public function serverEncrypt($plainData)
 {
     $key = $this->getKey($this->config->getServerPrivateKey(), self::TYPE_PRIVATE);
     $encryptedData = '';
     if (!openssl_private_encrypt($plainData, $encryptedData, $key)) {
         throw new \RuntimeException('Server data encryption failed');
     }
     unset($key);
     gc_collect_cycles();
     //Remove key from memory
     return $encryptedData;
 }