A passphrase like cobalt-ripple-tundra-mosaic-lantern-orbit looks less
secure than q7#Vd!2pLx9@rT4m. It is not — provided the words were
chosen at random. Here is how to compare the two.
Measuring strength
The strength of a randomly generated secret is the number of equally likely possibilities, usually written in bits: n bits means 2ⁿ possibilities.
- A random character from the 94 printable ASCII symbols adds log₂ 94 ≈ 6.55 bits.
- A random word from the EFF long wordlist of 7,776 words adds log₂ 7776 ≈ 12.9 bits.
Side by side
| Secret | Strength |
|---|---|
| 4 random words | about 52 bits |
| 6 random words | about 78 bits |
| 8 random words | about 103 bits |
| 12 random characters | about 79 bits |
| 16 random characters | about 105 bits |
Six random words are roughly as strong as twelve random characters, and much easier to type and remember.
The catch: "random" means random
The calculation assumes each word was picked by a die roll or a computer, not by you. A phrase from a song, a quote or a "random" sequence you came up with is far weaker, because attackers try exactly those first.
Separators and capitals add little. If you need more strength, add a word.
Which one to use where
- Things you type from memory — the password manager's master password, disk encryption, your computer login: a passphrase of 6 or more random words.
- Everything else — website accounts stored in a password manager: a random password of 16 characters or more. You never type it, so it might as well be unreadable.
Either way, the rule from the previous guide still applies: one secret per account, never reused.