1

I am working on a Rijndael256 encrypt and decrypt method in C# and it appears that my encrypt method is "working", however; my decrypt method randomly returns an error about the IV or Data I want to be decrypted stating "Invalid length for a Base-64 char array or string." The decrypt will work once or twice and then error. I am guessing it has something to do with the randomly generated IV size or something simple, but any guidance would be great. 

  private string encryptData(string data)
    {

        byte[] encKey = ASCIIEncoding.UTF8.GetBytes("pemgail9uzpgzl88");

        Rijndael aes = Rijndael.Create();
        aes.KeySize = 256;
        aes.BlockSize = 256;
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;
        aes.Key = encKey;

        ICryptoTransform crypto = aes.CreateEncryptor(aes.Key, aes.IV);
        byte[] txt = ASCIIEncoding.UTF8.GetBytes(data);
        byte[] cipherText = crypto.TransformFinalBlock(txt, 0, txt.Length);


        return Convert.ToBase64String(cipherText) + "&iv=" + Convert.ToBase64String(aes.IV); 
    }

My decrypt method:

    private string decryptData(string encData, string encIV)
    {

        byte[] encKey = ASCIIEncoding.UTF8.GetBytes("pemgail9uzpgzl88");
        string returnValue = Convert.ToBase64String(encKey);

        byte[] myIv = Convert.FromBase64String(encIV);

        byte[] myMessage = ASCIIEncoding.UTF8.GetBytes(encData);

        Rijndael aes = Rijndael.Create();
        aes.KeySize = 256;
        aes.BlockSize = 256;
        aes.IV = myIv;
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;
        aes.Key = encKey;

        ICryptoTransform crypto = aes.CreateDecryptor(aes.Key, aes.IV);
        byte[] txt = Convert.FromBase64String(encData);
        byte[] cipherText = crypto.TransformFinalBlock(txt, 0, txt.Length);

        return Encoding.UTF8.GetString(cipherText);
    }

As a test I am encrypting the data, redirecting the test page to itself and then taking the values in the QueryStrings to use for the decrypt method.

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.QueryString["data"] != null && Request.QueryString["iv"] != null)
        {
            string test = decryptData(Request.QueryString["data"], Request.QueryString["iv"]);
            Response.Write(test);
        }
        else
        {
            string test = encryptData("BrassMonkey");
            Response.Redirect("Rijindael.aspx?data=" + test);
        }

    }
Chris Lombardi
  • 861
  • 2
  • 14
  • 31
  • 1
    You're not showing how you parse the return of encrypt to eventually pass to decrypt. It's complaining at you what you're giving it is not really valid base64 so most likely you parsed your inputs incorrectly. – pvg Mar 29 '17 at 15:01
  • 1
    Do not use `Encoding.GetBytes()` to turn a password into a key. Look up the DeriveBytes class. – H H Mar 29 '17 at 15:05
  • 1
    And what exactly is `ASCIIEncoding.UTF8` ? I know it works but it is so wrong. – H H Mar 29 '17 at 15:09
  • I was using ASCII.GetBytes() but I changed it around hoping for a different result. – Chris Lombardi Mar 29 '17 at 15:10
  • 1
    Your "key" consists of 16 ASCII character which is 128 bit. So, your key size would be 128 and not 256. Also, why are you using Rijndael-256 instead of AES (Rijndael-128)? AES was cryptoanalysed much more in depth. Rijndael didn't get this much attention. You should use AES (`aes.BlockSize = 128`). – Artjom B. Mar 29 '17 at 15:18

0 Answers0