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·SECRET MA <;~ ~!{;/~~v EXTRACTS FRCl! RESFARCH & DEVELOPMENT :) 

PROGRESS REP<m - JAr."1IARY 1947 ADMIRAUTY SIGNAL ESTABLISHD!I 

l~ It has been f'ouni tor D example that to g1 ve co.111111Unica.ti~n during 6a/, . ~ 

of' the 24 hours only med.ium powers are requind. For the .full 24 hours, 

. however, the powers necessary incr~ase J!'&pidl.y'. Again thft present Naval .. ' .. "" - requirements are tor telephol11' and automatic telegraphy, both of mich 

requin much higher poW"er.a than does the existing .form ot hand operated morse 

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signall.ing. It seems probable tram. the results or analysis made so tar that 

powers of about S·P (radiated) JJ&Y be needed to satis.f'7 the requirements I 

compl.etel,y. It is the opinion of many or the Starr that th~ requiremsnta in 

the future can best be met b7 a series or eq.iipnents operating within the . . 

frequency range 100 -· ll>O 11.C/s. One or the ruling factors in 11911' designs 

is that the ability to work with the Americans must be provided, and a 

mission has been to the USA to establish a canmon technical. .foundation on 

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which t~ future 1147 be built. The report ot this mission which is now returned. will ,shortly be available. 

AUTQlATIC TELmRAPHY . . For reasons or .propogation, long distance automatic telegraphy 11>rking. must 

be carried on in the part ot the high frequency comq.unicff.tion bard lying 

betwen tour and twent:r-one lllll!lgacyc.les. The congestion in. this band is such 

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that the m&ximum use must be made ot each .frequenc7 al1ocation. This can best 

be done by employ.ing the highest degree Ot frequency stabil1t7 that the 

present state at development will permit 1 and b:r using high k8;ving speeds or 

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mult1 .. channelling, ~ speeds~ and suitable tor direct printiDg because ot 1hl 

•chani.cal characteristics ot printing apparatus. Kulti-channelling is, howSECRtl . 

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Declassified and approved for release by NSA on 05-29-2014 pursuantto E.O. 1352a 
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ever, quite practicable and will be considered in some detail. We speak 

ot multi-channel time division and Jl.lUl.ti-channel frequency division. This 

f'ive unit code is 111.th minor variations in use as a standard teleprinted 

code in the USA, Great Britian and most Continental Countries and at the 

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Bermuta Telecommunications Conterence in November 1945 the f'iw unit code 

with atart--atop s:ynchronizing was recommen:led as the World's Stan:iard 

Teleiprinted. Code tor Radio and Land Liile Working. For tl'lese reasons it 

would be very difficult to produce an argument tor &nJ' other teleprinted code, 

but there is little doubt that it a tree choice of' code could be. made today, 

the six unit code. would be adopted in preference to the rive or seven unit. 

Using a six unit code 63 basic canbinations will result ( 6 spaces are not used 

as a combination). Also tor certain ld.nds of traffic such as stock market 

reports and the like where letters and numerals are mixed the speed of this 

code JD.a7 actuall.J' be faster (that is requiring a narrow bandwidth for a given 

speed of signal.ling than the normal f'ive unit code). Now a seven unit code 

is introduced because of' its ao called error detecting properties. Error 

detection finds its chief value in coded or ciphered messages where it might 

be spectcid to reduce thl number of corrupt groups that would otherwise have to 

wait for decoding or deciphering before a repitition could be requested. The 

error rate on the better class T"adio teleprinted networks is trequentl.7 less 

than one error in ten thoμsand characters, and the value of error detciction 

under these conditions is doubtful. For minor circuit a whare it is found 

impossible to obt1dn a lower rate an erro'.I"' detecting code "IOul.d be of advantage 

but would involve the use ot code converters ro~ the exchange ot trattic with 

other rou.tes. The admirality in common with aU other services is committed 

. for the next f;lve 79ars to the start-stop synchronizing arrangelDll!lnts on its 

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main track routes and this system is quite suitable tor normal book ciphering arrang•enta. Recentl.7, however, lll8D)" adT&ne9S have been .mde in 

machim or on-line clphering which opens up possibilities of' rapid tra.n&-

.mission of 'secret inf'omation by simply feeding plain language tape into a 

ciphering machine which delivers a ciphered t•pe read7 .,or tranamis sion. 

The converse operation being performed at the receiving end. It will be seen 

at once tha'b this system fits in admirably with the tape rel.q aysts b1it 

unt"ortlma.tely start atop synchronism cannot be used because of' the danger or 

mischaracters, which altho of no particular consequence in book ciphe;r might 

with on-line ciphering make ..U the information after the lost chara'Cter 

campletel)" indecipherable. 'fJ!here ei'ther ot the s1ftchronizing arrangements 

other thari the start 1ttop are used although the character itself' 11181' be lost 

its position in time is n~ted by the receiving apparatus ard it is this that 

the ciphering machiB req~res to know to enable the coding to b~ changed. 

A poss;:Lble compramiso would be to send the start atop code syncbronou.al.J' 

in which. case the advantage or 8111-Chronoua woning_ could be combined with the 

tlexibilit7 of' the start stop system tor the slight di~ad.vantage of a slower 

code than is absolutely necesaar,.. As tor the teleprinter proper it seems 

to have before it a very great tuture, tne ease with which a message in letter 

form. JDa7 be transmitted a.nd received am the facility with which copies mq 

. be taken make it the ideal form of canmunication wherever a record is required. 

In its essentials it is merely an fllttension of printing which has been with 

us for almost six hundred 19ara. Altho this article baa been given the broad , 

heading ot Automatic Telegraphy no mention has heen made ot the alteniatives 

to the teleprinter, mainly the hellacriber ard the various facsimile systems. 

These have been deliberatefy ignored because it is felt that while the1' 1181' 

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have a very extensive tactical. application in the tuture the7 are not well 

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auited tor long distance telegraphing signalling on account ot the relatively 

high baud rate requ1red, 

SPEECH SECRECY SYSTEMS 

The tact remains, however, that the original speech elements theJDSelves mat 

be trorusmitted :in some form and the7 1118.7 be capabl.fl of' being extracted. f'rom 

the scramble 'Without previous knowledge ot the code. In all interception 

ot scramble or part~all.y' scrambled speech the training and experience ot the 

interceptors are or the g:reatest importance. A practiced operator can oft.en 

extract scwe; sanst.f'ran the elements ot the transmitted speech, altho to a 

casual listener the signal appears to be a can.pletely unintelligible noise. 

An assea81D.ent ot the securit7 ot UJ7 speech scrambling system is a veey 

difficult process am 111.thout maldn,g a nuaber ot qual.ity:l.ng statemnts it is 

usually quite impossible to estimate how long an interceptor will take to 

obtain a knowledge or the contents of' scram.bled messages. Tlie most pessimiattc > 

ostil!late is obtained b7 assuming (1) t.hat the en91117 can :receive messages either 

directly or b7 :rel.&7 at Interception Stations provided with recording equipment assoclat.,d with all known cracking devices. (2) Spare no expense in 

material and man power to perfect these stations. (3) Capturtid appropriate 

rece;J.Ying ttquipment or that information from intel.ligenee sources baa allowed 

hi.Jn to conatrt1ct. it. Under tl\ese conditions onl.7 the system which makes UBfll 

of a number ot ditf'icult codea or 'Which uaes a non-repeating code can give 

8IJ1' usetul aecurit7 and the s79tem must ot course be proot against the possibility ot extracting the aenae ot the speech by partial descrambling without 

the use ot ttie proper code. Scrambling equipmnt under these conditions and 

given a security period ot at least some hours can certa.1nl.7 be built but its 

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bulk would probably preclude its use in ships except, for a few important 

radio circuits. For traffic of iJ!lllediate operational importance there is 

us'! tor a scrambling s19tem or a securit1 time or upwards or 15 minutes ard 

this appears to be within reaclt with moderately compact equipnP1nt which mi_ght 

for example be carried in an aircraft. The average security can be increased 

by the common methods of saturating the enem.y' s interception station with 

dUlllllll' trattic. It it can be assumed that the enemy will not use hi11 resources to deal with all such traffic the average seaurit7 mtf.7 be much better • . There will always be a risk, hoW8'Ver, that he 111&1 be torturate in quickly 

determining part of a code. They speak of inversion and the use or the "secret 

telephone". In this aytem the range or frequencies say 250 to 2500 cycles is 

reversed so tM.t. 250 c;ycles became a 2SOO, .300 becomes 24501 350 becomes 2400, 

eir. This system gives no security at all on the radio link, as it is only 

necessary' for an, eavesdropper to set his receiver hetrod1fte to 2'750 qclea 

to reimrert one of the side bands llhich then gives clear &Jl'ech to a mak b7 

the hetrodyne whistle and the other side band. The whist.le 111&1' be reduced by 

filtering. In the same class with inversion sometimes combined with it is the 

process ot shitting alt the speech. trequencie s up or down by constant aJDDWJt. 

This process again otters no real aecurit7, altho plain inversion and frequency 

shitt givea more measurable securit7 than when used alone, Both methods conform equal part.a of other more elaborate a7st.ema. For example both inversions 

in band shifts form PLrt.a of split band shirts discussed below and w:ith the 

addition of a time variation to the frequency shitt on the basis ot German 

devices developed at the Feuerstein Laboratories. The next systems of 

importance to be considered are those whiah emplo7 band splitting and scrambling as exempli~ied by the GPO modulator 2C developed. f'or Naval use in speech 

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control ouhtits, and from what has been said about it it will be clear 

that the long time security ot the 2C is negligible. An example or more 

complicated band scramblers are to be touni in the iell Tela phone AlA.2 and 

A3 equipnenta used on the London New York Circuits at Tarioua dates. Ir 

these systems beside the large number ot alternatives of automatic switching 

is provided to switch periodically tran one condition to another in a coded 

sequence which again is periodically changed. As a pr1.ma17 switcbing code 

allows tor 20 seconds on each condition interception can be ettected it the 

intercept.er keeps separate equip119nt aet up, etc. 

TIME DIYISION SCRAUBLING 

The best known ezam.plea ot this method of scrambling are the ~·eetem Electric 

TDS .machines or which Jllodel PF mq be taken as typical. In. this s;ystem 

the original speech is broken ll.P into successive elements on a time basis 

instead or into frequency band. The duration or each or these time elements 

is apnroximate].y' 40 mil. seconds and the scrambling consists in rearranging 

" the order in which the7 are transmitted. In the PF machine 20 such elements 

tom a cycle in the code used beside the order of the rearrangement of these 

20 elements. In the method ot time switching employed is the double series 

of 732 cod.ea available., giving about a halt million possible cod.ea, changeable 

by means or punch cards supplied b7 the machine. The security ot ttie syatm 

is not. classed as high as that of the mcdulated 2c. It is possible rran 

a recorded message am appropriate equipnent to discover the code used and 

subsequently a~ramble the message and any further Ol')ea made ldth the same 

code. M:ore recently V!estern Eleetric have designed an attachment t.o the PF 

equipment to provide continuous code changing over a long secondary cycle. 

It is no doubt that this considf9rabl.7 increA.ses the security and will result 

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in greatly increasing the time in scrambling and require the continuous 

use of the enemies decoding recourses. These methods or scrambling a:re 

exam.pl ified in the rnodu.la. ted type 90 now being developed b7 the G P & 0 on 

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an air administered contract tor common use of the senines. Th111 s7atem 

ie a combination or band scrambling and 'l'DS and it the speech ia first 

divided on a frequency basis into three bands which a.re the!' transposed with 

or without inversion accord.inf: to a code which changes five times in one 

c:rcle ot operations and then repeats. The resulting 15 speech elements comprising one cycle are then scrambled on a time basis so that in the final scramble 

:i..v one of the original elements can occuw a~.r one or the 15 positions, three 

in frequency d five in time beside possibly being inverted in frequency. 

The securit7 of this systeA could be classed as moderate. The MJ1111 required 

to determine the code for recorded sample has been estimated at 3 to 4 hours < 

to .ma:f ntain reasonable security. Tha poseibili~ies ot the vocoding in a 

speech secrecy syl!ltem. are well known in the U. s. where the vocoder orig:lnated. 

Poat war interrogations have shown that the Germans were all so tull;y aware 

ot its ad.vantages but the7 had not. completed developnent or their system at the 

end ot hoatilit7, In this count1"7 the GPO have undertaken the developnent of 

an experimental equipunt which 1lJ&7 also .fultill a requirement tor the war 

office. For the pulse t1P8 radio teletype; presumably similar to our pulse 

cade modulation equipnent. 

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