Recent technological progress brings into reach stable compact multisections semiconductor lasers. Such devices may be very suitable for chaotic secure communication. We report results of numerical investigations of the dynamical behaviour of continuous-wave semiconductor lasers under the influence of a multiple feedbacks. The optimal conditions for chaos generation are identified. The comparison of the dynamics of this configuration with that of conventional optical feedback is presented. Synchronization of two unidirectional coupled (master-slave) semiconductor lasers is studied. We report also on the influence of parameters mismatch on the synchronization quality and show how the features of the external cavities have an influence on the laser behaviour. Finally, examples of message encoding and decoding are presented.