public string Decrypt(string pToDecrypt, string sKey)
        {
            byte[] buffer = Convert.FromBase64String(pToDecrypt); 
            DESCryptoServiceProvider provider = new DESCryptoServiceProvider();
            provider.Key = Encoding.ASCII.GetBytes(sKey);
            provider.IV = Encoding.ASCII.GetBytes(sKey);
            MemoryStream stream = new MemoryStream();
            CryptoStream stream2 = new CryptoStream(stream, provider.CreateDecryptor(), CryptoStreamMode.Write);
            stream2.Write(buffer, 0, buffer.Length);
            stream2.FlushFinalBlock();
            stream2.Close(); 
            string str = Encoding.UTF8.GetString(stream.ToArray());
            stream.Close();
            return str;
        }要有效的代码。