Bcryptハッシュ生成・照合

A bcrypt tool that hashes a password at a cost you choose, and verifies a password against an existing bcrypt hash. Everything runs locally in your browser, so passwords stay on your device.

Bcrypt is an adaptive password-hashing function designed specifically for storing passwords. Unlike a fast hash such as SHA-256, it is deliberately slow and includes a built-in salt, which is exactly what you want when defending stored passwords.

The cost factor (the rounds) sets how much work each hash takes. Every extra round doubles the computation, so raising the cost makes large-scale brute-force and GPU attacks far slower, while a single login stays fast enough. A value of 10 to 12 is a common choice.

Bcrypt mixes a random salt into every hash, so the same password produces a different hash each time. That defeats precomputed rainbow tables, and verification still works because the salt is stored inside the hash itself.

To check a password, the verify mode reads the salt and cost out of the stored hash, hashes the candidate the same way, and compares, which is why you only need the hash and the password, not the original salt.

Hashing and verifying run entirely in your browser, so nothing is uploaded. Even so, avoid pasting real production passwords on a shared computer.