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)

Answer 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.