How to Hash Passwords in Python
Part of the Hashing Toolkithash = PasswordHasher().hash(password)argon2-cffi — defaults to Argon2id with a random salt generated automatically
Explanation
argon2-cffi (pip install argon2-cffi) is the current recommended choice for Python — it wraps the real, native Argon2 reference implementation and defaults to Argon2id with a random salt generated automatically:
from argon2 import PasswordHasher
ph = PasswordHasher()
hash = ph.hash(password)
ph.verify(hash, password)The one real gotcha: verify() doesn't return False on a wrong password the way you might expect from a function named verify — it raises argon2.exceptions.VerifyMismatchError instead. Code that calls if ph.verify(hash, password): without a try/except around it will work fine for a correct password and crash with an uncaught exception for an incorrect one, rather than cleanly rejecting the login attempt:
from argon2.exceptions import VerifyMismatchError
try:
ph.verify(hash, password)
# password is correct
except VerifyMismatchError:
# password is wrong
passPasswordHasher() with no arguments defaults to RFC 9106's low-memory profile (64 MiB, 3 iterations, 4 lanes) — already reasonable, and stricter on memory than OWASP's baseline. To set OWASP's exact numbers (m=19456, t=2, p=1) explicitly instead:
ph = PasswordHasher(memory_cost=19456, time_cost=2, parallelism=1)For what each of these parameters actually does internally, see Argon2 Explained.
Valid examples
ph = PasswordHasher() hash = ph.hash(password) # "$argon2id$v=19$m=65536,t=3,p=4$..."Defaults to Argon2id with RFC 9106's low-memory profile — the salt and every parameter are embedded in the returned string.
try: ph.verify(hash, password) except VerifyMismatchError: pass # wrong passwordverify() raises on mismatch instead of returning False — this is the correct way to handle it.
PasswordHasher(memory_cost=19456, time_cost=2, parallelism=1)Explicit OWASP-baseline parameters instead of the library's RFC 9106 low-memory defaults.
Invalid examples
if ph.verify(hash, password): login()verify() doesn't return False on a wrong password — it raises VerifyMismatchError. Without a try/except, a wrong password crashes the request instead of just failing the login.
import hashlib hashlib.sha256(password.encode()).hexdigest()A raw SHA-256 digest — no salt, no cost factor. See Why SHA-256 Should Not Be Used for Passwords.
hash == ph.hash(password) # comparing two fresh hashesEvery hash gets a new random salt, so hashing the password again and comparing strings will never match the stored hash, even for the correct password — always use verify(), never re-hash-and-compare.