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SubjectRe: Fwd: [PATCH] CPU Jitter RNG: inclusion into kernel crypto API and /dev/random
Am Montag, 14. Oktober 2013, 16:12:24 schrieb Stephan Mueller:

Hi Sandy,

>(PS: I am aware that in case none of the individual bits would contain
>one full bit of entropy, the folding operation may --mathematically
>spoken-- not deliver one full bit of entropy. However, after speaking
>with a mathematician, that slight inconsistency is ok, if I can show
>that the distribution of the folded bit is 50% zeros and 50% ones. That
>is what I did in section 5.2.1. Thus, the conclusion is that I receive
>one bit of entropy after the folding loop.)

One followup on this issue: if one believes that he has a problem with
that consideration, he can initialize the CPU Jitter RNG with an
oversampling rate. That rate simply performs the folding operation 64
times oversampling rate.

To fill the entropy pool completely once, the RNG needs 64 time deltas
which are folded into the one bit. All the oversampling rate now does is
to calculate more than once the complete entropy pool.

For example, when you set the oversampling rate to 2, you need twice as
long for the random value as each bit the random value is calculated
twice. And the two independent 64 bit random values are simply XORed

You can set the oversampling rate to any value above 1.


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