Re: How can I build OSSP UUID support on Windows to avoid duplicate UUIDs?

On Thu, Oct 31, 2013 at 3:42 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Oct 31, 2013 at 2:44 PM, Garick Hamlin <ghamlin@isc.upenn.edu> wrote:
>> I think using /dev/urandom directly would be surprising. At least it would
>> have probably have taken me a while to figure out what was depleting the
>> entropy pool here.
>
> Perhaps so; a bigger problem IMHO is that it's not portable. I think
> the only way to solve this problem is to import (or have an option to
> link with) a strong, sophisticated PRNG with much larger internal
> state than pg_lrand48, which uses precisely 48 bits of internal state.
> For this kind of thing, I'm fairly sure that we need something with
> at least 128 bits of internal state (as wide as the random value we
> want to generate) and I suspect it might be advantageous to have
> something a whole lot wider, maybe a few kB.

I mentioned the notion of building an entropy pool, into which one might
add various sorts of random inputs, under separate cover...

The last time I had need of a rather non-repeating RNG, I went with
a Fibonacci-based one, namely Mersenne Twister...

<http://en.wikipedia.org/wiki/Mersenne_twister>

The sample has 624 integers (presumably that means 624x32 bits) as
its internal state. Apparently not terribly suitable for cryptographic purposes,
but definitely highly non-repetitive, which is what we're notably
worried about for UUIDs.
--
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"