Goal

You will write a program in C, in the Ubuntu Linux environment, to provide the end user with the ability to encrypt and decrypt messages, using a secret key. Your program will prompt the user to indicate whether they wish to encrypt a readable ("plaintext") message or decrypt an already encrypted sequence of numbers ("ciphertext") back to its readable form. You will implement the encryption and decryption algorithm described in the instructions below. In order to prevent your enemies from easily cracking your encrypted messages, the algorithm will use an incrementing counter to encrypt each character in a slightly different way. Your program will output the result (either the ciphertext or the plaintext) to the screen. You will begin with the skeleton code found here.

Learning Objectives

• familiarize yourself with the Linux programming environment
• write a small program in C that is modular, correctly designed and documented
• manipulate values at the bit level