What Is a Diceware Passphrase? EFF Wordlist and NCSC Guide

Quick Answer: A Diceware passphrase is a cryptographic password method where words are selected completely at random from a curated 7,776-word list ($6^5$, equivalent to rolling five 6-sided dice per word). Each word contributes exactly 12.925 bits of entropy ($\log_2(7776)$), meaning a 5-word passphrase provides 64.6 bits of base entropy (or ~74.6 bits with capitalization and a digit) while remaining effortless for a human to memorize and type.

Instead of rolling physical dice for 15 minutes, you can generate an instant, mathematically unbiased multi-word passphrase inside your browser using our free Web Crypto Passphrase Generator.

How the EFF Long Wordlist Improved Classic Diceware

Originally invented by Arnold Reinhold in 1995, classic Diceware mapped every five-dice roll (`11111` through `66666`) to a list of 7,776 tokens. In 2016, cryptographers at the Electronic Frontier Foundation (EFF) published the EFF Long Wordlist, which kept the exact $6^5 = 7,776$ mathematical structure (12.925 bits per word) while improving usability and security:

• 3 to 9 Characters Per Word: Removes obscure 1- and 2-letter abbreviations and arcane symbols that caused typing mistakes.
• Prefix-Free & Spell-Check Friendly: Uses familiar English nouns, verbs, and adjectives so users can visualize a mental scene to remember their master password without writing it on a sticky note.
• Zero Compound-Word Ambiguity: Ensures that even if spaces or separators are omitted, no two word combinations collide into the same string.

Diceware Word Count vs. Entropy & Crack-Time Table (2026)

UK NCSC "Three Random Words" vs. 5-Word EFF Diceware: Which Should You Choose?

In the United Kingdom, the National Cyber Security Centre (NCSC) popularized the "Three Random Words" campaign to move the public away from predictable 8-character passwords like Summer2026!. While 3 random words with capitalization and a digit (~48.8 bits of entropy) easily stops online login guessing where rate-limiting is active, it is not strong enough for offline cryptographic keys.

For your password manager master password (Bitwarden, 1Password, Proton Pass, KeePassXC) or full-disk encryption (Windows BitLocker, macOS FileVault, Linux LUKS), always choose 5 to 6 random words via our Passphrase Generator so that even a dedicated offline GPU cluster cannot brute-force your vault.

Why Human-Invented Sentences Fail the Diceware Test

A common mistake is picking four words from a song lyric, proverb, or book quote — or choosing words that go together grammatically (like blue-ocean-sunny-beach). Natural English has roughly 1.1 to 1.5 bits of entropy per character because words follow predictable grammar and cultural associations. True Diceware security requires cryptographic randomness (window.crypto.getRandomValues()) to pick each word independently.

Frequently Asked Questions

Why is "correct horse battery staple" famous in password security?

Popularized by Randall Munroe in XKCD #936, the 4-word phrase illustrated that four random common words have higher entropy and are far easier to remember than a short, mangled password like Tr0ub4dor&3. Note, however, that you must never use the literal phrase "correct horse battery staple" because it is in every hacker dictionary on Earth.

How many words should my password manager master passphrase have?

Use 5 to 6 random words with a separator (such as a hyphen), title-case capitalization, and a random number. That gives you 74.6 to 87.5 bits of cryptographic entropy on top of Argon2id or PBKDF2 key stretching.

Do word separators like hyphens or periods add entropy to a passphrase?

Using a consistent separator across all word boundaries adds a small constant factor and significantly improves readability and typing accuracy. Even if an attacker knows you used hyphens, 5 to 6 random words from a 7,776-word list remain computationally infeasible to brute-force.