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March 29, 1949. , . 

W. F. FRIEDMAN ET AL - 2,465,367 

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SYSTEM FOR ENCIPHERING FACSIMILES 

Filed March 12, 1943 

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@'pp roved for Release by NSA on 08-12-2014 pursuantto E .0. 1352a 
REF ID:A362761 

Patented Mar. 29, 1949 2· 465 36·7· 

' ' 

UNITED STATES PATENT OFFICE 

2,465,367 

SYSTElI FOR ENCIPHERING FACSIMILES 

William F. Friedman, Washington, D. C., and 

Joseph 0. Mauborgne, Red Bank, N. J. 

Application ~larch 12, 1943, Serial No. 478,868 

'7 Claims. (Cl. 178-5.1) 

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 

1 

The invention described herein may be manu- factured and used by or for the Government for 

governmental purposes, without the payment to us of any royalty thereon. 

This invention relates to a system for secretly 

communicating by means of facsimile transmission. 

In other words, by means of our invention, a message in written, printed or picture form is 

transmitted, under the control of a screen or camouflage element, to another station at which 

the transmission is received and reproduced un- der the control of a duplicate of said screen or camouflage element. These screens or camou- flage elements interrupt the transmissio~1 in an irregular or unpredictable manner which renders 

derivation of the intelligence contained in the 

transmission by unauthorized persons difficult, 

if not indeed impossible. 

More specifically, it is an object of our invention to provide a facsimile transmission system 

having a transmitting means provided with a balanced bridge circuit. The mes.;;age to be transmitted causes variations in the ft.ow of electricity 

in one branch of this bridge circuit. Any arbitrarily selected screen or control element causes variations in another branch of this bridge circuit. These two branches are connected together so that equal and opposite potentials are established across the circuit of an electric lamp whose 

output therefore varies whenever the voltages of 

these two branches are not substantially equal. A 

transmitter is mounted under the control of the 

output from said lamp. At the place to which 

2 

In the drawings, Figures 1 and 2 are circuit 

diagrams with parts shown as blocks and designated with appropriate labels. 

In that embodiment ·Of our invention selected 

5 from among others for illustration in the dra.wings and description in the specification, our device is shown as comprising an electric lamp I 

which serves as a source of light, the light being 

concentrated by means of lens 2 upon the mes- 10 sage sheet 3, which is to be transmitted. This 

message may be in an opaque form, such as on a. 

sheet of paper, to reflect the light falling thereon, or in a transparent form, such as a film, to allow 

the light to pass therethrough. In either event, 

15 the reflected or transmitted beam of light, varied 

in accordance with the white and black portions 

of the ?4essage, falls on a light-sensitive cell 4, 

such as a photo-electric cell. Cell 4 is connected as part of an amplifying circuit, generally indI20 cated by block .5 since any well-known type of 

amplifying circuit may be employed. 

A second electric lamp ·6 forms a second source of light formed by a lens 1 into a beam directed 

upon a screen <Jr control sheet or element 8, whieh 

25 may be any arbitrarily sciected pattern having 

relatively light and dark portions, such as a writing, print, drawing or ranuom arrangement of 

dots. 

Relative motion is prnvided between lamp f 

30 and message 3 and between lamp 6 and control 

8 so that the beam emitted by each of said lamps 

falls upon and scans the message and the control, 

respectively, in a manner well known in the art 

of facsimile transmission. 

The beam of light varied 1by contrnl element <8 

falls on a second light-sensitiv:e .cell connected as part of an .amplifying circuit identified by the genera~ reference character IO. 

it is desired to transmit the intelligence, a re- 35 ception means is located, provided with a second 

balanced bridge circuit. A receiver in communicat:on with said transmitter causes variations in 

the ftow of electricity in one branch of the sec- ond bridge circuit. A duplicate of said screen The outputs of the amplifying circuits 5 and IG 

40 are oppositely connected as ·the arms .or branches 

11 and 1.2 of a balanced bridge circuit having .a 

diagonal or cross wire .13 connected to the .terminals of a third .electric lamp .14.. Amplifying 

circuits 5 and IQ hav.e as their output a pulsating 

or control element causes variations in another 

branch of this second bridge circuit. These two 

branches of this second bridge circuit are con- nected together so that equal and opposite 

potentials are established across the circuits of an output electric lamp whose output therefore 

varies whenever the output voltages of these 

branches of this second bridge circuit are not 

substantially equal. A light-sensitive element, 

such as a photographic film or the like, is located so as to receive and record the variations in the 

output of said output electri:: lamp in the form 

of a facsimile of the original message. 

For a further description of our invention ref- erence may be had to the annexed drawings and 

spec:fication, at the end whereof the novel features of our invention will be specifically pointed 

out and claimed. 

45 direct current .of constant polarity and ar.e .c.on- nected so .that equal and opposite p.o_ten.t!aJs are established across lamp 14 by the signals transmitted under the control of message 3 and.control 

8. Lamp II! is sens!tized by a local battery 15 

50 regulated by adjmtable resistor 16. 

Lens 11 concentrates the light. from lamp ! 4 

into a beam directed upon a third light-sensitive 

cell 18 forming part of a c'rcuit including an amplifier 19, _a transmitter 20, and an output ele55 mer:t, such as an antenna 21, or the terminals of a wire transmission system. 

At the location or p'.ace at which the message 

is to be received, there is provided a receiving 
REF ID:A362761 

a,463,367 

3 4 

member, such as antenna 22, as shown, or the op- exist. That ls to say, when there ls present in 

posite terminals of the wire transmission system. output circuit 33 a pulse corresponding to either 

A receiver 23 with an amplifier has its output a black or a white spot in the original message 

connected to a lamp 24 which is energ:zcd by a 3 and there Is simultaneously present in output 

local battery 25. Lens 26 concentrates the light 5 circuit 34 a pulse corresponding to a spot of the 

from lamp 24 upon llght-sensitive cell 41 form- oppasite hue in the duplicate control 30, a varlaing part of a circuit including a third amplifier 21. tion in the light output of lamp 36 occurs. ConAn electric lamp 28 emits light which is beamed versely when the simultaneous impulses present 

by lens 29 onto a screen or control element 30 in the output circuits 33 and 34 correspond to 

which is a duplicate of control 8. Relative move- 10 spots of like hue in message 3 and duplicate con- ment is provided between lamp 28 and duplicate trol 30. no variation takes place in the output " 

control 30 so that exact synchronism is main- of output lamp 36. These variations of the outtained between the scanning of controls 8 and 30. put of the light from lamp 36 expose the photoThe light from source 28, reflected or transmitted graphic element 40, spot by spot as the element 

by duplicate control 30, is passed to light-sensitive 15 is scanned, and thus reproduce the original mes- cell 31 forming a part of a circuit which also in- sage 3. 

eludes an amplifier 32. The output circuits 33 We do not intend to be limited save as the 

and 34 of amplifier circuits 21 and 32 are con- scope of the attached claims may require. 

nected as arms or branches1of a second balanced We claim: 

bridge circuit having a diagonal or cross-wire 35 20 1. Means for secretly transmitting pictorial lnwhich connects to the terminals of a third output formation, said means comprising, a scanner electric lamp 36 energized by local battery 31 arranged to scan and reproduce a pictorial mes- under the control of adjustable resistor 38. The sage as a series of electric impulses of varying 

light output of lamp 36 is collected by lens 39 and intensity, a screen having varying partions, a falls in a beam on recorder 40 which may be any 25 second scanner arranged to scan and reproduce 

light-sensitive device such as a photographic plate the variations of said screen as a second series or film. Relative movement is maintained be- of electric impulses of varying intensity, an electween lamp 36 and recorder 40 in exact syn- tric light connected across the output circuits of 

chronism with the relative movement between said scanners so that its output varies in intenlamp I and message 3 so that recorder 40 repro- 30 sity when the potentials across said output cirduces identically the message 3 as varied by con- cults are not equal, a photo-electric cell mounttrols 8 and 30. ed so as to vary in response to the output of said 

The operation of our device ls as follows: Mes- light, a transmitter connected to emit signals 

sage 3 is scanned by the beam of light from lamp in accordance with the variations of said photo1 and produces variations in this beam depend- 35 electric cell, a receiver arranged to receive the 

ing upon whether or not the portion of the mes- signals emitted by said transmitter and having 

sage which intercepts the beam is black or white. an output potential varying in accordance with 

These variations are transmitted by cell 4 and said signals, a second screen duplicating said 

amplified in circuit 5. Control 8 varies the beam first mentioned screen, a second receiver havof light from source 6 and affects cell 9 and cir- 40 ing an output potential varying under the con- cuit I 0 in the same way. Since the output volt- trol of said second screen, another electric light 

ages of circuits 5 and I 0 are balanced against connected across the output circuits of said re- each other there is no change In the output of ceivers so that its output varies in intensity when 

lamp 14 unless there ls a difference between these the potentials across said output circuits are not 

output voltages in the arm or branch circuits 11 ,1;:; equal, and a light-sensitive element mounted so as and 12. In other words, of the four possible to be rcanned and to record the variations in inconditions of message 3 and control 8, two con- tensity of said other light and to thereby record 

ditions cause a variation in the output of lamp 14 the message. 

and two conditions cause no variation in the out- 2. Mean=. for secretly transmitting pictorial input of lamp 14. These conditions which cause a 50 formation. said means comprising. a scanner ar- variation occur when the spot of message 3 on ranged to scan and reproduce a pictorial message 

which the beam of Ught falls ls black or white and as a series of electric impulses of varying lnthe simultaneously exposed spot of control 8 is the tensity, a screen having varying portions. a second reverse. The conditions which cause no varia- scanner arranged to scan and reproduce the 

tion occur when the simultaneously exposed spots 55 variation~ of said screen as a second series of elecof message 3 and control 8 are of the same hue. tric impulses of varying intensity, an electric 

The variations in the intensity of the light light connected across the output circuits of said 

emitted by lamp 14 cause pulses or oscillations scanners so that its output varies in intensity 

in the circuit containing amplifier 19 and trans- when the potentials across said output circuits are 

mitter 20. These pulses or oscillations are sent 60 not equal, a photo-electric cell mounted w as to 

to receiver 23, where they cause corresponding vary in response to the output of said light, a variations in the light emitted by output lamp transmitter connected to emit signals in accord24 and, therefore, in the output of the circuit ance with the variations of satd photo-electric 

containing the third amplifier 21. Simultane- cell, a receiver arranged to receive the signals 

ously with the scanning of control 8, duplicate 65 emitted by said transmitter, a second electric 

control 30 causes variations of the beam of light light connected to said receiver so that its outfrom source 28, which variations actuate cell 31 put varies in intensity in accordance w1th th'! <'!<rand appear in the output circuit 34 of the circuit nals received by said receiver, an amplifier circuit 

containing the fourth amplifier 32. Lamp 36 including a second photo-electric ce1l responsive 

is mounted across the output circuits 33 and 34 70 to variations in the intensity of the output of said 

of the circuit containing third amplifier 41 and second electric light, a second screen duplicating 

fourth amplifier 32 respectively. Because the said first mentioned screen, a second receiver havvoltages of output circuits 33 and 34 are equal ing an output potential varying under the con- and opposed, the light emitted by lamp 36 varies trol of said second screen, a third electric light 

only when two of the four possible conditions 75 connected across the output circuits of said re-
REF ID:A362761 

12,460,367 

5 

ceivers so that its output varies in intensity when 

the potentials across said output circuits are not 

equal, and a light-sensitive element mounted so as to record the variations in intensity of said third 

light and to thereby receive the message. 

3. A transmitting and receiving system for 

secretly communicating messages in pictured 

form in which there is provided, a first electric 

circuit constructed so as to emit a direct current 

voltage which varies in response to the variations 

in light transmission of a sheet bearing a message, 

a control element having portions of varying 

light transmitting characteristics, a second electric circuit constructed so as to emit a direct 

current voltage which varies in response to the 

variations in light transmission of said control 

element, a transmitter mounted under the con- trol of said circuits so that the transmitter emits a signal only when the output voltage of one of 

said circuits differs from that of the other, a receiver tuned to respond to signals emitted by 

said tram:mitter and to provide an outp'.lt varying with said signals, a second control element 

substantially identical to the first mentioned 

control element, a third electric circuit constructed so as to emit a direct current voltage which 

varies in response to the variations in light transmission of mid second control element, a light 

emitter mounted under the control of said re- ceiver and of said third electric circuit and arranged so that the light emitted thereby varies 

only when the voltage output of said receiver 

difl'e1·s from that of said third circuit, and a recording device located so as to record the vari::Ltions of the light emitted by said emitter and 

thus to reproduce the message. 

4. In a secret facsimile communication system, 

a balanced bridge circuit having an output element supplying an output varying in response to 

the output of an amplifying circuit controlled by 

the message to be sent and to the output of a second amplifying circuit controlled by a screen, means for balancing the outputs of said amplifying c!rcuit against each other so that there is no output from said bridge circuit except when there 

is a difference between the outputs of said amplifying circuits, a transmitter having an output 

element supplying an output varying in response 

to the output from said bridge circuit, a second 

balanced bridge circuit having an output element supplying an output varying in response 

to the output of a third amplifying circuit con- trolled by a receiver controlled in turn by the output from said transmitter and to the output of a fourth amplifying circuit controlled by a duplicate of said screen, means for balancing the outputs of said third and fourth amplifying circuits 

against each other so that there is no output 

from said second bridge circuit except when there 

8 

screen, a second amplifying circuit including said 

second cell, a lamp connected scross the outputs 

of said amplifying circuits so that the light 

emitted thereby varies when there is a difference 

5 between the outputs of said amplifying circuits, 

a third light-sensitive cell arranged to receive 

light from said lamp and to cause variations in consonance with the variations in said light, a transmitter connected in circuit under the con- 10 trol of said third cell so as to vary its' transmission in consonance with the variations effected by 

said third cell, a receiver in communication with 

said transmitter, a second lamp connected to 

vary in consonance with the variations in output 

15 of said receiver, a fourth light-sensitive cell ar- ranged to receive light from said second lamp, a third amplifying circuit including said fourth 

cell, a third source arranged to emit a beam of 

light, a duplicate screen located so as to vary 

20 said beam of light from said third source as varied by said duplicate screen, a fourth amplifying circuit including said fourth cell, a third 

lamp connected across the outputs of said third 

and fourth amplifying circuits so that the light 

25 emitted thereby varies when there is a difference 

between the outputs of said third and fourth am- plifying circuits, and a light-sensitive device ar- ranged to receive light from said third lamp and 

to record the variations of said light in the form 

30 of the original message. 

6. In a facsimile privacy apparatus, a first device for scanning a subject, a lamp associated 

with said device the intensity of its 1llumination 

being varied responsive to the output of said de35 vice, a second device for scanning a subject con- currently with the first device the output of said 

second device acting on said lamp to vary the 

intensity of illumination thereof, and light sensitive means for providing a signal responsive to 

40 the illumination of said lamp. 

7. In a facsimile privacy apparatus, a first device for scanning a subject, a lamp associated 

with said device the intensity of its illumination 

being varied responsive to the output of said de45 vice, a second device for scanning a subject con- currently with the first device the output of said 

second device acting on said lamp to vary the 

intensity of illumination thereof, light sensitive means for providing a signal responsive to the 

50 illumination of said lamp, another lamp and means for varying the intensity of its illumination in response to the output of said light sensitive means, another light sensitive means responsive to said other lamp, means for effectively sub55 tracting from the output of said other light sensitive means a signal equivalent to the output of 

said other device, and means for graphically re- cording the result. 

is a difference between the outputs of said third 60 

and fourth amplifying circuits, and a recorder 

responsive to the output of said second bridge 

circuit to furnish a facsimile of said message. 

WILLIAM F. FRIEDMAN. 

JOSEPH 0. MAUBORGNE. 

REFERENCES CITED 

The following references are of record in the 

5. A system for secret communication compris- flle of this patent: ing, a source arranged to emit a beam of light, a 65 

mesrnge located so as to vary said beam of light 

from said source, a light-sensitive cell arranged 

to receive said beam of light from said source as varied by said message, an amplifying circuit including said cell, a second source arranged to emit 70 

a beam of light, a screen located so as to vary said 

beam of light from said second source, a second 

light-sensitive cell arranged to receive said beam 

of light from said second source as varied by said 

UNITED STATES PATENTS 

Number 

1,310,719 

1,312,574 

1,657,366 

1,763,358 

1,868,967 

2,066,261 

2,300,664 

Name Date 

Vernam ------------ July 22, 1919 

Pierce ------------- Aug, 12, 1919 

Belin ------------- Jan. 24, 1925 

Jenkins ---------- June 10, 1930 

Cartier ------------ July 26, 1932 

Finch --------------Dec. 29, 1936 

Francis ------------ Nov. 3. 1942