how to decrypt a base 64 string? - flutter

Question

I'll explain my problem, I'm trying to encrypt a password, then save it locally so that I can go and retrieve it when necessary, decrypt it and assign it wherever I want.
In the encryption phase I do not get any problems in the sense that the encrypt method can easily return a string while in the decrypt method I have problems, because the return type seems to have to be of the Encrypt type.
By doing so it is impossible for me to go and get the string saved locally thanks to sharedPreferences and be able to decrypt it, I am going to give you the code below to better understand my problem:
class _State extends State<SettingsPage> {
static final key = encrypt.Key.fromLength(32);
static final iv = encrypt.IV.fromLength(16);
static final encrypter = encrypt.Encrypter(encrypt.AES(key));
static encryptAES(text) {
final encrypted = encrypter.encrypt(text, iv: iv);
return encrypted;
}
static decryptAES(text) {
print(text.base64);
String decrypted = encrypter.decrypt(text, iv: iv);
print(decrypted);
return decrypted;
}
SettingsPage.inputPassword = input[0];
// SettingsPage.inputPassword = tec.text;
encryptedText = encryptAES(SettingsPage.inputPassword).base64;
setState(() {
String encryptedText =
encryptAES(SettingsPage.inputPassword).base64;
print("PROVA ENCRYPTED TEXT " + encryptedText);
});
prefs.setString('savedPass', encryptedText.base64);
String decryptedText = decryptAES(encryptedText).base64;
print("PROVA TESTO DECRIPTATO " + decryptedText);
}
},
Everything proceeds as required until the password is saved, then I ask you how to decrypt a string in order to be able to assign the variable DecryptedText to the String variable correctly, since at this moment I am told:
Unhandled Exception: NoSuchMethodError: Class 'String' has no instance getter 'base64'.
This is because it would appear that the decrypted method can only return an Encrypt type.
The pub.dev API used is encrypt: ^5.0.1.
THANKS.

Answer 1

I'm not familiar with package:encrypt, but skimming over the documentation you should be using Encrypted.fromBase64 to construct an Encrypted object to pass to Encrypter.decrypt:
static String decryptAES(String base64Text) {
print(base64Text);
String decrypted = encrypter.decrypt(Encrypted.fromBase64(base64Text), iv: iv);
print(decrypted);
return decrypted;
}
Note that you also should be calling just decryptAES(...), not decryptAES(...).base64. (You want the original text back, not a base64-encoded version.)
encryptedTextBase64 = encryptAES(SettingsPage.inputPassword).base64;
...
String decryptedText = decryptAES(encryptedTextBase64);
I will point out that your code is very hard to follow (which is especially bad for security-related code) because:
Your functions do not declare argument types nor return types and therefore take and return dynamic types. This makes it hard to understand what arguments they expect and what they are expected to return.
You should name your variables to make it clear what is base64-encoded and what isn't. (I renamed the variables in the example above.)