How Symmetric Encryption Works


What is encryption

When we want to exchange a message with someone we want to make sure that it reaches the receiver safe and sound. Throughout history, there were different methods in securing the message. In this article, we talk about the symmetric type of encryption algorithms.

It began in Ancient Greece with the sender writing the message on top of the messenger’s head. The receiving side would then shave the head of the messenger and read it. Obviously, it took some time for messenger’s hair to grow so he/she could take it to the receiver.

Then there was the method of writing on the paper tape wrapped around the stick. The receiving side would need to have the stick with the exact same dimensions. They would wrap the tape they got around the stick and the message would be readable. If the stick wasn’t the same dimension as the sender’s stick, it wouldn’t compose a readable message.

Centuries later Romans invented Cezar's code which meant that letters in the alphabet would need to be shifted by a certain number of positions and then the message would be written. For example, A would become D, B becomes E, and so on. This example uses the encryption key shift by 3. This means that the letters are shifted 3 places to the right for encryption. To the left for decryption.

Cezar's code diagram
Cezar’s code diagram

It is important to distinguish between encryption and “hiding” (stenography) plain text messages. The first example we mentioned in this text (message written on top of the messenger’s head) is an example of stenography. The sender hidden the message didn’t change its form. Cezar’s code is an example of encryption. Stenography hides the open message, encryption codes the open message.

Symmetric Encryption Key

In order for us to apply encryption, we need to define a key to be used for encryption. In the example of the Cezar’s code, the key is “shift by 3 right” – X is the number of places we are shifting the alphabet for.

Another example would be the older example, Spartans’ stick would be the key for that encryption “algorithm”. This stick would need to be made with a specific dimension for it to work, which makes it a key. It’s used for encryption and decryption so, we call it Symmetric key.

Symmetric Encryption

Name Symmetric encryption comes from the method of using the encryption key – the same key is used for encryption and decryption. Today, keys have become much complicated due to a need to protect the data from any attack strength. To illustrate the use of the symmetric key take a look at the following illustration:

Symmetric Key use case
Symmetric Key use case

So, as the illustration shows, we are using the same key to encrypt and later to decrypt the ciphertext.

Blocks and Streams

When the encrypting program loads the open text for encryption it will specific methodology to do it. When we think about how the encryption is applied to the open text block or file, we can distinguish these two methods as shown in the illustrations below. Block and Stream processing illustrated:

Block Ciphers Encryption:

Cipher Block Chain (CBC) Encryption Diagram
Cipher Block Chain (CBC) Encryption Diagram

Block Cipher Decryption:

Cipher Block Chain (CBC) Decryption Diagram
Cipher Block Chain (CBC) Decryption Diagram

Stream Cipher Encryption:

Stream Cipher Encryption Diagram
Stream Cipher Encryption Diagram

Stream Cipher Decryption:

Stream Cipher Decryption Diagram
Stream Cipher Decryption Diagram

Some of the most important symmetric encryption algorithm are the following:

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