cipher.py implements one of the example ciphers taught as part of Duke's Pre-College "Exploring Cryptography Through Gamified Programming" course.

cipher_break.py demonstrates a simple brute-force attack against the cipher, and succeeds in a matter of seconds on a standard laptop machine.

cipher_break2.py illustrates the importance of key length, as a brute-force attack against the same cipher using a key that's triple the original length would take over 100 years.