Can I decrypt password using the private key generated in Django backend in Flutter? - django

Question

I am making a password manager app where I am using asymmetric encryption to store passwords. I have created a Django backend for the app where I have stored the user's public key in the User model. During registration, I am storing the public key in the database and sending the user their private key to the Flutter app.
I am using the following function to encrypt the password and store it in the password store model:
def encrypt(data, key):
key = serialization.load_pem_public_key(
key.encode(),
backend=default_backend()
)
data = key.encrypt(
data.encode(),
padding.OAEP(
mgf=padding.MGF1(algorithm=hashes.SHA256()),
algorithm=hashes.SHA256(),
label=None
)
)
return data
Now, I want to know if I can decrypt passwords or any other string data in Flutter using the private key that is generated in the Django backend. If yes, how can I do it?
Also, I don't want to pass the decrypted password from the backend to the Flutter app. I want the client-side to handle it. For this, I am storing the private key in the user's device using shared preferences in Flutter:
SharedPreferences.getInstance().then((prefs) {
prefs.setString("privateKey", widget.privateKey);
});
Can anyone help me with this?
I tried using the decryptByPrivateKey function below to decrypt a password on the client side in my Flutter app using a private key generated on my Django backend:
dynamic decryptByPrivateKey(String content) async {
final prefs = await SharedPreferences.getInstance();
final private = prefs.getString('privateKey')!;
RSAKeyParser parser = RSAKeyParser();
RSAPrivateKey privateKey = parser.parse(private) as RSAPrivateKey;
AsymmetricBlockCipher cipher = PKCS1Encoding(RSAEngine());
cipher..init(false, PrivateKeyParameter<RSAPrivateKey>(privateKey));
return utf8.decode(cipher.process(Encrypted.fromBase64(content).bytes));
}
However, I got the following error related to the content parameter, and I'm not sure how to resolve it:
FormatException: Invalid character (at character 2) b'\rV\x86ldn\x171*^c\xabsAc;\xead\xea\x05C\x996o\x0e#\xe2\xed\x1c\xa21\x80d... ^
Also, I am generating and sending the private key to the client as shown in the code snippet below:
private_key = rsa.generate_private_key(
public_exponent=65537,
key_size=2048,
backend=default_backend()
)
public_key = private_key.public_key()
public_key = public_key.public_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PublicFormat.SubjectPublicKeyInfo
)
private_key = private_key.private_bytes(
encoding=serialization.Encoding.PEM,
format=serialization.PrivateFormat.PKCS8,
encryption_algorithm=serialization.NoEncryption()
)
private_key = private_key.decode('utf-8')
public_key = public_key.decode('utf-8')
I am hoping to be able to decrypt the password on the client side using the private key without passing the decrypted password from the backend. Can anyone help me with this issue?"