用C#写DES加密算法解密出错

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string result = DESStr("guwei4037");
            Console.WriteLine("这是你的加密结果：{0}", result);//1tE8zvi9ouQJNb4FlxlKFQ==
 
            string src = FromDESStr(result);
            Console.WriteLine("这是我的解密结果：{0}", src);//guwei4037
        }
 
        /// <summary>
        /// DES加密
        /// </summary>
        /// <param name="src"></param>
        /// <returns></returns>
        public static string DESStr(string src)
        {
            string des = string.Empty;
            byte[] bysData = Encoding.UTF8.GetBytes(src);
 
            DESCryptoServiceProvider objDESCryptoServiceProvider = new DESCryptoServiceProvider();
            objDESCryptoServiceProvider.Key = Encoding.ASCII.GetBytes("12345678");//密钥
            objDESCryptoServiceProvider.Mode = CipherMode.ECB;
            objDESCryptoServiceProvider.Padding = PaddingMode.None;
 
            byte[] bysFixSizeData = new byte[(int)Math.Ceiling(bysData.Length / 8.0) * 8];
            Array.Copy(bysData, bysFixSizeData, bysData.Length);
 
            byte[] bysEncrypted = objDESCryptoServiceProvider.CreateEncryptor().TransformFinalBlock(bysFixSizeData, 0, bysFixSizeData.Length);//加密
            des = Convert.ToBase64String(bysEncrypted);//加密后的字符串
            if (des.Equals("")) des = "error";
            return des;
        }
 
        /// <summary>
        /// DES解密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string FromDESStr(string str)
        {
            string des = string.Empty;
            byte[] inputByteArray = Convert.FromBase64String(str);
 
            DESCryptoServiceProvider objDESCryptoServiceProvider = new DESCryptoServiceProvider();
            objDESCryptoServiceProvider.Key = Encoding.ASCII.GetBytes("12345678");//密钥
            objDESCryptoServiceProvider.Mode = CipherMode.ECB;
            objDESCryptoServiceProvider.Padding = PaddingMode.None;
 
            byte[] bysDEcrypted = objDESCryptoServiceProvider.CreateDecryptor().TransformFinalBlock(inputByteArray, 0, inputByteArray.Length);//解密
            byte[] bysFixSizeData = new byte[(int)Math.Ceiling(bysDEcrypted.Length / 8.0) * 8];
            Array.Copy(bysDEcrypted, bysFixSizeData, bysDEcrypted.Length);
 
            des = Encoding.UTF8.GetString(bysFixSizeData);//解密后的字符串
            if (des.Equals("")) des = "error";
            return des;
        }
    }
}