US2405991A - Secrecy system - Google Patents

Description

Patented Aug. 20, 1946 UNITED STATES PATENT GFFIC SECRECY SYSTEM of Delaware Application July 31, 1940, Serial No. 348,756

12 Claims. l

This invention relates to signalling systems and especially to telegraph systems. Its object is to insure secrecy in the transmission of messages and, further, to provide a system in which messages may be transmitted and received in characters of a well known code, but only the signalling impulses are so altered before transmission over the transmitting medium that they are unintelligible to unauthorized persons intercepting them,

The invention is particularly applicable to a multiplex communication system designed to transmit a combination of signals having equal length code characters and signals having unequal length code characters, such as may emanate from printer apparatus and Morse code telegraph transmitting devices, respectively.

In brief, the present invention employs at each channel or transmitting position an interrupting device such as a cam or switch for reversing the sense of the signals at arbitrarily selected intervals; and at the central station at which the multipleX distributor is located for assigning the individual message channels to a common transmission medium, it is proposed to interlace or scramble the individual message channels as they are assigned to the distributor at arbitrarily selected intervals. At the receiver there is provided similar mechanisms for unscrambling the channels and similar cams and switches for restoring the sense of the signal characters so that they can be recorded correctly. For a detailed description of the type of multiplex system to which the present invention is particularly applicable, reference is made to United States Patent No. 2,010,505, granted August 6, 1935, to Callahan et al.

Apparatus for accomplishing the results of the present invention is shown in the accompanying drawings, wherein:

Figure l illustrates schematically a complete transmitting system in accordance with the present invention;

Figure 2 illustrates the manner in which interlacing is effected at the banks of the rotary switch;

Figure 3 illustrates a receiving system in accordance with the present invention; and

Figure 4 illustrates a feature which can be used. in the receiving system of Figure 3 to overcome possible contact transition difficulties in the receiving system.

Referring to Figure 1 in more detail, there are shown three individual message channels (labeled channel #1, channel #2, and channel #3) over which regular Morse signal characters of unf equal length are transmitted. The machines for transmitting the signals are labeled I, 2, 3 and are well known automatic transmitters which respond to signal characters impressed on the perforated tape 4. The perforations of the tape may be effected by any suitable perforator (not shown) such as the Kleinschmidt apparatus, well known in the art. This tape is utilized to control the transmitters I, 2, and 3 which may be of the Wheatstone automatic tape transmitter type for actuating a circuit in accordance with the perforations in the tape. The individual transmitters are each driven by a shaft which is connected to a motor 6. The motors S, 6 of the transmitters I, 2 and 3 rotate at the same speed and are synchronized as to speed and phase by pulses received over lead 50 from a commutator 5l mounted on motor 39 in a manner shown and described in more detail in Figure l of United States Patent 2,010,505, supra. Of course, any other suitable synchronization circuit may be employed. The power supply apparatus which serves to supply positive and negative potentials to the contacts 9.and I 0 of each transmitter is arranged in circuit with a suitable double pole switch II, which in turn responds to movement of a cam follower I2 resting on the periphery of a cam I3, in turn linked through a shaft I4 and gears to the shaft l. The output energy from each tape transmitter I, 2, 3 is derived from an armature I5 adapted to contact either 9 or I0,

depending upon the perforations in the tape, and passes over connection I6 to a wiper arm of a multi-bank rotary selector switch before being passed on to the multiplex distributor. Although tape transmitters have been shown for the individual channels, it should be understood that if desired any tape transmitter can be replaced by suitable printer apparatus of the well known teletype start-stop type, in which case there will be associated with each printer and located between and 20 are closelj, adjacent to one another and have their wiper arms I'I, l'! simultaneously controlled and movable over correspondingly located contacts by means of a stepping magnet 2 I. The dash line 22 extending from the stepping magnet of the multiplex distributor.

2| to the wiper arms I?, I1 is intended to indicate the unicontrol action of all three wiper arms. This type of rotary selector switch is well known in the art and is of a type commonly used in telephone and telegraph practice.

Connected to the first contacts o f the bank of the rotary switch are lines 23, 24 and 25, re-` spectively, which extend to distributor segments 26, 21 and 2B of the multiplex distributor, each segment being individual to a channel. The contacts on the rotary switch are interlaced or scrambled in such manner that each channel i6 is connected at an arbitrary interVaL'depending upon the position of the wiper, in turn controlled by the stepping magnet 2l to a diierent segment Only three contacts of each bank of the rotary selector switch are shown suitably connected and interlaced in Figure 1, in order to illustrate the method of interlacing, although al1 ten contacts of each rotary switch are shown interlaced in more detail in Figure 2. More specifically, it will be noted by referring to Figure 2 that the first contact of the rst bank I8 (to which lead 23 is connected) is connected to the second contact of the third bank, and then to the third contact of the third bank, and to the fourth contact of the second bank, etc. i9 (to which lead 24 is connected) is shown connected to the second contact of the `i'lrst bank and to the third contact of the second bank and to the fourth contact of the third bank, etc. The rst contact of the third bank 20 (to which lead 25 is connected) is co-nnected to the second contact of the second bank and the third contact of the rst bank, and to the fourth contact of the rst bank, etc. It will thus be seen that as the wiper arms I1, l1 move over the contacts of the rotary selector switch, that when thewiper arms are on the first contacts, the rst channel will be connected through line I6 to lead 23, the second channel will be connected through its particular line It to the lead-2 4, while the third channel will be connected through its line I6 to lead 25. However, when the wiper arms I1, l1 are on the second contacts of the switch, the iirst channel will now be connected to lead 24, while the second channel will be connected to lead 25, and the third channel will be connected to lead 23. In this way there is obtained a scrambling or interlacing of channels with the leads 23, 24 and 25 extending to the segments of the multiplex distributor, thus assuring additional secrecy, that is, more than that provided by the feature of the cams I3, i3. The stepping magnet 2|, of course, determines when the wiper arms should advance to the next contact, and the operation of this stepping magnet can be arbitrarily selected to provide random interlacing, and this is done by connecting the stepping magnet to a cam follower 29 whose closure with a contact 30 leading to a source of positive potential is determined by a cam 3l. This cam has'any desired number of arbitrarily selected cam segments to cause the closure of contacts 29 and 30 at certain intervals. By means of the cam 3l and its driving mechanism, the stepping magnet 2| `may be caused to operate the selector switch at every The rst contact of the second bankV baud or at any desired integral number of bauds 4 comprises a plurality of segments 26, 21 and 28, each segment being associated with a single channel at a time, and a brush assemblage 33 adapted to sweep over the segments and to obtain therefrom the signal units or pulses transmitted by the channel equipment comprising transmitters I, 2 and 3. The brush assemblage 33 (which is connected to the multiplex equipment 32) is arranged to make one revolution for each dot length of the automatic transmitter equipment, this dot length comprising the basic unit (the baud) which is equal in length to the individual unit pulsetransmitted over each channel I3. In the present instance, since a three channel circuit is shown, the distributor is arranged to supply to the multiplex transmitting keyer 32 at most onethird of a baud from Veach signal unit, this onethird being the length of each unit of signal taken from each of the respective channels successively, thus throwing away the other two-thirds of the dot unit of each signal in each channel which is later restored by rebuilding the signal in the receiver. The multiplex transmitting keyer equipment 32 which in turn actuates the radio transmitting equipment 34 is assigned to each of the channels #1, #2 and #3 and their respective lines i6, I5 in succession, for a time equal to one of these one-third dot or baud portions.

It will be apparent from Figure 1 that although three channels are shown, any number of channels may be used. For three channel working, normally only one-third of each signal component is actually operative for each channel, and similarly for other numbers of channels. Although for the sake of simplicity it has been mentioned that one-third of a dot length of each unit is assigned to .the transmitter keyer 32, actually it is preferred to use only a very small part of each one-third portion, and to discard the remainder of the dot length of each channel unit. This mode of operation has been found to increase the tolerance of Variation permitted a signal due to fluctuations andV bias distortion, noise,v etc. The multiplex transmitting equipment 32 functions to produce a composite signal composed of successive one-third dot length portions from the three channels consecutively. This equipment with which the distributing brush assemblage 33 is connected comprises essentially a locking circuit and a shunt keyer arrangement for producing tone signals in transmission line 35 which tone signals c-orrespond to the composite signal received from the multiplex distributor, these tone signals in turn, controlling the radio frequencyemanations in line 35 extending to the antenna `3l. The locking circuit in 32 comprises essentially two electron discharge devices (not shown), which have their anodes and their control electrodes resistively interconnected in a manner such that the performance has two degrees of electrical stability. These devices are unstable when both are drawing current but stable when one tube is passing current and the other blocked or prevented from passing current. The change from one condition of stable equilibrium, such as when one tube is blocked and the other passing current to the other condition When the last tube is passing current and the rst tube blocked, or the reverse, is caused by the presence of predetermined potential on the brush assemblage 33. For a more amplified description of such manner of telegraph communication reference is made to United States Patent '15 2,010,505, supra, and also to United States Patent 1,844,950, granted February 16, 1932, to J. L. Finch. Y

The multiplex distributor is driven by means of a shaft 38 which is geared to drive motor 39, the latter in turn .being also geared to the cam 3|. This gearing controls the speed of rotation of the multiplex distributor and the cam 3l Referring now to the receiver of Figure 3, the composite signals are received over any suitable type of antenna system 40, amplified and detected in well known manner in equipment 4I, andthen transmitted over transmission line 42 to a suitable central ofce where the receiving multiplex distributor -43 assigns the received incoming signals to their respective channels, in which the received signals are rebuiltA to their original form as in the transmitting station, the portions suppressed at the transmitting station being restored in the receiving system.

Distributor arrangement y43 is driven by a drive motor 44 which is held in synchronism with the multiplex distributor driving mechanism 39 at the transmitting station by means of a suitable correction unit (not shown) which may be controlled by the incoming signals. This correction unit for synchronizing the motor M with the motor 39 of the transmitter may be of a type described in United States Patent 2,010,505, supra, or of a type shown in Mathes United States Patent No. 2,062,009, granted November 24, 1936.

Associated with the individual segments of the multiplex distributor d3 are the banks IS', I9 and of a rotary selector switch of a type identical with that described in connection with the transmitter. The contacts of this rotary selector switch at the receiver are interlaced in the same way as the contacts of the rotary switch at the transmitter, and the stepping magnet 2i for the rotary switch at the receiver is arranged to operate by means of cam 3i in synchronism with the operation of the cam 3i at the transmitter. Cam 3i' at the receiver is, of course, of identical construction as the cam di at the transmitter, and both of these cams rotate in synchronism, whereby the rotary selector switch at the receiver unscrambles the signals caused by the scrambling arrangement of the rotary switch at the transmitter, thus producing on leads 23', 24 and 25 signals substantially identical in form to the signals on leads i5, i5 and It respectively, at the transmitter.

Associated with each ci the leads 23', 2li and 25' there is provided a suitable relay 45 of the vacuum or electromagnetic type which is operm ated by the rectined signal assigned to its associated lead extending te the rotary switch. In the output of relay i5 there is provided a double pole switch II' which is moved in response to the,

movement of a cam follower i.. resting on a periphery of cam i3. The cams i3, i3 at the receiver are of identical construction as the cams I3, I3 at the transmitter, and are driven simultaneously at the same speeds as the cams at the transmitter. For this purpose there is provided at the receiver a drive motor At which drives the cams through a suitable shaft and gearing arrangement indicated by the dotted line 4l. The Inotor 46 is, of course, synchronized to operate at exactly the same speed as the motor Ei, which is at the transmitter and is controlled as to speed and phase from commutator 52 mounted on motor #3Q in the same manner as is described in connection with motor E in the transmitter. At

this time it should be noted that the transmitting and receiving cams i3, I3 for the same channel are identical in construction, although, if desired, the cams for the diierent channels may be constructed differently to have a diierent number of segments. The received message signals which are changed in character by the cams I 3, I3 at the receiver (that is, restored in sense to their original form) are passed on to suitable locking circuits 48. These locking circuits consist essentially of a pair of electron discharge devices which have their anodes and control electrodes resistively interconnected to provide two degrees of electrical stability in the same manner as the locking circuits in apparatus 32 oi the transmitter, the locking circuits at the transmitter and receiver being substantially of the same construction. Reference is here made to United States PatentsV 2,010,505 and"1,844,950, supra; for further details of a well known form of locking circuit which may be employed. A suitable utilization device, such as an ink recorder or other instrument, may be connected to each locking circuit 48 of the receiver.

In order .to avoid the production of undesirable extraneous short clicks in the locking circuit 4S of Figure 3, due to the fact that the closure of the contacts of relay 65 and those of cam I3 might not be exactly simultaneous, it is proposed to employ a circuit as shown in Figure 4 which includes a kicker commutator 52 to be inserted between each locking circuit 48 and its associated cam i3 in each channel. The knicker commutator 52 includes a pair of brushes 53 designed to be connected together at predetermined intervals by a short-circuiting copper bar 54 mounted on the insulated surface of 4a rotating drum-like element driven by `a shaft 55. The rotation of the drive shaft 55 is of course synchronized as to speed with the other driving units to produce closure of the controls 53 only at the central portion of each band of received signal. Thus the kicker 52 selects the central portion of each band as it is passed to the locking circuit 48 and uses the kicks produced thereby for the operation of the locking circuit 43. In this way the kicker commutator permits a certain degree of transition time at the contacts of relay l5 and cam I3 without affecting the signal produced by the locking circuit. For a more detailed description of this form of kicker commutator reference is made to Mathes Patent 2,038,375, April 2l, 1936 (Figure 2 thereof).

In the operation of the transmitter of Figure l, the rotation of cam I3 in each channel will move the cam follower i2 up and down in accordance with depressions on the cam. Movement of the cam follower I2 will accordingly cause movement of the double pole switch II, thus changing the polarities applied to contacts 9 and I0 by the power supply. The circuit path from the power supply through the switch il to the contacts S and i0 of the automatic transmitter of each channel will be obvious from a mere inspection of the drawings. The change in sense of the polarities applied to contacts 9 and I0 by the cam I3 is arranged to occur in synchronism with the mechanism in its associated transmitter I, 2 or 3, whenever it tends to move armature I5. Putting it another way, the polarity reversals produced by the cam I3 in each transmitter mair occur where a dot or baud of unit length is to be transmitted only at the end of the baud; where a dash having a length equal to a plurality of bauds is to be transmitted, the polarity reversal may occur at the end of any of the component bauds constituting the dash, The occurrence of lthese reversals is determined bythe arrangement of the cam and Ymay occur at the end of every baud or at multiple sequences thereof. For example, the cam may be constructed to produce reversals at the end of every four bauds, or to produce reversals at non-uniform periods so long as these periods include an integral number of bauds, although the cams for different transmitters may have different constructions to produce reversals at the end of a different number of bauds.

The signals sent out by the transmitters of the three channels over lines I6, I6 are assigned at random to different ones of the leads 23, 24 and 25 depending upon the interlacing at .the banks I8, I9 and 20 of the rotary selector switch. 'I'he stepping magnet 2l under control of the cam 3| will determine the intervals at which the interlacing occurs. The multiplex equipment per se illustrated by .the multiplex distributor assigns only a very small portion of the sign-a1 on each channel to the keyer and locking circuit 32 for transmission over the antenna 31.

Thus, it will be seen that there are four coperative features which contribute to assure secrecy in the transmission of the signals. The iirst feature comprises cam I3, which produces reversals in sense of the signals at arbitrarily selected intervals. The second feature is the rotary selector switch which by its interlacing causes the signals to go to the multiplex distributor over different leads at different times. The third feature resides in the cam 3| at the transmitter which controls the random or arbitarry stepping or operation of the magnet 2I which causes the wiper arms I'I to change position at arbitrary intervals determined by cam 3l and its speed of rotation. The fourth feature lies in the multiplex equipment per se which selects only a small portion of each signal unit and discards the remaining portion of the signal.

At the receiver there are employed means which correspond to the foregoing means at the transmitter for unscrambling and restoring the signals to their original form. For example, the L.

cams I3 at the receiver function to restore the signals back to their true sense or true polarity, which they had before they were affected at the transmitter by the polarity reversal cams.-V The three bank rotary selector switch at the receiver is interlaced in identical manner as the rotary selector switch at the transmitter for unscrambling signals produced by the interlacing at the transmitter; and the cam 3l at the receiver of like construction as cam 3i at the transmitter and operating at the same speed, causes the wiper arms of the receiving rotary switch to move in synchronism with the movement of the wiper arms on the rotary switch at the transmitter. Finally, the locking circuits 48 at the receiver associated with the channels function to restore or rebuild the individual signal units to their original full length, whereby the portions of the signal units discarded at the transmitter are filled in at the receiver.

It should be understood that the present invention is not limited to the precise arrangements of parts illustrated in the drawings, since various modifications may be made without departing from the spirit and scope of the invention. The rotary switches may be of any suitable form and may comprise any desired number of contacts. The cams may be of any suitable construction and are not limited in form to those illustrated in the drawings and may be changed frequently to further insure secrecy. Further, the cams may be replaced by tape transmitters serving thev signing said lines in a predetermined irregular Y n sequence to a transmission medium.

2. In a-multiplex telegraph system, the method of signal communication which comprises transmitting over individual lines a plurality of message signals corresponding to the number of channels in the system and whose elements are of unit length and multiples of unit length, assigning said lines in irregular order to a transmission medium, dividing the successive basic time units of the message characters of each channel into substantially equal portions of like number not less than the total number of channels used, and transmitting over said medium a composite signal formed by combining equal portions from thesuccessive channels consecutively.

3. In a multiplex telegraph system, the method of signal communication which comprises transmitting over individual lines a plurality of message signals corresponding to the number of channels in the system and whose elements are of unit length and multiples of unit length, changing the sense of some of the signals prior to transmission over said lines and at predetermined discrete intervals, assigning said lines in irregular order and at arbitrarily selected intervals to a transmission medium, dividing the successive basic time units of the message characters into equal portions of like number as the total number of channels used, and transmitting over said medium a composite signal formed by combining equal portions from the successive channels consecutively.

4. In a multiplex telegraph system, the method of signal communication which comprises transmitting over individual lines a plurality of message signals corresponding to the number of channels in the system and whose elements are of unit length and multiples of unit length, changing the sense of some of the signals prior to transmission over said lines and at predetermined discrete intervals, and assigning said lines in irregular order at arbitrarily selected intervals to a transmission medium.

5. In a multiplex telegraph system, the method of signal communication which comprises transmitting over individual lines a plurality of message signals corresponding to the number oi' channels in the system and whosel elements are of unit length and multiples of unit length, changing the sense of some of the signals prior to transmission over said lines and at predetermined discrete intervals, which terminate only at the end of a unit length, and assigning said lines in irregular order at arbitrarily selected intervals to a transmission medium.

6. In a multiplex telegraph system, a transmitfrom a transmitting multiplex distributor to said transmitters, switching means associated with said leads and located between said transmitters and said distributor for assigning said transmitters at different .predetermined irregularly spaced times to diierent ones of said leads, a transmission medium, said distributor serving to assign said medium to said leads in succession and to each for a period of time equal at most to the longest period of which the duration of the fundamental time unit is an exact multiple of the number of channels.

7. -A multiplex -telegraph system in accordance with claim 6, characterized in this that said means for assigning said transmitters at different times to different ones of said leads comprises a multibank rotary selector switch, the contacts of said banks being interlaced to provide connections between said leads and said transmitters which change in accordance with a predetermined schedule as said switch advances.

8. In a multiplex telegraph system, a transmit- Iter employing for each channel a code having characters composed of one or more signal units of fundamental time duration, leads extending from a transmitting multiplex distributor to said transmitters, switching means associated with said leads and located between said transmitters and said distributor for assigning said transmitters at different times to diierent ones of said leads, a transmission medium, said distributor serving to assign said medium ,to said lines in succession and to each for a period or time equal at most to the longest period of which the duration of the fundamental time unit is an exact multiple of the number of channels, a receiver for receiving the signals sent out over said transmission medium, a plurality of receiving circuits associated with the different channels of said system, a receiving multiplex distributor for successively assigning the output of said receiver to different ones of said receiving circuits for a period of time to each receiving circuit equal to a fraction of the period during which each transmitteiis assigned to the transmission medium, switching means located between said last distributor and said receiving circuits for changing the connections of said receiving circuits to said distributor at such times and in predetermined manner to conform with the changing assignment of the transmitters to their associated leads, whereby the receiving circuit of each channel is associated only with the transmitter for the same channel.

9. A multiplex telegraph system in accordance with claim 8, characterized in this that the switching means associated with both the transmitting and receiving multiplex distributors are similarly arranged multi-bank rotary selector switches, the banks of each switch having its contacts interlaced in predetermined manner, said selector switches operating in synchronism, there being motor operated means provided for driving the distributors synchronously.

10. In a multiplex telegraph system, a transmitter for each channel employing a code having characters Composed of one or more signal units of fundamental time duration, means at each transmitter for reversing at `predetermined intervals the sense of the signals to be transmitted, said reversals in sense being arranged to occur only at the end of a unit length of signal constituting a component element of a character, rotating mechanisms for said transmitters, means for synchronizing the speed of said mechanisms, leads extending from a transmitting multiplex distributor to said transmitters, switching means associated with said leads and located between said transmitters and said distributor for assigning said transmitters at different times to different ones of said leads, a transmission medium, said distributor serving to assign said medium to said lines in succession and to each for a period of time equal at most to the longest period of which the duration of the fundamental time unit is an exact multiple of the number of channels.

l1. In a multiplex telegraph system, a transmitter for each channel employing a code having characters composed of one or more signal units of fundamental time duration, means at each transmitter for reversing at predetermined intervals the sense of the signals to be transmitted, said reversals in sense being arranged to occur only at the end of a unit length of signal constituting a component element of a character, rotating mechanisms for said transmitters, means for synchronizing the speed of said mechanisms,

leads extending from a transmitting multiplex distributor to said transmitters, switching means associated with said leads and located between said transmitters and said distributor for assigning said transmitters at different times to diierent ones of said leads, a transmission medium, said distributor serving to assign said medium to said lines in succession and to each for a period of time equal at most to the longest period of which the duration of the fundamental time unit is an exact multiple of the number of channels, a receiver for receiving the signals sent out over said transmission medium, a plurality of receiving circuits associated with the diierent channels of said system, a receiving multiplex distributor for successively assigning the output of said receiver to different ones of said receiving circuits for a period of time to each receiving circuit equal to a fraction of the period during which each transmitter is assigned to the transmission medium, switching means located between said last distributor and said receiving circuits for changing the connections of said receiving circuits to said distributor at such times and in predetermined manner to conform with the changing assignment of the transmitters to their associated leads, whereby the receiving circuit of each channel is associated only with the transmitter for the same channel, and means at each receiver operative in synchronism with the sense reversal means at the transmitter for the same channel for restoring the sense of the signals.

l2. In a multiplex telegraph system wherein signals are composed of marking and spacing elements of unit length and multiples of unit length, the method of rendering communication secret which comprises periodically reversing the polarity of the impulses corresponding to said marking and spacing elements, assigning signal impulses of one message at irregular intervals to different ones of a plurality of multiplex channels in the system, and assigning signal impulses of other messages at the same irregular intervals to the remaining ones of said channels.

HAROLD H. BEVERAGE. RICHARD E. MATHES.

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