Modern symmetric encryption


Block ciphers

Stream ciphers


Increased computer power. How to be secure?

kerckhoff’s principle. choose cipher such that secure even if everything but key is known

Symmetric encryption


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