Table of Contents
Password hashing is not ordinary hashing
A password hash must do three things ordinary hashes do not: be salted (unique per password), slow (costly to brute-force), and ideally memory-hard (costly to parallelize on GPUs). That is why bcrypt, scrypt, and Argon2 exist.
Side by side
| bcrypt | scrypt | Argon2id | |
|---|---|---|---|
| Year | 1999 | 2009 | 2015 (PHC winner) |
| Tunable cost | rounds (cost) | N (CPU), r (mem), p (parallel) | m (memory), t (time), p (parallel) |
| Memory-hard | No (some) | Yes | Yes |
| Salt | Built in | Built in | Built in |
| Output | cost$salt$hash | Nrp$salt$hash | v=19$m=...,t=...,p=...$salt$hash |
bcrypt
The veteran. Simple, battle-tested, salt built in. Its weakness is low memory use, so dedicated hardware can parallelize it. Keep the cost factor at 12+ today.
$2b$12$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdCE...scrypt
Adds a memory cost (r) on top of CPU cost, raising the bar against GPU farms. Good choice when you cannot use Argon2.
params: N=2^14, r=8, p=1 (tune memory with r)Argon2id
The modern default. id (data-independent + data-dependent) resists both side-channel and GPU attacks. Tune memory m, iterations t, and parallelism p.
m=19456, t=2, p=1 (≈19 MiB — a common starting point)How to choose
- New project: Argon2id, memory ≈ 19–64 MiB, tune
tto keep a hash under ~500 ms. - Need broad legacy support: scrypt, or bcrypt with cost ≥ 12.
- Anything: never use raw SHA-256/MD5, and always use a library that verifies in constant time.
Generate and verify
Hash passwords locally with the matching tools:
- Bcrypt Hash on Toolbox
- Scrypt Hash on Toolbox
- Argon2 Hash on Toolbox
- Generate strong inputs with the Password Generator on Toolbox
Related tools
- Bcrypt Hash on Toolbox
- Scrypt Hash on Toolbox
- Argon2 Hash on Toolbox
- Password Generator on Toolbox
- Bcrypt Hash Generator on Toolhub
- Password Generator on Toolhub
- Password Generator on DevTools
Next steps
- Cipher parameters differ from hashing — see SM4 vs AES.
- Tokens fail verification the same way — JWT signature verification failed.
Frequently asked questions
Plain SHA-256 is a hash, why not use it for passwords?
SHA-256 is fast and unsalted by default, so attackers brute-force or use rainbow tables cheaply. Password hashing needs salt and deliberate slowness, which SHA alone does not provide.
Which is the safest?
Argon2id is the current recommendation — it won the Password Hashing Competition and is memory-hard. scrypt is a strong fallback, and bcrypt is still acceptable if bumping the cost factor.
What is a salt?
A random value mixed into the hash so two users with the same password get different hashes, defeating precomputed rainbow tables.
Guide Info
- Category
- Explained
- Difficulty
- Intermediate
- Reading Time
- 2 min
- Tags
- #bcrypt #scrypt #argon2 #password #hashing
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