3DS / Wii U titlekey generation

<?php
function secret($start,$len) {
    $ret = "";
    $add = $start + $len;
    for ($i = 0; $i < $len; $i++) {
        $ret .= pack("H*", substr(sprintf("%02x", $start), -2));
        $next = $start + $add;
        $add = $start; $start = $next;
    }
    return $ret;
}

function mungetid($tid) {
    while (substr($tid,0,2) == "00")
        $tid = substr($tid, 2); if ($tid == "") $tid = "00";
    return pack("H*", $tid);
}

$SECRET = secret(-3, 10);

function derive($tid, $pass) {
    global $SECRET;
    return hash_pbkdf2("sha1", $pass, md5($SECRET . mungetid($tid), true), 20, 32);
}

function derive_all($tid) {
    $passes = ["nintendo", "mypass"];
    foreach ($passes as $pass)
        printf("%s : %s [%s]\n", $tid, derive($tid, $pass), $pass);
}

derive_all("000100014e414150");