asp.net中使用cookie与md5加密实现记住密码功能的实现代码

在做一个前台的登陆和后台的信息审核管理功能时，需要用到记住密码的模块：
虽然.net内置了登陆控件，有记住密码的功能，但还是想自己实践一下，以下代码主要应用了cookie，包括安全加密的过程等。

//设置，删除cookie
//provider jb51.net
        protected void set_cookie()
        {
            httpcookie usernamecookie = request.cookies["usernamecookie"];
            httpcookie userpasswordcookie = request.cookies["userpasswordcookie"];
            if (this.chesave.checked)
            {
                lblcookie.text = "1";
                //保存用户名和密码到cookie
                if (usernamecookie == null)
                {
                    usernamecookie = new httpcookie("usernamecookie");
                    usernamecookie.values.add("username", txtusername.text);
                    usernamecookie.expires = datetime.now.adddays(30);
                    response.cookies.add(usernamecookie);
                }
                //修改cookie
                else if (usernamecookie.values["username"] != txtusername.text)
                {
                    settocookie(usernamecookie, "username", txtusername.text);
                }
                if (userpasswordcookie == null)
                {
                    userpasswordcookie = new httpcookie("userpasswordcookie");
                    string password1 = formsauthentication.hashpasswordforstoringinconfigfile(txtuserpassword.text, "md5");     //如果重新指定用户密码，则重新加密密码
                    userpasswordcookie.values.add("userpassword", password1);
                    userpasswordcookie.expires = datetime.now.adddays(30);
                    response.cookies.add(userpasswordcookie);
                }
                else if (userpasswordcookie.values["userpassword"] != formsauthentication.hashpasswordforstoringinconfigfile(txtuserpassword.text, "md5") && txtuserpassword.text != "1234567890") 
                //“1234567890”是程现在密码框中的十个字符。
                {
                    settocookie(userpasswordcookie, "userpassword", formsauthentication.hashpasswordforstoringinconfigfile(txtuserpassword.text, "md5"));
                }
            }
            else
            {
                lblcookie.text = "0";
                //从cookie删除用户名和密码
                if (response.cookies["usernamecookie"] != null)
                {
                    httpcookie mycookie = new httpcookie("usernamecookie");
                    mycookie.expires = datetime.now.adddays(-1d);
                    response.cookies.add(mycookie);
                }
                if (response.cookies["userpasswordcookie"] != null)
                {
                    httpcookie mycookie = new httpcookie("userpasswordcookie");
                    mycookie.expires = datetime.now.adddays(-1d);
                    response.cookies.add(mycookie);
                }
            }
        }
        //检查是否存在cookie情况
        public void check_cookie()
        {
            httpcookie usernamecookie = request.cookies["usernamecookie"];
            httpcookie userpasswordcookie = request.cookies["userpasswordcookie"];
            if (usernamecookie != null)
            {
                this.chesave.checked = true;
                txtusername.text = usernamecookie.values["username"];
            }
            if (userpasswordcookie != null)
            {
                txtuserpassword.attributes.add("value", "1234567890");//设置密码框初始值
            }
        }
        public string getpassword()
        {
            httpcookie userpasswordcookie = request.cookies["userpasswordcookie"];
            string strpwd = "";  //获取此密码字符串与数据库存中的密布相比。
            if (lblcookie.text == "1")
            {
                strpwd = userpasswordcookie.values["userpassword"];//直接获取cookie中的密码值
            }
            else
            {
                strpwd= formsauthentication.hashpasswordforstoringinconfigfile(txtuserpassword.text, "md5"); //对密码进行加密
            }
            return strpwd;  //返回密码字段   
        } 
        //修改cookie这段的方法
        public void settocookie(httpcookie httpcookie, string cookiename, string cookievalue)
        {
            httpcookie.values[cookiename] = cookievalue;
            httpcookie.expires = datetime.now.adddays(30);
            response.cookies.add(httpcookie);
        }
    }