One Time Passwords, hotp and totp according to RFC4226 and RFC6238

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1.4.3 2015-10-08 08:17 UTC


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Use composer and require the library in your composer.json

    "require": {
        "christian-riesen/otp": "1.*",



use Otp\Otp;
use Otp\GoogleAuthenticator;

// Seperate class, see
use Base32\Base32;

// Get a Pseudo Secret
// Defaults to 16 characters
$secret = GoogleAuthenticator::generateRandom();

// Url for the QR code
// Using totp method
$url = GoogleAuthenticator::getQrCodeUrl('totp', 'Label like', $secret);

// Save the secret with the users account
// Display QR Code to the user

// Now how to check
$otp = new Otp();

// $key is a 6 digit number, coming from the User
// Assuming this is present and sanitized
// Allows for a 1 code time drift by default
// Third parameter can alter that behavior
if ($otp->checkTotp(Base32::decode($secret), $key)) {
    // Correct key
    // IMPORTANT! Note this key as being used
    // so nobody could launch a replay attack.
    // Cache that for the next minutes and you
    // should be good.
} else {
    // Wrong key

// Just to create a key for display (testing)
$key = $otp->totp($secret);

Sample script in example folder. Requires sessions to work (for secret storage).

Class Otp

Implements hotp according to RFC4226 and totp according to RFC6238 (only sha1 algorithm). Once you have a secret, you can use it directly in this class to create the passwords themselves (mainly for debugging use) or use the check functions to safely check the validity of the keys. The checkTotp function also includes a helper to battle timedrift.

Class GoogleAuthenticator

Static function class to generate a correct url for the QR code, so you can easy scan it with your device. Google Authenticator is avaiaible as application for iPhone and Android. This removes the burden to create such an app from the developers of websites by using this set of classes.

There are also older open source versions of the Google Authenticator app for both iPhone and Android

This helper class uses the random_int function from PHP7, or the polyfill method from paragonie/random_compat if present and falls back on other (less "secure") random generators.



PHP 5.3.x+

Uses Base32 class.

If you want to run the tests, PHPUnit 3.6 or up is required.


Christian Riesen


The classes have been inspired by many different places that were talking about otp and Google Authenticator. Thank you all for your help.

Project setup ideas blantently taken from