Because plain xorshift generators (without a non-linear step) fail some statistical tests, they have been accused of being unreliable. This weakness is amended by combining them with a non-linear function, as described in the original paper. However, they do not pass every statistical test without further refinement. įor execution in software, xorshift generators are among the fastest non- cryptographically-secure random number generators, requiring very small code and state. Like all LFSRs, the parameters have to be chosen very carefully in order to achieve a long period.
This makes execution extremely efficient on modern computer architectures, but it does not benefit efficiency in a hardware implementation. They generate the next number in their sequence by repeatedly taking the exclusive or of a number with a bit-shifted version of itself. They are a subset of linear-feedback shift registers (LFSRs) which allow a particularly efficient implementation in software without the excessive use of sparse polynomials. Xorshift random number generators, also called shift-register generators, are a class of pseudorandom number generators that were invented by George Marsaglia. Future work could focus on methods to increase the speed of the generator without a loss of excellent cryptographic properties.Example random distribution of Xorshift128 Our scheme produced consistently excellent results under NIST testing but is computationally too slow for many practical uses as a stream cipher.
We identified lower bounds on the input parameters to increase the probability that the combiner would perform well under the NIST test suite. We then evaluated their cryptographic suitability with the National Institute of Standards and Technology NIST statistical test suite. We sought to answer the questions 1 What are the strengths and weaknesses of this type of combiner 2 What constraints must be placed on the input parameters to ensure good cryptographic properties of the output sequence We generated sequences using variations of this combiner. Abstract: The purpose of this thesis is to analyze the cryptographic properties of a pseudorandom bit generator that combines Blum Blum Shub and linear feedback shift register sequences using a shrinking generator configuration.
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