Patent GB-1458698-A (GB)
Title: Method of and apparatus for the transmission of coded messages
IPC: H04K1/06
Filed: 1974-03-15
Abstract: 1458698 Digital transmission; ciphering systems PATELHOLD PATENTVERWERTUNGS & ELEKTRO-HOLDING AG 15 March 1974 [19 March 1973] 11701/74 Heading H4P An apparatus for the enciphered transmission of messages splits up the signal to be transmitted x into elements e 1 -e 7 , Fig. 7, of equal length, transposes selected pairs of the elements e 2 , e 3  and e 5 , eg at the transmitting end ZT, Fig. 16, and re-transposes them at the receiving end ZT*, Fig. 17, under control of irregular pulse trains such as obtained from cipher signal generators SG, SG* and cipher signal addition circuits SZ, SZ*. The elements, e 1 , e 4  which do not belong to the selected pairs are delayed by a predetermined amount T, such as in retarders R 1 , R 3 , R 1 *, R 3 *, at the transmitting and receiving ends, while the earlier occurring element e 2 , e 5  of each pair is delayed at the transmitting end by 2T and the later occurring element e 3 , e 6  of the pair is undelayed, while at the receiving end the first arriving element of the pair is delayed by 2T and that arriving later is undelayed. The transposition of pairs of elements as shown in Fig. 7 corresponds to a retarder R 1  having a delay of T 0  shown in a pair exchanger PT 1 , Fig. 11, and used in the second stage of transposition of both the transmitting end ZT and the receiving end ZTx shown in Fig. 16 and 17. The required transpositions are obtained by appropriate control of change over switches H 1 , H 1  by a cipher signal addition circuit SZ 1  which includes a retarder V 1  and an interrupter U 1 . The cipher signal addition circuit SZ 1  functions to eliminate the second "1" output W 1  of a pair of "1" outputs from a cipher signal generator SG so that the control output a 1  fed to control the switches H 1 , H 2  are irregular. As shown in Fig. 11 the switches H 1 , H 2  normally connect the input element directly to the output without delay. When these switches H 1  and H 2  are controlled by a 1  to their other position the output of the retarder R is fed back to its input so as to introduce the required delay, e.g. for element e 2  relative to e 3 . The retarders may be digital or analogue stores such as delay lines, electro-mechanical retarders (e.g. acoustic systems) or electro-magnetic stores (e.g. magnetic sound recording with moving medium or electrical shift registers). Delta modulation is possible instead of binary coding. The changeover switches H 1 , H 2  and the interrupter U 1  may be semiconductor switching elements. The retarder R 3  in the first stages of the transmitting and receiving ends ZT, ZT*, Figs. 16 and 17, have a delay of 3T 0  and function to transpose the pairs of elements in accordance with (Figs. 14 and 15, not shown). A modified pair exchanger (ZT 0 , Fig. 20, not shown) is disclosed which has three sets of switches (A 1 , A 2 ; B 1 , B 2  and C 1 , C 2 ) two of which co-operate with retarders (R 1 , R 2 ) the switches being controlled for additional permutation of the message elements with a fixed program. This pair exchanger (ZT 0 ) is interposed between other pair exchangers PT 1 , PT 2  at the transmitting and receiving ends (Fig. 23, not shown).