I created a Python program that implements the affine cipher for encryption and decryption, as well as a tool to determine the key shift from a given ciphertext. The program accepts command-line arguments to specify input and output files, the type of operation (encrypt, decrypt, or shift detection), and relevant keys. Throughout the project, I deepened my understanding of modular arithmetic, cryptographic principles, and file I/O in Python. Additionally, I refined my skills in argument parsing, user input validation, and structuring clear, maintainable code for real-world command-line applications.