用Encrypt、Decrypt對密碼進行編碼和解碼操作。

    在程序中調用這個類Encryption:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace DBTools
{
    public class Encryption
    {
        /// <summary> 
        /// 加密數據 
        /// </summary> 
        /// <param name="Text"></param> 
        /// <param name="sKey"></param> 
        /// <returns></returns> 
        public static string Encrypt(string Text, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            byte[] inputByteArray;
            inputByteArray = Encoding.Default.GetBytes(Text);
            des.Key = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            des.IV = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            StringBuilder ret = new StringBuilder();
            foreach (byte b in ms.ToArray())
            {
                ret.AppendFormat("{0:X2}", b);
            }
            return ret.ToString();
        }
        /// <summary> 
        /// 解密數據 
        /// </summary> 
        /// <param name="Text"></param> 
        /// <param name="sKey"></param> 
        /// <returns></returns> 
        public static string Decrypt(string Text, string sKey)
        {
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            int len;
            len = Text.Length / 2;
            byte[] inputByteArray = new byte[len];
            int x, i;
            for (x = 0; x < len; x++)
            {
                i = Convert.ToInt32(Text.Substring(x * 2, 2), 16);
                inputByteArray[x] = (byte)i;
            }
            des.Key = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            des.IV = ASCIIEncoding.ASCII.GetBytes(System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(sKey, "md5").Substring(0, 8));
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            return Encoding.Default.GetString(ms.ToArray());
        } 
        // MD5 32 位
        public static String Encrypt32(String convertString)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] bytes = System.Text.Encoding.UTF8.GetBytes(convertString);
            bytes = md5.ComputeHash(bytes);
            md5.Clear();
            string ret = "";
            for (int i = 0; i < bytes.Length; i++)
            {
                ret += Convert.ToString(bytes[i], 16).PadLeft(2, '0');
            }
            return ret.PadLeft(32, '0').ToLower();
        }
        // MD5 16 位
        public static string Encrypt16(string convertString)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            string t2 = BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(convertString)), 4, 8);
            t2 = t2.Replace("-", "");
            return t2.ToLower();
        }
    }
}

    cs:

編碼時：string Pwd = DBTools.Encryption.Encrypt(LoginPwd, "Master");    
            //LoginPwd--要加密的數據。也可以將二進制值傳遞給此函數。此參數區分大小寫，即使是在不區分大小寫的數據庫中也是如此。
            //Master--用來對 LoginPwd 進行加密的加密密鑰。解密時必須使用同一密鑰才能獲得原始值。此參數區分大小寫，即使是在不區分大小寫的數據庫中也是如此。
與大多數口令一樣，最好選擇無法被輕易猜到的密鑰值。建議選擇滿足以下條件的密鑰值：長度至少爲 16 個字符，混合使用大小寫幷包含數字、字母和特殊字符。每次要對數據進行解密時，都需要使用此密鑰。

解碼時：string Pwd = DBTools.Encryption.Decrypt(LoginPwd, "Master"); //跟編碼講解一致