In 2011, a now-famous webcomic made the case that a password like Tr0ub4dor&3 — a complex-looking password — is actually weaker and much harder to remember than correct horse battery staple. That's the Diceware insight, and it changed how security professionals think about passwords.
What is Diceware?
Diceware is a method for creating passphrases invented by security researcher Arnold Reinhold in 1995. The original method works like this:
- You have a numbered wordlist — the EFF's large wordlist has 7,776 words (6^5, since you roll five dice).
- Roll five physical dice. Note the five-digit number (e.g., 3-4-2-1-5 → 34215).
- Look up that number in the wordlist. It maps to a word (e.g., 34215 → "ketch").
- Repeat to get 5–7 words.
- Your passphrase is those words in order.
Today, this process is automated by cryptographically secure random number generators — the dice are no longer needed, but the wordlist-based approach remains the same.
Why random words are so strong
The EFF large wordlist has 7,776 words. Each word adds log₂(7776) ≈ 12.9 bits of entropy. That means:
| Words | Entropy | Example | Verdict |
|---|---|---|---|
| 3 words | ~39 bits | apple-river-lamp | Too weak |
| 4 words | ~51 bits | apple-river-lamp-stone | Borderline |
| 5 words | ~64 bits | apple-river-lamp-stone-frost | Good |
| 6 words | ~77 bits | apple-river-lamp-stone-frost-pilot | Strong |
| 7 words | ~90 bits | …-pilot-badge | Very strong |
A 6-word passphrase has 77 bits of entropy. For comparison, Tr0ub4dor&3 — the "complex" password — has about 28 bits because an attacker who knows the pattern (common word, substitutions, number appended) can brute-force it quickly.
The memorability advantage
The reason Diceware passphrases are also easier to remember comes from how human memory works. We're good at remembering stories and images, terrible at remembering arbitrary strings of characters.
Given frost-pilot-badge-river-lamp, your brain can form a mental image: a frost-covered pilot shows her badge to a guard standing by a river lamp. That story is memorable. Vg!92^hJqP#mR is not.
The critical rule: words must be random
The entire security of a Diceware passphrase depends on the words being chosen randomly from the wordlist. If you choose words yourself — "my dog's name and my street" — an attacker can exploit your predictable human choices and the security collapses dramatically.
This is why you need a cryptographically secure random number generator, not your own judgment. Our Diceware Passphrase Generator uses crypto.getRandomValues() for genuine randomness.
When to use a passphrase vs a random password
Best for passphrases
- • Master password for a password manager
- • Disk encryption (LUKS, FileVault, BitLocker)
- • Passwords you need to type from memory
- • Passwords you can't paste (some terminals)
- • SSH key passphrases
Best for random passwords
- • Accounts managed by a password manager
- • Situations with strict length limits
- • Character requirement policies
- • When copying from a manager anyway
The EFF wordlists
The Electronic Frontier Foundation (EFF) published updated Diceware wordlists in 2016. They improved on Reinhold's original list by removing confusing or offensive words and ensuring all words are common and easy to type. They published three lists:
- Large list — 7,776 words (5 dice, ~12.9 bits/word) — best security per word
- Short list 1 — 1,296 words (4 dice, ~10.3 bits/word) — shorter words, easier to type
- Short list 2 — 1,296 words, max length 5 chars — for mobile typing
Frequently asked questions
Should I add numbers or symbols to my passphrase?
It doesn't hurt, but with 6+ random words you don't need to. Adding a number increases entropy by ~3-4 bits — less than adding another word (~13 bits). If a site requires special characters, appending one at the end is fine.
Can I use spaces between words?
Spaces are the most natural separator and work in most contexts. However, some systems reject spaces in passwords. Hyphens and underscores are common alternatives that work universally.
What about passphrase patterns like 'three random words'?
The UK's NCSC recommends 'three random words' as a significant improvement over typical passwords. However, for your most important accounts (password manager master password, disk encryption), 5-6 Diceware words provide substantially more security.
Are Diceware passphrases vulnerable to dictionary attacks?
Not when generated randomly. A dictionary attack on a 6-word Diceware passphrase from the EFF large list would require trying 7,776^6 ≈ 2^77 combinations. That's computationally infeasible with any foreseeable hardware.