PHP随机密码的生成

<?php
function genPassword($min = 5, $max = 8)
{
$validchars="abcdefghijklmnopqrstuvwxyz123456789";
$max_char=strlen($validchars)-1;
$length=mt_rand($min,$max);
$password = "";
for($i=0;$i<$length;$i++)
{
$password.=$validchars[mt_rand(0,$max_char)];
}
return $password;
}
echo "新密码：".genPassword()."<br>";
echo "新密码：".genPassword(4,10)."<br>";
?>