[Cryptography] Entropy Needed for SSH Keys?

[Tom Mitchell]

On Fri, May 27, 2016 at 1:17 PM, Ray Dillinger <bear at sonic.net> wrote:

>
>
> On 05/27/2016 07:12 AM, Kent Borg wrote:
>
> > Is there a term for how far a photon can travel in a clock period? Well,
> > whatever that might be called, if the physical distance of a second
> > clock is on-order that far away--inches in this case--it feels like the
> > problem changes.
>
> IIRC, one nanosecond was once defined to me as the approximate
> amount of time it takes for light to travel fifteen centimeters.
>

Aha yes  Grace Hopper had an answer to the nano second.
One key is that it is a wire not C in a vacuum.  A trace will have
a slightly different length.

https://www.youtube.com/watch?v=JEpsKnWZrJ8  <-- Grace Hopper

Of interest an external entropy generator could be quite small and only need
three or four pins.  A lot of energy has been given to precision components
but entropy generators could be in an easy to manufacture less precise
category.

Some of the phase lock loop clock recovery logic blocks could also be
coaxed into generating entropy.   PLL blocks are key to many of the
very fast links between devices like SATA disks and DRAM.
https://www.rambus.com/dllpll-on-a-dram/
http://www.ti.com.cn/cn/lit/ug/sprufw0b/sprufw0b.pdf

Communication of these fast links demands a quality clock but behind the
curtain will be a sub block that maintains that quality with tiny push/
pull surges
into the clock generator (VCO) block and other tricks.  Those pulses could
suffice as one component of entropy in a system.





-- 
  T o m    M i t c h e l l
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