Passphrase vs Password: Which Is More Secure?
You’ve probably seen the famous comic suggesting that correct horse battery staple is a better password than Tr0ub4dor&3. Is that actually true? The answer is “yes, if you do it right”, and doing it right is surprisingly simple. Let’s compare the two approaches.
Measuring strength: entropy
Security people measure password strength in bits of entropy: the number of yes/no questions an attacker would need to answer to be sure of your password. Every additional bit doubles the number of guesses. For a password chosen randomly, entropy is easy to calculate:
entropy = length × log2(size of the pool you’re choosing from)
Random-character passwords
If each character is picked at random from about 74 possible characters (letters, digits and common symbols), each one adds about 6.2 bits. So:
- 8 characters ≈ 50 bits
- 12 characters ≈ 74 bits
- 16 characters ≈ 99 bits
Random-word passphrases
If each word is picked at random from the EFF’s list of 7,776 words (the list our passphrase generator uses), each word adds about 12.9 bits:
- 4 words ≈ 52 bits
- 5 words ≈ 65 bits
- 6 words ≈ 78 bits
- 7 words ≈ 90 bits
Notice that these numbers hold even if the attacker knows you used this exact wordlist. The secret is which words were picked, not where they came from.
Head-to-head
| 16 random characters | 6 random words | |
|---|---|---|
| Example | k8#Tm2!qZr@9Lw4e |
gravy-tusk-nimble-fiber-oasis-plank |
| Entropy | ≈ 99 bits | ≈ 78 bits |
| Easy to remember? | No | Yes, with a mental image |
| Easy to type on a phone? | Awkward (symbol keyboards) | Easy |
| Accepted by all sites? | Almost always | Usually; a few sites cap length |
Where the comic’s example goes wrong in real life
Tr0ub4dor&3 is weak not because it’s short, but because it’s a human-chosen word with predictable substitutions. Cracking tools try exactly those tweaks. A passphrase only beats it if the words are chosen by a random process. Picking four words you like (“blue sky happy dog”), using a song lyric or a famous quote gives you very little security, because attackers’ dictionaries include common phrases.
So which should you use?
- Use a passphrase for the handful of secrets you must type from memory: your password manager’s master password, your computer or phone login, full-disk encryption. Use at least 6 words for these.
- Use random characters for everything stored in your password manager. You never type them, so memorability doesn’t matter, and you get the most strength per character.
- Use a pronounceable password only for low-risk, temporary situations like reading out a guest Wi-Fi password.
Making a passphrase stick
- Generate a few options and choose the one you can picture most vividly, but don’t edit the words.
- Invent a short, absurd story connecting them in order.
- Type it ten times now, and a few times over the next few days.
- Keep a paper copy somewhere safe until you’re confident you know it.