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
          $content = base64_decode($content);
          //把需要解密的内容，按128位拆开解密
          $result  = '';
          for ($i = 0; $i < strlen($content)/128; $i++) {
              $data = substr($content, $i * 128, 128);
              openssl_private_decrypt($data, $decrypt, $res);
              $result .= $decrypt;
          }
          openssl_free_key($res);
          return $result;
      }
docs: RSA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