Bcrypt Generator

Why bcrypt and not a fast hash

General-purpose hashes such as SHA-256 are designed to be fast, which is exactly wrong for passwords: modern hardware computes billions per second, so a stolen table of unsalted SHA-256 hashes is cracked at enormous rates. Bcrypt is deliberately slow and its cost is adjustable, so it can be made to stay slow as hardware improves.

The salt is inside the hash

Bcrypt generates a random salt per password and embeds it in the output string alongside the algorithm identifier and cost factor. You do not store the salt separately, and you must not reuse one. This is why hashing the same password twice produces two different strings, and why verification takes the stored hash rather than requiring you to recover the salt yourself.

Cost factor

The cost is a power of two: raising it by one doubles the work. A cost of 12 is a reasonable current default on server hardware, taking roughly a quarter of a second. Too low and cracking is cheap; too high and your login endpoint becomes a denial-of-service target against yourself. Benchmark on your actual hardware and revisit every couple of years.

The 72-byte limit

Bcrypt silently ignores anything past 72 bytes of input. A long passphrase is truncated, so two passwords sharing their first 72 bytes hash identically. It also means pre-hashing a password with SHA-256 and base64-encoding the result can exceed the limit if done carelessly. Where very long passwords matter, Argon2id has no such restriction.

Argon2id is the current recommendation

Bcrypt remains acceptable and widely deployed, but Argon2id is memory-hard, which resists GPU and ASIC attacks far better than bcrypt's modest memory use. For new systems Argon2id is the better default, with bcrypt and scrypt as accepted alternatives. Migrating is straightforward: rehash on next successful login.

Never hash a real password in a web tool

This includes this one. Use it to understand the format or to generate a test fixture. Production hashing belongs in your application with a vetted library.