SHA-256 vs bcrypt vs Argon2 for Password Storage

SHA-256 is a fine hash function; it's just the wrong hash function for passwords. General-purpose cryptographic hashes like SHA-256 and SHA-512 are designed to be fast, because they're used for things like checksums and digital signatures where speed is a feature. Speed is the opposite of what you want when hashing passwords.

Why speed is the problem

If an attacker gets a database of password hashes, they don't need to break the hash function itself; they just guess candidate passwords, hash each one, and compare. Modern GPUs can compute billions of SHA-256 hashes per second, which means a fast hash turns password cracking into a raw throughput problem an attacker can brute-force through in a reasonable amount of time, especially against weak or reused passwords. Salting prevents precomputed rainbow-table attacks, but it does nothing to slow down this kind of brute force.

Password hashing algorithms are deliberately slow

bcrypt, scrypt, and Argon2 exist specifically to make each guess expensive. They use a configurable “work factor” that controls how many iterations, how much memory, or both, are required per hash, tunable so the cost stays roughly constant (a few hundred milliseconds per attempt) even as hardware gets faster. That's the entire design goal: make one login check tolerably fast for a real user, while making a billion guesses prohibitively slow for an attacker.

bcrypt vs Argon2

• bcrypt.Been in production since 1999, has a fixed, relatively small memory footprint, and is well-supported across nearly every language. A safe, battle-tested default, though its memory cost can't scale the way Argon2's can.
• Argon2. Winner of the 2015 Password Hashing Competition, and the current recommendation from OWASP. Argon2id (the hybrid variant) lets you tune memory cost independently of time cost, which specifically defeats GPU and ASIC cracking rigs, since those devices have abundant compute but comparatively little fast memory per core.

For new systems, OWASP's current guidance is Argon2id first, bcrypt as a well-supported fallback where Argon2 isn't available. SHA-256/SHA-512 should never be used alone for password storage, only ever as a general-purpose hash for data integrity, not secrets. This site's own Encrypt / Decrypt tool supports SHA-256 and SHA-1 for exactly that non-password use case, with a warning banner on the legacy algorithms.