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how to use google recaptcha in asp.net.

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Introduction

In this post, I am explain how to use google recaptcha in asp.net.

Google reCAPTCHA  is a free service from Google that helps protect websites from spam and abuse that restricts the automated input sent by a system and allows only input from a real human.

We can create a CAPTCHA in many ways but Google provides a free reCAPTCHA with better security without any cost.

Let us learn about  how to use google recaptcha in asp.net

Steps :

Step - 1 : Create New Project.

Go to File > New > Project > Select asp.net web forms application > Entry Application Name > Click OK.

Step-2: Sign up & Generate Key for Google reCaptcha.

Go to http://www.google.com/recaptcha > Sign up for Google reCaptcha > Create Key(for Google reCaptcha).

Step-3: Add a Database.

Go to Solution Explorer > Right Click on App_Data folder > Add > New item > Select SQL Server Database Under Data > Enter Database name > Add.

Step-4: Create table for Save Data.

Open Database > Right Click on Table > Add New Table > Add Columns > Save > Enter table name > Ok.
In this example, I have used one tables as below


Step-5: Add Entity Data Model.

Go to Solution Explorer > Right Click on Project name form Solution Explorer > Add > New item > Select ADO.net Entity Data Model under data > Enter model name > Add.
A popup window will come (Entity Data Model Wizard) > Select Generate from database > Next >
Chose your data connection > select your database > next > Select tables > enter Model Namespace > Finish.

Step-6: Add a Webpage and Design for use Google Captcha.

Go to Solution Explorer > Right Click on Project name form Solution Explorer > Add > New item > Select web form/ web form using master page under Web > Enter page name > Add.

HTML Code 
  1.             <h3>Contact Us form in ASP.NET with Google Captcha</h3>
  2.             <div>
  3.                 <table>
  4.                     <tr>
  5.                         <td>Full Name:</td>
  6.                         <td>
  7.                             <asp:TextBox ID="txtFullName" runat="server" />
  8.                         </td>
  9.                     </tr>
  10.                     <tr>
  11.                         <td>Email:</td>
  12.                         <td>
  13.                             <asp:TextBox ID="txtEmail" runat="server" />
  14.                         </td>
  15.                     </tr>
  16.                     <tr>
  17.                         <td>Contact No:</td>
  18.                         <td>
  19.                             <asp:TextBox ID="txtContactNo" runat="server" />
  20.                         </td>
  21.                     </tr>
  22.                     <tr>
  23.                         <td>Query</td>
  24.                         <td>
  25.                             <asp:TextBox ID="txtQuery" runat="server" TextMode="MultiLine" Height="66px" Width="297px" />
  26.                         </td>
  27.                     </tr>
  28.                     <tr>
  29.                         <td>Security Code</td>
  30.                         <td>
  31.                             <%--  We Can get the code from : https://developers.google.com/recaptcha/docs/display  --%>                    <%-- Here Please place you public key(google captcha public key) your_public_key--%>
  32.                             <%-- Here Please place you public key(google captcha public key) your_public_key--%>
  33.                             <script type="text/javascript"
  34.                                  src="http://www.google.com/recaptcha/api/challenge?k=your_public_key">
  35.                               </script>
  36.                               <noscript>
  37.                                  <iframe src="http://www.google.com/recaptcha/api/noscript?k=your_public_key"
  38.                                      height="300" width="500" frameborder="0"></iframe><br>
  39.                                  <textarea name="recaptcha_challenge_field" rows="3" cols="40">
  40.                                  </textarea>
  41.                                  <input type="hidden" name="recaptcha_response_field"
  42.                                      value="manual_challenge">
  43.                               </noscript>
  44.                         </td>
  45.                     </tr>
  46.                     <tr>
  47.                         <td></td>
  48.                         <td>
  49.                             <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
  50.                         </td>
  51.                     </tr>
  52.                     <tr>
  53.                         <td>&nbsp;</td>
  54.                         <td>
  55.                             <asp:Label ID="lblMsg" runat="server" ></asp:Label>
  56.                         </td>
  57.                     </tr>
  58.                 </table>
  59.             </div>
  60.

Step-7: Write this into Button Click event for validate captcha & Save data to database.


  1.             
  2.         protected void btnSubmit_Click(object sender, EventArgs e)
  3.         {
  4.             if (txtFullName.Text.Trim() == "")
  5.             {
  6.                 lblMsg.Text = "Please provide your full name";
  7.                 return;
  8.             }
  9.  
  10.             // here we will check captcha code is valid or not
  11.  
  12.             var isValidDic = CaptchaValidate();
  13.             string val = "";
  14.             try
  15.             {
  16.                 isValidDic.TryGetValue(true, out val);
  17.                 if (val == null)
  18.                 {
  19.                     lblMsg.Text = "provided security code is not valid! please try again.";
  20.                     return;
  21.                 }
  22.             }
  23.             catch (Exception ex)
  24.             {
  25.                 lblMsg.Text = "provided security code is not valid! please try again.";
  26.                 return;
  27.             }
  28.  
  29.             ContactQuery c = new ContactQuery
  30.             {
  31.                 Fullname = txtFullName.Text.Trim(),
  32.                  EmailID = txtEmail.Text.Trim(),
  33.                   ContactNo = txtContactNo.Text.Trim(),
  34.                    Query = txtQuery.Text.Trim()
  35.             };
  36.             // here MyDatabaseEntities is dbContext
  37.             using (MyDatabaseEntities dc = new MyDatabaseEntities())
  38.             {
  39.                 dc.ContactQueries.Add(c);
  40.                 dc.SaveChanges();
  41.                 lblMsg.Text = "Successfully Done!";
  42.                 txtFullName.Text = "";
  43.                 txtEmail.Text = "";
  44.                 txtContactNo.Text = "";
  45.                 txtQuery.Text = "";
  46.             }
  47.         }
  48.

and here is the function...
  1.             
  2.             private Dictionary<bool,string> CaptchaValidate()
  3.             {
  4.                 // Validate Captcha here
  5.                 var isValidDic = new Dictionary<bool, string>();
  6.                 string[] resultFromGoogle;
  7.                 HttpWebRequest req = (HttpWebRequest)WebRequest.Create("http://www.google.com/recaptcha/api/verify");
  8.  
  9.                 req.ProtocolVersion = HttpVersion.Version10;
  10.                 req.Timeout = 0x7530;
  11.                 req.Method = "POST";
  12.                 req.UserAgent = "reCAPTCHA/ASP.NET";
  13.                 req.ContentType = "application/x-www-form-urlencoded";
  14.                 string Fdata = string.Format("privatekey={0}&remoteip={1}&challenge={2}&response={3}",
  15.                     new object[]{
  16.                         HttpUtility.UrlEncode("your_private_key"),
  17.                         HttpUtility.UrlEncode(Dns.GetHostEntry(Dns.GetHostName()).AddressList[1].ToString()), 
  18.                         HttpUtility.UrlEncode(Request.Form["recaptcha_challenge_field"]), 
  19.                         HttpUtility.UrlEncode(Request.Form["recaptcha_response_field"]) 
  20.                     });
  21.  
  22.                 byte[] resData = Encoding.ASCII.GetBytes(Fdata);
  23.                 using (Stream rStream = req.GetRequestStream())
  24.                 {
  25.                     rStream.Write(resData, 0, resData.Length);
  26.                 }
  27.                 try
  28.                 {
  29.                     using (WebResponse wResponse = req.GetResponse())
  30.                     {
  31.                         using (TextReader readStream = new StreamReader(wResponse.GetResponseStream(), Encoding.UTF8))
  32.                         {
  33.                             resultFromGoogle = readStream.ReadToEnd().Split(new string[] { "\n", @"\n" }, StringSplitOptions.RemoveEmptyEntries);
  34.                         }
  35.                     }
  36.                 }
  37.                 catch (WebException ex)
  38.                 {
  39.                     isValidDic.Add(false, ex.InnerException.ToString());
  40.                     return isValidDic;
  41.                 }
  42.  
  43.                 isValidDic.Add(resultFromGoogle[0] == "true", resultFromGoogle[1]);
  44.                 return isValidDic;
  45.             }
  46.

Step-8: Run Application.


Download     Live Demo


Related Post :

Hello ! My name is Sourav Mondal. I am a software developer working in Microsoft .NET technologies since 2010.

I like to share my working experience, research and knowledge through my site.

I love developing applications in Microsoft Technologies including Asp.Net webforms, mvc, winforms, c#.net, sql server, entity framework, Ajax, Jquery, web api, web service and more.

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