refactor: replace pointycastle with cryptography for AES-GCM

TODO.md

@@ -0,0 +1,7 @@
+- [ ] Translations
+- [ ] Drop file
+- [ ] Keep file name
+- [ ] Use streams
+- [ ] Better UI/UX
+- [ ] Remove snackbars
+- [x] Use https://pub.dev/packages/webcrypto or https://pub.dev/packages/cryptography for efficient web crypto operations

lib/functions/decrypt_blob.dart

@@ -1,10 +1,10 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:pointycastle/export.dart';
+import 'package:cryptography/cryptography.dart';
 
 /// Decrypts data using AES-256-GCM
-/// [encryptedBytes] - the encrypted data
+/// [encryptedBytes] - the encrypted data (ciphertext + MAC)
 /// [key] - base64 encoded encryption key
 /// [nonce] - base64 encoded nonce (salt)
 Future<Uint8List> decryptBlob({
@@ -12,20 +12,37 @@ Future<Uint8List> decryptBlob({
   required String key,
   required String nonce,
 }) async {
+  final algorithm = AesGcm.with256bits();
+
   // Decode base64 key and nonce
   final keyBytes = base64Decode(key);
   final nonceBytes = base64Decode(nonce);
 
-  // Set up AES-GCM parameters
-  final keyParam = KeyParameter(keyBytes);
-  final params = ParametersWithIV(keyParam, nonceBytes);
+  // Extract ciphertext and MAC (MAC is last 16 bytes)
+  final macLength = algorithm.macAlgorithm.macLength;
+  final ciphertext = encryptedBytes.sublist(
+    0,
+    encryptedBytes.length - macLength,
+  );
+  final macBytes = encryptedBytes.sublist(
+    encryptedBytes.length - macLength,
+  );
 
-  // Create and initialize the cipher for decryption (false = decrypt)
-  final aesGcm = GCMBlockCipher(AESEngine());
-  aesGcm.init(false, params);
+  // Create secret key from bytes
+  final secretKey = SecretKey(keyBytes);
+
+  // Create secret box with ciphertext, nonce, and MAC
+  final secretBox = SecretBox(
+    ciphertext,
+    nonce: nonceBytes,
+    mac: Mac(macBytes),
+  );
 
   // Decrypt the data
-  final decryptedData = aesGcm.process(encryptedBytes);
+  final decryptedData = await algorithm.decrypt(
+    secretBox,
+    secretKey: secretKey,
+  );
 
-  return decryptedData;
+  return Uint8List.fromList(decryptedData);
 }

lib/functions/encrypt_blob.dart

@@ -1,44 +1,29 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
+import 'package:cryptography/cryptography.dart';
 import 'package:file_transfer/models/encrypted_blob.dart';
-import 'package:pointycastle/export.dart';
 
 /// Encrypts data using AES-256-GCM
 /// Returns the encrypted blob with key, nonce, and auth tag
 Future<EncryptedBlob> encryptBlob(Uint8List bytes) async {
-  // Generate random 256-bit key (32 bytes)
-  final key = _generateRandomBytes(32);
+  final algorithm = AesGcm.with256bits();
 
-  // Generate random 12-byte nonce (96 bits - recommended for GCM)
-  final nonce = _generateRandomBytes(12);
+  // Generate random secret key
+  final secretKey = await algorithm.newSecretKey();
 
-  // Set up AES-GCM parameters
-  final keyParam = KeyParameter(key);
-  final params = ParametersWithIV(keyParam, nonce);
+  // Encrypt with the key
+  final secretBox = await algorithm.encrypt(bytes, secretKey: secretKey);
 
-  // Create and initialize the cipher for encryption (true = encrypt)
-  final aesGcm = GCMBlockCipher(AESEngine());
-  aesGcm.init(true, params);
-
-  // Encrypt the data
-  final encryptedData = aesGcm.process(bytes);
+  // Concatenate ciphertext + MAC for storage
+  final macBytes = secretBox.mac.bytes;
+  final encryptedData = Uint8List.fromList(
+    [...secretBox.cipherText, ...macBytes],
+  );
 
   return EncryptedBlob(
     bytes: encryptedData,
-    key: base64Encode(key),
-    nonce: base64Encode(nonce),
+    key: base64Encode(await secretKey.extractBytes()),
+    nonce: base64Encode(secretBox.nonce),
   );
 }
-
-Uint8List _generateRandomBytes(int length) {
-  final secureRandom = SecureRandom('Fortuna');
-  // Seed with platform entropy
-  final seed = Uint8List(32);
-  for (var i = 0; i < 32; i++) {
-    seed[i] = (DateTime.now().microsecondsSinceEpoch >> (i % 32)) & 0xFF;
-  }
-  secureRandom.seed(KeyParameter(seed));
-
-  return secureRandom.nextBytes(length);
-}

pubspec.lock

@@ -106,7 +106,7 @@ packages:
     source: hosted
     version: "3.0.7"
   cryptography:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: cryptography
       sha256: "3eda3029d34ec9095a27a198ac9785630fe525c0eb6a49f3d575272f8e792ef0"
@@ -558,7 +558,7 @@ packages:
     source: hosted
     version: "2.1.8"
   pointycastle:
-    dependency: "direct main"
+    dependency: transitive
     description:
       name: pointycastle
       sha256: "92aa3841d083cc4b0f4709b5c74fd6409a3e6ba833ffc7dc6a8fee096366acf5"

pubspec.yaml

@@ -8,6 +8,7 @@ environment:
 
 dependencies:
   crypto: ^3.0.7
+  cryptography: ^2.9.0
   file_picker: ^10.3.10
   file_saver: ^0.3.1
   flutter:
@@ -17,7 +18,6 @@ dependencies:
   ndk: ^0.7.1-dev.19
   ndk_flutter: ^0.0.2-dev.13
   nip49: ^1.1.2
-  pointycastle: ^4.0.0
 
 dev_dependencies:
   flutter_test: