Add key size support

lib/symmetrical_crypto.dart

@@ -2,19 +2,26 @@
 // Author: Hugo Pointcheval
 import 'dart:typed_data';
 
-import 'package:native_crypto/native_crypto.dart';
+import 'package:native_crypto/src/native_crypto.dart';
 import 'package:native_crypto/src/exceptions.dart';
 
+/// Defines all available key sizes.
 enum KeySize { bits128, bits192, bits256 }
+
+/// Defines all available ciphers.
 enum Cipher { AES }
 
 /// AES Helper
 ///
 /// You can generate AES keys, encrypt and decrypt data.
 class AES {
+  /// This key is used for encryption and decryption.
   Uint8List key;
 
+  /// Check if the AES object is intialized with a valid key before perform any operation.
   bool isInitialized = false;
+
+  /// Defines the size of the generated or passed key.
   KeySize keySize;
 
   /// You can pass a key in constructor.
@@ -28,6 +35,7 @@ class AES {
     }
   }
 
+  /// [Private]
   /// Tests if the key is valid.
   ///
   /// The key must be 128, 192 or 256 bits long.
@@ -53,13 +61,31 @@ class AES {
   }
 
   /// Generate an AES key.
-  init(KeySize keySize) async {
+  ///
+  /// You can specify a `keySize`. Default is 256 bits.
+  /// Return `null` if the key is already set.
+  init({KeySize keySize}) async {
     if (this.key != null) return null;
 
-    if (keySize != KeySize.bits256)
-      throw NotImplementedException('This key size is not implemented yet.');
+    int size;
 
-    this.key = await NativeCrypto().symKeygen();
+    switch (keySize) {
+      case KeySize.bits128:
+        size = 128;
+        break;
+      case KeySize.bits192:
+        size = 192;
+        break;
+      case KeySize.bits256:
+        size = 256;
+        break;
+      default:
+        // Default size = 256 bits
+        size = 256;
+        break;
+    }
+
+    this.key = await NativeCrypto().symKeygen(size);
     try {
       bool isValidKey = _testKey();
       this.isInitialized = isValidKey;
@@ -69,11 +95,13 @@ class AES {
     }
   }
 
-  /// Encrypt data
-  ///
-  /// Returns an `Encrypted` object.
+  /// Encrypts data.
+  /// 
+  /// Takes `Uint8List` data as parameter.
+  /// And returns an `Encrypted` object.
   Future<Encrypted> encrypt(Uint8List data) async {
-    if (!this.isInitialized) throw EncryptionException('Instance not initialized.');
+    if (!this.isInitialized)
+      throw EncryptionException('Instance not initialized.');
     List<Uint8List> encryptedPayload =
         await NativeCrypto().symEncrypt(data, this.key);
     Encrypted encrypted = Encrypted.fromList(Cipher.AES, encryptedPayload);
@@ -81,8 +109,13 @@ class AES {
     return encrypted;
   }
 
+  /// Decrypts data.
+  /// 
+  /// Takes `Encrypted` object as parameter.
+  /// And returns plain text data as `Uint8List`.
   Future<Uint8List> decrypt(Encrypted encrypted) async {
-    if (!this.isInitialized) throw DecryptionException('Instance not initialized.');
+    if (!this.isInitialized)
+      throw DecryptionException('Instance not initialized.');
     Uint8List decryptedPayload =
         await NativeCrypto().symDecrypt(encrypted.toList(), this.key);
     return decryptedPayload;
@@ -92,21 +125,36 @@ class AES {
 /// Contains data of an encrypted payload.
 /// More practical than a list.
 class Encrypted {
+  /// Contains encryption algorithm.
   Cipher cipher;
+
+  /// Contains encrypted bytes.
   Uint8List cipherText;
+
+  /// Contains IV used for encryption.
+  /// 
+  /// Needed for decryption.
   Uint8List iv;
+
+  /// Contains MAC.
+  ///
+  /// Used in decryption to authenticate the data.
   Uint8List mac;
 
-  Encrypted();
-
+  /// Creates an encrypted from payload `List<Uint8List>`.
   Encrypted.fromList(this.cipher, List<Uint8List> encryptedPayload) {
     this.mac = encryptedPayload[0].sublist(0, 32);
-    this.cipherText = encryptedPayload[0].sublist(32, encryptedPayload[0].length);
+    this.cipherText =
+        encryptedPayload[0].sublist(32, encryptedPayload[0].length);
     this.iv = encryptedPayload[1];
   }
 
+  /// Returns a payload `List<Uint8List>` from this encrypted.
   List<Uint8List> toList() {
-    List<Uint8List> encryptedPayload = [Uint8List.fromList(this.mac + this.cipherText), this.iv];
+    List<Uint8List> encryptedPayload = [
+      Uint8List.fromList(this.mac + this.cipherText),
+      this.iv
+    ];
     return encryptedPayload;
   }
 }