4.1 Preliminaries
In this chapter, we are going to talk about how to achieve confidentiality, the first of the three security goals in the CIA triad. For this, we need encryption (and also decryption) functions. In order to be able to describe these functions precisely and to put them into the right context, we need some mathematical jargon.
Figure 4.1: A function f can be seen as a table in which every element in set X is assigned to precisely one element in set Y
First of all, the term function has a precise mathematical meaning. A function f is a mapping from a set X (called the domain of f) to some other set Y (called f’s co-domain) such that each element in X is mapped to precisely one element in Y , as illustrated in Figure 4.1. Symbolically, ones writes f : X → Y .
If x is an element of the set X, formally written as x ∈ X, and the function f maps x to an element y ∈ Y , then y is said to be the image of x, and x is said to be a preimage...