# Modern symmetric encryption

## Methods

### Block ciphers

### Stream ciphers

### Motivation

Increased computer power. How to be secure?

kerckhoffâ€™s principle. choose cipher such that secure even if everything but key is known

## Symmetric encryption

### Symmetric

We have a document we want to be able to transfer on an insecure medium.

We use a key to encrypt the file, and a key to decrypt the file.

With symmetric encryption these are the same key.

## Options for algorithms

### Integer factorisation

Option for algorithm.

### Elliptical-curve cryptography