Passphrases vs Passwords: Which Is More Secure?

A passphrase is a sequence of random words — something like copper-falcon-river-arbitrate — instead of a single dense string like xK9#mQ2vL. Both approaches can be secure. The question is which is more practical, and the answer depends on what you're securing and how you'll store it.

The maths, briefly

Security in both cases comes down to entropy — how many guesses an attacker would need on average to find the right answer. For a random password, entropy is length × log2(character set size). For a passphrase built from a wordlist, it's number of words × log2(wordlist size).

Using a common 7,776-word list (about 12.9 bits per word), four random words give roughly 51.6 bits of entropy. A 12-character password using upper, lower, numbers and symbols (a set of roughly 94 characters) gives about 78.7 bits. On paper, the character-based password wins for the same rough "effort" of typing. But that comparison misses something important: what people actually do when left to choose for themselves.

Where passphrases win

Left unassisted, people don't generate 12 truly random characters — they generate memorable, pattern-heavy strings that are far weaker than they look. A passphrase built from genuinely random word selection is something a person can actually memorise and reproduce accurately, without falling back on a predictable pattern. That makes passphrases a strong choice for the handful of passwords you actually need to type from memory — your device unlock, your password manager's master password.

Where traditional passwords win

For anything stored in a password manager and never typed by hand, a maximally random character-based password is strictly better per character typed, because you never pay the "memorability tax." There's no reason to make it pronounceable or memorable if you'll never need to remember it.

What NIST recommends

NIST's digital identity guidelines (SP 800-63B) emphasise length over composition rules, explicitly support passphrases as a valid credential type, and recommend systems allow at least 64 characters. They also recommend screening new passwords against lists of known-breached credentials and dropping mandatory periodic rotation and arbitrary complexity rules, since both tend to push people toward weaker, more predictable choices.

The practical rule

Use a passphrase for anything you must type from memory. Use a fully random generated password — stored in a password manager — for everything else. Both beat the alternative most people actually use: a short, reused, pattern-based password that feels secure but isn't.