**The most important and interesting about encryption.**

##### A series of articles understandable even to non-specialists.

You can read about encryption basic concepts in our previous article. Here we are talking about symmetric encryption.

Symmetric encryption is characterized by the fact that the **same key** is used to encrypt the original data and then decrypt it.

The main goal of symmetric encryption is to transform the original information into a set of characters close to random, so that Eva if she looks at the encrypted message, sees only the utter confusion.

**Operations in symmetric encryption: simulation of chaos.**

To make the original message become complete nonsense for the uninitiated, the following operations are applied:**Replacement**: original characters are replaced by others.**Permutation**: original characters are swapped according to a certain rule.**Dispersion**: The meaning of dispersion is to eliminate in the encrypted text the patterns inherent to the original text. Dispersion is achieved by permutations.**Mixing** is intended to avoid statistical regularities between the original text and the encrypted one.

**Types of symmetric encryption.**

There are two types of symmetric encryption: block and stream.

In **block encryption**, the source data are processed in blocks of a certain length (typically 64 or 128 bits). Blocks are encrypted several times, or, as they say in cryptography specialists, the key is applied to the block in several rounds. This is done to eliminate the regularities between the blocks of the source and encrypted data. And in **stream encryption**, every bit of the original information is encrypted. To eliminate the correspondence between the original and encrypted data, the XOR cipher is used – “overlaying” of the sequence of randomized numbers on the original data.