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