PHP实战：thinkphp微信开发（消息加密解密）

/**
  * 对密文进行解密
  * @param string $encrypt 密文
  * @return string   明文
  */
 public function decrypt($encrypt){
  //BASE64解码
  $encrypt = base64_decode($encrypt);
  //打开加密算法模块
  $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
  //初始化加密算法模块
  mcrypt_generic_init($td, $this->cyptKey, substr($this->cyptKey, 0, 16));
  //执行解密
  $decrypt = mdecrypt_generic($td, $encrypt);
  
  //去除PKCS7补位
  $decrypt = self::PKCS7Decode($decrypt, mcrypt_enc_get_key_size($td));
  //关闭加密算法模块
  mcrypt_generic_deinit($td);
  mcrypt_module_close($td);
  if(strlen($decrypt) < 16){
   throw new \Exception("非法密文字符串!");
  }
  //去除随机字符串
  $decrypt = substr($decrypt, 16);
  //获取网络字节序
  $size = unpack("N", substr($decrypt, 0, 4));
  $size = $size[1];
  //APP_ID
  $appid = substr($decrypt, $size + 4);
  //验证APP_ID
  if($appid !== $this->appId){
   throw new \Exception("非法APP_ID!");
  }
  
  //明文内容
  $text = substr($decrypt, 4, $size);
  return $text;
 }
 /**
  * PKCS7填充字符
  * @param string $text 被填充字符
  * @param integer $size Block长度
  */
 private static function PKCS7Encode($text, $size){
  //字符串长度
  $str_size = strlen($text);
  //填充长度
  $pad_size = $size - ($str_size % $size);
  $pad_size = $pad_size ? : $size;
  
  //填充的字符
  $pad_chr = chr($pad_size);
  //执行填充
  $text = str_pad($text, $str_size + $pad_size, $pad_chr, STR_PAD_RIGHT);
  return $text;
 }
 /**
  * 删除PKCS7填充的字符
  * @param string $text 已填充的字符
  * @param integer $size Block长度
  */
 private static function PKCS7Decode($text, $size){
  //获取补位字符
  $pad_str = ord(substr($text, -1));
  if ($pad_str < 1 || $pad_str > $size) {
   $pad_str= 0;
  } 
   return substr($text, 0, strlen($text) - $pad_str);
  
 }

<xml>
<ToUserName><![CDATA[gh_249aeb986d99]]><\/ToUserName>\n
<FromUserName><![CDATA[oopVmxHZaeQkDPsRcbpwXKkH-J2Q]]><\/FromUserName>\n
<CreateTime>1448944621<\/CreateTime>\n
<MsgType><![CDATA[text]]><\/MsgType>\n
<Content><![CDATA[\u7ecf\u7406]]><\/Content>\n
<MsgId>6223169761311044588<\/MsgId>\n
<\/xml>

//明文内容
$text = substr($decrypt, 4, $size);
 //去掉多余的内容
$text=str_replace('<\/','</', $text);  
 $text=str_replace('>\n','>', $text);
 return $text;