MD5加密 和 自定义加密解密

public class EncryptString
    {
        /// <summary>
        /// MD5加密
        /// </summary>
        /// <param name="instr"></param>
        /// <returns></returns>
        public static string EncryptMD5(string instr)
        {
            string result;
            try
            {
                byte[] toByte = Encoding.Default.GetBytes(instr);
                MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
                toByte = md5.ComputeHash(toByte);
                result = BitConverter.ToString(toByte).ToLower().Replace("-", "");
            }
            catch
            {
                result = "";
            }
            return result;
        }

        /// <summary>
        /// 加密（自定义的字节加密）
        /// </summary>
        /// <param name="str"></param>
        /// <param name="bo">是否加随机数</param>
        /// <returns></returns>
        public static string MyEncrypt(string str, bool bo)
        {
            char[] cs = str.ToCharArray();
            byte[] by;
            string results = "", temp = "";
            for (int i = 0; i < cs.Length; i++)
            {
                by = System.Text.Encoding.UTF8.GetBytes(cs[i].ToString());
                temp = Convert.ToBase64String(by);//每个字转换为四位
                if (bo)
                {
                    temp += Common.GetMes.Random(10, 99).ToString();//同时加两个随机变量
                }
                results += temp;//（每个变为6位）全部相加
            }
            return results;
        }
        /// <summary>
        /// 解密(自定义的字节加密)
        /// </summary>
        /// <param name="str"></param>
        /// <param name="t">要和上面的对应，如果加了随机数则t值应该为6，不加的话是4，否则出错</param>
        /// <returns></returns>
        public static string DeMyEnncrypt(string str, int t)
        {
            string result = "", strtemp = "";
            try
            {
                char[] cs = str.ToCharArray();
                string[] temp = Common.GetMes.ArrayListstr(str, t);
                byte[] by;
                for (int i = 0; i < temp.Length; i++)
                {
                    strtemp = (temp[i].ToString()).Substring(0, 4);
                    by = Convert.FromBase64String(strtemp);
                    result += System.Text.Encoding.UTF8.GetString(by);
                }
                return result;
            }
            catch
            {
                return "";
            }
        }

        /// <summary>
        /// 把一个字符串按照n位长度分割为数组
        /// </summary>
        /// <param name="str"></param>
        /// <param name="n"></param>
        /// <returns></returns>
        public static string[] ArrayListstr(string str, int n)
        {
            string[] result;
            try
            {
                if (n <= 0)
                {
                    n = str.Length;
                }
                int arrynum = 0;
                arrynum = (int)(str.Length / n);
                if (arrynum <= 0)
                {
                    arrynum = 1;
                }
                result = new string[arrynum];
                for (int i = 0; i < arrynum; i++)
                {
                    result[i] = str.Substring(n * i, n);
                }
            }
            catch
            {
                result = new string[1] { "" };
            }
            return result;
        }
    }