A passphrase trades symbol soup for length: several ordinary words chosen at random. This guide covers the wordlist maths, why the words must be chosen by dice or software rather than by you, and how to handle separators, capitals and sites that insist on a digit.
A passphrase is a password built from whole words — something like lantern-copper-willow-raft-ember. Its strength does not come from the words being unusual or meaningful to you. It comes from how many words there are and how large the list they were drawn from is. Five words picked at random from a list of 7,776 words carry about 64.6 bits of entropy, because each word contributes log2(7,776) ≈ 12.9 bits — and unlike a string of random symbols, you stand a real chance of remembering and typing it correctly.
The idea is often credited to diceware, a method from the 1990s where physical dice rolls selected words from a printed list. The medium has changed — your browser can roll the dice now — but the security argument is identical, and it is worth understanding before you trust any phrase with your email account.
Key takeaways
- Each randomly chosen word adds a fixed, calculable amount of entropy — about 12.9 bits from a 7,776-word list.
- Random selection is non-negotiable: a phrase you invent yourself is predictable in ways a dice roll is not.
- Five words is a sensible floor for important accounts; six is better and still typeable.
- Separators and capitalisation barely change strength — spend your effort on one more word instead.
The arithmetic, word by word
| Words (from a 7,776-word list) | Entropy | Roughly comparable to |
|---|---|---|
| 3 words | ≈ 38.8 bits | a 6-character random password — too weak for anything important |
| 4 words | ≈ 51.7 bits | an 8-character random password |
| 5 words | ≈ 64.6 bits | a 10-character random password |
| 6 words | ≈ 77.5 bits | a 12-character random password |
| 7 words | ≈ 90.4 bits | a 14-character random password |
Two things matter in that table. First, the growth is steady and predictable — there are no surprises, because the selection process is uniform. Second, list size matters as much as word count: the same five words drawn from a small 1,000-word list give only about 49.9 bits, because each word then carries just under 10 bits. A generator that will not tell you how its words were chosen is asking you to take its strength on faith.
Why you must not choose the words yourself
Human-chosen phrases collapse for the same reason human-chosen passwords do: our choices cluster. Asked to invent a memorable phrase, people reach for quotes, song lyrics, proverbs, family names and grammatical sentences about their own lives. Attackers' wordlists contain all of those. Even a "random-feeling" sentence you compose is usually a normal English sentence, and modern guessing tools model grammar — a determiner is followed by an adjective or noun, and each slot has a small set of likely fillings.
Random selection removes you from the equation entirely. willow is not in the phrase because it means something to you; it is there because a number came up. The resulting phrase often looks faintly absurd, and that absurdity is the point: it sits in a part of the search space that human-shaped guessing does not reach early.
Building one you can live with
- Generate, do not compose. Use a generator (or dice and a published list) and accept the first phrase it gives you. Re-rolling until a phrase "feels right" quietly reintroduces your preferences.
- Pick five words minimum, six for your email and banking. Your email account resets everything else, so it deserves the extra word.
- Choose a separator your fingers like. Hyphens, spaces and dots are all fine cryptographically. Pick the one you can type on a phone keyboard without hunting.
- Add policy decorations last. If a site demands a capital letter and a digit, capitalise one word and append a number. The decoration adds almost no entropy, but it satisfies the form without weakening the phrase.
- Practise typing it a few times on day one. Muscle memory forms fast; a phrase you have typed ten times stops feeling like a password and starts feeling like a signature.
Where passphrases beat character passwords — and where they do not
Passphrases win wherever a human has to type: unlocking a laptop, a password manager's master password, a Wi-Fi key read over the phone. They lose on length-limited forms — a site that caps passwords at 16 characters cannot hold five words — and they are no better than random strings for credentials a machine stores and submits for you, such as API keys or app passwords in a manager. The rule of thumb: if your fingers and memory are involved, use a passphrase; if only software is, length in characters is free, so take a long random string instead.
Mistakes and pitfalls
Using a quote, lyric or saying
Famous phrases exist in cracking dictionaries as complete units. A line from a film is effectively one "word" from a small list, no matter how many characters it contains.
Swapping in personal words
Replacing a generated word with your dog's name because it is easier to remember feels harmless, but personal vocabulary is exactly what targeted guessing tries early. Keep the generated words; learn them by repetition instead.
Counting characters instead of words
Judging a passphrase by its character count flatters it. Twenty-five characters of phrase is five choices from a wordlist — about 65 bits — not the 160+ bits a random 25-character string would have. Count the choices, not the keystrokes.
Common questions
Are spaces or hyphens safer as separators?
Neither, in any way that matters. The separator is not secret and attackers try the common ones. Choose for typing comfort. If a site forbids one, switch without worrying.
Can I keep the same passphrase and change the last word per site?
No — that is a pattern, and patterns are what guessing tools exploit. If one account leaks, the variations for your other accounts become easy to enumerate. Each account gets its own independently generated phrase, stored in a manager.
Is a passphrase safe as my password-manager master password?
It is the recommended shape for exactly that job: long, high-entropy and memorable. Use at least five, ideally six, randomly generated words, and turn on the manager's two-factor authentication as well.
To wrap up
A passphrase is not a weaker, friendlier password — at five or six randomly chosen words it is stronger than most character passwords people actually use, and it survives being typed on a bad keyboard at midnight. Its only real demand is discipline at the moment of creation: let the dice decide.
Store each generated phrase in your password manager as you create it, even the ones you fully intend to memorise. Memory is for the master password and the handful of phrases you type constantly; the vault is for everything else. That division of labour is what makes the system survivable: the phrases you memorise unlock the vault, and the vault remembers the phrases you do not. If you ever forget an unstored phrase, the account's recovery flow — not your memory — has to save you, and on well-built services that process is deliberately slow, public and stressful. A stored copy turns that bad day into a non-event.
Try it yourself
The passphrase generator here draws each word uniformly at random and shows the entropy of the phrase it made, so you can see exactly how many bits your word count buys you.