Why passphrases work
The strength of a passphrase comes from the number of possible combinations, not from the words being obscure. Each word picked at random from 7,776 words adds 12.9 bits of entropy:
| Words | Entropy | Offline crack time at 10 billion guesses/s |
|---|---|---|
| 4 | 52 bits | about 3 days |
| 5 | 65 bits | about 45 years |
| 6 | 78 bits | about 340,000 years |
| 7 | 90 bits | billions of years |
The catch: the words must be chosen by a random generator, not by you. A sentence you made up yourself, a song lyric or a quote is far weaker, because attackers have lists of those too.
Where to use a passphrase
- The master password of your password manager.
- Your computer or phone login.
- Disk encryption like BitLocker, FileVault or VeraCrypt.
- Wi-Fi networks you share with guests.
Everywhere else, let your password manager generate and remember a long random password for you.
Frequently asked questions
What is Diceware?
Diceware is a method for making passphrases by rolling dice to pick words from a numbered list. This tool does the same with a cryptographic random generator instead of dice, using the EFF long word list.
How many words should my passphrase have?
Six words is a good default and gives about 78 bits of entropy. Use seven for a password manager master password or disk encryption.
Can I add numbers or symbols?
Yes. Turn on 'Add a number' or pick a separator. Some sites demand a digit or a capital letter, and this keeps the passphrase accepted without making it weaker.
Is it safe that the word list is public?
Yes. The security comes from the random choice, not from a secret list. The math in the table above assumes the attacker knows the exact list.