Reconstructing the keystream from a chaotic encryption scheme

A new technique of secure communication was developed which uses a synchronizing chaotic communication channel to transmit an encrypted message. The important feature of this system is that the keystream used in the encryption stage is not transmitted but may be dynamically reconstructed by the intended receiver. Since an additional level of encryption is employed, it was claimed that an eavesdropper may have limited success using nonlinear dynamic (NLD) forecasting techniques to extract the message. In this paper we show that there may be sufficient geometric information in the transmission to extract an estimate of the keystream (although it could require a difficult search) as well as characteristics of the encrypting function. Consequently, it may be possible to recover the hidden message with good accuracy