entropy

[Patrick O'Callaghan]

On Thu, 2010-01-07 at 21:42 +0100, Roberto Ragusa wrote:
> Tony Nelson wrote:
> > On 10-01-07 12:40:02, Roberto Ragusa wrote:
> >> Luca wrote:
> >>> Hi all,
> >>>  if I simply write to /dev/random, will that increase the entropy 
> >>> of my  system? (I'm assuming that the data I'm writing are random 
> >>> and that somehow I got them).
> >> Wikipedia says so.
> >>
> >> My tests say no.
> >>
> >> In particular this brutal approach does not increase the entropy
> >>   cat /dev/urandom >/dev/random
> >> (it is stupid to do that, I know, but it's just a test)
> >  ...
> > 
> > `man 4 random` says that the current entropy can be read and written 
> > from /dev/urandom, not /dev/random.  This is used to preserver entropy 
> > across reboots.
> 
> That's true.
> But as far as I can see neither writing to random nor to urandom will
> increase the entropy availability.

AFAIK the purpose of writing to /dev/urandom is simply to preserve the
entropy state across reboots (at least that's the standard example).
There's no implication that it "increases the entropy".

The effect of writing to /dev/random doesn't seem to be defined.

poc