[cryptography] Kernel space vs userspace RNG

dj at deadhat.com dj at deadhat.com
Sat May 7 17:35:24 EDT 2016


>
> Russell Leidich (at Friday, May 6, 2016, 10:16:12 PM):
>> Most of the entropy in a system is manifest in terms of the clock
>> skew between direct memory access (DMA) transfers from external
>> devices and the CPU core clocks, which unfortunately does not
>> traverse the kernel in any directly observable manner.
>
> someone please confirm this, because i'm not a linux expert, but i
> don't believe user space code can do dma without the kernel knowing
> about it.
>
> also, i assert that such clock drifts provide much less entropy than
> you make it look like.
>
The premise is generally wrong these days. Well designed entropy sources
on silicon generate between 200Mbits/s and 5Gbits/s per source. I think
most vendors are getting in on the act. We have been pretty open with our
ES designs and I've seen very smart ES papers. I particularly like
Samsung's ring of rings for a process agnostic circuit.


>
>> interrupt timing, unless we extend the definition of "interrupt" to
>> include quasiperiodic memory accesses from external clients.
>
> again, i'm no exert in low level kernel stuff, but to my knowledge,
> everything happens through interrupts, even dma uses it to report the
> end of an operation.
>
>
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