Caesar Cipher Implementation in Python

The Caesar Cipher can also be called Shift Cipher, Substitution Cipher, Caesar's Code, or Caesar's Shift. This is going to be a short tutorial on how to create a Caesar Cipher in Python.

A Brief History of Caesar Cipher

This is the first and well-known cipher that was used by Julius Caesar. It was said to have been developed around 100 BC. He shifted each letter in his messages in order to make the messages meaningless should the enemy intercept them. Although the shift key varies, he originally used it with a shift of three. Therefore A becomes D when encrypting, and D becomes A when decrypting. A diagrammatic representation of the cipher system that uses a left shift value of 3 is shown below.

Implementation in Python

In order to make our cipher more flexible, we would allow the user to determine the shift value. I encountered this problem when I was trying to solve an assessment question. Below is the function

Next, I am going to explain what is happening on every line

1. In line 1, we create the function
2. In line 3, we used the ordinal(ASCII) value of lowercase a to z alphabet in a list comprehension.
3. In line 4, we converted the input string to lowercase in order to match with the list of lowercase alphabets that we created
4. In line 6, we create an empty string to store the ciphered string
5. In line 7, we loop through the input string that we converted to lowercase
6. In line 8, we determine the position of the current alphabet
7. In line 9, we get the offset position by subtracting the shift value(offset) from where the alphabet is located
8. In line 10, the ciphered alphabet will be the value of the position where the shift has landed us
9. In line 11, we add the ciphered alphabet to the ciphered string
10. In line 12, we return the ciphered string

So, we are not only restricted to the left shift offset of 3, we can use any value we like.

That's all for today, feel free to like or comment your opinions below