PHP micro-channel payment background verification

<?php
//签名验证
public function check_sigh($data,$wxkey)
{
	$newstring = '';
	ksort($data);
	foreach ($data as $key => $value) {
		if($key == 'sign' || $key == 'm' || $key == 'f' || $key == 'payment' || $key == 'module'||$key == 'file'){
			continue;
		}else if(empty($value)){
			continue;
		}else if($newstring == ''){
			$newstring = $key.'='.$value;
		}else{
			$newstring .= '&'.$key.'='.$value;
		}
	} 
	$stringSignTemp=$newstring."&key=".$wxkey;
	$sign = strtoupper(MD5($stringSignTemp));
	if( $sign == $data['sign']){
		return true;
	} else {
		return false;
	}
}