unpredictableSeed

[Ivan Kazmenko]

> Can anyone advise on the theoretical basis for the 
> unpredictableSeed method in std.random?  I've tried googling 
> around for the theory of good thread-safe seed generation 
> methods but haven't really found anything. :-(

I have to ask: what would be a good unpredictableSeed by 
definition?  With the current implementation, three downsides 
come to my mind:

1. Process ID, thread ID and system tick are insecure sources of 
randomness and can provide just a few bits of randomness in 
certain situations.  I don't know how to address this in a 
portable way.

2. Once we know the first seed, it is easy to predict all 
subsequent seeds.  A solution would be to use a secure RNG 
instead, not just the one which gives away its state.

3. It would be a particularly bad idea to initialize MinstdRand0 
instances with consecutive unpredictableSeeds and then consider 
them independent.  This is just a consequence of a particular 
choice of RNG on the previous step.

So, which of these do you consider the real problems, and what 
more do you need from unpredictableSeed?

-----
Ivan Kazmenko.