SecureGameDataManager.py

import json
import os
from cryptography.fernet import Fernet
import base64
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC

class SecureSaveSystem:
    def __init__(self, password: str):
        # パスワードから安全な鍵を生成
        salt = b'salt_for_python_save'
        kdf = PBKDF2HMAC(
            algorithm=hashes.SHA256(),
            length=32,
            salt=salt,
            iterations=100000,
        )
        key = base64.urlsafe_b64encode(kdf.derive(password.encode()))
        self.fernet = Fernet(key)
        self.filename = "game_data.sav"
        self.backup = "game_data.bak"

    def save(self, data):
        try:
            # 1. バックアップ
            if os.path.exists(self.filename):
                os.replace(self.filename, self.backup)

            # 2. シリアライズ & 暗号化
            json_str = json.dumps(data).encode()
            encrypted_data = self.fernet.encrypt(json_str)

            # 3. 書き込み
            with open(self.filename, "wb") as f:
                f.write(encrypted_data)
            print(f">>> [Py] 保存完了 (Size: {len(encrypted_data)} bytes)")
        except Exception as e:
            print(f"Save Error: {e}")

    def load(self):
        if not os.path.exists(self.filename):
            return {"name": "PythonHero", "lv": 1, "items": []}

        try:
            with open(self.filename, "rb") as f:
                encrypted_data = f.read()

            # 4. 復号 (改ざんがあればここで例外が発生する)
            decrypted_data = self.fernet.decrypt(encrypted_data)
            print(">>> [Py] ロード成功 (整合性確認済み)")
            return json.loads(decrypted_data.decode())
        except Exception as e:
            print(f"Load Error (改ざん検知): {e}")
            return None

# 実行テスト
if __name__ == "__main__":
    manager = SecureSaveSystem("Strong_Password_Python_99")
    game_state = manager.load()
    print(f"現在データ: {game_state}")
    
    game_state["lv"] += 1
    game_state["items"].append("Master Sword")
    manager.save(game_state)