Passphrases vs Passwords

What a passphrase is

A passphrase is a sequence of multiple random words used as an authentication credential. Unlike a traditional password — which is typically a short, complex, hard-to-type string — a passphrase is longer, composed of real words, and (theoretically) easier to remember. The classic example comes from an xkcd comic: "correct horse battery staple" — four random words that are easy to read and recall but have substantial length and entropy. Diceware is the most systematic method: you roll physical dice to select words from a standardised list, ensuring true randomness in your word selection.

Entropy comparison: passphrases vs random passwords

A 6-word diceware passphrase (words chosen from a list of 7,776 options) has log₂(7776⁶) ≈ 77.5 bits of entropy. A 16-character random password using all printable ASCII characters has log₂(95¹⁶) ≈ 105 bits. A 7-word passphrase has about 90 bits. An 8-word passphrase reaches about 103 bits — comparable to a 16-character random password. In terms of entropy, a long passphrase and a 16+ character random password are roughly equivalent defences against brute force, though random passwords achieve the same entropy in fewer characters.

Where passphrases have an advantage

Memorability is the primary advantage. A well-generated diceware passphrase of four to six words is substantially easier to remember than a 20-character random string like "Xk9&mLpQ2#rNvFwJ". For credentials you must type or remember without a password manager — your computer login password, your password manager's master password, your disk encryption key — a passphrase is a practical choice. These are the exact situations where you genuinely need to hold something in memory, and a passphrase serves this need while maintaining strong security.

Where random passwords have an advantage

For accounts stored in a password manager — which should be the vast majority of your accounts — random passwords generated by the manager are the better choice. They are shorter for the same entropy, they do not require the diceware process to generate, and they are never typed by hand anyway (the manager fills them in). A 16-character random password with all character types has about 105 bits of entropy and is immune to all practical attacks. There is no benefit to using a passphrase for accounts you never need to type manually.

The critical requirement: genuine randomness

Both passphrases and passwords are only as secure as the randomness of the generation process. A passphrase of words that mean something to you — your favourite movie quote, a memorable phrase, words you find easy to remember because they form a coherent sentence — is not a secure passphrase. Human selection introduces massive statistical bias. The words must be chosen by a random process: physical dice with a diceware word list, a trusted digital random word generator, or similar. Similarly, a "random" password generated by a human is far less random than one generated by crypto.getRandomValues().

Practical recommendations for 2026

Use a diceware passphrase (at least 6 words, and 7 or more for your password manager master password) for credentials you must memorise: your computer login, disk encryption, and critically, your password manager master password. Use randomly generated passwords of at least 16 characters (with all character types) for all accounts stored in your password manager. Never use the same passphrase or password on multiple accounts. The combination — a strong passphrase protecting your password manager, and the manager generating unique random passwords for everything else — covers both the memorability problem and the uniqueness requirement.

Why the word list matters

The entropy figures above depend on the size of the list the words come from, not on how obscure the words look. The original Diceware list and the EFF long list both contain 7,776 words, so each word adds about 12.9 bits. The EFF also publishes shorter lists of 1,296 words, which are easier to type and remember but add only about 10.3 bits per word — a six-word phrase from a short list gives roughly 62 bits, not 77. Count the bits using the list you actually used, and add a word if you pick a shorter list. Security rests on the random selection, not on keeping your method or list secret.

Common passphrase mistakes

• Choosing words yourself because they feel random, or re-rolling a word you dislike. Either one removes the randomness the entropy calculation relies on.
• Using a famous quote, song lyric or line from a book, which can be guessed from published text.
• Adding a predictable twist such as capitalising the first letter or appending "1!". Attackers try these patterns early, so they add very little.
• Reusing one passphrase for several services, so a single breach exposes all of them.