IN REPLY 

REFER TO 

, 

REF ID:AlP-iQ77 

WAR DEPARTMENT 

-

OFFICE OF THE CHIEF SIGNAL OFFICER 

WASHINGTON 

May 12, 1936 

MEMO re Joint Invention of a System and Means for En.cipheriJli 

an« Deciphering Magnetica~-Recoried Signals. 

1. Thia is to record the fact that on this date the undersigned conceived the invention described in the accompanying 

sketches, the object of which is to provide a system and means 

for enciphering and deciphering magnetica~-recorded signals, 

such as telephone conversations, radiotelegraph Morse code 

transmissions and the like, so as to insure privacy. 

2. It is agreed that the proprietary interests of each of 

the undersigned in such rights and benefits as may accrue from 

the invention are equal, to the extent of fifty percentum (5o%) 

for each. 

9,v;_ep.o ~_illiam .... F. ~~ Friedfuan - - - . 

Attached: 

Two sketches. 

@'pp roved for Release bv NSA on 09-11-2013 pursuant to E .0. 1352\3 
Arnpli"lier 

Spool 

Stee.I 

Modulator 

Tape.TRANSMITTER 

Rece\vin.9 ....._ __ 

Amplifier 

Steel 

Tape 

o' c' s' -- 4·"" .... lmpyess1!' Ma,9nets 

RECEIVER 

.__ ___ +-I 

S=Se.cYe-f La".9ua'je. 

P= Pld1n Lan_9ua9e. 

output 

Amplit\e .. 1--.......... -

Feed Back 

Outp11t. 

SYSTEM AND MEANS FOR ENCIPHERING AND DECIPHERING 

MAGNETICALLY-REGOROEO SIGNALS. 

Trar.Lmittlng end: lleetric11l oscillations corresponding to input sigr.ala are recorded msgneticall7 on a movin,g metal tape, the ta~e passing s'llcceseivel7 between the paired impressi1:g magnets ABCD which are in 

aeries. Thua, the final or resultant megnetization of the tape correspond& to a cequence or block1 or 

alt;ebraicall7 sUperin.posed rreq•.ienc:!.es representable by the sequence .A., .AB, ABC, .ABCD, BCDE, CDE1, ... , the 11A11 block coming at the head ot the train. lhen the record h paued between the paired reading magnets at 

2, eil'tlals corres~onding to the resultant masnetization are emitted or tr~nsmitted. These are enciphered 

11b:n11lt. 

/ 

P.e~eiving end: The impreaeing gsgneta, 3, record the received signals l'l!lgnetically on a metal tape moviric ~t 11p~!"'JximPtely the s11me rate of speed as at the transmitting end, The record pa1ses between the paired m~r.nets 8t 11, The magnet A' i• a reading magnet and its output is led to the amplifier, where part or the 

energy is tr8nslated into final output, and part is fed back into the impressing macnets B', c•, and D•. 

The.electrical circuits are such 11s to cause the feed-back alternations impressed on B', 0' and D' to be 

of onnosite i:>h11Re from the alternations fed by A' into the 8DfPlifier, This results in neutralizing and 

removinr, the homolo~us mar,netic equiTelents on the tape, leaving only the original ~lain lant:Uege on the 

t&ne when it reaches Ciec,net A1 • The signal• at this point are deciphered signals. The Cl'l'Ptcgranhic prin- Qiole consist• in micrometricall7 varying the distances between magnets A, B, C, and D an~-maKi~ homologous micrometric adjustments or the dlstanees between MBl?r!Pt• .A. 1 , B', c• and D', the VG.riationa beinc 

determined b;y prePrranged Cipher ke79, ··.,h_ . . J _ & ('} • fl 

u~ /r.,o{}I .(., ... ! ~ iD ·f'"ri 

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