Asp. NET Random code Generation example

Now many web sites use the random image of the way, is a simple, effective means of preventing malicious attacks. Today, I read some information on the Internet to understand its generative principle: from the sample, get the random string, the random string is saved into the session, and a bitmap form random code picture.

Realize:

Add namespaces

Using System.Drawing;

Using System.Drawing.Imaging;

Using System.Drawing.Drawing2D;

Generate page code

using System;


using System.Data;


using System.Configuration;


using System.Collections;


using System.Web;


using System.Web.Security;


using System.Web.UI;


using System.Web.UI.WebControls;


using System.Web.UI.WebControls.WebParts;


using System.Web.UI.HtmlControls;


using System.Drawing;


using System.Drawing.Imaging;


using System.Drawing.Drawing2D;


public partial class GetRandImg:System.Web.UI.Page


{


protected void Page_Load (object sender, EventArgs e)


{


//Generate random code picture


Setvalidatecode ();


//Build page not saved to cache


Response.Cache.SetNoStore ();


　　 }


//Set Verification code


private void Setvalidatecode ()


　　 {


//New bitmap


Bitmap newbitmap = new Bitmap (


71,


23,


Pixelformat.format32bppargb


　　　　　　　　　　　　　　　　　　 );


//Get drawing picture from bitmap


Graphics g = graphics.fromimage (Newbitmap);


//random number generator


Random r = new Random ();


//Drawing screen empty


g.clear (Color.White);


//Drawing screen interference


for (int i = 0; i < i++)


　　　　 {


int x1 = R.next (newbitmap.width);


int x2 = R.next (newbitmap.width);


int y1 = R.next (newbitmap.height);


int y2 = r.next (newbitmap.height);


g.drawline (New Pen


Color.FromArgb (R.next ()),


X1,


Y1,


x2,


y2


　　　　　　　　　　　　　　　 );


　　　　 }


//Drawing screen points interference


for (int i = 0; i < i++)


　　　　 {


int x = R.next (newbitmap.width);


int y = r.next (newbitmap.height);


Newbitmap.setpixel (


x,


y,


Color.FromArgb (R.next ())


　　　　　　　　　　　　　　　 );


　　　　 }


//Get random string (5-bit length)


String value = Generaterandom (5);


//Random string assignment to session


session["Randcode"] = value;


//Definition picture Display font style


font font = new Font (


"Arial",


14,


FontStyle.Bold


　　　　　　　　　　　　　　 );


Random rr = new Random ();


int yy = RR. Next (1, 4);


//define random string display picture brush


LinearGradientBrush brush = new LinearGradientBrush (


New Rectangle (0, 0, 71, 23),


color.red,


Color.Blue,


1.2f,


true


　　　　　　　　　　　　　　　　　　　　　　　　　　　　　 );


g.drawstring (value, font, brush, 2, yy);


G.drawrectangle (New Pen (


color.silver),


0,


0,


70,


22


　　　　　　　　　　　　　　　　 );


System.IO.MemoryStream ms = new System.IO.MemoryStream ();


Newbitmap.save (MS, Imageformat.gif);


//Output picture


response.clearcontent ();


Response.ContentType = "Image/gif";


Response.BinaryWrite (Ms. ToArray ());


　　 }


//Constant Set


private static char[] constant ={


' 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 '


};


//Generate random string


public static string generaterandom (int Length)


　　 {


System.Text.StringBuilder newrandom = new System.Text.StringBuilder (36);


Random rd = new Random ();


for (int i = 0; i < Length; i++)


　　　　 {


Newrandom.append (constant[rd. Next (36)]);


　　　　 }


return newrandom.tostring ();


　　 }


}

Using a random picture page, the image control is written as follows:

<asp:image id= "Image1" imageurl= "~/getrandimg.aspx" runat= "Server"/>

Sample code: Http://www.cnblogs.com/Files/heekui/RandCode.rar