Caesar Cipher: About one of the earliest know ciphers and how it was broken.
A cipher is a set of simple steps for performing encryption and decryption, it does not have any meaning it's just a mechanical operation that is applied to a message or information to encrypt or decrypt.
One of the earliest know and simplest ciphers is Caesar Cipher. The method is named after Julius Caesar who apparently used it around 58 BC to communicate with his general so that even if his messages were to be intercepted they wouldn’t make any sense to the enemies.
What is Caesar Cipher? Well, it is a type of substitution cipher in which each letter is replaced by a different letter which is a fixed number of letters away from it down the alphabet (three in this case). This cipher went on to be used for hundreds of years by military generals after Caesar.
It is interesting to see how cryptography played an important role in 58 BC, It is also just as interesting to see how an Arab Mathematician named Al-Kindi after nearly 800 years managed to break it. He used an important property of the language which is called letter frequency. In the English language, if you plot the letter frequency of an extract of appreciable size (which is the number of times a particular letter appears in an extract ) you will find that the letter E has the maximum frequency and z the minimum in general.
When you apply a shift the graph will change and now a different letter will have the maximum frequency which will, of course, depend on the shift you applied. Since the method is based on statistics, to be able to work out the shit you would need a sample of appreciable size.
On comparing the two graphs one can find out the shift that was used.
