PYTHON
CRYPTOGRAPHY – CAESAR CIPHER

DESCRIPTION

You will write code related to the Caesar cipher that can be used in encrypting/decrypting messages.

THE CAESAR CIPHER

The Caesar cipher which was apparently used by Julius Caesar, is a subgroup of substitution ciphers. A Caesar cipher is a cipher that shifts each letter in the plaintext by a shift_amount.

For example, if we shift the letter A by 2, then we get the letter C. If we shift the letter Z by 2, we wrap around the alphabet and we get the letter B.

Ceasar cipher (shift by 2)	Ceasar cipher (shift by 10)
A -> C B -> D C -> E … X -> Z Y -> A Z -> B	A -> K B -> L C -> M … X -> H Y -> I Z -> J

To decrypt a ciphertext, we can simply shift the by negative amount that we shifted initially.

For example, if we shift C by -2, we get A.

WORK

QUESTION 1

In a Python file called Caesar, write the enc and dec functions for Caesar ciphers. They only need to work with lowercase letters.

enc (word, shift_amount)

dec (word, shift_amount)

Test your code.

QUESTION 2

One special case of the Caesar ciphers, is the one that shifts by 13. Why is it special?

Hint: Try encrypting a plaintext twice.

QUESTION 3

The following sentence has been encrypted using the Caesar cipher with a shift of 16. Use your program to decrypt it.

JXUIUQHUDJJXUTHEYTIOEKHUBEEAYDWVEH