thinkphp WeChat development: safe mode message encryption and decryption

Using the official WeChat package of thinkphp, different modes can be used successfully, but the safe mode is not working. Now we will record the analysis and solution results.

                                                                                                                                                                                                                          Decrypting WeChat server messages is always unsuccessful. Download the official decrypted file provided by the WeChat public platform and compare it with WechatCrypt.class.php and find that there is no problem. Use the file_put_contents function to save the decrypted file for analysis. It was found that the xml decrypted by the official package is not in the standard xml format, so the simplexml_load_string function cannot handle it.

<span>/*</span><span>*
     * 对密文进行解密
     * @param  string $encrypt 密文
     * @return string          明文
     </span><span>*/</span><span>public</span><span>function</span> decrypt(<span>$encrypt</span><span>){
        </span><span>//</span><span>BASE64解码</span><span>$encrypt</span> = <span>base64_decode</span>(<span>$encrypt</span><span>);

        </span><span>//</span><span>打开加密算法模块</span><span>$td</span> = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, ''<span>);

        </span><span>//</span><span>初始化加密算法模块</span>        mcrypt_generic_init(<span>$td</span>, <span>$this</span>->cyptKey, <span>substr</span>(<span>$this</span>->cyptKey, 0, 16<span>));

        </span><span>//</span><span>执行解密</span><span>$decrypt</span> = mdecrypt_generic(<span>$td</span>, <span>$encrypt</span><span>);
       
        </span><span>//</span><span>去除PKCS7补位</span><span>$decrypt</span> = self::PKCS7Decode(<span>$decrypt</span>, mcrypt_enc_get_key_size(<span>$td</span><span>));

        </span><span>//</span><span>关闭加密算法模块</span>        mcrypt_generic_deinit(<span>$td</span><span>);
        mcrypt_module_close(</span><span>$td</span><span>);

        </span><span>if</span>(<span>strlen</span>(<span>$decrypt</span>) < 16<span>){
            </span><span>throw</span><span>new</span> \<span><strong>Exception</strong></span>("非法密文字符串！"<span>);
        }

        </span><span>//</span><span>去除随机字符串</span><span>$decrypt</span> = <span>substr</span>(<span>$decrypt</span>, 16<span>);

        </span><span>//</span><span>获取网络字节序</span><span>$size</span> = <span>unpack</span>("N", <span>substr</span>(<span>$decrypt</span>, 0, 4<span>));
        </span><span>$size</span> = <span>$size</span>[1<span>];

        </span><span>//</span><span>APP_ID</span><span>$appid</span> = <span>substr</span>(<span>$decrypt</span>, <span>$size</span> + 4<span>);

        </span><span>//</span><span>验证APP_ID</span><span>if</span>(<span>$appid</span> !== <span>$this</span>-><span>appId){
            </span><span>throw</span><span>new</span> \<span><strong>Exception</strong></span>("非法APP_ID！"<span>);
        }
        
        </span><span>//</span><span>明文内容</span><span>$text</span> = <span>substr</span>(<span>$decrypt</span>, 4, <span>$size</span><span>);
        </span><span>return</span><span>$text</span><span>;
    }

    </span><span>/*</span><span>*
     * PKCS7填充字符
     * @param string  $text 被填充字符
     * @param integer $size Block长度
     </span><span>*/</span><span>private</span><span>static</span><span>function</span> PKCS7Encode(<span>$text</span>, <span>$size</span><span>){
        </span><span>//</span><span>字符串长度</span><span>$str_size</span> = <span>strlen</span>(<span>$text</span><span>);

        </span><span>//</span><span>填充长度</span><span>$pad_size</span> = <span>$size</span> - (<span>$str_size</span> % <span>$size</span><span>);
        </span><span>$pad_size</span> = <span>$pad_size</span> ? : <span>$size</span><span>;
        
        </span><span>//</span><span>填充的字符</span><span>$pad_chr</span> = <span>chr</span>(<span>$pad_size</span><span>);

        </span><span>//</span><span>执行填充</span><span>$text</span> = <span>str_pad</span>(<span>$text</span>, <span>$str_size</span> + <span>$pad_size</span>, <span>$pad_chr</span>,<span> STR_PAD_RIGHT);

        </span><span>return</span><span>$text</span><span>;
    }

    </span><span>/*</span><span>*
     * 删除PKCS7填充的字符
     * @param string  $text 已填充的字符
     * @param integer $size Block长度
     </span><span>*/</span><span>private</span><span>static</span><span>function</span> PKCS7Decode(<span>$text</span>, <span>$size</span><span>){
        </span><span>//</span><span>获取补位字符</span><span>$pad_str</span> = <span>ord</span>(<span>substr</span>(<span>$text</span>, -1<span>));

        </span><span>if</span> (<span>$pad_str</span> < 1 || <span>$pad_str</span> > <span>$size</span><span>) {
            </span><span>$pad_str</span>= 0<span>;
        } 
            </span><span>return</span><span>substr</span>(<span>$text</span>, 0, <span>strlen</span>(<span>$text</span>) - <span>$pad_str</span><span>);
        
    }</span>

Solution:

                                                                  using

                                                          ’ ‐ ’ s

<span>1</span><span><</span><span>xml</span><span>></span><span>2</span><span><</span><span>ToUserName</span><span>></span><span><![CDATA[</span><span>gh_249aeb986d99</span><span>]]></span><span><</span><span>\/ToUserName</span><span>></span><span>\n
</span><span>3</span><span><</span><span>FromUserName</span><span>></span><span><![CDATA[</span><span>oopVmxHZaeQkDPsRcbpwXKkH-J2Q</span><span>]]></span><span><</span><span>\/FromUserName</span><span>></span><span>\n
</span><span>4</span><span><</span><span>CreateTime</span><span>></span>1448944621<span><</span><span>\/CreateTime</span><span>></span><span>\n
</span><span>5</span><span><</span><span>MsgType</span><span>></span><span><![CDATA[</span><span>text</span><span>]]></span><span><</span><span>\/MsgType</span><span>></span><span>\n
</span><span>6</span><span><</span><span>Content</span><span>></span><span><![CDATA[</span><span>\u7ecf\u7406</span><span>]]></span><span><</span><span>\/Content</span><span>></span><span>\n
</span><span>7</span><span><</span><span>MsgId</span><span>></span>6223169761311044588<span><</span><span>\/MsgId</span><span>></span><span>\n
</span><span>8</span><span><</span><span>\/xml</span><span>></span>

Safe mode will work fine used.

The above introduces thinkphp WeChat development: safe mode message encryption and decryption, including Exception content. I hope it will be helpful to friends who are interested in PHP tutorials.