On Wed, Dec 02, 2009 at 02:25:57PM +0100, Otto Moerbeek wrote:
> On Wed, Dec 02, 2009 at 01:09:02PM +0000, Michael Shalayeff wrote:
>
> > On Wed, Dec 02, 2009 at 10:38:10AM +0100, Otto Moerbeek wrote:
> > > Hi,
> > re
> >
> > > apart from the random page addresses obtained form mmap(2) malloc(3)
> > > itself also randomizes cache en chunk operations. It uses a nibble of
> > > randomness per call, so optimize that to not waste half the random
> > > bits.
> >
> > arc4 random does not use entropy and is very cheap
> > almost the speed of memory copy. "caching" arc4 output
> > like this is the same as running rot13 twice (:
>
> at least it saves on calls to arc4_stir() and thus on sysctl(2) and
> getpid(2) calls.
I was a bit puzzled by mickeys comment, remenbering that the kernel
arc4 does use entropy, and indeed rc4random_buf() in the kernel which
provides the random data for stirring the userland arc4random(3) calls
arc4maybeinit() which potentially consumes entropy via arc4_stir() and
get_random_bytes(). The the trigger to stir in the kernel is timer
based, not consumption based.
-Otto
