Pin Generation

Question

I am looking to develop a system in which i need to assign every user a unique pin code for security. The user will only enter this pin code as a means of identifying himself. T

Answer 1

If we assume 100,000 users maximum then they can have unique PINs with 0-99,999 ie. 5 digits.

However, this would make it easier to guess the PINs with the maximum number of users. If you can restrict the number of attempts on the PIN then you can have a shorter PIN. eg. maximum of 10 failed attempts per IP per day.

It also depends on the value of what you are protecting and how catastrophic it would be if the odd one did get out.

I'd go for 9 digits if you want to keep it short or 12 digits if you want a bit more security from automated guessing.

To generate the PINs, I would take a high resolution version of the time along with some salt and maybe a pseudo-random number, generate a hash and use the first 9 or 12 digits. Make sure there is a reasonable and random delay between new PIN generations so don't generate them in a loop, and if possible make them user initiated.

eg. Left(Sha1(DateTime + Salt + PseudoRandom),9)