Embodiments include bitstring generators and methods of their operation. A sampling parameter of the bitstring generator is set to a current value, and values of one or more bits are then repeatedly sampled based on the current value of the sampling parameter. The repeated sampling results in a set of test bits, which is analyzed to determine a randomness measurement associated with the set of test bits. A determination is made whether the randomness measurement meets a criterion. If not, the current value of the sampling parameter is changed to a different value that corresponds to a lower probability of being able to correctly predict the values of the one or more bits produced by the bitstring generator. The steps of repeatedly sampling, analyzing the set of test bits, and determining whether the randomness measurement meets the criteria are then repeated.