder's disclosures have not been tampered with since
confirmation occurred;
* the Holder intended to address the SD-CWT to the Verifier
specified in the audience (aud) claim;
* the Holder's disclosure is linked to the creation time (iat) of
the key binding.
The SD-KBT prevents an attacker from copying and pasting disclosures,
or from adding or removing disclosures without detection.
Confirmation is established according to RFC 8747, using the cnf
claim in the payload of the SD-CWT.
The Holder signs the SD-KBT using the key specified in the cnf claim
in the SD-CWT. This proves possession of the Holder's private key.
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kbt-cwt = #6.18([
protected: bstr .cbor kbt-protected,
kbt-unprotected,
payload: bstr .cbor kbt-payload,
signature: bstr
])
kbt-protected = {
&(typ: 16) ^ => "application/kb+cwt",
&(alg: 1) ^ => int,
&(kcwt: 13) ^ => sd-cwt-issued,
* key => any
}
kbt-unprotected = {
* key => any
}
kbt-payload = {
&(aud: 3) ^ => tstr, ; "https://verifier.example"
? &(exp: 4) ^ => int, ; 1883000000
? &(nbf: 5) ^ => int, ; 1683000000
&(iat: 6) ^ => int, ; 1683000000
? &(cnonce: 39) ^ => bstr,
* key => any
}
The SD-KBT payload MAY include a cnonce claim. If included, the
cnonce is a bstr and MUST be treated as opaque to the Holder. All
other claims are OPTIONAL in an SD-KBT.
9. SD-KBT and SD-CWT Verifier Validation
The exact order of the following steps MAY be changed, as long as all
checks are performed before deciding if an SD-CWT is valid. First
the Verifier must open the protected headers of the SD-KBT and find
the issuer SD-CWT present in the kcwt field. Next the Verifier must
validate the SD-CWT as described in Section 7.2 of [RFC8392]. The
Verifier extract the confirmation key from the cnf claim in the SD-
CWT payload. Using the confirmation key, the Verifier validates the
SD-KBT as described in Section 7.2 of [RFC8392].
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Finally, the Verifier MUST extract and decode the disclosed claims
from the sd_claims in the unprotected header of the SD-CWT. The
decoded sd_claims are converted to an intermediate data structure
called a Digest To Disclosed Claim Map which is used to transform the
Presented Disclosed Claimset, into a Validated Disclosed Claimset.
The Verifier MUST compute the hash of each Salted Disclosed Claim
(salted), in order to match each disclosed value to each entry of the
Presented Disclosed Claimset.
One possible concrete representation of the intermediate data
structure for the Digest To Disclosed Claim Map could be:
{
&(digested-salted-disclosed-claim) => salted
}
The Verifier constructs an empty cbor map called the Validated
Disclosed Claimset, and initializes it with all mandatory to disclose
claims from the verified Presented Disclosed Claimset. Next the
Verifier performs a breadth first or depth first traversal of the
Presented Disclosed Claimset, Validated Disclosed Claimset, using the
Digest To Disclosed Claim Map to insert claims into the Validated
Disclosed Claimset when they appear in the Presented Disclosed
Claimset. By performing these steps, the recipient can
cryptographically verify the integrity of the protected claims and
verify they have not been tampered with. If there remain unused
Digest To Disclosed Claim Map at the end of this procedure the SD-CWT
MUST be considered invalid, as if the signature had failed to verify.
Otherwise the SD-CWT is considered valid, and the Validated Disclosed
Claimset is now a CWT Claimset with no claims marked for redaction.
Further validation logic can be applied to the Validated Disclosed
Claimset, as it might normally be applied to a validated CWT
claimset.
10. Decoy Digests
*TODO*
11. Encrypted Disclosures
Some uses of SD-CWT involve verifiers which have internal structure.
In these cases, encrypted disclosures allow more fine-grained
disclosure inside a single presentation.
In the Remote Attestation Procedures (RATS) architecture
[RFC9334], an SD-CWT is a RATS conceptual message that represents
evidence. Different evidence claims could be processed by
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different attesters within the same Verifier. For example, one
SD-KBT could include an SD-CWT with one set of claims about the
workload, and one set of claims about the platform. It would be
desirable to have each RATS appraiser see a different subset of
disclosures in the SD-CWT / SD-KBT.
In the Messaging Layer Security (MLS) protocol [RFC9420], an SD-
CWT credential [I-D.mahy-mls-sd-cwt-credential] could present one
subset of its disclosures to the MLS Distribution Service, and a
different subset of those disclosures to the other members of the
MLS group.
Taking the first example disclosure from above:
<<[
/salt/ h'2008c50a62d9b59813318abd06df8a89',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>
The corresponding bstr is encrypted with an IANA registered
Authenticated Encryption with Additional Data (AEAD) algorithm
[RFC5116] such as AEAD_AES_128_GCM, using the salt as the nonce. The
salt, the algorithm used (alg), and the resulting ciphertext and mac
are put in an array. The bstr encoding of the array is placed in the
sd_encrypted_claims unprotected header field array of the SD-CWT.
The entire SD-CWT is included in the protected header of the SD-KBT,
which integrity protects both encrypted and regular disclosures
alike. Neither encrypted nor regular disclosures can appear in the
unprotected header of a SD-KBT.
/ sd_encrypted_claims / 19 : [ / encrypted disclosures /
<<[
/salt/ h'2008c50a62d9b59813318abd06df8a89',
/alg/ 1, / AEAD_AES_128_GCM /
/ciphertext/ h'b8cf6ed5905b6b0d9c1e7f274ecee4cb
ac8f5ad4dac6ba88e7673e70bafa87b5
9a61c7',
/mac/ h'4ea90eef6b3d05d632e6f19b49aa9de5'
]>>,
...
]
In the example above the key in hex is
'1eb2d67081ee9950fb3a14c6e8896203'.
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The blinded claim hash is still over the unencrypted disclosure. The
receiver of an encrypted disclosure locates the appropriate key by
looking up the unique salt. If the verifier is able to decrypt and
verify an encrypted disclosure, the decrypted disclosure is then
processed as if it where in the sd_claims unprotected header in the
SD-CWT.
Details of key management are left to the specific protocols which
make use of encrypted disclosures.
The CDDL for encrypted disclosures is described below.
encrypted-array = [ +bstr .cbor encrypted ]
encrypted = [
bstr .size 16, ; 128-bit salt
uint16, ; IANA AEAD Algorithm number
bstr, ; the ciphertext output of a bstr-encoded-salted
; with a matching salt
bstr ; the corresponding MAC
]
;bstr-encoded-salted = bstr .cbor salted
*TODO*: consider moving the AEAD algorithm for all encrypted
disclosures into a new protected header field.
Note: because the algorithm is in a registry which contains only
AEAD algorithms, an attacker cannot replace the algorithm or the
message, without a decryption verification failure.
12. Credential Types
This specification defines the CWT claim vct (for verifiable
credential type). The vct value MUST be a case-sensitive StringOrURI
(see [RFC7519]) value serving as an identifier for the type of the
SD-CWT claimset. The vct value MUST be a Collision-Resistant Name as
defined in Section 2 of [RFC7515].
This claim is defined for COSE based verifiable credentials, similar
to the JOSE based verifiable credentials claim (vct) described in
Section 3.2.2.1.1 of [I-D.draft-ietf-oauth-sd-jwt-vc].
Profiles built on this specification are also encouraged to use more
specific media types, as described in [RFC9596].
13. Examples
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13.1. Minimal spanning example
The following example contains claims needed to demonstrate redaction
of key-value pairs and array elements.
/ cose-sign1 / 18( / sd_kbt / [
/ KBT protected / << {
/ alg / 1: -7, / ES256 /
/ typ / 16: "application/kb+cwt",
/ kcwt / 13: 18([ / issuer SD-CWT /
/ CWT protected / << {
/ alg / 1 : -35, / ES384 /
/ typ / 16 : "application/sd+cwt",
/ kid / 4 : 'https://issuer.example/cwt-key3',
/ sd_alg / 18 : -16 / SHA256 /
} >>,
/ CWT unprotected / {
/ sd_claims / 17 : [ / these are the disclosures /
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/claim/ "region", / region=California /
/value/ "ca"
]>>,
]
}
/ CWT payload / << {
/ iss / 1 : "https://issuer.example",
/ sub / 2 : "https://device.example",
/ exp / 4 : 1725330600, /2024-09-03T02:30:00+00:00Z/
/ nbf / 5 : 1725243900, /2024-09-02T02:25:00+00:00Z/
/ iat / 6 : 1725244200, /2024-09-02T02:30:00+00:00Z/
/ cnf / 8 : {
/ cose key / 1 : {
/ kty / 1: 2, / EC2 /
/ crv / -1: 1, / P-256 /
/ x / -2: h'8554eb275dcd6fbd1c7ac641aa2c90d9
2022fd0d3024b5af18c7cc61ad527a2d',
/ y / -3: h'4dc7ae2c677e96d0cc82597655ce92d5
503f54293d87875d1e79ce4770194343'
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}
},
/most_recent_inspection_passed/ 500: true,
/ redacted_claim_keys / 59(0) : [
/ redacted inspector_license_number /
h'0ad0f76dcb7fd812ca64c3ada3f543be
96d0e351e1e576fbab5cb659b49e599e'
],
/inspection_dates/ 502 : [
/ redacted inspection date 7-Feb-2019 /
60(h'f468b68dd7432030d7f33a8783acb3a4
d6afc215bbc184dce8831c64b539f335'),
/ redacted inspection date 4-Feb-2021 /
60(h'0839dcbdd9ed55c8aac3e573ccf59c81
0fa8d9f6ec551cb9737621faf3584e1f'),
1674004740, / 2023-01-17T17:19:00 /
],
/ inspection_location / 503 : {
"country" : "us", / United States /
/ redacted_claim_keys / 59(0) : [
/ redacted region /
h'dff0cb7a6ff555544554c527d5e32eed
ee6a9d80a1dae2e0ac611796674ce281'
/ redacted postal_code /
h'5f5e6bfc2de598c80df58ff84090125a
f8bb1ada795a37e5cfcf8f480e445755'
]
}
} >>,
/ CWT signature / h'd6b1f5143a3f6b2e54a1ea29ed98e9ed
7abb2927b34ba100fe91ed493d66062b
d71716eed6b209b9d6c6861a6886ad47
5716220bcb3a0276a205002c3f6d3e86
a52d3e990f869bd38c5a476f73ee3319
64dee2cb51321b7bf2e64e62811a9b22'
])
/ end of issuer SD-CWT /
} >>, / end of KBT protected header /
/ KBT unprotected / {},
/ KBT payload / << {
/ cnonce / 39 : h'8c0f5f523b95bea44a9a48c649240803',
/ aud / 3 : "https://verifier.example/app",
/ iat / 6 : 1725244237, / 2024-09-02T02:30:37+00:00Z /
} >>, / end of KBT payload /
/ KBT signature / h'feb37bac837b25d3510962ac706297cd
2ef1ace1b47a382e911124c9a4c32287
280f48931c2988d71b297d57dd9d392f
5792d8f87a95166c5ea5110a81c1bfc7'
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]) / end of kbt /
Figure 6: An EDN Example
13.2. Nested example
Instead of the structure from the previous example, imagine the
payload contains an inspection history log with the following
structure. It could be blinded at multiple levels of the claim set
hierarchy.
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{
/ iss / 1 : "https://issuer.example",
/ sub / 2 : "https://device.example",
/ exp / 4 : 1725330600, /2024-09-02T19:30:00Z/
/ nbf / 5 : 1725243840, /2024-09-01T19:25:00Z/
/ iat / 6 : 1725244200, /2024-09-01T19:30:00Z/
/ cnf / 8 : { ... },
504: [ / inspection history log /
{
500: True, / inspection passed /
502: 1549560720, / 2019-02-07T17:32:00 /
501: "DCBA-101777", / inspector license /
503: {
1: "us", / United States /
2: "co", / region=Colorado /
3: "80302" / postcode /
}
},
{
500: True, / inspection passed /
502: 1612560720, / 2021-02-04T20:14:00 /
501: "EFGH-789012", / inspector license /
503: {
1: "us", / United States /
2: "nv", / region=Nevada /
3: "89155" / postcode /
}
},
{
500: True, / inspection passed /
502: 17183928, / 2023-01-17T17:19:00 /
501: "ABCD-123456", / inspector license /
503: {
1: "us", / United States /
2: "ca", / region=California /
3: "94188" / postcode /
}
},
]
}
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For example, looking at the nested disclosures below, the first
disclosure unblinds the entire January 2023 inspection record.
However, when the record is disclosed, the inspector license number
and inspection location are redacted inside the record. The next
disclosure unblinds the inspector_license_number, and the next
disclosure unblinds the inspection location record, but the region
and postcode claims inside the location record are also individually
blinded. The fourth disclosure unblinds the inspection region.
The fifth disclosure unblinds the earliest inspection record, and the
last disclosure unblinds the inspector_license_number for that
record.
Verifiers start unblinding claims for which they have blinded claim
hashes. They continue descending until there are no blinded claim
hashes at any level of the hierarchy for which they have a
corresponding disclosure.
/ sd_claims / 17 : [ / these are the disclosures /
<<[
/salt/ h'e3aa33644123fdbf819ad534653f4aaa',
/claim/ 504, / inspection 17-Jan-2023 /
/value/ [
59(h'2893a00665f1ca2cfeb7456e1eeb8eba
f21d5c12a73d9fbcb8902822f3ecb635'),
59(h'92c0262b0ed6891c6e46d6fca5554caf
79bd8d05c74dbb06a25c9edd304c6e22'),
{
500: True,
502: 17183928,
simple(59): [
h'0ad0f76dcb7fd812ca64c3ada3f543be
96d0e351e1e576fbab5cb659b49e599e',
h'f34c3ea2292d02b92bde25e68e94acd7
f1e011fd6eea6c490f841f09a7a01a48'
]
}
]
]>>,
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/claim/ 501, / inspector_license_number /
/value/ "ABCD-123456"
]>>,
<<[
/salt/ h'7d2505257e7850b70295a87b3c8748e5',
/claim/ 503, / San Francisco location /
/value/ {
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1: "us",
simple(59): [
h'de03a7a0b4359511a7dc0edd8f4ebc00
b5783d8a0d36e715679e23c703011d16',
h'5a98ac2381cb59dee7a43daa073eab48
9773e2830a0b9c4e1efd55737dbb1c06'
]
}
]>>,
<<[
/salt/ h'52da9de5dc61b33775f9348b991d3d78',
/claim/ 2, / region=California /
/value/ "ca"
]>>,
<<[
/salt/ h'b52272341715f2a0b476e33e55ce7501',
/value/ {
500: True,
502: 1549560720,
simple(59): [
h'cd88763edb2485b8109613546051f606
e6b822456da1bf09f604b886e1def45a',
h'0a45eb75de44741bea78dc48b1898d40
09601dbf567279f3042a24cee9fdcab5'
]
} / inspection 7-Feb-2019 /
]>>,
<<[
/salt/ h'591eb2081b05be2dcbb6f8459cc0fe51',
/claim/ 501, / inspector_license_number /
/value/ "DCBA-101777"
]>>
]
After applying the disclosures of the nested structure above, the
disclosed claim set visible to the verifier would look like the
following:
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{
/ iss / 1 : "https://issuer.example",
/ sub / 2 : "https://device.example",
/ exp / 4 : 1725330600, /2024-09-02T19:30:00Z/
/ nbf / 5 : 1725243840, /2024-09-01T19:25:00Z/
/ iat / 6 : 1725244200, /2024-09-01T19:30:00Z/
/ cnf / 8 : { ... },
504: [ / inspection history log /
{
500: True, / inspection passed /
502: 1549560720, / 2019-02-07T17:32:00 /
501: "DCBA-101777", / inspector license /
503: {
1: "us" / United States /
}
},
{
500: True, / inspection passed /
502: 17183928, / 2023-01-17T17:19:00 /
501: "ABCD-123456", / inspector license /
503: {
1: "us", / United States /
2: "ca" / region=California /
}
},
]
}
14. Implementation Status
Note to RFC Editor: Please remove this section as well as references
to [BCP205] before AUTH48.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [BCP205].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
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According to [BCP205], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
14.1. Transmute Prototype
Organization: Transmute Industries Inc
Name: github.com/transmute-industries/sd-cwt (https://github.com/
transmute-industries/sd-cwt)
Description: An open source implementation of this draft.
Maturity: Prototype
Coverage: The current version ('main') implements functionality
similar to that described in this document, and will be revised, with
breaking changes to support the generation of example data to support
this specification.
License: Apache-2.0
Implementation Experience: No interop testing has been done yet. The
code works as proof of concept, but is not yet production ready.
Contact: Orie Steele (orie@transmute.industries)
15. Security Considerations
Security considerations from COSE {(RFC9052)} and CWT [RFC8392] apply
to this specification.
15.1. Transparency
Verification of an SD-CWT requires that the verifier have access to a
verification key (public key) that is associated with the issuer.
Compromise of the issuer's signing key enables an attacker to forge
credentials for any subject associated with the issuer. Certificate
transparency as described in [RFC9162], or key transparency as
described in [I-D.draft-ietf-keytrans-protocol] can enable the
observation of incorrectly issued certificates or fraudulent bindings
between verification keys and issuer identifiers. Issuers choose
which claims to include in an SD-CWT, and whether they are mandatory
to disclose, including self asserted claims such as "iss". All
mandatory to disclose data elements are visible to the verifier as
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part of verification, some of these elements reveal information about
the issuer, such as key or certificate thumbprints, supported digital
signature algorithms, or operational windows which can be inferred
from analysis of timestamps.
15.2. Traceability
Presentations of the same SD-CWT to multiple verifiers can be
correlated by matching on the signature component of the COSE_Sign1.
Signature based linkability can be mitigated by leveraging batch
issuance of single use tokens, for a credential management complexity
cost. Any claim value with sufficiently low "anonymity set" can be
used track the subject. For example, a high precision issuance time
might match the issuance of only a few credentials for a given
issuer, and as such any presentation of a credential issued at that
time can be determined to be associated with the set of credentials
issued at that time, for those subjects.
15.3. Credential Types
The mandatory and optional to disclose data elements in an SD-CWT are
credential type specific. Several distinct credential types might be
applicable to a given use case. Issuers MUST perform a privacy and
confidentiality assessment regarding each credential type they intend
to issue prior to issuance.
15.4. Determinism & Augmentation
It is possible to encode additional information through the choices
made during the serialization stage of producing an SD-CWT, for
example, by adjusting the order of CBOR map keys, or by choosing
different numeric encodings for certain data elements.
[I-D.draft-ietf-cbor-cde] provides guidance for constructing
application profiles that constrain serialization optionality beyond
CBOR Common Deterministic Encoding rulesets (CDE). The construction
of such profiles has a significant impact on the privacy properties
of a credential type.
15.5. Threat Model
Each use case will have a unique threat model which MUST be
considered before the applicability of SD-CWT based credential types
can be determined. This section provides a non exahustive list of
topics to be consider when developing a threat model for applying SD-
CWT to a given use case.
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Has there been a t-closeness, k-anonymity and l-diverity assessment
(see [t-Closeness]) assuming compromise of the one or more issuers,
verifiers or holders, for all relevant credential types?
How many issuers exist for the credential type? Is the size of the
set of issuers growing or shrinking over time? For a given
credential type, will subjects be able to hold instances of the same
credential type from multiple issuers, or just a single issuer? Does
the credential type require or offer the ability to disclose a
globally unique identifier? Does the credential type require high
precision time or other claims that have sufficient entropy such that
they can serve as a unique fingerprint for a specific subject. Does
the credential type contain Personally Identifiable Information
(PII), or other sensitive information which might have value in a
market.
How many verifiers exist for the credential type? Is the size of the
set of verifiers growing or shrinking over time? Are the verifiers a
superset, subset, or disjoint set of the issuers or subjects? Are
there any legally required reporting or disclosure requirements
associated with the verifiers? Is there reason to believe that a
verifier's historic data will be aggregated and analyzed? Assuming
multiple verifiers are simultaneously compromised, what knowledge
regarding subjects can be inferred from analyzing the resulting
dataset?
How many subjects exist for the credential type? Is the size of the
set of subjects growing or shrinking over time? Does the credential
type require specific hardware, or algorithms that limit the set of
possible subjects to owners of a specific device or subscribers to a
given service.
15.6. Random Numbers
Each salt used to protect disclosed claims MUST be generated
independently from the salts of other claims. The salts MUST be
generated from a source of entropy that is acceptable to the issuer.
Poor choice of salts can lead to brute force attacks that can reveal
redacted claims.
15.7. Binding the KBT and the CWT
The issuer claim in the SD-CWT is self-asserted by the issuer.
Because confirmation is mandatory, the subject claim of an SD-CWT,
when present, is always related directly to the confirmation claim.
There might be many subject claims and many confirmation keys that
identify the same entity or that are controlled by the same entity,
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while the identifiers and keys are distinct values. Reusing an
identifier or key enables traceability, but MUST be evaluated in
terms of the confidential and privacy constraints associated with the
credential type. Conceptually, the Holder is both the issuer and the
subject of the SD-KBT, even if the issuer or subject claims are not
present. If they are present, they are self-asserted by the Holder.
All three are represented by the confirmation (public) key in the SD-
CWT.
As with any self-assigned identifiers, Verifiers need to take care to
verify that the SD-KBT issuer and subject claims match the subject in
the SD-KBT, and are a valid representation of the Holder and
correspond to the Holder's confirmation key. Extra care should be
taken in case the SD-CWT subject claim is redacted. Likewise,
Holders and Verifiers need to verify that the issuer claim of the SD-
CWT corresponds to the Issuer and the key described in the protected
header of the SD-CWT.
16. IANA Considerations
16.1. COSE Header Parameters
IANA is requested to add the following entries to the CWT claims
registry (https://www.iana.org/assignments/cose/cose.xhtml#header-
parameters).
16.1.1. sd_claims
The following completed registration template per RFC8152 is
provided:
* Name: sd_claims
* Label: TBD1 (requested assignment 17)
* Value Type: bstr
* Value Registry: (empty)
* Description: A list of selectively disclosed claims, which were
originally redacted, then later disclosed at the discretion of the
sender.
* Reference: RFC XXXX
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16.1.2. sd_alg
The following completed registration template per RFC8152 is
provided:
* Name: sd_alg
* Label: TBD2 (requested assignment 18)
* Value Type: int
* Value Registry: COSE Algorithms
* Description: The hash algorithm used for redacting disclosures.
* Reference: RFC XXXX
16.1.3. sd_encrypted_claims
The following completed registration template per RFC8152 is
provided:
* Name: sd_encrypted claims
* Label: TBD6 (requested assignment 19)
* Value Type: bstr
* Value Registry: (empty)
* Description: A list of encrypted selectively disclosed claims,
which were originally redacted, then later disclosed at the
discretion of the sender.
* Reference: RFC XXXX
16.2. CBOR Tags
16.2.1. To be redacted tag
The array claim element, or map key and value inside the "To be
redacted" tag is intended to be redacted using selective disclosure.
* Tag: TBD3 (requested assignment 58)
* Data Item: (any)
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* Semantics: An array claim element, or map key and value intended
to be redacted.
* Specification Document(s): RFC XXXX
16.2.2. Redacted claim keys tag
This tag encloses the integer claim key 0 (reserved as a CWT claim
key). It indicates that the claim value is an array of redacted
claim keys at the same level.
* Tag: TBD4 (requested assignment 59)
* Data Item: unsigned integer 0
* Semantics: Tags the claim key 0. The value of the key is an array
of selective disclosure redacted claim keys.
* Specification Document(s): RFC XXXX
16.2.3. Redacted claim element tag
The binary string inside the tag is a selective disclosure redacted
claim element of an array.
* Tag: TBD5 (requested assignment 60)
* Data Item: byte string
* Semantics: A selective disclosure redacted (array) claim element.
* Specification Document(s): RFC XXXX
16.3. CBOR Web Token (CWT) Claims
IANA is requested to add the following entries to the CWT claims
registry (https://www.iana.org/assignments/cwt/cwt.xhtml).
16.3.1. vct
The following completed registration template per RFC8392 is
provided:
* Claim Name: vct
* Claim Description: Verifiable credential type
* JWT Claim Name: vct
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* Claim Key: TBD6 (request assignment 11)
* Claim Value Type(s): bstr
* Change Controller: IETF
* Specification Document(s): RFC XXXX
16.4. Media Types
This section requests the registration of new media types in
https://www.iana.org/assignments/media-types/media-types.xhtml.
16.4.1. application/sd+cwt
IANA is requested to add the following entry to the media types
registry in accordance with RFC6838, RFC4289, and RFC6657.
The following completed registration template is provided:
* Type name: application
* Subtype name: sd+cwt
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: binary
* Security considerations: See the Security Considerations section
of RFC XXXX, and [RFC8392]
* Interoperability considerations: n/a
* Published specification: RFC XXXX
* Applications that use this media type: TBD
* Fragment identifier considerations: n/a
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
- Macintosh file type code(s): n/a
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* Person & email address to contact for further information: SPICE
WG mailing list (spice@ietf.org) or IETF Security Area
(saag@ietf.org)
* Intended usage: COMMON
* Restrictions on usage: none
* Author: See Author's Addresses section
* Change controller: IETF
* Provisional registration? No
16.4.2. application/kb+cwt
IANA is requested to add the following entry to the media types
registry in accordance with RFC6838, RFC4289, and RFC6657.
The following completed registration template is provided:
* Type name: application
* Subtype name: kb+cwt
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: binary
* Security considerations: See the Security Considerations section
of RFC XXXX, and [RFC8392]
* Interoperability considerations: n/a
* Published specification: RFC XXXX
* Applications that use this media type: TBD
* Fragment identifier considerations: n/a
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
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- Macintosh file type code(s): n/a
* Person & email address to contact for further information: SPICE
WG mailing list (spice@ietf.org) or IETF Security Area
(saag@ietf.org)
* Intended usage: COMMON
* Restrictions on usage: none
* Author: See Author's Addresses section
* Change controller: IETF
* Provisional registration? No
16.5. Content-Formats
// RFC Editor: Please replace "RFCthis" with the RFC number assigned
to this document.
// RFC Editor: IANA is requested to register the following Content-
Format numbers in the "CoAP Content-Formats" registry, within the
"Constrained RESTful Environments (CoRE) Parameters" registry group
[IANA.core-parameters]:
+====================+================+======+===========+
| Content-Type | Content Coding | ID | Reference |
+====================+================+======+===========+
| application/sd+cwt | - | TBD1 | RFCthis |
+--------------------+----------------+------+-----------+
| application/kb+cwt | - | TBD2 | RFCthis |
+--------------------+----------------+------+-----------+
Table 1: New CoAP Content Formats
If possible, TBD1 and TBD2 should be assigned in the 256..9999 range.
17. References
17.1. Normative References
[BCP205] Best Current Practice 205,
<https://www.rfc-editor.org/info/bcp205>.
At the time of writing, this BCP comprises the following:
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Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[I-D.ietf-cbor-edn-literals]
Bormann, C., "CBOR Extended Diagnostic Notation (EDN)",
Work in Progress, Internet-Draft, draft-ietf-cbor-edn-
literals-16, 8 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-cbor-
edn-literals-16>.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters",
<https://www.iana.org/assignments/core-parameters>.
[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/rfc/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/rfc/rfc5116>.
[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/rfc/rfc7515>.
[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/rfc/rfc7519>.
[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/rfc/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/rfc/rfc8747>.
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[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
DOI 10.17487/RFC9528, March 2024,
<https://www.rfc-editor.org/rfc/rfc9528>.
[RFC9596] Jones, M.B. and O. Steele, "CBOR Object Signing and
Encryption (COSE) "typ" (type) Header Parameter",
RFC 9596, DOI 10.17487/RFC9596, June 2024,
<https://www.rfc-editor.org/rfc/rfc9596>.
[RFC9679] Isobe, K., Tschofenig, H., and O. Steele, "CBOR Object
Signing and Encryption (COSE) Key Thumbprint", RFC 9679,
DOI 10.17487/RFC9679, December 2024,
<https://www.rfc-editor.org/rfc/rfc9679>.
17.2. Informative References
[I-D.draft-ietf-cbor-cde]
Bormann, C., "CBOR Common Deterministic Encoding (CDE)",
Work in Progress, Internet-Draft, draft-ietf-cbor-cde-08,
10 February 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-cbor-cde-08>.
[I-D.draft-ietf-keytrans-protocol]
McMillion, B. and F. Linker, "Key Transparency Protocol",
Work in Progress, Internet-Draft, draft-ietf-keytrans-
protocol-00, 10 December 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-
keytrans-protocol-00>.
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[I-D.draft-ietf-oauth-sd-jwt-vc]
Terbu, O., Fett, D., and B. Campbell, "SD-JWT-based
Verifiable Credentials (SD-JWT VC)", Work in Progress,
Internet-Draft, draft-ietf-oauth-sd-jwt-vc-08, 3 December
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
oauth-sd-jwt-vc-08>.
[I-D.draft-ietf-oauth-selective-disclosure-jwt]
Fett, D., Yasuda, K., and B. Campbell, "Selective
Disclosure for JWTs (SD-JWT)", Work in Progress, Internet-
Draft, draft-ietf-oauth-selective-disclosure-jwt-17, 1
March 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-oauth-selective-disclosure-jwt-17>.
[I-D.ietf-httpbis-unprompted-auth]
Schinazi, D., Oliver, D., and J. Hoyland, "The Concealed
HTTP Authentication Scheme", Work in Progress, Internet-
Draft, draft-ietf-httpbis-unprompted-auth-12, 19 September
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
httpbis-unprompted-auth-12>.
[I-D.mahy-mls-sd-cwt-credential]
Mahy, R., "Messaging Layer Security credentials using
Selective Disclosure CBOR Web Tokens", Work in Progress,
Internet-Draft, draft-mahy-mls-sd-cwt-credential-00, 2
March 2025, <https://datatracker.ietf.org/doc/html/draft-
mahy-mls-sd-cwt-credential-00>.
[RFC9162] Laurie, B., Messeri, E., and R. Stradling, "Certificate
Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
December 2021, <https://www.rfc-editor.org/rfc/rfc9162>.
[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/rfc/rfc9334>.
[RFC9420] Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
Omara, E., and K. Cohn-Gordon, "The Messaging Layer
Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420,
July 2023, <https://www.rfc-editor.org/rfc/rfc9420>.
[t-Closeness]
"t-Closeness: Privacy Beyond k-Anonymity and l-Diversity",
4 June 2007,
<https://ieeexplore.ieee.org/document/4221659>.
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Appendix A. Complete CDDL Schema
sd-cwt-types = sd-cwt-issued / kbt-cwt
sd-cwt-issued = #6.18([
protected: bstr .cbor sd-protected,
sd-unprotected,
payload: bstr .cbor sd-payload,
signature: bstr
])
kbt-cwt = #6.18([
protected: bstr .cbor kbt-protected,
kbt-unprotected,
payload: bstr .cbor kbt-payload,
signature: bstr
])
sd-protected = {
&(typ: 16) ^ => "application/sd+cwt",
&(alg: 1) ^ => int,
&(sd_alg: TBD2) ^= int, ; -16 for sha-256
* key => any
}
kbt-protected = {
&(typ: 16) ^ => "application/kb+cwt",
&(alg: 1) ^ => int,
&(kcwt: 13) ^ => sd-cwt-issued,
* key => any
}
sd-unprotected = {
? &(sd_claims: TBD1) ^ => salted-array,
? &(sd_encrypted_claims: TBD6) ^ => encrypted-array
* key => any
}
kbt-unprotected = {
* key => any
}
sd-payload = {
; standard claims
&(iss: 1) ^ => tstr, ; "https://issuer.example"
? &(sub: 2) ^ => tstr, ; "https://device.example"
? &(aud: 3) ^ => tstr, ; "https://verifier.example"
? &(exp: 4) ^ => int, ; 1883000000
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? &(nbf: 5) ^ => int, ; 1683000000
? &(iat: 6) ^ => int, ; 1683000000
? &(cti: 7) ^ => bstr,
&(cnf: 8) ^ => { * key => any }, ; key confirmation
? &(cnonce: 39) ^ => bstr,
;
? &(redacted_claim_keys: TBD3) ^ => [ * bstr ],
* key => any
}
kbt-payload = {
&(aud: 3) ^ => tstr, ; "https://verifier.example"
? &(exp: 4) ^ => int, ; 1883000000
? &(nbf: 5) ^ => int, ; 1683000000
&(iat: 6) ^ => int, ; 1683000000
? &(cnonce: 39) ^ => bstr,
* key => any
}
salted-array = [ +bstr .cbor salted ]
salted = salted-claim / salted-element / decoy
salted-claim = [
bstr .size 16, ; 128-bit salt
(int / text), ; claim name
any ; claim value
]
salted-element = [
bstr .size 16, ; 128-bit salt
any ; claim value
]
decoy = [
bstr .size 16 ; 128-bit salt
]
encrypted-array = [ +bstr .cbor encrypted ]
encrypted = [
bstr .size 16, ; 128-bit salt
uint16, ; IANA AEAD Algorithm number
bstr, ; the ciphertext output of a bstr-encoded-salted
; with a matching salt
bstr ; the corresponding MAC
]
;bstr-encoded-salted = bstr .cbor salted
key = int / text
TBD1 = 17
TBD2 = 18
;TBD3 = #6.58(any) ; CBOR tag wrapping to-be-redacted keys or elements
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TBD4 = #6.59(0) ; CBOR tag 59 wrapping reserved integer claim key 0
;TBD5 = #6.60( bstr ) ;redacted_claim_element
TBD6 = 19
Figure 7: A complete CDDL description of SD-CWT
Appendix B. Comparison to SD-JWT
SD-CWT is modeled after SD-JWT, with adjustments to align with
conventions in CBOR and COSE.
B.1. Media Types
The COSE equivalent of application/sd-jwt is application/sd+cwt.
THe COSE equivalent of application/kb+jwt is application/kb+cwt.
B.2. Redaction Claims
The COSE equivalent of _sd is a CBOR tag (requested assignment 59) of
the claim key 0. The corresponding claim value is an array of the
redacted claim keys.
The COSE equivalent of ... is a CBOR tag (requested assignment 60) of
the digested salted claim.
B.3. Issuance
The issuance process for SD-CWT is similar to SD-JWT, with the
exception that a confirmation claim is REQUIRED.
B.4. Presentation
The presentation process for SD-CWT is similar to SD-JWT, except that
a Key Binding Token is REQUIRED. The Key Binding Token then includes
the issued SD-CWT, including the Holder-selected disclosures.
Because the entire SD-CWT is included as a claim in the SD-KBT, the
disclosures are covered by the Holder's signature in the SD-KBT, but
not by the Issuer's signature in the SD-CWT.
B.5. Validation
The validation process for SD-CWT is similar to SD-JWT, however, JSON
Objects are replaced with CBOR Maps which can contain integer keys
and CBOR Tags.
Appendix C. Keys used in the examples
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C.1. Subject / Holder
Holder COSE key pair in EDN format
{
/kty/ 1 : 2, /EC/
/alg/ 3 : -7, /ES256/
/crv/ -1 : 1, /P-256/
/x/ -2 : h'8554eb275dcd6fbd1c7ac641aa2c90d9
2022fd0d3024b5af18c7cc61ad527a2d',
/y/ -3 : h'4dc7ae2c677e96d0cc82597655ce92d5
503f54293d87875d1e79ce4770194343',
/d/ -4 : h'5759a86e59bb3b002dde467da4b52f3d
06e6c2cd439456cf0485b9b864294ce5'
}
The fields necessary for the COSE Key Thumbprint [RFC9679] in EDN
format:
{
/kty/ 1 : 2, /EC/
/crv/ -1 : 1, /P-256/
/x/ -2 : h'8554eb275dcd6fbd1c7ac641aa2c90d9
2022fd0d3024b5af18c7cc61ad527a2d',
/y/ -3 : h'4dc7ae2c677e96d0cc82597655ce92d5
503f54293d87875d1e79ce4770194343'
}
The same map in CBOR pretty printing
A4 # map(4)
01 # unsigned(1)
02 # unsigned(2)
20 # negative(0)
01 # unsigned(1)
21 # negative(1)
58 20 # bytes(32)
8554EB275DCD6FBD1C7AC641AA2C90D92022FD0D3024B5AF18C7CC61AD527A2D
22 # negative(2)
58 20 # bytes(32)
4DC7AE2C677E96D0CC82597655CE92D5503F54293D87875D1E79CE4770194343
The COSE thumbprint (in hexadecimal)--SHA256 hash of the thumbprint
fields:
8343d73cdfcb81f2c7cd11a5f317be8eb34e4807ec8c9ceb282495cffdf037e0
Holder key pair in JWK format
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{
"kty": "EC",
"alg": "ES256",
"kid": "WRQ2RbY5RYJCIxfDQL9agl9fFSCYVu4Xocqb6zerc1M",
"crv": "P-256",
"x": "hVTrJ13Nb70cesZBqiyQ2SAi_Q0wJLWvGMfMYa1Sei0",
"y": "TceuLGd-ltDMgll2Vc6S1VA_VCk9h4ddHnnOR3AZQ0M",
"d": "V1moblm7OwAt3kZ9pLUvPQbmws1DlFbPBIW5uGQpTOU"
}
Input to Holder public JWK thumbprint (ignore line breaks)
{"crv":"P-256","kty":"EC","x":"hVTrJ13Nb70cesZBqiyQ2SAi_Q0wJLWvGMfMYa1S
ei0","y":"TceuLGd-ltDMgll2Vc6S1VA_VCk9h4ddHnnOR3AZQ0M"}
SHA-256 of the Holder public JWK input string (in hex)
59143645b6394582422317c340bf5a825f5f15209856ee17a1ca9beb37ab7353
Holder public JWK thumbprint
WRQ2RbY5RYJCIxfDQL9agl9fFSCYVu4Xocqb6zerc1M
Holder public key in PEM format
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEhVTrJ13Nb70cesZBqiyQ2SAi/Q0w
JLWvGMfMYa1Sei1Nx64sZ36W0MyCWXZVzpLVUD9UKT2Hh10eec5HcBlDQw==
-----END PUBLIC KEY-----
Holder private key in PEM format
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgV1moblm7OwAt3kZ9
pLUvPQbmws1DlFbPBIW5uGQpTOWhRANCAASFVOsnXc1vvRx6xkGqLJDZICL9DTAk
ta8Yx8xhrVJ6LU3HrixnfpbQzIJZdlXOktVQP1QpPYeHXR55zkdwGUND
-----END PRIVATE KEY-----
C.2. Issuer
Issuer COSE key pair in Extended Diagnostic Notation (EDN)
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{
/kty/ 1 : 2, /EC/
/kid/ 2 : "https://issuer.example/cwk3.cbor",
/alg/ 3 : -35, /ES384/
/crv/ -1 : 2, /P-384/
/x/ -2 : h'c31798b0c7885fa3528fbf877e5b4c3a6dc67a5a5dc6b307
b728c3725926f2abe5fb4964cd91e3948a5493f6ebb6cbbf',
/y/ -3 : h'8f6c7ec761691cad374c4daa9387453f18058ece58eb0a8e
84a055a31fb7f9214b27509522c159e764f8711e11609554',
/d/ -4 : h'71c54d2221937ea612db1221f0d3ddf771c9381c4e3be41d
5aa0a89d685f09cfef74c4bbf104783fd57e87ab227d074c'
}
The fields necessary for the COSE Key Thumbprint [RFC9679] in EDN
format:
{
/kty/ 1 : 2, /EC/
/crv/ -1 : 2, /P-384/
/x/ -2 : h'c31798b0c7885fa3528fbf877e5b4c3a6dc67a5a5dc6b307
b728c3725926f2abe5fb4964cd91e3948a5493f6ebb6cbbf',
/y/ -3 : h'8f6c7ec761691cad374c4daa9387453f18058ece58eb0a8e
84a055a31fb7f9214b27509522c159e764f8711e11609554'
}
The same map in CBOR pretty printing
A4 # map(5)
01 # unsigned(1)
02 # unsigned(2)
20 # negative(0)
02 # unsigned(2)
21 # negative(1)
58 30 # bytes(48)
C31798B0C7885FA3528FBF877E5B4C3A6DC67A5A5DC6B307
B728C3725926F2ABE5FB4964CD91E3948A5493F6EBB6CBBF
22 # negative(2)
58 30 # bytes(48)
8F6C7EC761691CAD374C4DAA9387453F18058ECE58EB0A8E
84A055A31FB7F9214B27509522C159E764F8711E11609554
The COSE thumbprint (in hexadecimal)--SHA256 hash of the thumbprint
fields:
554550a611c9807b3462cfec4a690a1119bc43b571da1219782133f5fd6dbcb0
Issuer key pair in JWK format
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{
"kty": "EC",
"alg": "ES384",
"kid": "https://issuer.example/cwk3.cbor",
"crv": "P-384",
"x":"wxeYsMeIX6NSj7-HfltMOm3GelpdxrMHtyjDclkm8qvl-0lkzZHjlIpUk_brtsu_",
"y":"j2x-x2FpHK03TE2qk4dFPxgFjs5Y6wqOhKBVox-3-SFLJ1CVIsFZ52T4cR4RYJVU",
"d":"ccVNIiGTfqYS2xIh8NPd93HJOBxOO-QdWqConWhfCc_vdMS78QR4P9V-h6sifQdM"
}
Input to Issuer JWK thumbprint (ignore line breaks)
{"crv":"P-384","kty":"EC","x":"wxeYsMeIX6NSj7-HfltMOm3GelpdxrMHtyjDclkm
8qvl-0lkzZHjlIpUk_brtsu_","y":"j2x-x2FpHK03TE2qk4dFPxgFjs5Y6wqOhKBVox-3
-SFLJ1CVIsFZ52T4cR4RYJVU"}
SHA-256 of the Issuer JWK input string (in hex)
18d4ddb7065d945357e3972dee76af4eddc7c285fb42efcfa900c6a4f8437850
Issuer JWK thumbprint
GNTdtwZdlFNX45ct7navTt3HwoX7Qu_PqQDGpPhDeFA
Issuer public key in PEM format
-----BEGIN PUBLIC KEY-----
MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEwxeYsMeIX6NSj7+HfltMOm3GelpdxrMH
tyjDclkm8qvl+0lkzZHjlIpUk/brtsu/j2x+x2FpHK03TE2qk4dFPxgFjs5Y6wqO
hKBVox+3+SFLJ1CVIsFZ52T4cR4RYJVU
-----END PUBLIC KEY-----
Issuer private key in PEM format
-----BEGIN PRIVATE KEY-----
MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDBxxU0iIZN+phLbEiHw
0933cck4HE475B1aoKidaF8Jz+90xLvxBHg/1X6HqyJ9B0yhZANiAATDF5iwx4hf
o1KPv4d+W0w6bcZ6Wl3Gswe3KMNyWSbyq+X7SWTNkeOUilST9uu2y7+PbH7HYWkc
rTdMTaqTh0U/GAWOzljrCo6EoFWjH7f5IUsnUJUiwVnnZPhxHhFglVQ=
-----END PRIVATE KEY-----
Appendix D. Document History
Note: RFC Editor, please remove this entire section on publication.
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D.1. draft-ietf-spice-sd-cwt-03
* remove bstr encoding from sd_claims array (but not the individual
disclosures)
* clarify which claims are optional/mandatory
* correct that an SD-CWT may have zero redacted claims
* improve the walkthrough of computing a disclosure
* clarify that duplicate map keys are not allowed, and how tagged
keys are represented.
* added security considerations section (#42) and text about privacy
and linkability risks (#43)
* register SD-CWT and SD-KBT as content formats in CoAP registry
(#39)
* updated media types registrations to have more useful contacts
(#44)
* build most of the values (signatures/salts/hashes/dates) in the
examples automatically using a script that implements SD-CWT
* regenerate all examples with correct signatures
* add nested example
* add optional encrypted disclosures
* add description of decoy digests *TODO*
* provide test vectors *TODO*
D.2. draft-ietf-spice-sd-cwt-02
* KBT now includes the entire SD-CWT in the Confirmation Key CWT
(kcwt) existing COSE protected header. Has algorithm now
specified in new sd_alg COSE protected header. No more sd_hash
claim. (PR #34, 32)
* Introduced tags for redacted and to-be-redacted claim keys and
elements. (PR#31, 28)
* Updated example to be a generic inspection certificate. (PR#33)
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* Add section saying SD-CWT updates the CWT spec (RFC8392). (PR#29)
D.3. draft-ietf-spice-sd-cwt-01
* Added Overview section
* Rewrote the main normative section
* Made redaacted_claim_keys use an unlikely to collide claim key
integer
* Make cnonce optional (it now says SHOULD)
* Made most standard claims optional.
* Consistently avoid use of bare term "key" - to make crypto keys
and map keys clear
* Make clear issued SD-CWT can contain zero or more redactions;
presented SD-CWT can disclose zero, some, or all redacted claims.
* Clarified use of sd_hash for issuer to holder case._
* Lots of editorial cleanup
* Added Rohan as an author and Brian Campbell to Acknowledgements
* Updated implementation status section to be BCP205-compatible
* Updated draft metadata
D.4. draft-ietf-spice-sd-cwt-00
* Initial working group version based on draft-prorock-spice-cose-
sd-cwt-01.
Acknowledgments
The authors would like to thank those that have worked on similar
items for providing selective disclosure mechanisms in JSON,
especially: Brent Zundel, Roy Williams, Tobias Looker, Kristina
Yasuda, Daniel Fett, Brian Campbell, Oliver Terbu, and Michael Jones.
Authors' Addresses
Michael Prorock
mesur.io
Email: mprorock@mesur.io
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Orie Steele
Transmute
Email: orie@transmute.industries
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@ietf.contact
Rohan Mahy
Rohan Mahy Consulting Services
Email: rohan.ietf@gmail.com
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