| 摘要 |
In a communication system, in which a great number of communication stations operate on the same telecommunication channel, such as a radio frequency, secret information transfer for selective calls as well as group calls is secured by cryptographic transmission of speech signals, in which enciphering and deciphering of the speech signals in transmitting and receiving stations, respectively, are performed by means of a secret binary transformation code associated selectively with the speech communication in question. By adding a communication identification signal generated in each participating station as an unambiguous irreversible function of the transformation code to start and stop commands initiating and finalizing, respectively, the cryptographic speech transmission from a sending station to one or more receiving stations, as well as to synchronizing signal which may possibly be transmitted during a speech communication and utilizing these communication identification signals as a criterion for initiation and finalization of deciphering of speech signals in the receiving station or stations, a further security is obtained against disturbance or the cryptographic information transfer by third parties through introduction of false messages or commands.
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