The work developed in this manuscript addresses the synchronization of chaotic systems. It is organized around two main axes : the observer synthesis and the mode detection. In a first step, we recall the main architectures of chaotic encryption systems and show how chaotic systems with polynomial nonlinearities or switched affi ne dynamics can be rewritten in a polytopic LPV form. A review of the main LMI based results for polytopic LPV observers synthesis is made. An extension to polytopic unknown input observers, both in the deterministic case and noisy or uncertain case, is proposed. These observers ensure chaos synchronization and information recovering in the framework of the following encryption systems : "parametric modulation", "chaotic switching", "two channels transmission" and "inclusion encryption". For affi ne switched systems used as a generator of chaos, the case where the discrete state is not available is considered. A unif ed presentation of modes detection methods based on parity spaces proposed in the literature for linear and a ffine switched discrete time systems is proposed. The problem of discernibility is the subject of a complete study. An approach to estimate time varying delays for a ffine switched discrete time systems, formulated in terms of modes detection, is proposed as a solution for delay injection-based encryption.
