Creating a unique alphanumeric 10-character string

Question

I\'m looking to create a simple short-lived reservation system, and I\'d like to generate confirmation numbers that are

• unique
• random-looking

Answer 1

You can use whatever, even a plain random number generator; however, you should check that the reservation code isn't already present. If this is the case, add characters ('x') to the string (date+user) until you get a new random/sha1/etc.

I'm only looking to have ~500 reservations, so I don't imagine high likelyhood of collissions.

Another stupid idea: generate 1000 or 2000 unique random numbers with the desired properties, store them somewhere, and assign them to the users as they register :)