A generator for counter- and time based authentication codes. PHP 7.4+

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4.0.0 2020-10-23 06:50 UTC

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Last update: 2021-11-03 13:32:27 UTC


A generator for counter based (RFC 4226) and time based (RFC 6238) authentication codes. (a.k.a. Yet Another Google Authenticator Implementation!)

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Continuous Integration



  • PHP 7.4+
    • 64bit


requires composer

via terminal: composer require chillerlan/php-authenticator

composer.json (note: replace dev-master with a version boundary)

	"require": {
		"php": "^7.4",
		"chillerlan/php-authenticator": "dev-main"

Note: replace dev-main with a version constraint, e.g. ^3.1 - see releases for valid versions.



Create a secret

The secret is usually being created once during the activation process in a user control panel. So all you need to do there is to display it to the user in a convenient way - as a text string and QR code for example - and save it somewhere with the user data.

use chillerlan\Authenticator\{Authenticator, AuthenticatorOptions};

$options = new AuthenticatorOptions;
$options->secret_length = 32;

$authenticator = new Authenticator($options);

// create a secret (stored somewhere in a *safe* place on the server. safe... hahaha jk)
$secret = $authenticator->createSecret();

// you can also specify the length of the secret key, which overrides the options setting
$secret = $authenticator->createSecret(20);

// set an existing secret

// via the constructor:
$authenticator = new Authenticator($options, $secret);

A secret created with Authenticator::createSecret() will also be stored internally, so that you don't need to provide the secret you just created on follow-up operations with the current instance.

Verify a one time code

Now during the login process - after the user has successfully entered their credentials - you would ask them for a one time code to check it against the secret from your user database.

// verify the code
	// that's it - 2FA has never been easier! :D

time based (TOTP)

Verify adjacent codes

// try the first adjacent
$authenticator->verify($code, time() - $options->period); // -> true

// try the second adjacent, default is 1
$authenticator->verify($code, time() + 2 * $options->period); // -> false

// allow 2 adjacent codes
$authenticator->verify($code, time() + 2 * $options->period, 2); // -> true

Create a code for a UNIX timestamp

// let's assume your server's timezone is an hour off and beyond your control
$timeslice = $authenticator->timeslice(time() - 3600);

// current code
$code = $authenticator->code($timeslice);

// adjacent codes
$prev = $authenticator->code($timeslice - 1);
$next = $authenticator->code($timeslice + 1);

counter based (HOTP)

// switch mode to HOTP
$options->mode = 'hotp';

// user sends code #42, equivalent to
$code = $authenticator->code(42); // -> 123456

// verify [123456, 42]
$authenticator->verify($code, $counterValueFromUserDatabase) // -> true

URI creation

In order to display a QR code for a mobile authenticator you'll need an otpauth:// URI, which can be created using the following method.

  • $label should be something that identifies the account to which the secret belongs
  • $issuer is the name of your website or company for example, so that the user is able to identify multiple accounts.
$uri = $authenticator->getUri($label, $issuer);

// -> otpauth://totp/my%20label?secret=NKSOQG7UKKID4IXW&



method return description
__construct(SettingsContainerInterface $options = null, string $secret = null) -
setOptions(SettingsContainerInterface $options) Authenticator called internally by __construct()
setSecret(string $secret) Authenticator called internally by __construct()
getSecret() string
createSecret(int $length = null) string $length overrides AuthenticatorOptions setting
timeslice(int $timestamp = null) int
code(int $data = null) string $data may be a UNIX timestamp (TOTP) or a counter value (HOTP)
verify(string $code, int $data = null) bool see Authenticator::code(), $data will override the current counter value in HOTP mode
getUri(string $label, string $issuer, int $hotpCounter = null) string

AuthenticatorOptions properties

property type default allowed description
$digits int 6 6 or 8 auth code length
$period int 30 15 - 60 validation period (seconds)
$secret_length int 20 >= 16 length of the secret phrase (bytes, unencoded binary)
$algorithm string SHA1 SHA1, SHA256 or SHA512 HMAC hash algorithm
$mode string totp totp or hotp Authenticator mode: time- or counter based, respectively
$adjacent int 1 >= 0 number of allowed adjacent codes


Keep in mind that several URI settings are not (yet) recognized by all authenticators. Check the Google Authenticator wiki for more info.