Some seem familiar. I think A Levels got cover some. Or must
have seen them elsewhere while looking for things to do.
Shift ciphers, check digits error detection should be easy.
Or at least to me, because I do all those stuffs in my spare time.
ISBN checking is too easy, once you grabbed the hang of it.
Breaking alls of ISBN codes shouldn't be too hard, provided that
they are 10 digits.
RSA cryptosystem... good luck. I never understood this in my IT
studies, I think Maths guys may be able to.
