Hardware Random Number Generator

Hardware Random Number Generator

Random numbers are used in both symmetric and asymmetric cryptography as a way of generating keys and for the random values used in the operation of some algorithms. Since integrity of the communication between the two parties is conditional on the continued secrecy of these keys, using a random number generator which does not have adequate randomness may be expected to compromise the security of messages.

In computing, a hardware random number generator is an apparatus that generates random numbers from a physical process, rather than a computer program. Such devices are often based on microscopic phenomena that generate a low-level, statistically random "noise" signal, such as thermal noise or the photoelectric effect or other quantum phenomena. These processes are, in theory, completely unpredictable, and the theory's assertions of unpredictability are subject to experimental test. A hardware random number generator typically consists of a transducer to convert some aspect of the physical phenomena to an electrical signal, an amplifier and other electronic circuitry to increase the amplitude of the random fluctuations to a macroscopic level, and some type of analog to digital converter to convert the output into a digital number, often a simple binary digit 0 or 1. By repeatedly sampling the randomly varying signal, a series of random numbers is obtained.

Random number generators can also be built from "random" macroscopic processes, using devices such as coin flipping, dice, roulette wheels and lottery machines. The presence of unpredictability in these phenomena can be justified by the theory of unstable dynamical systems and chaos theory. Even though macroscopic processes are deterministic under Newtonian mechanics, the output of a well-designed device like a roulette wheel cannot be predicted in practice, because it depends on the sensitive, micro-details of the initial conditions of each use.

Although dice have been mostly used in gambling, and in more recent times as "randomizing" elements in games (e.g. role playing games), the Victorian scientist Francis Galton described a way to use dice to explicitly generate random numbers for scientific purposes in 1890.

Hardware random number generators are often relatively slow, that is they produce a limited number of random bits per second. In order to increase the data rate, they are often used to generate the "seed" for a faster cryptographic PRNG, which then generates the pseudorandom output sequence.