refactor: CryptoStore.createHmacKey() is now CryptoStore.hmacSecretKey. Also dropped support of memEquals in favor of hashlib isEqual.

Author: Skyost

lib/model/backup.dart

@@ -2,7 +2,6 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
-import 'package:cipherlib/hashlib.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:open_authenticator/app.dart';
@@ -148,8 +147,7 @@ class Backup implements Comparable<Backup> {
 
       Map<String, dynamic> jsonData = jsonDecode(file.readAsStringSync());
       CryptoStore cryptoStore = CryptoStore.fromPassword(password, Salt.fromRawValue(value: base64.decode(jsonData[kSaltKey])));
-      MACHashBase hmacSecretKey = cryptoStore.createHmacKey();
-      if (!(hmacSecretKey.verify(base64.decode(jsonData[kPasswordSignatureKey]), utf8.encode(password)))) {
+      if (!(cryptoStore.hmacSecretKey.verify(base64.decode(jsonData[kPasswordSignatureKey]), utf8.encode(password)))) {
         throw InvalidPasswordException();
       }
 
@@ -201,11 +199,10 @@ class Backup implements Comparable<Backup> {
         DecryptedTotp? decryptedTotp = totp.changeEncryptionKey(currentCryptoStore, newStore);
         toBackup.add(decryptedTotp ?? totp);
       }
-      MACHashBase hmacSecretKey = newStore.createHmacKey();
       File file = await getBackupPath(createDirectory: true);
       await file.writeAsString(
         jsonEncode({
-          kPasswordSignatureKey: hmacSecretKey.string(password, utf8).base64(),
+          kPasswordSignatureKey: newStore.hmacSecretKey.string(password, utf8).base64(),
           kSaltKey: base64.encode(newStore.salt.value),
           kTotpsKey: [
             for (Totp totp in toBackup) totp.toJson(),

lib/model/crypto.dart

@@ -110,20 +110,20 @@ class CryptoStore {
 
   /// Creates a [CryptoStoreWithPasswordSignature] from the given [password].
   CryptoStore.fromPassword(String password, Salt salt) : this._(
-      key: _deriveKey(password, salt),
+      key: _deriveKey(password, salt).bytes,
       salt: salt,
     );
 
   /// Generates a derived key from the given [password] and save it to the device secure storage.
   /// Also returns the salt that has been used.
-  static Uint8List _deriveKey(String password, Salt salt) {
+  static Argon2HashDigest _deriveKey(String password, Salt salt) {
     Argon2 argon2 = Argon2(
       iterations: Argon2Parameters.iterations,
       memorySizeKB: Argon2Parameters.memorySize,
       parallelism: Argon2Parameters.parallelism,
       salt: salt.value,
     );
-    return argon2.convert(utf8.encode(password)).bytes;
+    return argon2.convert(utf8.encode(password));
   }
 
   /// Encrypts the given text.
@@ -151,10 +151,7 @@ class CryptoStore {
   }
 
   /// Checks if the given password is valid.
-  bool checkPasswordValidity(String password) {
-    Uint8List derivedKey = _deriveKey(password, salt);
-    return memEquals(derivedKey, key);
-  }
+  bool checkPasswordValidity(String password) => _deriveKey(password, salt).isEqual(key);
 
   /// Checks if the given [encryptedData] could be decrypted using [decrypt].
   /// There seems to be no better way of doing this.
@@ -164,7 +161,7 @@ class CryptoStore {
   bool canDecrypt(Uint8List encryptedData) => decrypt(encryptedData) != null;
 
   /// Returns the HMAC secret key corresponding to the [key].
-  MACHashBase createHmacKey() => sha256.hmac.by(key);
+  MACHashBase get hmacSecretKey => sha256.hmac.by(key);
 }
 
 /// Represents a decoded salt.

lib/model/password_verification/methods/password_signature.dart

@@ -1,8 +1,6 @@
 import 'dart:async';
 import 'dart:convert';
-import 'dart:typed_data';
 
-import 'package:cipherlib/hashlib.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:open_authenticator/model/crypto.dart';
 import 'package:open_authenticator/model/password_verification/methods/method.dart';
@@ -48,8 +46,7 @@ class PasswordSignatureVerificationMethodNotifier extends AsyncNotifier<Password
   /// Generates the [password] signature with the given [salt].
   Future<String> _generatePasswordSignature(String password, Salt salt) async {
     CryptoStore cryptoStore = CryptoStore.fromPassword(password, salt);
-    MACHashBase hmacSecretKey = cryptoStore.createHmacKey();
-    String passwordSignature = hmacSecretKey.string(password, utf8).base64();
+    String passwordSignature = cryptoStore.hmacSecretKey.string(password, utf8).base64();
     return passwordSignature;
   }
 }
@@ -77,8 +74,6 @@ class PasswordSignatureVerificationMethod with PasswordVerificationMethod {
       return false;
     }
     CryptoStore cryptoStore = CryptoStore.fromPassword(password, salt);
-    MACHashBase hmacSecretKey = cryptoStore.createHmacKey();
-    Uint8List decodedSignature = base64.decode(passwordSignature!);
-    return hmacSecretKey.verify(decodedSignature, utf8.encode(password));
+    return cryptoStore.hmacSecretKey.verify(base64.decode(passwordSignature!), utf8.encode(password));
   }
 }

lib/utils/utils.dart

@@ -44,38 +44,6 @@ void handleException(Object? ex, StackTrace? stackTrace, {bool? sendToSentry}) {
 /// Returns whether the given type [S] is a subtype of type [T].
 bool isSubtype<S, T>() => <S>[] is List<T>;
 
-/// Compares two [Uint8List]s by comparing 8 bytes at a time.
-/// Kudos to https://stackoverflow.com/a/70751501/3608831.
-bool memEquals(Uint8List bytes1, Uint8List bytes2) {
-  if (identical(bytes1, bytes2)) {
-    return true;
-  }
-
-  if (bytes1.lengthInBytes != bytes2.lengthInBytes) {
-    return false;
-  }
-
-  // Treat the original byte lists as lists of 8-byte words.
-  var numWords = bytes1.lengthInBytes ~/ 8;
-  var words1 = bytes1.buffer.asUint64List(0, numWords);
-  var words2 = bytes2.buffer.asUint64List(0, numWords);
-
-  for (var i = 0; i < words1.length; i += 1) {
-    if (words1[i] != words2[i]) {
-      return false;
-    }
-  }
-
-  // Compare any remaining bytes.
-  for (var i = words1.lengthInBytes; i < bytes1.lengthInBytes; i += 1) {
-    if (bytes1[i] != bytes2[i]) {
-      return false;
-    }
-  }
-
-  return true;
-}
-
 /// A simple transparent image. Represented as a Uint8List, which was originally extracted from the Flutter codebase.
 Uint8List kTransparentImage = Uint8List.fromList([
   0x89,