nsec3hash.php

<?php

echo nsec3hash("434FFFA6F0", "jp", 8), "\n"; // OULDMHVB61HBUBCG40NBLF4UEPS26THV
echo nsec3hash("DEAD", "dnsex.nl", 0), "\n"; // ROCCJAE8BJJU7HN6T7NG3TNM8ACRS87J
echo nsec3hash("DEAD", "a.b.c.example.org", 2), "\n"; // 6LQ07OAHBTOOEU2R9ANI2AT70K5O0RCG

function nsec3hash($salt, $label, $iter) {
    $raw_salt = hex2bin($salt);
    $label = normalize_rr(strtolower($label));

    $hash = sha1($label.$raw_salt, true);
    while ($iter--) {
        $hash = sha1($hash.$raw_salt, true);
    }
    return strtoupper(gmp_strval(gmp_init(bin2hex($hash), 16), 32));
}
function normalize_rr($label) {
    $ret = preg_replace('/\.+/', '.', ".${label}.");
    $ret = preg_replace_callback('/\.([^.]*)/',
                                 function ($matches) {
                                     return chr(strlen($matches[1])).$matches[1];
                                 },
                                 $ret);
    return $ret;
}