Scan me to return to the original page.
Scan me to return to the original page.
```
## HMAC Algorithms
To comply with [RFC6238](https://tools.ietf.org/html/rfc6238), this package supports SHA1, SHA256 and SHA512. It defaults to SHA1, so to use a different algorithm you just have to use the method `setAlgorith()`:
``` php
$google2fa->setAlgorithm(Constants::SHA512);
```
## Server Time
It's really important that you keep your server time in sync with some NTP server, on Ubuntu you can add this to the crontab:
```bash
sudo service ntp stop
sudo ntpd -gq
sudo service ntp start
```
## Validation Window
To avoid problems with clocks that are slightly out of sync, we do not check against the current key only but also consider `$window` keys each from the past and future. You can pass `$window` as optional third parameter to `verifyKey`, it defaults to `4`. A new key is generated every 30 seconds, so this window includes keys from the previous two and next two minutes.
```php
$secret = $request->input('secret');
$window = 8; // 8 keys (respectively 4 minutes) past and future
$valid = $google2fa->verifyKey($user->google2fa_secret, $secret, $window);
```
An attacker might be able to watch the user entering his credentials and one time key.
Without further precautions, the key remains valid until it is no longer within the window of the server time. In order to prevent usage of a one time key that has already been used, you can utilize the `verifyKeyNewer` function.
```php
$secret = $request->input('secret');
$timestamp = $google2fa->verifyKeyNewer($user->google2fa_secret, $secret, $user->google2fa_ts);
if ($timestamp !== false) {
$user->update(['google2fa_ts' => $timestamp]);
// successful
} else {
// failed
}
```
Note that `$timestamp` either `false` (if the key is invalid or has been used before) or the provided key's unix timestamp divided by the key regeneration period of 30 seconds.
## Using a Bigger and Prefixing the Secret Key
Although the probability of collision of a 16 bytes (128 bits) random string is very low, you can harden it by:
#### Use a bigger key
```php
$secretKey = $google2fa->generateSecretKey(32); // defaults to 16 bytes
```
#### You can prefix your secret keys
You may prefix your secret keys, but you have to understand that, as your secret key must have length in power of 2, your prefix will have to have a complementary size. So if your key is 16 bytes long, if you add a prefix it must be also 16 bytes long, but as your prefixes will be converted to base 32, the max length of your prefix is 10 bytes. So, those are the sizes you can use in your prefixes:
```
1, 2, 5, 10, 20, 40, 80...
```
And it can be used like so:
```php
$prefix = strpad($userId, 10, 'X');
$secretKey = $google2fa->generateSecretKey(16, $prefix);
```
#### Window
The Window property defines how long a OTP will work, or how many cycles it will last. A key has a 30 seconds cycle, setting the window to 0 will make the key lasts for those 30 seconds, setting it to 2 will make it last for 120 seconds. This is how you set the window:
```php
$secretKey = $google2fa->setWindow(4);
```
But you can also set the window while checking the key. If you need to set a window of 4 during key verification, this is how you do:
```php
$isValid = $google2fa->verifyKey($seed, $key, 4);
```
#### Key Regeneration Interval
You can change key regeneration interval, which defaults to 30 seconds, but remember that this is a default value on most authentication apps, like Google Authenticator, which will, basically, make your app out of sync with them.
```php
$google2fa->setKeyRegeneration(40);
```
## Google Authenticator secret key compatibility
To be compatible with Google Authenticator, your (converted to base 32) secret key length must be at least 8 chars and be a power of 2: 8, 16, 32, 64...
So, to prevent errors, you can do something like this while generating it:
```php
$secretKey = '123456789';
$secretKey = str_pad($secretKey, pow(2,ceil(log(strlen($secretKey),2))), 'X');
```
And it will generate
```
123456789XXXXXXX
```
By default, this package will enforce compatibility, but, if Google Authenticator is not a target, you can disable it by doing
```php
$google2fa->setEnforceGoogleAuthenticatorCompatibility(false);
```
## Google Authenticator Apps:
To use the two factor authentication, your user will have to install a Google Authenticator compatible app, those are some of the currently available:
* [Authy for iOS, Android, Chrome, OS X](https://www.authy.com/)
* [FreeOTP for iOS, Android and Pebble](https://apps.getpebble.com/en_US/application/52f1a4c3c4117252f9000bb8)
* [Google Authenticator for iOS](https://itunes.apple.com/us/app/google-authenticator/id388497605?mt=8)
* [Google Authenticator for Android](https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2)
* [Google Authenticator (port) on Windows Store](https://www.microsoft.com/en-us/store/p/google-authenticator/9wzdncrdnkrf)
* [Microsoft Authenticator for Windows Phone](https://www.microsoft.com/en-us/store/apps/authenticator/9wzdncrfj3rj)
* [LastPass Authenticator for iOS, Android, OS X, Windows](https://lastpass.com/auth/)
* [1Password for iOS, Android, OS X, Windows](https://1password.com)
## Deprecation Warning
Google API for QR generator is turned off. All version of that package prior to 5.0.0 are deprecated. Please upgrade and check documentation regarding [QRCode generation](https://github.com/antonioribeiro/google2fa#generating-qrcodes).
## Testing
The package tests were written with [PHPUnit](https://phpunit.de/). There are some Composer scripts to help you run tests and analysis:
PHPUnit:
````
composer test
````
PHPStan analysis:
````
composer analyse
````
## Authors
- [Antonio Carlos Ribeiro](http://twitter.com/iantonioribeiro)
- [Phil (Orginal author of this class)](https://www.idontplaydarts.com/static/ga.php_.txt)
- [All Contributors](https://github.com/antonioribeiro/google2fa/graphs/contributors)
## License
Google2FA is licensed under the MIT License - see the [LICENSE](LICENSE.md) file for details.
## Contributing
Pull requests and issues are more than welcome.