1. take a 256 byte key.
2. pad a file out so it can be perfectly divided into 256 parts.
3. divide the file into sections, and assign each section to a byte of the key.
4. sort the key according to some predetermined algorithm, swapping parts of the file as you go.
5. subdivide with the same key, or perhaps a key generated with md5 or something.
6. lather, rinse, repeat until the file is very confusing.