$cipher->encrypt($data) 

Encrypt data. The size of $data must be a multiple of blocksize 
(16 bytes), otherwise this function will croak. Apart from that, 
it can be of (almost) any length. 

##</code><code>##

# this requires $username < 16 bytes and prefix packs with spaces
sprintf '%16s', $username;
  
# this will give you a data length divisible by 16 for any length
# we use null byte prefix packing
sub get16 {
    my $data = shift;
  return "\0" x ( 16 - length($data)%16 ) . $data;
}