Abstract:

In this paper, we propose an algorithm that consists of two phases. The first phase is the preprocessing phase where our proposed work is based on. The second phase is a cipher block chaining (CBC) which is a general model used to produce a MAC value. The preprocessing phase is an important one which is developed to modify the text message before starting the cipher block chaining phase to produce the MAC value, it is consisted of several steps discussed later, it modifies the text message length and the value (ASCII Code) of each character in the text, the modification is based on text, so any changes to the text leads to a new modification. Preprocessing phase is important because it achieves the paper objective, which is to prevent the
existence of two messages having the same MAC value.