Rule pick with count allows multiple credentials for a single input_descriptor

[TimoGlastra]

• I'm submitting a ...
  [x] bug report

• Summary

The PEX v1 specification mentions:

The Submission Requirement Object MAY contain a count property. If present, its value MUST be an integer greater than zero. This indicates the number of input Descriptors or Submission Requirement Objects to be submitted.

To me this indicates that if you have e.g. a count of 2, at least 2 of the input descriptors need to be submitted. When i query the PEX library using a presentation definition that has a count: 2 it will allow 2 credentials that match the same input descriptor to satisfy the definition requirements. However, I think it should throw an error in this case, as the presentation definition cannot be satisfied. It needs at least two input descriptors, and in this case it will only satisfy one input descriptor, but have two credential for that one input descriptor.

See the JSON documents below for an example of what I mean.

• Other information (e.g. detailed explanation, stack traces, related issues, suggestions how to fix, links for us to have context, eg. StackOverflow, personal fork, etc.)

Credentials

[
   {
      "@context":[
         "https://www.w3.org/2018/credentials/v1",
         "https://www.w3.org/2018/credentials/examples/v2"
      ],
      "id":"http://example.gov/credentials/1231231",
      "type":[
         "VerifiableCredential",
         "UniversityDegreeCredential"
      ],
      "issuer":"did:web:animo.id",
      "issuanceDate":"2020-03-16T22:37:26.544Z",
      "credentialSubject":{
         "id":"did:key:z6MkjRagNiMu91DduvCvgEsqLZDVzrJzFrwahc4tXLt9DoHd",
         "degree":{
            "type":"BachelorDegree",
            "name":"Bachelor of Fights"
         }
      },
      "proof":{
         "type":"Ed25519Signature2018",
         "created":"2020-04-02T18:28:08Z",
         "verificationMethod":"did:web:animo.id#z6MksHh7qHWvybLg5QTPPdG2DgEjjduBDArV9EF9mRiRzMBN",
         "proofPurpose":"assertionMethod",
         "jws":"eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..YtqjEYnFENT7fNW-COD0HAACxeuQxPKAmp4nIl8jYAu__6IH2FpSxv81w-l5PvE1og50tS9tH8WyXMlXyo45CA"
      }
   },
   {
      "@context":[
         "https://www.w3.org/2018/credentials/v1",
         "https://www.w3.org/2018/credentials/examples/v1"
      ],
      "id":"http://example.gov/credentials/131313123",
      "type":[
         "VerifiableCredential",
         "UniversityDegreeCredential"
      ],
      "issuer":"did:web:animo.id",
      "issuanceDate":"2020-03-16T22:37:26.544Z",
      "credentialSubject":{
         "id":"did:key:z6MkjRagNiMu91DduvCvgEsqLZDVzrJzFrwahc4tXLt9DoHd",
         "degree":{
            "type":"BachelorDegree",
            "name":"Bachelor of Something"
         }
      },
      "proof":{
         "type":"Ed25519Signature2018",
         "created":"2020-04-02T18:28:08Z",
         "verificationMethod":"did:web:animo.id#z6MksHh7qHWvybLg5QTPPdG2DgEjjduBDArV9EF9mRiRzMBN",
         "proofPurpose":"assertionMethod",
         "jws":"eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..YtqjEYnFENT7fNW-COD0HAACxeuQxPKAmp4nIl8jYAu__6IH2FpSxv81w-l5PvE1og50tS9tH8WyXMlXyo45CA"
      }
   }
]

Presentation Definition

{
   "id":"31e2f0f1-6b70-411d-b239-56aed5321884",
   "purpose":"To check if you have a valid college degree.",
   "input_descriptors":[
      {
         "id":"df2accf9-1ecb-4f4e-af6d-21be152a881b",
         "group":[
            "A"
         ],
         "purpose":"You must have a valid Bachelor Degree issued by Animo.",
         "schema":[
            {
               "uri":"https://www.w3.org/2018/credentials/v1"
            }
         ],
         "constraints":{
            "fields":[
               {
                  "path":[
                     "$.issuer",
                     "$.vc.issuer",
                     "$.iss"
                  ],
                  "filter":{
                     "type":"string",
                     "pattern":"did:web:animo.id"
                  }
               }
            ]
         }
      },
      {
         "id":"867bfe7a-5b91-46b2-9ba4-70028b8d9cc8",
         "purpose":"You must have a valid Bachelor Degree issued by Transmute.",
         "group":[
            "A"
         ],
         "schema":[
            {
               "uri":"https://www.w3.org/2018/credentials/v1"
            }
         ],
         "constraints":{
            "fields":[
               {
                  "path":[
                     "$.issuer",
                     "$.vc.issuer",
                     "$.iss"
                  ],
                  "filter":{
                     "type":"string",
                     "pattern":"did:web:vc.transmute.world"
                  }
               }
            ]
         }
      }
   ],
   "submission_requirements":[
      {
         "name":"Pick Count",
         "rule":"pick",
         "from":"A",
         "count":2
      }
   ]
}

Select Results

{
   "errors":[
      
   ],
   "matches":[
      {
         "rule":"pick",
         "from":[
            "A"
         ],
         "vc_path":[
            "$.verifiableCredential[0]",
            "$.verifiableCredential[1]"
         ],
         "name":"df2accf9-1ecb-4f4e-af6d-21be152a881b",
         "count":2
      }
   ],
   "areRequiredCredentialsPresent":"info",
   "verifiableCredential":[
      {
         "@context":[
            "https://www.w3.org/2018/credentials/v1",
            "https://www.w3.org/2018/credentials/examples/v2"
         ],
         "id":"http://example.gov/credentials/1231231",
         "type":[
            "VerifiableCredential",
            "UniversityDegreeCredential"
         ],
         "issuer":"did:web:animo.id",
         "issuanceDate":"2020-03-16T22:37:26.544Z",
         "credentialSubject":{
            "id":"did:key:z6MkjRagNiMu91DduvCvgEsqLZDVzrJzFrwahc4tXLt9DoHd",
            "degree":{
               "type":"BachelorDegree",
               "name":"Bachelor of Fights"
            }
         },
         "proof":{
            "type":"Ed25519Signature2018",
            "created":"2020-04-02T18:28:08Z",
            "verificationMethod":"did:web:animo.id#z6MksHh7qHWvybLg5QTPPdG2DgEjjduBDArV9EF9mRiRzMBN",
            "proofPurpose":"assertionMethod",
            "jws":"eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..YtqjEYnFENT7fNW-COD0HAACxeuQxPKAmp4nIl8jYAu__6IH2FpSxv81w-l5PvE1og50tS9tH8WyXMlXyo45CA"
         }
      },
      {
         "@context":[
            "https://www.w3.org/2018/credentials/v1",
            "https://www.w3.org/2018/credentials/examples/v1"
         ],
         "id":"http://example.gov/credentials/131313123",
         "type":[
            "VerifiableCredential",
            "UniversityDegreeCredential"
         ],
         "issuer":"did:web:animo.id",
         "issuanceDate":"2020-03-16T22:37:26.544Z",
         "credentialSubject":{
            "id":"did:key:z6MkjRagNiMu91DduvCvgEsqLZDVzrJzFrwahc4tXLt9DoHd",
            "degree":{
               "type":"BachelorDegree",
               "name":"Bachelor of Something"
            }
         },
         "proof":{
            "type":"Ed25519Signature2018",
            "created":"2020-04-02T18:28:08Z",
            "verificationMethod":"did:web:animo.id#z6MksHh7qHWvybLg5QTPPdG2DgEjjduBDArV9EF9mRiRzMBN",
            "proofPurpose":"assertionMethod",
            "jws":"eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..YtqjEYnFENT7fNW-COD0HAACxeuQxPKAmp4nIl8jYAu__6IH2FpSxv81w-l5PvE1og50tS9tH8WyXMlXyo45CA"
         }
      }
   ],
   "warnings":[
      
   ]
}

[nklomp]

Should be fixed in release 2.1.0