Add AES layer api

lib/symmetrical_crypto.dart

@@ -0,0 +1,112 @@
+// Copyright (c) 2020
+// Author: Hugo Pointcheval
+import 'dart:typed_data';
+
+import 'package:native_crypto/native_crypto.dart';
+import 'package:native_crypto/src/exceptions.dart';
+
+enum KeySize { bits128, bits192, bits256 }
+enum Cipher { AES }
+
+/// AES Helper
+///
+/// You can generate AES keys, encrypt and decrypt data.
+class AES {
+  Uint8List key;
+
+  bool isInitialized = false;
+  KeySize keySize;
+
+  /// You can pass a key in constructor.
+  AES({this.key}) {
+    try {
+      bool isValidKey = _testKey();
+      this.isInitialized = isValidKey;
+    } on KeyException {
+      this.isInitialized = false;
+      throw KeyException('Invalid key length.');
+    }
+  }
+
+  /// Tests if the key is valid.
+  ///
+  /// The key must be 128, 192 or 256 bits long.
+  bool _testKey() {
+    if (this.key != null) {
+      switch (this.key.length) {
+        case 16:
+          this.keySize = KeySize.bits128;
+          break;
+        case 24:
+          this.keySize = KeySize.bits192;
+          break;
+        case 32:
+          this.keySize = KeySize.bits256;
+          break;
+        default:
+          throw KeyException('Invalid key length.');
+      }
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  /// Generate an AES key.
+  init(KeySize keySize) async {
+    if (this.key != null) return null;
+
+    if (keySize != KeySize.bits256)
+      throw NotImplementedException('This key size is not implemented yet.');
+
+    this.key = await NativeCrypto().symKeygen();
+    try {
+      bool isValidKey = _testKey();
+      this.isInitialized = isValidKey;
+    } on KeyException {
+      this.isInitialized = false;
+      throw KeyException('Invalid key length.');
+    }
+  }
+
+  /// Encrypt data
+  ///
+  /// Returns an `Encrypted` object.
+  Future<Encrypted> encrypt(Uint8List data) async {
+    if (!this.isInitialized) throw EncryptionException('Instance not initialized.');
+    List<Uint8List> encryptedPayload =
+        await NativeCrypto().symEncrypt(data, this.key);
+    Encrypted encrypted = Encrypted.fromList(Cipher.AES, encryptedPayload);
+
+    return encrypted;
+  }
+
+  Future<Uint8List> decrypt(Encrypted encrypted) async {
+    if (!this.isInitialized) throw DecryptionException('Instance not initialized.');
+    Uint8List decryptedPayload =
+        await NativeCrypto().symDecrypt(encrypted.toList(), this.key);
+    return decryptedPayload;
+  }
+}
+
+/// Contains data of an encrypted payload.
+/// More practical than a list.
+class Encrypted {
+  Cipher cipher;
+  Uint8List cipherText;
+  Uint8List iv;
+  Uint8List mac;
+
+  Encrypted();
+
+  Encrypted.fromList(this.cipher, List<Uint8List> encryptedPayload) {
+    this.mac = encryptedPayload[0].sublist(0, 32);
+    this.cipherText = encryptedPayload[0].sublist(32, encryptedPayload[0].length);
+    this.iv = encryptedPayload[1];
+  }
+
+  List<Uint8List> toList() {
+    List<Uint8List> encryptedPayload = [Uint8List.fromList(this.mac + this.cipherText), this.iv];
+    return encryptedPayload;
+  }
+}