Maybe a piece of code can help you.

use Crypt::CBC;
use strict;

my $cipher = Crypt::CBC->new(
  {    
    'key'           => 'a' x 32,      # change this to a decent key wi
+th 32 chars
    'cipher'        => 'Rijndael',
    'iv'            => 'm_?.5fP}',
    'regenerate_key'=> 0,
    'padding'       => 'space',
    'prepend_iv'    => 0
  }
);

my $data_to_encrypt = 'what\'s up, doc ?';
my $cipheredtext = $cipher->encrypt($data_to_encrypt);
print "ciphered : $cipheredtext \n";

my $plaintext = $cipher->decrypt($cipheredtext);
print "plaintext : $plaintext\n";

$cipher->finish;
[download]

Rijndael has implementations in several languages, so portability should not be an issue, but consider other, faster encryptions you should.