Re: Re: [RFC][DISCUSSION] Improve uniqid() uniqueness

The list was missed off of Yasuo's replies to me, replying including the list On Wed, 5 Oct 2016 at 01:07 Yasuo Ohgaki <yohgaki@ohgaki.net> wrote: > Hi Leigh, > > On Tue, Oct 4, 2016 at 7:06 PM, Leigh <leight@gmail.com> wrote: > > Since we want to preserve BC > > > > entropy = random_int(0, 99999999); > > uniqid = strpprintf(0, "%s%08x%05x.%08d", prefix, sec, usec, entropy); > > Current entropy is _double_ from php_combined_lcg() and has 10 chars > length, > has [0-9].[0-9]{8} format. > > "F"->"d" does not work. It should be something like > > entropy = (double) random_int(0, 9999999999); > No it shouldn't. Don't do this. It is an unnecessary conversion. The fact the lcg returns a double is irrelevant. What is relevant is the 8 digits in order to maintain BC. The 8 digits you receive from random_int will still be higher quality than the 10 you get from the lcg rounded to 8 places. > uniqid = strpprintf(0, "%s%08x%05x.%08F", prefix, sec, usec, > entropy/100000000); > On Wed, 5 Oct 2016 at 01:16 Yasuo Ohgaki <yohgaki@ohgaki.net> wrote: > On Wed, Oct 5, 2016 at 9:06 AM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote: > > Current entropy is _double_ from php_combined_lcg() and has 10 chars > length, > > has [0-9].[0-9]{8} format. > > > > "F"->"d" does not work. It should be something like > > > > entropy = (double) random_int(0, 9999999999); > > uniqid = strpprintf(0, "%s%08x%05x.%08F", prefix, sec, usec, > entropy/100000000); > > Forgot to mention, this code leak more information about PRNG state > than my patch because php_random_int() copies random binary data into > long. It's still part of it and exposure of random data shouldn't > matter, so this is minor issue. > I think there is a misunderstanding here. You're using the CSPRNG which is designed such that the _entire_ output can be made public without you being able to predict the next result. That is the definition of a CSPRNG. Also remember this is "output" not "state". While researching how to implement these CSPRNG functions, I spoke with real security experts on the subject, they all said the same thing: Use the system CSPRNG, and yes, it is fine to expose the output directly. Also if you really are worried (which you shouldn't be), requesting 8 digits from random_int will effectively discard 5 or 37 bits of output depending on whether you're on a 32 or 64 bit platform. You cannot know the value of sequential outputs. > I'll update gist. > Any more comments? > > Regards, > > -- > Yasuo Ohgaki > yohgaki@ohgaki.net