1. A non-transitory computer-readable memory for caching digital random numbers, the non-transitory computer-readable memory comprising: a state-machine; a plurality of cache entries operable to store digital random numbers generated by a digital random number generator, wherein the digital random numbers are supplied to the cache entries under control of the state-machine; and a plurality of validity entries corresponding to each of the plurality of cache entries to track whether an entry contains a valid random number.