Select Credentials (#81)

packages/web5/lib/src/pexv2/presentation_definition.dart

@@ -0,0 +1,266 @@
+import 'dart:convert';
+import 'dart:math';
+import 'dart:typed_data';
+import 'package:collection/collection.dart';
+import 'package:convert/convert.dart';
+import 'package:json_path/json_path.dart';
+import 'package:json_schema/json_schema.dart';
+
+class _JsonSchema {
+  String schema = 'http://json-schema.org/draft-07/schema#';
+  String type = 'object';
+  Map<String, dynamic> properties = {};
+  List<String> required = [];
+
+  _JsonSchema();
+
+  void addProperty(String name, Map<String, dynamic> property) {
+    properties[name] = property;
+    required.add(name);
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      '/$schema': schema,
+      'type': type,
+      'properties': properties,
+      'required': required,
+    };
+  }
+}
+
+/// PresentationDefinition represents a DIF Presentation Definition defined
+/// [here](https://identity.foundation/presentation-exchange/#presentation-definition).
+/// Presentation Definitions are objects that articulate what proofs a Verifier requires.
+class PresentationDefinition {
+  String id;
+  String? name;
+  String? purpose;
+  List<InputDescriptor> inputDescriptors;
+
+  PresentationDefinition({
+    required this.id,
+    this.name,
+    this.purpose,
+    required this.inputDescriptors,
+  });
+
+  factory PresentationDefinition.fromJson(Map<String, dynamic> json) =>
+      PresentationDefinition(
+        id: json['id'],
+        name: json['name'],
+        purpose: json['purpose'],
+        inputDescriptors: List<InputDescriptor>.from(
+          json['input_descriptors'].map((x) => InputDescriptor.fromJson(x)),
+        ),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'name': name,
+        'purpose': purpose,
+        'input_descriptors':
+            inputDescriptors.map((ind) => ind.toJson()).toList(),
+      };
+
+  List<String> selectCredentials(List<String> vcJwts) {
+    final Set<String> matches = {};
+
+    for (final inputDescriptor in inputDescriptors) {
+      final matchingVcJwts = inputDescriptor.selectCredentials(vcJwts);
+      if (matchingVcJwts.isEmpty) {
+        return [];
+      }
+      matches.addAll(matchingVcJwts);
+    }
+
+    return matches.toList();
+  }
+}
+
+class _TokenizedPath {
+  String path;
+  String token;
+
+  _TokenizedPath({required this.path, required this.token});
+}
+
+/// InputDescriptor represents a DIF Input Descriptor defined
+/// [here](https://identity.foundation/presentation-exchange/#input-descriptor).
+/// Input Descriptors are used to describe the information a Verifier requires of a Holder.
+class InputDescriptor {
+  String id;
+  String? name;
+  String? purpose;
+  Constraints constraints;
+
+  InputDescriptor({
+    required this.id,
+    this.name,
+    this.purpose,
+    required this.constraints,
+  });
+
+  factory InputDescriptor.fromJson(Map<String, dynamic> json) =>
+      InputDescriptor(
+        id: json['id'],
+        name: json['name'],
+        purpose: json['purpose'],
+        constraints: Constraints.fromJson(json['constraints']),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'name': name,
+        'purpose': purpose,
+        'constraints': constraints.toJson(),
+      };
+
+  String _generateRandomToken() {
+    final rand = Random.secure();
+    final bytes = Uint8List(16);
+    for (int i = 0; i < 16; i++) {
+      bytes[i] = rand.nextInt(256);
+    }
+    return hex.encode(bytes);
+  }
+
+  List<String> selectCredentials(List<String> vcJwts) {
+    final List<String> answer = [];
+    final List<_TokenizedPath> tokenizedPaths = [];
+    final schema = _JsonSchema();
+
+    // Populate JSON schema and generate tokens for each field
+    for (Field field in constraints.fields ?? []) {
+      final token = _generateRandomToken();
+      for (String path in field.path ?? []) {
+        tokenizedPaths.add(_TokenizedPath(token: token, path: path));
+      }
+
+      if (field.filter != null) {
+        schema.addProperty(token, field.filter!.toJson());
+      } else {
+        schema.addProperty(token, {});
+      }
+    }
+    final jsonSchema = JsonSchema.create(schema.toJson());
+
+    // Tokenize each vcJwt and validate it against the JSON schema
+    for (var vcJwt in vcJwts) {
+      final decoded = json.decode(vcJwt);
+
+      final selectionCandidate = <String, dynamic>{};
+
+      for (final tokenizedPath in tokenizedPaths) {
+        selectionCandidate[tokenizedPath.token] ??=
+            JsonPath(tokenizedPath.path).read(decoded).firstOrNull;
+      }
+      selectionCandidate.removeWhere((_, value) => value == null);
+
+      if (selectionCandidate.keys.length < tokenizedPaths.length) {
+        // Did not find values for all `field`s in the input desciptor
+        continue;
+      }
+
+      final validationResult = jsonSchema.validate(selectionCandidate);
+      if (validationResult.isValid) {
+        answer.add(vcJwt);
+      }
+    }
+
+    return answer;
+  }
+}
+
+/// Constraints contains the requirements for a given Input Descriptor.
+class Constraints {
+  List<Field>? fields;
+
+  Constraints({this.fields});
+
+  factory Constraints.fromJson(Map<String, dynamic> json) => Constraints(
+        fields: json['fields'] == null
+            ? null
+            : List<Field>.from(json['fields'].map((x) => Field.fromJson(x))),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'fields': fields == null
+            ? null
+            : List<dynamic>.from(fields!.map((x) => x.toJson())),
+      };
+}
+
+/// Field contains the requirements for a given field within a proof.
+class Field {
+  String? id;
+  String? name;
+  List<String>? path;
+  String? purpose;
+  Filter? filter;
+  bool? optional;
+  Optionality? predicate;
+
+  Field({
+    this.id,
+    this.name,
+    this.path,
+    this.purpose,
+    this.filter,
+    this.optional,
+    this.predicate,
+  });
+
+  factory Field.fromJson(Map<String, dynamic> json) => Field(
+        id: json['id'],
+        name: json['name'],
+        path: json['path'] == null ? null : List<String>.from(json['path']),
+        purpose: json['purpose'],
+        filter: json['filter'] == null ? null : Filter.fromJson(json['filter']),
+        optional: json['optional'],
+        predicate: Optionality.values
+            .firstWhereOrNull((val) => val.toString() == json['predicate']),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'name': name,
+        'path': path,
+        'purpose': purpose,
+        'filter': filter?.toJson(),
+        'optional': optional,
+        'predicate': predicate?.toString(),
+      };
+}
+
+enum Optionality { required, preferred }
+
+/// Filter is a JSON Schema that is applied against the value of a field.
+class Filter {
+  String? type;
+  String? pattern;
+  String? constValue;
+  Filter? contains;
+
+  Filter({
+    this.type,
+    this.pattern,
+    this.constValue,
+    this.contains,
+  });
+
+  factory Filter.fromJson(Map<String, dynamic> json) => Filter(
+        type: json['type'],
+        pattern: json['pattern'],
+        constValue: json['const'],
+        contains:
+            json['contains'] == null ? null : Filter.fromJson(json['contains']),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'type': type,
+        'pattern': pattern,
+        'const': constValue,
+        'contains': contains?.toJson(),
+      };
+}

packages/web5/lib/src/vc/vc.dart

@@ -111,7 +111,8 @@ class VerifiableCredential {
     final credentialSubject = json['credentialSubject'] as Map<String, dynamic>;
     final subject = credentialSubject.remove('id');
     final credentialSchema = (json['credentialSchema'] as List<dynamic>)
-        .map((e) => CredentialSchema(id: e['id'], type: e['type'])).toList();
+        .map((e) => CredentialSchema(id: e['id'], type: e['type']))
+        .toList();
     final context = (json['@context'] as List<dynamic>).cast<String>();
     final type = (json['type'] as List<dynamic>).cast<String>();
 
@@ -141,9 +142,11 @@ class VerifiableCredential {
       'issuanceDate': issuanceDate,
       if (expirationDate != null) 'expirationDate': expirationDate,
       if (credentialSchema != null)
-        'credentialSchema': credentialSchema!.map(
-          (e) => e.toJson(),
-        ).toList(),
+        'credentialSchema': credentialSchema!
+            .map(
+              (e) => e.toJson(),
+            )
+            .toList(),
     };
   }
 }

packages/web5/pubspec.yaml

@@ -13,6 +13,8 @@ dependencies:
   pointycastle: ^3.7.3
   http: ^1.2.0
   uuid: ^4.4.0
+  json_path: ^0.7.1
+  json_schema: ^5.1.7
 
 dev_dependencies:
   lints: ^3.0.0

packages/web5/test/crypto/secp256k1_test.dart

@@ -72,13 +72,11 @@ void main() {
         final file = File(vectorPath);
         late List<TestVector> vectors;
         try {
-          // Read the file as a string
           final contents = file.readAsStringSync();
           final jsonVectors = json.decode(contents);
 
           vectors = TestVectors.fromJson(jsonVectors).vectors;
         } catch (e) {
-          // If encountering an error, print it
           throw Exception('Failed to load verify test vectors: $e');
         }
 
@@ -88,14 +86,20 @@ void main() {
                 Uint8List.fromList(hex.decode(vector.input.signature));
             final payload = Uint8List.fromList(hex.decode(vector.input.data));
 
+            // Since some other web5 implementations of this Secp256k1.verify()
+            // return `false` rather than throwing, we should interpret the
+            // test vectors as expecting failure when either `errors` is true
+            // or `output` is false.
+            final shouldThrow = vector.errors || vector.output == false;
+
             try {
               await Secp256k1.verify(vector.input.key, payload, signature);
 
-              if (vector.errors == true) {
+              if (shouldThrow) {
                 fail('Expected an error but none was thrown');
               }
             } catch (e) {
-              if (vector.errors == false) {
+              if (!shouldThrow) {
                 fail('Expected no error but got: $e');
               }
             }

packages/web5/test/helpers/test_vector_helpers.dart

@@ -0,0 +1,17 @@
+import 'dart:convert';
+import 'dart:io';
+
+final thisDir = Directory.current.path;
+final vectorDir = '$thisDir/../../web5-spec/test-vectors/';
+
+Map<String, dynamic> getJsonVectors(String vectorSubPath) {
+  final vectorPath = '$vectorDir$vectorSubPath';
+  final file = File(vectorPath);
+
+  try {
+    final contents = file.readAsStringSync();
+    return json.decode(contents);
+  } catch (e) {
+    throw Exception('Failed to load verify test vectors: $e');
+  }
+}