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<?php
final class CaptchaChallenge extends SimpleORMap
{
public const ALGORITHM = 'SHA-256';
public const CHALLENGE_EXPIRATION = 5 * 60;
protected static function configure($config = [])
{
$config['db_table'] = 'captcha_challenges';
parent::configure($config);
}
protected static function getKey(): string
{
$key = Config::get()->CAPTCHA_KEY;
if ($key === '') {
$key = bin2hex(random_bytes(32));
Config::get()->store('CAPTCHA_KEY', $key);
}
return $key;
}
public static function createChallenge(string $salt, int $number): array
{
$algorithm = 'sha256';
$challenge = hash($algorithm, $salt . $number);
$signature = hash_hmac($algorithm, $challenge, self::getKey());
return [
'algorithm' => self::ALGORITHM,
'challenge' => $challenge,
'salt' => $salt,
'signature' => $signature,
];
}
public static function createNewChallenge(): array
{
do {
$salt = md5(time() . '-' . bin2hex(random_bytes(12)));
$number = random_int(1e3, 1e5);
} while (self::countBySql('salt = ? AND number = ?', [$salt, $number]) > 0);
return self::createChallenge($salt, $number);
}
public static function decodePayload(string $payload): array|null
{
return json_decode(base64_decode($payload), true);
}
public static function validatePayload(string $payload): string|bool
{
$json = self::decodePayload($payload);
if ($json === null) {
return _('Sie haben nicht bestÃĪtigt, dass Sie kein Roboter sind');
}
$time = explode('-', $json['salt'])[0];
if ($time < time() - self::CHALLENGE_EXPIRATION) {
return _('Die Challenge ist abgelaufen');
}
// Replay?
if (\CaptchaChallenge::countBySql('salt = ? AND number = ?', [$json['salt'], $json['number']]) > 0) {
return _('Nicht schummeln!');
}
$check = self::createChallenge($json['salt'], $json['number']);
if (
$json['algorithm'] !== $check['algorithm']
|| $json['challenge'] !== $check['challenge']
|| $json['signature'] !== $check['signature']
) {
return _('Sie sind scheinbar ein Roboter...');
}
return true;
}
public static function gc(): void
{
self::deleteBySQL("mkdate < UNIX_TIMESTAMP() - ?", [self::CHALLENGE_EXPIRATION]);
}
}
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