20-character password generator
This generator creates a random 20-character password using uppercase and lowercase letters, numbers, and symbols — 128.5 bits of entropy drawn from 4.9 x 10^38 possible combinations. Excess capacity, and that is fine when you never type it by hand.
- Entropy
- 128.5 bits
- Possible passwords
- 4.9 x 10^38
- GPU, fast hash
- 10^19 years
- GPU, PBKDF2 600k
- 10^25 years
Is 20 characters enough?
Twenty characters is beyond any conceivable brute-force attack, so the extra bits buy no additional protection against guessing. What they do buy is margin against a future where the site's hashing turns out to have been weak all along.
Compared with a 16-character password, this is roughly 55 million times more work for an attacker — the cost of guessing grows by a factor of 86 for every single character you add.
When to use a 20-character password
Passwords autofilled by a manager or regenerated on demand, and root or administrator credentials where the blast radius of a compromise is the whole system.
What to watch out for
Long random strings are painful to read aloud or copy across devices manually. If you will ever have to type this, a passphrase of five or six words gives comparable strength with far less pain.
How long this password survives each attack
"Time to crack" is meaningless without naming the attack. The same password fails in an afternoon or outlives the sun depending on how the website stored it. These are average times — half the keyspace — for this password:
| Attack scenario | Guesses / second | Average time |
|---|---|---|
| Throttled login form | 100 | 10^28 years |
| Stolen database, unsalted fast hash | 100 billion | 10^19 years |
| Stolen database, PBKDF2 with 600,000 iterations | ~167,000 | 10^25 years |
The third row is why key stretching matters so much. MoolKey runs PBKDF2 at 600,000 iterations for the same reason: it costs you a fraction of a second and costs an attacker a factor of 600,000.
You still have to keep it somewhere
A 20-character random string is not memorable, and pretending otherwise is how people end up with a sticky note. Either store it in a password manager, or use a generator that can recreate it on demand from one phrase you already remember — which means there is no stored copy for anyone to steal.
20-character password questions
- Is a 20-character password strong enough?
- A random 20-character password using uppercase, lowercase, numbers, and symbols carries 128.5 bits of entropy. Excess capacity, and that is fine when you never type it by hand. Against an offline attack on a fast hash at 100 billion guesses per second, the average time to crack it is 10^19 years.
- How many 20-character passwords are possible?
- With a pool of 86 symbols there are 4.9 x 10^38 possible 20-character passwords. That figure only protects you if your password was chosen at random from all of them — a password you invented sits in a far smaller set that attackers search first.
- How long does it take to crack a 20-character password?
- It depends entirely on how the site stored it. On a rate-limited login form at 100 guesses per second: 10^28 years. Against a stolen database of fast hashes on a GPU cluster: 10^19 years. Against a properly stretched PBKDF2 hash with 600,000 iterations: 10^25 years.
- Is this 20-character generator safe?
- Yes. It runs entirely in your browser using crypto.getRandomValues, the cryptographic random source provided by your operating system. No password is transmitted, logged, or stored. You can disconnect from the network and the generator still works.
More free tools
Every tool runs in your browser without an account. The generators, strength checker, and entropy calculator keep inputs local. The breach checker sends only a five-character hash prefix to Have I Been Pwned.
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Strength checker
A password strength checker estimates how many guesses an attacker needs before reaching your password.
Breach check
A breach check tells you whether a password already appears in leaked data.
Entropy calculator
Password entropy measures how many guesses an attacker needs, expressed in bits.
Make one account easier today.
Start with the password you keep reusing or the bank card that still shares a PIN. MoolKey is free, and you do not need to move everything at once.