Cryptographicexception at encrypting string

Question

At the moment, I'm working on a project that involves encryption. Therefore, I have a class, which worked fine in .NET 4.0, but now that I changed it so it would work in .NET 2.0, it fails to encrypt almost any string... I don't know why, but it fails every time and throws a CryptographicException. Decrypting works fine as far as I can tell, and everything else too. Anyway, here's the code:

public class Encryption
{
    static readonly string PasswordHash = "P@@Sw0rd";
    static readonly string SaltKey = "S@LT&KEY";
    static readonly string VIKey = "@1B2c3D4e5F6g7H8";
    public static string Encrypt(string plainText, string passwordHash)
    {
        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
        byte[] keyBytes = new Rfc2898DeriveBytes(passwordHash, Encoding.ASCII.GetBytes(SaltKey)).GetBytes(256 / 8);
        RijndaelManaged symmetricKey = new RijndaelManaged();
        symmetricKey.Mode = CipherMode.CBC;
        symmetricKey.Padding = PaddingMode.None;
        ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, Encoding.ASCII.GetBytes(VIKey));
        byte[] cipherTextBytes;
        using (MemoryStream memoryStream = new MemoryStream())
        {
            using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
            {
                cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
                cryptoStream.FlushFinalBlock();
                cipherTextBytes = memoryStream.ToArray();
                cryptoStream.Close();
            }
            memoryStream.Close();
        }
        return Convert.ToBase64String(cipherTextBytes);
    }
    public static string Decrypt(string encryptedText, string passwordHash)
    {
        byte[] cipherTextBytes = Convert.FromBase64String(encryptedText);
        byte[] keyBytes = new Rfc2898DeriveBytes(passwordHash, Encoding.ASCII.GetBytes(SaltKey)).GetBytes(256 / 8);
        RijndaelManaged symmetricKey = new RijndaelManaged(); 
        symmetricKey.Mode = CipherMode.CBC;
        symmetricKey.Padding = PaddingMode.None;
        ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, Encoding.ASCII.GetBytes(VIKey));
        MemoryStream memoryStream = new MemoryStream(cipherTextBytes);
        CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
        byte[] plainTextBytes = new byte[cipherTextBytes.Length];
        int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
        memoryStream.Close();
        cryptoStream.Close();
        return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount).TrimEnd("\0".ToCharArray());
    }
}

The error message is (translated from German):

CryptographicException: Length of the data to encrypt is invalid. at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount) at System.Security.Cryptography.CryptoStream.FlushFinalBlock() at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)

You said "almost any string". Please show the strings that work. Also, where is the exception thrown? — Artjom B.
– Artjom B., Commented Feb 14, 2015 at 20:31
You need to give more details than just "throws a CryptographicException". What is the exact error and message? From what I can tell, you should not be setting the Padding to None because arbitrary strings aren't going to completely fill blocks. Just remove that line from Encrypt. — Mike Zboray
– Mike Zboray, Commented Feb 14, 2015 at 20:37
Encryption.Encrypt("Client connected!", "elit3Nase") does not work Encryption.Encrypt("Client connectedasdssssssssssssssssssssssssssss!", "elit3Nase") does work... I was just playing around and spammed some chars, and it suddently worked — chesta
– chesta, Commented Feb 14, 2015 at 20:43
Just try it, there's a CryptographicException on cryptoStream.FlushFinalBlock(); call. — rducom
– rducom, Commented Feb 14, 2015 at 20:44

Alex K. · Accepted Answer · 2015-02-14 20:50:24Z

1

Encryption.Encrypt("Client connected!", "elit3Nase") does not work

"Client connected!" is not long enough to fully fill a block (16 bytes) and you are not using padding:

symmetricKey.Padding = PaddingMode.None;

Change to symmetricKey.Padding = PaddingMode.PKCS7; to ensure padding is applied.

edited Feb 14, 2015 at 20:50

answered Feb 14, 2015 at 20:45

Alex K.

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2 Comments

chesta Over a year ago

Would it alternatively be possible to change the password? And would a 16+ bytes long password solve the problem?

Alex K. Over a year ago

Sorry I mean the input text "Client connected!" is not a multiple of the block size (128 bits = 16 bytes) - yes you can add characters as needed to make sure it always is

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