This
article will show you in asp.net to display captcha on 3 failed login attempts
using c#. In this if user add 3 time invalid login detail on 4th
time a captcha will come.
For first we will create a table for user login.
For first we will create a table for user login.
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Captcha.aspx.cs" Inherits="Shoping_Cart.Captcha" %>
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Here I have removed all the html tag of the page and left only the page tag. Now check the code for captcha.
using System;
using
System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Web;
using System.Web.UI;
using
System.Web.UI.WebControls;
namespace Shoping_Cart
{
public partial class Captcha : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string[] strArray = new string[36];
strArray = new string[] { "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", "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", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };
Random autoRand = new Random();
string strCaptcha = string.Empty;
for (int i = 0; i < 6; i++)
{
int j = Convert.ToInt32(autoRand.Next(0,
62));
strCaptcha += strArray[j].ToString();
}
Session["Captcha"] = strCaptcha;
ImageConverter
converter = new ImageConverter();
Response.BinaryWrite((byte[])converter.ConvertTo(CaptchaGeneration(strCaptcha), typeof(byte[])));
}
public Bitmap
CaptchaGeneration(string captchatxt)
{
Bitmap bmp = new Bitmap(133, 48);
using (Graphics graphics = Graphics.FromImage(bmp))
{
Font font = new Font("Tahoma", 14);
graphics.FillRectangle(new SolidBrush(Color.Gray), 0, 0, bmp.Width, bmp.Height);
graphics.DrawString(captchatxt, font, new SolidBrush(Color.Gold), 25, 10);
graphics.Flush();
font.Dispose();
graphics.Dispose();
}
return bmp;
}
}
}
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In above
code I have saved the captcha code value into session. By using this session I will
validate the user entered captcha.
Now we will
create the login form .
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Login-Captcha.aspx.cs" Inherits="Shoping_Cart.Login_Captcha" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Asp.Net Captcha C#</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<table width="100%">
<tr>
<td style="text-align: right;">User
Id</td>
<td style="text-align: right;">
<asp:TextBox ID="txtUSerId"
runat="server"></asp:TextBox></td>
</tr>
<tr>
<td style="text-align: right;">Password</td>
<td style="text-align: right;">
<asp:TextBox ID="txtPassword"
runat="server" TextMode="Password"></asp:TextBox></td>
</tr>
<tr>
<td style="text-align: center;" colspan="2">
<asp:Image runat="server" ImageUrl="~/Captcha.aspx" ID="imgCaptcha"></asp:Image><br />
<asp:TextBox ID="txtcaptchaValue" runat="server"></asp:TextBox> <br />
<asp:Button ID="Button1" runat="server" Text="Submit" OnClick="Button1_Click" />
<br />
<asp:Label ID="lblmessage"
runat="server" Style="color: #FF3300" Text=""></asp:Label></td>
</tr>
</table>
</div>
</form>
</body>
</html>
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In above code I have created the login form with captcha code. Now we will check the code.
using System;
using
System.Collections.Generic;
using System.Data;
using
System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using
System.Web.UI.WebControls;
namespace Shoping_Cart
{
public partial class Login_Captcha :
System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
imgCaptcha.Visible = false;
txtcaptchaValue.Visible = false;
if (Session["LoginCount"]
!= null)
{
if (Convert.ToInt32(Session["LoginCount"])
>= 3)
{
imgCaptcha.Visible = true;
txtcaptchaValue.Visible = true;
}
}
}
protected void Button1_Click(object sender, EventArgs e)
{
string captcha = "";
if (Session["Captcha"] != null)
{
captcha = Session["Captcha"].ToString();
}
try
{
DataSet ds = new DataSet();
SqlConnection con = new SqlConnection(@"Data
Source=.\SQLEXPRESS;Initial Catalog=Demo;Integrated
Security=True");
string query = "select * from UserLoginDetail Where
[UserId]='" + txtUSerId.Text + "' and [Password]='" + txtPassword.Text + "';";
con.Open();
SqlDataAdapter da = new SqlDataAdapter(query,
con);
da.Fill(ds);
con.Close();
if (ds.Tables[0].Rows.Count
> 0 && Convert.ToInt32(Session["LoginCount"]) >= 3)
{
if (Convert.ToInt32(Session["LoginCount"])
>= 3)
{
if
(captcha == txtcaptchaValue.Text)
{
Response.Redirect("SuccessPage.aspx");
}
else
{
lblmessage.Text =
"Please enter a valid
captcha.";
}
}
else
{
Response.Redirect("SuccessPage.aspx");
}
}
else
{
if (Convert.ToInt32(Session["LoginCount"])
>= 3)
{
if
(captcha == txtcaptchaValue.Text)
{
Session["LoginCount"]
= Convert.ToInt32(Session["LoginCount"])
+ 1;
lblmessage.Text =
"Please enter a valid login
detail.";
}
else
{
lblmessage.Text =
"Please enter a valid
captcha.";
}
}
else
{
Session["LoginCount"] = Convert.ToInt32(Session["LoginCount"]) + 1;
lblmessage.Text = "Please
enter a valid login detail.";
}
}
}
catch
{
}
}
}
}
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In above I have created a session named as LoginCount. In this I am saving the fail login count. After 3 fail login I am enabling the captcha.
Now we have
done run the application to check the output.
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