$signature = $_GET["signature"];  //微信加密签名，signature结合了开发者填写的token参数和请求中的timestamp参数、nonce参数。
$timestamp = $_GET["timestamp"]; //时间戳
$nonce = $_GET["nonce"];        //随机数
$token = TOKEN;         //TOKEN 开发者模式下所填写的TOKEN 
$tmpArr = array($token, $timestamp, $nonce);
sort($tmpArr, SORT_STRING);
$tmpStr = implode( $tmpArr );
$tmpStr = sha1( $tmpStr );

if( $tmpStr == $signature ){
	return true;
}else{
	return false;
}

echo $_GET["echostr"];