DES-ECB encryption and decryption

Question

I'm using DES-ECB + base64 encryption in my application. That's the code of the class I called "Crypto"

public class Crypto
{

    public static string Decrypt(string encryptedString)
    {
        DESCryptoServiceProvider desProvider = new DESCryptoServiceProvider();
        desProvider.Mode = CipherMode.ECB;
        desProvider.Padding = PaddingMode.PKCS7;
        desProvider.Key = Encoding.ASCII.GetBytes("e5d66cf8");
        using (MemoryStream stream = new MemoryStream(Convert.FromBase64String(encryptedString)))
        {
            using (CryptoStream cs = new CryptoStream(stream, desProvider.CreateDecryptor(), CryptoStreamMode.Read))
            {
                using (StreamReader sr = new StreamReader(cs, Encoding.ASCII))
                {
                    return sr.ReadToEnd();
                }
            }
        }
    }

    public static string Encrypt(string decryptedString)
    {
        DESCryptoServiceProvider desProvider = new DESCryptoServiceProvider();
        desProvider.Mode = CipherMode.ECB;
        desProvider.Padding = PaddingMode.PKCS7;
        desProvider.Key = Encoding.ASCII.GetBytes("e5d66cf8");
        using (MemoryStream stream = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(stream, desProvider.CreateEncryptor(), CryptoStreamMode.Write))
            {
                byte[] data = Encoding.Default.GetBytes(decryptedString);
                cs.Write(data, 0, data.Length);
                return Convert.ToBase64String(stream.ToArray());
            }
        }
    }
}

but when I encrypt a string, then decrypt it again and encrypt one more time, the encrypted string is not the same as previous encrypted was. So that's the first encrypted string:

kEN0HUp/dqz8kXA7nYivJG6Jl3haLJjhBq1UfEtQTwaPwizW//03M0UxF8dBuYZo2BoZ5vsVcXRJF1LpFZLWxDsdeKAC43L2K2OoYRxTn/dA6KmM13YS9xOezGiROQfVj5qrkdokJRCvj0gYfFoH2oeDGyN+EAw5Dgzsp697kj4=

and here comes the second encrypted string:

kEN0HUp/dqz8kXA7nYivJG6Jl3haLJjhBq1UfEtQTwaPwizW//03M0UxF8dBuYZo2BoZ5vsVcXRJF1LpFZLWxDsdeKAC43L2K2OoYRxTn/dA6KmM13YS9xOezGiROQfVj5qrkdokJRCvj0gYfFoH2oeDGyN+EAw5

They are almost same, except this "Dgzsp697kj4=" in the first string.
What's wrong?
Thanks in advance.

Answer 1

You are losing data. In your Encrypt() method you need to call EncryptFinalBlock() to let the padding algorithm know that you are done so that it can add the padding:

using (CryptoStream cs = new CryptoStream(stream, desProvider.CreateEncryptor(), CryptoStreamMode.Write))
{
  byte[] data = Encoding.Default.GetBytes(decryptedString);
  cs.Write(data, 0, data.Length);
  cs.FlushFinalBlock(); // <-- Add this
  return Convert.ToBase64String(stream.ToArray());
}