Add key derivation interface and pbkdf2 implementation

lib/src/keyderivation.dart

@@ -0,0 +1,81 @@
+// Copyright (c) 2020
+// Author: Hugo Pointcheval
+
+import 'dart:typed_data';
+
+import 'package:native_crypto/src/digest.dart';
+import 'package:native_crypto/src/exceptions.dart';
+import 'package:native_crypto/src/key.dart';
+
+import 'platform.dart';
+
+enum KdfAlgorithm { PBKDF2, SCrypt }
+
+/// Represents a Key Derivation Function
+abstract class KeyDerivation {
+  /// Returns the standard algorithm name for this key derivation function
+  KdfAlgorithm get algorithm;
+
+  /// Returns the derivated key
+  SecretKey get key;
+
+  /// Derive key
+  Future<void> derive();
+}
+
+class PBKDF2 implements KeyDerivation {
+  SecretKey _sk;
+
+  int _length;
+  int _iteration;
+  HashAlgorithm _hash;
+
+  @override
+  KdfAlgorithm get algorithm => KdfAlgorithm.PBKDF2;
+
+  @override
+  SecretKey get key => _sk;
+
+  PBKDF2({
+    int keyLength: 32,
+    int iteration: 10000,
+    HashAlgorithm hash: HashAlgorithm.SHA256,
+  }) {
+    _length = keyLength;
+    _iteration = iteration;
+    _hash = hash;
+  }
+
+  @override
+  Future<void> derive({String password, String salt}) async {
+    if (password == null || salt == null) {
+      throw KeyDerivationException("Password or Salt can't be null!");
+    }
+    if (_hash == null) {
+      throw KeyDerivationException("Hash Algorithm can't be null!");
+    }
+
+    Uint8List derivation = await Platform().pbkdf2(
+      password,
+      salt,
+      keyLength: _length,
+      iteration: _iteration,
+      algorithm: _hash,
+    );
+
+    _sk = SecretKey.fromBytes(derivation);
+  }
+}
+
+class Scrypt implements KeyDerivation {
+  @override
+  KdfAlgorithm get algorithm => KdfAlgorithm.SCrypt;
+
+  @override
+  SecretKey get key => throw UnimplementedError();
+
+  @override
+  Future<void> derive() {
+    throw UnimplementedError();
+  }
+}