Re: [Boost-users] Newbie question: Random numbers.

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-05-19 11:39:43

Greg Link wrote:

> [...] Re-seeding naively can be
> dangerous, as it's not just entropy you want in a seed - it's things
> like relative primality, etc. As noted, seeding with a clock isn't
> nearly as effective as most think. Process ID's tend to be 'low' (not
> 11+ bits long, at least), as do ThreadID's, and other such things.
> Not nearly as much entropy as many think.

Well, that's why one would typically combine as many entropy sources as 
possible using a hash function (MD5, SHA, even boost::hash if 32 bits are 
enough.) :-)

For more demanding uses there's always CryptGenRandom, or RtlGenRandom on 
XP+. On VC 8.0 there's also rand_s.

http://blogs.msdn.com/michael_howard/archive/2005/01/14/353379.aspx