SPICE SD-CWT

1.1. High-Level Flow

Figure 1: High-level SD-CWT Issuance and Presentation Flow¶

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.¶

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.¶

{
    / 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:¶

/ cose-sign1 / 18([  / issuer SD-CWT /
  / CWT protected / << {
    / alg /    1  : -35, / ES384 /
    / typ /    16 : "application/sd-cwt",
    / kid /    4  : 'https://issuer.example/cwt-key3',
    / sd_alg / 18 : -16  / SHA256 /
  } >>,
  / CWT unprotected / {
    / sd_claims / 17 : [ / these are all the disclosures /
        <<[
            /salt/   h'bae611067bb823486797da1ebbb52f83',
            /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'
      }
    },
    /most_recent_inspection_passed/ 500: true,
    / redacted_claim_keys / simple(59) : [
        / redacted inspector_license_number /
        h'3fc9748e00684e6442641e58ea965468
          085024da253ed46b507ae56d4c204434'
    ],
    /inspection_dates/ 502 : [
        / redacted inspection date 7-Feb-2019 /
        60(h'f468b68dd7432030d7f33a8783acb3a4
             d6afc215bbc184dce8831c64b539f335'),
        / redacted inspection date 4-Feb-2021 /
        60(h'0839dcbdd9ed55c8aac3e573ccf59c81
             0fa8d9f6ec551cb9737621faf3584e1f'),
        1674004740,   / 2023-01-17T17:19:00 /
    ],
    / inspection_location / 503 : {
        "country" : "us",            / United States /
        / redacted_claim_keys / simple(59) : [
            / redacted region /
            h'2ff24f519a1bdfc66292263de2415a36
              6b9a4302d2a9f36b9791f8eab1867513'
            / redacted postal_code /
            h'f907645d118184af56331cb07b7b8c31
              826ac7d18d051bcec37a3a8afb8581c3'
      ]
    }
  } >>,
  / CWT signature / h'9280a520b8686183bf72cd07c714e603
                      ff0975b357975a1391de51a248d554e1
                      b93d0d101edb6bf11a4a98aa9714d823
                      c84d1d6c438e5d733a4f67c16e1ff030
                      ae3f4b1c546ecc9e9add168da97e32e1
                      c5b8de5b873c9572ecb9f219399c5a9f'
])

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 name, and claim value.¶

        <<[
            /salt/   h'bae611067bb823486797da1ebbb52f83',
            /value/  "ABCD-123456",
            /claim/  501   / inspector_license_number /
        ]>>,

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)

The cryptographic hash, using the hash algorithm identified by the sd_alg header parameter in the protected headers, of that byte string is the Digested Salted Disclosed Claim (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

Finally, since this redacted claim is a map key and value, the Digested Salted Disclosed Claim is placed in a redacted_claim_keys array in the SD-CWT payload at the same level of hierarchy as the original claim. Redacted claims that are array elements are handled slightly differently, as described in Section 6.1.¶

  / redacted_claim_keys / simple(59) : [
      / redacted inspector_license_number /
      h'd9df03da474fcb3c65771748e2e0608c
        f437504ecc24f450aaeacd40dd552b3f',
      / ... next redacted claim at the same level would go here /  ],

6.1. 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.¶

salted = salted-claim / salted-element / decoy
salted-claim = [
  bstr .size 16,     ; 128-bit salt
  any,               ; claim value
  (int / text)       ; claim name
]
salted-element = [
  bstr .size 16,     ; 128-bit salt
  any                ; claim value
]
decoy = [
  bstr .size 16      ; 128-bit salt
]

; a collection of Salted Disclosed Claims
salted-array = [ +bstr .cbor salted ]

When a blinded claim is a key in a map, its blinded claim hash is added to a redacted_claim_keys array claim in the CWT payload that is at the same level of hierarchy as the key being blinded. The redacted_claim_keys key is the CBOR simple type TBD4 registered for that purpose (with the requested value of 59).¶

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 TBD5 (requested tag number 60).¶

; redacted_claim_element = #6.<TBD5>( bstr ) -- RFC 9682 syntax
redacted_claim_element = #6.60( 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 13.2.¶

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.¶

7.1. Issuer Generation

The Issuer follows all the requirements of generating a valid SD-CWT, largely a CWT extended by Section 5. 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;¶

• 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 13.2) has a corresponding Salted Disclosed Claim, and vice versa;¶

• all the Salted Disclosed Claims are correct in their unblinded context in the payload.¶

The following informative CDDL is provided to describe the syntax for SD-CWT issuance. A complete CDDL schema is in Appendix A.¶

sd-cwt-issued = #6.18([
   protected: bstr .cbor sd-protected,
   sd-unprotected,
   payload: bstr .cbor sd-payload,
   signature: bstr
])

sd-protected = {
   &(typ: 16) ^ => "application/sd-cwt" / TBD11,
   &(alg: 1) ^ => int,
   &(sd_alg: TBD2) ^ => int,        ; -16 for sha-256
   ? &(sd_aead: TBD7) ^ => uint .size 2
   * key => any
}

sd-unprotected = {
   ? &(sd_claims: TBD1) ^ => salted-array,
   ? &(sd_encrypted_claims: TBD6) ^ => encrypted-array,
   ? &(sd_cose_encrypted_claims: TBD8) ^ => cose-encrypted-array,
   * key => any
}

sd-payload = {
    ; standard claims
      &(iss: 1) ^ => tstr, ; "https://issuer.example"
    ? &(sub: 2) ^ => tstr, ; "https://device.example"
    ? &(aud: 3) ^ => tstr, ; "https://verifier.example/app"
    ? &(exp: 4) ^ => int,  ; 1883000000
    ? &(nbf: 5) ^ => int,  ; 1683000000
    ? &(iat: 6) ^ => int,  ; 1683000000
    ? &(cti: 7) ^ => bstr,
      &(cnf: 8) ^ => { * key => any }, ; key confirmation
    ? &(cnonce: 39) ^ => bstr,
    ;
    ? &(redacted_claim_keys: REDACTED_KEYS) ^ => [ * bstr ],
    * key => any
}

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 TBD12.¶

The SD-KBT provides the following assurances to the Verifier:¶

• the Holder of the SD-CWT controls the confirmation method chosen by the Issuer;¶

• the Holder's disclosures have not been tampered with since confirmation occurred;¶

• the Holder intended to address the SD-CWT to the Verifier specified in the audience (aud) claim;¶

• the Holder's disclosure is linked to the creation time (iat) of the key binding.¶

The SD-KBT prevents an attacker from copying and pasting disclosures, or from adding or removing disclosures without detection. Confirmation is established according to [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) ^ => "application/kb+cwt" / TBD12,
   &(alg: 1) ^ => int,
   &(kcwt: 13) ^ => sd-cwt-issued,
   * key => any
}

kbt-unprotected = {
   * key => any
}

kbt-payload = {
      &(aud: 3) ^ => tstr, ; "https://verifier.example/app"
    ? &(exp: 4) ^ => int,  ; 1883000000
    ? &(nbf: 5) ^ => int,  ; 1683000000
      &(iat: 6) ^ => int,  ; 1683000000
    ? &(cnonce: 39) ^ => bstr,
    * key => any
}

The SD-KBT payload MAY include a cnonce claim. If included, the cnonce is a bstr and MUST be treated as opaque to the Holder. All other claims are OPTIONAL in an SD-KBT.¶

11.1. AEAD Encrypted Disclosures

This section defines two new COSE Header Parameters. If present in the protected headers, the first header parameter (sd_aead) specifies an IANA registered Authenticated Encryption with Additional Data (AEAD) algorithm [RFC5116]. The second header parameter (sd_encrypted_claims) contains a 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 nonce (nonce), and the resulting ciphertext and mac are put in an array. The resulting array is placed in the sd_encrypted_claims header parameter in the unprotected headers of the SD-CWT.¶

• The encryption mechanism in this section uses the AEAD algorithm directly instead of COSE encryption, because AEAD is more broadly applicable to some of the other protocols in which encrypted disclosures might be used.¶

/ sd_encrypted_claims / 19 : [ / encrypted disclosures /
    [
        / nonce /      h'95d0040fe650e5baf51c907c31be15dc',
        / ciphertext / h'208cda279ca86444681503830469b705
                         89654084156c9e65ca02f9ac40cd62b5
                         a2470d',
        / mac /        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 encrypted disclosure locates the appropriate key by looking up the mac. If the verifier is able to 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 the specific protocols that make use of encrypted disclosures.¶

The CDDL for encrypted disclosures is below.¶

encrypted-array = [ +encrypted ]
encrypted = [
  bstr,              ; nonce value
  bstr,              ; the ciphertext output of a bstr-encoded-salted
                     ;   with a matching salt
  bstr               ; the corresponding MAC
]
;bstr-encoded-salted = bstr .cbor salted

• Note: Because the algorithm is in a registry that contains only AEAD algorithms, an attacker cannot replace the algorithm or the message, without a decryption verification failure.¶

11.2. COSE Encrypted Disclosures

This section defines the new COSE Header Parameter (sd_cose_encrypted_claims) that contains a list of tagged COSE_Encrypt0 or COSE_Encrypt encrypted disclosures, following the rules defined in [RFC9502].¶

Its contents have the same semantics as the AEAD encrypted disclosures in the previous section.¶

Taking the bstr encoding of the example disclosure in the previous section as the payload, the key and nonce from the previous section, and encrypting with COSE_Encrypt0 using the COSE A128GCM algorithm, yields the following COSE encrypted disclosure.¶

/ sd_cose_encrypted_claims / 21 : [
    /COSE_Encrypt0/  16([
      /protected/ {
        /alg/ 1: 1, /A128GCM/
        /IV/  5: h'95d0040fe650e5baf51c907c31be15dc'
      },
      /unprotected/ {},
      /ciphertext/ h'f5e33642feca31cacb5325db179663e8
                     540336178526f0803c0b13b17e3eb2f9
                     e3c323087a0345c76c163d300b1b3346
                     49ce511302fd147b2ab125297cf540cf
                     4f9e'
    ]),
    ...
]

The CDDL for COSE encrypted disclosures is below:¶

cose-encrypted-array = [ +cose-encrypted ]
cose-encrypted = COSE_Encrypt0_Tagged / COSE_Encrypt_Tagged

The IANA COSE Algorithms registry contains deprecated and unsafe algorithms. Implementations using COSE encrypted disclosures MUST select only fully-specified signature algorithms, authenticated encryption (AEAD) algorithms, and SHOULD preferably use algorithms that have a "Yes" in the "Recommended" column of the IANA COSE Algorithms registry.¶

13.1. Minimal Spanning Example

The following example contains claims needed to demonstrate redaction of key-value pairs and array elements.¶

/ cose-sign1 / 18( / sd_kbt / [
  / KBT protected / << {
    / alg /    1:  -7, / ES256 /
    / typ /   16:  "application/kb+cwt",
    / kcwt /  13:  18([  / issuer SD-CWT /
      / CWT protected / << {
        / alg /    1  : -35, / ES384 /
        / typ /    16 : "application/sd-cwt",
        / kid /    4  : 'https://issuer.example/cwt-key3',
        / sd_alg / 18 : -16  / SHA256 /
      } >>,
      / CWT unprotected / {
        / sd_claims / 17 : [ / these are the disclosures /
            <<[
                /salt/   h'bae611067bb823486797da1ebbb52f83',
                /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'
          }
        },
        /most_recent_inspection_passed/ 500: true,
        / redacted_claim_keys / simple(59) : [
            / redacted inspector_license_number /
            h'3fc9748e00684e6442641e58ea965468
              085024da253ed46b507ae56d4c204434'
        ],
        /inspection_dates/ 502 : [
            / redacted inspection date 7-Feb-2019 /
            60(h'f468b68dd7432030d7f33a8783acb3a4
                 d6afc215bbc184dce8831c64b539f335'),
            / redacted inspection date 4-Feb-2021 /
            60(h'0839dcbdd9ed55c8aac3e573ccf59c81
                 0fa8d9f6ec551cb9737621faf3584e1f'),
            1674004740,   / 2023-01-17T17:19:00 /
        ],
        / inspection_location / 503 : {
            "country" : "us",            / United States /
            / redacted_claim_keys / simple(59) : [
                / redacted region /
                h'2ff24f519a1bdfc66292263de2415a36
                  6b9a4302d2a9f36b9791f8eab1867513'
                / redacted postal_code /
                h'f907645d118184af56331cb07b7b8c31
                  826ac7d18d051bcec37a3a8afb8581c3'
          ]
        }
      } >>,
      / CWT signature / h'9280a520b8686183bf72cd07c714e603
                          ff0975b357975a1391de51a248d554e1
                          b93d0d101edb6bf11a4a98aa9714d823
                          c84d1d6c438e5d733a4f67c16e1ff030
                          ae3f4b1c546ecc9e9add168da97e32e1
                          c5b8de5b873c9572ecb9f219399c5a9f'
    ])
     / end of issuer SD-CWT /
  } >>,     / end of KBT protected header /
  / KBT unprotected / {},
  / KBT payload / << {
    / cnonce / 39    : h'8c0f5f523b95bea44a9a48c649240803',
    / aud    /  3    : "https://verifier.example/app",
    / iat    /  6    : 1725244237, / 2024-09-02T02:30:37+00:00Z /
  } >>,      / end of KBT payload /
  / KBT signature / h'18889767bd8f2faf18dc6a99571724d7
                      b1051ff1c1b694d3bb2e304891b3b8bd
                      a36b133e9ab920fe8a8a45b7d41deba0
                      44c226f87d8b663c5f049d445594aec5'
])   / end of kbt /

13.2. 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.¶

{
    / 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 /
            }
        },
    ]
}

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'
                     ]
                 },
        /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:¶

{
    / iss / 1  : "https://issuer.example",
    / sub / 2  : "https://device.example",
    / exp / 4  : 1725330600, /2024-09-02T19:30:00Z/
    / nbf / 5  : 1725243840, /2024-09-01T19:25:00Z/
    / iat / 6  : 1725244200, /2024-09-01T19:30:00Z/
    / cnf / 8  : { ... },
    504: [                      / inspection history log /
        {
            500: True,          / inspection passed /
            502: 1549560720,    / 2019-02-07T17:32:00 /
            501: "DCBA-101777", / inspector license /
            503: {
                1: "us"         / United States /
            }
        },
        {
            500: True,          / inspection passed /
            502: 17183928,      / 2023-01-17T17:19:00 /
            501: "ABCD-123456", / inspector license /
            503: {
                1: "us",        / United States /
                2: "ca"         / region=California /
            }
        },
    ]
}

14.1. Transparency

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 associated with the issuer. Certificate transparency, as described in [RFC9162], or key transparency, as described in [I-D.draft-ietf-keytrans-protocol], can enable the observation of incorrectly issued certificates or fraudulent bindings between verification keys and issuer identifiers. Issuers choose which claims to include in an SD-CWT, and whether they are mandatory to disclose, including self-asserted claims such as "iss". All mandatory to disclose data elements are visible to the verifier as part of verification. Some of these elements reveal information about the issuer, such as key or certificate thumbprints, supported digital signature algorithms, and operational windows that can be inferred from analysis of timestamps.¶

14.2. 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 with sufficiently low "anonymity set" can be used to track the subject. For example, a high precision issuance time might match the issuance of only a few credentials for a given issuer, and as such, any presentation of a credential issued at that time can be determined to be associated with the set of credentials issued at that time, for those subjects.¶

14.3. Credential Types

The mandatory- and optional-to-disclose data elements in an SD-CWT are credential type specific. Several distinct credential types might be applicable to a given use case. Issuers MUST perform a privacy and confidentiality assessment regarding each credential type they intend to issue prior to issuance.¶

14.4. Determinism & Augmentation

It is possible to encode additional information through the choices made during the serialization stage of producing an SD-CWT, for example, by adjusting the order of CBOR map keys, or by choosing different numeric encodings for certain data elements. [I-D.draft-ietf-cbor-cde] provides guidance for constructing application profiles that constrain serialization optionality beyond CBOR Common Deterministic Encoding rulesets (CDE). The construction of such profiles has a significant impact on the privacy properties of a credential type.¶

14.5. Threat Model

Each use case will have a unique threat model that MUST be considered before the applicability of SD-CWT-based credential types can be determined. This section provides a non-exhaustive list of topics to be considered when developing a threat model for applying SD-CWT to a given use case.¶

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:¶

   1. How many issuers exist for the credential type?¶

   2. Is the size of the set of issuers growing or shrinking over time?¶

   3. 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?¶

   4. Does the credential type require or offer the ability to disclose a globally unique identifier?¶

   5. 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?¶

   6. Does the credential type contain Personally Identifiable Information (PII), or other sensitive information that might have value in a market?¶

3. Verifier questions:¶

   1. How many verifiers exist for the credential type?¶

   2. Is the size of the set of verifiers growing or shrinking over time?¶

   3. Are the verifiers a superset, subset, or disjoint set of the issuers or subjects?¶

   4. Are there any legally required reporting or disclosure requirements associated with the verifiers?¶

   5. Is there reason to believe that a verifier's historic data will be aggregated and analyzed?¶

   6. Assuming multiple verifiers are simultaneously compromised, what knowledge regarding subjects can be inferred from analyzing the resulting dataset?¶

4. Subject questions:¶

   1. How many subjects exist for the credential type?¶

   2. Is the size of the set of subjects growing or shrinking over time?¶

   3. 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?¶

14.6. Random Numbers

Each salt used to protect disclosed claims MUST be generated independently from the salts of other claims. The salts MUST be generated from a source of entropy that is acceptable to the issuer. Poor choice of salts can lead to brute force attacks that can reveal redacted claims.¶

14.7. Binding the KBT and the CWT

The issuer claim in the SD-CWT is self-asserted by the issuer.¶

Because confirmation is mandatory, the subject claim of an SD-CWT, when present, is always related directly to the confirmation claim. There might be many subject claims and many confirmation keys that identify the same entity or that are controlled by the same entity, 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 issuer or subject claims are not present. If they are present, they are self-asserted by the Holder. All three are represented by the confirmation (public) key in the SD-CWT.¶

As with any self-assigned identifiers, Verifiers need to take care to verify that the SD-KBT issuer and subject claims match the subject in the SD-KBT, and are a valid representation of the Holder and correspond to the Holder's confirmation key. Extra care should be taken in case the SD-CWT subject claim is redacted. Likewise, Holders and Verifiers MUST verify that the issuer claim of the SD-CWT corresponds to the Issuer and the key described in the protected header of the SD-CWT.¶

14.8. 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.¶

14.9. 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.¶

14.10. 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.¶

15.1. COSE Header Parameters

IANA is requested to add the following entries to the IANA "COSE Header Parameters" registry:¶

15.2. CBOR Simple Values

IANA is requested to add the following entry to the IANA "CBOR Simple Values" registry:¶

• Value: TBD4 (requested assignment 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 6.1 of this specification¶

15.3. CBOR Tags

IANA is requested to add the following entries to the IANA "CBOR Tags" registry:¶

15.4. CBOR Web Token (CWT) Claims

IANA is requested to add the following entry to the IANA "CWT Claims" registry:¶

15.5. 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):¶

15.6. Structured Syntax Suffix

IANA is requested to add the following entry to the IANA "Structured Syntax Suffix" registry:¶

• Name: SD-CWT¶

• +suffix: +sd-cwt¶

• References: Section 6 of this specification¶

• Encoding considerations: binary¶

• Interoperability considerations: n/a¶

• Fragment identifier considerations: n/a¶

• Security considerations: Section 14 of this specification¶

• Contact: See Author's Addresses section¶

• Author/Change controller: IETF¶

15.7. Content-Formats

IANA is requested to register the following entries in the IANA "CoAP Content-Formats" registry:¶

If possible, TBD11 and TBD12 should be assigned in the 256..9999 range.¶

15.8. Verifiable Credential Type Identifiers

This specification establishes the Verifiable Credential Type Identifiers registry, under the IANA "CBOR Web Token (CWT) Claims" group registry heading. 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:¶

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 is followed 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 be perceived as creating a conflict of interest for a particular Expert, that Expert should defer to the judgment of the other Experts.¶

16.1. 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>.

[I-D.ietf-cbor-edn-literals]

Bormann, C., "CBOR Extended Diagnostic Notation (EDN)", Work in Progress, Internet-Draft, draft-ietf-cbor-edn-literals-17, 12 May 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-cbor-edn-literals-17>.

[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>.

[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>.

[RFC9502]

Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica, R., and P. Psenak, "IGP Flexible Algorithm in IP Networks", RFC 9502, DOI 10.17487/RFC9502, November 2023, <https://www.rfc-editor.org/rfc/rfc9502>.

[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>.

16.2. Informative References

[I-D.draft-ietf-cbor-cde]

Bormann, C., "CBOR Common Deterministic Encoding (CDE)", Work in Progress, Internet-Draft, draft-ietf-cbor-cde-11, 12 May 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-cbor-cde-11>.

[I-D.draft-ietf-keytrans-protocol]

McMillion, B. and F. Linker, "Key Transparency Protocol", Work in Progress, Internet-Draft, draft-ietf-keytrans-protocol-01, 4 June 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-keytrans-protocol-01>.

[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-09, 28 May 2025, <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-sd-jwt-vc-09>.

[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>.

[I-D.ietf-httpbis-unprompted-auth]

Schinazi, D., Oliver, D., and J. Hoyland, "The Concealed HTTP Authentication Scheme", Work in Progress, Internet-Draft, draft-ietf-httpbis-unprompted-auth-12, 19 September 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-unprompted-auth-12>.

[I-D.mahy-mls-sd-cwt-credential]

Mahy, R., "Messaging Layer Security credentials using Selective Disclosure CBOR Web Tokens", Work in Progress, Internet-Draft, draft-mahy-mls-sd-cwt-credential-00, 2 March 2025, <https://datatracker.ietf.org/doc/html/draft-mahy-mls-sd-cwt-credential-00>.

[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>.

[RFC9162]

Laurie, B., Messeri, E., and R. Stradling, "Certificate Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162, December 2021, <https://www.rfc-editor.org/rfc/rfc9162>.

[RFC9334]

Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote ATtestation procedureS (RATS) Architecture", RFC 9334, DOI 10.17487/RFC9334, January 2023, <https://www.rfc-editor.org/rfc/rfc9334>.

[RFC9420]

Barnes, R., Beurdouche, B., Robert, R., Millican, J., Omara, E., and K. Cohn-Gordon, "The Messaging Layer Security (MLS) Protocol", RFC 9420, DOI 10.17487/RFC9420, July 2023, <https://www.rfc-editor.org/rfc/rfc9420>.

[t-Closeness]

"t-Closeness: Privacy Beyond k-Anonymity and l-Diversity", 4 June 2007, <https://ieeexplore.ieee.org/document/4221659>.

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.¶

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.¶

C.1. Subject / Holder

Holder COSE key pair in EDN format¶

{
  /kty/  1 : 2, /EC/
  /alg/  3 : -9, /ESP256/
  /crv/ -1 : 1, /P-256/
  /x/   -2 : h'8554eb275dcd6fbd1c7ac641aa2c90d9
               2022fd0d3024b5af18c7cc61ad527a2d',
  /y/   -3 : h'4dc7ae2c677e96d0cc82597655ce92d5
               503f54293d87875d1e79ce4770194343',
  /d/   -4 : h'5759a86e59bb3b002dde467da4b52f3d
               06e6c2cd439456cf0485b9b864294ce5'
}

The fields necessary for the COSE Key Thumbprint [RFC9679] in EDN format:¶

{
  /kty/  1 : 2, /EC/
  /crv/ -1 : 1, /P-256/
  /x/   -2 : h'8554eb275dcd6fbd1c7ac641aa2c90d9
               2022fd0d3024b5af18c7cc61ad527a2d',
  /y/   -3 : h'4dc7ae2c677e96d0cc82597655ce92d5
               503f54293d87875d1e79ce4770194343'
}

The same map in CBOR pretty printing¶

A4                                      # map(4)
   01                                   # unsigned(1)
   02                                   # unsigned(2)
   20                                   # negative(0)
   01                                   # unsigned(1)
   21                                   # negative(1)
   58 20                                # bytes(32)
      8554EB275DCD6FBD1C7AC641AA2C90D92022FD0D3024B5AF18C7CC61AD527A2D
   22                                   # negative(2)
   58 20                                # bytes(32)
      4DC7AE2C677E96D0CC82597655CE92D5503F54293D87875D1E79CE4770194343

The COSE thumbprint (in hexadecimal)--SHA256 hash of the thumbprint fields:¶

8343d73cdfcb81f2c7cd11a5f317be8eb34e4807ec8c9ceb282495cffdf037e0

Holder key pair in JWK format¶

{
  "kty": "EC",
  "alg": "ES256",
  "kid": "WRQ2RbY5RYJCIxfDQL9agl9fFSCYVu4Xocqb6zerc1M",
  "crv": "P-256",
  "x": "hVTrJ13Nb70cesZBqiyQ2SAi_Q0wJLWvGMfMYa1Sei0",
  "y": "TceuLGd-ltDMgll2Vc6S1VA_VCk9h4ddHnnOR3AZQ0M",
  "d": "V1moblm7OwAt3kZ9pLUvPQbmws1DlFbPBIW5uGQpTOU"
}

Input to Holder public JWK thumbprint (ignore line breaks)¶

{"crv":"P-256","kty":"EC","x":"hVTrJ13Nb70cesZBqiyQ2SAi_Q0wJLWvGMfMYa1S
ei0","y":"TceuLGd-ltDMgll2Vc6S1VA_VCk9h4ddHnnOR3AZQ0M"}

SHA-256 of the Holder public JWK input string (in hex)¶

59143645b6394582422317c340bf5a825f5f15209856ee17a1ca9beb37ab7353

Holder public JWK thumbprint¶

WRQ2RbY5RYJCIxfDQL9agl9fFSCYVu4Xocqb6zerc1M

Holder public key in PEM format¶

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEhVTrJ13Nb70cesZBqiyQ2SAi/Q0w
JLWvGMfMYa1Sei1Nx64sZ36W0MyCWXZVzpLVUD9UKT2Hh10eec5HcBlDQw==
-----END PUBLIC KEY-----

Holder private key in PEM format¶

-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgV1moblm7OwAt3kZ9
pLUvPQbmws1DlFbPBIW5uGQpTOWhRANCAASFVOsnXc1vvRx6xkGqLJDZICL9DTAk
ta8Yx8xhrVJ6LU3HrixnfpbQzIJZdlXOktVQP1QpPYeHXR55zkdwGUND
-----END PRIVATE KEY-----

C.2. Issuer

Issuer COSE key pair in Extended Diagnostic Notation (EDN)¶

{
  /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'
}

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¶

-----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-----

D.1. Transmute Prototype

Organization: Transmute Industries Inc¶

Name: github.com/transmute-industries/sd-cwt¶

Description: An open-source implementation of this specification.¶

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@transmute.industries)¶

D.2. Rust Prototype

Organization: SimpleLogin¶

Name: 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)¶

E.1. draft-ietf-spice-sd-cwt-04

• use CBOR simple value 59 for the redacted_key_claims¶

• add description of decoy digests TODO¶

• provide test vectors TODO¶

• add AEAD and COSE 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.¶

E.2. 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¶

E.3. draft-ietf-spice-sd-cwt-02

• KBT now includes the entire SD-CWT in the Confirmation Key CWT (kcwt) existing COSE protected header. Has algorithm now specified in new sd_alg COSE protected header. No more sd_hash claim. (PR #34, 32)¶

• Introduced tags for redacted and to-be-redacted claim keys and elements. (PR#31, 28)¶

• Updated example to be a generic inspection certificate. (PR#33)¶

• Add section saying SD-CWT updates the CWT spec (RFC8392). (PR#29)¶

E.4. draft-ietf-spice-sd-cwt-01

• Added Overview section¶

• Rewrote 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¶

E.5. draft-ietf-spice-sd-cwt-00

• Initial working group version based on draft-prorock-spice-cose-sd-cwt-01.¶