In this assignment, you will implement encrypted communications between two parties, Alice and Bob, and evaluate the performance of AES and RSA under different parameters. For simplicity, Alice and Bob will be simulated by two programs running on the same computer. When Alice sends a message to Bob, she writes the message to a file. Bob receives the message through reading from the file.

Part 1: Implement encryption and decryption using AES with 192-bit key. Assume that Alice and Bob already have a shared secret key k (e.g., they can read the key from the same file). Alice encrypts an 18-byte message m (the message is manually input from command line), and writes the ciphetext into a file named ctext. Bob reads the ciphertext from the file, decrypts it, and prints the message m. The encryption should use the CBC mode