In this article I will explain with an example, how to generate unique random OTP (One Time Password) in ASP.Net MVC.
Note: For beginners in ASP.Net MVC, please refer my article ASP.Net MVC Hello World Tutorial with Sample Program example.
 
OTPs (One Time Passwords) are widely used by banks and other firms to validate the Mobile Numbers of their users. OTPs can be Alphanumeric as well as Numeric and generally have length between 5-10 characters.
The simplest example of an OTP is when you try to connect to a public Wi-Fi network, your mobile device receives an SMS containing a unique password and once you register with the correct password, the device gets connected to the network.
 
 

Controller

The controller consists of following Action methods.

Action method for handling GET operation

Inside this Action method, simply the View is returned.
 

Action method for handling POST operation

This Action method gets called when Submit Button is clicked and it accepts selected value of DropDownList and RadioButtonList as parameters.
Note: The DropDownList value will be the length of OTP and RadioButtonList value will be the type of OTP i.e. Alphanumeric and Numeric.
The following three string variables are created:
capital_alphabets – For storing Upper Case Alphabets.
small_alphabets – For storing Lower Case Alphabets.
numbers – For storing 10 digits (0-9).
A variable is created with name characters which stores the value of numbers variable.
After that, it checks if the selected type of OTP is 1 which indicates that OTP must be Alphanumeric in nature. Inside this condition, the string variables i.e. capital_alphabets, small_alphabets and numbers are concatenated and stored into a characters variable.
Next, a FOR loop is executed for the selected length inside which a DO WHILE loop is used to avoid repetition of the characters.
Inside the DO WHILE loop, a random number is used to fetch the character from characters variable based on the type selected in the RadioButtonList.
Finally, the generated unique random OTP i.e. One Time Password is set into a ViewBag object.
public class HomeController : Controller
{
    // GET: Home
    public ActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public ActionResult Index(int length, string type)
    {
        string capital_alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        string small_alphabets = "abcdefghijklmnopqrstuvwxyz";
        string numbers = "0123456789";
 
        string characters = numbers;
        if  (type == "1")
        {
             characters += capital_alphabets + small_alphabets + numbers;
        }
 
        string otp = string.Empty;
        for (int i = 0; i < length; i++)
        {
            string character = string.Empty;
            do
            {
                int index = new Random().Next(0,characters.Length);
                character  = characters.ToCharArray()[index].ToString();
            } while (otp.IndexOf(character) != -1);
            otp += character;
        }
 
        ViewBag.Message = otp;
        return View();
    }
}
 
 

View

HTML Markup

The View consists of an HTML Form which has been created using the Html.BeginForm method with the following parameters.
ActionName – Name of the Action. In this case the name is Index.
ControllerName – Name of the Controller. In this case the name is Home.
FormMethod – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of an HTML Table which consists of an HTML SELECT (DropDownList) and two RadioButton elements and a Submit button.
 

Submitting the Form

When the Submit Button is clicked, the value of the ViewBag object i.e. Generated OTP is displayed.
@{
     Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    @using (Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        <table border="0" cellpadding="0" cellspacing="0">
            <tr>
                <td>
                    <select name="length">
                        <option value="">Please select</option>
                        <option value="5">5</option>
                        <option value="8">8</option>
                        <option value="10">10</option>
                    </select>
                </td>
                <td>
                    <input name="type" type="radio" value="1" />Alphanumeric
                    <input name="type" type="radio" value="2" />Numeric
                </td>
                < td><input type="submit" value="Genderate OTP" /></td> 
            </tr>
            <tr>
                <td>&nbsp;</td> 
            </tr>
            <tr>
                <td colspan="3">
                     OTP:@ViewBag.Message
                </td>
            </tr>
        </table>
    }
</body>
</html>
 
 

Screenshot

ASP.Net MVC: Generate Unique Random OTP (One Time Password)
 
 

Demo

View Demo
 
 

Downloads

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