US3678198A

US3678198A - Circuit for generating a series of cipher pulses

Info

Publication number: US3678198A
Application number: US250119A
Authority: US
Inventors: Kurt Ehrat
Original assignee: Kurt Ehrat
Current assignee: OMNISEC AG TROCKENLOOSTRASSE 91 CH-8105 REGENSDORF SWITZERLAND A Co OF SWITZERLAND
Priority date: 1962-01-10
Filing date: 1963-01-08
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: CH408109A; DE1257843B; BE626963A; NL287518A; NL142301B; GB973537A

Abstract

15. A message transmission installation comprising at least two stations each capable of acting as a transmitter and receiver, each station comprising apparatus capable of acting as a transmitter and receiver of information, a mixer, and a circuit for generating reproducible series of code pulses having a long period, said circuit comprising a binary counting chain having at least 20 members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shift register element in the chain and to a switching distributor the state of which is determined by a switching criterion, the arrangement being such that the mixers mix the information content of one counting member of the counting chain with the information of one shift register element and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain, and that the information of one shift register element is delivered to the next shift register element unchanged if the state of the switching distributor differs from the switching state of the corresponding member of the counting chain.

Description

i ited tates 'Patet Ehrat July 18, 1972 [54] CIRCUIT FOR GENERATING A SERIES OF CIPIER PULSES Kurt Ehrat, Scheuchzerstrasse 28, Zurich, Switzerland Filed: Jan. 8, 1963 Appl.No.: 250,119

[ 72] Inventor:

Primary Examiner-Richard A. Farley Attorney-Pierce, Schefiler & Parker CODE PULSE EXEMPLARY CLAIM 15. A message transmission installation comprising at least two stations each capable of acting as a transmitter and receiver, each station comprising apparatus capable of acting as a transmitter and receiver of information, a mixer, and a circuit for generating reproducible series of code pulses having a long period, said circuit comprising a binary counting chain having at least 20 members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shift register element in the chain and to a switching distributor the state of which is determined by a switching criterion, the arrangement being such that the mixers mix the information content of one counting 'member of the counting chain with the information of one shift register element and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain, and that the information of one shift register element is delivered to the next shift register element unchanged if the state of the switching distributor differs from the switching state of the corresponding member of the counting chain.

15 Claims, 7 Drawing Figures CODE PULSE GENERATOR ER Q GENERATOR EP so z ws so zws LOCK M RS- -MRS SIP TI TI I TRANSMlT TER/ gg 'gg C IP KI P R\ECEIVER II MIXING I3 MIXING I4 CIRCUIT Patented July 18, 1972 5 Sheets-Sheet 1.

CODE PULSE GENERATOR RECEIVER P P I [I 6- S K WU w 7 mm Ml C 3 W c M fl mm 1 mm T C P \I C I T J n mm mm mm C MIXING AND CALCULATING CIRCUIT TRANSMITTER FIG] Jiwmvfm T J M u h fi p m b T P z E m m 5 4 G. 5 T S ll z 4 4 M L F Z4 m w M m L Z J m s W 2 2 I m m w 52 4 z 1 1 m L 2 E. m s 1 M l.l.l .HL 8 N u m Kurt Ehraf Patented July 18, 1972 3,678,198

5 Sheets-Sheet 5 FIGA SIP

lfurfi Ehraf [L /Lou JVL WXD 1 0% Patented July 18, 1972 5 Sheets-Sheet I l l fullllll|lllrlll1llllllll|lllllIlllllL LL 1 r m 0E H t r U K Patented July 18, 1972 3,678,198

5 Sheets-Sheet 5 Sum 4 6/ CIRCUIT FOR GENERATING A SERIES OF CIPHER PULSES This invention relates to mixing and calculating circuits for generating reproducible series of cipher pulses having a long period, which forms constituents of cipher pulse generators. Cipher pulse generators are used in ciphering messages, particularly messages which are transmitted in the form of pulses.

In the ciphering of such messages, the individual pulses (or combinations of pulses) are first mixed at a transmitter with as random as possible a series of corresponding pulses (or combinations of pulses), called the cipher pulses (or cipher pulse combinations) and are transmitted in the form of the new pulses obtained by the mixing. At the receiving end, the original message is reproduced with the aid of a second identical series of cipher pulses. The said cipher pulse series must be generated in identical format the transmitter and receiver. This purpose is served by the likewise identical cipher pulse generators which are present at the transmitter and receiver.

The cipher pulse series (code pulse program), and hence also the actual cipher pulse generator, must satisfy specific requirements in order reliably to exclude the possibility of the message being deciphered along the transmission path by unauthorized persons. First of all, the period of cycle length of the cipher pulse series i.e., the period of time within which the cipher pulse series does not repeat itself must be sufficiently great to make it impossible for the entire cipher pulse series to be reproduced sufiiciently quickly to be of use, even when the most rapid electronic means are used. Furthermore, the distribution of the pulses within the cipher pulse series should be random (statistical) to the utmost possible extent. The cipher pulse series must also be created according to such complicated rules that it is impossible from a knowledge of the series to deduce the state of the individual circuit elements of the cipher pulse generators. Furthermore, the cipher pulse series must be reproducible i.e., a quite definite and unequivocal pulse series must be produced for a specific initial state of a cipher pulse generator.

According to the present invention there is provided a circuit for generating reproducible series of code pulses having a long period, said circuit comprising a binary counting chain having at least 20 members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shift register element in the chain and to a switching distributor the state of which is determined by a criterion, the arrangement being such that the mixers mix the information content of one counting member of the counting chain with the information of one shift register element at a time and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain.

The mixers used may advantageously be so-called modulus 2 mixers. However it is also possible to use, instead of such modulus 2 mixers, AND-gates and OR-gates known from the logical art, equal numbers of AND-gates and OR-gates being advantageously used in each case. In both cases that is to say, both where modulus 2 mixers are used and also when equal numerical quantities of AND-gates and OR-gates are used, the average frequency of occurrence of the states and 1 remains approximately unchanged. Therefore, if a negative counter-like countingchain such as that described in my copending U.S. Pat. application, Ser. No. 227,344 filed Oct. 1, 1962 be used, wherein the frequency of occurrence of the states 0" and 1" is approximately of equal magnitude, then the said frequency distribution is, on average, unmodified by the mixers.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and byway of example some embodiments thereof, and in which:

FIG. I is a block circuit diagram of a message transmission installation with automatic ciphering and deciphering;

FIG. 2 is a simplified circuit diagram of a mixing and calculating circuit;

FIG. 3 is a simplified circuit diagram of another mixing and calculating circuit;

FIG. 4 shows a greatly simplified circuit diagram similar to FIG. 3 in order to explain the switching cycle;

FIG. 5 is a simplified circuit diagram of yet another mixing and calculating circuit; and

FIGS. 6 and 7 show two circuit details, FIG. 6 showing a coincidence detector and FIG. 7 showing a modulus 2 mixing circuit.

Referring now to FIG. 1, there is shown a message transmission installation in which clear message pulses KIP (clear pulse program) emanating from a transmitter 11 pass to a modulus 2 adder 12, where they are mixed with a cipher pulse series SIP of a cipher pulse generator 8G,, and the mixture the enciphered pulse program CIP is transmitted to a receiver, where it is mixed in a modulus 2 adder 13 with a cipher pulse series SIP of a cipher pulse generator 86 whereupon the clear pulse program KIP is recovered and fed to a message receiver l4. Since the cipher pulse series SIP constitutes a continuously changing series of cipher pulses, synchronization of the cipher pulses at the transmitting end SG and the receiving end 86 is necessary. This synchronization may be controlled for example by timing pulses TI which are generated in a clock 15 and are added to the ciphered pulse program CIP by means of a mixing circuit 16. On the receiving side, the timing pulses TI are then taken out again from the ciphered message by means of a mixing circuit 17 and supplied to the cipher pulse generator 86 for synchronization. Each of the cipher pulse generators consists substantially of a counter circuit ZWS and of a mixing and calculating circuit MRS. It is advantageous to use a counting chain such as that described in my aforesaid Patent Application No. 227,334 because the latter .fulfils the condition that O and l pulses occur with almost equals frequency even over short periods.

A simple type of mixing and calculating circuit, and its cooperation with the counter circuit, will now be described with reference to FIG. 2. Referring now to FIG. 2, a counter circuit ZWS consists of n counting elements 2,, Z Z 2,,. Each counting element has a respective connection E,, E E E,,, acting as outputs from the counter circuit ZWS and as inputs to the mixing and calculating circuit MRS. Each of the inputs E, Q, E, is capable of assuming the states 0 or 1. Advantageously, binary counter circuits ZWS are used, which are connected together in the manner described in my aforesaid copending patent application, Ser. No. 227,344 and have the principle of operation therein set forth. In the case of such a counting chain, the switching state of practically all the members of the counting chain changes from counting step to counting step. Furthermore, the counting chain reverts to its initial state only after passing through all the possible combinations of positions.

The counting process is controlled by the timing pulses Tl so that, for example, each timing pulse initiates a counting step. The inputs E E E E, (outputs from the counter circuit) are taken in the mixing and calculating circuit MRS to input gate circuits TE,, TE TE TE,,, the second inputs of which are fed from a switching distributor SV. The outputs of the gate circuits are taken to modulators M8,, M5 M8,, MS which are, for example, modulus 2 adders, which may be constructed in the manner shown in FIG. 7. The modulators are connected into a shift register having shift register stages SR SR SR SR,,, substantially so that each modulator is located between two shift register stages. By means of the timing pulses TI, which act as shift pulses, the information in the shift register stages is shifted in the direction of the arrow 21 (to the right in FIG. 2), namely from one shift register stage into the next one on its right hand side in each case and for each timing pulse. During shifting, the shifted information is mixed in the modulator MS with the information present at the output of the gate TE, and the mixed information passes to the shift register stage on the right. At the right hand end, that is to say, at its output, the shift register chain is connected a divider circuit U, which consists, for example, of a normal flipflop divider stage, the information from the output 22 of which is mixed in a modulus 2 mixer or adder MU with the information from the output of the shift register chain and fed back via a line 23 to the input of the shift register chain. Simultaneously, the pulse program is passed out from the line 23 as the cipher pulse program SIP.

The principle of operation of the circuit shown in FIG. 2 is as follows. Due to the adoption of the binary system, the switching states of the individual members of the counting chain and of the individual shift register stages may be either or 1. These switching states can be varied in the rhythm of the timing pulses TI, which advance the counting in the counting chain from counting step to counting step, and which are responsible for shifting the switching states in the shift register chain that is to say, for displacing the switching state of a shift register stage to the next shift register stage located to the right thereof for one timing pulse. By means of the mixers of the modulators M8,, M MS MS,,, it is possible for the switching states of the counter stages to be mixed via the gates TE with those of the shift register stages. Mixing occurs in every case when the first inputs of the input gates TE,, TE. TE are open that is to say, whenever the said first inputs are brought into the switching state 1. Control of the said first inputs is exercised by the switching distributor SV the state of which is determined by a switching criterion such as are indicated by the arrows 24. For example, the circuit may function in such a manner that from time to time all the input gates TE are simultaneously opened, so that at that instant the switching states of all the counter elements are simultaneously mixed with those of the shift register stages, or that only certain input gates are open, so that only certain switching states of counter elements are mixed with switching states of the shift register stages.

The divider stage U likewise has two possible switching states 0 or 1 and changes its switching state whenever the switching state 1 occurs at the input 25. Continuous totalling without carrying takes place in the said divider stage. The output 22 of the divider stage U is mixed in the modulus 2 adder MU with the particular switching state of the output on the right hand side of the shift register chain, whereby a pulse series totally difierent from the said output is produced in the line 23, is delivered as a cipher pulse series SIP and is fed via the modulator MS, to the first shift register stage SR,. A divider stage U together with the modulus 2 adder MU, produces a great additional complication of the cipher pulse series, and also makes it impossible for the switching states of the individual shift register stages to be deduced from the cipher pulse series. It is easy to see that the cipher pulse series SIP thus obtained has been produced according to extremely complex rules, and also that, by the use ofa negative-counterlike chain such as that described in the Specification of the aforesaid patent application, Ser. No. 227,344 and in conjunction with modulus 2 mixers, an equally great probability of the occurrence of the switching states 0 or 1, and an extremely good approximately random pulse distribution (0 or I) is achieved. Finally it will be seen that, by the action of the counter circuit, the cipher pulse series will possess an extremely long cycle period if there is a sufficient number of counter elements.

The circuit shown in FIG. 3 is of similar construction to that shown in FIG. 2. But in this case, additionally to the circuit of FIG. 2, a coincidence detector circuit KDS is provided. This circuit consists of coincidence detectors KD,, KD KD KD, and of gate circuits TD,, TD,,, TD,, TD,,. The circuit of an individual coincidence detector is indicated by way of example in FIG. 6, and the principle of operation ofsuch a coincidence detector is as follows:

If both inputs ED, and ED, (input arrows) have the same switching state that is to say, the switching state of both inputs is l or the switching state of both inputs is 0 then the switching state I occurs at the output AD of the coincidence detector. But if the two inputs ED, and ED have different switching states then the switching state 0 occurs at the output AD. Coincidence of the switching states of the two inputs is therefore marked by a l at the output AD.

In FIG. 3, the switching state of a shift register stage is compared in each case with that of a counting element, and the coincidence indication is fed to the gate circuit TD, to TD,,. A sole exception is constituted by the coincidence detector KD,,, which in this case ascertains coincidences between the switching state of the shift register stage SR, and the shift register stage SR,,. The gate circuit TD, transmits when the switching state 1 occurs at its input i.e., when the coincidence detector KD, delivers a l at its output, which is the case when the shift register stage SR, and counting element 2, exhibit the same switching state (coincidence). The gate circuit TD, is open or transmits when KD, and KDg are simultaneously in coincidence that is to say. that it is necessary simultaneously for Z, and SR, on the one hand and Z and SR on the other hand to be in coincidence. Analogously, three coincidences must be fulfilled simultaneously in the case of gate circuit TD,,, four coincidences simultaneously in the case of gate circuit TD,,, and n (5 as shown) coincidences simultaneously in the case of gate circuit TD,,, in order to bring their outputs to switching state 1. The outputs 31 to 35 of the gate circuits TD, TD,, act as first inputs of the input gate circuits TE,, TE, TE,,. In the form of construction illustrated in FIG. 3, the coincidence detector circuit produces the result that the counter state of Z, is mixed into the shift register chain via TE,, MS, whenever Z, and SR, are in coincidence, and furthermore that the switching state of the counting element 2 is mixed into the shift registers chain (via T5 MS when Z, and SR, and also Z and SR are simultaneously coincident. Furthermore it produces the result that the switching state of the counting element Z is mixed into the shift register chain via TE MS when Z, and SR,, Z and SR,, and Z and SR, are simultaneously coincident, and so on. Groups of coincidence detectors of different group size l, 2, 3 detectors) are therefore formed, so that a switching operation i.e., the mixing of a switching state of a counting element into the shift register chain is initiated via the gate circuits TD, TD,, whenever all the coincidence detectors of the group concerned exhibit coincidence simultaneously. Since the groups of coincidence detectors have different sizes (1, 2, 3, 4 n coincidence detectors), the frequency of the switching processes thus initiated is also different. For example, in the case of a totally random distribution of the switching states in the elements of the counting chain and in the shift register stages, the average frequency of coincidence between 2, and SR, would be one-half (50 percent). Likewise of course the average frequency of coincidence between Z and SR, or between 2 and SR,; but the average frequency of simultaneous coincidence between Z, and SR, on the one hand and Z and SR on the other hand is 1:2 and the average frequency of simultaneous coincidence between 2,, SR,, Z and SR and Z and SR, is 1:2", and so on. The simultaneous coincidence of a group of three coincidence detectors is 4 times less frequent than that having only one coincidence detector. The switching processes which are initiated by the outputs of the gates TD,, TD TD,, (

lines

31, 32, 33, 34, 35) thus exhibit greatly different average frequencies. The coincidence detector circuit is a feedback circuit, which very substantially increases the complexity of the cipher pulse series. It is simultaneously possible for all the switching states of the counting elements to be mixed into the shift register chain via an input line S0 to the switching distributor.

The circuit shown in FIG. 4 has a similar structure and principle of operation to that shown in FIG. 3. It is proposed to show, with reference to FIG. 4, an example of the switching cycle over a plurality of timing pulses, and the generation of a cipher pulse series SIP. For the sake of simplicity, the number of counting elements and of shift register stages has here been restricted to 4. (This would be too few according to the invention.) The switching cycle can easily be ascertained by the laws of logic circuits, and is recorded in the following Table l.

TABLE 1 Schedule of the chronological cycle of switching states of the example according to FIG. 4.

TI 1 2 3 4 5 6 7 8 9 10 ll l2 l3 l4 I6 l7 I8 40 I y 40 40 40 I I I I Z, O I 0 l O l O l O l O l 0 l O l 0 l Z 0 l l O O l l O 0 l l O O l l 0 O I Z O l l 0 I 0 0 l 0 l I 0 I 0 0 l O I Z, O I l 0 l O l O l 0 O l O l 0 l 0 1 SR, 0 O 0 O 0 l l O l l 0 l l l O O O l SR O 0 0 0 O 0 l l O l l 0 I l l O 0 0 SR, 0 O 0 0 0 l O l l 0 O O 0 l l I O 0 SR, 0 0 O l O l l O l l O 0 I 0 O l l 0 KD, l O I O l I 0 0 O l l l 0 l l O l l KD, l O 0 l l O l O l l l l O l I l l 0 KB, 1 O O l O 0 l l 0 O O l 0 0 0 l l O KD, l O 0 O O 0 0 l l 0 l 0 O 0 l l O 0 TD, 1 O l 0 l l O 0 O l l l O l l 0 l 1 TD, 1 O O 0 l O 0 O 0 l l l O l l 0 l 0 TD,, 1 O O O O O 0 O 0 O 0 l 0 0 0 0 l 0 TD,, 1 O O 0 0 0 0 O O 0 O O O 0 0 0 l 0 TE, 0 0 O 0 O O 0 O 0 O O O O O 0 O O 0 TE, 0 O 0 0 0 0 0 0 O O O O 0 0 0 0 0 0 TE, 0 0 O O l O O O O l l O O O O 0 0 0 TE, 0 O l O l O O 0 0 O O l O l O O O l U 0 0 0 l l O l l O l l l O 0 0 l 0 0 SIP 0 0 O 0 l l 0 l l O l l l 0 In Table l, the switching state at the outputs of the individual switching elements is shown as O or I. The timing pulses Tl, which bring about the modification of the switching states, are indicated schematically in the top line and are numbered from one to 18 (chronological sequence). The counting elements Z, to 2,, shift register stages SR, SR,, and the divider stage U are storing switching elements, whereas the coincidence detectors KD, to KD the gates TE, to TE and the gates TD, to TD, are non-storing. At the commencement of the switching cycle recorded by way of example in the schedule, the output of the counting elements Z, to Z, are at O of the shift register stage SR, to SR, are at 0, of the divider stage U is at 0,

whereby the switching states of the outputs of the remaining circuit elements are fixed by the laws of logic, namely the outputs of the coincidence detectors KD, to KD, are at l, the outputs of TD, to TD, are at 1, and the outputs of TE, to TE are at 0 The formation of a cipher pulse SIP will now be ascertained by way of example with reference to FIG. 4 and to Table l. The initial switching state of the circuit will be assumed to correspond to that after the eight beat pulse (column between 8th and 9th beat pulses in Table I). Therefore, under these conditions, for example, the output of Z, is at O 2 is at O 2,, is at 0 L is at l. the output of SR, is at l SR is at 0 SR is at 1 SR, is at 1. this gives the output of KD, as 0, (since no coincidence between Z, and SR, the output of KD, as 1 (since 2, and SR, are in coincidence) and so on. The outputs of TD, to TD, and of TE, to TE, are all found to be 0, and if the output of U 0, then an SIP state of l is obtained (mixture of U with SR, in MU).

The subsequent timing pulse (9th Tl) changes Z, from O to l Z from 0 to 1 2,, from 0 to I Z, from 1 to 0.

(Column between 9th and 10th timing pulse in Table I).

The switching state of SR, is shifted unchanged (since TE 0) to SR,,, likewise the switching state of SR to SR, (because TE, 0).

The switching state of SR, l) is mixed with U in MU 0) and TE, 0) and is shifted as 1 into SR,. The divider U changes its switching state at the 9th TI, since the output of SR, was previously I and the gate TU is therefore open. By this means, the output of U becomes 1, and since SR,, output is again I, the output of MU becomes 0 i.e.,

A number of delay circuits, not shown, are also requisite to the proper functioning of the circuit.

The circuit shown in FIG. 5 is again of another structure to that in FIG. 3, but it exhibits certain modifications and additions. Thus, the gate circuit with the gates TD,, TD,, TD,, TD,, in the coincidence detector circuit in FIG. 3 is replaced by a gate circuit with gates TK,, TK TI( TK, TK,, in FIG. 5. However, the principle of operation of this gate circuit is the same as of that in FIG. 3.

Thus, for example, the gate TK, delivers an output pulse 1, when the coincidence detector KD, alone has coincidence. The gate TK, delivers an output pulse when two coincidence detectors (KD, and KD,,,) have coincidence simultaneously, the gate TK delivers an output pulse when three coincidence detectors (KD,,, KD and KD,,,) have coincidence, and so on. The outputs of the gates in the coincidence circuit pass via OR-gates T0,, T0,, T0,, T0,,, to the input gates (as first input) TE,, TE TE, TE where they in turn control the switching processes that is to say, the mixing of the switching states of the counting elements into the shift registers. The majority of the coincidence detectors shown ascertain coincidence each between one counting element and one shift register stage. By contrast, the coincidence detector KD, ascertains coincidence between two counting elements, namely Z, and 2,, whereas the coincidence detectors KD, and KD, each ascertain coincidence between two shift register stages. In contradistinction to the form of construction shown in FIG. 3, three self-contained shift register chains are provided in the construction shown in FIG. 5 instead of only one. The top shift register chain possesses the shift register stages SR,, SR,, SR SR,,, and is closed via a circuit containing a divider U, and a modulator MU, back to the modulator M5,. The central shift register chain having shift register stages SR SR,,, SR,,, SR,, is closed via the circuit containing a divider stage U and a modulator MU The third shift register chain having the shift register stages SR SR SR,,, and SR is closed via the circuit containing a divider stage U and a modulator MU The cipher pulse series SIP is again derived at the output of the modulators (MU MU MU In this case therefore, it is possible to obtain simultaneously three parallel outputs of cipher pulse series. The circuit example in FIG. 5 moreover contains an interchanger circuit VS having interchanger gates TV,, TV TV TV TV and TV and divider U The divider U.,, which is for example a flip-flop circuit, has two outputs, of which one is at and the other at l at any time. Each input pulse to the divider U interchanges the switching states at the two outputs. For example, if the right hand output of the divider U is at 1, then the interchanger gates TV,, TV TV are conductive and the shift register stage SR passes on its information, upon shifting, to SR SR to SR and SR to SR On the other hand, ifthe left hand output of the divider U is at I, then the interchanger gates TV TV TV are conductive and the switching state SR passes to SR that of SR to SR and that of SR to SR... The change in the switching state in the divider U has thus brought about an interchange of the flow of information in the three shift register chains. Control of the divider U is exercised by a pulse at the output of the gate TK in the coincidence detector circuit that is to say, whenever KD KD KD KD and KD have coincidence simultaneously. A further additional circuit arrangement as compared with the construction shown in F IG. 3 is the connection of a binary counter 82 at the output of the three shift register chains. The binary counter BZ consists here of the three binary counting stages ZB 2B ZB and therefore possesses a counting period of 2 8. The counting steps occur in rhythm with the timing pulses T]. The principle of operation of this binary counter is as follows:

When the maximum binary number 111 is reached, the output gate TB becomes conductive (at the moment when a timing pulse TI occurs), and the switching processes are initiated via the line SO and the OR-gates T0,, T0 T0 etc., which may be for example that the switching states of the counting elements are mixed into the shift register chain via the input gates TE,, TE etc., and furthermore that the interchanger circuit VS is interchanged via the divider U But simultaneously the output pulse of the output gate T8,, passing through the line 64 and the input gates TB TB and TB;,, causes the switching states of the outputs of the shift register chains (output of SR1 SR and SR to be imprinted into the individual counting elements ZB,, 2B and ZB via

lines

61, 62 and 63. This imprinted binary number is now an initial position, from whence the binary counter 82 is stepped on by the action of the timing pulses Tl until the binary counter again reaches the maximum binary number 111 and the process already described is repeated. This circuit arrangement also makes a very substantial contribution towards increasing the complexity of the switching cycle i.e., to the complexity of the cipher pulse series.

The invention is of course not restricted to the number of circuit elements indicated in the example. For example, it would also be possible to provide a plurality of interchanger circuits instead of only one, and in the same way five or any desired number of shift register chains might be provided instead ofonly three.

What is claimed is:

l. A circuit for generating reproducible series of cipher pulses having a long period, said circuit comprising a binary counting chain having at least members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shift register element in the chain, and to a switching distributor the state of which is determined by a switching criterion, the arrangement being such that the mixers mix the information content of one counting member of the counting chain with the information of one shift register element and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain, and that the information of one shift register element is delivered to the next shift register element unchanged if the state of the switching distributor differs from the switching state of the corresponding member of the counting chain.

2. The circuit of claim 1, wherein said mixers are modulus 2 mixers.

3. The circuit of claim 1, wherein each mixer is composed of substantially equal numbers of AND-gates and OR-gates.

4. A circuit for generating reproducible series of cipher pulses having a long period, comprising at least 20 counting members constituting a binary counting chain, at least 20 mixers each connected to a respective counting member, a plurality of shift register elements constituting together with the mixers a shift register chain, the mixers and the shift register elements being connected alternately in series, at least one binary divider stage coupled to at least one point of the shift register, and at least one further mixer the input of which is connected to the output of a respective binary divider stage and the output of which is connected to at least one further shift register element, the arrangement being such that, the mixers mix the information content of one binary divider stage with the information of one shift register element at a time and deliver the mixed information to the next shift register element.

5. The circuit of claim 4, wherein said mixers are modulus 2 mixers.

6. The circuit of claim 4, wherein the code pulse program is obtained from said further mixer and is derived from the information content of the divider stage and the shift register stage.

7. The circuit of claim 4, wherein the shift register chain is divided into a plurality of self contained shift register chains.

8. The circuit of claim 7 and further comprising at least one interchanger circuit for interchanging the flow of information of one shift register chain to another shift register chain, interchangement taking place at least between any element of one shift register chain with any element of another shift register chain.

9. A circuit for generating reproducible series of cipher pulses having a long period, comprising at least 20 counting members constituting a binary counting chain, at least 20 mixers each connected to a respective counting member, a plurality of shift register elements constituting together with the mixers a shift register chain, the mixers and the shift register elements being connected alternately in series, at least one binary divider stage coupled to at least one point of the shift register, at least one further mixer the input of which is connected to the output of a respective binary divider stage and the output of which is connected to at least one further shift register element, a plurality of gate circuits, and a plurality of coincidence detectors, the gate circuits and coincidence detectors being interconnected between the counting members and the mixers in such manner that, in the case of coincidence between the switching states of two freely selected members of the counting chain and elements of the shift register, a switching pulse is delivered at the output of the coincidence detector, different sized groups of coincidence detectors being associated through the gate circuits in such manner that switching processes are initiated through the outputs of the gate circuits whenever there is simultaneous delivery of switching pulses by all the coincidence detectors belonging to the relevant group.

10. The circuit of claim 9, wherein the shift register chain is divided into a plurality of self-contained shift register chains.

11. The circuit of claim 10, and further comprising at least one interchanger circuit for interchanging the flow of information of one shift register chain to another register shift register chain, interchangement taking place at least between any element of one shift register chain with any element of another shift register chain.

12. A circuit for generating reproducible series of cipher pulses having a long period, comprising at least 20 counting members constituting a binary counting chain, at least 20 mixers each connected to a respective counting member, a plurality of shift register elements constituting together with the mixers a shift register chain, the mixers and the shift register elements being connected alternately in series, at least one binary divider stage coupled to at least one point of the shift register, at least one further mixer the input of which is connected to the output of a respective binary divider stage and the output of which is connected to at least one further shift register element, a plurality of gate circuits, a plurality of coincidence detectors, the gate circuits and coincidence detectors being interconnected between the counting members and the mixers in such manner that, in the case of coincidence between the switching states of two freely selected members of the counting chain and elements of the shift register, a switching pulse is delivered at the output of the coincidence detector, different sized groups of coincidence detectors being associated through the gate circuits in such manner that switching processes are initiated through the outputs of the gate circuits whenever there is simultaneous delivery of switching pulses by all the coincidence detectors belonging to the relevant group, at least one binary counter, means for imprinting the information content of at least one plurality of shift register stages into the binary counter at intervals whereby the binary counter runs in the rhythm of the counting steps up to its maximum number, means operable by the binary counter when it reaches its maximum number to initiate a switching process to imprint the information content present at that moment at the shift register stage as a new binary number into the binary counter.

13. The circuit of claim 12, wherein the shift register chain is divided into a plurality of self-contained shift register chains.

14. The circuit of claim 13, and further comprising at least one interchanger circuit for interchanging the flow of information of one shift register chain to another shift register chain, interchangement taking place at least between any element of one shift register chain with any element of another shift register chain.

15. A message transmission installation comprising at least two stations each capable of acting as a transmitter and receiver, each station comprising apparatus capable of acting as a transmitter and receiver of information, a mixer, and a circuit for generating reproducible series of code pulses having a long period, said circuit comprising a binary counting chain having at least 20 members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shifi register element in the chain and to a switching distributor the state of which is determined by a switching criterion, the arrangement being such that the mixers mix the information content of one counting member of the counting chain with the information of one shift register element and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain, and that the information of one shift register element is delivered to the next shift register element unchanged if the state of the switching distributor differs from the switching state of the corresponding member of the counting chain.

Claims

1. A circuit for generating reproducible series of cipher pulses having a long period, said circuit comprising a binary counting chain having at least 20 members, connections connecting each of said members to a respective mixer, a plurality of shift register elements constituting a shift register chain, connections connecting each mixer to a respective shift register element, to a previous shift register element in the chain, and to a switching distributor the state of which is determined by a switching criterion, the arrangement being such that the mixers mix the information content of one counting member of the counting chain with the information of one shift register element and this mixed information is delivered to the next shift register element if the state of the switching distributor is in accordance with the switching state of the corresponding member of the counting chain, anD that the information of one shift register element is delivered to the next shift register element unchanged if the state of the switching distributor differs from the switching state of the corresponding member of the counting chain.

2. The circuit of claim 1, wherein said mixers are modulus 2 mixers.

5. The circuit of claim 4, wherein said mixers are modulus 2 mixers.