GB1164490A - Ciphering and Deciphering Apparatus - Google Patents

Abstract

1,164,490. Digital transmission systems. CSF-COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. 13 Dec., 1966 [15 Dec., 1965], No. 55893/66. Heading H4P. A cipher key generator comprises a source 1 of a sequence of random signals and a counter 5 for completing an alphabet if all letters of the alphabet have not been generated by source 1 when the source has emitted a preset number N of signals. Source 1 emits a parallel-bit signal representing a letter for each pulse from a clock 2. The signal passes to cipher key output K and also to unit 7 which triggers a store 8 corresponding to the signal. OR gate 10 gives a pulse D when an untriggered store is triggered. Counter 4 counts N clock pulses and then reverses switch 3 and enables gate 11. If not all the stores 8 are triggered, counter 5 provides parallel-bit signals which pass to output K and also trigger the stores 8. When all stores are triggered gate 9 gives a pulse C and, via gate 11, stops clock 2. Thus, in this one cycle of operation output K contains all letters at least once. Ciphering.-Various arrangements are described, in each of which upon coincidence of a clear signal to be ciphered and a cipher key signal another key signal is transmitted to represent the clear signal. This other key signal may be, for example, the signal prior to that which caused coincidence, Fig. 4 (not shown). In such a case if the signal causing coincidence is the first signal in the key sequence then the clear letter is sent unciphered. In a further embodiment, Fig. 7 (not shown), the clear signals are compared (300) only with key signals occurring for the first time, i.e. those causing a pulse D. Each such key signal is passed to one of a number of stores (43), selected by a switch (42) controlled by the D pulses. A further switch (45) connects the system output (46) to the stores in an order controlled by the pulses D. When coincidence of the clear and cipher signals occurs, the further switch stops scanning and, when a C pulse arrives, the cipher signal in the selected store is transmitted to represent the clear signal. Deciphering.-The deciphering processes are the reverse of the ciphering processes.