zakirkun Insecure Key Derivation
Overview
Passwords must not be used directly as cryptographic keys or passed through fast hash functions. Proper Key Derivation Functions (KDFs) intentionally add computational cost and mandatory salting:
- PBKDF2: NIST-approved, configurable iteration count (minimum 600,000 for SHA-256)
- bcrypt: Adaptive work factor, built-in salt
- scrypt: Memory-hard, resistant to GPU cracking
- Argon2id: Winner of Password Hashing Competition, recommended
Remediation
Always derive keys from passwords using a KDF with a random salt.
Vulnerable:
key = hashlib.sha256(password.encode()).digest()
cipher = AES.new(key, AES.MODE_GCM)
Safe:
import os
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.hazmat.primitives import hashes
salt = os.urandom(16)
kdf = PBKDF2HMAC(algorithm=hashes.SHA256(), length=32, salt=salt, iterations=600000)
key = kdf.derive(password.encode())