Random PIN generator

A PIN is a short number, and short numbers are weak by construction — a four-digit PIN has ten thousand possibilities. That is fine when something limits the number of attempts, which is exactly the setting PINs are designed for, and useless anywhere an attacker can guess freely.

The reason to use a generator rather than picking a number is that human PINs cluster hard. Analyses of leaked PIN sets repeatedly find that a handful of numbers — 1234, 1111, 0000 and four-digit years starting 19 — cover a startling share of all PINs in use. A random draw has no such clustering, and keeping leading zeros matters because dropping them quietly removes a tenth of the possible values.