흔한 Python 암호화 실수와 안전한 패턴

가장 위험한 암호화 실수

함정 1: 키 하드코딩

# WRONG
SECRET_KEY = b"my_secret_key_12"  # visible in git!

# RIGHT
import os
SECRET_KEY = os.environb.get(b"SECRET_KEY") or os.urandom(32)
# Or load from KMS at startup

함정 2: ECB 모드

# WRONG — never use ECB
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
cipher = Cipher(algorithms.AES(key), modes.ECB())  # insecure!

# RIGHT
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
aesgcm = AESGCM(key)  # authenticated encryption

함정 3: 일정 시간이 아닌 MAC 비교

import hmac

# WRONG — leaks timing
if received_mac == expected_mac:
    pass

# RIGHT — constant-time
if hmac.compare_digest(received_mac, expected_mac):
    pass

함정 4: 취약한 난수 생성

import random, secrets, os

# WRONG
key = bytes([random.randint(0, 255) for _ in range(32)])  # predictable!

# RIGHT
key = os.urandom(32)          # OS CSPRNG
token = secrets.token_bytes(32)  # secrets module wrapper

함정 5: IV/논스 재사용

import os
from cryptography.hazmat.primitives.ciphers.aead import AESGCM

key = AESGCM.generate_key(bit_length=256)
aesgcm = AESGCM(key)

# WRONG — fixed nonce
nonce = b"\x00" * 12  # reuse breaks GCM!

# RIGHT — fresh nonce every time
nonce = os.urandom(12)
ciphertext = aesgcm.encrypt(nonce, b"data", None)

함정 6: 보안에 MD5 또는 SHA-1 사용

함정 7: 암호화 직접 구현

안전한 패턴: 고수준 암호화에 PyNaCl 사용

# pip install PyNaCl
import nacl.secret
import nacl.utils

key = nacl.utils.random(nacl.secret.SecretBox.KEY_SIZE)
box = nacl.secret.SecretBox(key)

encrypted = box.encrypt(b"my secret message")
decrypted = box.decrypt(encrypted)
print("Decrypted:", decrypted)  # Uses XSalsa20-Poly1305

안전한 패턴: Argon2를 사용한 비밀번호 해싱

# pip install argon2-cffi
from argon2 import PasswordHasher

ph = PasswordHasher(time_cost=3, memory_cost=65536, parallelism=4)
hash_val = ph.hash("user_password")
print("Hash:", hash_val[:40], "...")

# Verify
try:
    ph.verify(hash_val, "user_password")
    print("Password correct")
except Exception:
    print("Wrong password")

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