METHOD FOR CRYPTOGRAPHIC TRANSMISSION OF SPEECH SIGNALS AND A COMMUNICATION STATION FOR PERFORMING THE METHOD

摘要

A method for cryptographic transmission of speech signalsand a communication station for performing the method.ABSTRACTIn a communication system, in which a great numberof communication stations operate on the same telecommu-nication channel, such as a radio frequency, secret informationtransfer for selective calls as well as group calls in securedby cryptographic transmission of speech signals, in which en-ciphering and deciphering of the speech signals in transmittingand receiving stations, respectively, are performed by means ofa secret binary transformation code associated selectively withthe speech communication in question. By adding a communicationidentification signal generated in each participating stationas an unambiguous irreversible function of the transformationcode to start and stop commands initiating and finalizing, re-spectively, the cryptographic speech transmission from a sendingstation to one or more receiving stations, as well as tosynchronizing signal which may possibly be transmitted duringa speech communication and utilizing these communicationidentification signals as a criterion for initiation andfinalization of deciphering of speech signals in the receivingstation or stations, a further security is obtained againstdisturbance or the cryptographic information transfer by thirdparties through introduction of false messages or commands.