With flutter_sodium you get access to the modern, easy-to-use libsodium crypto library in your Flutter apps. One set of crypto APIs supporting both Android and iOS.

In your flutter project add the dependency:

dependencies:
  ...
  flutter_sodium: ^0.2.0

Import the plugin and initialize it. Sodium.init() initializes the plugin and should be called before any other function provided by flutter_sodium.

import 'package:flutter_sodium/flutter_sodium.dart';

// initialize sodium
Sodium.init();

// Password hashing (using Argon)
final password = 'my password';
final str = PasswordHash.hashStringStorage(password);

print(str);

// verify hash str
final valid = PasswordHash.verifyStorage(str, password);

assert(valid);

This project includes an extensive example app with runnable code samples. Be sure to check it out!

The flutter_sodium plugin implements the following libsodium APIs:

• crypto_aead
• crypto_auth
• crypto_box
• crypto_generichash
• crypto_hash
• crypto_kdf
• crypto_kx
• crypto_onetimeauth
• crypto_pwhash
• crypto_scalarmult
• crypto_secretbox
• crypto_secretstream
• crypto_shorthash
• crypto_sign
• crypto_stream
• randombytes
• sodium_version

API coverage is not 100% complete, track the progress in issue #61

The plugin includes a core API that maps native libsodium functions 1:1 to Dart equivalents. The core API is available in the class Sodium. Dart naming conventions are used for core API function names. A native libsodium function such as crypto_pwhash_str, is available in flutter as Sodium.cryptoPwhashStr.

Also included in flutter_sodium is a high-level, opinionated API providing access to libsodium in a Dart friendly manner. The various functions are available in separate Dart classes. Password hashing for example is available in the PasswordHash class. The high-level API depends on the core API to get things done.

The FFI implementation of flutter_sodium is backwards incompatible with the previous platform channel implementation. The list of changes:

• the entire FFI API is now synchronous, while the previous implementation was entirely asynchronous
• all hardcoded libsodium constants are now available as properties on the Sodium class.
• in the platform channel versions the Android and iOS implementations were not in sync. Some functions were available only in iOS, others only in Android. With the FFI implementation, there is a single API covering both platforms.

Since the entire FFI API is synchronous, you'll need to do some extra work to execute long running crypto function on a background thread. Luckily this is very easy with Flutter's compute function.

The following code snippet demonstrates running a password hash on the background thread.

final pw = 'hello world';
final str = await compute(PasswordHash.hashStringStorageModerate, pw);

print(str);