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TwoFactorAuth.php
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TwoFactorAuth.php
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<?php
declare(strict_types=1);
namespace RobThree\Auth;
use RobThree\Auth\Providers\Qr\IQRCodeProvider;
use RobThree\Auth\Providers\Qr\QRServerProvider;
use RobThree\Auth\Providers\Rng\CSRNGProvider;
use RobThree\Auth\Providers\Rng\HashRNGProvider;
use RobThree\Auth\Providers\Rng\IRNGProvider;
use RobThree\Auth\Providers\Rng\OpenSSLRNGProvider;
use RobThree\Auth\Providers\Time\HttpTimeProvider;
use RobThree\Auth\Providers\Time\ITimeProvider;
use RobThree\Auth\Providers\Time\LocalMachineTimeProvider;
use RobThree\Auth\Providers\Time\NTPTimeProvider;
// Based on / inspired by: https://github.com/PHPGangsta/GoogleAuthenticator
// Algorithms, digits, period etc. explained: https://github.com/google/google-authenticator/wiki/Key-Uri-Format
class TwoFactorAuth
{
private static string $_base32dict = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=';
/** @var array<string> */
private static array $_base32;
/** @var array<string, int> */
private static array $_base32lookup = array();
public function __construct(
private ?string $issuer = null,
private int $digits = 6,
private int $period = 30,
private Algorithm $algorithm = Algorithm::Sha1,
private ?IQRCodeProvider $qrcodeprovider = null,
private ?IRNGProvider $rngprovider = null,
private ?ITimeProvider $timeprovider = null
) {
if ($this->digits <= 0) {
throw new TwoFactorAuthException('Digits must be > 0');
}
if ($this->period <= 0) {
throw new TwoFactorAuthException('Period must be int > 0');
}
self::$_base32 = str_split(self::$_base32dict);
self::$_base32lookup = array_flip(self::$_base32);
}
/**
* Create a new secret
*/
public function createSecret(int $bits = 80, bool $requirecryptosecure = true): string
{
$secret = '';
$bytes = (int) ceil($bits / 5); // We use 5 bits of each byte (since we have a 32-character 'alphabet' / BASE32)
$rngprovider = $this->getRngProvider();
if ($requirecryptosecure && !$rngprovider->isCryptographicallySecure()) {
throw new TwoFactorAuthException('RNG provider is not cryptographically secure');
}
$rnd = $rngprovider->getRandomBytes($bytes);
for ($i = 0; $i < $bytes; $i++) {
$secret .= self::$_base32[ord($rnd[$i]) & 31]; //Mask out left 3 bits for 0-31 values
}
return $secret;
}
/**
* Calculate the code with given secret and point in time
*/
public function getCode(string $secret, ?int $time = null): string
{
$secretkey = $this->base32Decode($secret);
$timestamp = "\0\0\0\0" . pack('N*', $this->getTimeSlice($this->getTime($time))); // Pack time into binary string
$hashhmac = hash_hmac($this->algorithm->value, $timestamp, $secretkey, true); // Hash it with users secret key
$hashpart = substr($hashhmac, ord(substr($hashhmac, -1)) & 0x0F, 4); // Use last nibble of result as index/offset and grab 4 bytes of the result
$value = unpack('N', $hashpart); // Unpack binary value
$value = $value[1] & 0x7FFFFFFF; // Drop MSB, keep only 31 bits
return str_pad((string) ($value % 10** $this->digits), $this->digits, '0', STR_PAD_LEFT);
}
/**
* Check if the code is correct. This will accept codes starting from ($discrepancy * $period) sec ago to ($discrepancy * period) sec from now
*/
public function verifyCode(string $secret, string $code, int $discrepancy = 1, ?int $time = null, ?int &$timeslice = 0): bool
{
$timestamp = $this->getTime($time);
$timeslice = 0;
// To keep safe from timing-attacks we iterate *all* possible codes even though we already may have
// verified a code is correct. We use the timeslice variable to hold either 0 (no match) or the timeslice
// of the match. Each iteration we either set the timeslice variable to the timeslice of the match
// or set the value to itself. This is an effort to maintain constant execution time for the code.
for ($i = -$discrepancy; $i <= $discrepancy; $i++) {
$ts = $timestamp + ($i * $this->period);
$slice = $this->getTimeSlice($ts);
$timeslice = $this->codeEquals($this->getCode($secret, $ts), $code) ? $slice : $timeslice;
}
return $timeslice > 0;
}
/**
* Get data-uri of QRCode
*/
public function getQRCodeImageAsDataUri(string $label, string $secret, int $size = 200): string
{
if ($size <= 0) {
throw new TwoFactorAuthException('Size must be > 0');
}
$qrcodeprovider = $this->getQrCodeProvider();
return 'data:'
. $qrcodeprovider->getMimeType()
. ';base64,'
. base64_encode($qrcodeprovider->getQRCodeImage($this->getQRText($label, $secret), $size));
}
/**
* Compare default timeprovider with specified timeproviders and ensure the time is within the specified number of seconds (leniency)
* @param array<ITimeProvider> $timeproviders
*/
public function ensureCorrectTime(?array $timeproviders = null, int $leniency = 5): void
{
if ($timeproviders === null) {
$timeproviders = array(
new NTPTimeProvider(),
new HttpTimeProvider(),
);
}
// Get default time provider
$timeprovider = $this->getTimeProvider();
// Iterate specified time providers
foreach ($timeproviders as $t) {
if (!($t instanceof ITimeProvider)) {
throw new TwoFactorAuthException('Object does not implement ITimeProvider');
}
// Get time from default time provider and compare to specific time provider and throw if time difference is more than specified number of seconds leniency
if (abs($timeprovider->getTime() - $t->getTime()) > $leniency) {
throw new TwoFactorAuthException(sprintf('Time for timeprovider is off by more than %d seconds when compared to %s', $leniency, get_class($t)));
}
}
}
/**
* Builds a string to be encoded in a QR code
*/
public function getQRText(string $label, string $secret): string
{
return 'otpauth://totp/' . rawurlencode($label)
. '?secret=' . rawurlencode($secret)
. '&issuer=' . rawurlencode((string)$this->issuer)
. '&period=' . intval($this->period)
. '&algorithm=' . rawurlencode(strtoupper($this->algorithm->value))
. '&digits=' . intval($this->digits);
}
/**
* @throws TwoFactorAuthException
*/
public function getQrCodeProvider(): IQRCodeProvider
{
// Set default QR Code provider if none was specified
if (null === $this->qrcodeprovider) {
return $this->qrcodeprovider = new QRServerProvider();
}
return $this->qrcodeprovider;
}
/**
* @throws TwoFactorAuthException
*/
public function getRngProvider(): IRNGProvider
{
if (null !== $this->rngprovider) {
return $this->rngprovider;
}
if (function_exists('random_bytes')) {
return $this->rngprovider = new CSRNGProvider();
}
if (function_exists('openssl_random_pseudo_bytes')) {
return $this->rngprovider = new OpenSSLRNGProvider();
}
if (function_exists('hash')) {
return $this->rngprovider = new HashRNGProvider();
}
throw new TwoFactorAuthException('Unable to find a suited RNGProvider');
}
/**
* @throws TwoFactorAuthException
*/
public function getTimeProvider(): ITimeProvider
{
// Set default time provider if none was specified
if (null === $this->timeprovider) {
return $this->timeprovider = new LocalMachineTimeProvider();
}
return $this->timeprovider;
}
/**
* Timing-attack safe comparison of 2 codes (see http://blog.ircmaxell.com/2014/11/its-all-about-time.html)
*/
private function codeEquals(string $safe, string $user): bool
{
if (function_exists('hash_equals')) {
return hash_equals($safe, $user);
}
// In general, it's not possible to prevent length leaks. So it's OK to leak the length. The important part is that
// we don't leak information about the difference of the two strings.
if (strlen($safe) === strlen($user)) {
$result = 0;
for ($i = 0; $i < strlen($safe); $i++) {
$result |= (ord($safe[$i]) ^ ord($user[$i]));
}
return $result === 0;
}
return false;
}
private function getTime(?int $time = null): int
{
return ($time === null) ? $this->getTimeProvider()->getTime() : $time;
}
private function getTimeSlice(?int $time = null, int $offset = 0): int
{
return (int) floor($time / $this->period) + ($offset * $this->period);
}
private function base32Decode(string $value): string
{
if (strlen($value) == 0) {
return '';
}
if (preg_match('/[^' . preg_quote(self::$_base32dict) . ']/', $value) !== 0) {
throw new TwoFactorAuthException('Invalid base32 string');
}
$buffer = '';
foreach (str_split($value) as $char) {
if ($char !== '=') {
$buffer .= str_pad(decbin(self::$_base32lookup[$char]), 5, '0', STR_PAD_LEFT);
}
}
$length = strlen($buffer);
$blocks = trim(chunk_split(substr($buffer, 0, $length - ($length % 8)), 8, ' '));
$output = '';
foreach (explode(' ', $blocks) as $block) {
$output .= chr(bindec(str_pad($block, 8, '0', STR_PAD_RIGHT)));
}
return $output;
}
}