Re: monitoring entropy

H. Peter Anvin (hpa@transmeta.com)
14 Oct 1997 07:34:52 GMT

Followup to: <19971013182050.28960@test.legislate.com>
By author: Raul Miller <rdm@test.legislate.com>
In newsgroup: linux.dev.kernel
>
> I recently ran into a situation where I'd like to monitor how
> much entropy is available in /dev/random. As I understand it,
> this shouldn't be a problem -- essentially, it's just telling
> me when a read will block. [I'm thinking of leaving a little
> thermometer up in a window and futzing with keyboard or mouse
> when it gets low].
>
> If there's some risk to this, could someone in the know (e.g.
> Ted) tell me?
>

Allowing user processes to do this probably would be a security hole,
as you could tell when /dev/urandom was "faking" it, and hence
processes using it were being less secure.

>
> For my purposes, a /proc/entropy file that did something like
> sprintf(buffer, "%d\n", random_state.entropy_count);
> would be perfect.
>
> Comments? Jeers?
>

A root-only ioctl() on /dev/(u)random is probably the right way to do
this.

-hpa

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