The development of information society, which has led to an impressive increase in the volume of information, mainly economic, circulated in computer networks, accelerated the development and mostly the use of modern cryptography tools. In the last years, researchers have pointed out that there is a possible similarity between chaos and cryptography, many of the properties of chaotic dynamic systems having correlation among the cryptographic systems that are based on computational methods. Studies carried out on chaotic dynamic systems usage in digital crypto-systems have determined the occurrence of similar to classic techniques, but also of some specific techniques and methods that have been analyzed and evaluated. The attempts to develop new encryption ?lgorithms based on chaos theory have evolved gradually from simple solutions, which suppose the iteration of a din?mic system to obtain binary sequence used for text masking, to methods that imply coupled din?mic systems and hybrid techniques that would combine the chaos advantages with classical methods. In this article there are presented 3 encryption algorithms based on chaos theory: RC4, Fractal Encryption and Cellular Automata, implemented in a system of encryption and operation mode analysis for each algorithm separately.