Gan, Jimmy
69cc62a931
HIGH: Previous implementation used 30-second timestamp windows, allowing TOTP codes to be reused multiple times within the same window via concurrent requests or brute force attacks. Changes: - Track individual used codes instead of timestamps - Store last 5 used codes with expiration (90 seconds) - Reduce acceptance window to ±30s (valid_window=1) - Automatically clean up expired codes Security Impact: - Prevents TOTP code reuse attacks - Blocks brute force attempts within time windows - Strengthens 2FA protection significantly Tests: All TOTP tests passing, replay protection verified