I've used the simple rot13 perl filter from the pod (for amusement). If you start the debugger (perl -d <rot13_encrypted_file>) and do a
l 1-10 (list rows 1-10) you'll get them fully readable and decrypted.
I haven't tried any C language perl filters, but you can try to have a peek your self with perl -d.
You'll probably need to statically link the decrypter in perl and also disable debugging to have some small ammount of security.