PHP RFC4648-base32 to hex conversion for Google Authenticator

googleauth.php

# $key = hex2bin(rfc4648tohex('AAAAAAAAAAAAAAAA')); # Your secret Auth-Key
# $token = googleauth($key, floor(time()/30));
function googleauth($key, $stamp)
{
  $mac = hash_hmac('SHA1', substr(chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).chr(0).pack('N', floor($stamp)),-8), $key, true);
  $val = unpack('N', substr($mac, (ord(substr($mac, -1)) & 15), 4));
  $val = $val[1]&0x7fffffff;
  return substr("000000$val", -6);
}

rfc4648tohex.php

# Input:  base32hex
# Output: hex-string
function base32hex2hex($s)
{
  $l = strlen($s);
  if ($n = ($l%4))
    $s = str_pad($s, $l+4-$n, '0', STR_PAD_LEFT);
  $x = '';
  foreach (str_split($s, 4) as $v)
    $x .= str_pad(base_convert($v, 32, 16), 5, '0', STR_PAD_LEFT);
  return $x;
}

# Input:  string with RFC4648-base32
# Output: converted value into hex-string
function rfc4648tohex($s)
{
  return base32hex2hex(strtr($s,
                             'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567',
                             '0123456789ABCDEFGHIJKLMNOPQRSTUV'
                      )     );
}

I like short things which are easy to understand and to use. Not tested much, though (Google-Auth thingie works so far at my side).