encrypt method
Implementation
EncryptedMessage encrypt(Uint8List plainText, {Uint8List? nonce}) {
final nonce1 = nonce ?? TweetNaCl.randombytes(TweetNaCl.nonceLength);
final m = Uint8List(TweetNaCl.zerobytesLength).toList() + plainText;
final c = Uint8List(m.length);
final cipherText = doEncrypt(c, Uint8List.fromList(m), m.length,
Uint8List.fromList(nonce1), key.asTypedList);
return EncryptedMessage(nonce: nonce1, cipherText: cipherText);
}