private static byte[] Decode(byte[] cipherData, byte[] key, byte[] initVector)
{
    MemoryStream memoryStream = new MemoryStream();
    Rijndael algorythmus = Rijndael.Create();
    algorythmus .Key = key;
    algorythmus .IV = initVector;
    
    CryptoStream cs = new CryptoStream(memoryStream, algorythmus .CreateDecryptor(), CryptoStreamMode.Write);
    cs.Write(cipherData, 0, cipherData.Length);
    cs.Close();
    
    byte[] decryptedData = memoryStream.ToArray();

    return decryptedData;
}