一、软件中使用验证码的作用
现在软件中的很多地方有用到验证码，比如注册账号、登录的时候等等。验证码的使用是为了防止“爆破”既暴力破解，那什么是暴力破解呢，暴力破解就是利用程序，按照一定的规律往表单中输入数据，逐个测试。验证码 是随机产生的同时它不仅仅是单纯的图片或数字，只有输入的验证码正确之后才会去后台数据库做验证，从而防止暴力破解。
二、示例讲解
创建一个ASP.NET程序，单独添加一个Web页面用于生成验证码，相关代码如下：
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Drawing; using System.IO; using System.Drawing.Imaging; namespace UI { public partial class ValidateCodeCopy : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if(!IsPostBack) { //生成一个四位的随机码 string validateCode = RndNum(4); //将随机码保存到session中 Session["ValidateCode"] = validateCode; CreateImage(validateCode); } } /// <summary> /// 生成一个随机码 /// </summary> /// <param name="VCodeNum">随机码的位数</param> /// <returns></returns> public string RndNum(int VCodeNum ) { string VNUM = ""; string Vchar = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z"; String[] VcArray = Vchar.Split(new char[]{','}); Random rd = new Random(); for (int i = 0; i <= VCodeNum - 1;i++) { int t = rd.Next(36); VNUM += VcArray[t]; } return VNUM; } /// <summary> /// 生成随机颜色 /// </summary> /// <returns></returns> public Color GetRandomColor() { Random Rd_First = new Random((int)DateTime.Now.Ticks); Random Rd_Second = new Random((int)DateTime.Now.Ticks); //生成三个随机数 int red = Rd_First.Next(256); int Green = Rd_Second.Next(256); int blue = (red + Green) > 400 ? 0 : 400 - red + Green; blue = blue > 255 ? 255 : blue; return Color.FromArgb(red,Green, blue); } /// <summary> /// 将随机码绘制到图像，写入输出流 /// </summary> /// <param name="str_ValidateCode">随机码</param> public void CreateImage(string str_ValidateCode) { int int_imageWidth = str_ValidateCode.Length * 20; Bitmap thebitmap = new Bitmap(int_imageWidth,40); Random rd = new Random(); Graphics Gr = Graphics.FromImage(thebitmap); Gr.Clear(Color.White); Gr.DrawRectangle(new Pen(Color.LightGray, 1),0,0,int_imageWidth-1,39); Font font = new Font("Arial",16); for (int int_index = 0; int_index < str_ValidateCode.Length;int_index++ ) { string str_char = str_ValidateCode.Substring(int_index,1); Brush newBrush = new SolidBrush(GetRandomColor()); Point thePos = new Point(int_index * 20 + 1 + rd.Next(3), 3+ rd.Next(3)); Gr.DrawString(str_char, font, newBrush, thePos); } MemoryStream ms = new MemoryStream(); thebitmap.Save(ms, ImageFormat.Jpeg); Response.ClearContent(); Response.ContentType = "image/jpeg"; Response.BinaryWrite(ms.ToArray()); Gr.Dispose(); thebitmap.Dispose(); Response.End(); } } }
另外添加一张web页面 用于获取验证码，其前端HTML代码如下：
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Test.aspx.cs" Inherits="UI.Test" %> <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> <title></title> </head> <body> <form id="form1" runat="server"> <table> <tr> <td><img src="ValidateCodeCopy.aspx" name="yzm" id="yzm" alt="" /></td> <td><a href="#" onclick="yzm.src='ValidateCodeCopy.aspx?t='+(new Date().getTime());return false;">看不清，换一张？</a></td> </tr> </table> </form> </body> </html>
这样一个简单的验证码就实现了。
不积跬步无以至千里