Puoi fare cosi.
Codice PHP:
<?php
function idCrypt($nb_char) {
$randval = "";
$str = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$length = strlen($str);
mt_srand();
for ($i=1;$i<=$nb_char;$i++) {
$pos = mt_rand(0,$length-1);
$randval .= substr($str , $pos, 1 );
}
return $randval;
} // function idCrypt()
print idCrypt(30);
print "<br/>";
print idCrypt(30);
print "<br/>";
print idCrypt(30);
print "<br/>";
print idCrypt(30);
print "<br/>";
print idCrypt(30);
print "<br/>";
?>