Re: entropy gathering (was Re: Why does reading from /dev/urandom deplete entropy so much?)

Jon Masters
2007-12-09T01:09:20Z

On Sat, 2007-12-08 at 18:47 -0500, Theodore Tso wrote:
> On Sat, Dec 08, 2007 at 09:42:39PM +0100, Willy Tarreau wrote:
> > I remember having installed openssh on an AIX machines years ago, and
> > being amazed by the number of sources it collected entropy from. Simple
> > commands such as "ifconfig -a", "netstat -i" and "du -a", "ps -ef", "w"
> > provided a lot of entropy.
>
> Well.... not as many bits of entropy as you might think. But every
> little bit helps, especially if some of it is not available to
> adversary.

I was always especially fond of the "du" entropy source with Solaris
installations of OpenSSH (the PRNG used commands like "du" too). It was
always amusing that a single network outage at the University would
prevent anyone from ssh'ing into the "UNIX" machines. So yeah, if we
want to take a giant leap backwards, I suggest jumping at this.

Lots of these are not actually random - you can guess the free space on
a network drive in some certain cases, you know what processes are
likely to be created on a LiveCD, and many dmesg outputs are very
similar, especially when there aren't precie timestamps included.

But I do think it's time some of this got addressed :-)

Cheers,

Jon.