use MIME::Base64;

$num = 123;

$encoded = encode_base64(pack("V", $num), '');
$encoded =~ s/==$//;
print($encoded, $/);  # ewAAAA (always 6 chars)

$encoded .= '==';
$num = unpack("V", decode_base64($encoded));
print($num, $/);  # 123