Please use https://github.com/jiripudil/otp for an up-to-date, more feature-rich implementation of one-time passwords.

Oops/TotpAuthenticator implements the TOTP algorithm that lets you easily set up a two-factor authentication mechanism. The TOTP, in short, generates a pseudo-random six-digit number based on current Unix time and given seed (a base32 string of at least 16 characters). The seed is shared between you and mobile app and passed to the app via a QR code. Whenever you need to authenticate the user, ask them to enter the code generated by the application, and verify it against the code generated by your server.

$ composer require oops/totp-authenticator

Oops/TotpAuthenticator requires PHP >= 7.2.

If you use Nette's DI container, you can easily integrate Oops/TotpAuthenticator with a few lines of configuration:

extensions:
	totp: Oops\TotpAuthenticator\DI\TotpAuthenticatorExtension

totp:
	timeWindow: 1
	issuer: MyApp

Otherwise, you can directly instantiate Oops\TotpAuthenticator\Security\TotpAuthenticator and optionally configure it:

$totpAuthenticator = (new Oops\TotpAuthenticator\Security\TotpAuthenticator)
   ->setIssuer('MyApp')
   ->setTimeWindow(1);

The timeWindow option sets a benevolence that compensates for possible differences between your server's time and the app's time. The default value is 1, which means the code for previous or next 30-second block would be also considered valid. You can set it to zero if you want to be super strict, but I'd strongly recommend not setting it to a higher value than one.

The issuer is optional, but is quite useful if you use some generic value as the user's account name, such as their email address. As multiple services can use that same value as a way of identifying the user, you should provide issuer to distinguish your app's code in the TOTP app.

First, you need to generate a secret - a base32 string - that is shared between you and the application. TotpAuthenticator provides a method for that. The secret must be unique to the user and should thus be stored somewhere with other user data, e.g. in the database. Just remember to encrypt it as it is a very sensitive piece of information.

$secret = $totpAuthenticator->getRandomSecret();

Then, you can display the secret and unique account name (e.g. user's email address) to the user, or, more conveniently, provide them with a QR code containing the URI in a specific format. Again, TotpAuthenticator can build the URI for you:

$uri = $totpAuthenticator->getTotpUri($secret, $accountName);

Once the user has set up the account in their TOTP app, you can ask them to enter the 6-digit code and easily verify it against the secret:

if ($totpAuthenticator->verifyCode($code, $secret)) {
	// successfully verified

} else {
	// incorrect code
}