code: public function decrypt($content)
      {
          if ($this->key === false) {
              return '';
          }
  
          $res = openssl_get_privatekey($this->key);
          if (empty($res)) {
              throw new \Exception('您使用的私钥格式错误，请检查RSA私钥配置');
          }
  
          //用base64将内容还原成二进制
          $decodes = base64_decode($content);
  
          $str = '';
          $dcyCont = '';
          foreach ($decodes as $n => $decode) {
              if (!openssl_private_decrypt($decode, $dcyCont, $res)) {
                  echo "<br/>" . openssl_error_string() . "<br/>";
              }
              $str .= $dcyCont;
          }
  
          openssl_free_key($res);
          return $str;
      }
docs: RSA2解密 此处秘钥是用户私有秘钥
  @param string $content 需要解密的内容，密文
  @throws \Exception
  @return string
  @author helei