US2401877A - Enciphering and deciphering system - Google Patents

Description

`une il, l946 R E MA1-HES 2,40L877 ENCIPHERING AND DECIPHERING SYSTEM Filed 0G13. 17, 1942 2 Sheets-Sheet l jim@ my w46- R. E. MATHEs ENCIPHERING AND DEGIPHERING SYSTEM 2 Sheets-Sheet 2 ATTORNEY v Filed Oct. 17, l942 Patented June 11, 1946 UNITED ST Richard E. Mathes, Silver Spring, Md., assigner to Radio Corporation of America, a corporation of Delaware Application October 17, 1942, Serial No. 462,355.

(Cl. 17g-22) 13 Claims. l

This invention relates to secret signalling systems and has particularly to do with apparatus and a method of enciphering and deciphering telegraph code signals so as to insure secrecy in transmission. My system is adapted for use in connection with any of the well-known code systems of telegraphy, as used for example, on radio channels and wire lines. The technique which I preferably adopt is somewhat similar to that which is disclosed in a copending application,

kSerial No. 444,658, ii'led jointly 0n May 27, 1942,

by Loyd A. Briggs and James A. Spencer, and assigned to the assignee of the instant application.

As will be pointed out in more detail in the description to follow, my system and my method are intended to preserve secrecy with respect to an enciphering or deciphering tape by locking the same in a sealed magazine. Such a magazine may be readily transported from place to place without permitting the messenger who handles the same to inspect or make copies of the tape. Furthermore, the tape is arranged to be kept concealed from the View of an operator who transmits and receives cryptographic messages.

In order to avoid the use of an excessively long enciphering tape While at the same time subjecting each baud element I the signal code combinations to the possibility of a random polarity reversal, I have found that such polarity reversals may be conveniently accomplished by supplementing the perforated tape controls with random polarit7 reversals to be derived from the operation of a plurality of cam-operated switches. The cams for such switches may have coded peripheries and the number of code elements in the periphery of one cam preferably differs from that of the other. The purpose of the cams, or coding disks, in combination with the encipheri-ng tape, is to provide such interaction that repetition of a given train of enciphering controls or polarity reversals will seldom occur.

Accordingly, it is an object of my invention to provide a cryptographic system for telegraph communications such that the signals as transmitted shall be substantially undecipherable by an unauthorized recipient.

It is another object of my invention to provide means including a magazine for completely enclosing an enciphering or a deciphering tape and for maintaining the tape concealed from vieW at all times, even while it is in operation.

It is another object of my invention to provide a combination of enciphering tape and enciphering code. disks, the cooperation between which is such as to produce long trains of essentially random reversals of signaling elements of a message train and, at the Same time, permitting the use of a relatively short length of enciphering tape.

Other objects and advantages of my invention will be made apparent in the description to folloW. This description is accompanied by drawings, in which:

Fig. l shows diagrammatically a circuit diagram and apparatus to' be used' at' a transmitting station; and

Fig. 2 shows a corresponding circuit diagram and apparatus to be used at a receiving station.

Referring to Fig. 1, I show therein a telegraph transmitting unit 'I which is usually termed a tape transmitting head by those skilled in the art. The transmitting head is driven at a synchronous speed by a motor 4 working through a one-point clutch 8. This clutch is preferably equipped with a magnetic control for remote operation to start the transmitter head and the code disks at a predetermined instant. Such a magnetic control is shown and described in the aforementioned application of Briggs et al.

The motor 4 is of a synchronoustype and is supplied with Valternating current from a synchronous drive amplifier 24. Control impulses for maintaining this amplifier in synchronism With a multiplex distributor are derived from a synchronous multiplex commutator 25, which will be understood to be mounted on the shaft of the transmitting channel distributor. The details of the circuit connections applicable to a synchronous drive amplier are not shown since they are fully illustrated and described in my Patent No. 2,194,509, granted March 26, 1940.

The coding tape 23 issues from a delivery reel 2S and is fed over suitable guide rollers 21 on the input and output sides of the transmitting head. A switch 2 operated by the tape slack, in a device shown generally at 28, controls the closing and opening of a circuit to a motor I9, the function of which is to rotate a Wind-up reel 30. The tape 23 issuing from the transmitter is thus fed (with occasional pauses) to the reel 30.

The two reel-s 26 and 3&1 are suitably mounted within` a sealed container or magazine 3|. This magazine has a lip'6 for egress of the tape from the loaded reel 26.

The shaft of the transmitter head i carries one of two clutch engaging members of the unit 8. This shaft drives a cam I I having preferably two steps on its periphery such that a lever 32 may be moved downwardly by tension of a spring 33 twice for each revolution of the shaft. Mounted on the lever 32 is a pawl 34 which is arranged to actuate a lO-tooth ratchet wheel 35 for feeding the tape intermittently and at one-tenth the normal speed for usual tape transmission.

The drive shaft for the transmitter head I is sufficiently elongated to carry two worms 36 and 31. Worm 35 meshes with a worm wheel 38 having a shaft in common with code cam 2. Worm 31 meshes with a worm wheel 39, the shaft of which also carries a code cam 3.

The peripheries of cams 2 and 3 are irregularly notched for random control of a pair of doublepole double-throw switches.v One of the switches is operated by cam follower 40 in association with cam 2. The other switch is similarly operated by cam follower 40a in association with cam 3. The gear ratio obtained by the worm 3G meshing with worm wheel 38 on the shaft of cam 2 is pref-- erably of the order of 50: 1. For cam 3 the worm 31 and worm wheel 39 have a ratio of say, 49:1.

This difference in gear ratios causes cam 2 to ro-V tate 49 times during 50 revolutions of cam 3. The peripheral contours of the cams are such as to operate the switches at times determined bythe baud frequency of the coded intelligence signals. Thus, if the raised and depressed peripheral arcs of the cams were to representmarking and spacing elements of Morse code signals, then such elements on the circumference of cam 2 would be commensurate with 100 bauds, and on cam 3, with 98 bauds.

By connecting the output terminals of `one switch to the input terminals of the other switch, a train of random polarity reversals is produced which does not repeat itself until cam 2 has made 49 revolutions.

The cam follower member 49 controls two movable contact springs a and b in a D, P. D. T. switch 8l. These movable contact springs are sandwiched between stationary contacts c, d, and e. Contacts c and e are both supplied with minus D. C. potential, while contact d is supplied with plus (-i-) D. C. potential from any suitable source. When the follower 40 drops into a depression in the code cam 2, contact a makes with contact c and contact b makes with contact d. When, however, the follower 40 rides over a tooth of the cam 2, then contact a makes with'contact d and contact b makes with contact e. The two positions of the contacts a and b, therefore, provide polarity reversals of the circuit connections which lead to stationary contacts of a D. P. D. T. switch 82 controlled by the cam 3.

Cam 3 operates follower 49a for controlling the positions of two movable contact springs f and g in switch 82. These contact springs are sandwiched between stationary contacts h, a', and k. The interconnections between the two switches 8| and 82 are such that contacts h and lc are connected to contact b, and contact y' is connected to contact a.

The combination of random controls of the two switches 8| and 82 by the cams 2 and 3 results in the application of a long train of random polarity reversals to the conductors 4| and 42. T hese conductors 4| and 42 connect respectively with back contacts m and n Vof a relay 45 whose armature-controlled contacts o and p normally engage with back contacts mand n, thus feeding the potential of conductor 4| to conductor 43 and the potential of conductor 42 to conductor .44, The front contacts q and r are used upon energization of relay 45 when it is desired to produce a phasing impulse once per revolution of the cam 3. Mounted on the same shaft of this cam 3 is a phasing cam 46 having one tooth 41 on its periphery.

In cooperation with the cam 46 is a follower 4B, the function of which is to actuate a reversing switch 49 which is similar in construction to the switches 8| and 82. The movable contacts in switch 49 are connected to front contacts q and 1', respectively in the relay 45. The stationary contacts inswitch 49 are supplied with plus (-i) and minus polarities as shown.

When relay 45 is energized by remote control, as by closing 'a switch 50 at the operators control station, then the switches 8| and 82 are rendered ineffective. A single polarity reversal takes place in response 'to the actuation of the follower 48 whenever it rides over the tooth 41 of the cam 46.

For the sake of simplicity-in tracing the circuits for polarity reversals, I have shown the several cam-operated switches las though comprising contact spring-pile-ups, where, each spring pile-up has its movable contacts actuated by a cam follower such as 4D and 40a. In practice, however, I have found it advantageous to utilize a so-called microswitch which has snap-acting contact elementsV therein. The switch operation is by means of a lever arm external to the contact housing. The lever aims correspond with cam followers 49 and 40a. Issuing from the switch housing are switch terminals for connection inY such circuits -as are shown and described heref inabove.

The code cams 2 and 3 are preferably settable by hand in a direction opposite to the direction of their normal rotation. VMeans (not shown) including aknob 5| and a ratchet mechanism for engagement of each code cam 2 or 3 with a hub on its shaft are provided for the purpose of setting the code wheels in a mutually xed phase relation, one to the other, before starting the transmitter. If desired, the knob can be arranged to engage with the ratchet mechanism only when pushed in. Furthermore, a convenient gear reduction may be provided ybetween the knob 5| and the cam shaft so as to bring the phasing to a proper setting with precision. ThisV setting may also be facilitated by alignment of a movable index point on the periphery of each cam with respect to a stationary indexpoint such as shown at the position 52.

A revolution counter I6 is driven by a star wheel riding in the center-hole perforations of the tape 23. This revolution counter is provided as a guide to enable operators at each end of the circuit to set up and restart at a common spot on the tape, if for any reason reception has been interrupted and synchronism lost. The wind-up relay 30 is coupled to and operated by a separate motor |9. This motor is controlled by a switch 20, preferably a microswitch, in response to variations in the tape slack. -The tape slack control unit 28 includes movable and stationary spools 29 for guiding the tape. The amount of slack in the tape as it issues from the transmitter determines the operation of the microswitch 20 for closing and opening the circuit of the motor 9.

The message tape transmitter A message tape transmitting head rBil is driven by a motor 6|, the power for which may bederived from a synchronous drive amplifier 62 Whose synchronism is maintained' by the aforementioned multiplex commutator 25. Within the transmiting unit El! is a keying device, or double-throw switch 63 operated by seeker pins under control ofi the message tapeperforat'ions. The stationary contacts of a tape-controlled polarity reversing switch 63 are connected respectively to plus (--l and minus terminals of the D. C. source. The vibratory tongue lin the switch i3 is connected to one terminal on the coil ci relay 32. The other terminal of this coil is connected to a grounded neutral point intermediate between the plus andv minus terminals of the D. C. source.

In'Y the transmitting head l a similar tape-controlled polarity reversing switch G4 is provided. Switch 6% also has stationary contacts connected with :plus and minus terminals or the D. C. source and a vibratory tongue connected through the winding of a polarized relay E5 to a grounded neutral point intermediate between the plus and minus potentials of thev D. C. source.

The tongueV of relay 32': follows the movements of the message tape-controlled switch 53 while the tongue of relay (35 follows the movements oi' switch unit 64 under control of the enciphering tape.

Impulses or brief duration are supplied upon each revolution of the commutator in a signal regenerator unit 1. These impulses originate at a grounded neutral potential and are fed to the tongue of relay 32 during a fractional part of each signaling baud time unit. Whether the signaling baud shall be characterized as a marking or a spacing element is determined by the position of the tongue oi relay 32.

The stationary contacts of relay s2 are normally connected through a manually operable switch 57 to the outer terminals oi two coils A and B of a keying relay @5. Positive or negative potentials are applied to the connecting link ESS between coils A and B, in dependence upon the coordination of polarity controls exercised by the enciphering tape and the cams 2 and 3.

The coils A and B are so wound that a positive potential applied to link G9 will move the relay tongue 10 to the right when it energizes coil A, and will move tongue lll to the left when coil B is energized. A negative potential so applied reverses the movements of the tongue lil. Hence the operation of relay 56 vlull depend not only upon the current polarity as determined by the enciphering end of the circuit, but also upon the marking and spacing conditions of the message tape, since the latter are reflected in the coil selection in relay EHS- whether coil A or coil B.

The resultant output from relay 66 is constituted as a plus or minus impulse, derived from the two stationary contacts of this relay. These impulses are fed to the tongue I0 and thence to a so-called transmitting kicker 1I which keys the signal output circuit. The kicker 'll is mounted on a synchronous commutator of the transmitting machine and times the eiective portions of signals from relay 65 in accordance with the synchronousr speed of the multiplex transmitting distributor. Relay 66 is supplied with plus and minus polarities on its two stationaryV contacts respectively.

Mode of operation In theory, the enciphering of messages by the use of' the apparatus hereinabove described is comparable with that of a system fully described and shown in the aforementioned copending application of Briggs et al. The marking and spacing elements of the message tape are at times transmitted as such, but when the vpolarities thereof. are reversed by the enciphering tape or by the code cams, then the signals are rendered unintelligible because of the random effects of these reversals. By the use of identical enciphering and deciphering tapes at the transmitting and receiving stations respectively and by the use of code cams 2 and 3 started insynchronism at the transmitting and receiving stations, the polarity reversals of the signals is made such that deciphering at the receiving stationis readily eiected, but otherwise the signals are substantially undecipherable;

The receiving apparatus Referring now to Fig. 2, the receiving apparatus comprises a magazine` 31a containing the deciphering tape 23a and cooperating mechanism, the same asshown and described in Fig. 1.

Also there are shown in Fig, 2 various elements of a deciphering unit including a transmitting head lf2, code cams 'I3- and- 74', and cam-operated switches l5 and i6, the same as in the'enciphering system of Fig. 1. The only difference between the arrangement at the receiving station and that at the transmitting station lies in the provision of certain phasing switches and an automatic starting device at the receiving station which are not needed at the transmitting sta-- tion. rhe starting and phasing devices for the receiving station are not herein described in detail since equivalent apparatus has beenA fully disclosed in the aforementioned copending application of Briggs et al.-

The incoming signals are applied to a locking circuit Tl whicltimayV be of any well-known type. The output from the locking circuit is normally connected across the winding of polarized relay '58. This'rel'ay has marking and spacing contacts associated with itsV tongue, the latter being impulsively grounded through a synchronously driven signal shaping commutator T9. One or the other of two winding circuits in polarized relay et is energized in dependence upon the position assumed by the armature of relay 18.

The references M and S, by' which the contacts of relay 'E8 are designated, refer to marking and spacing conditions to be assumed by this relay in response to incoming code signals.

Relay Sii has two windings which are respectively energizable by the marking and spacing contacts of relay i8. The interconnection between the two windings is normally connected through switch lSila to the tongue of relay 83. The marking and spacing contacts of relay 83 are connected to the output terminals of one cam-operated reversing switch 15. The other cam-operated reversing switch 1'5 has its input terminals supplied with positive and negative potentials. Conductors 84 connect each output terminal of switch 15 with one of the input terminals of switch 16, respectively.

The winding of relay S3, which is a polarized relay, is in circuit between the tongue of the tape controlled keyer switch B5 and ground. The stationary contacts of switch 85 are connected throughV suitable resistors 36 to the positive and negative power terminals respectively. This arrangement causes the tongue of relay S3 to follow the movements of the tape controlled keyer switch 85.

The cams 13 and 'M are manually settable to a predetermined starting phase, in the same manner as described above with respect to cams 2 and 3 at the transmitter. A phasing magnet 8'! is energized bythe operation of relayv 88 upon de'- pression of a key 89, and is unlocked at a precise moment by reception of a starting signal from the transmitting station. Relay 88 is self-locking and is unlockedupon breaking of its energizing circuit through the tongue and spacing contact of relay 80. The clutch members 8a are engaged upon release of magnet 81, thusY starting the tape unit 'l2 and the code cams 13 and 14.

VThe movablev member of switch 80 is connected to the marking contact of relay 8D. The tongue of relay 80 is connected through a resistor 9| to the negative terminal of a D. C. source for operating a recorder or printer, either of the latter being placed in service in accordance with the setting of switch 90. Observation of the signal response of relay 8D may be made by plugging a synchronoscope circuit into the jack 92. 'Ihis would be desirable when passing.

Deciphering of the cryptographic signals depends upon maintaining the deciphering tape in step with the enciphering tape. Also the code cams 'I3 and 14 must be properly phased with respect to the code wheels 2 and 3. The polarity reversals due to the use of the deciphering tape and the cams 13 and 14 are combined to determine the direction of current flowthrough one of the coils in relay 80. The sense of the received signals determines which of the coils in relay 80 shall be energized, and this nally determines the throw of the armature in relay 8i)r to one side or the other. Y

Recapitulation The method of coding is to reverse the senseviz, mark for space or space for mark-of the message signals. 'I'his reversal occurs at irregular intervals as called for by the coding key, but in no eventV can the message continue for more than, say ten dot lengths without the occurrence of a reversal.

The coding is accomplished by preparing paper tape of the type standard in the telegraph art. Decoding is done with an identical tape. The tape is to run through a standardV telegraph tape transmitter. The enciphering signals and message signals produce a coordinated effect in a polar relay such as to reverse the message signals when the coding transmitter is on mark but not when on space To conserve the amount of code tape required, the" coding transmitter is run at one-tenth the speed of the message transmitter. To retain the 'dot-by-dot coding feature above explained, code cams are provided which also reverse the sense of transmission on a dot length basis. Between them, these cams repeat only every 2450 dot lengths, although individually repeating about every 100 dot lengths. The reversing action of these cams is superimposed on the slower action of the coding transmitter with the net result of producing a non-repeating code while using one-tenth as much coding tape as otherwise required.

The enciphering device must beV drivensynchronously with the message transmitter. The decoding device must be driven from a phase-corrected source, also synchronously with the mes- *Y vals, said means includingv al cam-controlledl Y 8 switching device, and means vfor coordinating the effects of the two said transmitters and said means, thereby to produce a random interchange of signs of the mark and space signal elements issuing from the messagevtape transmitter.

2. The combination according to claim 1 and including means for maintaining synchronism between the operations of said transmitters and said pulse producing means.

3. The combination according to claim 1 and including means for sensing code perforationsin the tape of said message tape transmitter at a dot-unit rate per minute which is a multiple of the perforation sensing rate of said enciphering tape transmitter. Y,

4. The combination according to claim 1 and including means for sensing code perforations in the tape of said message tape transmitter at Va dot-unit rate per minute which is the same as that of said cam-controlled switching device.

5. In an enciphering and deciphering telegraph system, mechanism for producing pulses of different signs to represent the code elements of message characters, said code elements having marking and spacing characteristics of fixed baud unit length and Vintegral multiples thereof; an enciphering tape keyer including a perforated tape and means for sensing the perforations therein at a baud frequency rate which is an integral fraction of the operational rate of said pulse producing mechanism; cam-operated switching means jointly operable with said keyer for transposing the signs of said message pulses in a predetermined random mannerymeans for transmitting a train of signal impulses resultant from .the combined operation of said mechanism,Y

said keyer and said switching means; a receiving station, and deciphering means automatically fects of an enciphering device, relay means re-v sponsive to said signals, deciphering means in-f cluding a deciphering tape, a tape controlled double-throw switch, and cam-operated reversing switchk means jointly operable for duplicating the effects of said enciphering device, and responsive means operative under joint control of said relay means and said deciphering means for restoring the intelligence which would have been carried by said mark and space indications without interchange. Y

'7. Apparatus according to claim 6 and including an opaque housing for said deciphering tape and means for substantially concealing said tape from view while causing it to be utilized in the control of said double-throw switch.

8. In a secrecy telegraph system, a sending station, a code transmittery at said station for sending out mark and space signals, said transmitter comprising a perforated message tape, a

perforated enciphering tape, said tapes being cooperatively associated with tape-controlled switching means operable to select a predetermined polarity of potential for characterizing eachk mark and space signal, cam-controlled 'switching means for introducing further polare ity reversals into said characterization, a receiving station, and means at said receiving station for so transposing the characterization of said signals that the intelligence carried by said message tape is restored.

9. An enciphering system for transposing the marking and spacing elements of a telegraphic signal train in a random manner, said system comprising a message tape, an enciphering tape, means for reversing the polarity of the signal impulses, said means being operable under joint control of the two said tapes, cam-controlled means for subjecting said signal impulses to further polarity reversals, and means for effecting all polarity reversals in substantially fixed phase relation to the operation of a transmitting distributor.

10. In combination, for use in the enciphering system of claim 9, a pair of code-cams, a motor for continuously driving said cams, and transmission gears having such ratios that the phase relation between said cams changes at a relatively slow rate.

1l. In combination, for use in the enciphering system of claim 9, a pair of code-cams, a motor for continuously driving said cams, and transmission gears having such ratios that the phase relation between said cams changes at a relatively slow rate, said cams having a peripheral formation such that they cause polarity reversals to be produced by said switching means in synchronism with the signal impulses derived under control of said message tape.

12. In a deciphering system operative at a receiving station for restoring the original intelligence of a telegraphic signal train Which has been enciphered by the system of claim 9, a signal-responsive relay, a deciphering tape, a second relay responsive to control by perforations in said deciphering tape, cam-controlled means operative in conjunction with said second relay for further transposing the sense of the received signal impulses, and impulse-responsive means operable by said signal impulses, after successive transpositions by said second relay and by said cam-controlled means, for deriving said original intelligence.

13. In a telegraph system the combination of a transmitting station comprising message tape keying means, a rst cryptographic tape keying means, a first code-cam controlled keying means and an output relay operable in response to the coordinated enciphering action of al1 said keying means, a signal transmitter under control of said output relay, and a receiving station comprising relay means responsive to incoming signals derived from said transmitter, a second cryptographic tape keying means having a deciphering tape Which is a replica of the tape employed in said rst ycryptographic tape keying means, a second code-cam controlled keying means operable in synchronism with said rst code-cam controlled keying means, and a translating device operable in response to the coordinated deciphering action of said signal responsive relay means in conjunction with all of said receiving station keying means.

RICHARD E. MATHES.

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