Bcrypt Hash Generator & Verifier

What is Bcrypt Hashing?

Bcrypt is a password hashing function designed by Niels Provos and David Mazières, based on the Blowfish cipher. Unlike general-purpose hash functions like MD5 or SHA-256, bcrypt is specifically engineered for password storage. It incorporates a work factor (also called cost factor) that determines how computationally expensive the hashing process is. This intentional slowness is a feature, not a bug — it makes brute-force attacks prohibitively expensive for attackers trying to crack passwords.

A bcrypt hash string looks like $2b$10$ followed by 53 characters of encoded data. The structure encodes the algorithm version, the work factor, a salt value, and the resulting hash. The salt is generated randomly for each password, meaning two identical passwords will produce different hashes. This prevents rainbow table attacks where precomputed hash dictionaries are used to reverse passwords.

When Should You Use Bcrypt?

Bcrypt should be used whenever you need to store user passwords securely. This includes building login systems, implementing user registration flows, migrating from plaintext password storage, or updating legacy MD5/SHA password hashing to modern standards. Any system that handles user authentication benefits from bcrypt's built-in salt and adjustable work factor.

Developers building web applications, mobile backends, or API services that require user accounts should default to bcrypt or similar adaptive hashing functions like Argon2. The work factor should be calibrated so that hashing takes approximately 100-300 milliseconds on your production hardware — fast enough for legitimate login requests but slow enough to deter mass brute-force attempts.

How It Works

Bcrypt begins by generating a random 16-byte salt. It then initializes the Blowfish cipher with a modified key schedule that incorporates the salt through 2^cost iterations. The password is encrypted using this modified Blowfish state, and the process repeats 2^cost times to produce the final hash. The cost factor is logarithmic, meaning a cost of 10 is twice as expensive as a cost of 9. This allows you to increase security over time as hardware becomes faster, simply by raising the cost factor for new passwords while still verifying older hashes.

Tips for Best Results

Use a work factor of at least 10 for new applications, and consider 12-14 for high-security systems. When verifying passwords, always use the constant-time comparison built into bcrypt verification to prevent timing attacks. Never truncate passwords before hashing — bcrypt handles passwords up to 72 bytes internally. Store the full hash string in your database, as it contains all the information needed for verification.