Learn Encryption – Caesar Cipher Basic concepts 

Learn Encryption is a series of articles which will present the concept of encryption and the various methods of encryption to you in an easy to understand way. 

What is encryption? 

Encryption is defined as the process of concealing information in a way that snoops could not read it, lest they had a special key to decrypt the information. The process of encryption is applied all across the world, right from our daily bank transactions to our PCs hard disk.  

Type of Classical Encryption-Caesar cipher 

The name Caesar comes from Julius Caesar who used this method to communicate with his army's generals. This cipher is also called shift cipher and is one of the oldest methods of encryption. In this cipher, each letter in the plaintext (also known as original message) is substituted with a letter which corresponds to a number of letter 'shifted' up or down in the alphabet.  

If the shift is '+1', letter A will be replaced by letter B, letter B would be replaced by C, so on and so forth. Another example could be, if you have a key number representing shift then the letter corresponding to the key is shifted that many places in the alphabet, as represented by the key number. For example, for a key number '3' for letter D, the shift will make the letter D replaced by letter G. Likewise, all letters in the plaintext can be replaced. Let us look at an example ciphertext below using a right shift of '3'. 

Plaintext: 

WE ARE LEARNING ABOUT ENCRYPTION 

Ciphertext: 

ZH DUH OHDUQLQJ HQFUBSWLRQ 

You can see that an initially readable text has become unreadable as a resulting ciphertext. Although the ciphertext may seem to be unreadable, Caesar cipher is the most weakest forms of encryption methods available.  

The mathematical form of Caesar cipher for encryption process is:   

Literal meaning of the above mathematical form is that encryption of letter y is equal to shift of y+nwhere is the key number representing the number of letter shifted. The term mod 26 means that the result of the encryption function is then applied upon by modulo division which means that when a letter is shifted past the end of alphabet, it goes around to the beginning.  

Similarly, the decryption function for the ciphertext can be used as:   

We hope that you have understood the basic concept behind Caesar Cipher, encryption and cryptography. In the article, we will continue this series to learn about the next type of encryption method.