Passphrase: A Password Made of Words, Used Wisely

A passphrase is a sequence of randomly chosen words, easier to remember than a traditional password. It is only strong under one strict condition: the words must be genuinely random. Here's how to create one, how many words to aim for, and the rare cases where it's the right answer.

What is a passphrase?

A passphrase is a password made up of several whole words chosen at random - for example, "porthole cherry vertigo cauldron plunge barstool." Instead of combining characters, you combine words.

The standard method is called Diceware. It involves randomly selecting several words from a public list of roughly 7,800 words - historically using dice (hence the name), today using a generator. Two points define the method's value: the words are drawn at random, not chosen, and they have no connection to one another, whether grammatical or thematic. What makes a passphrase hard to remember is exactly what makes it secure. Any attempt to make it more convenient weakens it.

Is a passphrase strong because it's long?

No. A passphrase is strong because it's randomly generated, not because it's long. The moment it tells a story, its protection collapses.

This is the fundamental misconception. Passphrases are often described as long, memorable, and highly secure - as if those three qualities naturally go together. In reality, only the random origin of the words produces security. A made-up phrase and a randomly generated passphrase can look identical to the eye: only the method of creation separates them.

What is entropy, and why is it the only thing that matters?

Entropy measures how hard a secret is to guess. It's expressed in bits, and the rule is simple: every additional bit doubles the attacker's workload.

A few benchmarks:

The key insight: entropy doesn't describe the secret itself - it describes how it was chosen. A random generator could produce "hello," and that would be a legitimate draw; a user who types "hello" on their own has no protection at all. What matters isn't how a password looks, but the number of possibilities it was drawn from. This is the same mechanic that explains why the length of a password matters more than its complexity: adding length multiplies possibilities, while decorating it does almost nothing.

How many words does a safe passphrase need?

Six words at minimum. Seven or eight for a secret that protects everything else, such as the master password of a password manager or disk encryption.

Translated into computing time, against an attacker capable of one trillion guesses per second (a pessimistic assumption, implying a stolen secret with poor server-side protection): four words fall in under an hour, five words hold for a few months, six words for several thousand years, and seven words are out of reach.

Why be more demanding for a master password or disk encryption? Because those face offline attacks. An attacker who gets their hands on the data can attack it locally, without any limit on attempts. No server-side protection can stop them - only the entropy of the secret remains.

One useful detail: expanding the word list - that is, choosing uncommon words - is almost pointless. Going from 7,800 to 20,000 words gains only about one and a half bits per word, since you'd need to double the list to gain just one bit. The only lever that counts is the number of words.

Why does a passphrase need to be longer than a generated password?

Because a word contributes less security than it appears to. A word drawn at random from 7,800 options is worth roughly 13 bits - the equivalent of just two characters - yet it takes five or six keystrokes to type.

In other words, a passphrase delivers about three times less security per character typed than a generated password. This is the one case where displayed length and actual strength diverge significantly. A thirty-five-character passphrase looks impressive; it's worth a generated password of about twelve characters. The ratio is remarkably consistent: one randomly chosen word is worth roughly two random characters.

Can you use a meaningful phrase to make it easier to remember?

No - this is the most common mistake. In a coherent sentence, each word narrows the field of possible next words instead of multiplying it, which is the exact opposite of what's needed.

Take a passphrase that starts with "I went to the…" The first words form a common sequence: they contribute almost nothing, and an attacker will test them immediately. As for the next word, grammar and meaning confine it to a handful of plausible candidates: restaurant, movies, market, office, park. A few dozen options, where a random draw would have offered nearly eight thousand.

A meaningful English sentence caps out at around one bit per character, compared to 6.5 bits for true randomness. A forty-character phrase can therefore be worth less than a seven-character generated password. This isn't a theoretical concern: modern cracking tools incorporate language models and prioritize natural word sequences. Song lyrics, proverbs, titles, and famous quotes have been in attack dictionaries for years. A personal memory isn't an escape route: the attacker doesn't need to know your memory - only your language.

Should you add uppercase letters, numbers, and symbols?

There's no need. On a passphrase, these additions gain very little, whereas one more randomly drawn word changes everything.

What are the drawbacks of a passphrase?

Memorization takes real effort, and typing on mobile is painful - especially when characters aren't displayed. These limitations are rarely mentioned, but they determine when it's appropriate to use one.

Remembering six to eight completely unrelated words isn't instant: it requires deliberate memorization. It's easier than a generated password of equivalent strength, but it doesn't come free. Typing forty characters on a touchscreen keyboard several times a day, with autocorrect interfering, is a very real reason people give up. Finally, a character limit of twenty or thirty-two - still common - makes it impossible.

When should you actually use a passphrase?

Only for the rare secrets you need to remember by heart, because no tool can retrieve them for you. Everywhere else, a generated password does better.

The legitimate use cases are few:

• The master password of a password manager
• Disk or backup encryption
• A recovery phrase that can't be stored anywhere
• A shared secret communicated verbally or by phone

That last case is a rarely cited advantage: a sequence of words can be dictated, written by hand, and copied without errors - whereas a generated password turns every 0/O and l/1 into a source of confusion. For everything else - the dozens of everyday accounts - a generated, unique, never-memorized password is better in every way. The right question isn't "passphrase or generated password?" but "do I need to remember this secret by heart?" The answer should rarely be yes in a digital life, especially since passkeys further reduce the number of secrets to memorize. The generator built into Octopussian's password manager produces passphrases with the same cryptographic randomness as a regular password.

How do you create a passphrase correctly?

Let a machine draw the words at random, and resist any urge to rearrange them. The entropy is in the draw, not in how you remember it.

• Don't choose the words yourself. Contrary to our intuition, we're poor at selecting things at random: use dice or a cryptographic generator, not gut feeling.
• Don't reroll a word you don't like. Rejecting draws you dislike effectively shrinks the list. If the result is truly unworkable, regenerate the entire passphrase - not a single word.
• Don't shorten the word list. With a short list (around 1,300 words), you'd need about eight words to reach what six words deliver with a long list.
• A memory trick costs nothing. Inventing an absurd image to remember a random draw doesn't weaken the secret. What's not allowed is composing the phrase from a story.
• Writing the phrase on paper during the learning phase is a reasonable compromise, as long as you destroy the paper once it's memorized.
• A passphrase is never reused - no more than a password. And it doesn't replace a second factor: it protects against guessing, not against phishing, a keylogger, or a server-side breach.

Key takeaways

• A passphrase is strong because it's randomly generated, not because it's long.
• Six words minimum; seven or eight for a master password or disk encryption.
• Never use a meaningful phrase: every predictable word reduces security.
• One extra random word is worth more than all the uppercase letters, numbers, and symbols combined.
• Passphrases are only for secrets you need to remember by heart; for everything else, a generator is the better choice.