use MIME::Base64;

$num = 123;

$encoded = encode_base64(pack("V", $num), '');
$encoded =~ s/A+==$//;
print($encoded, $/);  # ew

$encoded = substr($encoded.'AAAAAA', 0, 6) . '==';
$num = unpack("V", decode_base64($encoded));
print($num, $/);  # 123