AesManaged - Padding is Invalid and Cannot Be Removed - Reading from .Txt File - encryption

Question

I am trying to save encrypted data to a Text file and then open and decrypt it. When I try to Decrypt it I receive the error "Padding is Invalid and Cannot Be Removed." I am using example code directly from Microsoft for encryption and decryption.
Here is MY code to encrypt and save file:
string json = JsonConvert.SerializeObject(credentials);
using (AesManaged myAes = new AesManaged())
{
byte[] encrypted = ControlHelperscs.EncryptStringToBytes_Aes(json, myAes.Key, myAes.IV);
File.WriteAllBytes(subPath, encrypted);
}
Here is my code to Retrieve and Decrypt file:
using (AesManaged myAes = new AesManaged())
{
byte[] file = File.ReadAllBytes(subPath);
string decrypt = ControlHelperscs.DecryptStringFromBytes_Aes(file, myAes.Key, myAes.IV);
credentials = JsonConvert.DeserializeObject<LoginModel>(decrypt);
}
Here are Encrypt and Decrypt methods:
public static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key, byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
byte[] encrypted;
// Create an AesManaged object
// with the specified key and IV.
using (AesManaged aesAlg = new AesManaged())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create an encryptor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return encrypted;
}
public static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key, byte[] IV)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
// Create an AesManaged object
// with the specified key and IV.
using (AesManaged aesAlg = new AesManaged())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decryptor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream(cipherText))
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
}
return plaintext;
}

Answer 1

I'm sorry I deleted my comment (it was wrong in that context), but I reworked your example to have a little less boilerplate and be able to encrypt and decrypt properly. The problem is that you're generating a new and different Key/IV pair to decrypt from the one you used to encrypt. Of course it won't be able to decrypt. So, here is the part to make it work:
byte[] key;
byte[] iv;
string json = JsonConvert.SerializeObject(credentials);
using (AesManaged myAes = new AesManaged())
{
key = myAes.Key;
iv = myAes.IV;
byte[] encrypted = ControlHelperscs.EncryptStringToBytes_Aes(json, key, iv);
File.WriteAllBytes(subPath, encrypted);
}
byte[] file = File.ReadAllBytes(subPath);
string decrypt = ControlHelperscs.DecryptStringFromBytes_Aes(file, key, iv);
credentials = JsonConvert.DeserializeObject<LoginModel>(decrypt);
and here are the slightly reworked heavy-lifting methods to be a bit more compact:
public static byte[] EncryptStringToBytes_Aes(string plainText, byte[] key, byte[] iv)
{
// Check arguments.
if (plainText is null)
{
throw new ArgumentNullException(nameof(plainText));
}
if (plainText.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(plainText), plainText, "length cannot be zero");
}
if (key is null)
{
throw new ArgumentNullException(nameof(key));
}
if (key.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(key), key, "length cannot be zero");
}
if (iv is null)
{
throw new ArgumentNullException(nameof(iv));
}
if (iv.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(iv), iv, "length cannot be zero");
}
// Create an AesManaged object
// with the specified key and IV.
// Create an encryptor to perform the stream transform.
// Create the streams used for encryption.
using (SymmetricAlgorithm aesAlg = new AesManaged { Key = key, IV = iv })
using (ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV))
using (MemoryStream msEncrypt = new MemoryStream())
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
using (TextWriter swEncrypt = new StreamWriter(csEncrypt))
{
// Write all data to the stream.
swEncrypt.Write(plainText);
swEncrypt.Flush();
csEncrypt.FlushFinalBlock();
// Return the encrypted bytes from the memory stream.
return msEncrypt.ToArray();
}
}
public static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] key, byte[] iv)
{
// Check arguments.
if (cipherText is null)
{
throw new ArgumentNullException(nameof(cipherText));
}
if (cipherText.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(cipherText), cipherText, "length cannot be zero");
}
if (key is null)
{
throw new ArgumentNullException(nameof(key));
}
if (key.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(key), key, "length cannot be zero");
}
if (iv is null)
{
throw new ArgumentNullException(nameof(iv));
}
if (iv.Length == 0)
{
throw new ArgumentOutOfRangeException(nameof(iv), iv, "length cannot be zero");
}
// Create an AesManaged object
// with the specified key and IV.
// Create a decryptor to perform the stream transform.
// Create the streams used for decryption.
using (SymmetricAlgorithm aesAlg = new AesManaged { Key = key, IV = iv })
using (ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV))
using (Stream msDecrypt = new MemoryStream(cipherText))
using (Stream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
using (TextReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
return srDecrypt.ReadToEnd();
}
}