Looking for some quick assistance

Hi,
My company is planning to sell some membership cards to its registered subscribers. These cards are supposed to have a unique activation key, which the users will use(online) to activate their account.
Now, the help I am looking for-
(1) How to generate this unique activation key?? The algorithm is basically what we need.

(2) The key needs to be something which will carry the datestamp, duration & userid etc....., so that when we get the key, we can get the details for official purpose.

Thanks in advance.

Regards.
Arijit Sarbagna