Random PIN generator.

How many PINs there are, and what that means

A PIN with n decimal digits has 10ⁿ possibilities, so its strength in bits is n × log₂(10), about 3.32 bits per digit. The generator prints the exact figure for your settings. The common lengths work out as follows:

• 4 digits: 10,000 PINs, about 13.3 bits.
• 6 digits: 1,000,000 PINs, about 19.9 bits.
• 8 digits: 100,000,000 PINs, about 26.6 bits.
• 12 digits: 10¹² PINs, about 39.9 bits.

Compare that with 77.5 bits for six random Diceware words, or about 95 bits for a 16-character random password. A PIN cannot reach those numbers at any practical length, which is exactly why PINs are only used where something else limits the guesses.

Worked example: what an attempt limit buys you

Suppose a system disables the authenticator after 100 consecutive wrong tries, the ceiling NIST SP 800-63B-4 sets for verifiers. An attacker who guesses 100 different PINs at random against a 4-digit PIN has a 100 in 10,000 chance, which is 1%. Against a 6-digit PIN the same 100 attempts have a 100 in 1,000,000 chance, which is 0.01%. Going from four digits to six makes a lucky guess a hundred times less likely without changing anything else. If the system had no limit at all, a program trying a thousand PINs a second would get through all 1,000,000 six-digit PINs in under 17 minutes, which is why you should never use a PIN to protect something that can be attacked offline, such as an encrypted file.

What the "skip obvious PINs" option does

With it ticked, the generator redraws any PIN made of one repeated digit or a straight ascending or descending run. For four digits that removes only 24 of the 10,000 possibilities, so the entropy drops from 13.29 to about 13.28 bits. A random draw is unlikely to produce one of them, but if it does, it is the first thing a person trying PINs by hand would test. The option does not exclude other guessable patterns, such as dates, because a random draw has no way of preferring them.

Why random beats chosen

The numbers above assume every PIN is equally likely. When people choose their own PIN the choices are rarely uniform, so an attacker can try the likeliest ones first and the real search is much smaller than 10,000. A PIN drawn at random from a cryptographic source has no pattern to exploit. This generator draws each digit using the browser's crypto.getRandomValues, which MDN describes as a cryptographically strong random number generator, and discards values that would bias the digits.

Common mistakes

• Regenerating until you get a PIN that looks memorable. Take the first result, or you reintroduce your own bias.
• Using the same PIN for a phone, a bank card and a door code.
• Choosing four digits when the system allows six or more.
• Writing the PIN on the card or device it protects.
• Using a PIN where a passphrase is possible. If the secret can be tried without a limit, use the Diceware passphrase generator or measure options in the Password Entropy Calculator.