discloseValues function

String discloseValues(dynamic plaintextCredential, List<String> valuesToDisclose)

Discloses all values in valuesToDisclose of plaintextCredential.

valuesToDisclose contains the keys of the attributes, that should be disclosed. Keys in nested object should be separated with . (point) from the parent-key, like here: Imagine your plaintext Credential look like this:

{
  "@context": [
    "https://bccm-ssi.hs-mittweida.de/credentials"
  ],
  "type": "ImmatrikulationCredential",
  "issuanceDate": {
    "value": "2021-03-09",
    "salt": "0830fac0-ae9e-4097-85b0-03ddb3557eb6",
    "hash": "0x9e51f7c66036d0eb2fcc3c1c5d9da18f96ae880681a676dcc92a3be22e4d7523"
  },
  "student": {
    "type": "Student",
    "givenName": {
      "value": "Max",
      "salt": "b36a876c-2029-417a-93fb-b4daf75ed959",
      "hash": "0x30aa2b081c358aafdbbeb9436a167ee9e5bb003a8bd892ef33d50ba78ce1834e"
    },
    "familyName": {
      "value": "Mustermann",
      "salt": "2f55f35d-72a9-4986-8986-93d4e4d6f3bf",
      "hash": "0x6be6118a83dd2b1c5a050da46ea301fe5512245d9cfb9966b88219b1ee54e8ba"
    },
    "address": {
      "type": "PostalAddress",
      "addressLocality": {
        "value": "Mittweida",
        "salt": "40f1403a-984f-41ed-8821-b987fe556a36",
        "hash": "0x97144b9ff02df331935d394cd790a1ab76bf9c6a5b0747c3f03db931103cdf56"
      },
      "postalCode": {
        "value": "09648",
        "salt": "83cd01c2-0a30-4907-b8cd-0bd5808a217e",
        "hash": "0x254cfac1490b2f8330925374de8a40b8c6d5efe41b3f80e0fe67c3c8cf783b8f"
      },
      "streetAddress": {
        "value": "Am Schwanenteich 8",
        "salt": "6fd7baf8-f798-4fde-86e2-d19203d9caf6",
        "hash": "0x4b2e396e631e5a391cf6415bd3110fa420fc7167509ef15407ee48b6f827be9c"
      }
    }
  }
}

and you only want to show your familyName and the postalCode of your living place, a working call of this function would be :

discloseValues(
plaintextCredential,
[issuanceDate,
  student.givenName,
  student.address.addressLocality,
  student.address.streetAddress
 ])

If there is an array in the plaintext-Credential the array elements that should be disclosed, could be given as follows: arrayKey.arrayIndex e.g. friends.1. ArrayIndex starts with 0.

Implementation

String discloseValues(
    dynamic plaintextCredential, List<String> valuesToDisclose) {
  Map<String, dynamic> plaintextMap = credentialToMap(plaintextCredential);
  Map<String, dynamic> result = {};
  plaintextMap.forEach((key, value) {
    result[key] = value;
    if (!(key == '@context' ||
        key == 'type' ||
        key == '@type' ||
        key == 'id' ||
        key == 'hashAlg')) {
      // if key is in map it should be a single string
      if (_hashedAttributeSchemaStrict.validate(value)) {
        // check if key should be disclosed
        if (valuesToDisclose.contains(key)) {
          result.remove(key);
        }
      }
      // new Object found
      else if (_mapOfHashedAttributesSchema.validate(value)) {
        List<String> valuesSeen = [];
        List<String> valuesToDiscloseNew = [];
        //search in valuesToDisclose if sth. starts with key
        for (var element in valuesToDisclose) {
          if (valuesSeen.contains(element)) {
          }
          //key of Object is in List
          else if (element == key) {
            Map<String, dynamic> valueMap = value as Map<String, dynamic>;
            valuesToDiscloseNew = valueMap.keys.toList();
          }
          // subkeys of Object are in List
          else if (element.split('.').first == key) {
            valuesToDiscloseNew.add(element.substring(key.length + 1));
            valuesSeen.add(element);
          }
        }
        var newValue = jsonDecode(discloseValues(value, valuesToDiscloseNew));
        result[key] = newValue;
      }
      // array found
      else if (value is List) {
        result[key] = value;
        int removed = 0;
        List<String> valuesSeen = [];
        for (var element in valuesToDisclose) {
          if (valuesSeen.contains(element)) {
          }
          //whole Array should be disclosed
          else if (element == key) {
            List<String> valuesToDiscloseNew = [];
            for (var i = 0; i < value.length; i++) {
              valuesToDiscloseNew.add('$key.$i');
            }
            result[key] = jsonDecode(
                discloseValues({key: value}, valuesToDiscloseNew))[key];
          }
          //elementwise disclosing
          else if (element.split('.').first == key) {
            int arrayIndex = int.parse(element.split('.')[1]);
            if (_hashedAttributeSchemaStrict
                .validate(value[arrayIndex - removed])) {
              result[key].removeAt(arrayIndex - removed);
              removed++;
            }
            //Object in Array
            else if (_mapOfHashedAttributesSchema.validate(value[arrayIndex])) {
              //search in given keys, if sth. else should be disclosed
              List<String> valuesToDiscloseNew = [];
              for (var element in valuesToDisclose) {
                if (element.split('.')[0] == key &&
                    int.parse(element.split('.')[1]) == arrayIndex) {
                  if (element.split('.').length > 2) {
                    valuesSeen.add(element);
                    valuesToDiscloseNew.add(element.substring(
                        key.length + 1 + arrayIndex.toString().length + 1));
                  } else {
                    valuesToDiscloseNew =
                        (value[arrayIndex] as Map<String, dynamic>)
                            .keys
                            .toList();
                  }
                }
              }
              result[key][arrayIndex] = jsonDecode(
                  discloseValues(value[arrayIndex], valuesToDiscloseNew));
            } else {
              throw Exception(
                  'Malformed array element in array with key $key at index $arrayIndex');
            }
          }
        }
      } else {
        throw Exception('Unknown data type at key $key');
      }
    }
  });
  return jsonEncode(result);
}