I'm starting to create a puzzle, but I'm going to need a cipher that will be impossible (or at least very difficult) to crack, but can be easily decoded with a key. I first looked at the one-time pad cipher, but the message I'll be encrypting will likely be longer than the key. Does anybody have recommendations?
As bobble pointed out, there are lots of different ciphers, so here are some criteria:
- Simple to encode / decode
- Extremely difficult to impossible to crack without the key
- Key can be any length (or at least smaller than the message, unlike OTP)
The checkmark will be given to the answer that meets these criteria best.