rand.php

<?php

function getId($chunks = 4, $chunkLen = 4) {
	$max = pow(36, $chunkLen) - 1;
	$id = '';

	for ($i = 0; $i < $chunks; ++$i) {
		$r = (mt_rand(0, $max) * (microtime(true) * 10000)) / mt_rand(0, $max);
	  	$id .= str_pad(base_convert($r, 10, 36), $chunkLen, "0", STR_PAD_LEFT);
	}
	return strtoupper($id);
}