对数组的键名进行排序

<?php
$pass="c7129fc2f9bee7c0273b76f6aa498789";
$fruits = array(
    "format" => "xml",
    "method" => "qqqq",
    "pass" => "c7129fc2f9bee7c0273b76f6aa498789",
    "uname" => "qqq",
    "type"=>"22"
);
ksort($fruits);
$str="";
foreach ($fruits as $key => $val) {
    $str.="$key=$val&";
}
$str=substr($str,0,-1);
$sign=md5(md5("$str").$pass);
?>