Weak Password Hashing

MD5 and SHA1 are general-purpose cryptographic hash functions designed for speed. This speed is catastrophic for password storage — modern GPUs can compute billions of MD5 hashes per second, making offline brute-force trivial.

Vulnerable storage (Python):

import hashlib

# NEVER do this for passwords
hashed = hashlib.md5(password.encode()).hexdigest()
hashed = hashlib.sha256(password.encode()).hexdigest()  # Still wrong!

Why rainbow tables make it worse: Unsalted hashes are vulnerable to precomputed rainbow tables. An attacker who obtains the database can look up millions of common password hashes instantly — no cracking needed.

Speed comparison:

• MD5: ~10 billion hashes/second on a consumer GPU
• SHA-256: ~2 billion hashes/second
• bcrypt (cost 12): ~100 hashes/second
• argon2id: ~10 hashes/second (configurable)

The 100-million-fold slowdown from bcrypt makes offline brute-force impractical even after a database breach.

Password hashing algorithms are specifically designed to be slow (computationally expensive) and include a salt automatically. They are the only acceptable choice for password storage.

bcrypt (Python):

import bcrypt

# Registration
password = b"user_password"
hashed = bcrypt.hashpw(password, bcrypt.gensalt(rounds=12))
# rounds=12 means 2^12 iterations — adjust based on server speed
# Target: ~100ms per hash

# Login verification
def verify_login(entered_password, stored_hash):
    return bcrypt.checkpw(entered_password.encode(), stored_hash)
    # checkpw is constant-time — prevents timing attacks

argon2 (Python — recommended for new projects):

from argon2 import PasswordHasher

ph = PasswordHasher(
    time_cost=3,      # iterations
    memory_cost=65536, # 64MB
    parallelism=4
)

# Hash
hash = ph.hash(password)

# Verify
try:
    ph.verify(hash, password)
except VerifyMismatchError:
    pass  # Wrong password

Defense checklist:

• Use bcrypt or argon2id — never MD5, SHA1, or bare SHA-256
• Set work factor so hashing takes ~100ms on your server
• Never store plaintext passwords or reversible encoding
• Re-hash on login if work factor needs upgrading