GB878645A - Enciphering and deciphering apparatus for secret telegraph systems - Google Patents

Abstract

878,645. Code telegraphy. OLIVETTI & C. S.p.A., ING. C. Dec. 1, 1958 [Nov. 30, 1957], No. 38609/58. Class 40(3) In a start-stop secret telegraph system clear code signals are ciphered by mixing with cipher signals, the ciphered signals being further mixed with the cipher signals to provide deciphered signals which are compared with the original clear code signals. An alarm system is actuated if the signals compared differ. The ciphering is of the form in which two like inputs to the ciphering circuitry give a positive output while unlike inputs give a negative output, the supply of pulses being controlled by a distributer. The deciphered signal is taken to a local receiver for translation into intelligence at the transmitter. On presentation of a clear code signal at terminal 40 the start pulse causes the distributer 55 to make one revolution, the rest position of the brush 56 being shown dotted. As the brush contacts R the flip-flop 53 is caused to send a start pulse over the line 42, while at R<SP>1</SP> the flip-flop 54 sends a start pulse to the local receiver over line 45. The unit 50 comprises five cipher keys set to mark or space positions according to the cipher signal to be used with any one clear code signal. The first code element of the clear code signal switches relay 39 to either mark or space (a mark as shown in the Figure). Assuming the first cipher code element to be a space as indicated at 50<SP>1</SP>, when a is contacted potentials appear at points 77 and 81 in an adding circuit 51 which causes flip-flop 53 to be triggered, relay 41 to be energized and a space pulse to be sent over the line 42. Relay 85 is also energized and when a<SP>1</SP> is contacted potentials are applied at points 92, 93 in a second adding circuit 52. The output pulse of this circuit triggers flip-flop 54 and relay 44 moves its tongue to the position shown to pass a mark pulse, corresponding to the original mark pulse, to the local receiver over line 45. The pulse in line 45 is also fed to a comparator bridge circuit 97 and should this pulse and the original pulse not be the same relay 98 is actuated. This may operate an alarm or stop the apparatus working. The remaining code elements cause the apparatus to work in a substantially similar way and after the last code element the distributer contacts S and finally S<SP>1</SP>. This results in a stop signal being sent both to the line 42 and to the receiver on line 45.