Posted by Jerry Stuckle on 08/02/05 19:25

mydejamail@yahoo.co.uk wrote:
> Looking around the web I see all sorts of theories for generation
> random numbers, some of which sound pretty complicated.
>
> Does PHP's simple command, generate something truly random?
>
> If I generate a range of 16 digit numbers, what chances are there for a
> repetition over the whole 10^16 range?
>
> I think my demands are over the top here, I don't know if my computer
> can generate that number I just want to have the warm feeling that it
> won't be possible in my lifetime.
>

It's pretty random, especially if you are generating these at different times
and seed the generator based on the current time. Then you can use general
statistics functions. I wrote a quick program to check, and it showed you would
have to generate 117,741,003 random numbers to have a 50% chance of getting a
duplicate.

Now - if you're trying to generate them all at the same time based on one seed,
the probability might be somewhat less, but shouldn't be that much.

BTW - who cares if there are duplicates? For instance - my bank assigns a 4
digit PIN for my ATM card. And I KNOW they have more than 10,000 users out
there. There are a lot of duplicates.

PINs don't need to be unique - just long enough that they can't be guessed
easily. And I don't think someone's going to guess a 16 digit PIN in any
reasonable time, even if it is computer generated. And you could always lock
them out after 1,000,000 consecutive failures :-).

--
==================
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Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
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