Caesar Cipher Encryption and Decryption with example

Key Takeaways

the Caesar cipher is one of the simplest and widely known ciphers it is also one of the earliest known ciphers through history the Caesar cipher being named after Julius Caesar and was used at the time to communicate with his generals hopefully in a secure way he lived in time 100 BC to 44 BC and during his time deciphered would have been considered relatively secure as the most during his era was unable to read and if they if someone came across one of his ciphered messages they would probably think it was written in another language but today this offers essentially no security so how does the Caesar cipher work well we it is quite simple we have 26 letters in the alphabet and for each of their letters it is being shifted a specific number forward in the alphabet so for example a if we use a shift that is a number three then a would become shifted forward three letters in the alphabet so a would become B C D so it become a become D and similarly for B we've become e C becomes F D becomes G and then at the end of the alphabet when we get to Zed then we will actually map it back to the beginning so said would become a B C for a shift of three so said would become C so in as we saw every letter is shifted by three and if we would have a plaintext attack at noon then encrypted this becomes something unreadable and we can notice here that a becomes shifted forward by three then becomes D and similarly T shifted forward by three is W and if we have this ciphertext and we can quite easily also Mack it map it back to the original message by by by subtracting the shift so D becomes backward shifted so subtracted 3 to become a so mathematically the encryption function is e of X we take the letter X and we add a shift and then we also have it modulus 26 so to be able to have that if we are at the end of the alphabet then we map it back to the beginning and the decryption function D of X is simply as we mentioned it's the letter and then we subtract the shift and then we take modulus 26 so as we saw in the previous example the shift was 3 but we could just as easily imagine any shift from 1 to 26 I in this case the length of our alphabet so for example we can use a shift by 4 or 4 5 etc so the problem with this cipher however is that it is very easily broken we can do it by brute force for example we can simply try with a shift of 1 and look at the the message does it is it readable and if it's not readable then we check a shift of 2 etc until we get to the end which is 26 and we continue doing that until we get a readable message and so since we have a fixed number of shifts to try on a message on a ciphered message then then this is done in a constant time so to be able to break the caesar cipher it is done in constant time which makes it a very bad very bad cipher so in the next video I will code the Caesar cipher in Python if you're interested in how that looks check out the next video the link will be in the description thank you so much for watching this video