Communication security of today heavily relies on the assumption that some mathematical problems are extremely difficult to solve and thus breaking encryptions based on such problems requires a very long time. While such encryptions are secure now, the probable diffusion of quantum computers in the foreseeable future makes the initial assumption fall short: quantum computations are efficient at breaking the most widespread algorithms in use. Post-quantum cryptographic systems are based on problems that are not (or marginally) affected by the peculiarity of quantum computing: AES and many other hashing functions fall in this category, with quantum operations just moving the problem from O(N) to O(sqrt(N)), with N being the number of operations needed to find a solution.