Encryption is one of many Protective Technologies that help keep us safe while using the Internet. Today’s encryption methods are quite sophisticated compared to those of the past, but before going into more modern methods, let’s look at the general concept. 

Caesar Cipher:

One of the oldest encryption methods require sharing a rule between parties wishing to send and receive a message securely. We are going to look at the Caesar cipher as an example of this.

Encryption:

Suppose we want to send the message “porties are great”. (Portie, by the way, is short for Portuguese Water Dog.)

Fig. 1: Portuguese Water Dog

We are going to use the lower-case alphabet to do the encryption and the rule for our example will be to shift the letters of the alphabet left by 2. 

So, with the shift of 2 the “a” will be changed to “c”, then it follows that “b” will be changed to “d”, etc. Finally, “a” and “b” are looped around to the other end, behind “y” and “z”.

Here is the regular alphabet followed by the alphabet shifted over by 2:

  • abcdefghijklmnopqrstuvwxyz
  • cdefghijklmnopqrstuvwxyzab

To encrypt the message, find the letter in the top row and use the corresponding letter directly under it in the second row. In our example the “p” becomes an “r”, the “o” becomes a “q”, and so on. The full message “porties are great” becomes “rqtvkgu ctg itgcv”.

Fig. 2: Encryption Guide

Decryption:

If we receive the message “rqtvkgu ctg itgcv” how are we going to read it? We must have agreed on the method of encryption. In this case, we have already agreed that the lower-case English alphabet is used, and it is being shifted to the left by 2.

We can create the following to help us decrypt the message:

  • cdefghijklmnopqrstuvwxyzab
  • abcdefghijklmnopqrstuvwxyz

Look up the message’s letters in the top row and use the letters below. In our example the “r” becomes a “p”, the “q” becomes an “o”, and so on. The message “rqtvkgu ctg itgcv” is then decrypted to “porties are great”.

Fig. 3: Decryption Guide

We are only using lower-case letters in this example. If we wish to include capital letters, the simplest way to do this is to agree that a capital letter in the original message will be translated to a capital letter in the encrypted message. We don’t have to make any other changes to our encryption rule.

Note that we aren’t encrypting spaces between words so the number of letters in a word is always fixed. If the text is long, this can be used to help decipher the message. We will discuss adding complexity and security to the encryption methods in later posts.

Before we start exchanging secure messages, the sender and receiver have to agree on the method that will be used for the encryption/decryption. We can exchange the method we are going to use in a number of ways. We could do this in person, for example, that way there is less chance of the rules for our encryption/decryption being discovered. We can then separate and exchange secure messages.

In the next post we will look at the method that uses Encryption with a key instead of a simple rule.