reCAPTCHA : Free Captcha service for ASP.NET

Its a common requirement that we require a captcha to be integrated on our page. I would like to mention a free captcha service which can be implemented in integrated on websites.

What is reCaptcha?

  1. reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows.
  2. It’s Free! Yep, reCAPTCHA is free.
  3. It’s Easy. reCAPTCHA is a Web service. As such, adopting it is as simple as adding
    a few lines of code on your site.
  4. It’s Accessible. reCAPTCHA has an audio test that allows blind people to freely
    navigate your site.
  5. It’s Secure. Most other CAPTCHA implementations can be easily broken.
  6. It’s Popular. Over 100,000 sites use reCAPTCHA, including household names like Facebook, Ticketmaster, and Craigslist.
  7. Whenever uses input data in reCaptcha control, they actually help digitizing books.

Moreover is very easy to integrate reCaptcha in our websites. Below are the steps
which are required to integrate it into a ASP.NET page.

Steps to Integrate reCaptcha in ASP.NET

  1. Register for a reCaptcha key : As a first step we need to register for recaptcha keys. Navigate to Get reCaptcha URL to signup for the keys. After we register for the keys, we get a public and private keys which we need to use in our asp.net page. By default all keys work on localhost as well.

  2. Download reCaptcha library for ASP.NET: Download the dll file from here. Also add the reference to the dll in the asp.net project.
  3. Add reCaptcha widget on ASP.NET page : Insert the reCAPTCHA control into the form you wish to protect by adding the following code snippets:
    • At the top of the aspx page, insert this:
      <%@ register
                      tagprefix="recaptcha" namespace="Recaptcha" assembly="Recaptcha" %>
    • Then insert the reCAPTCHA control inside of the form tag:
                      <recaptcha:recaptchacontrol id="recaptcha" runat="server" publickey="your_public_key"
                          privatekey="your_private_key" />
                      
  4. Make sure you use ASP.NET validation to validate your form (you should check Page.IsValid on submission).

As an example I created a ASP.NET page whose markup and code behind code looks as given below:

Markup:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="RecaptchaPage.aspx.cs" Inherits="ContosoUniversity.RecaptchaPage" %>
<%@ Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
     <asp:Label Visible="true" ID="lblResult" runat="server" />

     <recaptcha:RecaptchaControl
              ID="recaptcha"
              runat="server"
              Theme="red"
              PublicKey="6LcoxcASAAAAAGAQQz_xOTk4-ALrRQri_Cf8AuhL"
              PrivateKey="6LcoxcASAAAAALfZhquqene7_4bTrzmuqHBrkuk0"
              />

          <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />

    </div>
    </form>
</body>
</html>

Code-behind

    public partial class RecaptchaPage : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void btnSubmit_Click(object sender, EventArgs e)
        {
            if (Page.IsValid) 
            {
              lblResult.Text = "Captcha sucessfull!";
              lblResult.ForeColor = System.Drawing.Color.Green;
            }
            else
            {
              lblResult.Text = "Incorrect";
              lblResult.ForeColor = System.Drawing.Color.Red;
            }
        }
    }

When I entered correct captcha text and pressed submit button following was the output:

When I entered incorrect captcha text and pressed submit button following was the output:

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Regular Expression for Email Address validation in C#

The task at hand is to validate the Textbox in asp.net for a valid email address.

We can attach a RegularExpressionValidator to the text box with the following regular expression:

<asp:RegularExpressionValidator ValidationExpression="^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$" ID="rxpEmail" runat="server"
ErrorMessage="Email Address is not valid" Text="*" Display="Static" ControlToValidate="txtEmail"></asp:RegularExpressionValidator>

UPDATES
Well i searched the net for the standards of a valid email id and i came across with a wonderful article at

I Knew How To Validate An Email Address Until I Read The RFC

It gives a an idea of what an exact RFC standard for the email id is.

I believe that we should follow validations which are quite obvious to the users and allow only standard email addresses.

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Twitter from ASP.NET Application

twitter
This post will throw a light on how we can update our status on Twitter from an asp.net application.

The task is pretty simple as we have libraries already available on the net.

I will be using twitterizer dll to perform the task.

The following are the steps to be followed:

  1. Download the twitterizer dll from here.
  2. Add the reference to the dll in your asp.net web application.
  3. Write the code. For example
    Twitter t = new Twitter(UserName, Password);
    t.Status.Update(UpdateString);

Following are the methods and the capabilities provided by these methods which are present in the library:

User Methods

  1. Followers
  2. Friends
  3. Follow User

Status Methods

  1. User Timeline
  2. Public Timeline
  3. Friends Timeline
  4. Show
  5. Update
  6. Destroy
  7. Replies

Direct Messages

  1. Sent To User
  2. Sent From User
  3. New Direct Message

References: Twitteriser Home Page

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