Added a SecureRandom implementation based on darts own Random class.

CONTRIBUTORS

@@ -15,3 +15,4 @@ Shammah Chancellor <https://github.com/schancel>
 Rick Bellens <https://github.com/rbellens>
 Deniz Türkoglu <https://github.com/denizt>
 Yurii Baryshev <https://github.com/YuriiBaryshev>
+Eric Prokop und Nils Wieler Hard- und Softwareentwicklung GbR <https://github.com/EPNW>

lib/export.dart

@@ -79,6 +79,7 @@ export 'package:pointycastle/paddings/iso7816d4.dart';
 export 'package:pointycastle/random/auto_seed_block_ctr_random.dart';
 export 'package:pointycastle/random/block_ctr_random.dart';
 export 'package:pointycastle/random/fortuna_random.dart';
+export 'package:pointycastle/random/dart_secure_random.dart';
 
 // signers
 export 'package:pointycastle/signers/ecdsa_signer.dart';

lib/random/dart_secure_random.dart

@@ -0,0 +1,48 @@
+// See file LICENSE for more information.
+
+library impl.secure_random.dart_secure_random;
+
+import 'dart:math';
+
+import 'package:pointycastle/api.dart';
+import 'package:pointycastle/src/impl/secure_random_base.dart';
+import 'package:pointycastle/src/registry/registry.dart';
+
+/// An implementation of [SecureRandom] that uses darts built-in
+/// [Random] to generate random bytes.
+///
+/// This implementation does not give any security guarantees, but
+/// trusts the dart [Random] implementation to be cryptographically secure.
+class DartSecureRandom extends SecureRandomBase implements SecureRandom {
+  static const String _algorithmName = 'DartSecure';
+  static final FactoryConfig factoryConfig = StaticFactoryConfig(
+      SecureRandom, _algorithmName, () => DartSecureRandom());
+
+  final Random _random;
+
+  /// A newly created secure dart [Random] is used for byte generation.
+  DartSecureRandom() : _random = Random.secure();
+
+  /// Uses an insecure dart [Random]. This constructor should not be used
+  /// in production!
+  ///
+  /// It is intended to be used during development when
+  /// generating many cryptographically secure numbers takes
+  /// to much time.
+  DartSecureRandom.insecure([int? seed]) : _random = Random(seed);
+
+  /// Uses an explicitly given dart [Random] for all operations.
+  DartSecureRandom.withRandom(Random random) : _random = random;
+
+  @override
+  String get algorithmName => _algorithmName;
+
+  @override
+  int nextUint8() {
+    return _random.nextInt(256);
+  }
+
+  /// The dart [Random] can not be seeded, so this is a no-op.
+  @override
+  void seed(CipherParameters params) {}
+}

lib/src/registry/registration.dart

@@ -91,6 +91,7 @@ import 'package:pointycastle/paddings/pkcs7.dart';
 import 'package:pointycastle/random/auto_seed_block_ctr_random.dart';
 import 'package:pointycastle/random/block_ctr_random.dart';
 import 'package:pointycastle/random/fortuna_random.dart';
+import 'package:pointycastle/random/dart_secure_random.dart';
 import 'package:pointycastle/signers/ecdsa_signer.dart';
 import 'package:pointycastle/signers/rsa_signer.dart';
 import 'package:pointycastle/src/registry/registry.dart';
@@ -239,6 +240,7 @@ void _registerRandoms(FactoryRegistry registry) {
   registry.register(AutoSeedBlockCtrRandom.factoryConfig);
   registry.register(BlockCtrRandom.factoryConfig);
   registry.register(FortunaRandom.factoryConfig);
+  registry.register(DartSecureRandom.factoryConfig);
 }
 
 void _registerSigners(FactoryRegistry registry) {

test/all_tests_web.dart

@@ -51,6 +51,7 @@ import 'random/auto_seed_block_ctr_random_test.dart'
     as auto_seed_block_ctr_random_test;
 import 'random/block_ctr_random_test.dart' as block_ctr_random_test;
 import 'random/fortuna_random_test.dart' as fortuna_random_test;
+import 'random/dart_secure_random_test.dart' as dart_secure_random_test;
 import 'random/fixed_rng_test.dart' as fixed_rng_test;
 import 'signers/ecdsa_signer_test.dart' as ecdsa_signer_test;
 import 'signers/pss_signer_test.dart' as pss_signer_test;
@@ -110,6 +111,7 @@ void main() {
   auto_seed_block_ctr_random_test.main();
   block_ctr_random_test.main();
   fortuna_random_test.main();
+  dart_secure_random_test.main();
   fixed_rng_test.main();
   ecdsa_signer_test.main();
   rsa_signer_test.main();

test/random/dart_secure_random_test.dart

@@ -0,0 +1,25 @@
+// See file LICENSE for more information.
+
+library test.random.dart_secure_random_test;
+
+import 'package:pointycastle/pointycastle.dart';
+
+import 'package:test/test.dart';
+
+void main() {
+  group('DartSecure:', () {
+    final rnd = SecureRandom('DartSecure');
+
+    test('${rnd.algorithmName}', () {
+      var randomBytes = rnd.nextBytes(256);
+      var allZero = true;
+      for (var i = 0; i < randomBytes.length; i++) {
+        if (randomBytes[i] != 0) {
+          allZero = false;
+          break;
+        }
+      }
+      expect(allZero, false);
+    });
+  });
+}