Password Generator

How many characters is enough?

The useful measure is entropy — how many equally likely possibilities the password was drawn from, expressed as a power of two. Sixty bits means 2⁶⁰candidates. It is a better unit than “strong” because you can do arithmetic with it: add a character from this tool’s 87-symbol alphabet and you gain about 6.4 bits, which multiplies the work by nearly ninety.

What that buys depends entirely on how the site stored your password, which you have no way of knowing. The table below assumes the pessimistic case that gets reported after most breaches: the hashes were fast, and the attacker rented GPUs.

The interesting part of that table is where it stops mattering. Past about sixteen random characters the brute-force question is settled permanently, and every remaining risk to that account is something else entirely — phishing, a keylogger, a breach at the provider, reuse somewhere else. Choosing twenty-four characters instead of twenty is not the decision that protects you.

Complexity rules made passwords worse

For twenty years the standard advice was eight characters with an uppercase, a number and a symbol. That rule produced Password1! in enormous quantities, because it describes exactly what a person does when told to satisfy it. The rule is satisfied and the password is in every cracking dictionary.

Randomness is what the rule was groping towards, and randomness is the thing a person cannot supply. Ask someone for a random character and the distribution is nothing like uniform; ask them where the digit goes and it is at the end. That is why the generator above chooses every character independently from the alphabet you selected, and re-draws the whole password rather than placing one symbol in a fixed slot — the second approach would satisfy the policy while quietly making the position of every required character predictable.

Which characters to include

Turning on all four sets gives an 87-character alphabet, worth 6.44 bits per character. Dropping symbols leaves 62 characters and 5.95 bits — a loss of about half a bit per character, which two extra characters more than repay. So if a site rejects symbols, or you are typing the password into a games console, drop them and add length instead. That is a real trade, not a compromise.

The Avoid look-alike characters option removes 0 O 1 l I | and the quote marks. It costs a fraction of a bit and prevents the specific, common failure of misreading a password off a screen and locking yourself out on the third attempt. Worth using for anything you will ever type by hand; pointless for anything that lives in a password manager.

When a passphrase is the right answer

You have perhaps three passwords you genuinely have to remember: the one that unlocks your password manager, the one that unlocks your laptop, and possibly your email. Everything else can be twenty random characters, because you will never type it.

For those three, a passphrase wins. picture-shallow-ranger-anvil-cobalt-drift is six words, about 66 bits, and you can hold it in your head after a few repetitions in a way that K7#mQ2vX!pL9 never will be. The catch is that the strength comes from the number of words, and people consistently pick too few. Four words is 44 bits — not enough for a password manager. Six is 66. Seven is 77.

It only works if the words are chosen by the machine. A phrase you compose yourself is drawn from the small set of phrases a person thinks of, not from the word list, and song lyrics and film quotes are in cracking dictionaries as whole strings.

The failure that actually happens

Almost nobody is brute-forced. What happens is this: a site you signed up to in 2015 is breached, the password file leaks, and within days automated tools are trying that email and password pair against banks, email providers and retailers. This is credential stuffing, and it is the dominant way accounts are lost. It does not care how strong your password was. It only cares whether you used it twice.

Which is why the single highest-value thing on this page is not the length slider. It is generating a different password for every site, which is only practical with a password manager, and which turns one breach into one problem instead of eleven.

Two-factor authentication is the other half. A password that has leaked is still useless to someone who cannot produce your second factor, and an app-based code or a hardware key beats SMS, which is vulnerable to having your number ported away from you.

Can you trust this page?

A fair question to ask of any online generator, and the answer should be checkable rather than asserted. Three things are true of this one:

• The password is generated by crypto.getRandomValues(), the browser’s cryptographic random source — never Math.random(), which is a fast statistical PRNG with no security properties and, in some engines, recoverable internal state.
• It is generated after the page loads, in your browser. Nothing about it is computed on our servers, so there is nothing for us to log even if we wanted to.
• It is not written to localStorage, not put in the URL, and not included in any analytics event. Closing the tab destroys it.

You can verify all three: open your browser’s developer tools, switch to the network tab, and click Generate another as many times as you like. Nothing is sent. That check works on any generator, and it is worth doing on any generator you have not read the source of.

If you would rather not extend the trust at all, that is reasonable too — the generator inside your password manager produces the same kind of output with one fewer party involved. The reason to use this one is convenience, not superiority.

Related

Already have a password and want to know what is wrong with it? The strength checker pulls it apart the way a cracking tool would and tells you which parts it recognised. For what your browser and connection give away — a separate problem from account security, and one people often conflate with it — the privacy check covers it in one pass.