Eavesdropping on message signals masked by hyperchaos in secure communications

We report the method of eavesdropping on message signals masked by hyperchaos without a receiver in secure communications. When an attractor of the transmitting signal is spread on the surface of an n-dimensional return map, the surface fluctuates according to the message signals. By detecting this fluctuation, we show that message signals can be eavesdropped on. The method is demonstrated in the hyperchaotic Rössler system.