It has to be my own algorithm, not a well known algorithm. So ROT13 cannot work. Any more ideas? Thanks anyways. I have not started coding it namely some issues are raised in my head. Like I said earlier. Should I convert everything to binary? There must be some function for that in C or Python. How do I determine key size. If the user wants to use a short key that is less than say 128 bits how do i pad that key? It is a graduate level course so it needs to fairly complex, but not too complex.

Thanks in advance