1.理论定义

       策略模式 定义了 多套算法，这些算法在 客户端 可以任意切换。

   2.应用举例

          需求描述：话说007在皇家赌场赌牌，突然接到M夫人的急电，要求立刻去非洲 寻找一个DES对称算法密钥，以破解敌人的军*情*机*密

　        　1、(英*国*军*情*六*局)MI6=Military Intelligence 6  截获了 一个非*洲战*区军*事*机*密文件，采用 MD5，RAS，加密，解密，都无法破解

　　           后来发现，这文件被DES加密， 必须找回对称密钥，才可以破解

　　        2、邦德 火速赶往 非洲，目标只有一个：找到密钥。

   3.具体编码

      1.定义安全 算法接口，里面有加密和解密方法

      

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace Com.Design.Gof.Strategy{    public interface ISecurity    {        /// 
        /// 加密        /// 
        /// 要加密字符串        /// 
             string Encrypt(string EncryptString);        /// 
        /// 解密        /// 
        /// 要解密字符串        /// 
             string Decrypt(string EncryptString);    }}

2.MD5加密

using System;using System.Collections.Generic;using System.Text;using System.IO;using System.Security.Cryptography;namespace Com.Design.Gof.Strategy{    public class MD5 : ISecurity    {        /// 
        /// 用MD5加密        /// 
        ///         /// 
             public  string Encrypt(string s)        {            byte[] b = Encoding.Default.GetBytes(s);            b = new MD5CryptoServiceProvider().ComputeHash(b);            string output = "";            for (int i = 0; i < b.Length; i++)                output += b[i].ToString("x").PadLeft(2, '0');            return output;        }        /// 
        /// MD5不提供解密        /// 
        ///         /// 
             public virtual string Decrypt(string EncryptString) { return string.Empty; }    }}

3.RSA加密

using System;using System.Text;using System.IO;using System.Security.Cryptography;using System.Security.Cryptography.X509Certificates;namespace Com.Design.Gof.Strategy{    public class RSA:ISecurity    {        private static readonly string key=new RSACryptoServiceProvider().ToXmlString(true);              /// 
        /// RSA加密函数        /// 
        /// 说明:KEY必须是XML的行式,返回的是字符串        ///         /// 
             public string Encrypt(string s)        {            try            {                byte[] PlainTextBArray;                byte[] CypherTextBArray;                string Result;                RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();                rsa.FromXmlString(key);                PlainTextBArray = (new UnicodeEncoding()).GetBytes(s);                CypherTextBArray = rsa.Encrypt(PlainTextBArray, false);                Result = Convert.ToBase64String(CypherTextBArray);                return Result;            }            catch { return "敌人密码太难破解，已经超过了RSA算法的承受能力，要采取分段加密"; }        }        /// 
        /// RSA解密函数        /// 
        ///         ///         /// 
             public string Decrypt(string s)        {             try            {            byte[] PlainTextBArray;            byte[] DypherTextBArray;            string Result;            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();            rsa.FromXmlString(key);            PlainTextBArray = Convert.FromBase64String(s);            DypherTextBArray = rsa.Decrypt(PlainTextBArray, false);            Result = (new UnicodeEncoding()).GetString(DypherTextBArray);            return Result;            }             catch { return "敌人密码太难破解，已经超过了RSA算法的承受能力，要采取分段解密"; }        }    }}

4.DES加密

using System;using System.Text;using System.IO;using System.Security.Cryptography; /// 
///MethodResult 的摘要说明/// 
namespace Com.Design.Gof.Strategy{    public class DES:ISecurity    {        private static byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF }; //密钥向量        //加密解密key        public string SymmetricKey { get; set; }        /// 
        /// 加密        /// 
        /// 待加密的字符串        /// 加密密钥        /// 
     
      加密成功返回加密后的字符串,失败返回源串
             public  string Encrypt(string EncryptString)        {            byte[] byKey = null;            byKey = System.Text.Encoding.UTF8.GetBytes(SymmetricKey.Substring(0, 8));            DESCryptoServiceProvider des = new DESCryptoServiceProvider();            byte[] inputByteArray = System.Text.Encoding.UTF8.GetBytes(EncryptString);            MemoryStream ms = new MemoryStream();            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(byKey, IV), CryptoStreamMode.Write);            cs.Write(inputByteArray, 0, inputByteArray.Length);            cs.FlushFinalBlock();            return Convert.ToBase64String(ms.ToArray());        }        /// 
        /// 解密        /// 
        /// 待解密的字符串        /// 
     
      解密成功返回解密后的字符串,失败返源串
             public  string Decrypt(string EncryptString)        {            byte[] byKey = null;            byte[] inputByteArray = new Byte[EncryptString.Length];            try            {                byKey = System.Text.Encoding.UTF8.GetBytes(SymmetricKey.Substring(0, 8));                DESCryptoServiceProvider des = new DESCryptoServiceProvider();                inputByteArray = Convert.FromBase64String(EncryptString);                MemoryStream ms = new MemoryStream();                CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(byKey, IV), CryptoStreamMode.Write);                cs.Write(inputByteArray, 0, inputByteArray.Length);                cs.FlushFinalBlock();                System.Text.Encoding encoding = new System.Text.UTF8Encoding();                return encoding.GetString(ms.ToArray());            }            catch            {                return "";            }        }       }}

5 (英*国*军*情*六*局)MI6=Military Intelligence 6

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace Com.Design.Gof.Strategy{    /// 
    /// (英*国*军*情*六*局)MI6=Military Intelligence 6    /// 
    public class MilitaryIntelligence6    {
    /// 
        /// 安全策略        /// 
        private ISecurity Security { get; set; }        /// 
        /// 被加密的军*情*信*息        /// 
        public string ClassifiedInfomation { get; set; }        /// 
        /// 加密        /// 
        ///         /// 
             public string Encrypt() {            return Security.Encrypt(ClassifiedInfomation);        }        /// 
        /// 解密        /// 
        ///         /// 
             public string Decrypt(string s) {            return Security.Decrypt(s);        }    }}

6.主函数

using System;using System.Collections.Generic;using System.Linq;using System.Text;using Com.Design.Gof.Strategy;namespace Com.Design.Gof.Test{    class Program    {        /// 
        /// 往期 设计模式测试项目是一起的，想测试谁，就调用谁        /// 
        ///         static void Main(string[] args)        {            MilitaryIntelligence6 MI6= new MilitaryIntelligence6            {                //默认密码策略 MD5                 Security = new MD5(),                //被加密的  军*情*信*息                ClassifiedInfomation = @"+30/SxY2HZ0UtqUVNGMsad0zfajsHQmja1NVC+639zC6y0dE/8XDZJefMl0NwBJ+sUA8LC8k/IPEeTtFqW6OWaaZH9A+TNWzrJ6MSV2qiM3px6wFAyDkJsMKex0mJNe5",            };            //用 MD5 破解            string result_md5 = MI6.Encrypt();            Console.WriteLine("用MD5破解敌*人机密文件：" + result_md5);            Console.WriteLine("MD5加密后，还是一团乱麻，机密文件无法破解");            Console.WriteLine();            //用 RSA  破解            MI6.Security = new RSA();            string Result_RSA = MI6.Encrypt();            Console.WriteLine(Result_RSA);                       //用 DES 破解            string symmetricKey = "AfricaArea";//007完成使命，拿到了密钥            MI6.Security = new DES { SymmetricKey = symmetricKey };                     //解密后的内容应该是：军-情-机-密-信-息:我军将要攻打 非*洲，战区指挥官：隆美尔，坦克：500辆，飞机：2000架            Console.WriteLine();            Console.WriteLine("007获取到了DES解密密码，打开了 军-事-机-密文件，内容如下：" + MI6.Decrypt(MI6.ClassifiedInfomation));            Console.ReadKey();        }    }}

 

7.运行结果

 

8.总结

  RSA算法还值得进一步去看下，字符过长时候，如何进行分段加密。

 借鉴了  的意见，去除了 枚举和 Switch，直接在客户端New 算法。

  附件里面包括了程序源码。

  这里是附件