新手求助:TripleDES要解密的数据的长度无效

[nuclear2011]

这个是逆向某个程序的代码,源代码经过混淆,整理过的代码如下

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace Database4Test
{
    class Program
    {
        private static TripleDESCryptoServiceProvider tdes;
        private static SHA256Managed sha256;
        private static string magic;
        private static string delimiter;

        static Program()
        {
            tdes=new TripleDESCryptoServiceProvider();
            sha256=new SHA256Managed();
            magic = "fishDatabase";
        }

        static void Main(string[] args)
        {
            Console.Write("Please input your data:");
            string serial = Console.ReadLine();
            Console.WriteLine("Now compute serial:{0}", ComputeExpression(Encoding.UTF8.GetBytes(serial.Trim()), GetTripleDESKey(Encoding.UTF8.GetBytes(magic))));
            Console.ReadKey();
        }

        private static byte[] GetTripleDESKey(byte[] input)
        {
            int length = tdes.Key.Length;
            if (length != input.Length)
            {
                byte[] output = new byte[length];
                Array.Copy(sha256.ComputeHash(input), output, length - 1);
                return output;
            }
            return input;
        }

        private static byte[] GetTripleDESIV(byte[] input, int length)
        {
            byte[] output = new byte[length];
            Array.Copy(sha256.ComputeHash(Encoding.UTF8.GetBytes(Encoding.UTF8.GetString(input))), output, length - 1);
            return output;
        }

        private static string ComputeExpression(byte[] input1, byte[] input2)
        {
            ICryptoTransform transform = null;
            string str = string.Empty;
            try
            {
                byte[] buffer1 = Convert.FromBase64String(Encoding.UTF8.GetString(input1));
                using (MemoryStream ms = new MemoryStream(buffer1))
                {
                    byte[] buffer2 = new byte[buffer1.Length + 1];
                    transform = tdes.CreateDecryptor(input2, GetTripleDESIV(input2, tdes.IV.Length));
                    using (CryptoStream cs = new CryptoStream(ms, transform, CryptoStreamMode.Read))
                    {
                        cs.Read(buffer2, 0, buffer2.Length);
                    }
                    str = Encoding.UTF8.GetString(buffer2).Replace("\0", "");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                transform.Dispose();
            }
            return str;
        }
    }
}

在执行到解密的时候会出现 要解密的数据长度无效
我不知道该怎么解决 求各位大神帮忙

另:希望有人能据此写出加密算法
谢谢