The Caesar cipher is a very simple way of creating coded messages. The original cipher, attributed to Julius Caesar, involves shifting every letter in a plaintext message 3 positions further down in the alphabet to get the corresponding ciphertext message. For example, a Q in the plaintext message would be shifted by three postions to become a T in the ciphertext. A plaintext message of "YAK AND ZEBRA" would be transformed to the ciphertext message "BDN DQG CHEUD". Note that letters near the end of the alphabet wrap around to the beginning (e.g. Y + 3 = B). You can, of course, perform a Caesar cipher transformation using other values than 3 for the shift. "YAK AND ZEBRA" with a shift of 4, for example, becomes "CEO ERH DIFVE".
In this assignment, you will write a function that implements the Caesar cipher. This will give you some practice encapsulating a collection of operations into a Python function. This assignment will also introduce the use of command-line arguments in Python programs.
Write a program that:
caesar
(see below for details) to obtain
the ciphertext, andYour caesar
function should look like this:
A typical session with your completed program might look like this:
prompt> python caesar.py What is your plaintext? follow the elk What shift do you want to use? 3 Your ciphertext is: iroorz wkh hon prompt>
We will discuss all of these ideas in class.
Start early, have fun, and ask questions.