EFF Short Wordlist 2 Passphrase Generator (Prefix)

EFF Short Wordlist 2: the autocomplete-friendly Diceware

The EFF Short Wordlist 2 was published in 2018 by the Electronic Frontier Foundation as an extension of Joseph Bonneau's original Short list. It keeps the 1296-word count and the short-word philosophy, but adds one extra constraint: every word has a unique 3-letter prefix. Type abi and there is exactly one word it can be (ability); type abo and you get above. That single property turns Short 2 into the friendliest Diceware list ever shipped for mobile keyboards and password-manager UIs.

Why a unique 3-letter prefix matters

Two real-world wins come from that constraint:

• Autocomplete in password managers — 1Password's Watchtower, Bitwarden, and KeePassXC all support typing a prefix and resolving to the full word. With Short 2, three keystrokes per word is the worst case. Eight words become 24 keystrokes plus separators, not 60+.
• Typo tolerance — if you mistype the 4th, 5th, or 6th letter, the prefix still uniquely identifies the word. Some implementations auto-correct silently using the prefix table.
• Voice dictation reliability — Siri / Google Assistant transcribe the first syllable reliably; the prefix property means even partial transcripts map to one word.
• Sight-reading from paper — printed passphrases stay readable even if the print is smudged after the third letter.

Entropy: identical to Short 1

Both Short lists carry the same log₂(1296) ≈ 10.34 bits per word. The unique-prefix property doesn't cost entropy — it's a structural property of the word selection, not a reduction of the word pool. Concrete cumulative strength:

• 6 words ≈ 62 bits — borderline. Good for low-stakes accounts behind rate limiting.
• 7 words ≈ 72 bits — the modern minimum for any account you actually care about.
• 8 words ≈ 83 bits — the safe floor for a password-manager master key in 2026.
• 10 words ≈ 103 bits — quantum-resistant margin, sensible for crypto cold-storage protection.

Short 2 vs Short 1 vs Large 7776

Pick Short 2 when a password manager with prefix-autocomplete is part of your daily workflow, when you type the passphrase on phone keyboards, or when you want maximum typo tolerance for printed copies. Pick Short 1 when slightly more natural English words matter and you don't rely on autocomplete. Pick Large 7776 when storage and display real estate dominate over typing time — a Yubikey static slot, a server-side secret, a one-time cold-storage seed. The EFF Large list does not have a unique-prefix property; BIP39 (used by Bitcoin/Ethereum seeds) does have a unique 4-letter prefix for the same reasons Short 2 has a 3-letter one.

Tooling and availability

EFF publishes the raw eff_short_wordlist_2_0.txt at eff.org/dice under CC0. Both Bitwarden and 1Password use Short 2 internally for their "word-style" generated passwords. KeePassXC ships it as a built-in option. iOS Suggested Strong Passwords use a similar prefix-friendly construction so Apple's autofill UI can match partial input. On the developer side, dicewareGen (npm), diceware (Python), and Rust's passphrase crate all support Short 2. There is no official Portuguese version; for Brazilian PT contexts that need a prefix-friendly list, BIP39 PT (2048 words, 4-letter prefix, 11 bits/word) is the closest equivalent.

FAQ

How is Short 2 different from Short 1? Same size (1296), same entropy (10.34 bits/word), but Short 2 guarantees every word has a unique 3-letter prefix — designed for autocomplete and typo tolerance.

Minimum word count for a master password? 8 words (~83 bits) is the safe floor today. 6 words (~62 bits) is acceptable for accounts behind strong server-side rate limiting.

Does my password manager actually use the prefix property? Bitwarden, 1Password, and KeePassXC do internally; whether the typing UI exposes prefix autocomplete depends on the client. The property still pays off in typo tolerance even without UI support.

Can I mix words across separators (hyphen vs space)? Yes — separator choice doesn't affect entropy. Pick the one your target system accepts; hyphen is the safest cross-system default.