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Tuesday, 7 March 2017

Show Asp.net Captcha on 3 Failed Login Attempts

3/07/2017 - By Pranav Singh 0

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.

 Now we will create an asp.net application an add the below code for creating the captcha code.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Captcha.aspx.cs" Inherits="Shoping_Cart.Captcha" %>

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;
        }
    }
}

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>

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
            {

            }

        }
    }
}

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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