Diceware Passphrase Generator

A strong password like x#kP9!mQw2 is hard to crack but impossible to type on a phone, impossible to dictate over the phone, and virtually impossible to memorise without writing it down. A passphrase trades character-level complexity for word-level length: five ordinary dictionary words joined by hyphens give more entropy than most random character passwords, and you can actually remember them. Diceware Passphrase Generator builds them with crypto.getRandomValues so each word is drawn from a genuine cryptographic source, not a seeded pseudo-random number.

The entropy meter updates as you move the word-count slider, making the security trade-off visible before you generate. At five words from the 512-word list the passphrase carries 45 bits of entropy — enough for a service with rate-limited login attempts. At eight words it passes 72 bits, which exceeds the practical limit for offline cracking on today's hardware.

Worked Example: Generating a Memorable Passphrase

With the default settings — 5 words, hyphen separator, no capitalisation, no digit — clicking Generate Passphrase might produce something like barrel-river-token-silent-maple. All five words are independently and uniformly chosen from the 512-word list using crypto.getRandomValues, so every draw is statistically independent.

• Enable Capitalize each word and the same phrase becomes Barrel-River-Token-Silent-Maple. Title case adds visual separation and satisfies the "must contain uppercase" requirement on most sign-up forms without losing memorability.
• Enable Insert a random digit and one cryptographically chosen digit is spliced into a random position: Barrel-River-4-Token-Silent-Maple. This handles the "must contain a number" requirement without the digit being predictably placed at the start or end.
• The Recent passphrases panel (hidden by default) stores the last 5 generations in the current session. It is the non-obvious feature that lets you flick back to a phrase you liked before the next generate overwrites it.

The Formula Behind Passphrase Entropy

• Each word adds log₂(512) = 9 bits of entropy. Five words give 45 bits; eight words give 72 bits; ten words give 90 bits.
• The meter labels the result: 40 bits is Moderate, 60 bits is Strong, 80 bits is Very Strong. These thresholds assume an offline attacker can test roughly one billion guesses per second — a conservative figure for a purpose-built cracker on consumer hardware.
• The digit insertion adds approximately 3 extra bits (log₂(10) × 1), but the meter does not include this because the digit position is itself exposed when the phrase structure is known. Treat the meter as a lower bound.

When Not to Use a Passphrase Generator

• If the target service limits passwords to 16 characters, a 5-word hyphenated passphrase will be truncated. Check the character limit first and use the strong-password generator for short caps.
• Passphrases are weakest when the attacker knows you used a word-list generator and knows the list. Against a targeted dictionary attack on a specific 512-word list, 5 words gives only 45 bits. Increase to 7+ words or switch to random characters for high-value accounts.
• Nothing generated in this tool is stored or transmitted. The wordlist is bundled in the page. The crypto.getRandomValues call runs entirely on your device.