questions about RNGs and FIPS 140

[travis+ml-cryptography at subspacefield.org]

On Thu, Aug 26, 2010 at 06:25:55AM -0400, Jerry Leichter wrote:
> [F]IPS doesn't tell you how to *seed* your deterministic generator.  In  
> effect, a FIPS-compliant generator has the property that if you start it 
> with an unpredictable seed, it will produce unpredictable values.   

That brings up an interesting question... if you have a source of
unpredictable values in the first place, why use a CSPRNG? ;-)

Actually, I know I'm being snarky; I'm aware that they're handy for
"stretching" your random bits, if you don't have enough for the task.

I suppose some people feel they're also handy for whitening them, so
that if they're not entirely random, the structure isn't completely
obvious from the output alone, but I think that's probably a separate
property that needs to be evaluated independent of the others.

Last I checked Linux /dev/{u,}random uses SHA-1 hash over the pool,
which suggests they had this in mind.  However, it also makes using it
very slow for wiping disks or any other high-bandwidth tasks, at least
when compared to something like Yarrow.

I heard from a colleague that /dev/urandom exists on Android, but
/dev/random does not.  Our best guess is that it's the same as the
standard Linux /dev/urandom, but we're not really sure.  Presumably
they dumped /dev/random because there just weren't enough sources of
unpredicability on that platform.  I'd like to hear from anyone who
knows details.

Also, please do check out the links about RNGs on the aformentioned
page.  Seth Hardy's /dev/erandom looks very interesting, and has
languished in relative obscurity for nearly a decade.

I'll take the rest of my comments to this list:
http://lists.bitrot.info/mailman/listinfo/rng
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