In computing, a hardware random number generator, true random number generator, non-deterministic random bit generator, or physical random number generator is a device that generates random numbers from a physical process capable of producing entropy (in other words, the device always has access to a physical entropy source), unlike the pseudorandom number generator (PRNG, a.k.a.

The Lehmer random number generator (named after D. H. Lehmer), sometimes also referred to as the Park–Miller random number generator (after Stephen K. Park and Keith W. Miller), is a type of linear congruential generator that operates in multiplicative group of integers modulo n.

The security of cryptographic systems depends on some secret data that is known to authorized persons but unknown and unpredictable to others.