用Encrypt、Decrypt对密码进行编码和解码操作。

    在程序中调用这个类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
    {
        /// 
 
        /// 加密数据 
        /// 
 
        ///  
        ///  
        ///  
        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();
        }
        /// 
 
        /// 解密数据 
        /// 
 
        ///  
        ///  
        ///  
        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:

编码时：string Pwd = DBTools.Encryption.Encrypt(LoginPwd, "Master");    
            //LoginPwd--要加密的数据。也可以将二进制值传递给此函数。此参数区分大小写，即使是在不区分大小写的数据库中也是如此。
            //Master--用来对 LoginPwd 进行加密的加密密钥。解密时必须使用同一密钥才能获得原始值。此参数区分大小写，即使是在不区分大小写的数据库中也是如此。
与大多数口令一样，最好选择无法被轻易猜到的密钥值。建议选择满足以下条件的密钥值：长度至少为 16 个字符，混合使用大小写并包含数字、字母和特殊字符。每次要对数据进行解密时，都需要使用此密钥。

解码时：string Pwd = DBTools.Encryption.Decrypt(LoginPwd, "Master"); //跟编码讲解一致