Complex sentence: In some cases keys are randomly generated using a random number generator (RNG) or pseudorandom number generator (PRNG), the latter being a computer algorithm that produces data which appears random under analysis.
Split into simpler sentences: In some cases keys are randomly generated using a "random number generator (RNG)" or "pseudorandom number generator (PRNG)". A PRNG is a computer algorithm that produces data that appears random under analysis.