Make a unique filesystem path, without creating the file
marko at pacujo.net
Tue Feb 23 14:04:15 EST 2016
Paul Rubin <no.email at nospam.invalid>:
> Marko Rauhamaa <marko at pacujo.net> writes:
>> It is also correct that /dev/urandom depletes the entropy pool as
>> effectively as /dev/random.
> I think see what's confusing you: the above is a misconception that is
> probably held by lots of people. Entropy is not water and from a
> cryptographic standpoint there is essentially no such thing as
> "depleting" an entropy pool. There is either enough entropy (say 256
> bits or more) in the PRNG or else there isn't. If there's not enough,
> urandom can misbehave by giving you bad output because it doesn't block
> until more is gathered. If there is enough, /dev/random misbehaves by
> blocking under this bogus concept of "depletion".
You are making my point. /dev/random is correct to block until
top-quality random numbers can be supplied. That's not misbehaving.
> So once /dev/random unblocks, it should never again block, the behavior
> of getrandom.
What you are saying is that /dev/random has no reason to exist (and the
GRND_RANDOM flag to getrandom() is redundant).
I'm no cryptographer and can't judge that. However, as long as the
distinction is maintained, I have to abide by the documented
> No really, all you've done is repeat bad advice. The people cited in
> that article are very knowledgeable and the stuff they say makes good
> mathematical sense. The stuff you say makes no sense and you haven't
> given any convincing reason for anyone to listen to you.
Thing is, neither you nor me nor the cited articles has provided any
more info than insisting on a position, my position being relying on the
So we have
* /dev/urandom vs /dev/random
* getrandom(0) vs getrandom(GRND_RANDOM)
* GCRY_STRONG_RANDOM ("Use this level for session keys and similar
purposes") vs GCRY_VERY_STRONG_RANDOM ("Use this level for long term
key material") (in libgcrypt)
You don't need to convince me that that distinction is silly. You need
to convince the crypto facility providers.
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