Asp. The writing of the Net Verification code

Asp.net| Verification Code

Using System.Drawing;
Using System.Drawing.Imaging;
private void Page_Load (object sender, System.EventArgs e)
{
Place user code here to initialize page
Rndnum is a custom function
String Vnum=rndnum (4); The number 4 here represents the 4-bit validation string shown!
session["Vnum"]=vnum;
Validatecode (Vnum);
}
Generating image functions
private void Validatecode (String vnum)
{
int gheight= (int) (VNUM.LENGTH * 11.5);
Gheight for picture width, automatically change picture width based on character length
System.Drawing.Bitmap Img = new System.Drawing.Bitmap (gheight,20);
Graphics g = graphics.fromimage (IMG);
g.DrawString (vnum,new System.Drawing.Font ("Arial"), New System.Drawing.SolidBrush (Color.Red), 3, 3);
Draws a string within a rectangle (string, font, brush color, upper left X. Upper-Left Y)
System.IO.MemoryStream ms=new System.IO.MemoryStream ();
Img.save (ms,system.drawing.imaging.imageformat.png);
Response.clearcontent (); Need to output image information to modify HTTP headers
Response.contenttype= "Image/png";
Response.BinaryWrite (Ms. ToArray ());
G.dispose ();
Img.dispose ();
Response.End ();
}

http://community.csdn.net/Expert/topic/3342/3342222.xml?temp=.5347406
Random extraction from a Vchar array in the generation of random number functions
Letter Case Sensitive
public string rndnum (int vcodenum)
{
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,w,x,y,z";

string[] Vcarray = Vchar.split (', ');
String vnum = "";//because the strings are very short, you don't have to StringBuilder.
int temp =-1;//Record last random value, try to avoid producing a few of the same random numbers

A simple algorithm is used to guarantee the difference of generating random numbers
Random Rand =new Random ();
for (int i = 1; i < vcodenum+1; i++)
{
if (temp!=-1)
{
Rand =new Random (i*temp*unchecked (int) DateTime.Now.Ticks));
}
int t = rand. Next (35);
int T=rand. Next (35);
if (temp!=-1 && temp = t)
{
Return Rndnum (Vcodenum);
}
temp = t;
Vnum + = vcarray[t];

}
return vnum;
}
-----------------------------------End--------------------------------------------

The following is login.aspx in response to the call to the Submit button
public void doit (object sender, System.EventArgs e)
{
if (Page.IsValid)
{

String Vnum;
vnum=session["Vnum"]. ToString ();
Session.Abandon ();
viewstate["Vnum"]=vnum;
if (this. vcode.text==viewstate["Vnum"]. ToString ())
{

Hover.Manage.CheckLogin obj=new Hover.Manage.CheckLogin ();
String Name=username. Text;
String Password=formsauthentication.hashpasswordforstoringinconfigfile (pass. Text.tostring (), "MD5");
if (!obj.checklogin (Name,password))
{
Response.Redirect (".. /error.aspx?action=errorlogin ");
Response.End ();
Return
}
Else
{
Session.add ("AdminName", name);
Session.add ("AdminPass", password);
Response.Redirect ("default.aspx");
Response.End ();
Return
}

}
Else
{
Response.Write ("<script>alert" Please enter the correct add-on code!) \ ");</script>");
}
}
}
If the validation string submitted over is correct, verify that it is a legitimate user!
Otherwise pop-up prompts to return to the landing page! You can also simplify this page!
if (this. vcode.text==viewstate["Vnum"]. ToString ())
{
Response.Write ("Verify code correct");
}
Else
{
Response.Write ("Authentication code Error!");
}