PayU\Configuration::getSecretKey PHP Method

    public function getSecretKey()
    {
        return $this->secretKey;
    }

 protected function calculateHash($rawData)
 {
     ksort($rawData);
     $buffer = '';
     foreach ($rawData as $key => $value) {
         $buffer .= strlen($value) . $value;
     }
     return hash_hmac('md5', $buffer, $this->configuration->getSecretKey());
 }