How Passphrases Get Cracked
October 7, 2026
Key Numbers
- 470 billion: combinations in three words from a 7,776-word list.
- 12.92 bits: added by each extra word.
- ×7,776: work added by one more word.
- ×10: work added by separator and capitalization choices.
How Attackers Guess Passwords
The main way to break a randomly generated passphrase is brute force: trying candidates until one works. How fast that goes depends on where the guessing happens.
- Online guessing. The attacker types guesses into a live login page. Lockouts, delays and CAPTCHAs cap this at a few guesses per second, so it is the slowest route.
- Offline cracking. The attacker steals a database of password hashes, or an encrypted file or vault, and guesses on their own hardware. Nothing limits the speed except the hash type and the computer power available. This is the realistic worst case.
- Wordlist (dictionary) attacks. The attacker assumes you picked words from a published list such as the EFF diceware wordlists, and tries word combinations instead of random characters. Rule-based variants also try capital letters and common separators. For a randomly chosen passphrase this is the same as brute force over the list, which is why the math below uses 7,776 words.
Time to Crack a Three-Word Passphrase
Three words from a 7,776-word list give 470,184,984,576 combinations (about 38.8 bits). The Dice Word Roller app also lets you choose one of 5 separators (space, hyphen, period, underscore, none) and capitalize all words or none, which makes 10 formats. If the attacker does not know your format, they must try all of them: 4,701,849,845,760 combinations (about 42.1 bits). If they know or guess your format, the extra protection disappears.
The table shows the time to try every combination. On average an attacker finds the passphrase after about half that time. The guess rates are round-number estimates, not measured speeds.
| Guess rate | Attack scenario | Format known | Format unknown (10 formats) |
|---|---|---|---|
| 1,000 per second | Online login with throttling | about 15 years | about 149 years |
| 100,000 per second | Offline, slow hash such as bcrypt | about 54 days | about 544 days |
| 1 billion per second | Offline, fast hash on one GPU-class machine | about 8 minutes | about 78 minutes |
| 1 trillion per second | Offline, fast hash on a large GPU cluster | under 1 second | about 5 seconds |
Two points follow. First, the separator and capitalization choices only help when you choose them unpredictably each time; a habit of always using a hyphen and lowercase can be guessed. Second, they multiply the work by only 10, while one extra word multiplies it by 7,776.
How Many Words to Use
Choose the word count by what an attacker could do with a stolen copy. Each word adds about 12.92 bits and multiplies the work by 7,776. Five words need about 11 months to try at a trillion guesses per second; six words need about 7,000 years.
| Use | Words | Entropy | Why |
|---|---|---|---|
| Login with lockouts or rate limits, such as a bank or email site | 4 | about 52 bits | Online guessing is throttled, so the guess rate stays low. Turn on two-factor sign-in as well. |
| Account whose password hash could leak from a breached site | 5 | about 65 bits | Sound sites use slow hashes, but you cannot see how a site stores yours. |
| Phone, laptop or computer sign-in | 5 to 6 | 65 to 78 bits | Device limits slow guessing, but a stolen device can be attacked offline. |
| Password manager master password, encrypted drive or backup | 6 to 7 | 78 to 90 bits | A copy of the vault or drive can be attacked offline with no limit and no deadline. |
| Crypto wallet passphrase, encryption key, anything protecting large value for years | 8 or more | 103 bits or more | Computers will keep getting faster and the data may stay exposed for decades. |
Note: Use the capitalization and separator options for readability and to meet site rules, and do not count them toward these totals.
Keeping the Numbers True
These figures hold only if the passphrase is truly random and used once.
- Take the words exactly as the dice give them. Swapping in words you like, or rerolling until it reads well, shrinks the pool and lowers the strength.
- Use a different passphrase for every account. A passphrase reused on a breached site is simply looked up, and the guessing math no longer matters.
- Turn on two-factor sign-in wherever it is offered, because it covers phishing and stolen-password risks that no word count can.
- Generate and use passphrases offline when you can, and keep them out of screenshots, chats and unencrypted notes.
Guess rates are round-number estimates for comparison, not measurements. Word counts assume words chosen at random from the 7,776-word EFF Large Wordlist.