Re: Good random seeds.

[Petite Abeille <petite.abeille@...>]

On May 15, 2008, at 7:03 PM, Jorge Visca wrote:

> I was wondering what people use as seeds for the random generator.
> os.time() seems ok, but the to-the-second precission and my usage
> patterns make this a risky option. Not very probable, but when it
> happens it means very weird behaviour.

If the quality of the PRNG is important to you, don't use math.random :)

Perhaps you would be better off with LHF's lrandom, a library for  
generating random numbers based on the Mersenne Twister:

http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/#lrandom

> I'm on linux, and the ideal would be lua only solution, with no extra
> libraries. I could parse MAC adresses from runing "ifconfig", and hash
> them. Or somehow get a number from /dev/urandom... Sadly, "date +%N"
> doesn't work on my platform. Any ideas?

For the humble purpose of generating slowly changing string token, I  
use a combination of math.random and hashing:

http://dev.alt.textdrive.com/browser/HTTP/Token.lua#L66

Those tokens are used as more or less random HTML form identifiers, to  
slowdown spambots [1], e.g.:

<input type='text' name='dsr'
<textarea name='ojdmrdwtx'
<input type='hidden' name='faqn'

http://svr225.stepx.com:3388/main/editor


[1] http://nedbatchelder.com/text/stopbots.html