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Re: entropy

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.

After checking the sources of rngd, I found it uses a specific ioctl:
  ioctl(random_fd, RNDADDENTROPY, &entropy);

So I think Luca can inject entropy by using the same ioctl in his
own application, or by using rngd in some way (you can tell it where
to take entropy from).

   Roberto Ragusa    mail at robertoragusa.it

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