Random numbers

Anon

Hi all, PHP profs; I need your help again: I'm building an user authentication/registration system.

The user inserts:

name
password wanted
email

and when the registration is successful I want the system to give him an unique RANDOM authentication number.

I user MYSQL: how can I generate random numbers?

Thanks in advance,
Alberto

Anon

$randnum = mt_rand(1,10);

will be random between 1 and 10 look at mt_rand at php.net.

kparker

unique RANDOM authentication number

But actually, 'unique' and 'random' are conflicting requirements. What exactly are you intending to use this number for?

Anon

Well suppose you're an user subscribing with my auth system: I want it to give you an UNIQUE number that only you will use to log in.

But it has to be RANDOM for every user...that subscribes...

Thanks
Alberto

kparker

OK, the Unique part makes sense if you're using it as some kind of identifier, but why does it need to be random? The problem with asking for something to be simultaneously Random and Unique is that Random by definition does not, and can not, prevent the occurance of duplicate numbers. Thus, you would have to retain a memory of every number handed out and retry whenever you do get a duplicate. <i>This spoils the randomness of the numbers generated</i>, at least in a strict cryptographic sense, but if all you're after is an opaque identifier, it probably won't hurt.