cryptography without complexity randomness rising today you mix the message with random key mix it as thoroughly as you can to get something out there which will be so complex that it will be impossible to undo it the problem is that what looks complex to you look simple to somebody smarter than you so complexity works against damp adversaries not good enough suppose now we associate each letter of the alphabet with a string of bits a secret string of bits that only Alice and Bob share and then when Alice wants to tell Bob hi Bob she goes to the string that represents H and sends it to Bob but then the string that represents I and then B and then o and they'll be again Bob takes those bits he has the same table and finds out what the message was but after using it a few times even stupid adversary will figure out what this table is and read the messages instead Alice does something very strange she flips the identity of exactly half of the bits in the string exactly half exactly and sends the flipped string to Bob so Bob receives the flipped H string and has to identify this string as the letter H but the string that he has and the flipped string have 50% of the bits opposite and that's the key this string will have let's say 40% of bits in agreement with a and 60% with B and 70% with Z and 10% with all the only string that will have 50% of the bits in agreement between the flip and the regular is H and that's above knows that L is and what about the adversary he doesn't see the string with MUX that says these are the bits that were flip what he sees is one less and for him every bit as a 50% chance to be what it is not to be the opposite 50% chance to be what it is or to be the opposite 50% every bit total darkness how secure is it as long as the choice of which bits to flip the choice is kept completely random each time it is used each time randomly select 50% of the bits if you do that then the longer the list the greater the security plain and simple solid combinatorics no algorithmic complexity simple numeric analysis the bit flip cipher is order of magnitude faster several orders of magnitude faster than the prevailing algorithms we don't need modular logarithmic computation we count bits compare bit and flip bits these are the simplest things that you can do with computers and security is not provided by complexity but by randomness sheer raw Random randomness galore yes you pay with more bits to communicate but you earn the security that you shooting for guaranteed by randomness the boundary of knowledge

## noshalom says:

correct me if I'm wrong, I'm a cryptography novice. but how does Bob get the "pure" alphabet in the first place? doesn't that need to be transmitted securely?