PHP Genera clave RAMDOM

//***********************************
function createRandomPassword()
{
$chars = "1234567890QAZWSXEDCRFVTGBYHNUJMIKOLPaqzwsxedcrfvtgbyhnujmikolp";

srand((double)microtime()*1000000);
$i = 0;
$pass = '' ;

do
{
$num = rand() % strlen($chars);
$tmp = substr($chars, $num, 1);
$pass = $pass . $tmp;
$i++;
}
while (strlen($pass)!=15);

return $pass;
}




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