From: Greg Link (link_at_[hidden])
Date: 2006-05-19 11:16:19
One particularly effective technique is to seed it once, and only
once. Iterate (through the random stream) a bit, then save that value
to a file. Anytime your program closes, just grab one last number
from the stream, save it to the file, and re-load that as your next
seed. That way you're using one (and only one) random sequence for
all runs of your program, and since any good random number generator
(e.g. Mersenne Twister, etc) is pretty close to random along an
entire stream, you're doing pretty well. 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.
- Greg
On May 19, 2006, at 11:08 AM, Peter Dimov wrote:
> Andrew Holden wrote:
>
>> Does anybody else know of other good sources of entropy to seed the
>> generator?
>
> On Windows I use QueryPerformanceCounter, GetCurrentProcessId,
> GetCurrentThreadId and GlobalMemoryStatus as entropy sources.
> OpenSSL uses
> the contents of the screen.
>
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