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Date: Mon, 12 Jan 2015 23:14:41 +0000
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Subject: Re: [PHP-DEV] rand(), mt_rand() and limits
From: leight@gmail.com (Leigh)

I fail at reply to all.

On 12 January 2015 at 16:52, Leigh <leight@gmail.com> wrote:
> On 12 January 2015 at 09:31, Andrea Faulds <ajf@ajf.me> wrote:
>> - To produce a repeatable sequence of random numbers (works, but only if=
 you and the sole user of the global random number  generator, which is not=
 guaranteed by any means)
>>
>
> If you're talking about the libc implementation then this is not the
> case, the RNG state is not shared between processes. If you mean
> across threads / web requests, then yes rand() is not reentrant,
> although this is easily fixed by using rand_r() at the cost an
> additional uint per thread. (MT is quite a bit more expensive to make
> reentrant)
>
> On 12 January 2015 at 09:37, Andrea Faulds <ajf@ajf.me> wrote:
>> - To generate cryptographic keys - a seeded random number generator shou=
ld NEVER be used for this, but because PHP is so lacking in good facilities=
 to obtain random data for cryptographic purposes, unfortunately rand() is =
used more than it should be. rand() is already pretty bad, but the existenc=
e of srand() makes this a particular problem. Everything shares the same ra=
ndom number generator, which makes it worse, as something might seed it and=
 now your key is easily predictable.
>
> Nobody with any real desire to produce secure cryptographic keys will
> use rand() for this. I've mentioned in a previous thread I would like
> to see a generic get_random_bytes() function outside of any
> cryptography extensions that would fall back through /dev/?random /
> CryptGenRandom / MT to get the best possible random for a string of
> bytes for a platform in a quick manner, instead of people trying to
> loop over mt_rand(0,255) per byte.