Re: [RFC] [VOTE] Vote open for reliable user-land CSPRNG

On 15 March 2015 at 10:29, Matteo Beccati <php@beccati.com> wrote: > > I want to vote yes, but naming is something that scares me a bit. Without > any indication that it's CSPRNG, people might start using it even when > unnecessary, and I'd be worried about potential negative effects, such as > exhausting the entropy pool. It's probably more of a documentation problem, > but we know many won't read the docs and a "hint" in the function name > could help guiding users. > I wouldn't worry about exhausting the entropy pool, on systems like Linux there is kind of a feedback system where data is mixed back into the pool when you request data. You can pipe /dev/urandom into /dev/null for hours and not suffer any problems. > For example, it would be overkill to use random_int() to randomly pick the > content of a boxes at each reload of a web page, but if what I need is a > *random int*, then random_int() seems a far better choice than some obscure > rand() or mt_rand(). > Of course it would, but that's something that needs to be done through education and via the manual. I understand the concern, but I'm not sure how much I'll worry about it. Or in the poker deck example, wouldn't it be enough just to seed mt_srand > with a crypto-secure number to remove the biasing and using mt_rand to > shuffle the deck? > The biasing comes from how the result is restricted to a certain range of numbers, it's not related to the quality of the seed. We avoid that by throwing away numbers that would give a biased result, and picking a new number. The poker deck example isn't a brilliant one, because the effects of biasing become more apparent the closer you get to the maximum upper bound, but it's still important to cater for the unlikely-but-possible scenarios.