Bcrypt Generator

About Bcrypt Generator

bcrypt is a deliberately slow password hashing function with a built-in random salt and an adjustable cost factor. This page creates bcrypt hashes and also checks a password against an existing hash, which helps when you are seeding a test database, debugging a login that will not accept a known password, or choosing a cost value for production.

How to use it

1. On the Generate Hash tab, type the password into the Password box and watch the byte counter beneath it.
2. Drag the Cost (Rounds) slider. It runs from 4 to 18 and starts at 10.
3. Select Generate Bcrypt Hash and wait while it computes, then copy the string from the Generated Hash card.
4. To test a password, switch to Verify Hash, enter the password, paste the hash, and select Verify Password.

Hash and check the password hunter2 at the lowest cost

Password: hunter2, Cost: 4

$2a$04$VwAS1JmrjvNuqFc951IR6uOYzE9tyS0gqvSUl.vhhY1NNhozd.tXq (60 characters; your salt, and so the rest of the string, will differ every run, and Verify Password accepts it)

When to use it

• Seeding a development database with users whose password hashes your login code can really verify.
• Working out why a login fails by verifying the password against the stored hash directly.
• Trying several cost values to see how long each takes on your own hardware before choosing one.
• Producing a hash for an application config that expects a pre-hashed administrator password.

Questions about Bcrypt Generator

Why do I get a different hash every time for the same password?

bcrypt generates a fresh random 22-character salt on each run and stores it inside the output. The hash is still verifiable, because the verifier reads the salt back out of the string.

What do the parts of the hash mean?

The string starts with the version such as $2a$, then the cost as two digits, then 22 characters of salt and 31 characters of digest. The cost is a power of two, so each extra step doubles the work.

What is the 72-byte warning about?

bcrypt only reads the first 72 bytes of a password, counting multi-byte characters as several bytes. A longer password is silently truncated, so two passwords sharing those first bytes verify against the same hash.

Which prefixes can the verifier read?

It accepts $2a$, $2b$ and $2y$ hashes. The generator writes $2a$, and the three prefixes differ only in how historical implementations handled edge-case bugs, not in the format.

Why does a high cost freeze the page?

The hash runs in the browser on the main thread. Above cost 14 a warning appears, and cost 18 can take around half a minute, during which the tab cannot respond.

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