Score a diceware passphrase in bits, using the EFF 7776-word list at 12.925 bits per word, and see its crack time.
A passphrase is a random draw with replacement from a known wordlist, so its entropy is the number of words times the bits per word — and the attacker is assumed to know the wordlist. Six EFF words give 77.5 bits, which beats a 12-character random alphanumeric password while staying typeable from memory. Passphrases are the only construction that reaches 80+ bits and still survives contact with a human being, so knowing the bits per word tells you exactly how many words your standard should demand.
Passphrase Strength
entropy = words × log2(wordlist size), plus 1 bit per randomly capitalised word, plus 3.322 bits per random digit.
Offline crack time
crack time = 2^entropy ÷ (2 × 10^11 guesses per second) for an MD5 hash on one 8-GPU rig.
entropy = words × log2(wordlist size), plus 1 bit per randomly capitalised word, plus 3.322 bits per random digit. A passphrase is a random draw with replacement from a known wordlist, so its entropy is the number of words times the bits per word — and the attacker is assumed to know the wordlist. Six EFF words give 77.5 bits, which beats a 12-character random alphanumeric password while staying typeable from memory.
Passphrases are the only construction that reaches 80+ bits and still survives contact with a human being, so knowing the bits per word tells you exactly how many words your standard should demand.
This calculator takes 5 inputs: Number of words, Wordlist, Random digit between words, Randomly capitalise each word, Random digits appended. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
No. Kerckhoffs's principle applies: the strength is in the random selection, not the secrecy of the list. The maths above already assumes the attacker has the list and is guessing word combinations, not characters.
Four words is 51.7 bits and falls to a determined offline attack. Six words is 77.5 bits and is the usual recommendation. Eight words is 103.4 bits, appropriate for a password-manager master password or a disk-encryption key.