Storing Passwords

Hash, never encrypt

Passwords must be stored with a slow, salted, one-way password hashing function, never encrypted (encryption is reversible) and never with a fast hash like plain SHA-256 or MD5 (GPUs try billions of guesses per second). The OWASP Password Storage Cheat Sheet recommends Argon2id first, then scrypt, with bcrypt for legacy systems and PBKDF2 where FIPS compliance is required. A unique random salt per password defeats precomputed tables and makes identical passwords hash differently; modern libraries generate it and embed it in the output string together with the parameters. Tune the cost so a hash takes a noticeable fraction of a second on your hardware, and raise it over time. Check the cheat sheet for current recommended parameters.

Store, verify, recover

Passwords are still everywhere. Hash them slowly, verify them carefully and recover accounts without opening new holes.

Argon2id in Python

Using the argon2-cffi library; parameters and salt are encoded in the hash string.

from argon2 import PasswordHasher
from argon2.exceptions import VerifyMismatchError

ph = PasswordHasher()  # Argon2id with library defaults; tune for your hardware

def register(email: str, password: str) -> None:
    hashed = ph.hash(password)        # '$argon2id$v=19$m=...,t=...,p=...$salt$hash'
    db.users.insert(email=email, password_hash=hashed)

def check_password(user, password: str) -> bool:
    try:
        ph.verify(user.password_hash, password)
    except VerifyMismatchError:
        return False
    if ph.check_needs_rehash(user.password_hash):  # parameters were raised
        db.users.update(user.id, password_hash=ph.hash(password))
    return True

Know the bcrypt limits

bcrypt only uses the first 72 bytes of input, and some implementations truncate silently. Prefer Argon2id for new systems, and use a vetted library rather than pre-hashing tricks you design yourself.

त्वरित जाँच: Why is plain SHA-256 a poor choice for password storage?

• It is reversible with the right key
• It is designed to be fast, so offline guessing is cheap
• It produces outputs that are too long to store
• It cannot be used with a salt