Selective Disclosure CBOR Web Tokens (SD-CWT)
draft-ietf-spice-sd-cwt-06
| Document | Type | Active Internet-Draft (spice WG) | |
|---|---|---|---|
| Authors | Michael Prorock , Orie Steele , Henk Birkholz , Rohan Mahy | ||
| Last updated | 2026-01-13 | ||
| Replaces | draft-prorock-spice-cose-sd-cwt | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-spice-sd-cwt-06
Secure Patterns for Internet CrEdentials M. Prorock
Internet-Draft mesur.io
Intended status: Standards Track O. Steele
Expires: 17 July 2026 Tradeverifyd
H. Birkholz
Fraunhofer SIT
R. Mahy
13 January 2026
Selective Disclosure CBOR Web Tokens (SD-CWT)
draft-ietf-spice-sd-cwt-06
Abstract
This specification describes a data minimization technique for use
with CBOR Web Tokens (CWTs). The approach is based on the Selective
Disclosure JSON Web Token (SD-JWT), with changes to align with CBOR
Object Signing and Encryption (COSE) and CWTs.
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
(mailto:spice@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/spice/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-spice/draft-ietf-spice-sd-cwt.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 17 July 2026.
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Copyright (c) 2026 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. High-Level Flow . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview of Selective Disclosure CWT . . . . . . . . . . . . 10
3.1. A CWT without Selective Disclosure . . . . . . . . . . . 10
3.2. Holder gets an SD-CWT from the Issuer . . . . . . . . . . 11
4. Holder prepares an SD-CWT for a Verifier . . . . . . . . . . 15
5. SD-CWT Definition . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Types of Blinded Claims . . . . . . . . . . . . . . . . . 17
6. Differences from the CBOR Web Token Specification . . . . . . 18
6.1. Definite Length CBOR Required . . . . . . . . . . . . . . 18
6.2. Finite values for standard date claims . . . . . . . . . 18
6.3. Allowed types of CBOR map keys . . . . . . . . . . . . . 19
6.4. Duplicate map key detection . . . . . . . . . . . . . . . 22
6.5. Level of Nesting of Claims . . . . . . . . . . . . . . . 23
6.6. Use of Structured Suffixes . . . . . . . . . . . . . . . 24
7. SD-CWT Issuance . . . . . . . . . . . . . . . . . . . . . . . 24
7.1. Issuer Generation . . . . . . . . . . . . . . . . . . . . 25
7.2. Holder Validation . . . . . . . . . . . . . . . . . . . . 25
8. SD-CWT Presentation . . . . . . . . . . . . . . . . . . . . . 27
8.1. Creating a Key Binding Token . . . . . . . . . . . . . . 28
9. SD-KBT and SD-CWT Verifier Validation . . . . . . . . . . . . 30
10. Decoy Digests . . . . . . . . . . . . . . . . . . . . . . . . 31
11. Tags Used Before SD-CWT Issuance . . . . . . . . . . . . . . 33
11.1. To Be Redacted Tag Definition . . . . . . . . . . . . . 33
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11.2. To Be Decoy . . . . . . . . . . . . . . . . . . . . . . 34
12. Encrypted Disclosures . . . . . . . . . . . . . . . . . . . . 35
12.1. AEAD Encrypted Disclosures Mechanism . . . . . . . . . . 36
13. Credential Types . . . . . . . . . . . . . . . . . . . . . . 37
14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 37
14.1. Minimal Spanning Example . . . . . . . . . . . . . . . . 38
14.2. Nested Example . . . . . . . . . . . . . . . . . . . . . 40
15. Privacy Considerations . . . . . . . . . . . . . . . . . . . 44
15.1. Correlation . . . . . . . . . . . . . . . . . . . . . . 44
15.2. Determinism . . . . . . . . . . . . . . . . . . . . . . 45
15.3. Audience . . . . . . . . . . . . . . . . . . . . . . . . 45
15.4. Credential Types . . . . . . . . . . . . . . . . . . . . 45
16. Security Considerations . . . . . . . . . . . . . . . . . . . 46
16.1. Issuer Key Compromise . . . . . . . . . . . . . . . . . 46
16.2. Disclosure Coercion and Over-identification . . . . . . 47
16.3. Threat Model Development Guidance . . . . . . . . . . . 47
16.4. Random Numbers . . . . . . . . . . . . . . . . . . . . . 49
16.5. Binding the KBT and the CWT . . . . . . . . . . . . . . 49
16.6. Covert Channels . . . . . . . . . . . . . . . . . . . . 50
16.7. Nested Disclosure Ordering . . . . . . . . . . . . . . . 50
16.8. Choice of AEAD algorithms . . . . . . . . . . . . . . . 50
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
17.1. COSE Header Parameters . . . . . . . . . . . . . . . . . 51
17.1.1. sd_claims . . . . . . . . . . . . . . . . . . . . . 51
17.1.2. sd_alg . . . . . . . . . . . . . . . . . . . . . . . 51
17.1.3. sd_aead_encrypted_claims . . . . . . . . . . . . . . 51
17.1.4. sd_aead . . . . . . . . . . . . . . . . . . . . . . 52
17.2. CBOR Simple Values . . . . . . . . . . . . . . . . . . . 52
17.3. CBOR Tags . . . . . . . . . . . . . . . . . . . . . . . 53
17.3.1. To Be Redacted Tag . . . . . . . . . . . . . . . . . 53
17.3.2. Redacted Claim Element Tag . . . . . . . . . . . . . 53
17.3.3. To Be Decoy Tag . . . . . . . . . . . . . . . . . . 53
17.4. CBOR Web Token (CWT) Claims . . . . . . . . . . . . . . 54
17.4.1. vct . . . . . . . . . . . . . . . . . . . . . . . . 54
17.5. Media Types . . . . . . . . . . . . . . . . . . . . . . 54
17.5.1. application/sd-cwt . . . . . . . . . . . . . . . . . 54
17.5.2. application/kb+cwt . . . . . . . . . . . . . . . . . 55
17.6. Structured Syntax Suffix . . . . . . . . . . . . . . . . 56
17.7. Content-Formats . . . . . . . . . . . . . . . . . . . . 57
17.8. Verifiable Credential Type Identifiers . . . . . . . . . 57
17.8.1. Registration Template . . . . . . . . . . . . . . . 59
17.8.2. Initial Registry Contents . . . . . . . . . . . . . 59
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 59
18.1. Normative References . . . . . . . . . . . . . . . . . . 59
18.2. Informative References . . . . . . . . . . . . . . . . . 61
Appendix A. Complete CDDL Schema . . . . . . . . . . . . . . . . 63
Appendix B. Comparison to SD-JWT . . . . . . . . . . . . . . . . 66
B.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 66
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B.2. Redaction Claims . . . . . . . . . . . . . . . . . . . . 66
B.3. Issuance . . . . . . . . . . . . . . . . . . . . . . . . 67
B.4. Presentation . . . . . . . . . . . . . . . . . . . . . . 67
B.5. Validation . . . . . . . . . . . . . . . . . . . . . . . 67
Appendix C. Keys Used in the Examples . . . . . . . . . . . . . 67
C.1. Subject / Holder . . . . . . . . . . . . . . . . . . . . 67
C.2. Issuer . . . . . . . . . . . . . . . . . . . . . . . . . 69
Appendix D. Implementation Status . . . . . . . . . . . . . . . 71
D.1. Transmute Prototype . . . . . . . . . . . . . . . . . . . 71
D.2. Rust Prototype . . . . . . . . . . . . . . . . . . . . . 72
D.3. Python Prototype . . . . . . . . . . . . . . . . . . . . 72
Appendix E. Relationship between RATS Architecture and Verifiable
Credentials . . . . . . . . . . . . . . . . . . . . . . . 73
E.1. Three-Party Verifiable Credentials Model . . . . . . . . 73
E.2. RATS Architecture Roles . . . . . . . . . . . . . . . . . 73
E.3. Role Mappings in the Three-Party Model . . . . . . . . . 74
E.3.1. Verifiable Credential Issuer as RATS Endorser . . . . 74
E.3.2. Verifiable Credential Holder as RATS Verifier . . . . 74
E.3.3. Verifiable Credential Verifier as RATS Relying
Party . . . . . . . . . . . . . . . . . . . . . . . . 75
E.3.4. All Parties Can Be Attesters . . . . . . . . . . . . 75
E.4. Comparison with RATS Interaction Models . . . . . . . . . 76
E.5. Roles That Don't Map to the Three-Party Model . . . . . . 76
E.6. Application to SD-CWT . . . . . . . . . . . . . . . . . . 77
Appendix F. Sample Disclosure Matching Algorithm for Verifier . 77
Appendix G. Document History . . . . . . . . . . . . . . . . . . 78
G.1. draft-ietf-spice-sd-cwt-06 . . . . . . . . . . . . . . . 78
G.2. draft-ietf-spice-sd-cwt-05 . . . . . . . . . . . . . . . 79
G.3. draft-ietf-spice-sd-cwt-04 . . . . . . . . . . . . . . . 80
G.4. draft-ietf-spice-sd-cwt-03 . . . . . . . . . . . . . . . 81
G.5. draft-ietf-spice-sd-cwt-02 . . . . . . . . . . . . . . . 81
G.6. draft-ietf-spice-sd-cwt-01 . . . . . . . . . . . . . . . 82
G.7. draft-ietf-spice-sd-cwt-00 . . . . . . . . . . . . . . . 82
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 82
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 83
1. Introduction
This specification creates a new format based on the CBOR Web Token
(CWT) specification [RFC8392], enabling the Holder of a CWT to
disclose or redact special claims marked as selectively 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] and CWT. 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.
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Although techniques such as one time use and batch issuance can
improve the confidentiality and security characteristics of CWT-based
credential protocols, SD-CWTs remain traceable. Selective Disclosure
CBOR Web Tokens (SD-CWTs) can be deployed in protocols that are
already using CWTs with minor changes, 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
specification, and the examples used in this specification 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 Verifier that does not
understand selective disclosure at all can only act on unblinded
claims sent by the Holder; it will ignore Blinded Claims representing
array items, and will fail to process any SD-CWT containing Blinded
Claims that represent map keys. Optional Claim Keys, whether they
are disclosed or not, can only be processed by a Verifier that
understands this specification. However, Claim Keys and Claim Values
that 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 that 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
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 specification uses terms from CWT [RFC8392], COSE [RFC9052]
[RFC9053] and JWT [RFC7519].
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The terms Claim Name, Claim Key, and Claim Value are defined in
[RFC8392].
This specification 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 with
an SD-CWT.
Assertion Key: A key used by the Issuer to sign a Claim Values.
Confirmation Key: A key used by the Holder to sign a Selected Salted
Disclosed Claims.
Issuer: An entity that produces a Selective Disclosure CBOR Web
Token by signing a Claim Values with an Assertion Key.
Holder: An entity that presents a Selective Disclosure Key Binding
Token, containing a Selective Disclosure CBOR Web Token and
Selected Salted Disclosed Claims signed with a Confirmation Key.
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
(when all claims are marked as 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.
Blinded Claim Hash: A hash digest of a Salted Disclosed Claim.
Blinded Claim: Any Redacted Claim Key or Redacted Claim Element that
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.
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Presented Disclosed Claims Set: The CBOR map containing zero or more
Redacted Claim Keys or Redacted Claim Elements.
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.
The following diagram explains the relationships between the
terminology used in this specification.
+-----------+ +--------------------+
| Issuer |<----+ Assertion Key |
+-----+-----+ +--------------------+
|
v
+------------------------------------------+
| Issuer Signed Blinded Claims |
| All Salted Disclosed Claims |
+-------+----------------------------------+
|
v
+--------------+ +--------------------+
| Holder |<----+ Confirmation Key |
+-----+--------+ +--------------------+
|
v
+----------------------------------------------+
| Holder Signed Key Binding Token |
| +-----------------------------------------+ |
| | Issuer Signed Blinded Claims | |
| | Holder Selected Salted Disclosed Claims | |
| +-----------------------------------------+ |
| |
+-------+--------------------------------------+
|
v
+--------------+
| Verifier |
+-----+--------+
|
v
+------------------------------------------+
| Validated Disclosed Claim Set |
+------------------------------------------+
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This diagram relates the terminology specific to selective disclosure
and redaction.
+-----------+
| Issuer |
+-----+-----+
|
| 1. Creates Salted Disclosed Claim
| [salt, value, key]
v
+------------------------------------------+
| Salted Disclosed Claim |
+-----+------------------------------------+
|
| 2. Hashes to create
v
+------------------------------------------+
| Blinded Claim Hash |
+-----+------------------------------------+
|
| 3. Replaces Claim Value with
v
+------------------------------------------+
| Blinded Claim (in CWT payload) |
| |
| +----------------------------------+ |
| | Original Claim Value is replaced | |
| | with Blinded Claim Hash | |
| +----------------------------------+ |
| |
+-----+------------------------------------+
|
v
+-----------+
| Holder |
+-----+-----+
|
| 4. Presents selected
| Salted Disclosed Claims
v
+-----------+
| Verifier |
+-----+-----+
|
| 5. Hashes Salted Disclosed Claim
v
+------------------------------------------+
| Blinded Claim Hash (computed) |
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+-----+------------------------------------+
|
| 6. Matches with hash in payload
| to recover original
v
+------------------------------------------+
| Claim Value (recovered) |
+------------------------------------------+
3. Overview of Selective Disclosure CWT
3.1. A CWT without Selective Disclosure
Below is the payload of a standard CWT not using 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.
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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 : {
/ 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"
}
}
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 dates 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 claims that are always present in
the SD-CWT. After the Holder requests an SD-CWT from the Issuer, the
Issuer generates the following SD-CWT:
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/ cose-sign1 / 18([ / issuer SD-CWT /
/ CWT protected / << {
/ alg / 1 : -35, / ES384 /
/ kid / 4 : 'https://issuer.example/cose-key3',
/ typ / 16 : 293, # application/sd-cwt
/ sd_alg / 170 : -16 / SHA256 /
} >>,
/ CWT unprotected / {
/ sd_claims / 17 : [ / these are all the disclosures /
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'7af7084b50badeb57d49ea34627c7a52',
/value/ 1612560720 / inspected 4-Feb-2021 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/value/ "ca",
/claim/ "region" / region=California /
]>>,
<<[
/salt/ h'37c23d4ec4db0806601e6b6dc6670df9',
/value/ "94188",
/claim/ "postal_code"
]>>,
]
},
/ 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,
/inspection_dates/ 502 : [
/ redacted inspection date 7-Feb-2019 /
60(h'1b7fc8ecf4b1290712497d226c04b503
b4aa126c603c83b75d2679c3c613f3fd'),
/ redacted inspection date 4-Feb-2021 /
60(h'64afccd3ad52da405329ad935de1fb36
814ec48fdfd79e3a108ef858e291e146'),
1674004740, / 2023-01-17T17:19:00 /
],
/ inspection_location / 503 : {
"country" : "us", / United States /
/ redacted_claim_keys / simple(59) : [
/ redacted region /
h'0d4b8c6123f287a1698ff2db15764564
a976fb742606e8fd00e2140656ba0df3'
/ redacted postal_code /
h'c0b7747f960fc2e201c4d47c64fee141
b78e3ab768ce941863dc8914e8f5815f'
]
},
/ redacted_claim_keys / simple(59) : [
/ redacted inspector_license_number /
h'af375dc3fba1d082448642c00be7b2f7
bb05c9d8fb61cfc230ddfdfb4616a693'
]
} >>,
/ CWT signature / h'536b3797c8f396d6dc4fedfa54fa605f
be897df02267ede5b40b257cba5eb2b3
cbf7d4f5733e0ca2e77783d860b8d74a
2b98878930be6c8e3d1de63df909d484
2a800f9d377fa41e9bd5f72743c06cfb
1e5d59892fac51a806cd4caf6cb30cce'
])
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 header parameter. For example, the
inspector_license_number claim is a Salted Disclosed Claim,
consisting of a per-disclosure random salt, the Claim Key, and Claim
Value.
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<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
Figure 2: CBOR extended diagnostic notation representation of
inspector_license_number disclosure
This is represented in CBOR pretty-printed format as follows (with
end-of-line comments and spaces inserted for clarity):
83 # array(3)
50 # bytes(16)
bae611067bb823486797da1ebbb52f83 # 16-byte salt
6b # text(11)
414243442d313233343536 # "ABCD-123456"
19 01f5 # unsigned(501)
Figure 3: CBOR encoding of inspector_license_number disclosure
The cryptographic hash, using the hash algorithm identified by the
sd_alg header parameter in the protected headers, of that byte string
is the Blinded Claim Hash (shown 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 (for example, for the redacted claim element of
inspection_dates).
d9df03da474fcb3c65771748e2e0608cf437504ecc24f450aaeacd40dd552b3f
Figure 4: SHA-256 hash of inspector_license_number disclosure
Finally, since this redacted claim is a map key and value, the
Blinded Claim Hash 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 that are array elements are handled slightly
differently, as described in Section 5.1.
/ redacted_claim_keys / simple(59) : [
/ redacted inspector_license_number /
h'd9df03da474fcb3c65771748e2e0608c
f437504ecc24f450aaeacd40dd552b3f',
/ ... next redacted claim at the same level would go here / ],
Figure 5: redacted inspector_license_number claim in the issued
CWT payload
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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 header parameter in the unprotected
header. If the Holder does not disclose any claims, it MUST omit the
sd_claims header parameter.
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',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/value/ "ca",
/claim/ "region" / region=California /
]>>,
]
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].
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]).
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/ cose-sign1 / 18( / sd_kbt / [
/ KBT protected / << {
/ alg / 1: -7, / ES256 /
/ 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 /
/ typ / 16: 294 # application/kb+cwt,
} >>, / end of KBT protected header /
/ KBT unprotected / {},
/ KBT payload / << {
/ aud / 3 : "https://verifier.example/app",
/ iat / 6 : 1725244237, / 2024-09-02T02:30:37+00:00Z /
/ cnonce / 39 : h'8c0f5f523b95bea44a9a48c649240803'
} >>, / end of KBT payload /
/ KBT signature / h'67116f888eab35fe82c171db146262c9
922fb3d4fd769641c80569e3c6010f90
251fa2b1dd335bc6bd8314603f57fd03
af7ddb5eb4cce1e59ac07d11dfdce742'
]) / end of kbt /
The digests in protected parts of the issued SD-CWT and the
disclosures hashed in unprotected header of the issuer_sd_cwt are
used together 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 that the Holder
included the sent list of disclosures.
5. SD-CWT Definition
SD-CWT is modeled after SD-JWT, with adjustments to align with
conventions in CBOR, COSE, and CWT. An SD-CWT MUST include the
protected header parameter typ [RFC9596] with a value declaring that
the object is an SD-CWT. This value MAY be the string content type
value application/sd-cwt, the uint Constrained Application Protocol
(CoAP) [RFC7252] content-format value 293, or a value declaring that
the object is a more specific kind of SD-CWT, such as a content type
value using the +sd-cwt structured suffix. The Issuer SHOULD use the
value 293 instead of application/sd-cwt, as the CBOR representation
is considerably smaller (3 bytes versus of 19).
An SD-CWT is a format based on CWT, but it allows some additional
types in maps to indicate values that were or should be redacted, and
includes some additional constraints to improve robustness. Unlike
CWT, SD-CWT requires key binding.
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An SD-CWT can contain blinded claims (each expressed as a Blinded
Claim Hash), at the root level or in any arrays or maps inside that
claim set. It is not required to contain any blinded claims.
Optionally the salted Claim Values (and often Claim Keys) for the
corresponding Blinded Claim Hash are disclosed in the sd_claims
header parameter 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 header parameter
is not present in the unprotected header.
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.
5.1. Types of Blinded Claims
Salted Disclosed Claims for named claims are structured as a 128-bit
salt, the disclosed value, and the name of the redacted element. For
Salted Disclosed Claims of items in an array, the name is omitted.
; an array of bstr-encoded Salted Disclosed Claims
salted-array = [ +bstr-encoded-salted ]
bstr-encoded-salted = bstr .cbor salted-entry
salted-entry = salted-claim / salted-element / decoy
salted-claim = [
bstr .size 16, ; 128-bit salt
any, ; Claim Value
(int / text) ; Claim Key
]
salted-element = [
bstr .size 16, ; 128-bit salt
any ; Claim Value
]
decoy = [
bstr .size 16 ; 128-bit salt
]
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 CBOR simple value 59 registered for
that purpose.
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When blinding an individual item in an array, the value of the item
is replaced with the digested salted hash as a CBOR byte string,
wrapped with the CBOR tag 60.
; redacted_claim_keys is used as a map key. The corresponding value is
; an array of Blinded Claim Hashes whose corresponding unblinded map keys
; and values are in the same map.
redacted_claim_keys = #7.59 ; CBOR simple value 59
; CBOR tag for wrapping a redacted element in an array
REDACTED_ELEMENT_TAGNUM = 60
; redacted_claim_element is used in CDDL payloads that contain
; array elements that are meant to be redacted.
redacted_claim_element = #6.<REDACTED_ELEMENT_TAGNUM>( bstr )
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 14.2.
Finally, an Issuer MAY create decoy digests, which look like blinded
claim hashes but have only a salt. Decoy digests are discussed in
Section 10.
6. Differences from the CBOR Web Token Specification
The following subsections discuss differences between CWT and SD-CWT
or clarify ambiguities in CWT. Some of these changes are necessary
to enable the new functionality of SD-CWT, while some constraints
were made in the interest of more robustness.
Variability in serialization can also be exploited to impact
privacy. See Section 16 for more details on the privacy impact of
serialization and profiling.
6.1. Definite Length CBOR Required
Encoders of SD-CWT and SD-KBT MUST NOT send indefinite length CBOR.
Decoders of SD-CWT and SD-KBT MUST reject any SD-CWT or SD-KBT
received containing indefinite length CBOR.
6.2. Finite values for standard date claims
The standard CWT claims exp, nbf, and iat MUST be finite numbers.
For the avoidance of doubt, not a number (NaN) values and positive
and negative infinity are not acceptable in those claims.
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In [RFC8392], these three claims are of type NumericDate.
Section 2 of the same spec refers to NumericDate as a JWT
NumericDate, "except that it is represented as [an untagged] CBOR
numeric date (from Section 2.4.1 of [RFC7049]) instead of a JSON
number". In CBOR, a NumericDate can be represented as an unsigned
integer, a negative integer, or a floating point value. CBOR
(both [RFC7049] and [RFC8949]) refers to floating-point values to
include NaNs, and floating-point numbers that include finite and
infinite numbers. Neither JSON [RFC8259] nor JWT [RFC7519] can
represent infinite values.
As IEEE double-precision floating point numbers smaller than -(2^53)
and larger than 2^53 are no longer as precise as CBOR integers, use
of floating point values outside this range are FORBIDDEN.
6.3. Allowed types of CBOR map keys
According to Section 1.1 of the CBOR Web Token Specification
[RFC8392], "CBOR uses text strings, negative integers, and unsigned
integers as map keys." Section 1.5 of CBOR Object Signing and
Encryption (COSE): Structures and Process [RFC9052] states: "In COSE,
we use text strings, negative integers, and unsigned integers as map
keys." While a CBOR map key can contain any CBOR type, this
statement implies that CWT map keys only contain those types.
An SD-CWT payload is typically its COSE payload. [RFC9597] also
defines the CWT Claims COSE Header Parameter (value 15) that can
appear in the protected headers; if it exists, it contains a CBOR map
with additional claims that are treated as if they were in the SD-CWT
payload. Both of these maps are described as SD-CWT Claims Maps.
Note that CWT Claims is a separate CBOR map from the COSE payload
and can contain the same Claim Keys as the COSE payload CBOR map.
The same valid CWT claim keys could be present in both SD-CWT Claims
Maps, but if so, they MUST have the same unblinded value. Neither,
one, or both could be redacted. If both are redacted they would have
different disclosures, salts, and Blinded Claim Hashes.
In addition to map keys that are valid in CWT, SD-CWT Claims Maps MAY
contain the CBOR simple value registered in this specification in
Section 17.2. In SD-CWTs exchanged between the Holder and the Issuer
prior to issuance, map keys MAY also consist of the To Be Redacted
tag (defined in Section 11.1), containing an integer or text string;
or a To Be Decoy tag (defined in Section 11.2), containing a positive
integer. These two tags provide a way for the Holder to indicate
specific claims to be redacted or decoys to be inserted.
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The following list summarizes the map key constraints on SD-CWTs and
SD-KBTs:
* The SD-KBT protected headers kcwt Header Parameter exclusively
contains:
- a single valid SD-CWT
* The SD-KBT protected headers MUST NOT contain a CWT Claims Header
Parameter.
* The SD-KBT payload map; unprotected headers map; and protected
headers map (excluding the kcwt Header Parameter) exclusively
contain map keys (at any level of depth) with the following map
key types:
- unsigned integers
- negative integers
- text strings with a length no greater than 255 octets
* The SD-CWT unprotected headers map; and the protected headers map
(excluding the CWT Claims Header Parameter) exclusively contain
map keys (at any level of depth) with the following map key types:
- unsigned integers
- negative integers
- text strings with a length no greater than 255 octets
* The SD-CWT Claims Maps at any level of depth, exclusively contain
map keys with the following map key types:
- unsigned integers;
- negative integers;
- text strings with a length no greater than 255 octets;
- the simple value 59; or
- when disclosable claims are communicated to the Issuer, prior
to issuance:
o the To Be Decoy tag 62 Section 11.2 containing a positive
integer, or
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o the To Be Redacted tag 58 Section 11.1 containing:
+ an unsigned integer,
+ a negative integer, or
+ a text strings with a length no greater than 255 octets.
In other words, there are exactly three places that can contain map
keys (including values that might contain nested maps) with the SD-
CWT values that are not allowed in a CWT:
* in the payload Claims Map of an SD-CWT
* in the CWT Claims Header Parameter Claims Map in the protected
headers of an SD-CWT
* in the kcwt Header Parameter of an SD-KBT (in one of the embedded
SD-CWT Claims Maps).
All the other Header Parameters, and the KBT payload need to contain
values valid in a CWT. These values are represented by the safe-
value CDDL type.
; CWT claim legal values only
safe_map = { * label => safe_value }
safe_value =
int / tstr / bstr /
[ * safe_value ] /
safe_map /
#6.<safe_tag>(safe_value) / #7.<safe_simple> / float
; legal values in issued SD-CWT
issued_sd_cwt_map = {
? redacted_claim_keys ^ => [ * bstr ],
* label => issued_sd_cwt_value
}
issued_array_element = redacted_claim_element / issued_sd_cwt_value
issued_sd_cwt_value =
int / tstr / bstr /
[ * issued_array_element ] /
issued_sd_cwt_map /
#6.<safe_tag>(issued_sd_cwt_value) / #7.<safe_simple> / float
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; legal values in claim set sent to Issuer
preissuance_label = label /
#6.<TO_BE_REDACTED_TAGNUM>(label) /
#6.<TO_BE_DECOY_TAGNUM>(int .gt 0)
preissuance_map = { * preissuance_label => preissuance_value }
preissuance_value =
int / tstr / bstr /
[ * preissuance_value ] /
preissuance_map /
#6.<safe_tag>(preissuance_value) / #7.<safe_simple> / float
; CBOR tag number for wrapping to-be-redacted keys or elements
TO_BE_REDACTED_TAGNUM = 58
; CBOR tag number for indicating a decoy value is to be inserted here
TO_BE_DECOY_TAGNUM = 62
label = int / tstr .size (1..255)
safe_tag = uint .ne (TO_BE_REDACTED_TAGNUM /
TO_BE_DECOY_TAGNUM /
REDACTED_ELEMENT_TAGNUM)
safe_simple = 0..23 / 32..58 / 60..255 ; exclude redacted keys array
secs = int / float53
float53 = -9007199254740992.0..9007199254740992.0 ; from 2^53 to 2^53
Note that Holders presenting to a Verifier that does not support this
specification would need to present a CWT without tagged map keys or
simple value 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 map key are not permitted.
6.4. Duplicate map key detection
Implementations MUST NOT send multiple map keys inside the same CBOR
map having the same CBOR Preferred Encoding (see Section 4.1 of
[RFC8949]). This applies to any map anywhere in an SD-CWT or an SD-
KBT.
Note that it is not necessary to actually encode the map keys
using Preferred Encoding to satisfy this requirement.
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Likewise, a single SD-CWT claim set MUST NOT contain a map (at any
level of depth) with both a map key k, and k tagged with the To Be
Redacted tag (see Section 11.1). Map keys and their To Be Redacted
tagged verison are considered duplicate map keys for the purposes of
this specification.
For example, if the map below is contained inside a payload, it is
invalid because the map key 500 and the map key 58(500) cannot both
be present.
{
500: "ABCD-123456", # map key 500
58(500): "DEFG-456789" # to be redacted tag containing 500
}
6.5. Level of Nesting of Claims
Selective disclosure of deeply nested structures (exceeding a depth
of 16 levels), is NOT RECOMMENDED as it could lead to resource
exhaustion vulnerabilities.
The individual map key / value pairs in a Claim Set are defined as
the "top level", or level 1. For each value that is an array, a map,
or a tagged item, each of the elements of the array, each value
corresponding to each map key in the map, and the tagged item are at
the next level of depth.
For example, considering the following abbreviated document, the
following table shows the level of depth of the corresponding values:
+=======+========================+
| Level | Value |
+=======+========================+
| 1 | https://issuer.example |
+-------+------------------------+
| 2 | 1549560720 |
+-------+------------------------+
| 3 | DCBA-101777 |
+-------+------------------------+
| 4 | us |
+-------+------------------------+
| 5 | 27315 |
+-------+------------------------+
Table 1
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{ # contents are level 1
1: "https://issuer.example",
...
502: 1(1549560720), # tagged value is level 2
504: [ # contents are level 2
{ # contents are level 3
...
501: "DCBA-101777",
503: { # contents are level 4
1: "us",
...
},
505: 4( # decimal fraction tag
[ # 273.15
-2,
27315 # level 5
]
)
},
...
]
}
The contents of the top-level claims map are level 1. The contents
of the array for map key 504 are level 2. The contents of the map
inside that array are level 3 (ex: the value of map key 505). The
value of tag 4 is at level 4. The values in the array inside tag 4
are at level 5.
6.6. Use of Structured Suffixes
Any type which contains the +sd-cwt structured suffix MUST be a legal
SD-CWT. A type that is a legal CWT and does not contain any blinded
claims SHOULD use the +cwt structure suffix instead, unless the CBOR
map being secured contains claim keys with different semantics than
those registered in the CBOR Web Token Claims IANA registry.
7. SD-CWT Issuance
How the Holder communicates to the Issuer to request a CWT or an SD-
CWT is out of scope for 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.
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The protected header MAY contain the sd_alg header parameter
identifying the algorithm (from the COSE Algorithms registry) used to
hash the Salted Disclosed Claims. If no sd_alg header parameter is
present, the default hash function SHA-256 is used.
If no Salted Disclosed Claims or Decoys are present, the unprotected
header MUST contain the sd_claims header parameter 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 parameter value is omitted. The
payload also MUST include a key confirmation element (cnf) [RFC8747]
for the Holder's public key.
In an SD-CWT, either the subject sub / 2 claim MUST be present, or
the redacted form of the subject MUST be present. The iss / 1 claim
SHOULD be present unless the protected header contains a certificate
or certificate-like entity that 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 /
8 claim, the cnonce / 39 claim, and the standard claims other than
the subject MUST NOT be redacted. Any other claims are OPTIONAL and
MAY be redacted. Profiles of this specification MAY specify
additional claims that MUST, MUST NOT, and MAY be redacted.
To further reduce the size of the SD-CWT, a COSE Key Thumbprint (ckt)
[RFC9679] MAY be used in the cnf claim.
7.1. Issuer Generation
The Issuer follows all the requirements of generating a valid SD-CWT,
largely a CWT extended by Section 6. The Issuer MUST implement
COSE_Sign1 using an appropriate fully-specified asymmetric signature
algorithm (for example, ESP256 or 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 MUST 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;
* if an audience (aud) is present, it is acceptable;
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* 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 identified by the sd_alg header parameter in
the protected headers 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 that violate its
privacy policies;
* every blinded claim hash (some of which may be nested as in
Section 14.2) has a corresponding Salted Disclosed Claim, and vice
versa;
* the values of the Salted Disclosed Claims when placed in their
unblinded context in the payload are acceptable to the Holder.
A Holder MAY choose to validate the appropriateness or correctness
of some or all of the information in a token, should it have the
ability to do so, and it MAY choose to not present information to
a Verifier that it deems to be incorrect.
The following informative CDDL is provided to describe the syntax for
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) ^ => 293 / "application/sd-cwt",
&(alg: 1) ^ => int,
? &(kid: 4) ^ => bstr,
? &(CWT_Claims: 15) ^ => issued_sd_cwt_map,
? &(sd_alg: 170) ^ => int, ; -16 for sha-256
? &(sd_aead: 172) ^ => uint .size 2,
* label => safe_value
}
sd-unprotected = {
? &(sd_claims: 17) ^ => salted-array,
? &(sd_aead_encrypted_claims: 171) ^ => aead-encrypted-array,
* label => safe_value
}
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) ^ => secs, ; 1883000000
? &(nbf: 5) ^ => secs, ; 1683000000
? &(iat: 6) ^ => secs, ; 1683000000
? &(cti: 7) ^ => bstr,
&(cnf: 8) ^ => safe_map, ; key confirmation
? &(vct: 11) ^ => bstr,
? &(cnonce: 39) ^ => bstr,
;
? redacted_claim_keys ^ => [ * bstr ],
* label => issued_sd_cwt_value
}
8. SD-CWT Presentation
When issuing an SD-CWT to a Holder, the Issuer includes all the
Salted Disclosed Claims in the unprotected header.
By contrast, 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 blinded claims, it includes that subset of its
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Salted Disclosed Claims in the sd_claims header parameter of the
unprotected header. If there is nothing to be disclosed, the
sd_claims header parameter is omitted.
An SD-CWT presentation to a Verifier has the same syntax as an SD-CWT
issued to a Holder, except the Holder chooses the subset of
disclosures included in the sd_claims header parameter.
Since the unprotected header is not included in the Issuer's
signature, the list of disclosed claims can differ without
invalidating the corresponding signature.
Finally, the SD-CWT used for presentation to a Verifier is included
in a key binding token, as discussed 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 MUST NOT be present in
the SD-KBT. (Profiles of this specification MAY define additional
semantics.)
The aud claim MUST be included and MUST correspond to the Verifier.
The SD-KBT payload MUST contain the iat (issued at) claim. The
protected header of the SD-KBT MUST include the typ header parameter
with the value application/kb+cwt or the uint value of 294. The
Holder SHOULD use the value 294 instead of application/kb+cwt, as the
CBOR representation is considerably smaller (3 bytes versus of 19).
The SD-KBT MUST NOT be valid for any time period when its contained
SD-CWT is invalid.
The SD-KBT provides the following assurances to the Verifier:
* the Holder of the SD-CWT controls the confirmation method chosen
by the Issuer;
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* 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 [RFC8747], 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.
kbt-cwt = #6.18([
protected: bstr .cbor kbt-protected,
kbt-unprotected,
payload: bstr .cbor kbt-payload,
signature: bstr
])
kbt-protected = {
&(typ: 16) ^ => 294 / "application/kb+cwt",
&(alg: 1) ^ => int,
&(kcwt: 13) ^ => sd-cwt-issued,
* label => safe_value
}
kbt-unprotected = {
* label => safe_value
}
kbt-payload = {
&(aud: 3) ^ => tstr, ; "https://verifier.example/app"
? &(exp: 4) ^ => secs, ; 1883000000
? &(nbf: 5) ^ => secs, ; 1683000000
&(iat: 6) ^ => secs, ; 1683000000
? &(cnonce: 39) ^ => bstr,
* label => safe_value
}
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.
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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.
1. First the Verifier must open the protected headers of the SD-KBT
and find the Issuer SD-CWT present in the kcwt field.
2. Next, the Verifier must validate the SD-CWT as described in
Section 7.2 of [RFC8392].
3. The Verifier checks the time claims in the SD-CWT as follows:
* nbf <= iat (if both exist)
* nbf < exp (if both exist)
* iat < exp (if both exist)
4. The Verifier extracts the confirmation key from the cnf claim in
the SD-CWT payload.
5. Using the confirmation key, the Verifier validates the SD-KBT as
described in Section 7.2 of [RFC8392].
6. The Verifier checks the time claims in the SD-KBT as follows:
* nbf in the SD-KBT <= iat in the SD-KBT (if both exist)
* iat in the SD-KBT < exp in the SD-KBT (if both exist)
* exp in the SD-KBT <= exp in the SD-CWT (if both exist)
* nbf in the SD-KBT >= nbf in the SD-CWT (if both exist)
* iat in the SD-KBT >= iat in the SD-CWT (if both exist)
* nbf in the SD-KBT <= exp in the SD-CWT (if both exist)
* iat in the SD-KBT < exp in the SD-CWT (if both exist)
* iat in the SD-KBT >= nbf in the SD-CWT (if both exist)
7. The Verifier MUST extract and decode the disclosed claims from
the sd_claims header parameter in the unprotected header of the
SD-CWT. Each decoded disclosure is treated as if it is a claim
key or claim element at the location corresponding to its Blinded
Claim Hash in the payload. If there are any disclosures that do
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not have a corresponding Blinded Claim Hash, the entire SD-CWT is
invalid. If any decoded Redacted Claim Key duplicates another
claim key in the same position, the entire SD-CWT is invalid.
Note: A Verifier MUST be prepared to process disclosures in
any order. When disclosures are nested, a disclosed value
could appear before the disclosure of its parent.
8. A Verifier MUST reject the SD-CWT if the audience claim in either
the SD-CWT or the SD-KBT contains a value that does not
correspond to the intended recipient.
9. Otherwise, the SD-CWT is considered valid. Once any remaining
redacted elements (either redacted claims or decoys) are deleted,
the Validated Disclosed Claims Set is now a CWT Claims Set with
no claims marked for redaction.
Note: Undisclosed Redacted Claim Elements will be removed from
the Validated Disclosed Claims Set, changing the length of the
array. If the semantics of the position of items in the array
is important, the issuer should instead disclose or redact the
entire array.
10. Further validation logic can be applied to the Validated
Disclosed Claims Set, just as it might be applied to a validated
CWT Claims Set.
By performing these steps, the recipient can cryptographically verify
the integrity of the protected claims and verify they have not been
tampered with.
10. Decoy Digests
An Issuer MAY add additional digests to the SD-CWT payload (including
nested maps and arrays within the payload) that are not associated
with any unblinded claim. The purpose of such "decoy" digests is to
make it more difficult for an adversarial Verifier to infer private
information based on the number of Redacted Claim Keys or Redacted
Claim Elements.
The list of disclosures sent by the Issuer to the Holder contains one
disclosure for each decoy digest. Each disclosure contains a single
element array with a per-decoy salt.
<<[ h'C1069BC056E234D64F58BAFF8A7B776B' ]>>
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The Blinded Claim Hash for each disclosure is calculated using the
same algorithm for decoys as for Redacted Claim Keys and Redacted
Claim Elements. An example issued SD-CWT containing decoy digests is
shown below.
/ cose-sign1 / 18([ / issuer SD-CWT /
/ CWT protected / << {
/ alg / 1 : -35, / ES384 /
/ kid / 4 : 'https://issuer.example/cose-key3',
/ typ / 16 : 293, # application/sd-cwt
/ sd_alg / 170 : -16 / SHA256 /
} >>,
/ CWT unprotected / {
/ sd_claims / 17 : [ / these are all the disclosures /
<<[
/salt/ h'2bfeab9315829fe0c82a15b2c57a47b2',
/value/ "fr" / France /
]>>,
<<[
/salt/ h'c1069bc056e234d64f58baff8a7b776b',
]>>,
<<[
/salt/ h'b0392772caefd08178218f86f3e2b3a9',
/value/ true,
/claim/ 500 / inspection result /
]>>,
<<[
/salt/ h'89c41c270dd06cd3517d371c9ddf2bab',
]>>,
]
},
/ 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'
}
},
/countries array/ 98: [
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/redacted country == "fr" /
60(h'dc5f753b66acd89d78481039934a86cc
14f9959c64c4037dea3f872b9a8453f1')
/decoy country #1 /
60(h'3f80963a1246b412d6567f2a5ca446fd
19a01dd8cfc291bed69e8c575c5abfb8')
],
/ redacted_claim_keys / simple(59) : [
/ redacted claim 500 (== true) /
h'bd0fd88127b3071ff5433eef59a5e3c5
f18341f25c5bd119c41fd34802a9797b'
/ decoy claim #2 /
h'eeec970897a5b9108f24f44751baedab
b53a1f3d241ab6b60c9f309f114ecf88'
]
} >>,
/ CWT signature / h'fd0b7edae0fa5bd429f07809762a32c5
c160c089091a5c3abbee91710fa388d8
3c1ad6a5a3d219c4265b9f89aef1f511
ff362cbbea6f46bae08978822b672aa5
75cd6fc519394af2a883c394faf16ac1
781afb01f626bdd6fee1205a29dcc203'
])
11. Tags Used Before SD-CWT Issuance
This section describes the semantics of two CBOR tags that are
(optionally) only used to convey information to the Issuer about
disclosures to create.
11.1. To Be Redacted Tag Definition
In order to indicate specific claims that must be redacted in a Claim
Set, this specification defines a new CBOR tag "To Be Redacted". The
tag can be used by a library to automatically convert a Claim Set
with "To Be Redacted" tags into a) a new Claim Set containing
Redacted Claim Keys and Redacted Claim Elements replacing the tagged
claim keys or claim elements, and b) a set of corresponding Salted
Disclosed Claims.
When used on an element in an array, the value to be redacted is
present inside the tag. When used on a map key and value, the tag is
placed around the map key, while the map value remains.
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Examples in this draft use the To Be Redacted tag in order to
distinguish their pre-issued, post-issued, and post-presented
representations in EDN and CDDL. The snippet of EDN shown below
shows one mechanism to communicate to the Issuer to redact the
inspector license number claim, and two of the inspection dates in
our primary example.
{
...
58(501): "ABCD-123456", # redact inspector license number claim
/inspection dates/ 502: [
58(1549560720), # redact 07-Feb-2019
58(1612560720), # redact 04-Feb-2021
1674004740 # don't redact 17-Jan-2023
]
...
}
11.2. To Be Decoy
In order to indicate a location that should contain a decoy digest
Section 10 in the issued SD-CWT, this specification defines a new
CBOR tag "To Be Decoy". This tag can be used by a library to
automatically a) add a decoy digest at a particular location in an
array, or at a particular level in a map; and b) create the
corresponding Salted Disclosed Claims. The value inside is a
positive integer that MUST be unique for each decoy location within
the SD-CWT. The integer could be used to look up the salt for the
decoy deterministically, but does not impose any ordering. When a
decoy digest is requested in a map, the map value is always null.
In the example fragment below, the transit countries claim contains
an array of countries. The Claim Elements array contains Germany
(de) and the Philippines (ph). The Holder wants to redact each
country, but add decoys to obfuscate the number of component origin
countries. The example fragment also shows two decoy digests in the
same map.
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{
...
/component origin countries/ 607: [
58("de"),
58("ph"),
62(1), # add two decoys in this array
62(2)
],
62(3): null, # add a decoy in this map
62(4): null, # add a second decoy in the same map
...
}
12. Encrypted Disclosures
The RATS architecture [RFC9334] defines a model where the Verifier is
split into separate entities, with an initial verifier called an
Attester, and a target entity called a Relying Party. Other
protocols have a similar type of internal structure for the Verifier.
In some of these use cases, there is existing usage of AES-128 GCM
and other Authenticated Encryption with Additional Data (AEAD)
[RFC5116] algorithms.
This section describes how to use AEADs to encrypt disclosures to a
target entity, while enabling a initial verifier to confirm the
authenticity of the presentation from the Holder.
In these systems, an appropriate symmetric key and its context are
provided completely out-of-band.
The entire SD-CWT is included in the protected header of the SD-KBT,
which secures the entire Issuer-signed SD-CWT including its
unprotected headers that include its disclosures.
When encrypted disclosures are present, they MUST be in the
unprotected headers of the Issuer-signed SD-CWT, before the SD-KBT
can be generated by the Holder.
The initial Verifier of the key binding token might not be able to
decrypt encrypted disclosures and MAY decide to forward them to an
inner Verifier that can decrypt them.
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12.1. AEAD Encrypted Disclosures Mechanism
This section defines two new COSE Header Parameters. If present in
the protected headers, the first header parameter (sd_aead) specifies
an Authenticated Encryption with Additional Data (AEAD) algorithm
[RFC5116] registered in the IANA AEAD Algorithms registry
(https://www.iana.org/assignments/aead-parameters/aead-
parameters.xhtml) . (Guidance on specific algorithms is discussed in
Section 16.8.) The second header parameter
(sd_aead_encrypted_claims), if present, contains a non-empty list of
AEAD encrypted disclosures. Taking the first example disclosure from
above:
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
The corresponding bstr is encrypted with an AEAD algorithm [RFC5116].
If present, the algorithm of the sd_aead protected header field is
used, or AEAD_AES_128_GCM if no algorithm was specified. The bstr is
encrypted with a unique, random 16-octet nonce. The AEAD ciphertext
consists of its encryption algorithm's ciphertext and its
authentication tag. (For example, in AEAD_AES_128_GCM the
authentication tag is 16 octets.) The nonce (nonce), the encryption
algorithm's ciphertext (ciphertext) and authentication tag (tag) are
put in an array. The resulting array is placed in the
sd_aead_encrypted_claims header parameter in the unprotected headers
of the SD-CWT.
/ sd_aead_encrypted_claims / 171 : [ / AEAD encrypted disclosures /
[
/ nonce / h'95d0040fe650e5baf51c907c31be15dc',
/ ciphertext / h'208cda279ca86444681503830469b705
89654084156c9e65ca02f9ac40cd62b5
a2470d',
/ tag / h'1c6e732977453ab2cacbfd578bd238c0'
],
...
]
In the example above, the key in hex is
a061c27a3273721e210d031863ad81b6.
The blinded claim hash is still over the unencrypted disclosure. The
receiver of an AEAD encrypted disclosure locates the appropriate key
by looking up the authentication tag. If the Verifier is able to
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decrypt and verify an encrypted disclosure, the decrypted disclosure
is then processed as if it were in the sd_claims header parameter in
the unprotected headers of the SD-CWT.
Details of key management are left to profiles of the specific
protocols that make use of AEAD encrypted disclosures.
The CDDL for AEAD encrypted disclosures is below.
aead-encrypted-array = [ +aead-encrypted ]
aead-encrypted = [
bstr .size 16, ; 128-bit nonce
bstr, ; the encryption ciphertext output of a
; bstr-encoded-salted
bstr ; the corresponding authentication tag
]
Note: Because the encryption algorithm is in a registry that
contains only AEAD algorithms, an attacker cannot replace the
algorithm or the message, without a decryption verification
failure.
13. Credential Types
This specification defines the CWT claim vct (for Verifiable
Credential Type). The vct value is an identifier for the type of the
SD-CWT Claims Set. Like the typ header parameter [RFC9596], its value
can be either a string or an integer. For size reasons, it is
RECOMMENDED that the numeric representation be used.
If its value is a string, it is a case-sensitive StringOrURI, as
defined in [RFC7519]. In this case, the vct string MUST either be
registered in the IANA "Verifiable Credential Type Identifiers"
registry established in Section 17.8, or be a Collision-Resistant
Name, as defined in Section 2 of [RFC7515].
If its value is an integer, it is either a value in the range 0-64999
registered in the IANA "Verifiable Credential Type Identifiers"
registry established in Section 17.8 or an Experimental Use value in
the range 65000-65535, which is not to be used in operational
deployments.
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].
14. Examples
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14.1. 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 /
/ kcwt / 13: 18([ / issuer SD-CWT /
/ CWT protected / << {
/ alg / 1 : -35, / ES384 /
/ kid / 4 : 'https://issuer.example/cose-key3',
/ typ / 16 : 293, # application/sd-cwt
/ sd_alg / 170 : -16 / SHA256 /
} >>,
/ CWT unprotected / {
/ sd_claims / 17 : [ / these are the disclosures /
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
<<[
/salt/ h'8de86a012b3043ae6e4457b9e1aaab80',
/value/ 1549560720 / inspected 7-Feb-2019 /
]>>,
<<[
/salt/ h'ec615c3035d5a4ff2f5ae29ded683c8e',
/value/ "ca",
/claim/ "region" / region=California /
]>>,
]
},
/ 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,
/inspection_dates/ 502 : [
/ redacted inspection date 7-Feb-2019 /
60(h'1b7fc8ecf4b1290712497d226c04b503
b4aa126c603c83b75d2679c3c613f3fd'),
/ redacted inspection date 4-Feb-2021 /
60(h'64afccd3ad52da405329ad935de1fb36
814ec48fdfd79e3a108ef858e291e146'),
1674004740, / 2023-01-17T17:19:00 /
],
/ inspection_location / 503 : {
"country" : "us", / United States /
/ redacted_claim_keys / simple(59) : [
/ redacted region /
h'0d4b8c6123f287a1698ff2db15764564
a976fb742606e8fd00e2140656ba0df3'
/ redacted postal_code /
h'c0b7747f960fc2e201c4d47c64fee141
b78e3ab768ce941863dc8914e8f5815f'
]
},
/ redacted_claim_keys / simple(59) : [
/ redacted inspector_license_number /
h'af375dc3fba1d082448642c00be7b2f7
bb05c9d8fb61cfc230ddfdfb4616a693'
]
} >>,
/ CWT signature / h'536b3797c8f396d6dc4fedfa54fa605f
be897df02267ede5b40b257cba5eb2b3
cbf7d4f5733e0ca2e77783d860b8d74a
2b98878930be6c8e3d1de63df909d484
2a800f9d377fa41e9bd5f72743c06cfb
1e5d59892fac51a806cd4caf6cb30cce'
]),
/ end of issuer SD-CWT /
/ typ / 16: 294 # application/kb+cwt,
} >>, / end of KBT protected header /
/ KBT unprotected / {},
/ KBT payload / << {
/ aud / 3 : "https://verifier.example/app",
/ iat / 6 : 1725244237, / 2024-09-02T02:30:37+00:00Z /
/ cnonce / 39 : h'8c0f5f523b95bea44a9a48c649240803'
} >>, / end of KBT payload /
/ KBT signature / h'67116f888eab35fe82c171db146262c9
922fb3d4fd769641c80569e3c6010f90
251fa2b1dd335bc6bd8314603f57fd03
af7ddb5eb4cce1e59ac07d11dfdce742'
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]) / end of kbt /
Figure 6: An EDN Example
14.2. Nested Example
Instead of the structure from the previous example, imagine that the
payload contains an inspection history log with the following
structure. It could be blinded at multiple levels of the claims 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'2e9a833949c163ce845813c258a8f13c',
/value/ {
500: true,
502: 17183928,
simple(59): [
h'3fc9748e00684e6442641e58ea965468
085024da253ed46b507ae56d4c204434',
h'a5124745703ea9023bf92a2028ba4547
b830ce9705161eaad56729cab8e1d807'
]
} / inspection 17-Jan-2023 /
]>>,
<<[
/salt/ h'bae611067bb823486797da1ebbb52f83',
/value/ "ABCD-123456",
/claim/ 501 / inspector_license_number /
]>>,
<<[
/salt/ h'd5c7494eb16a8ff11fba507cbc7c816b',
/value/ {
1: "us",
simple(59): [
h'3bf93977377099c66997303ddbce67b4
ca7ee95d2c8cf2b8b45f451362493460',
h'231e125d192de099e91bc59e2ae914f0
c891cbc3329b7fea70a3aa636c87a0a4'
]
},
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/claim/ 503 / San Francisco location /
]>>,
<<[
/salt/ h'52da9de5dc61b33775f9348b991d3d78',
/value/ "ca",
/claim/ 2 / region=California /
]>>,
<<[
/salt/ h'9adcf14141f8607a44a130a4b341e162',
/value/ {
500: true,
502: 1549560720,
simple(59): [
h'94d61c995d4fa25ad4d3cc4752f6ffaf
9e67f7f0b4836c8252a9ad23c20499f5',
h'4ff0ecad5f767923582febd69714f3f8
0cb00f58390a0825bc402febfa3548bf'
]
} / inspection 7-Feb-2019 /
]>>,
<<[
/salt/ h'591eb2081b05be2dcbb6f8459cc0fe51',
/value/ "DCBA-101777",
/claim/ 501 / inspector_license_number /
]>>,
<<[
/salt/ h'95b006410a1b6908997eed7d2a10f958',
/value/ {
1: "us",
simple(59): [
h'2bc86e391ec9b663de195ae9680bf614
21666bc9073b1ebaf80c77be3adb379f',
h'e11c93b44fb150a73212edec5bde46d3
d7db23d0d43bfd6a465f82ee8cf72503'
]
},
/claim/ 503 / Denver location /
]>>,
]
After applying the disclosures of the nested structure above, the
disclosed Claims 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 /
501: "DCBA-101777", / inspector license /
502: 1549560720, / 2019-02-07T17:32:00 /
503: {
1: "us" / United States /
}
},
{
500: True, / inspection passed /
501: "ABCD-123456", / inspector license /
502: 17183928, / 2023-01-17T17:19:00 /
503: {
1: "us", / United States /
2: "ca" / region=California /
}
}
]
}
15. Privacy Considerations
This section describes the privacy considerations in accordance with
the recommendations from [RFC6973]. Many of the topics discussed in
[RFC6973] apply to SD-CWT, but are not repeated here.
15.1. Correlation
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, at a credential management complexity
cost. Any Claim Value that pertains to a sufficiently small set of
subjects can be used to facilitate tracking 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.
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15.2. Determinism
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.
15.3. Audience
If the audience claim is present in both the SD-CWT and the SD-KBT,
they are not required to be the same. SD-CWTs with audience claims
that do not correspond to the intended recipients MUST be rejected,
to protect against accidental disclosure of sensitive data.
15.4. Credential Types
The privacy implications of selective disclosure vary significantly
across different credential types due to their inherent
characteristics and intended use cases. The mandatory and optional-
to-disclose data elements in an SD-CWT must be carefully chosen based
on the specific privacy risks associated with each credential type.
For example, a passport credential contains highly sensitive personal
information where even partial disclosure can have significant
privacy implications: - Revealing citizenship status may expose an
individual to discrimination - Date of birth combined with any other
attribute enables age-based profiling - Biometric data, even if
selectively disclosed, presents irreversible privacy risks - The mere
possession of a passport from certain countries can be sensitive
information
In contrast, a legal entity certificate has fundamentally different
privacy considerations: - The entity's legal name and registration
number are often public information - Business addresses and contact
details may already be in public registries - Authorized signatories'
names might be required for legal validity - The primary concern is
often business confidentiality rather than personal privacy
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These differences mean that: - Passport credentials should minimize
mandatory disclosures and maximize holder control over optional
elements - Legal entity certificates might reasonably require
disclosure of more fields to establish business legitimacy - The
granularity of selective disclosure should match the credential
type's privacy sensitivity - Default disclosure sets must be
carefully calibrated to each credential's risk profile
Several distinct credential types might be applicable to a given use
case, each with unique privacy trade-offs. Issuers MUST perform a
comprehensive privacy and confidentiality assessment for each
credential type they intend to issue, considering: - The sensitivity
spectrum of contained attributes - Likely disclosure scenarios and
their privacy impacts - Correlation risks when attributes are
combined - Long-term privacy implications of disclosed information -
Cultural and jurisdictional privacy expectations
16. Security Considerations
Security considerations from COSE [RFC9052] and CWT [RFC8392] apply
to this specification.
16.1. Issuer Key Compromise
Verification of an SD-CWT requires that the Verifier have access to a
verification key (public key) associated with the Issuer. Compromise
of the Issuer's signing key would enable an attacker to forge
credentials for any subject, potentially undermining the entire trust
model of the credential system. Beyond key compromise, attacks
targeting the provisioning and binding between issuer names and their
cryptographic key material pose significant risks. An attacker who
can manipulate these bindings could substitute their own keys for
legitimate issuer keys, enabling credential forgery while appearing
to be a trusted issuer.
Certificate transparency, as described in [RFC9162], or key
transparency, as described in [I-D.draft-ietf-keytrans-protocol], can
help detect and prevent such attacks by: - Enabling public
observation of all issued certificates or key bindings - Detecting
unauthorized or fraudulent bindings between verification keys and
Issuer identifiers - Providing cryptographic proof of inclusion for
legitimate keys - Creating an append-only audit trail that makes key
substitution attacks discoverable
Verifiers SHOULD leverage transparency mechanisms where available to
validate that the issuer's keys have not been compromised or
fraudulently substituted.
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16.2. Disclosure Coercion and Over-identification
The Security Considerations from Section 10.2. of
[I-D.draft-ietf-oauth-selective-disclosure-jwt] apply, with
additional attention to disclosure coercion risks. Holders face
risks of being coerced into disclosing more claims than necessary.
This threat warrants special attention because:
1. Verifier Trust: Holders MUST be able to verify that a Verifier
will handle disclosed claims appropriately and only for stated
purposes.
2. Elevated Risk: Claims from trusted authorities (e.g., government-
issued credentials) carry higher misuse potential due to their
inherent legitimacy.
3. Irreversibility: Disclosed claims cannot be withdrawn. This
permanent exposure risk MUST be considered in any disclosure
decision.
Mitigation Measures: 1. Verifiers SHOULD demonstrate eligibility to
receive claims 2. Holders MUST conduct risk assessments when
Verifier eligibility cannot be established 3. Trust lists maintained
by trusted parties can help identify authorized Verifiers
Without proper safeguards (such as Verifier trust lists), Holders
remain vulnerable to over-identification and long-term misuse of
their disclosed information.
16.3. Threat Model Development Guidance
This section provides guidance for developing threat models when
applying SD-CWT to specific use cases. It is NOT a threat model
itself, but rather a framework to help implementers create
appropriate threat models for their particular contexts. Each use
case will have unique security characteristics that MUST be analyzed
before determining the applicability of SD-CWT-based credential
types.
The following non-exhaustive list of questions and considerations
should guide the development of a use-case-specific threat model:
1. Has there been a t-closeness, k-anonymity, and l-diversity
assessment (see [t-Closeness]) assuming compromise of the one or
more Issuers, Verifiers or Holders, for all relevant credential
types?
2. Issuer questions:
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a. How many Issuers exist for the credential type?
b. Is the size of the set of Issuers growing or shrinking over
time?
c. 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?
d. Does the credential type require or offer the ability to
disclose a globally unique identifier?
e. 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?
f. Does the credential type contain Personally Identifiable
Information (PII), or other sensitive information that might
have value in a market?
3. Holder questions:
a. What steps has the Holder taken to improve their operation
security regarding presenting credentials to verifiers?
b. How can the Holder be convinced the Verifier that received
presentations is legitimate?
c. How can the Holder be convinced the Verifier will not share,
sell, leak, or otherwise disclose the Holder's presentations
or Issuer or Holder signed material?
d. What steps has the Holder taken to understand and confirm the
consequences resulting from their support for the aggregate-
use of digital credential presentations?
4. Verifier questions:
a. How many Verifiers exist for the credential type?
b. Is the size of the set of Verifiers growing or shrinking over
time?
c. Are the Verifiers a superset, subset, or disjoint set of the
Issuers or subjects?
d. Are there any legally required reporting or disclosure
requirements associated with the Verifiers?
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e. Is there reason to believe that a Verifier's historic data
will be aggregated and analyzed?
f. Assuming multiple Verifiers are simultaneously compromised,
what knowledge regarding subjects can be inferred from
analyzing the resulting dataset?
5. Subject questions:
a. How many subjects exist for the credential type?
b. Is the size of the set of subjects growing or shrinking over
time?
c. Does the credential type require specific hardware, or
algorithms that limit the set of possible subjects to owners
of specific devices or subscribers to specific services?
16.4. 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.
16.5. Binding the KBT and the CWT
The "iss" 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,
while the identifiers and keys are distinct values. Reusing an
identifier or key enables correlation, 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 "iss" or "sub" 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 "iss" and "sub" 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,
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Holders and Verifiers MUST verify that the "iss" claim of the SD-CWT
corresponds to the Issuer and the key described in the protected
header of the SD-CWT.
Finally, the Verifier MUST verify that the time claims in both the
SD-CWT and SD-KBT are self-consistent and that the SD-KBT is not
valid for any period of time when the SD-CWT is not. Specific tests
for time claims are described in steps 3 and 6 of Section 9.
Likewise, if there is a notion of SD-CWT revocation, an SD-KBT
containing a revoked SD-CWT is not valid.
16.6. Covert Channels
Any data element that is supplied by the Issuer, and that appears
random to the Holder might be used to produce a covert channel
between the Issuer and the Verifier. The ordering of claims, and
precision of timestamps can also be used to produce a covert channel.
This is more of a concern for SD-CWT than typical CWTs, because the
Holder is usually considered to be aware of the Issuer claims they
are disclosing to a Verifier.
16.7. Nested Disclosure Ordering
The Holder has flexibility in determining the order of nested
disclosures when making presentations. The order can be sorted,
randomized, or optimized for performance based on the Holder's needs.
This ordering choice has no security impact on encrypted disclosures.
However, the order can affect the runtime of the verification
process.
16.8. Choice of AEAD algorithms
The AEAD encrypted disclosures mechanism discussed in Section 12.1
can refer to any AEAD alogithm in the IANA AEAD Algorithms registry
(https://www.iana.org/assignments/aead-parameters/aead-
parameters.xhtml) .
When choosing an AEAD algorithm, the tag length is critical for the
integrity of encrypted disclosures in SD-CWT. As such,
implementations MUST NOT use any AEAD algorithm with a tag length
less than 16 octets.
Algorithms using AES-CCM are NOT RECOMMENDED.
As of this writing, implementations MUST NOT use algorithms 3 through
14, 18, 19, 21, 22, 24, 25, 27, or 28. Implementations using the
AEGIS algorithms containing an X MUST only use the 256-bit tag
variant.
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17. IANA Considerations
17.1. COSE Header Parameters
IANA is requested to add the following entries to the IANA "COSE
Header Parameters" registry (https://www.iana.org/assignments/cose/
cose.xhtml#header-parameters):
17.1.1. sd_claims
The following completed registration template per RFC8152 is
provided:
* Name: sd_claims
* Label: 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: Section 4 of this specification
17.1.2. sd_alg
The following completed registration template per RFC8152 is
provided:
* Name: sd_alg
* Label: 170
* Value Type: int
* Value Registry: IANA COSE Algorithms
* Description: The hash algorithm used for redacting disclosures.
* Reference: Section 7 of this specification
17.1.3. sd_aead_encrypted_claims
The following completed registration template per RFC8152 is
provided:
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* Name: sd_aead_encrypted_claims
* Label: 171
* Value Type: [ +[bstr,bstr,bstr] ]
* Value Registry: (empty)
* Description: A list of AEAD encrypted selectively disclosed
claims, which were originally redacted, then later disclosed at
the discretion of the sender.
* Reference: Section 12.1 of this specification
17.1.4. sd_aead
The following completed registration template per RFC8152 is
provided:
* Name: sd_aead
* Label: 172
* Value Type: uint .size 2
* Value Registry: IANA AEAD Algorithm number
* Description: The AEAD algorithm used for encrypting disclosures.
* Reference: Section 12.1 of this specification
17.2. CBOR Simple Values
IANA is requested to add the following entry to the IANA "CBOR Simple
Values" registry (https://www.iana.org/assignments/cbor-simple-
values#simple):
* Value: 59
* Semantics: This value as a map key indicates that the Claim Value
is an array of redacted Claim Keys at the same level as the map
key.
* Specification Document(s): Section 5.1 of this specification
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17.3. CBOR Tags
IANA is requested to add the following entries to the IANA "CBOR
Tags" registry (https://www.iana.org/assignments/cbor-tags/cbor-
tags.xhtml#tags):
17.3.1. 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: 58
* Data Item: (any)
* Semantics: An array claim element intended to be redacted, or a
map key whose key and value are intended to be redacted.
* Specification Document(s): Section 11.1 of this specification
17.3.2. Redacted Claim Element Tag
The byte string inside the tag is a selective disclosure redacted
claim element of an array.
* Tag: 60
* Data Item: byte string
* Semantics: A selective disclosure redacted (array) claim element.
* Specification Document(s): Section 5.1 of this specification
17.3.3. To Be Decoy Tag
The positive integer inside the tag is a unique number to indicate a
specific decoy instance among all the instances in the document.
* Tag: 62 (requested)
* Data Item: uint .gt 0
* Semantics: A marker of a location in a map or an array where a
decoy is intended to be inserted.
* Specification Document(s): Section 11.2 of this specification
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17.4. CBOR Web Token (CWT) Claims
IANA is requested to add the following entry to the IANA "CWT Claims"
registry (https://www.iana.org/assignments/cwt/cwt.xhtml#claims-
registry):
17.4.1. vct
The following completed registration template per RFC8392 is
provided:
* Claim Name: vct
* Claim Description: Verifiable credential type
* JWT Claim Name: vct
* Claim Key: 11
* Claim Value Type(s): bstr
* Change Controller: IETF
* Specification Document(s): Section 13 of this specification
17.5. Media Types
IANA is requested to add the following entries to the IANA "Media
Types" registry (https://www.iana.org/assignments/media-types/media-
types.xhtml#application):
17.5.1. application/sd-cwt
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: Section 16 of this specification and
[RFC8392]
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* Interoperability considerations: n/a
* Published specification: Section 5 of this specification
* 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
* 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
17.5.2. application/kb+cwt
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: Section 16 of this specification and
[RFC8392]
* Interoperability considerations: n/a
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* Published specification: Section 8.1 of this specification
* 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
* 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
17.6. Structured Syntax Suffix
IANA is requested to add the following entry to the IANA "Structured
Syntax Suffix" registry (https://www.iana.org/assignments/media-type-
structured-suffix/media-type-structured-suffix.xhtml#structured-
syntax-suffix):
* Name: SD-CWT
* +suffix: +sd-cwt
* References: Section 5 of this specification
* Encoding considerations: binary
* Interoperability considerations: n/a
* Fragment identifier considerations: n/a
* Security considerations: Section 16 of this specification
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* Contact: See Author's Addresses section
* Author/Change controller: IETF
17.7. Content-Formats
IANA is requested to register the following entries in the IANA "CoAP
Content-Formats" registry (https://www.iana.org/assignments/core-
parameters/core-parameters.xhtml#content-formats):
+====================+================+=====+====================+
| Content-Type | Content Coding | ID | Reference |
+====================+================+=====+====================+
| application/sd-cwt | - | 293 | Section 5 of this |
| | | | specification |
+--------------------+----------------+-----+--------------------+
| application/kb+cwt | - | 294 | Section 8.1 of |
| | | | this specification |
+--------------------+----------------+-----+--------------------+
Table 2: New CoAP Content Formats
17.8. Verifiable Credential Type Identifiers
This specification establishes the Verifiable Credential Type
Identifiers registry, under the IANA "CBOR Web Token (CWT) Claims"
group registry heading (https://www.iana.org/assignments/cwt/
cwt.xhtml). It registers identifiers for the type of the SD-CWT
Claims Set.
It enables short integers in the range 0-65535 to be used as vct
Claim Values, similarly to how CoAP Content-Formats (Section 12.3 of
[RFC7252]) enable short integers to be used as typ header parameter
[RFC9596] values.
The registration procedures for numbers in specific ranges are as
described below:
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+=============+=======================================+
| Range | Registration Procedure |
+=============+=======================================+
| 0-9999 | Specification Required |
+-------------+---------------------------------------+
| 10000-64999 | First Come First Served |
+-------------+---------------------------------------+
| 65000-65535 | Experimental Use (no operational use) |
+-------------+---------------------------------------+
Table 3
Values in the Specification Required [RFC8126] range are registered
after a two-week review period on the spice-ext-review@ietf.org
mailing list, on the advice of one or more Designated Experts. To
allow for the allocation of values prior to publication of the final
version of a specification, the Designated Experts may approve
registration once they are satisfied that the specification will be
completed and published. However, if the specification is not
completed and published in a timely manner, as determined by the
Designated Experts, the Designated Experts may request that IANA
withdraw the registration.
Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register VCT value").
Within the review period, the Designated Experts will either approve
or deny the registration request, communicating this decision to the
review list and IANA. Denials should include an explanation and, if
applicable, suggestions as to how to make the request successful.
The IANA escalation process can be initiated by the party requesting
registration when the Designated Experts are not responsive within 14
days.
Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, determining whether it is likely to be of general
applicability or whether it is useful only for a single application,
and whether the registration makes sense.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration in the Specification
Required range to the review mailing list.
It is suggested that multiple Designated Experts be appointed who are
able to represent the perspectives of different applications using
this specification, in order to enable broadly-informed review of
registration decisions. In cases where a registration decision could
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be perceived as creating a conflict of interest for a particular
Expert, that Expert should defer to the judgment of the other
Experts.
17.8.1. Registration Template
Verifiable Credential Type Identifier String: String identifier for
use as a JWT vct or CWT vct Claim Value. It is a StringOrURI
value.
Verifiable Credential Type Identifier Number: Integer in the range
0-64999 for use as a CWT vct Claim Value. (Integers in the range
65000-65535 are not to be registered.)
Description: Brief description of the verifiable credential type
Change Controller: For IETF stream RFCs, use "IETF". For others,
give the name of the responsible party. Other details (e.g.,
postal address, e-mail address, home page URI) may also be
included.
Specification Document(s): Reference to the document or documents
that specify the values to be registered, preferably including
URLs that can be used to retrieve the documents. An indication of
the relevant sections may also be included, but is not required.
17.8.2. Initial Registry Contents
No initial values are provided for the registry.
18. References
18.1. Normative References
[BCP205] Best Current Practice 205,
<https://www.rfc-editor.org/info/bcp205>.
At the time of writing, this BCP comprises the following:
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>.
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[I-D.ietf-cbor-edn-literals]
Bormann, C., "CBOR Extended Diagnostic Notation (EDN)",
Work in Progress, Internet-Draft, draft-ietf-cbor-edn-
literals-19, 16 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-cbor-
edn-literals-19>.
[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>.
[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>.
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[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>.
18.2. Informative References
[I-D.draft-ietf-cbor-cde]
Bormann, C., "CBOR Common Deterministic Encoding (CDE)",
Work in Progress, Internet-Draft, draft-ietf-cbor-cde-13,
13 October 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-cbor-cde-13>.
[I-D.draft-ietf-keytrans-protocol]
McMillion, B. and F. Linker, "Key Transparency Protocol",
Work in Progress, Internet-Draft, draft-ietf-keytrans-
protocol-03, 19 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-
keytrans-protocol-03>.
[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-13, 6 November
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
oauth-sd-jwt-vc-13>.
[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-22, 29
May 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-oauth-selective-disclosure-jwt-22>.
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[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>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/rfc/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[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>.
[RFC9597] Looker, T. and M.B. Jones, "CBOR Web Token (CWT) Claims in
COSE Headers", RFC 9597, DOI 10.17487/RFC9597, June 2024,
<https://www.rfc-editor.org/rfc/rfc9597>.
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[t-Closeness]
"t-Closeness: Privacy Beyond k-Anonymity and l-Diversity",
4 June 2007,
<https://ieeexplore.ieee.org/document/4221659>.
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) ^ => 293 / "application/sd-cwt",
&(alg: 1) ^ => int,
? &(kid: 4) ^ => bstr,
? &(CWT_Claims: 15) ^ => issued_sd_cwt_map,
? &(sd_alg: 170) ^ => int, ; -16 for sha-256
? &(sd_aead: 172) ^ => uint .size 2,
* label => safe_value
}
kbt-protected = {
&(typ: 16) ^ => 294 / "application/kb+cwt",
&(alg: 1) ^ => int,
&(kcwt: 13) ^ => sd-cwt-issued,
* label => safe_value
}
sd-unprotected = {
? &(sd_claims: 17) ^ => salted-array,
? &(sd_aead_encrypted_claims: 171) ^ => aead-encrypted-array,
* label => safe_value
}
kbt-unprotected = {
* label => safe_value
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}
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) ^ => secs, ; 1883000000
? &(nbf: 5) ^ => secs, ; 1683000000
? &(iat: 6) ^ => secs, ; 1683000000
? &(cti: 7) ^ => bstr,
&(cnf: 8) ^ => safe_map, ; key confirmation
? &(vct: 11) ^ => bstr,
? &(cnonce: 39) ^ => bstr,
;
? redacted_claim_keys ^ => [ * bstr ],
* label => issued_sd_cwt_value
}
kbt-payload = {
&(aud: 3) ^ => tstr, ; "https://verifier.example/app"
? &(exp: 4) ^ => secs, ; 1883000000
? &(nbf: 5) ^ => secs, ; 1683000000
&(iat: 6) ^ => secs, ; 1683000000
? &(cnonce: 39) ^ => bstr,
* label => safe_value
}
; CWT claim legal values only
safe_map = { * label => safe_value }
safe_value =
int / tstr / bstr /
[ * safe_value ] /
safe_map /
#6.<safe_tag>(safe_value) / #7.<safe_simple> / float
; legal values in issued SD-CWT
issued_sd_cwt_map = {
? redacted_claim_keys ^ => [ * bstr ],
* label => issued_sd_cwt_value
}
issued_array_element = redacted_claim_element / issued_sd_cwt_value
issued_sd_cwt_value =
int / tstr / bstr /
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[ * issued_array_element ] /
issued_sd_cwt_map /
#6.<safe_tag>(issued_sd_cwt_value) / #7.<safe_simple> / float
; legal values in claim set sent to Issuer
preissuance_label = label /
#6.<TO_BE_REDACTED_TAGNUM>(label) /
#6.<TO_BE_DECOY_TAGNUM>(int .gt 0)
preissuance_map = { * preissuance_label => preissuance_value }
preissuance_value =
int / tstr / bstr /
[ * preissuance_value ] /
preissuance_map /
#6.<safe_tag>(preissuance_value) / #7.<safe_simple> / float
label = int / tstr .size (1..255)
safe_tag = uint .ne (TO_BE_REDACTED_TAGNUM /
TO_BE_DECOY_TAGNUM /
REDACTED_ELEMENT_TAGNUM)
safe_simple = 0..23 / 32..58 / 60..255 ; exclude redacted keys array
secs = int / float53
float53 = -9007199254740992.0..9007199254740992.0 ; from 2^53 to 2^53
salted-array = [ +bstr-encoded-salted ]
bstr-encoded-salted = bstr .cbor salted-entry
salted-entry = salted-claim / salted-element / decoy
salted-claim = [
bstr .size 16, ; 128-bit salt
any, ; Claim Value
(int / text) ; Claim Key
]
salted-element = [
bstr .size 16, ; 128-bit salt
any ; Claim Value
]
decoy = [
bstr .size 16 ; 128-bit salt
]
aead-encrypted-array = [ +aead-encrypted ]
aead-encrypted = [
bstr .size 16, ; 128-bit nonce
bstr, ; the encryption ciphertext output of a
; bstr-encoded-salted
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bstr ; the corresponding authentication tag
]
; CBOR tag number for wrapping to-be-redacted keys or elements
TO_BE_REDACTED_TAGNUM = 58
; CBOR tag number for indicating a decoy value is to be inserted here
TO_BE_DECOY_TAGNUM = 62
; CBOR tag for wrapping a redacted element in an array
REDACTED_ELEMENT_TAGNUM = 60
; redacted_claim_keys is used as a map key. The corresponding value is
; an array of Blinded Claim Hashes whose corresponding unblinded map keys
; and values are in the same map.
redacted_claim_keys = #7.59 ; CBOR simple value 59
; redacted_claim_element is used in CDDL payloads that contain
; array elements that are meant to be redacted.
redacted_claim_element = #6.<REDACTED_ELEMENT_TAGNUM>( bstr )
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, COSE, and CWT.
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.
The COSE equivalent of the +sd-jwt structured suffix is +sd-cwt.
B.2. Redaction Claims
The COSE equivalent of _sd is a CBOR Simple Value (requested
assignment 59). The following 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.
In SD-CWT, the order of the fields in a disclosure is salt, value,
key. In SD-JWT the order of fields in a disclosure is salt, key,
value. This choice ensures that the second element in the CBOR array
is always the value, which makes parsing faster and more efficient in
strongly-typed programming languages.
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In SD-CWT, all decoy digests are disclosed between the Issuer and the
Holder. In SD-JWT, no disclosure is sent for a decoy digest.
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
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:
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{
/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
{
"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
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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)
{
/kty/ 1 : 2, /EC/
/kid/ 2 : "https://issuer.example/cwk3.cbor",
/alg/ 3 : -51, /ESP384/
/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'
}
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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
{
"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
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-----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. Implementation Status
Note to the 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 made 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.
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".
D.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 specification.
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Maturity: Prototype
Coverage: The current version ('main') implements functionality
similar to that described in this specification, 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 a proof of concept, but is not yet production ready.
Contact: Orie Steele (orie.steele@tradeverifyd.com)
D.2. Rust Prototype
Organization: SimpleLogin
Name: github.com/beltram/esdicawt (https://github.com/beltram/
esdicawt)
Description: An open-source Rust implementation of this specification
in Rust.
Maturity: Prototype
Coverage: The current version is close to the spec with the exception
of redacted_claim_keys using a CBOR SimpleValue as label instead of a
tagged key. Not all of the verifications have been implemented yet.
License: Apache-2.0
Implementation Experience: No interop testing has been done yet. The
code works as a proof of concept, but is not yet production ready.
Contact: Beltram Maldant (beltram.ietf.spice@pm.me)
D.3. Python Prototype
Organization: Tradeverifyd
Name: github.com/tradeverifyd/sd-cwt
(https://github.com/tradeverifyd/sd-cwt)
Description: An open-source Python implementation of this
specification.
Maturity: Prototype
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Coverage: The current version does not implement decoys, but does
verify the test vectors in draft-ietf-spice-sd-cwt-05.
License: Apache-2.0
Implementation Experience: No interop testing has been done yet. The
code works as a proof of concept, but is not yet production ready.
Contact: Orie Steele (orie.steele@tradeverifyd.com)
Appendix E. Relationship between RATS Architecture and Verifiable
Credentials
This appendix describes the relationship between the Remote
ATtestation procedureS (RATS) architecture defined in [RFC9334] and
the three-party model used in verifiable credentials.
E.1. Three-Party Verifiable Credentials Model
The verifiable credentials model involves three distinct parties:
* *Issuer*: Creates and signs credentials containing claims about a
subject
* *Holder*: Controls the credential and presents it to verifiers
(the holder is typically the subject of the credential)
* *Verifier*: Receives and validates presented credentials to make
authorization or access decisions. In this appendix we refer to
this role as a *Credential Verifier*
In SD-CWT, these roles are explicitly represented: the Issuer signs
claims using an Assertion Key (Section 2), the Holder controls the
credential and creates presentations using a Confirmation Key, and
the Verifier validates both the Issuer's signature over the
credential and the Holder's signature over the presentation (key
binding token).
E.2. RATS Architecture Roles
The RATS architecture defines the following key roles:
* *Attester*: Produces Evidence about its own trustworthiness and
operational state
* *Endorser*: Provides Endorsements about an Attester (typically a
manufacturer)
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* *Reference Value Provider*: Supplies Reference Values used by
Verifiers to evaluate Evidence
* *Verifier*: Appraises Evidence and produces Attestation Results.
In this appendix we refer to this role as a *RATS Verifier*
* *Relying Party*: Consumes Attestation Results to make
authorization decisions
E.3. Role Mappings in the Three-Party Model
The mapping between RATS roles and verifiable credential roles can be
understood as follows:
E.3.1. Verifiable Credential Issuer as RATS Endorser
A verifiable credential Issuer functions as a RATS Endorser. The
Endorser role in RATS produces Endorsements - secure statements about
an Attester's capabilities, identity, or trustworthiness. Similarly,
a credential Issuer produces signed credentials containing claims
about a subject (the Holder). Both roles:
* Make authoritative statements about another party's attributes or
capabilities
* Use cryptographic signatures to ensure integrity and authenticity
* Are typically trusted third parties in their respective ecosystems
* Provide information that enables downstream authorization
decisions
The credential issued by the Issuer serves the same function as an
Endorsement in RATS: it is a signed assertion about the Holder's
attributes that can be used by Credential Verifiers to make trust
decisions.
E.3.2. Verifiable Credential Holder as RATS Verifier
A verifiable credential Holder functions as a RATS Verifier. The
RATS Verifier appraises Evidence and Endorsements and produces
Attestation Results. In the credentials model, the Holder:
* Receives credentials (analogous to Endorsements) from Issuers
* Evaluates which credentials to present and which claims to
disclose
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* Produces presentations (analogous to Attestation Results) that are
sent to Credential Verifiers
* Uses their Confirmation Key to create key binding tokens that
prove control
The Holder's presentation, which includes the Issuer's credential
plus the Holder's signature over selected disclosures, functions as
an Attestation Result - a processed, signed assertion derived from
the original credential (Endorsement).
E.3.3. Verifiable Credential Verifier as RATS Relying Party
A verifiable credential Credential Verifier functions as a RATS
Relying Party. The Relying Party:
* Consumes Attestation Results (credential presentations) to make
authorization decisions
* Validates the cryptographic integrity of received assertions
* Makes access control or authorization decisions based on the
claims received
* Does not directly interact with the original Endorsement source
(the Issuer)
The Credential Verifier appraises the Holder's presentation in the
same way a Relying Party appraises Attestation Results from a RATS
Verifier.
E.3.4. All Parties Can Be Attesters
Importantly, any of these parties - Issuer, Holder, or Credential
Verifier - can simultaneously function as a RATS Attester. The
Attester role in RATS is about producing Evidence about one's own
trustworthiness:
* An *Issuer* may be an Attester when it needs to prove its own
integrity, platform state, or authorization to issue certain
credential types. For example, an Issuer might provide Evidence
about its secure enclave or certified infrastructure when
establishing trust with Holders or during credential issuance.
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* A *Holder* may be an Attester when presenting credentials,
particularly when the presentation itself requires proof of the
Holder's platform integrity. For example, a Holder might provide
Evidence about their device's secure boot state, firmware version,
or trusted execution environment alongside their credential
presentation.
* A *Credential Verifier* may be an Attester when it needs to prove
its own trustworthiness to Holders or to upstream systems. For
example, a Credential Verifier might provide Evidence about its
data protection capabilities, compliance certifications, or secure
processing environment before Holders agree to disclose sensitive
claims.
The Attester role is orthogonal to the three primary roles - it
represents the ability to produce evidence about one's own state,
while the Issuer/Holder/Credential Verifier roles represent the flow
of credentials and claims about subjects.
E.4. Comparison with RATS Interaction Models
RATS defines two interaction models:
*Passport Model*: The Attester sends Evidence to a RATS Verifier,
receives Attestation Results, and presents these results to Relying
Parties. This maps to the three-party credentials model where the
Holder obtains credentials from Issuers and presents them to
Credential Verifiers.
*Background-Check Model*: The Attester sends Evidence to a Relying
Party, which forwards it to a RATS Verifier. The RATS Verifier
returns results directly to the Relying Party. This is a two-party
model from the Attester's perspective and does not map well to the
three-party credentials model, as it lacks Holder mediation and
control over presentations.
E.5. Roles That Don't Map to the Three-Party Model
The *Reference Value Provider* role from RATS does not have a direct
equivalent in the three-party verifiable credentials model. This
role supplies reference values (known-good measurements or
configurations) that RATS Verifiers use to appraise Endorsements and
Evidence. In credentials systems, equivalent functionality might be
provided through:
* Trust registries that list authorized Issuers
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* Schema registries, or lists of valid claims that define credential
formats
* Governance frameworks that specify validation rules
* Revocation registries
However, these are typically considered part of the trust
infrastructure rather than a distinct party in the presentation
protocol. The Reference Value Provider role is primarily relevant in
scenarios where raw Evidence must be evaluated against known-good
values - a pattern more common in the two-party background-check
model than in the three-party credentials model where Issuers have
already performed evaluation and produced credentials.
E.6. Application to SD-CWT
When applying RATS concepts to SD-CWT:
* SD-CWT credentials function as Endorsements about the Holder
(subject)
* The Holder's key binding token and selective disclosure act as the
RATS Verifier's appraisal and production of Attestation Results
* The Credential Verifier consumes these presentations as a Relying
Party consumes Attestation Results
* Any party can additionally provide Evidence about their own
platform or operational state (act as an Attester)
* The three-party model with selective disclosure maps naturally to
the RATS passport model
* Reference Value Provider functionality is addressed through trust
infrastructure and out-of-band mechanisms rather than protocol-
level roles
Appendix F. Sample Disclosure Matching Algorithm for Verifier
The Verifier of an SD-CWT needs to decode disclosed claims match them
with their redacted versions. The following example algorithm
describes a way to accomplish this.
1. The decoded sd_claims are converted to an intermediate data
structure called a Digest To Disclosed Claim Map that is used to
transform the Presented Disclosed Claims Set into a Validated
Disclosed Claims Set.
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2. 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 Claims Set.
One possible concrete representation of the intermediate data
structure for the Digest To Disclosed Claim Map is a CBOR map with
the hash of the bstr-encoded-salted data structure (from the CDDL)
as the map key and its value as the contents of the corresponding
salted-entry data structure.
3. The Verifier constructs an empty CBOR map called the Validated
Disclosed Claims Set, and initializes it with all mandatory to
disclose claims from the verified Presented Disclosed Claims Set.
4. Next, the Verifier performs a depth-first traversal of the
Presented Disclosed Claims Set and Validated Disclosed Claims
Set, using the Digest To Disclosed Claim Map to insert claims
into the Validated Disclosed Claims Set when they appear in the
Presented Disclosed Claims Set.
5. The Verifier repeats the fourth step if the previous iteration
resulted in any new Presented Disclosed Claims.
6. If there remain unused claims in the Digest To Disclosed Claim
Map at the end of this procedure the SD-CWT MUST be considered
invalid. Likewise, if this algorithm results in any duplicate
CBOR map keys, the entire SD-CWT MUST be considered invalid.
Note: If there are remaining digests without corresponding
disclosures, this means that either the holder intentionally did
not disclose a claim, or that the digest is a decoy digest
Section 10.
Appendix G. Document History
Note: RFC Editor, please remove this entire section on publication.
G.1. draft-ietf-spice-sd-cwt-06
* Refactored deterministic draft generation code (PR#152).
* Added pointer to a Python implementation (PR#155).
* Added decoy digests (PR#157).
* Addressed early IANA feedback about the escalation process
(PR#160).
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* Used the CoAP Content Type in the examples instead of the text
strings "application/sd-cwt" and "application/kb+cwt" (PR#162).
* Added a section on specific CBOR encoding and data model
considerations (PR#163).
* Swapped the order of Sections 5 and 6 (PR#167).
* Split the CDDL definitions for payload maps in Issued CWT and pre-
issued (PR#168).
* Used the IANA early assigned values in the draft (PR#169).
* Defined the To Be Decoy tag (PR#171).
* Made use of the CoAP Content Type a SHOULD (PR#172).
* Made the draft generation code agnostic to hash algorithm (PR#173)
* Added time claim verification rules and security considerations
(PR#175)
* Instead of an empty array, sd_claims is now omitted if empty
(PR#176)
* Update the COSE header values to use their newly assigned values
(also PR#176)
* Fix some kramdown-xml bracket errors (PR#177)
* Add IANA Considerations for To Be Decoy tag (PR#180)
* Clarify that remaining redacted claims are removed in validated
claim set (PR#181)
* Restrict floating point dates to -2^53 to 2^53 (PR#182)
* Rename CDDL production using a standard prelude name (PR#183)
G.2. draft-ietf-spice-sd-cwt-05
* Added this change log (PR#150)
* Moved non-normative validation algorithm to an appendix (PR#149)
* Added appendix describing mapping to RATS concepts (#147)
* Provided guidance on choice of AEAD algorithm (#148)
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* Fixed algorithm in COSE key examples (#145)
* Updated contact information (PR#142, PR #150)
* Removed SPICE from the title of the document (PR#139)
* Made clear extent to which verifiers cannot process unknown claims
(PR#138)
* Sorted CBOR map keys in examples to facilitate use as test vectors
(PR#135)
* Consistently use term "tag" in context of AEAD algorithms (PR#134)
* Improved AASVG diagram in Terminology section (PR#129)
G.3. draft-ietf-spice-sd-cwt-04
* Place value before claim name in disclosures
* Use CBOR simple value 59 for the redacted_key_claims
* Greatly improved text around AEAD encrypted disclosures
* Applied clarifications and corrections suggested by Mike Jones.
* Do not update CWT [RFC8392].
* Use application/sd-cwt media type and define +sd-cwt structured
suffix.
* Made SHA-256 be the default sd_alg value.
* Created Verifiable Credential Type Identifiers registry.
* Corrected places where Claim Name was used when what was meant was
Claim Key.
* Defined the To Be Redacted CBOR tag
* In the SD-KBT, iss and sub are now forbidden
* Clarified text about aud
* Described Trust Lists
* EDN Examples are now in deterministic order
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* Expressed some validation steps as a list
* Clarified handling of nested claims
* Fixed the handling of the to be registered items in the CDDL; made
CDDL self consistent
* Fixed some references
G.4. 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
G.5. 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)
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* 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)
* Add section saying SD-CWT updates the CWT spec (RFC8392). (PR#29)
G.6. draft-ietf-spice-sd-cwt-01
* Added Overview section
* Rewritten the main normative section
* Made redacted_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
G.7. 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 B.
Jones.
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The authors would like to thank the following individuals for their
contributions to this specification: Michael B. Jones.
Contributors
Michael B. Jones
Self-Issued Consulting
United States
Email: michael_b_jones@hotmail.com
URI: https://self-issued.info/
Authors' Addresses
Michael Prorock
mesur.io
Email: mprorock@mesur.io
Orie Steele
Tradeverifyd
Email: orie@or13.io
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@ietf.contact
Rohan Mahy
Email: rohan.ietf@gmail.com
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