[erlang-questions] All possible internal states of Erlang/OTP random module are practically computable

Jesper Louis Andersen <>
Wed Dec 24 00:17:50 CET 2014


Hi Ian,

You are totally correct in your observation. Many of the randomness tests
are "passed" if your sequence follows a certain distribution obtained from
running the test. Of course, sometimes a generator will fail a test, but
this is to be expected, as per your notions. But if it fails the test "too
often", then it is grounds for worry as the generator doesn't seem to
handle the particular test well and this could expose a weakness in the
generator.
On Tue Dec 23 2014 at 9:24:05 PM Ian <> wrote:

> Hi All,
>
> On 23/12/2014 14:56, Jesper Louis Andersen wrote:
> > For a process to "look random", it must pass all of these tests, as we
> > otherwise can claim the generated sequence to be less random than a
> > (truly) random process.
> This is not true, and disfigures Jesper's otherwise excellent post.
>
> Its a subtle point but, a truly random sequence can be expected to fail
> 5% of randomness tests at 95% significance, and 1% at 99% significance.
>
> Different sequences will fail different sets of tests.
>
> Any sequence that passes all the tests is (with high confidence) not
> random, but fudged to pass the tests.
>
> Regards
>
> Ian
>
> --
> Ian Hobson
> Mid Auchentiber, Auchentiber, Kilwinning, North Ayrshire KA13 7RR
> Tel: 0203 287 1392
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