What is Encryption? Definition, History, and Examples

Encryption is a cryptographic process in which the original plaintext is converted into something called ciphertext. The idea behind encryption is that only certain parties can decipher the converted ciphertext back to its original form.

Put simply, encryption is like turning a message into a secret code. Only people with the special key can decode and read it.

Cambridge Dictionary defines encryption as “the process of changing electronic information or signals into a secret code (= system of letters, numbers, or symbols) that people cannot understand or use without special equipment:”

Brief history and importance in today’s digital age

Encryption has been around for thousands of years. Take, for example, the tomb in Egypt of Khnumhotep II, believed to have been carved around 1900 BC.

Inside this tomb, researchers found examples of “symbol replacement.” It’s a basic concept that involves replacing normal letters/symbols with different ones. For example, instead of writing “GOOD” it could look like “1223”. The letter G is replaced with the number 1, the letter O is replaced with the number 2, while the letter D is replaced with the letter 3. This is a basic example, but demonstrated early forms of encryption. 

Khnumhotep II depicted while hunting birds in the marshes
Khnumhotep II depicted while hunting birds in the marshes – Credit: Kurohito, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons


We looked at a very basic example of plain text and cipher text with symbol replacement found carved on the tomb of Khnumhotep. However, encryption can get a little more complex than that. As civilizations became more advanced, so did forms of encryption, and codes and ciphers became more intricate. They began to incorporate mathematical algorithms to make deciphering the messages more difficult.

For example, in ancient Rome there was a form of encryption known as the “Caesar cipher” names after Julius Caesar (12 July 100 BC – 15 March 44 BC). 

The Caesar cipher

Put simply, the Caesar Cipher changes letters by shifting them “x” spaces forward in the alphabet – historically three spaces forward. 

For example, take a look at the image below:

Encryption Example

S becomes V, E becomes H, C becomes F, etc. Each letter is moved three spaces forward. 

So, let’s say I want to use the Caesar cipher (three spaces forward) for the following sentence “Today I went to the park. I had a great time.” 

The “ciphered message” or “encrypted message would be “Wrgdb L zhqw wr wkh sdun. L kdg d juhdw wlph.”

Why’s this? Because each letter in the original text is shifted three places forward in the alphabet.

Modern encryption

Modern encryption uses advanced methods, not just simple letter shifts, to keep data safe. 

For example, modern encryption techniques use algorithms to convert information into complex strings of code. These codes are incredibly difficult to crack without a decryption key. 

Homomorphic Encryption

Homomorphic encryption operates by converting plaintext data into ciphertext. This ciphertext can then be analyzed and worked with as if it were still in its original (plaintext) form. The encrypted data retains the same structure, meaning identical mathematical operations will provide identical results—regardless of whether the operation is performed on the encrypted or decrypted data.

Put simply, with homomorphic encryption, you can do math directly on secret, scrambled data without unscrambling it first. After you’re done, the results stay secret until you choose to reveal them using a special key.

Simple Explanation

Imagine you have a secret letter that you put inside a sealed envelope. Now, let’s say there’s a magic pen that can change the letter inside without ever opening the envelope. After using this pen, when you eventually open the envelope, the message inside has changed just like you wanted, even though no one ever saw the original message.

This magic is a lot like “Homomorphic Encryption”:

What It Does: You can change or work with information (like our letter) without ever seeing it. Everything stays hidden inside its ‘envelope’.

Why It’s Useful: Even if you give someone else your sealed envelope to use the magic pen, they still can’t read your secret. So, you can ask others for help without risking your secrets.

Real-world Use: Think of doctors who have private patient details. They might want to use a computer service to analyze the data but worry about revealing personal info. With this magic envelope, they can get the computer’s help without exposing any private details. Even if someone tries to sneak a peek, all they see is the sealed envelope, not the secrets inside.

In short, it’s a way to keep information super safe, even when it’s being worked on or shared with others.