Messages in this thread | | | Date | Mon, 23 May 2011 21:35:54 +0200 | From | Ingo Molnar <> | Subject | Re: [BUG] perf: bogus correlation of kernel symbols |
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* Ray Lee <ray-lk@madrabbit.org> wrote:
> On Mon, May 23, 2011 at 3:49 AM, Ingo Molnar <mingo@elte.hu> wrote: > > Well, since entropy does not get reduced on addition of independent variables > > the right sequence is (pseudocode): > > > > rnd = entropy_cycles(); > > rnd += entropy_rdrand(); > > rnd += entropy_RTC(); > > rnd += entropy_system(); > > I think you mean concatenation rather than addition? Or perhaps XOR, or a > hash? [...]
Yeah.
In this special case probably concatenation works the best: the above 4 random variables have total randomness probably less than 32 bits, so we want to create 4 tight random numbers and concatenate them.
[ XOR would destroy some fair amount of entropy because most of these random variables have their randomness in their low bits, and a hash would probably lose about 2 bits and would also be slower. A hash would probably be safer and more robust though, if we mis-identify any of the random variables. ]
Thanks,
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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