Strong password generator

How to use it

1. Set the length and tick the character sets you want — lowercase, uppercase, numbers, symbols.
2. A new password is generated instantly; the meter shows a rough strength estimate.
3. Tap Copy, then paste it into your password manager.

Why Math.random would be a liability here

Math.random in V8 is xorshift128+, a fast non-cryptographic generator seeded once per context. Its 128-bit state can be recovered from a handful of consecutive outputs, after which every later value — and every earlier one — is predictable. Fine for shuffling a carousel, disqualifying for a credential. crypto.getRandomValues draws instead from the operating system’s cryptographic pool: getrandom(2) on Linux, BCryptGenRandom on Windows, the source that seeds TLS keys.

The second trap is turning random bytes into characters. Taking a byte modulo the alphabet length is the obvious approach and quietly wrong: 256 does not divide evenly by 94, so the first characters of the set appear marginally more often than the rest. Rejection sampling — discarding values that fall in the uneven tail and drawing again — removes the bias at no cost.

What the strength meter counts, and what it cannot see

Strength here is entropy: the base-2 logarithm of alphabet size raised to the length. Sixteen characters from the full 94-character printable ASCII set is roughly 105 bits; the same length in lowercase alone is 75. That arithmetic holds only because each character is chosen independently and uniformly — it assumes an attacker who knows the generator and the character set exactly and still has nothing better than brute force.

It says nothing about a password a person invented. Substitution patterns — a for @, o for zero, a digit and an exclamation mark at the end — have sat in cracking rulesets such as hashcat’s best64 for over a decade, so P@ssw0rd! falls in roughly the time password does. NIST SP 800-63B dropped composition rules and scheduled expiry in 2017 for exactly that reason.

Questions