Indirect coupled oscillators for keystream generation in secure chaotic communication

In this paper, we propose a secure communication system composed of four chaotic oscillators. Two of those oscillators are unidirectionally coupled and employed as transmitter and receiver. The other two oscillators are indirectly coupled and are employed as keystream generators. The novelty lies in the generation of the same chaotic key both in the transmitter and receiver side for encryption and decryption purposes. We show, in particular, that it is possible to synchronize the two keystream generators even though they are not directly coupled. So doing, an estimation of the keystream is obtained allowing decrypting the message. The performance of the proposed communication scheme is shown via simulation using Chua and the Lorenz oscillators.