Oubliette gives you a choice of encryption algorithms: Blowfish or Idea. The algorithms were chosen because they are cryptographically strong and free for non-commercial use. (Oubliette uses a great freeware library, DCPCrypt, written by David Barton, that implements the cryptographic algorithms. Oubliette comes with full source code, so you can inspect the program for any hidden doors (there are none), or modify it to create your own version.