The Comic That Embarrassed an Industry
Years ago, the webcomic xkcd compared two passwords. "Tr0ub4dor&3": hard for humans to remember, cracked by software in days. "correct horse battery staple": easy for humans to remember, centuries to crack. Security researchers winced because it was true, and password guidance (including NIST's official recommendations) eventually came around: length beats complexity.
The Math, Without Tears
Password strength is measured in entropy: how many guesses an attacker needs in the worst case. Every added character or word multiplies the search space.
- 8 character complex password (upper, lower, digits, symbols): roughly 52 bits of entropy IF truly random. Modern cracking rigs chew through that against fast hashes in hours to days.
- 4 random common words (from a 7,776 word list): about 51 bits, similar on paper, but trivially extended: five words is 64 bits, six words is 77, each additional word multiplying difficulty by 7,776.
- The human factor is the real gap: people don't create random 8 character passwords. They create "Summer2026!", and cracking software tries exactly those patterns first: dictionary words with capitalised first letters, appended years, symbol substitutions. Real-world "complex" passwords deliver a fraction of their theoretical entropy. Random words stay random.
The critical fine print: the words must be randomly chosen, dice or generator, not picked by you. "ilovepizzafriday" is a human phrase, and human phrases live in cracking wordlists. Randomness is the entire trick. Full cracking mechanics in our brute force explainer.
A passphrase's strength doesn't come from being long. It comes from being random. Length is just how randomness becomes memorable for humans.
A Worked Diceware Example
Diceware is the original, still-best method: roll five physical six-sided dice (or one die five times) to get a number like 4-2-5-1-6, look that number up in the public 7,776-word Diceware list, and the matching word is your first word. Repeat for word two, three, four, and five, each with a fresh set of rolls. Five independent rolls of five dice gives you five words pulled from a genuinely random, uniform distribution: no human bias about which words feel "memorable enough" or "clever," which is exactly the bias that makes human-chosen phrases guessable.
The entropy per word comes straight from the list size: log base 2 of 7,776 is about 12.9 bits. Multiply by word count for the total search space an attacker faces:
| Word count | Approximate entropy | Offline cracking time at 10 billion guesses/sec |
|---|---|---|
| 3 words | ~39 bits | Under a second to minutes |
| 4 words | ~52 bits | Hours to a few days |
| 5 words | ~65 bits | Years to decades |
| 6 words | ~77 bits | Millennia and beyond, for practical purposes |
That table is why the advice below insists on five or six words for anything that guards other secrets, and why four is only "acceptable" (not ideal) for accounts that rate-limit login attempts and can't be attacked offline.
What Memorability Research Actually Shows
This isn't just theory. Usability studies going back over a decade, including work cited in NIST's own password guidance revisions, consistently found the same pattern: users asked to create "complex" passwords (mixed case, digits, symbols) reliably produce weaker, more predictable results than the rules intend, because the human brain solves the "remember this" problem by falling back on patterns: a capital letter at the start, a digit or two at the end, a familiar word in the middle. Meanwhile, users given multi-word passphrases, even totally unfamiliar random words, could recall them accurately after a week with far less friction, because remembering four or five words in a made-up scene taps into ordinary human memory for narrative, while remembering an arbitrary jumble of characters does not. The comic wasn't just funny, it was measuring something real about how human memory works versus how brute-force software works.
Where Password Managers Change (and Don't Change) the Calculation
A password manager mostly settles the passphrase-versus-password debate for ordinary accounts: the manager generates and stores a long random string per site, you never see or type it, so there's no memorability constraint left to optimize for. Maximum entropy, zero human effort, problem solved for every site login.
But the manager itself has to be unlocked by something, and that something is usually a single master password or passphrase that you, a human, must recall from memory with no autofill available, often at the exact moment you're locked out of everything else. That one secret is where the entropy-versus-memorability tradeoff still matters completely, because it's the one secret in your entire digital life you can't outsource to a generator and forget about. The same logic applies to full-disk encryption passphrases and computer login passwords: anything typed from memory, with nothing to fall back on, is a passphrase problem. Anything a machine can generate and store for you is a random-password problem. That's the actual dividing line, not "which is stronger in the abstract."
Where Passphrases Fit (and Where Passwords Do)
Here's the practical division of labour in a modern setup:
| Secret | Best form | Why |
|---|---|---|
| Password manager master password | Passphrase (5+ words) | You type it from memory, often; it guards everything |
| Computer login | Passphrase | Typed daily, no autofill available at boot |
| Encrypted backups / disk encryption | Passphrase (6+ words) | Offline cracking is the threat model: maximum entropy |
| Every website account | Random generated password, 16+ chars | The manager types it, not you: no memorability needed |
| WiFi network | Passphrase | Shared verbally with guests, typed on TV remotes |
The pattern: memorised secrets should be passphrases; stored secrets should be machine-generated randomness. Our password generator produces both kinds in your browser, and the strength checker estimates survival time against cracking hardware.
How to Generate a Proper Passphrase
- Use real randomness: a diceware list (roll physical dice against the 7,776 word list) or a generator using cryptographic randomness. Never your own brain: it's a terrible randomness source that loves song lyrics.
- Five words minimum for a master password; six for encryption keys. Four is acceptable where an online service rate-limits guesses.
- Keep the words unmodified. "capital letter plus exclamation mark" rituals add trivial entropy while wrecking memorability. Add a word instead: it adds nearly 13 bits.
- Make up a vivid mental image linking the words in order. The absurdity is the mnemonic: a horse inspecting a battery, approvingly, stapled to a certificate. You'll have it memorised in three logins.
- Write it down for the first week, stored physically safe, then destroy the note once it's in your fingers.
What Passphrases Don't Fix
Perspective matters: the strongest passphrase in the world is still a single factor, and it still gets stolen by phishing pages and keyloggers, and leaked in breaches: strength is irrelevant in all three cases (a stolen 60-bit secret and a stolen 20-bit secret are equally stolen). The complete stack:
- Passphrase or generated password, unique per site, so credential stuffing finds nothing to reuse.
- 2FA on top, so theft of the secret isn't game over: our 2FA guide covers setup, and our free TOTP generator shows the codes working.
- Passkeys where offered, removing the memorised secret entirely: see what is a passkey.
Frequently Asked Questions
Is "correcthorsebatterystaple" itself safe to use?
No: it's the most famous passphrase on earth and sits at the top of every wordlist. Same for any example from any article, including this one. The method is public; your specific random words must not be.
Do spaces between words matter?
Only for typability: spaces, hyphens, or nothing are cryptographically equivalent (an attacker who knows the format gains nothing meaningful either way). Pick whatever your fingers like, and note some sites disallow spaces.
What if a site's password rules demand symbols and digits?
Append a fixed simple suffix like "7!" to satisfy the checker: the security still comes from the words. Those composition rules predate modern guidance; NIST now explicitly recommends length over forced complexity, but old forms linger.
Are foreign language or mixed language words better?
Only if randomly selected from a large list: cracking tools include wordlists for every major language, so the language itself adds little. Random selection from a bigger combined pool does help marginally. Randomness remains the whole game.
How often should I change my passphrase?
Modern guidance: don't rotate on a schedule (it breeds "Passphrase2!", "Passphrase3!" patterns). Change it when there's a reason: a breach notification, suspected compromise, a shoulder-surfed login. Spend the saved effort enabling 2FA instead.
