Reconstructing the keystream from a chaotic encryption scheme

A new technique of secure communication was developed in [1] which uses a s ynchronizing chaotic communication channel to transmit an encrypted message . The important feature of this system is that the keystream used in the en cryption stage is not transmitted but may be dynamically reconstructed by i ntended receiver. Since an additional level of encryption is employed, it w as claimed that an eavesdropper may have limited success using nonlinear dy namic (NLD) forecasting techniques to extract the message. In this paper we show that there may be sufficient geometric information in the transmissio n to extract an estimate of the keystream (although it could require a diff icult search) as well as characteristics of the encrypting function. Conseq uently, it may be possible to recover the hidden message with good accuracy .