Re: [RFC][PATCH] Make cryptoapi non-optional?

David Lang
2003-08-18T06:57:41Z

On Mon, 18 Aug 2003, Andreas Dilger wrote:

> Subject: Re: [RFC][PATCH] Make cryptoapi non-optional?
>
> On Aug 15, 2003 23:38 -0500, Matt Mackall wrote:
> > a) extract_entropy (pool->lock)
> >
> > For nitpickers, there remains a vanishingly small possibility that
> > two readers could get identical results from the pool by hitting a
> > window immediately after reseeding, after accounting, _and_ after
> > feedback mixing.
>
> It wasn't even vanishingly small... We had a problem in our code where
> two readers got the same 64-bit value calling get_random_bytes(), and
> we were depending on this 64-bit value being unique. This problem was
> fixed by putting a spinlock around the call to get_random_bytes().

if the number is truely random then there should be a (small but finite)
chance that any two reads will return the same data. counting on a random
number to be unique is not a good idea.

now if you can repeatably get the same number then you probably have a bug
in the random number code, but if you need uniqueness you need something
else.

David Lang