/**
*
* 产生随机字符串，不长于32位
* @param int $length
* @return 产生的随机字符串
*/
function getNonceStr($length = 32)
{
$chars = "abcdefghijklmnopqrstuvwxyz0123456789";
$str ="";
for ( $i = 0; $i < $length; $i++ ) {
$str .= substr($chars, mt_rand(0, strlen($chars)-1), 1);
}
return $str;
}