Patent GB-1432128-A (GB)
Title: Process and apparatus for the automatic enciphering operation  of teleprinter installations
IPC: H04L9/18
Filed: 1963-03-11
Abstract: 1432128 Data transmission; teleprinters; cyphering arrangements SIEMENS AG 11 March 1963 [9 March 1962] 9638/63 Heading H4P A teleprinter installation wherein a change from plain language operation to cipher operation and vice versa is produced by a sequence of more than six at least partly different characters, is characterized in that changeover is initiated on reception of at least 50% of the appropriate characters in their correct positions in the sequence and only after reception of the complete sequence. Figs. 2 and 3 show a transmitter including a punched tape reading unit LA and a timing generator G which produces recurring sequences of timing pulses t1- t15 through a distributer TV. When a tape is inserted in unit LA contact pk is closed, and when the start contact st is also closed the next t13 pulse is diverted from unit Inv1 to unit Ph1 and causes pulse ni (15) to be produced on the arrival of t15. The first ni(15) pulse is transmitted through switches S4 (closed) and S5 (closed) and becomes the start pulse ei (15) which passes through OR circuit O5 and opens switch St (blocking further ni (15) polses) and switch S7, and confirms that S6 is open. The pulse ei also closes switch S9, and, via OR gate O17 (Fig.3), the swithc S14. The next t1 pulse passes through S9 to the character counter ZZ and also passes thuough O16 and S14 to the output switch AS to produce a mark pulse (form ing the starting element of the first character of a 10 character pre-code. t3, t5, t7, t9, t11 and t13 produce spacing current, via O15 and AS for the pre-code characters. When the 10 pre-code charcters have been transmitted the counter ZZ is full and the next t1 pulse applied to it causes it to trigger the timing distributer ETV for the switch in code. The distributer ETV produces pulse et1-et10 which release the 10 switch-in code characters stored, in the code generator KGE. The elements e1-e5 of each character pass through OR gates O8-O12 to the parallel-series converter PSU. Marking pulses stored in PSU are released in series by t3, t5, t7, t9, t11, stretched in unit Iv2, and passed through S11 (closed by et 1 via 013) 016 and S14 to the output switch AS. Spacing pulses applied to AS by t3-t11 are blanked out if there is a simultaneous marking pulse since the marking pulse has been stretched. t1 and t13 respectively produce the start and stop pulses of each character. When the ten characters of the switch-in code have been transmitted, pulses et10 and t13 applied to Is8 produce a pulse which closes S15 and switches the cipher unit M to cipher operation. When unit M has been switched contacts uk are closed, and the state of these contacts is monitored by a timing pulse t14À5 to produce a pulse ui, if the contacts are closed, or a pulse kui if the contacts are open. Similarly emergency contacts nr are monitored by t13 to produce a pulse dai (no emergency) or dei (emergency). If these contacts are in the correct positions switches S1, S2, S6, S7 and S16 are closed by et10 and t1 then passes through S1 to start the tape feed (unit AM) and to read the tape through contacts lk1-lk5. the output from the tape passes via lines l1-l5, units Inv2-Inv6 and units O8-O12 to converter PSU, and from converter PSU to the output switch AS. Punched tape transmission can be stopped either by opening the start switch st or by the automatic opening of contact pk at the end of a tape. This prevents the production of pulse ni 15, and instead unit Invl produces pulse ki 13 which passes through 014 to produce pulse abi 13 which opens S2 and S15 and closes S13. When the cipher unit M changes to plain language operation, as a result of the opening of switch S15, contacts uk open to produce pulse kui 14À5 which opens switch S1 to stop feeding and reading of the tape in unit LA. Pulse kui 14À5 is delayed in unit Ph2 and passes through Is2, 02, S6 and 06 to become pulse ai (15). This pulse opens S6, S7 and S16; closes S13; confirms that S11 and S14 are closed and S5 open; and switches in the timing distributer ATV which causes the switch-out code to pass from code generator KGA to the output switch AS in a similar manner to the distributer ETV and generator KGE. The emergency call key nT allows cipher transmission to be interrupted for the transmission of a service message. When this key is closed a pulse dei 13 passes to O14 and causes the cipher unit M to change over and the switch out signal to be transmitted. The pulse also passes to unit Is 3 where, in combination with kui 14À5 it closes S10 and opens S8. The effect of this is to allow an eleventh character to be transmitted after the normal 10 character of the switch-out code, and after the eleventh character has been transmitted, pulse at11 from unit ATV passes through Ph5 and closes S12 to operate relay NS. One contact ns1 of relay NS switches the line to the service machine D to allow the message to be sent by hand, and the other contact ns2 lights a lamp NL. When contact nT is released the apparatus is switched back to cipher operation, preceded by the switch-in code, by pulses dai. Receiver.-At the receiver, part of which is shown in Figs. 7 and 8, received characters are stored in the memory matrix SM containing 10 columns of 5 rows. The latest character is stored in column 10, and moved progressively down to column 1 as further characters are received. During the time interval between each character unit SPTV generates 12 pulses spt1-spt12 which transfer the characters stored in SM one by one to comparator units VE and VA; here the characters are compared with the characters of the switch-in code and the switchout code respectively, and each time there is a coincidence a pulse is sent to counter ZE or ZA. When one of these counters records a count of  6 it produces an output pulse eki or aki which switches the receiver to cipher or plain language operation. After receipt of the switch-out code the next character received is passed to comparator VK32 to see whether the eleventh character is present which would be sent by the transmitter if the emergency call key were used. In lines susceptible to interference the receiver can be switched to synchronous operation by a comparator VBu which detects the pre-code transmitted before the switch-in code.