Simulating Brute Force Attacks on Vigenère and AES Ciphers in Python: Measuring Key Size Impact on Security

The security of modern digital communications depends heavily on the robustness of cryptographic algorithms against brute force attacks. This study investigates the impact of key size on the brute force resistance of two representative symmetric ciphers: the classical Vigenère cipher and the Advanced Encryption Standard (AES). Using Python, the research implements a systematic simulation that incrementally increases key sizes and measures the corresponding computational effort required to recover plaintext through exhaustive key search. The simulation spans key lengths of 2–5 characters for Vigenère and 12–20 bits for AES (with reduced keyspace for feasibility), recording both the average time and the number of attempts needed to break each cipher. Results show an exponential growth in attack effort with increasing key size for both algorithms: even modest increments in key length yield orders-of-magnitude improvements in brute force resistance. These findings provide concrete, empirical evidence supporting cryptographic best practices that mandate adequate key lengths for secure communications. The study underscores the continued relevance of key size as a fundamental defense mechanism in both legacy and modern symmetric encryption systems, offering valuable insights for security practitioners and educators alike.