lkml.org 
[lkml]   [2011]   [May]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [BUG] perf: bogus correlation of kernel symbols

    * 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/

    \
     
     \ /
      Last update: 2011-05-23 21:39    [W:0.024 / U:0.452 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site