UNCLASSIFIED AD NUMBER ADA800206 CLASSIFICATION CHANGES TO FROM unclassified secret LIMITATION CHANGES TO Approved for public release unlimited distribution FROM Distribution authorized to U S Gov't agencies and their contractors Administrative Operational Use OCT 1944 Other requests shall be referred to Office of Scientific Research and Development NRDC Div 13 Washington DC AUTHORITY Secretary of Defense memo dtd 2 Aug 1960 Secretary of Defense memo dtd 2 Aug 1960 THIS PAGE IS UNCLASSIFIED S G OVERN MENT IS ABSOLVED FROM ANY LITIGATION WHICH MAY ENSUE FROM THE CONTRACTORS IN FRINGING ON THE FOREIGN PATENT RIGHTS WHICH MAY BE INVOLVED WRIGHT FIELD DAYTON OHIO ARE MISSING IN ORIGINAL DOCUMENT I 7 SECRET NATIONAL DEFENSE RESEARCH OFFICE OF SCIENTIFIC T' o DIVISION COMMITTEE RESEARCH AND 13 _ DEVELOPMENT SECTION___ OEMsr - 435 FINAL REPORT ON PROJECT C 43 Continuation of Decoding Speech Codes PART I - SPEECH PRIVACY SYSTEMS- INTERCEPTION DIAGNOSIS DECODING EVALUATION THIs DOCUM ENT CON- ALNS ILNFORMATION AFFECT- ING THE NATIONAL DFVSE OF TIM UN Tr STATES WrTrIN THE MEANING OF THE ESPIONAGE ACT U S C 50 31 AND 32 MrsTrLANSMIMON OR THZ REVELATION OF rr3 OONTENoS oN ANY ' ANXER TO AN UNAUTHORJW PERSON IS PROHIBITED BY LAW S R D NO - SECTION 1 0 COPY NO 42 DAT Oct 12 1944 BELL TELEPHONE LABORATORIES INCORPORATED NEW YORK N Y SECRET Communioations Division National Defense Research Committee of the Office of Scientific Research and Development Section 3 Division 13 flNAIT REPORT ON PROECT C-43 Continuation of Decodinma Speech Codes PAKT I SPiCHE PRIVACY SYSTEMS INTIRCdoIMON DIAGN'OSIS DICODIVO EVALUATION October 12 1944 I SECRET Ol r-435 Contract No Contractor Western Aleotrio Company Inc 120 Broadway New York 5 N T Project Supervisor C H G GRAY Teohnical Report Prepared by W KOVfoG BILL ToLAPEON3 LABORATORIlS INC 463 West St New York 14 N T 4 TABLE OF CONTNTS EiSTORY oF PROacT 1 ZUTRODUCTION TO 2 TEGSICAL WORT CaA PTE I - INoC 7TI0 1 1 Types of Radio Systems 3 2 Intercepted Signal Quality 3 3 4 Reoeiving Sets Types of Radio Transmission 4 4 5 Reoordin 5 6 Decoding Tools 6 ORA MR II - THE SO E0TO0RAPR 1 History 7 2 Operation 7 3 Level Comprussion 11 4 Possible Inproversts 11 S Amplitude Representation 14 C11APR III - SPISCH'SCML YMT1 15TIOflS 1 Systems Involving Single Ucaulation 15 2 Systems Involvin 16 3 Triple Modulation - Reentrant Band Shift 17 4 5 Band-splitting Systems Tine Division Lultiplex 17 18 6 Systems Using Tape Recording 19 7 8 Co binations of Tine and Frequenoy Scrambling Wave Form Lodifioation 21 22 9 Masking Systems 22 10 Voooaer Systems 24 11 Channel Liuzng Systems 24 12 Summary 26 CHAPTER IV 1 'easurezents 2 3 o i-- Double Modulation - DIAOGT0SIS OF U1TE'rTF on Speotrograze Illustrations of Soranbled Speech Systems Not Illustrated II S-SYSTEM 27 27 30 tilL - -- -- 'TABIZ Q C01 T 3TS Contid 4 secCU R 7 - set ONGRYPTNOWEo C TOOLS AND O oTHOS or Yunotional Equivalent 33 1 Captured 2 Compromise Deooding Methods 34 3 Automatic Decoding 37 CEAPMTR VI - CRYPTOW APHIC TOCIS AND LZMT I S a Program Determination Matching Spectrograms 41 41 3 Latohing Variable Area Patterns 47 4 Matohin 47 5 indicator Methods 49 6 Application to Table 1 52 7 Determination of the Uessage 54 Osoilloarams CHAPTEBR VII - PRACTICAL BVALUATIO0 OP PRIVACY SYSTMIX 1 Cracking Tim 37 2 ilonrepeated Code Systems 57 3 Code Ansalyss a8 4 Yield Evaluation 58 TABIL I - SPZBCH SCAULING DMCXS 2AlLE II TABlLE III 103 NONCRYPTOGRAPHIC DECODING IMMMS - LIST OF PRELIUIQY REPO3 II- IN PART 105 APPENIX 106 LIST OF ILLUSTRATIONS Figure 1 D-165529 Sound Spoetrograph 8 2 Illustrating the Operation of the bound Speotrograpt 9 3 Spectrograws of Normal Speech 10 4 Amplitude Representation by Dot Spacing 12 5 Amplitude Representation by Contours 13 6 Modulators 15 7 Single Modulation 16 8 Split Phase Multiplex 16 9 10 11 12 Double Uodulation Reentrant Inversion One 7orm of Split Band Systea One Form of Tias Division Uultiplex 16 17 18 19 13 Variable Subband Delay 20 14 One Form of Time Division Scramble 20 15 Speed Wobble 21 16 Time Inversion 21 17 Wave Multiplication 22 18 Level Modulation 22 19 Subband Level Modulation 23 20 Noise Masking Using Two Channels 23 21 Masking Noise Applied at Receiving End 23 22 23 vocoder Systex Channel Mixing 25 25 24 Subband Channel Uixins 26 25 Calibration of Spectrograph Soales 28 26 Tine and Frequency Measurements 29 27 Illustrating Aided Tracking 33 28 Band Shift Filter 34 29 Variable Bartd Paso Filter 34 30 Peak Choppers and Compressor 35 31 Rectifiers 35 32 Illustrating Action of Rectifier 35 33 One Forn of Superposition Decoding 36 34 35 Directional Disorimination 37 Automatic Decoding - Total Eneruy 37 36 Sidebands 37 in Two Position Displace ent System Automatic Decoding - Energy Frequency Distribution 38 38 Matohing Speotrograph Patterns of Hoarepeated Code TDS 42 IV 37 LIST OF ILLUSTRATION S Cont'd Figure 39 Illustrating Inversion of Time and Frequency Scales in $Spaot rorama 43 40 Matohina Spectrograph Patterns of Two-dimensional Scramble 44 41 Latohing Variable Area Patterns of Nonrepeated Code TDS 46 42 43 Osaillographio Traces of Vocoder Channel Signals Showing Effect of Rectification on Normal and Band Shifted Speeoh 48 44 51 46 Band Shift Detector Adaptation of Spectrograph for Decoding Switched Split Band Scramble Illustrating Repeated Code Lultiplication Systes 47 48 Illustrating Uodulation Sidebands Sinple Inversion 81 683 45 S49 50 51 53 Alternate Inversion 65 50 Fixed Displaoement 67 51 Wobbled Displacement 69 52 Reentrant Inversion 71 53 54 Fixed Split Band Soranble 73 Rapidly Switohed Split Band Scramble - Ixample 1 75 55 Rapidly Switched Split Band Scramble - Example 2 77 56 Tine Division Multiplex 79 57 Tim Division Uultiplez with Noise Ohanal 81 58 Subbands Variously Delayed 83 59 60 Time Division Scranmbling TDS Combination of TDS and Rapidly Switched Split Band 85 87 Scramble 4-o % 61 llonsynohrnnoue Combinations of TDS and Split Band Scramble 89 62 Test for Two-dimonsional Scramble 91 63 Speed Wobble 93 64 Baokwards 95 65 Ulultiplioation 97 66 Time Division Channel UIxing 67 Subband Channel Uixing o 99 101 RISTORY OF PROTECT a This report covers work carried out for the National Defense Research Committee under Contract No O Mer-435 with the Western Electric Company Laboratories Iny Ina by the Bell Telephone pro-ided with suitable equipment and could ohtain trained personnel Based on the needs of the military this project was thrice extended Under the guidanee of the Subsection on Speech Secrecy Seotion 13 3 of N D R C the Early in October 1940 there was set up in the Communications Division of IT D R C a subcommittee on Speech Secrecy This group was to consider both the sorambling and unscrambling of telephone signals It was soon recognized by thea that the decoding problem was of primary importance both as a means for evaluating privacy systems for possible use by the Services and for decoding possible enemy signals Rualizine that the ear has very limited capabilities for anslyzing scrambled speech Mr R K Potter invented the sound speotroaraph to provide speech patterns which could be interpreted by the eye Early in 1941 a rouGh laboratory model of the sound spectrograph became available in Bell Telephone Laboratories Inc Throujh Dr 0 S Buckley chairman of the Speech Secrecy Section of N D R C arrangements were made for a demonstration of the sound spectroGraph to various N D R C representatives including Dr 7 Bush emphasis was placed at any given time on what was deemed to be most urgent This is reflected in the subject matter of the Preliminary Reports which were issued from time to time and which form the appendix to this report In addition to the specific investigations covered by these Preliminary Reports much work was carried on as the basis for more general coverage of the field of interception diagnosis decodina and evaluation of speech privacy systems described As a result of the above demonstration and subsequent Committee action Project C-32 the forerunner of Project C-43 wae organized in the fall of 1941 with the immediate objective of producing a sound speotrograph in such form that it would be useful for diagnosing and decoding speech sorambling systems In Projest C-32 Privacy Cracking a finished model of the sound spectrograph was constructed and its applioation to decoding work was successfully demonstrated to representatives of the Army Navy and V D R C Upon the termination of C-32 on February 1 1942 it was decided that the work initiated under that project should be continued Accordingly Project C-43 Continuation of Decoding Speech Codes was authorized for one year effective February 2 1942 The project anticipated some routine decoding the production of duplicate equipment to be used by the Army and Navy intelligence servioes and further studies of decoding tools and methods At that time the Army and Navy military officers were relying almost entirely upon this project to furnish the above services until they could be mentioned above dedodint equiptent was developed ded to the equiment dvlp andmoneae no dels furnished Army andwas lavy This decoding equipment included 1 two models of the sound spectrograph 2 a variable area pattern machine and 3 equipment for decoding two new enemy privacy systems intercepted by the project personnel at Point Reyes California In each case Army and Navy personnel were instruoted in the operation and maintenance of these equipment s Interceot activities of the project personnel included 1 the study of recording submitted early in the project by the Federal Cozzunications Commission 2 ezploratory work at the Bell Telephone Laboratories experimental radio reoeiving station at Holzdel New Tersey and 8 exploratory work and routine interception of radio telephone transtissiour at the American Telephone and Telegraph Co radio receiving etation at Point Reyes California Reports of the results of the above studies and recordings of intercepted material were submitted directly to the interested military authorities Lany speech privacy schemes were submitted through N D R C during the course of this project These were studied and evaluated This work led directly to the continued improvements of the sound spectrograph and the development of supplementary decoding tools and techniques Ls the Army and Navy became able to carry on decoding activities themselves with the aid of equipment and information furnished by N D R O as the result of work outlined above the activity on this project gradually decreased the Preliminary Reports covers all phases of the work on this project and constitutes a re- The technical repott which follows together with the Appendix which includes all of feranms work for future studies of speech privacy systems INTMROUOTION TO TZONHIOAL o0RT This report sunmarises the results of about three years' experience in diagnosing docoding and evaluatinG speech privacy systeas submitted for study on this project by the Army Navy and Ir D R O Some of the results of these studies have been described in a series of Preliminary Reports which were issued from time to tiM- to cover specific studies A great deal of acounulated experience however has never been This final report reported in this manner therefore is intended to make available infermation both positive and negative which would have to be accumulated by another croup if they analysis and cryptography which apply to telegraph types of comunication very little has been written on speech privacy systems or deooding methods applying to then Two moderately One comprehensive articles have been published appeared in the Post Office Engineers Journal October 1933 The other appeared in the Brown Boveri Review for Decenber 1941 The latter has been reproduced and discussed in Preliminary Report No 5 It covers a number of basic types of scrambling systems and in addition discloses one that is new The present report is intended to were to embark on a similar project The immediate pressure behind these studies was caused of course by the War The material here recorded should therefore be of service if a similar energency should arise in the future To keep up with the ever-ohanging art of oomzunication these studies should be continued under Government auspices during peacetime cover rather completely speech soranbling methods in wLioh the original seecoh is transmitted with its parts nodified displaced or interchanged When more detailed technical inforaation is desired reference may be made to the Preliminary Reports These are separately bound and fora an appendix to this report All of this material should be helpful in the development of prao- In contrast to a rather extensive literature on code and cipher systems on crypt- tical effective privacy systems and the evaluation of the security which they afford 2 L SINT' CEPTTON Speech privacy systems may be used in connection with radio telephone systems or with nals can not generally be picked up at great distances and whatever equipment an interceptor wire systems The unauthorized interception of wire comnunioations in wartime however is beyond the scope of the present report This chapter will therefore be confined to radio interception problems and expands the material in Preliminary Report No 25 The decoding techniques to be described subsequently of might use to oraok the privacy must also be mcbile Furthermore the decoding equipment must be operated by military personnel a large number of whom may be required if the enemy is making extensive use of mobile privacy 'kether it is worth while to attempt to decode a large number of small mobile communications is ques- course apply to wire as well as radio connumic- tionable tions Chapter VII 1 Intermediate types of radio systems are used for the higher echelons of comand For such applications the radio equipment is semimobile It can be transported in trucks and set up very rapidly and may have a conviderable range For such applications a high degree of Types of Radio Systems Radio telephone systems range and complexity from high power point to stations operatinS over great distances low power short range sets carried by i qu e in size point to the indivi- as discussed in greater detail in dual soldiers The high power systems are usuprivacy is required and a truckload of equipment ally designed to operate between specific points right be justified because the enemy could afusing specific assigned feiote frequencies are ford to devote considerable time personnel and with elboat aonsineras They whichrone Sequipped with elaborate fixed antennas which equipment to decoding the kind of messages which are usually of the directive type Privacy would be transmitted over such systens equipment associated with such terminals may be as large and complex as desired to achieve vir2 Intercepted Signal Quality tual secrecy A major consideration in such systems of course which adds to size and oomdecoding the material from this point on will plexity is that the privacy must not degrade be written from the point of view of the unauthe quality of the received speech to any appretiable extent h thorized rather than the authorized listener It is first of all desirable to get a good signal On the other hand any one can iuas free as possible from interference There are tercept these hiGhpower signals at great disseveral reasons for this First the process tanoes where he can have a well-equipped which unscrambles the speech also scrambles any centralized deoodina laboratory with no limitsnoise such as static which has been superposed tion on the size and complexity of the decoding on the scrambled signal This changes the time equipment he micht bring to bear This laboraor frequency distribution of the noise breaks up tory can be adequately manned by a relatively harmonic relationships etc thereby increasing few highly trained decoding specialists not the interferin4 effect of the noise Second the necessarily members of the arred services decoding is apt to be less perfectly accomplished than at the authorized terminals which tends to no_ortrast wit ts sitain the make the speech harder to understand Finally lot' power short range radio sets used in nilthere are usually language differences which tary operations are severely restricted as to still further add to the difficulty of undersize and tieight and these restrictions also apstanding the message Conversations can be oarply to privacy equipment The smallest privacy set submittedtoed on under extremely unfavorable conditions a 10 inch cube and was designed for mobile apby people speaking their own language but noise and poor quality rapidly degrade the intelligiplications like tanks planes and command cars bility of a language foreign to the listener ihoile it is difficult to achieve a high degree of inherent privacy in mobile equipment it should be noted that the very mobility of such systems adds to the security because the sig- In this connection it might be noted that it is very desirable to be able to hear both 3 4 sides of the conversation without interruptions In the case of in order to follow the context in general the point to point systems this will directions two the because require two receivers are transmitted over separate channels at differIf the two outputs are mixed eant frequencies for listening or recording however it shouldbe kept in mind that the noise on the weaker signal will be superposed on the stronger signal and say seriouisit Putting the two signals on seriously degrade two headphones will improve this situation because noise in one ear does not seriously affect the intelligibility of a signal in the other ear This problem does not arise in the case of the smaller radio systems because these are generally operated on the basis of switching betieen transmitting and receiving conditions on the sa carrier frequency al i Lev'_ -i A - Usthods of obtaining a good signal are the sane for the interceptor as for the intended receiver A few of the important oonsiderations are listed here further information on o any or all of them can be had from radio referonce works 1 Point to point systems usually on tat iterept station he intercept diectve the emplyatenas Semploy directsive antenas should therefore be located along or near threo line of the radio been 2 In locating atetioms to intercept radio transmissions in the HF raeng account should be taken of the skip dietances of the frequencies involved Better signeals will sometimes be obtained y moving farther away from the transmitter rather than closer 3 The use of directive antennas directed towards the transmitter being monitored will inprove the signal to noise ratio by discriminating against noise which is non-directional These antennas of course should be designed for the frequency and polarization of the signal and properly coupled to the receiving set 4 Stronger radio signals will be received if the antennas are located in the open with no trees or other obstructions in the foreground This is particularly important in the VU range 5 Radio signals increase in intensity as the height of the antenna above the immediate foreground is increased particularly for VU transmission Thus better results are obtained with the antennas located on high masts or on hills overlooking the foreground in the direction from which the signal is arriving If the signal is in the VHF range and other measures are inadequate it may even be desirable to consider receiving the signal in an airplane and recording it or retransmittiag it for decoding 6 Noise improvement can generally be obtained by keeping the receivrig equipment away from sources of man made noise such as ignition systems and power lines 3 ' Reoeiving Sets with regard to the receiving sets a distinctioa must be made between the various astivities of an intercept station One important activity is searching for possible enemy transThe object is to deternine all mission channels the location of their teruse in the channels minals the type of business transacted and prelimieary form Qf privacy chanelany Some special whether all thei of on mostuesred iseace on the channel Soae preliminary are described in Prelivisearcheportisos te nary Reports has 2 and 23 If no privacy is used other than the usual commercial types it is unlikely that information of military importaene is transmitted over the channel and it may not be necessary to monitor it continuously If a new privacy system is located however it is very likely to be worth monitoring and deoodin$ continuously or the searching and scanning activities the ordinary oomeroial sets of the communications type equipped with a beat frequey oscillator will serve very well for all types f transuission Zveu the suppressed carrier type can be handled very well provided the sigl nal is fairly strong It may require continual umnual adjustment of the looca oscillator but sufficiently good reception can be obtained to determine the nature of the channel Oases of extreme spread band transmission can also be hndled in this % or If a particular channel employing suppressed carrier is deternined to be worth memitortn6 continuously then a single sideband receiver will give improved reception These receivers are equipped to amplify the partly suppressed carrier or supply a new one with great stability and they may provide as such as 15 db improvement in signal to noise ratio in some oases They also permit selecting either the upper or the lower sideband of double sideband systems which may be of advantage in cases where interference occurs on one or the other sideband of such systems However these reoeivers are not suitable for searching 4 Types of Radio Transmission A knowledge of the types of radio transsmission which may be encountered is very important to the personnel of an intercept station Bxperience has shown that without such knowledge the nature of intercepted signals nay be completely misinterpreted It is possible to mistake certain norma types of transmission for new systems or conversely to fail to recog- nize new systems which should be monitored at once The commonest type of transmission the double sideband type in which theSis carrier in transmitted along with the sidebande which are usually about 3 000 cycles in width and are located immediately adjacent to the crrrier These are readily demodulated by the ordinary receiver This is true even if the carrier is rapidly wobbled provided the wobble does not cover too great a frequency range Such wobbles are sometimes used in combination with simple inversion to prevent reinverting with a locally supplied carrier at the edge of one aideband In the so-called spread band system some or all of the sidebands are displaced from the carrier Demodulated signals of this tym will cover an audio frequency range greater than 3 000 cycles usually as high as 6 000 cycles It is essential therefore that the receiver be capable of handling such a band To obtain the intelligence the signals must be further demodulated as described subsequently Bl in Table I In the ordinary transmissions described above the carrier level is high compared to the speech sidebands In order to avoid loading up the transmitter with carrier and thereby permit radiating a higher sideband level many channels operate on the suppressed carrier basis In this system the carrier is either eliminated completely or transmitted with greatly reduced level To demodulate such sienals properly the weak carrier must first be greatly amplified or a new one supplied locally If this is not done the siGnals will demodulate themselves around whichever component in the sideband happens to be predominant producing thoroughly scrambled speech which can thereafter not be restored This condition can be recognized by its ohuracteristio sound to the ear toGether with wide syllabic fluctuations of the meter which ordinarily indicates the carrier level With suppressed carrier systems usually only one of the speech sidebands is transmittod However a second sideband transmitting a second speech channel is sotetimes added usually displaced from the carrier by about 3 000 cycles to avoid crosstalk between thechannels This is called twin channel operation and gives on demodulation an audio siGnal covering about 6 ko The two channels must be separated and placed in their normal positions by the methods previously cited under spread band systems The above systems are the main types of radio transmission used commerolally with amplitude modulation In addition in the VE range and above there are frequency modulation systems and also pulse modulation systems both of which require receivers specially designed to handle their particular types of signals This is too large a subject to cover here and reference must again be made to the radio literature Finally it should be mentioned that in addition to speech a great deal of telegraph additionto swill ebea found Thde of are telerah transmission There several types of telegraph signals including hand keyed such as Morse code or machine keyed such as Boshne and teletype Any of these types may be transmitted by keying the carrier or by keying a tone modulated on the carrier The marks and spaces may be represented by changing the azplitude on - off or by changing the frequency two-tone Finally since telegraph requires a much smaller band than speech it is often operated on a multichannel basis that is a voice channel will be divided into a number of telegraph channels In addition there are facsimile transmission systems which also may be operated on an AZ or Fn basis If a new signal is encountered whose nature is in doubt these possibilities should be kept in mind for further investigation when the need arises 5 RecordinA The sane considerations discussed in section 2 above which make it desirable to obtain a good intercepted signal apply also to recording and reproducing scrambled speech In addition to the requirements as to quality and noise there is an even more serious one conerning speed regulation In general systems designed for a high degree of privacy require a high degroe of synchronization and in many oases ordinary recording methods are not good enouih not only in long time average speed regulation but in the steadiness of the instantaneous speed In the case of some of the systens described in Chapter III for instance the requirements are so severe that even the best conmercial recorders will not meet them The best solution of this problem is to decode before recording This will be possible in many oases although it may sometimes entail the loss of parts of the messase while adjustments are being made or the code is being determined It happens that some of the systems described in Chapter III which impose the severest requirements on speed regulation B3 in Table can be handled in this way Ahen prepared to diagnose and decode intercepted ene my signals must be equipped with a considerable variety of special tools These should include of course such well-known devices as oscillographs and oscilloscopes amplifiers oscillators modulators rectifiers fixed and variable filters and a supply of components for constructing special circuits that may be required Some of the less wsll-known devices whose mature and usefulness will be made clear in subsequent chapters include magnetio tape or wire recording and reproduoina equipment in the form of loops with multiple pickups commutators for sweep or timing circuits variable speed drive mechanisms channel shifters the variable area pattern machine and the sound spectrograph There should also be models of the more iaportant types of existing speech privacy systems Finally and perhaps most important of all then should be stationed at the intercept location a Group of highly trained technicians who should be thoroughly familiar with radio transmission problems radio facilities oryptanalytio pro- this method is feasible even poor quality recorders such as those designed to record a Vast deal of material in a izall area nay be good enough In some of the systems to be described it will not be possible to decode before recordimg It happens however that in the case of the Only kIown system for which this is tre 73 in Table I the requirements as to quality and speed can easily be met by good commercial type recordings The matter of convenience or ease of use of the reproducing system is very important in decoding work In this respect also the requiresents are different for different privacy systems The recording systems using the embossing process for instance are convenient because they produce no thread and they require little attention However they all suffer from poor tracking during reproduction which can be exceedingly burdensome especially where the material must be reproduced many tines over Recording magnetically on wire is attractive from the standpoint of convenience and also quality but back-tracking is very time-oonmmuing and laborious ad diagnosing and decodin methods cedures If these technicians are not oonversant with the lanCuaGe encountered in intercepted communicitreesshudeooiuoay tions interpreters should be continuously available The best solution at the presentton writing appears to be disk recording on acetate with a machine capable of recording at v rious speeds Low speeds oa be used where quality need not be too good and a long record is desired Higher speeds can be used where better quality is needed Such recording systems are commercially available 8 Even with a l of the special tools and a sth se ialto even it all of personnel decodin in many instances will be a difficult problem and patience and painstaking effort will bu required to obtain useful information from scrambled speech Unless the needs have been anticipated the enemy may have secret Decodina Tools sed above oornunication for a considerable period of time as a direct result of unpreparedness In addition to the facilities discusan intercept station if it is to be 6 THE SOUND SPCTROGWRPH This chapter is devoted to the sound 2 Operation spectrograph -- its history method of operation and capabilities The sound spectrograph analyzes speech in terms of its three basic dimenslones frequency amplitude and time and portrays the analysis in the form of spectr egrams These are helpful in understanding the complexities of speech and what various scrambling methods do to speech to make it unintelligible 1 So A schematic diagram of the sound epeetrograph is given in figure 2 together with a description of the method of operation There isi lproduced s r t o by athe p toperations e n w i h described s o s b in t the i h illustration a pattern which shows by its light and dark areas how the intensity in the signal varies as a function of both time and frequency It is the fact That both time and frequency variations are simultaneously displayed which makes spectrograts so valuable for decoding work History Scanning filters of various widths can If the filter be used for different purposes is wide it will give an analysis which is limited in the amount of detail it can portray in the frequency dimension but it will respond quickly to changes in amplitude with time and will therefore give sharp tine resolution The narrower the filter the more frequency detail is shown in the spectrograms at the sacrifice however of some of the time resolution With all the filters thus far used the shift in frequency range from line to line is only a fraction of the width of the filter Successive lines in the spectrogram therefore do not represent They represent fresuccessive frequency bands quency ranges which overlap by a large fraction of their total width The density of the patterns therefore changes very gradually along the frequency dimension kind of patterns produced by this In arch 1941 an early laboratory model of the sound spectrograph was demonstrated to Dr V Bush as an instrument that with further development might be useful in studies of telephone privacy It was appreciated at that time that the need might arise for intercepting communications in scrambled speech and decoding then It was also appreciated that new sorambling systems might be encountered and that means would be needed for dia nosing such systems For such a purpose the unaided aar has very limited capabilities Such things u oscillograms which show the wave form also provide little in the way of clues as to the mechanism by which the wave forn was ohanged Project 0-32 the forerunner of 0-43 was therefore organized in the Fall of 1941 and its immediate objective was to produce a sound spectrograph in such a form that it would be useful for diagnosina and decoding speech scrambling systems isbThe About a month before the attack on method of analysis is illustrated in figure 3 Pearl Harbor patterns that could be used for The upper spectrograz in the figure was made with decoding work were being produced with a breadboard model and the first finished model of the spectrograph was available by the end of that year Additional models of the spectrograph have since been built for the use of the armed services incorporating improvements in operation and in ruggedness The most recent model is shown in figure 1 The spectrograph has been used in studies of various privacy systems submitted by the Army Navy and IT D R C for the purpose of evaluating the degree of security a scanning filter about 300 cycles in width The separate words can be plainly distinguished The vowels are distinguished by dark bands with vertical striations The consonants are in gemeral less intense and show a different type of structure It will be noted that the dark bands are different in the different vowels and they change not only from one word to the next but also within each word Analyses of this type therefore graphically portray changes in the energy frequency distribution of a complex sig- studies it became evident that inprovements in the spectrograph would be useful in this work Accordingly a calibrating circuit was built into the spectrograph and control circuits were udced in the form of an applique unit emphasized however that the relative intensities of the various components of this particular differ consonats the of s Sample of speech notably the consonants differ to a far greater extent than would be judged by whiot they afforded In the cource of t ose nal with both time and frequency 7 It should be RECORDER UNIT 2t4 RECTIFIER UNI7 UNITS INTERCONNECTED AND READY FOR USE Figure 1 - D-165529 Bound Speotrograph p 4 u 0i4N 4 r-4 4 F-4 IX b h6 W4 0 0 9 2 o CQ F-4 r- 0w 3 11012O 0 q 0 Z 4a in 0 9-4 cct0 ix t4 0 l 4 01 0 40- 9-4 0 3 01l4 9 o E-434 AVH 1 1000 U 01 144 UI I4 W4 43 A 4 '% g 00 to4- a 4 cc i I j48 '- 4 vw aa the relative blackness of their patterns In mess the lowest level components will be invi- is so adjusted other words a very large amount of level con- sible preesion is incorporated in these patterns as will be described in the following section that the low leiel components appear in the pattern the high level components will severely overload the recording paper In order to show both the high and low level components ocourina in speech therefore it is necessary to compress the instantaneous signal into a much marrower range The lower spectrogram in the figure sholhs the same words analyzed with a filter only 45 cycles wide This filter is narrow enough to resolve the individual harmonics of which vowel sounds are uomposed Conversely if the level The harmonices con- sist of the fundamental voice pitch together with both odd and even multiples of this freQuenoy Sone of the harmonics are stronger than the others because they are reinforced by resonance in the oral cavities as the words are fumred It will be noted that the dark areas in these patterns correspond in frequency and in trend with those in the upper spectrogram The fact that vowel sounds consist of discrete hernonics causes the vertical striations in the patterns made with the wider filter 'henever the filter is wide enough to pass several harmonies at once these harnonics beat with each other and form maima and minima in the output of the filter The frequency of the beats ocrresponds exactly to the frequency of the voice pitch In the earliest models of the spectrograph the marking amplifier shown in figure 2 was given a compressing action by means of a thyrite varistor across the grid of the output stage Whenever the output of the scanning fiiter was low the gain of the amplifier was effectively raised from an average condition and whenever the output was high the gain was effectively lowered This tended to equalize changes in level with both frequency and time Vore recently the compressor has been replaced by devices which can exercise certain types of discrimination in controlling the instantaneous gain of the marking amplifier These devices are known as control circuits They provide patterns with better resolution in both time and frequency than can be obtained nith the compressor The patterns shown in figure 3 were made with these control circuits in operation The circuits are desoribed in Preliminary Report IO 27 It will be noted in the 45 cycle spectrogran that the harnonics rise and fall in frequency from moment to moment This reflects the chaniCng pitch of the voice known as inflection Inflection is normally used in conmected speech and this fact is of assistance in decoding work because the spaoina and trend of the individual harmonics in spectrograms provide important clues in diasenoting privocy systems as will be ceostrte din suseprevacyhtoeras willbe demonstrated in subsequent chapters 4 Possible Improvements %49 spectrograph patterns he undergone continual improvement in the course of this project but they can probably be still further improved The control circuits thus far produced are by no means the final word Circuits 3 Level Gomprbscion of this type can be adapted to affect the patterns in various ways and it is conceivable that different control circuits could be developed for decoding different types of scrambles In normal speech there is a tremendous change in level from moment to nouent particularly in the level of consonants as compared to voifels There is also a considerable difference in the average level at low frequencies as conpared to high frequencies This latter differ- One definite line of improvement concorns the time resolution I any scrambling methods as will be seen subsequently pro- once can be corrected by predietortion and duos sharp discontinuities of the scrambled present models of the spectrograph contain chaping networks for this purpose There are however changes from moment to moment in the relative levels of hiCh and low frequencies in different speech sounds which cannot be corrected by shaping networks The facsimile paper on which spectrograms are made has a range of betileen 10 and 15 db The range of levels in speech greatly exceeds this value This means that if the averag'y level is adjusted so that the highest conponents appear at maximum black- speech in the time dimension The process of analyzing the scrambled signal in such a way as to obtain high frequency resolution tends to obscure the signal at these sharp boundaries This is a basic situation which affects not only the spectrograph but all types of analyzers In order to obtain a high degree of frequency resolution a narrow filter must be used The narrower the filter however the longer its response and decay time that is the output of the filter cannot be made to change as rapidly ii It T 3 x Ado-o 3 39 3de- 25 OH Ha z-033g 333 3gagging nEvngunduwu EH 3 Done 5 3 3 8 3 0 bowl 5w 3 ku d5 no 3 0 OHS own 3 52% ab 3 0 Er dunno E 9E- Epovu cannon 25 53 903 E a bong awash u 609 59 25 non gag Ha I vow av 5 nu Hence an no awn-H we 35 v0 8 53 H33 on 6054 nguonona an Gavan-Hush UH lab-3 35 we 93 sacrum 3 5- 254536 36 525 35 33 03 35 90 80-39 on a uwonluonu 13 gun gnaw H 593 our long 533 5 guano w I E5539 Sud- 3332- mvnawum p - - A 4 - 45-4 4 1 45 P4 Q4D 10-4 43 1600 14 e4 400 0 4 044 k ASQ 1 Q Ck C lui zI in level as the instantaneous level of the Bign l This oauses strong components to spill over across the time boundaries Ixamples of such spillover can be seen in the upper speotrograze in figures 54 55 59 and 60 In general this spillover does not interfere greatly with fore Le measured by measuring the dot spaoing with suitable equipment and comparing it with a scale showing dot spacing vs level Another type of representation if shown in figure 5 Here the levels are repre- sented by the type of technique used in repre- the recognition of various privaoy systems but it does interfere severely where spectrograms are to be used for decoding work Several posible remedies for this situation have been de- smntitg topographical variations in contour aw The contour lines each represent regions in which the signal reaches a particular fixed level The lines may be spaced so as to repre- vised which are recorded in Chapter TI sent steps of any desired number of db or any 5 Aazlitude Representation In the patterns thus far discussed the instantaaneous intensity of the signal in represented by the ligteness or darkness of the trace This representation is inin the spectrograns herently non-linear and practically inpossible Yor some types of work it to make quantitative if the amplitules desirable highly be would could be represented in such a way that they could be interpreted quantitatively Figure 4 shows a spectrogram which upon close inspectini will be seen to be madeup of discrete dots The dots are close together in the dark portions of the speotrogram and farther apart in the light portions The dots themselves are all of equal blackness The spacin of the dots is in fact quantitatively related to the instantaneous level of the signal The level at any point in the speotrogras can there- number of volts In the lower spectrogram spaces between the contour lines have been in with various densities of dot spacing permits instant recognition of equality of in different portions of the signals the filled This level quantitative mplitude representation may or may not prove useful in decoding work lor certain kinds of signal it should prove useful because it provides another disansion besides time and frequency which can be used for determining continuity or discontinuity in the signal In other cases however it may prove useless because changes in level have arbitrarily been introduced into the scranmble The developments mentioned above esphauize the fact that the sound spectrograph is a highly flexible device and its capabilities along any line can be ereat 7 yinoreased by adding features designed for tae specific pur'pose in Rind 1I CHAPTER III SPEECH SCRAMBLING UETHODS In this chapter we shall examine a wide variety of speech scrambling methods in order to become familiar with the devices which might be used alone or in combination to make up speech privacy systems Some of these systems are in commercial or military use others exist only on paper mostly in the form of patents or patent applications It is not intended to include all the variations of all the different methods but rather to cover basic scrambling methods with their most important variations in which the original speech is transmitted with its partb modified displaced or interchanged The two main dimensions of speech which are operated upon to make it unintelligible are the frequency dimension and the tine dimension Scrambling-systems usually depend on rearranging the components of speech in either or both of these dimensions In general it may be said that those that operate on the frequency dimension alone are capable of the best quality in the raproduced speech A complate list of the systems covered in the discussion is given in Table I together with other data concerning them Most of them are illustrated by means of spectrograms which will be discussed in Chapter IV INI OUT CARRIqER A Figure 6 CB RO CARRI - 1 Systems Involving Single Uodulation Modulators pass filter It is then modulated with a frequency of 3 000 cycles This produces an upper and a lower sideband of which only the latter is passed by the output filter The system is called inversion because the high frequencies in the original speech appear as low frequencies in the output and the low frequencies in original speech appear as high frequencies At the receiving end the inverted signal in A basic device in privacy systems is the modulator One form of modulator shown in figure 6A consists of four copperoxide varistor units between two balanced coils The carrier frequency is fed into the midpoints of ofn the te coils omilsedasas shown shown In in some somue cases cas the tthe coils can be omitted as shown in figure LB Figure 7 shows the method of produc- passing through an identical system in the same direction is ing simple inversion In this and in succeeding illustrations the numerical values are not necessarily the best values for practical peration but they serve to illustrate the manner in which the device operates reinverted back to normal speech A very commonly proposed variation of this system involves using a variable frequency instead of the steady 3 000 cycle carrier We might vary the frequency continuously or in discrete steps It should be noted however that the cut-off of the low-pass output filter In the system shown in figure 7 the speech band is limited to 3 000 cycles by a low15 LO P P O P I 3000 1igure 7 - Single Modulation ts fixed which limits the variation permissible in the carrier frequency A wide variation would either permit too much of the upper sideband to get through or would cut off some of the Two proposals of this type are lower sideband discussed in Preliminary Reptrts No 8 and 20 If the modulator in figure 7 is of the type shown in figure SA speech can be scrambled by introducing instead of the 3 000 cycle carrier a square wave whose changes fron positive to negative value are irregular in tins Each one of the reversals in the carrier wave causes The pata reversal of phase in the speech wave tern of these irreCular reversals moy be arrara so that the speech becomes unintelligible it the reoeiving end a coding wave must be introduced which is exactly- in step with the one at the receiving end with proper allowance for any delay there may be in the transmitting channel A two ochnnel system usinw one modulator for each channel is shown in figure 8 In this system the carrier fed into both modulators is the same in frequency but 6iffers 90 degrees 0 dgres ii reqenc he amein bt tiffrs can be in phase Two separate speech ohannls substantial transmitted by this method without mutual interference but both sidebands as well At the as the carrier must be transmitted receiving end the carrier must be split into two Each compocomponents with the proper phases nent will demodulate its own portion of the signal and thereby separate the two speech channels Naturally one of the channels may consist of noise or spurious speech from a reoording or the like which tends to mask the real message if the signal is demodulated with an ordinary set Tias soheme was origia lly proposed as a multiplex system but an obvious variation is to divide a single speech band into two halves with filters and then transmit the two halves on carriers differing by 9U degrees in phase Figure 8 - Split Phase Multiplex 2 Systems Invo vinag Double kodulation Figure 9 shows a much more flexible system Here the vignal is modulated twice with a band-pus filter between the two medulatore With this arrangement the carrier frequency fed into the second modulator can be varied in several ways In the illustration two carrier frequencies are shown for the second If the 8 kovalue is used the output modulator consists of the speech band right side up but displaced from its normal position by 2 000 oyoleo If the 16 ko value is used the output conjists of the 3 000 cycle speech band inverted We might use and displaced by 3 000 cycles these two values alternately at short intervals or we might have the carrier vary continuously back and forth say betwesu 13 and 16 ko Another variation is to use a multiplicity of values say 500 cycles or 1 000 cycles apart not between 10 and 13 ko for this illustration and switch between these values in a regular or irregular sequence A disadvantage of these systems of course is that the truameision channel need ' to be wider than that usually afforded by radio sets or telephone lines In all of these systems the speech is MOD Figur 161 9 sp MOD -Double Modulation LP restored by passing through identical equipment in the opposite direction Figure 10 shows a system of modulators and filters for accomplishing this kind of band The first modulator is followed by a highshift Triple Modulation - Reentrant Band Shift which selects the upper sideband pass filter This is comfrom 3 000 cycles to 6 000 cycles 3 bined with some of the original signal which ranges from 0 to 3 000 cycles The second modulator is fed with a carrier frequency of say7 kc which inverts the whole band This is followed by a bandpass filter passing the range from 3to 6ko A seeend modulator with its carrier frequency placed at the lower edge of the 3 to 6 ko input band moves inverted down to the usual the whole band still The upper sideband range of 0 to 3 000 cycles of this modulation step is removed by the output A variation of this arrangelow-pass filter ment isto allow the 7 kc carrier to vary in discrete steps according to some regular or irregular program or vary it continuously between the limits of 6 to 9 ke This provides a variable band shifting arrangement without using more than the normal 3 000 cycle transmission channel Going back to figure 7 suppose the carrier frequency were made 4 000 cycles instead of 3 000 but retaining the 3 000 cycle The output would input and output filters then be an inverted sideband ranging from 1 000 cycles to 3 000 cycles that portion of the sideband above 3 000 cycles would be cut off by Since however there is a the output filter 1 000 cycle gap at the lower edge of the transmitted band the portion which would be cut off might be modulated down and sent by the filter along with the rest of the sign4 in this lower In other words the parpart of the spectrum tion of the sideband which would otherwise disappear above the upper edge of the transmitted band might be made to reappear at the bottom 3 KC BP 3-6KC MOD MO PAD MO 3 LP KC uD 7 KC 3OKC Figure 10 4 - Reentrant Inversion ing the modulators are all alike passing the Band-splitting Systems band from 3 100 to 3 650 cycles A It will be seen that the uppermost modulator in figure 11 privacy system in wide commercial use known as the split band system involves with its carrier of 6 100 cycles will invert the splitting up the whole speech band into a number of subbands wnd shifting those around out of their normal positions in the frequency spectrum Figure 11 shows one manner in which this can The numerical values are be acconplished chosen so that the band from 250 to 3 000 cycles is divided into five subbands each 550 cycles wide speech band and displace it by such an amount that the frequency band which originally occupied the space from 2 450 to 3 000 cycles will pass In other words this modulathrough the filter tor in combination with its band filter selects the uppermost of the five subbands from the inSimilarly the lowest modulator in put signal selects the combination with its band filter The outlowest subband from the input signal puts of the band filters all occupy the same frequency range but they all came originally Th uweech band is fed to five modulators in purullel The five band filters follow17 INPUT OUTPUT 3WITCM 10e L 410 O31 AlI-10 ORTR 11-OeFrmo pi Eayt Figure 46 angs fequncyiaiarl the fromdiferet outpu ar no dsignd modlatos tht eah'o ylsed accepts_0 thPadfoC 0 t 6 shifts111 atclrbn itto oaio nte oupt h fv easginCnoohwe sn ec0scn mateeoe labeled MSSW'E output leads coert 5 i iiom MODi e T0U i i iiinalipe nwihms parte iflocuyn fIqec rnge aresnWvrasnl nylnho en rnmte ahsga sse tme Thn igh b ilusraed y homooth inl onceo OA the semet ofP Arpdyrttn buhpcsu h inlsoeatrt ohe racpal Anadto as lsto f frqece is 1760 hebrshmstmaeatles quliyhweer roa o peneon Oan astehgetf- arei intrete tds a allal nueerofaub anwhc lchtsho ing thatitt tof th prcioeid spee qualtsity idso tas boxcyclefrequency range anrconnecti beands asin istpossible tosift ditri e coapiderte rithout nprductinls herin r ytmw Tma Divstesrahrohn k ulitipez tal bang s isi theode o coo1 willu codulaine oaseve to thegne fc thae his can tpeeh chanel transm Ttima ivsionl s cycer as100 to36 eredOnt fnreqprien havcept been chaned asrofte aoert a th ie h necedin mnmanydesre wth hefiv Thseutn uptwl lwy opet a ra0g fro to3000-mttr alsadteewllb ooelpig ubns The S IT0 maybeFhagued as -Often Fince oe aro desi im occupying thesaere vethesestogt e lie - eutents oAourapidlyhrotatincobruthtor kseferrie frome 250 to 3p00ecoyt indcaedinth dawngfo to mn roa 12 whiciosprsicoilar frigureie te ecndse o to 11e highstcane qeny n hetrneitedsinas hi18az 4600' BP 5 3600y 0P FILteRs ALL ALIKE -- 300 Figure 12 - TO'38OO' One Form of Tine Division Multiplex accomplished by feeding all the output modula- loop over pulleys or attached firmly to the tors with the same carrier and connecting each modulator to a commutator segment In this illustration there are four 600 cycle subbands covering the range from 400 to 2 800 cycles It has been shown mathematically that the output of this system consists of sidebands around a perimeter of a disk The reoordimg is done by means of small electromagnetic pole-pieces The signal is picked up by similar pole-pieces which may be placed at a distance from the recording pole-piece depending on the amount of delay desired The outstanding advantage of the frequency corresponding to the rotation of the brush and also sidebands around frequencies corresponding to odd harmonics of the rotation frequency Each side-band however contains components from each of the subbands It has also been shown that the total channel width re- magnetic tape system for this type of application is that the signal nay be erased and the recording medium be used over end over again The quality of this type of transmission can be quired for good transmission need be no greater 2igure 13 shows a rather simple privacy system using magnetic tape The input signal is passed through a 3-way pad whereby it is impressed on a band filter and also recorded on the magnetic tape It is picked up by equally spaced pole-pieces each associated with a differsnt band filter With the arrangement shown in figure 13 the band from 0 to 1 000 cycles is transmitted without delay The band from i 000 to 2 000 cycles is transmitted with say 100 nilliseconds delay and the band from 2 000 to 3 000 is delayed 200 milliseconds At the re- then that of the original signal To increase the privacy of this systen one of the subbands nay be replaced by a band of noise This can be filtered out at the receiving end Obviously this systen requires a high degree of synchronism between the two ends 6 Systems Using Tape Recording Leaving the frequency substitution systems for the tine being we tFill introduce a device which permits thantha operatingofthe on therignalsigal time scale The 3iost versatile uurdevice for this pose is the tape recording and reproqucing system This takes the form of a tape of magnetic lils alloy a few thick cither run sa a made very good with proper design ceivin end the scrambled signal is passed acysysem singnageti through an identical system tae in the Tesaneiputsig way except that the'two extreme band filters are imtfrchonged magnetic In this way the band which received no delay in transmission is given maximum delay in the receiving machine and the band which re- qrrer However the number of segments pole-pieoes need not be the some as the number of pole- pieces A switch is provided whereby any seg- ment may be connected to any pole-piece With this system the speech is EAASF PAD cut up into time elements corresponding in length to These time elethe spacing of the pole-pieces For ments are transmitted in a scrambled order we which elements time instance 6 successive might label 1 2 3 4 5 6 might be transmit- Figure 13 - Variable Subband Delay ceived maximum delay in transmission is given In this way all the zero delay in the receiver bands are delayed the same amount and the speech is restored to normal This system alone does not provide any high degree of privacy but it can be con- bined with other systems as we will see subse- The possited in the order 2 4 1 3 6 5 of TDS coding are far too complex to bilities Analytical discussions are given cover here The in Preliminary Reports Nos 3 and 6 general requirements for all TDS systems may be Each element of the 1 stated as follows once and original speech must be transitted only once 2 The sum of the delay in the transmitting machine plus the delay in the receiving With machine must be equal for all elements obvious these two requirements fulfilled it is that the speech comes out of the receiving machine in however its normal order It is delayed by an amount equal to the sut of the quently transmitting and receiving delay An important class of scrambles involving magnetic tape is known as tine division A simplified diagram of this scrambling TDS system is shown in figure 14 There is a recording pole-piece and a number of pickup polepieces There is also a comutator driven in synchronism with the tape The length in time of each segment of the commutator is in general equal to the delay between successive pickup At the receiving end there are several ways of handling the scrambled signal 1 The pickup pole-pieces can be used as recording pole-pieces and the signal picked up by an additiona pole-piece shown at the right in figure 14 With this arrangement the connections between the commutator and the polepieces are the same in the transmitting and receiving machines The sigal can be recorded with the sae pole-piece used in the transmitting machine and the connections between the pole-pieces and the aegments rearranged for receiving by a push-totalk relay 3 The codes can be restricted to a particular class called self-converse codes These have the property of being self-decoding ERASE that is the same code which scrambles the speech in the transmitter restores it in the receiver An important variation of this system is called Interlace In this system the number of segments on the commutator is doubled The odd segments are connected to the polepieces according to one code and the even segm-ents are connected according to a completely independent code The reason for this device is to increase the difficulty encountered by the the enemy in trying one code after the other to Figure 14 One Form of Time Division Scramble find the right one particularly if the total number of codes available is pmall With the interlace system the total number of combinations possible is equal to the square of the number of codes The rotating commutator shown in figure 14 results in a repeated code that is each rotation produces the same scramble It is possible to substitute for the commutator and switch arrangement shown in figure 14 a more complex arrangement whereby the speech is scrambled in a never-repeating manner There are several ways of accomplishing this Perhaps the simplest way to represent it is as apunched tape which permits the pole-pieces to be connected to the output one at a time in any desired order permissible under the restrictions outlined above the motion of the tape and is in the same direction Therefore the relative motion of the tape and the pole-pieces is the reverse of that used in recording This is the same as running the tape backwards for reproduction IN IN i oSAME DIRECTION AS TAPE BUT TWICE AS FAST FLEXIBLE LEAD TAPE WHEEL OUT 0N Figure 16 7 ___ - Time Inversion Combinations of Time and Frequency Scrambling Obviously the two kinds of systems Figure 15 - described in the previous sections can be used together For instance some of the time elements of a TDS system might be inverted according to a regular or irregular program The next more complex step is to combine the band'splitting system- of figure 11 with the TDS system The codes of the band splitting system might be fixed or might be switched in synchronism with the IDS elements the time scale of the scrambled speech not being further broken up If they are switched nonsynchronously however the time Speed Wobble Another way of utilizing magnetic tape to scramble speech is shown in figure 15 Here the pickup pole-piece is oscillated back and forth along the tape mechanically With this arrangement or other variations equivalent to speech changes the speech time scale is alternately compressed and expanded The frequency scale is correspondingly expanded and r thvelyran euea compressed cpterespectively a io difficulty 4ith the orrangenent shown in figure 16 speech is broken up into time segments each of which is transmitted backwards The uotion of the pickup pole-pieces ib twice ua great au dimensions will be further broken up as will be seen subsequently Combinations of nonrepeated code TDS and rapidly switched split band coding can be made to afford a very high degree of privacy The two kinds of coding of course must not be so interrelated that one furnishes clues for the other If for instance a certain polepiece were systematically associated with a certain spiit band code the total privacy of the combination might be impaired rather than enhlanced A coding method for avoiding this ifiut No -'I is described in Preliminary Report A very special kind of scranble is ul oduced by a system which consists functionally of figure ii rapidly switched in tandem with 91 4 figare 13 with 5 bead#% followed by an additiou figure n1 Thia is not the simplest form Of tbO system but it serves to illuastrate the DrinetiPe Two frequency Lcrambles with a time ahift in between produce a partilcular kind of two-dimensional soramble in which the speech is brcsen up into both time and frequency alemerts Eaoh of these closestm may be shifted both in tim and in frequerny so as to be out of proximity with other elements with which they wrer ori inally associated either in tim or in frequency Another way of accomplishin% this kind ot scramble would be a mombination of rapidly switched splyi band with a separate TDS sPIKC'4s MWLTIPLIgR S -XC MULTIPt I R U C W Yigure 17 - Wave N ltltplioasion ceiving end a reciprooal of the coding wave is derived and system in each subband A two-dimensional systea has been described in the Brown Boveri Lrtiale reprodured in Freliniaa7 Report Nlo 5 and anaelyzed in Preliminary Report No 9 It is capable of a very Mg n degree of privaoy - used as a multiplier thereby re- storing the original speech Naturallr the coding waves at the two ends of the system must be in close agreement otherwise there will be considerable background noise in the decoded speech For the saxe of corpleteness two other ' freiuency shiftinG will be mentioned although as far as is known they exist only on paper Suppose a saple of speech were recorded on tape and then reproduced at twice its normal speed It would occupy only half the time it took to speak the words but its frequency ranwe would be twice the normal raueg Let the upper half of the expanded frequeney rane be separated by a filter and wodulated down to the normal range and used to fill up the unusse time The directly opposite but a alo ou system would involve reproducing recorded speech at half its normal speed the frequency range wcold then be only half the ormnal range Alternate seotions therefore could be modulated up to fill the unused frequency space thereby keepin the total tranisittin6 tin substantially unchanged In both of these systems there would be a delay equal to the length of one time element syste msinvolving ti - a 8 lgrse 18 - Level Modulation AMother method for changing the wave form is aho n in figure 18 The essential feature of this system is an amplifier whose gali can be varied rapidly with time Drastic ohanms in the level of speech if they occur rapidly enough will make the speech unintelligible The level ohanges night be made according to sow progras or they tight be made to follow the speech wave itself For instance extreme com- Wave formLodirfootion Thichfrequsncy fans werae cshided a in which frequ ency banse were shifted around or time elements were rearranged There are a few privacy systems whioh make speech unintelligible privcy wich ystes akespeeh uinteligble by a direct modification of the wave form One of these is shown diagramwatically in figure 17 It depends upon a process whereby two waves are multiplied together that is the instantaneous amplitude of the resulting wave is the product of the amplitudes of the two input waves One of the input waves to the multiplier is speech The other is a complex oodinr wave If the coding wave is sufficiently complex the resulting scramble is unintelligible At the re- pression or expansion sponding gain changes at the receiving end could be used Correof course must be lade A variation of this system is shown in figure 19 Here the speech band is first divided into sub-bands and these are individually oubjocted to level changes according to separate program 9 One of the first schemes which is likely to occur to a person considering how to 22 nak speech private is to add noise or other disturbing signal to the speech and remove it at the other end in other words to mask the speeh He wi U find however that it is necessary to use very high levels of maskin sig- nal in order to hide the intelligibility This of course nmaes it difficult to subtract out satisfaotorilyi the difficulties are such that 0 masking systems are more likely7 to be found on wire lines than on radio A few speculative masking systems are outlined below One form of masking system is shown in figure 20 In this system two telephone lines are used At the sending end noise is added to the speech in a mixing pad and the combination is sent over line 1 The noise lone is seat over a second line end it is used at the receiving end to cancel the noise trans mitted with the speech by simple subtraction This system has the advantage that the noise oan be CONTROLCKYS completely random However sinc thb enemy might take tape from both lines and thereby be able to make the sene subtraction a variation of this system consists in distorting the noise GENERtATOR Figure 19 - I Subband Level kodulation DISTORTION DISTORTION Figure 20 - Noise Masking Using Two Ohannels in sone predetermined manner before sending it over the second line At the rooeivino end this distortion is first nullified so that the noise nay be subtracted ' aturally the form of distortion uust be unknown to the enemy It can of course be varied from moment to moment SPEECH Another masking system is shown in figure 21 which uses only one line In this system noise is added to the line at the receivinz end instead of at the sending end Again the noise can be perfectly random Since the noise is Generated at the receivinZ end the process of cancellation can theoretically be made very exact This system however cannot be used for radio at all because the level of the Figure 21 23I MIXINGd M - c Masking Noise Applied at Receiving sa e level as the level of the 04eeeh in the corresponding band at the transmitting end This is accomplished by separating the signals in the various ohannels detecting them and us- noise decreases with distance from the receiving stations while the level of the signal increases The interceptor therefore will get good speech signals if he is close to the transmitter With ing the resulting fluotuating d-o to control the telephone lines this differential can be kept small variable gain amplifiers in their respective ohannels Another simple masking system itsto of tones superposed on the sigsequence a have end At the receiving transmittin4g the at nal end sharply tuned band elimination networks can be synchronously switched so as to remove the tones from the listener's ear Similarly short spurts of noise oovering the whole frequency band can be applied at the transmitting end and shorted out at the receiving end The spurts Ott be made to occur at irregular intervals ac- Te noise is of two types dependin on whether a voiced or unvoiced sound is to be simulated For an unvoiced sound it is a hiss like thermal noise For a voioed sound it is a bun which consists of a series of harmonics covering the whole frequency range A separate carrier is used to transmit information for operating this part of the system At the trausmItting end the pitch used by the talker is mea- thtse systems involve the loss of small portions of the speech either in the time scale or the frequency scale sured and this information is used to control The absence of a the pitch of the buss sound sound into the hiss the switches pitch signal system A system described in Preliminary Report No 4 might be classified as a masking eyeter although it might be better classified a means of communicating without the enemy's as knowledge This system by itself of course in not private since the enemy can build a similar system and use the signals to regenerate speech must be achieved by operating on the Privacy channel signals One method is to permute the oc ding to a never-repeating program 10 Both of channels at short intervals accordiag to a prearranged program Another method is to put a TIS system into the line or into each channel A still more effective method of separately this type is to apply a two-dimensional scramble such as was described in an earlier section to the channels so that signal elements are displaced in both time and frequency Vocoder Systems The vocoder system which has been de1 scribed in the Bell System Technical lournal 2 and the Acoustical Society ournal nay be made the basis for privacy systems of various kinds The system is shown schematically in figure 22 At the transmittiw end the speech is passed through a series of band filters the outputs of which are individually rectified to form a flucThese signals are individutuating d-o signal ally modulated in such a way that they Oan all be sent over a single trnsmisesion path At the receiving end synthetic speech is manufactured in accordance with the signals transmitted over the line A source of noise which covers the whole frequency range is passe through a set of band filters similar to those at the transmitting end The output of each of these filters is controlled so that it is the 11 Ohannel Ilizing Systems Thus far the methods we have examined apply to a single transmission path There is another class of privacy system which depends on using a multiplicity of paths This is of course inefficient if only a single message is to be transmitted However the method a number ofh d s two oasewh exapplbed an pointsandmatnumber of wo nages meseses would normally be transmitted over these channels simultaneously 1- Bell System Technical 3ournal Volume XIX Page 495 October 1940 2- Journal Acoustical Society of Anerica Volume 11 Paee 169 October 1939 24 L NE '4IHTANWTS-FSNPKI Figure 22 -Voooder Figure 23 shows one frem of channel mix ng system Here three channels are shown connected to the three seszente of a oommutator Three brushes on this commutator are omneeted to the outgoing oehnnels whioh ore thereby caused to pick up one channel after the other on a time division basis Each channel contains parts of messaGes from al l three ohannels Thea commutator of course is too simple to be very effective aind would in practice be replaced by a permnuting siiitoh capable of switchiag accord- One or more of ing to e nore complex progr the channels nay be fill2ed up with noise or spurious speech from a recording or other similar source System CHANNEL 2 I CHNE CANl -__________ 3 tj CHANNEL 3 r'iGre 23 -channel 1LixiZ8 An analogous system which divides the messages on a frequency basis is shown in figure 24 Here each ohannel is passed through three band filters which divide the speech into subbands Each of the outgoing channels contains@ subbands from each of the inoomiog channels CHANNELI To increase the privao7 a perzuting switch is shown which rearranges the subbands on a time If only one message is to be division basis tranemitted the other channels can be filled in with noise or spurious speech 12 CHANNgLS S nary SWTCH The above examples cover fairly comn- pletely the range of schemes that might be uied In to scramble speech at audio frequencies subsequent chapters we will examine each system from the decodina standpoint To facilitate reference to the various systems they are summarized in the attached Table 1 This table also refers to the places where methods of docoding the various systemo are discussed CHANN9l A Figure 24 26 - Subband Channel Vixing DIAV'OSIS 0 U Mra SYSTIU Before discussing the diagnosis of speech privacy systems it should be pointed out that facts concerning the origin of unknown sigasle are often very necessary to their correct interpretation Such things as the frequency strength and direction of the signals the location and type of receiver and the manner in which the signals were recorded can be very important pieces of data That is why it was stated in Chapter I that interceptors should be equipped with complete knowledge 4f the various kinds of radio systems and transmissions used by both sides including jamming and radar signals as well as telegraph and facsimile signals Some of these signals particularly if transmitted with asppressed carrier can give extremely puzzling results if demodulated with an ordinary radio set These possibilities should be taken into account if signals are found which do tnot seea to fit into the classes discussed below spectrograph can be established The spectrograph is equipped with a calibrating device which consists of means for producing a complex Wave rich in harmonics from the 60 cycle power supply Spectrograms of this wave made with both the 45 cycle filter and the 330 cycle filter are shown in figure 25 If the power frequanoy is known the horizontal and vertical striations in these patterns provide the time and frequency scales If the power frequency is not known the scales may be established by the fortulas given in the figure This involves additional measurements with a stop watch The application of this method to 11 ke speotrograns is not explicitly stated in the figure A value of I for this condition can be found by the same formulas This establishes the time scale for the 11 ko spectrograns or the frequency scale the same pattern is used as for the %1 5 ko speotrograms However each horilzonttL striation is labeled with a frequency obtained by multiplying the normal frequenoies by the ratio of the two K'se As stated in Chapter 1I the spaeotrograph is of tremendous assistance in recognizing the nature of an unknown scrambling system The ear can usually recognize the presence of time discontinuities It can also usually recognize the peculiar quality which results fro band shifting systems The exact nature of the scramble however is usually impossible to establish with the ear Xven scrutiny of the wave The strikinly graphio form may yield no clue analysis provided by the spectrograph however usually takes the mystery out of the scrambling method immediately 7igure 26 shows how these scales can be used to measure the time and frequency boundIt will be noted that for aries in a scramble aeacurizn the time elements speotrograms made with the 300 cycle filter are beet because they have sharper time boundaries 7or measuring frequency boundaries the seas filter must be used as was used in obtaining the scale It may be noted here that in present models of the spectrograph the wide filter has a different absolute location than the narrow filter and therefore should not be used to estimate the frequency of components or boundaries Speech privacy systems having frequency sub-bands will show horizontal discontinuities or boundaries in their spectrograms Similarly systems employina time division will show vertiA considerable variety of eyecal boundaries teas display both horizontal and vertical boundaries liow to tell these different sorabling systems apart is the subject of the disoussian -Illustrations of Scrambled Speech Spectrograns illustrating a lar e nunbar of privacy system scrambles are shown in figure 4 to 87 which are segregated at the back and illustrations in this chapter of this report 1 spectrograms were obtained with actual working models or systese In some cases they were made with a laboratory setup simulating the systems under scrutiny In a few cases also the illustrations were made by cutting up spectrograms and rearranging the parts It should be noted in these latter oases that the boundaries are Measurements on Spectrograms Since an important part of the diagno- ale procedure consists in detemining the length of time elements and the location of frequency boundaries let us first exa %ins the procedures whereby the time and frequency scales of the 27 In so far as possible these 4 IN- The speotrogazsrIlo with the narrow filter shows al2 the odd harmonics of tate 60-cycle input to a special harzonic generator this isa a portion of a spectrogram made with the wide filt er The striations Below represent a beat note of 120 cycles At the left 1 a ortion out off and inverted The fact that the harmonics can beas other shifted positions# illusatrates the line@rity of the trelined up in this as qu enoy scale At the right is a portion cut off and shifted downward by one component Since they are 2U harmoncs the base line will fall exactly between two harmonics if it represents exacilY zero frequency if the power frequency is exactly known$ both the time scale and the frequency scale are determined by the two Patter above If the power frequency is not known the time scale factor can be determined by the inches per second and the frequency by P aA equation X L a TotaLl length Of the spec troiram circumference of the recording drum Ft Number of rotations of the drum In T seconds s a Number of striations in X inches Figure 82i Calibration of Spectrograph Soales 28 29 AWE-35 1 1 4 Upper Spectrogram 45 cycle Filter Lower Spectrogram 300 cycle Filter The frequency boundaries are determined by comparing them with the harmonics of the calibrating save These are all 120 cycles apart but the lowest is only 60 cycles from the base line The frequencies of the harmonics therefore are given by the above formula The element length is best determined by using the 300 cycle filter lhICh gives sharp time boundaries comparing them with the striations obtained by making a spectrogram of the calibrating wave with the 300 cycle filter Each one represents 1 120th of a second Ten of the above elements cover 70 striations The length of each element is therefore 1 10 1 70 120 seconds Figure 26 - Tina and Frequency Heasnrenentn unnaturally clear and sharp because in praotice any discontinuity causes a transient which tends to obscure the true speech along the boundaries It will be noted that some of the spectrograms in the illustrations were made with the 45 cycle filter and some with the 300 cycle filter depending on what features were to be brought out most clearly The spectrograph with which these illustrations were made was equipped with the control circuits mentioned in Chapter II and described in greater detail in Preliminary Report No 27 The illustrations are therefore clearer and sharper than those included in Preliminary Report No 25 Yurtheorore a larger number of privacy systems are included than in the latter report Each of the illustrations contains not only reproductions of speotrograns but also written material describing the features whereby the different scraebling systems can be reeognized It was intended that these illustrations should be self-contained in so far as possibli for easy reference It will be noted that in some cases the spectrograms alone are not sufficient to determine the exact nature of the scramble Cmtain systems completely destroy the typical hermonis structure of speech leaviag structureless patterns which cannot be interpreted This indicates a distortion of the wave form One of these systems which had a repeating code and a laboratory The output appears just the same as if two speech channels or a speech channel and an interfering noise were simply superposed and then modulated with a single carrier The stepped displacement system BS is rather easy to visualize There will be time boundaries with two or more discrete conditions of displacement Obviously there are a great number of possible seQuences inoludlng the poesibility of some of the coditions consisting of inverted displacement The irregular wobbled displacement B4 will of course be similar to B3 except that the wobble pattern will not be as simple The continuously varied reentrant displacement 0 is praotically impossible to simulate artificially e@ was done with 01 If 01 is thoroughly understood however the appearance of a wobbled instead of stepped reentrant condition is not difficult to visualize Ron-repeated code TD 73 will have o-eeedoeT wilhe the same general appearance as repeated code TD It may or may not have the synchronizing pulse There will of course be no regularity in the patterns such as was pointed out in YL Ts plus inversion 01 is not difficult to visualize Some or all of the elements might be inverted as in AS The systems listed in 05 and 06 synchronizing pulse could be resolved by the oscilloscope as shown in Chapter VI figure 46 No general rules however can be given for diagnosing this type of system 3 Systems Not Illustrated will both show equally spaced time boundaries corresponding to the length of the elements In 05 the harmonies would be spaced much farther apart than in normal speech and show greater slopes and curvatures Alternate elements would show rather consistent differences in frequency distribuxtion and in the degree of slope or ourvature In G6 the harmonics would be spaced abnormally closely and show very little slope or curvature Words and spaces would be very long There would be a horizontal boundary in the middle of the band and the patterns in each half would appear like complete spectrograms with vowel and consonant structures apparent In both of these systens if the elements were out apart they could be rearranged to form continuous speech with the time and frequency scales compressed or expanded from the normal condition see Chapter VI Section 2 Azaeination of Table I shows that there are a few scrambling systems which are not represented in the illustrations These will be discussed in the following paragraphs In moat cases the appearance of the spectrogram pattern which would result can be visualized by analogy with other systems The phase reversal stitei A4 will produce a scramble indistinguishable fr the multiplication system 51 provided the phase reversals occur at irregular intervals and about as rapidly as the crossovers in the coding wave involved in El It is believed but not known for certain that they would have to occur about that often in order to make speech unintelligible The split phase system AS involving carriers 90 degrees apart was tried out in the Level modulations E2 and 3 would hardly show up in spectrograns because of the level compression incorporated in the epeotrograph This has been verified experimentally 30 In J1 and 2 if the noise were suffioient to mask the speech efteotively the speech oculd not be seen in speotrograms J3 is easy to visualize as is also N4 If the noise spurts are sufficiently close together however they tay produce a pattern like Hi J5 as far as is know exstsonlyon per Channel known exists only on paper VI on decoding methods The various methods of scrambling such signals Kl 2 3 4 will produos discontinuities in these traces which are easy to visualize A sample of E 5 has not been available mizxing L3 can be done in various ways and at various speeds It will not be very easy to recognize if done rapidly No actual systems are in use as far as is known In vocoder types of scrambling systems the speotrograph would show only the chanel sigmale which might be either amplitude or frequenoy modulated osoillograma of the For wavethis formtype of of eachscramble separate It is felt that the above illustrathand discussions cover the known scrambling meth ode fairly thoroughly It is hoped that with their help any system which might be encountered in the future can be recognised Deoodin of course is another matter which forms the subJeot of the next two chapters channel signal provide the best mems for diagnoeis and for decoding A sample of such oecillograms which was obtained from an actual vocoder system is shown in figre 42 in Chapter 3' ati V XONCRYTDOGUPHIC TOOTS AQ Beginners in the study of privacy eyeteon never fail to be amazed at the difficulty of scrambling speech suffiojently to destroy the intelligence The ear can tolerate or even ignore surprising amounts of noise nonlinearity frequency distortion misplaced components gaps superpositions and other forms of interferenoe We can therefore very often obtain partial or even complete intelligence from a privacy system by partial or ipe4rfeot decoding and this in turn oa often be accomplished by operating on the scramble in some way which the designer did not contemplate Incidentally the fact that the ear is 12oOTDS of this is simple inversion In this case the soranbled speech is quite unintelligible to diroot listeninog but if we kow it is inversion we can find the inversion frequency very quickly by trial Another example is the split phase system A5 The phase shifting network in the captured set could readily be adjusted to demodulate either of the two overlapping sidebands Slightly more complicated systems are t those with a simple program Again with a captured set or its equivalent it is usually easy to find the isprogram by trial The only possible difficulty in keeping step with the sending end particularly if there is no synchronizing such a good decoding tool in ombination with pulse these noncryptographio methods makes the produotion of privacy systems very difficult Scrazblin systems which look very effective 6n paper sometimes turn out on trial to degrade the intelligibility very little although the scrambled speech usually sounds unpleasant LMost methods if they are pushed to the point where they do succeed in hiding the intelligibility are impossible to restore with good quality There are in fact very few speech privacy systems which achieve a high degree of privacy with acceptable quality displacement BN It for instance the wobble is sinusoidal with the frequency and the sweep limits known the problem is to keep in synchronism In this connection a device might be mentioned which is familiar in gun-fire control circles namely aided trackin With thia system changes in both frequency and phase are made simultaneously This is illustrated in figure 27 Suppose we find ourselves slightly out of step with the signal By rotating the adjusting handle forwards or backwards we ean get back into step Suppose this adjustment was These noncryptographic methods are very important because they may reduce the delay in obtaining the intelligence substantially to zero Furthermore they may render completely futile the most elaborately irregular code oha ning hystems hich could be handled only with the greatest difficulty by straight cryptographic methods A number of noncryptographic methods are given below Some of then of course result in poor quality but the saving of time labor and equipment may be very great Each of the noncryptographic ethods has been given a designation whioh appears in Tables I and II and at to catch up is an indication that the motor is slow Therefore sons of the otion of the bandle required for catching up is used by means of gearing to change the frequency drivin the actor The gear ratios are chosen to suit the particular problem With this method it is possible to got the beginning of the following paragraphs in which they are discussed These designations An example of this is a wobbled band in the forward direction The fact that we had morAT NG AATOR ADJUIs NG CHANG POSITION PIANoLo OtRENTIAL Di AA-M SYNCHRONOUS o'ro should not be confused with the designations appearing in the text which denote privacy wthods 1 Captured Set or YtLnotiona l Equivalent 1 With many privacy eystems all that we need in order to listen in is a captured set or its functional equivalent built from knowledge of the soranbling rethod An extreme example CH4ANGE FREQUENCY VAf A5 -OCILATOMR igure 27 - Illustrating Aided Tracking bands are variously delayed F1 Conceivably# these delays could constantly be changed with tim according to a never repeating prcgraz however would be futile because with a band filter we need only listen to one of the lesti bands disregarding the others band is Tory narrow the intelligibility may be practically complete Similarly in band splitting systoes if the switching is not rapid Dl we can follow one of the bands around the frorange The lowest or second lowest band is usually the best Another example is theA tone sequence 3 instead of trying to filter out one tone at a time as it occurs 3r5 can leave all the filters in ll of the time and still have enough speech coming through to yield the intelligence into step with and stay in stop with systezs such as alternate displacements and regular wobbles NetodsThis onornis 2 Decdin The methods outlined in this section have all been tried at least in the laboratory Their success however naturally depends to s020 extent on the switching rates and similar variables It is possible therefore that a method might prove sauccessful against aquensy scramblin g system which seems to be in the same general class as the one that was tried in the laboratory A special case in which the rejection UPP90 CUTOFF 13KMO moo 0 To I$KCd I To f I ligure 28 makes decoding easier concerns those systems such as A5 which depend on carrier phase to mix and then separate components There is no phase requirement imposed on the demodulating carrier unless both sidebands are transmitted Therefore either sideband of such a system my be 0 Shift Filter -Band suppressed with a filter and the remaining sideband demodulated with a carrier of any phase The two signals in the sideband will then be AI IF mo For purposes such as those outlined P R- ---1- -CON A Mtrated 1 T T iTrelocated in figure 28 Wiith this devices a band of adjustable width can be taken from any partion 'of the signal frequency range 0-3000 and T0 TT in any other portion of the sane fro- A Take for example a system A 2 which involves inversion about a numnber of fre4uenoiee in succession If these frequencies arc not too far apart we can choose a single frequency somewhere in the middle range and demodulate the whole signal with this one frequency The rea ultin g band will be right side up but displaced by varying amounts not exceeding half the total range This has been found to be quite intelligible provided the switching rate is not too high or the range of frequencies too wide quency range either straight or inverted One form of band shift filter is described in Prelimitary Report Noe 11 It coneists essentially of a double modulator such as was described in Chapter Ilk but with a band filter of variable width If the frequency location of the band is not to be changed the switch in figure 28 should be in the left-hand position One form of variable band filter is shown in figu re 29 ncranoh rvdueu Ti olhsas systems such as the multiplication system Ell and the T system El a oretitms it is expedient to listen to a scramble only part of the time Some of the simpler coding programs can sometimes be brokendown in this nanner by trial For instance if k With som sytm it isexpedi ent to o th frquecyrance o oly lisen potin rather than the whole range An outstanding example of this is the system in which the sub- a codine cycle has N elements we can listen to every Nth element atln ake whatever adjustments are needed to macke this sound natural oca then listen to the next adjacent element and Figure 29 -Variable Band Pass Filter 34 to esooth the output and give the envelope wave The rectifyin action which we want here simply tbkes all the negative lobes of the signal amd turns them over As in the case of the limiter straight speech put through a rectifier of this type is about 95 per cent intelligible In the privacy system designateaA4 the phase of the speech signal is reversed at short adjust the syten so that these elements blenA properly This attack applies for istance to a system in which several different displaceA oaptu ed set of course zents are used B2 is the easiest way of selecting every Nth ele%ant because it is usually easy to make the other time elaeznts inoperative A nother useful devioe is the limiter or peak chopper In this sam class is the ornpressor These are illustrated in figures 30 They all tend to equalize the waocesA o o The peak chopper sive lobes of a complex wave simply chops off any peak which exceeds a oerThe compressor tan instantaneous volteage operates more gradually and leaves the waves If straight speech is put through well rounded any of these devices distortion products are generated because the wave form is radically irregular intervals If this signal is now rectified all the negative lobes will be adoe positive and the resulting wave will be inditinguiehable from rectified straight speech except for alight discontinuities at the points where the reversals occurred in the privaoy ystern This is illustrated in figure 32 Therefore a simple phase reversal system no matter PAI modified It is found however that this kim of distortion damages the intelligibility very little These devices should be useful eagains t any privacy system in which sudden changes of level occur A good example is the subband A separate limlevel modulAtion system 03 iter or compressor in each of the sub-banLds will tend to sooth out the level variations and make the speech intelligibleo moo A A nother nonlinear device is the restifier Two forms are shown in figures 31 k and o The reotifier as used here should not be oonfused with the detector The latter device also rectifies but then it has a time constant incorporated in the output circuit which tends jigun 31 SI - t Rectifiers I T ORIGINAL SIGNAL V I I n FROM P INTODE I OMRT RID - - I o V I I I COMIPRESSOR Figure 30 i GRID PENIOD 5 I Peak Choppers and Compressor Figure 32 35 - I OO RICTILECI iV I ORIGINAL RECcTIFIED I Illustrating Action of Reotifier a how irregular should yield to rectification oxsept that distortion in the transmission process tends to obane the Wave form and thereby degrade the quality of the resulting speech It should be noted that the multiplication process Hi also results in a phase reversal every tine the ooding wave passes through zero It has been found that reotification tends to make this kind of scramble more intelligible also I connections is made from each of the bandpais filters to the output modulators whereby each of the bands in the signal is placed in the desired bands in the output Steps should be taken of course that these cross-connections do not interfore with each other An amplifier after each band filter for instance will perform this function Figure 33 illustrates a simpler case of superposition applied to a system using 2 band shifts Es A very useful noncryptographic device is superpositico For inatane suppose we had a three-ohannal Miing system such as U or 2 If we simply listen to all three channels simultaneeouly we will hear three conversations at once or possibly one conversation with two noises superposed Experience has Shown that under such conditions it is usually easy to concentrate on the desired channel and ignore the others Wo AC woodials It nay be noted here that superposin time-displaoed elements does not appear to be successful For instance if all the segments of the commutator in a TDS machine are connected to all the pole-pieces the output will be straight speech with several sorazbles superposee This has been found to be completely unintelli- gible In certain cases which have been met in Project 043 the privacy sets are equipped with or similar means which were intended to provide an easy method for obtaining a large number of different codes In soe eases the different codes may not be Sufficiently different to be mutually private That is while there may be literally millions of different oombinatiots it sometimes happens that theresar thousands of combintios which will decode material scramlled with one of the combinations Various degrews of quality of course will reult fro theme sitfo partial or incorrect decoding thepailorncretdoig operations However as long au intelligibility can be extracted the codes cannot be considered mutually private In such cases it is possible with a captured machine to simply manipulate the dials systematically or unrystematically and listen to the result When the speech begins to sound Somewhat natural systematic trials of eas dial in turn will sometimes steadily improve the quality Something of this sort could be done with simple TDS systees also except that the use of interlaced codes makes this somewhat more difficult LP swa13 188C Figure 33o - One form of Superposition Decoding Another form of superposition is illuistrated by the rollowing Consider a split band system D2 in which 6 different codes are used in a never-repeating sequence This would be rather difficult to handle by cryptographic means Suppose however we had 6 separate docoding unite each set to decode one of the 6 codes If the sorazbled signal were fed into all 6 of these decoders sizultaneously one of then would always have straight speech in its output The other 5 would be sorambled If these 6 outputs are all superposed we will hear straight speech with 5 sorazbles superposed This straight speech can be understood quite easily It will be noted that the unwanted components in this kind of superposition are derived from the wanted components and always vary in level simultanoouely with the wanted components it appears that under these conditions they do not do much darAge hl In certain oases where there are a large number of codes possible but only a few of these codes are good codes from the standpoint of direct listening it would seem reasonable that asy code applied to the scranbled signal should turn the good code into a poor code In the 5-band split band system for inttanee there are soe 3840 possible codes but oly 12 or so are considered really good Any code in the decoding machine therefore should decrease the rivaey for direct listening This has been tried in the laboratory but has not been pushed to the point of determining whether it could The split band equipment illustrated in figure 11 of Chapter III is adapted for this kind of Suiperposition A multiplicity of cross36 compete with the superposition ethod It is mentioned because the idea Bay possibly apply to other systems which may be encountered o - o A very speoialized device which apDlies to wire line communication only should be mentioned here because it is not very well known It distinguishes between the two directions of In the masking privacy transmission over wires systex 12 for instance the clear signal in one 'jyD o LUP 81ASID RELAY AD direction is masked by noise sent in the other direction The device illustrated in figure 84 however discriminates against the noise allowing the speech to be heard It requires a small series resistance which is built up by a The step-up transformer to the line impedance Figure 35 occurs NOW _____ ___ Figure 34 3 - Automatic Deooodi - Total Inargy The same method can be used for level Instead of modulation systems H2 and H disconnecting the receiver the high level portions of the signal cause the receiver to be connected to a parallel path containing the required amount of loss to equalize the levels In the case of subbani level modulation HS of course a separate device of this type must secondary is connected to the other side of the line The direction of discrimination depends on the phasing of the transformr windings MC - be used in each subband --- SPttCH ONLY Directional Discrimination Automatic Decoding Whether speech is intelligible or unintelligible is a purely subjective matter However the uthod of ma ing speech unintelligible involves aking physical changes in the speech wave Certain kinds of physical changes can be detected quite readily by objective means and utilized to undo the scramble automatically h The system just described operates on a total energy basis Sometimes it is possible to obtain a switching rignal on the basis of ' energy frequency distribution Consider for instance the system using two different displacements B2 The alternate positions of the speech band are illustrated in figure 36 In one position the band is right side up an occupies the range from 2 to 5 ke The alternate position is inverted occupying the range from 3 to 6 ko Since most of the energy in the speech band is concentrated in the low frequency part of the original spectrum most oo the time the system illustrated in figure 37 can be used to decode this material automatically The signel is applied to two band filters one covering the range 2 to 3 ko the other passing 5 to 6 ko The out-uts of these band filters are reotified individually and fed to the two windings of a Obviously the moat elaborately irregular code program is completely futile if this kind of decoding can be applied A A very simple example of this is showm in figure 35 Suppose the system consists of uort spurts of noise applied in an irreguler aanner It has been pointed out that the noise must be high in level compared to the speech in order to uask the speech Therefore if the signal is applied to an amplifier detector connested to a relay or electronio switch the relay can be so biased that it operates only on the noise spurts The receiver is nomentarily disconnected from the line whenever a noise spurt TIME I 0 I I I 5C EUR REQUENCY Figure 36 37 Sidebands in Two Position Displacement System IOKC other way Consider a system in which the band is kept right side up but in w6bbled over a range sufficient so that demodulation with Ae intermediate carrier frequency will not give an intelligible signal Suppose the wobble follows an irregular nonrepeating program The decoding is proposed The signalrshed is ispressed on a network TONU -l MOD IN 6 6 K-C 1 ofollowing IKC having 'a If the speech band were not wobbled this network would simply tend to make the lowest harmonic of all voiced sounds the strongestoompontoa With the wobble the same thing will be true ezsept that the level of this component will undergo severe fluotuati oso Therefore the rosulting signal is subjected to some form of automatic volume control and also a limiting action tendin to derive a single frequency Forgetting voice inflections for the derived frequency would fluctate up moment and down this POLAR RELAY 7igure 37 - Automatic Deooding-Energy requeney Distribution polar relay Obviously the relative energy in polar the2 fl te wiolel7 be differenati sorte 2 2 lthe entd falters will be different for the 2 i diplaeaens an th rely i oAr o7oLllbe operated alternately in the 2 directions thereby r ie pe in figu n ea t the dutomaticalty conde automatically connectinG the proper carrier to the input mohlator in figure 33 to put the speech band in its normal position Obviously this will not be infallible but with displaceSednts as different as the oes used in the i2 lustration it should operate sufficiently well to yield most of the intelligence of the messaee Naturally the smaller the physical difference o' i between th- 2 positions being distinguished the ilb Ewvr hr mor f looeain moore false operations there will be Eswaver this method is instamtaseous even with an irregulerly switched system whereas cryptographie methods would be very tine-consuming rgvett n wi r to lde So o ois SImade n t this f trceha mup voiu e inlco tiwnsd in frequency in step with the band wobble In fact it could be used as a subearrier in a double modulation decoder to demodulate the signal to approzimately the correct position in the frequency range It will be in error however by an amount equal to the instantaneous voice pitch Possibly this amount of error will not prevent the signal from being intelligible weo know that this a ount of displacement does not destroy the intelligence of otherwise normal seech If it is desired to correct for this error two methods suggest themselves One possible method is to subtract from the derived frequenoy by a modulation process an amount equal to the average pitch of the voice being monitored This will leave a small fluctuating error Another possibility is to derive the aotual instantaneous voice pitch by difference tone methods as in the previous section and subtract this amount fron the derived suboarrier frequency If the displaced band is inverted inof right side up a similar procedure can be used with a network of opposite loss oharacterietics Obviously this method in either 2 Another variation of this general technique night be mentioned for the sake of coapleteness elthough it is somewhat more speoulative Consider a privacy system which depends on speed changes M4 Changes in speed cause changes in the pitch of the voice Suppose we apply this signal to a circuit which measures the voice pitch This teohzique has been worked out in conneotion with the voooder The output of this to is a of varying frequency Th a a motor the speed change which used circuit i d h t e a rstead motor is part of the drive of a magnetic tape recording and reproducing system through which the signal is passed As the motor speed is to change the tape speed changes in such a direction as to tend to keep the derived freo quency constant This takes out not only the speed variations but also the voice inflections However a monotone is quite intelligible been tried out very steep rising loss characteristic case will correctly demodulate only the voiced sufficient sufficient notsooze someki o carryover catryove eofIf not kind of feet migt be incorporated in the system to vent sudden ohaages in the suboarrier frequency and thereby tend to hold over correct demodulation for short unvoiced sounds also As mentioned above this method has not been tried but is felt to be worth recording because of the is intended to apply to irregu- 1cr band displacements or wobbles B4 which great difficulty of handling irregularly wobbled would be exceedingly difficult to handle any systems by any other method 38 j Another rather speculative automatic method might be mentioned because some for of the method might prove useful against certain aultiplication systems such as Hl The code wave in the particular case encountered was repeated many times per second and there was a synchronizing pulse ahead of each cycle If the signal is applied to a synchronized cathode ray oscilloscope with a highly persistent screen a definite pattern appears because the codingwave always passes through zero at the sao time Also the speech energy tends to average out sfter a few cycles so that the pattern reflects the aplitude of the coding wave It is quite conceivable that this pattern on the screen could be scanned optically and used to generate a decoding wave for atcratuially unscrw lUing the signal Obviously if the coding wave is changed periodically a new decodin wave is automatically produced The only requirement is that rectifier or limiter difference tones will be generated which will lseo be multiples of 100 cycles If however the speech band is displaced from its normal position in any way the difference tones will not coincide with the If for instance the whole speech components band has been displaced by 50 cycles then the speech components will be 150 250 850 etc The difference tones generated by a nonlinear system will be 100 200 300 etc If we now take a second difference between the output of the nonlinear system and the original components there will be generated multiples of 50 cycles The lowest component of this series will be This will be lower than the pitch of the voice true regardless of how far the original band has been shifted except for the special case where the shift happens to be an exact multiple of the voice pitch Since however the pitch is constantly varying this coincidence is of very the coding wave persist long enough to form an average pattern on the soreen brief duration Theoretically at least a low pass filter with a cut-off lower than the normal range of voice pitch can be used as a clue to deternmn whether a speech band is in its proper location The method then would consist in having sveral decoders in parallel but listen only to the one which did not generate a onponent in the low pads filter L Another variation of automatic decoding methods might be termed parallel automatic because two or nore complete decoding units are used in parallel but only the correct one is applied to the listening receiver To emphasize the difference between this method and the one previously discussed we will use the same example namely the system with two band dieplacements Referrins to figure 33 suppose instead of the parallel modulators there were two complete units in parallel inoluding tbe band filter the second modulator and the output filter One of the units is fed with the 8 ko carrier the other with the 16 ko carrier Each unit will have straight speech in its output half the time and the other half of the time will have inverted speech displaced by 1 000 i The above illustrations will serve to show the possibilities of noncryptographie types of attack on privacy systems When a new system is encountered this' type of attack should be given serious consideration because of the saying in time and equipment Naturally as pointed out above straightforward cryptographic attack can be made to yied'a better quality signal However experience has shown that the ear can become familiar with certain kinds of distortion and learn to extract the intelligence more and cycles A 1 000 cycle low pass filter can then be used in a device similar to figure 37 to switch the listener to whichever one of the decoding units has the straight speech For the particular system used in the illustration ther does not appear to be any particular advantage of one method over the other However the latter system coe be applied in oases where the other method might not be feasible j The parallel automatic method can be made to give a different type of switching signal For instanoe we might make use of the harmonic relationship between the oozponents of speech when the speech band is in its normal poeition If the voice pitch happens to be 10C cycles say then all the harmonics will be multiples of 100 cycles If this speech is put Sthrough a suitable nonlinear system such as a more readily with practice In general noncryptographic methods require that the signal as received be of fairly good quality In some oases the saving in time labor and equipment would be so great that if the signal as rooeived is too poor to pernit nonoryptographio attack the most reasonable thing to do is to move the intercept etation to get a better signal In Table I there is listed for each privacy system the type of nonoryptogrBphic atwhich might apply It should be euphasized once more however that the method which suecends at one switching speed nay fail at another The list therefore should be taken only as a reoomendation of systems which should be considered The nonoryptographic aecoding methods are suamarized in Table II S ntack 39 nYPTWRAPHIC TOOLS AM o2TEOlS uous changes with time presents formidable teohnical difficulties at the authorized as well as the unauthorized terminals A cryptographic decoding method involves 1 actually determining a code which will undo the scrsmble 2 restoring the speech by means of this code In the case of repeated codes this can sometimes be done rather quickly An example is the repeated code TDS system The actual codes used can be found in about 15 inutes Having found the code we can set it into our reoeiving machine and thereafter listen to the sprech directly In the case of zonrepeated codes every bit of the mestage must be hadled individually It may take a thousand or even a hundred thousand time as long to decode as it It may take hours or did to speak the words even days to obtain the intelligence from a short message meanwhile other messages will have been sent and it is obvious that we get farther and farther behind The only way we could avoid this is to have approximetely as many toeams workin in parallel as the ratio of decodiza time to message time which of cuarse is impractical if the ratio is large 2 In cases where the scrambling system of the speech elements in rearrangement involves time or in both time and frequency the basic method for determining the codes involves outtirg up spectrograms along the element boundarise and rearranging the elements so ae to An example is restore the straight speech shown in figure 38 The criterion for rearrangins the elements is that there should be conThis continuity tinuity at the boundaries includes the position and direction of the individual harmonics the position and direction of the resonance areas and in general the aMlitude as represented by the darkness or lightness of the patterns The pieces are numbered before the matching process begins and when the matchhas been copleted the numbers on the iiing Matching Spectrograms progran De t erminati pieces determine the code The simplest cases to handle are those involving a program which ca be determined di- If the scrambling process involves inversion of the time or frequency scales straight reotly from spectrograms by inspection or measurements The reentrant inverlion system 01 nig ht be used as an example Supose a nultiplicity of displacemnts were used in some irreguDiscontinuities marking the lar sequence inversion frequencies appear in the speotrogram and once they have been determined by masuremants on a large number of spectrograms the progran can thereafter be determined quite readThis template can be ily by using a template marked directly with the settings of the decodig naehine which will restore the speech to its normal position speech can be restored for matching puposes by making two spectrograms as shown in figure 39 Present models of the spectrograph include means for making a aeohanically inverted pattern as well as a normal pattern The spectrogran at the top of figure 39 shows a normal pattern Directly below it is an inverted pattern of the sam material A mechanically inverted pattern is indistinguishable from a pattern produced by Similarly electrical inversion of the speech if the whole inverted spectrogram is turned through 180 so that the base line is at the bottom and towards the observer the result is indistinguishable from the case in which the speech is transmitted backwards Therefore if an element in the scramble is inverted it nay be recovered as straight speech for matching purposes by cutting the element from the meohani oall inverted pattern If an element has been transmitted backwards it can be restored to normal by cutting it from the inverted pattern and If it is rotating it 180' as described above both backwards and inverted it may be restored by cutting it from the regular pattern and turning it around Another exa ple involving a program would be one like B2 in which two different displaoements were used alternately with the intervals irregular in duration Here the time boundaries will be quite apparent and they can be measured with a suitable time scale It In all likelihood chnges of the above types will occur in discrete steps for practioal reasons The use of a program involving cootin41 ram an rum 1 3 1 m m mm - 7 v 7 Nnt v 2 11 1 Mad 7n i 7' Inversion It tho scramblo contains invortod alum thou will oppoar right side up in mechani cally invortgd spoon-carom Tho tint mlo ho Morton by rotating tho olonontl 130 demos Rota tho positions of tho 11 no- 1n tho onnploo obovo Figure 39 - Illustrating lnmsion of Tim and Frequency Boole in Spootrogrono J W- mwx Hunk- 1 -455 44 - - gure 40 Hatching Spoon-amp Patterns of ho-dimmimnl Samhlo It has been found from experience that matching is facilitated b% oi1laring the spectrograma by a factor of about 2 to 1 Hot only is the increased size easier to handle but the heavy photogra tio paper is much better to handle than the facsimile paper The latter is delicate it texture and its surface is easily at aimed In this connection it should be noted that the process of enlarging the spectrogras does not appreciably affect the decoding tine in the case of nonrepeated code systems There will of course be an initial delay but in general the matohing time will be controlling Spoctrograms o be made enloaore and out up If it is found faster than they oan be matched necessary however to use spectrograas for matching purposes regularly then it might pay to adopt the technique described in Preliminary Report 'o 13 for producing large spectrogram photographically more serious of the two effects It causes energy frox a strong element to spill over into the adjacent following ele8ent in the spectrOgram This difficulty is unlikely to cause trouble in any application of the spectrograph except decoding Therefore it is felt that %eans for alleviating this difficulty shonld be recorded here A small amount of exploratory work has been done along these lines but the eibodiment of this isprovement in a speoltrograph has not been accomplished because the need was not sufficiently pressing in Project C-43 The basic idea for avoiding the ob- To facilitate matching appropriate means should be used for handling the elements It has been found that a slightly adhesive surIn the illustration of face is advantageous figure 38 this surface was provided by coating the boards and also the baoks of the elements with ordinary rubber cement This is also the case in figure 40 This latter example shows a two-dimensional scramble Horisontal strips of rubberised board were provided for atcinceloo th Bristol tis ais suitable for matching along the tine axis souring effects of spillover is to permit the spillover to take plane in such a way as to be ior instance suppose subsequently removable a sample of TDS were recorded on the tape and suppose the speotrograph were equipped with a suitable switching arrangement such that only every alternate element wu reproduced The spillover from each elemnt would then occur in a blank area and it could subsequently be trimA med off leaving a sharp clear boundary second'spectrocra could then be made of the alternate elements again trimning off the spillover$ A logical extension of this idea wic al extesion of th ide which would save acme time would be to have two lsannitc filtersseans and useRoth thenthealternately switching inputs and by the outputs of the filters would have to be Once a system has been thoroughly diagnosed certain numerical properties of the codinc process will be knowt iAyvotage should be taken of this knowledge to supplement and check the matching process Lxzaples are given in Preliminary Reports Nocs 10 14 22 and 26 switched and the two switches should be separated by the appropriate tine delay to take account of the tranmission time through the filter A third variation of this idea which requires loes equipment is to make one speotrogram in the usual manner and then make a second spectrogrma with the machine running backwards The spillover always occurs into the leading edges of the elements in spectrograms Cutting the first spectrogram in the proper ntepoe pcrga is h utn will places result in clear sharp right-hand edges on each element but earh left-hand edge the seepillover Cutti e e obscured by d will give will laces proper the end spectrogram in clear left-hand edges on eaoh eleaent wlatches on e lement rothe than edge cle could then be ads between elements from the normal and backwards spectrograms in such a way as to utilize the good edges of the elements The two examples thus far cited of speotrogra matching were artificially produced by cuttina up spectrograme of straight speech and the boundaries are therefore clear and sharp and hefrequency In practice the In time pactce ineand reqenc boundaries bondaies will be obscured by transients as may be seen in the illustrations accompanying Chapter IV trequency bondaries are filter cutoffs and they are marred by overlap or underlap and by phase distortion This however is not as serious as the transients occurring at the time boundaries There is a basic difficulty here arising from the desire to obtain a hiGh degree of frequency resolution which entails the use of a narrow scanning filter The response and decoy time of such a filter is appreciable in In other respects it is to be expected that the patterns produced by the speotrograph can be improved For instance studies have comparison with the element length in many been made which show that soranbling systems preseeted in such a way that they pan be inter- The decay time produces the 45 amplitudes can be re- PW -9 88 13 31 38 1 3351 9931 yuan mil alga align i 5 Ia a ln ii ii 111 a 1 - llun IllIla-I15 lilalliil 6 11 1111101 inning-1 Flirt uli LLII II-IL dla ll laill It gill ingot-9 1 13348 11 I lli 1v ilul Id it s 1 1 3 3 168 3 It if i xigm u sl mg II 11 1 ELEEH $31 11 if I'll- ill-Iii 31 11 11 x l 11 31 311181 ill-I ll i is its 1 1 Iii preted quantitatively This is an improvement simply related to the TDS elements No diffi-I culty however was found-in matching the variable area patterns to find the TDS code This is described in Preliminary Report go 19 This report also describes a scheme for nullifying the effect of split band coding on the wave form This consists of modulating all the frequency bands down into one frequency band Changes in the split band aode will then have no effect on the wave form of patterns produced in this %enter@ over the rather indefinite shades of gray in the usual spectrograzs It would provide another criterion for matching In sowe oases however this might loo a handicap lor instance in TDS systems the pole Pieces ea not all of equal otticiency The amplitudes of adjacent speech elements are affected by this change in efficiency and they might net appear to natch whom they really should This condition of course might be aggravated intentions lly as part of the privacy feature of the system On th whole however it looks as though amplitude representation should beean impr'ovement indecoding work It was also proposed at one time that the use of a whisper or monotone instead of nor- 8 _Ustoh1t Varifble Irea Patterns hs ben fund or omepurpsesit tawaeforsmepattrnsoffes iethaien fouandae v aptide or d caberti r that wave trornatern offe be akdieclmoe raeiplyd apectorasThey can o17 produce the original speech Intrinsically wae form patterns are not as good as spectregrans for diagnosing frequency shifts and the likes However they present the time scales move graphically and they are not subject to transients at time discontinuities such as the spillover effects discussed in the last section The particular type of wae form pat tt orus nfo ful ud wmas a v riabe a ea atwrask ataiabed are pat-n usefuld tern founla tosth pictures Variable area patterns are more dietinotive to the eye than osoillographic traces They forn geometric designs that catch the eyeon and facilitate matching The manter of producing and playing back these patterns is described in Preliminary Reports Ies 1 7 and 12 An example of variable area patterns in process of matching is sh wa in figure 41 taken from Prolsinry No 26 of Rpor Variable area patterns of this type have been found particularly good for decoding TDS systems especially repeated code systems It will be noted that amplitudes are clearly represented in these patterns By matching multiplicity of cycles of a repeating code eye- Thsi1ecibdi8 lniayRpr Another feature of the variable area patterns which might be useful is that the pattorus have characteristic shapesi Usually they look like a serises of damped oscillations with the highest amplitude at the beginning of each fundamental period This should enable the re c o g nitio n of cas es in which #peech is tr ans mitted backwards The characteristic periodicity a whether pattereqeicytbaldso be iusedtproper t rpe o whtheioreunybadin Towa rd the end of prjojet 0-4 8 it came to be rifoonized that there would be considerable advantage in using a compressor in the production of variable area pattefrus This tends to bring out low leve sound The distortion the wave forms resultitg fro a instantaneous 0ompressidon is immaterial if th 7 are to be tsed only for matchning This kind of compression however should be sharply distinguished from automatic volume control action The latter is to nake matches impossible 4 Matching Oscillograms though the wave tori itself might be obscured by other features of the privacy Ssytem For in stance the use of split band coding was once It was stalted in the previous sfection that osoillographic traces could be used instead proposed to increase the privacy of F11D systems This coonbination would be much more private than plain TDS if Judlgid on the basis of matching spectrograms particularly ifthe split band at eaie IO 6 relatively slow acting and it is obvious that in TDS systems for instance it would alter the amplitudes of certain elementc in such a way a tea simultaneously it ispossible to take advantage of this amplitude representation even codes were rapidly switched mally7 inflected speech would increase the privaoy of MS systems Again this is true in terns of spectrograms but it was found that variable area patterns could be matched almest as easily for whispered speech us for normal speech and with the monotone it was actually of variable area patterns although in general there will be a disadvantage There is one type of privacy system however for which osoillographic traces are required namely vocoder systems The signals in vocoder channels are intervals not 4' I - I I i I V -4 K 9 4 V 1K I GBP Ft S Q I I t4IR b I i ' L - ' I - - z 3 fiAr4 h 6 I er I-I- - I ' I jf Jc F V ___ ____ ______ 48 __ jut essentially fluctuating d-c signals after they re modulated down to their normal frequency location They can best be examined in the form of ozoillographio traces ligure 42 shows a set of uaistortea vocoder channel signals It will 9 noted that there is Litendency Ibe for the ampli- tudes to vaty sinultaneouly in the several track It has been found that if the signals in the various channels are perauted even with the sharp edges resulting from artificially produced scrambles the number of mismatohes tends to be about 40 percent This means that a acooder system with its channele permuted at short intervals provides a rather difficult privacy system to decode gi - enhances the value thealueofosi of otoillographic traces enanceso aphitra oes of of ax lithis type Without compression the lower tudes are obscured by the width of the traces Instantaneous compression makes changes in the magnitude or direction of the traces apparent in the lower level sounds The patterns shown in figure 42 were produced in this nanner 5 Indicator Methods A variation of this method which hu been suggested but not tried and which should be much faster is as folles Reproduce tWoe reoorded sample through a low-paus filter say 2500 oycles Pass it through a Ma machine end then through a high-paut filter with the same out-off View the output of the high-pass fitter on a cathode ray oscilloscope whose sweep is synchronised with the TDS cycle Transients will occur at the boundaries of elemearts which do not belong together These will generate frequencies higher than the out-off of the highpass filter and will appear as pulses on the scope The absence of a transient will indicate either that the elements belong together or that no energy was present Again a syetematic cycle roiy of codes should place most of the elements correetly Another example of the indicator mothod is the following Suppose in a split band D2 system 6 known codes are used in an irregular sequence and it is desired to determine the sequenoe The following procedure is suggested Record a sample uad reproduce it through a do coding machine equipped with one of the proper In the rollowing methods a visual indioation is obtained denoting which of several possible choices puts the speech eleoents in their proper order These methods of course are applicable only to sues where the possible number of choices is not overwhelmingly great A natural example of a visual indication occurs in the illuetration of TDS in figure 59 Whenever two originally adjacent speech elements remain adjacent in the scramble the two elements are not separated by a time boundary in the petrogram Elements which do not belong in adjacent positions have a boundary resulting from discontinuities in the harmonics and from spillover effects The absence of a time boundary can be taken as an indication that the two adja cent elements belong together To make use of this effect the following procedure is suggested Record a saz2le of the soranble on a loop of tape Reproduce this sample through a TDS machine and make a spectrogroa noting any adjaoenoies which occur Chamge the code in the TDS machine and make another speotrogram again noting adjacencies A systeatic set of codes shoul beore advaeeules ante which aet ofodes should be wpoked out in advance which explore Sall the possible combinations of elements At the end of such a cycle of operations it should be possible to place a large percentage of the elements correctly This oa be applied to nonrepeated or repeated code TDS doeodos and make a epectropaz Certain elements in the spectrogram will be seen to be norSal speech These elem4nts Of cousel are the ones to which the particlax esde applies It is much easier to determine whether a particular element consists of straight or serambled speech than to determine which particular code was used Repeat this procedure with each of the other five codes Iach element can thereby be identified with a particular code varation of this procedure which should gve more positive results is as follows The output of the decoding machine used as above is rectified before makin the spectroram Rectifying normal speech does not add iarmonie componet whereas rectifying speech which conccpotalc s band shifts results in inharmonic nents This is illustrated in figure 43 The upper speotrograa shows rectified straight speech This looks perfectly normal except that the frequency range is somewhat more completely covered with harmonics than is the case in norzal speech The second speotrogram shows a sequeies of split band scrambles The third epectrograz shows a similar salple rectified with none of the elements decoded Rectifying the undeooded elements results in a complete snear in the speotrogran compared to the reotifled straight speech Properly decoded elements will stand out more clearly against the background of rectified scrambled speech 49 h Afwv wk Ll IL 50 mam mm ame 1 CO v-umu 1 - Straight' dpeeoh Rootiflad WV - W nk 1130r ww Hm ngr P - 3 - Similar to 110 2 Rect1fied Figure 43 - Shaving Effect of Bootifiontiou on m1 and Band Shifted Speech NON Now- Ng o100 L g VICE oft RELAY I TE PW A AMROi CN APLWINiI SAIICk ITItC GBPIPM9iNT 0 I 4 SAAWLIK OF SCIRAM5LIED S K c ON T'APE NWO U k fCSIL TING PATTERN CODE AWrTCMINO POINT P4 N IILE 60WD SCRAMOh OLTA F1 IIit 0 2 C I L- TMOCLAO a-0FKUN1 A ii rCNII 4 APPL ICATION TO SPLIT BAND DICOOING I -____ 41 ______ - 4SILENT I 1I N 1CAM INTERVAL i ture 14ICTE TRUE POM74 N 44 - Band Shift Detector Adaptation of ipeoitrograph for Yigure 45 Decoding Switched Split Band Scranbie Tb output of the low-pass filter is fed to the marking saaplifier Whenever the output 'Of the low-PUs filter is Beroc there will be no 45 knother variation of the indicator method was touched upon in Chapter V It consista in sublecting the scrambled speech to a ones tone lower t'han the pitch of the voice ure omonnt fich scrambed s In are inort ance of cessively at each of its 10 values or 5 if invrswiong not is Tetie Rpal usure wisp osed o aus f t te tec 51mltr dtevies winbec awaernc thwese If asetheng trces iheagien tins ln ofqu upt each a th oc Th n theih o fact lie lowe larepresetsatsilent intwervach setingle blan in-ce foe beused toi decterminetfor each elseent is a iru wteilisem contnoksomethisgindicathe therv init popr reuncylocwtich freuncy band it ioll relte a these settings were the correct ones If none of the marks for a particular element are came rox that verted The spectrograph night Ie used to speed up the analysis process as illustrated in figure - tem has not actually been tried in this complete form but enough work has been done to show that 7X j2 51 it is possible to make use of the presence of inharaonic components in som such mazzr It appears therefore that a substantial fraction of the elements in a 2-dimensional scrambleo'mgt be identified as to frequency location One other possibility of this type might be menticced Variable area patterns of rowel sounds have characteristic oonfigurations These configurations depend on their harmonic structure and a disturbance of this structu Se should chamge these Patterns in a recognizable nanner For instance if the components are inharemnic there will be no perio4oioty at the It might therefore be fundamental pitch rate possible to use varitble area patterns which can be produced nuch nore rapidly then spectrograma as indicators along the lines of the above discussion 6 Application to Table I In this section we will examin e the application of oryptodraphic rethods to the specific soraoblizg systeos listed in Table I In this table the systems which might require cryptographic attack are indicated by a referi ence to a page in this section The follo wU paragraph numbers refer to privacy systeas in Table 1 iA4 Among the systems listed under single modulation the only one that might require oryptographic treatment is the phase reversal system This system is a special case of the multiplieation system which will be treated later B4 08 Among the double and triple modulation systems the irregular contir-ious displacements have not been handled by noncryptographic methods It might be necessary to take a continuous series of speotrograms to determine the displacements as a function of tins This might some day be done continuously and instantaneously in which case conpensatind frequency changes might be mude continuously by hand to decode the material systeMs i band splitticd Aoow the Dl e i od es can be the fixed or slowly switched solved by inspection as discussed in Chapter IV If the code is rapidly switched on diagnosis however single elements seldom contain suffioient information to deterUins the codes If the switsaing sequence is a repeated sequence it nay be worthwhile for the sake of quality to determine the sequence end get in stop with it In this cooe the nethods described in Section 5 above should be of assistance If the switching sequence is never repeated the indi- cated non-cryptographic methods apptar most reatonable 7 r S syetem yield very poorny to 7 attack For repeated code noncrytograhi systems however the code cat readily be determined by zatching either speetrograas or variable area patterns# taking advantage of the numerical properties of the codes These zethode are covered in Preliminary Report No 14 Nonrspeated code systems however have thus far been found exceedingly diffliult to handle although the methods of Sections 9 8 and 8 above apply Efforts in this direction are described in Preliminaery Report No 28 74 Speed variations according to sote preliminary laboratory tests are rather ineffective in maeking the intelligence of speech unless the variations are exceedingly wide and Technical difficulties then become so rapid this appears to be an unlikely prithat great vacy system by itself Small variations in speed heover might be used to make speatrograms of TDS system more difficult to match In this case however it will be unnecessary to determine the speed variation program if the MS scramble can be removed 01 0 G8 Coabinatione of TDS and froequency scrambles are interesting fro the cryptographic standpoint Since repated code TS systeus were found easy to break it was proposed to add various forms of split band scrambles It was argued that the continuously changing frequency scrambles would alter the shapes of variable area patterns so that they could not bm matohed Furthermore the changing frequency scrambles would sake speotrogrus unsuitable for matching especially if the split band codes were switched nonsyschronously compared with the o8 boundaries Each tine the frequency code was twitched a new vertical bourdary would appear in the speotrogram and in combination with the TS boundaries the spectrograms would be very severely broken up in the tinm scale It was found hovever as d esussed in Preliminary Report No 19 that if the TDS code is a reopated code the frequency scrambles can be practically ignored in matching variable area patterns Having found and removed the TS code the remaining frequency scramble can be solved by noncryptographbi methods In the case of nonrepeated IDS however the addition of split band coding would increase the difficulty considerably provided that the two coding systems do not provide clues to each other The most promising method for Figure 46 - Illustrating Repeated Code Uultiplioation System handling this system appears to be to determine the split band codes first by the methods of Section 5 above If the split band codes are then rtnovrd the remaiing scramble can be handled aa straight TDS Another possible method is to make variable area patterns with all tht do oodes superposed as described in Suotion St in Chapter V The resulting patterns however gardless of the value of speech signal at the mosent If several cycles of scrambled speech material are superposed therefore they have the appearanse shown in the photograph figure 46 The superposed traces show a definite pattern with regions of high and regions of low anplitude and also sharp indentations These lattsr are the crossover points of the ode wave will not be as satisfactory for matohing at patteWns of straight speech There iw also a marked tendency for the peaks to occur alternately above and below the center line but the amplitudes of the peaks are not al alike jince the speech amplitudes tend to average out over a nunber of cycles the amplitudes of the superposed peaks reflect pretty accurately the amplitudes of the coding wave at those points The probable shape of the coding wave based on this evidence has been partly traced in 04 The two-dimensional scramble can be handled by natching spectrograms if a repeited code is used Experiments along these liaes are described in Preliminaro Report No 22 If the code ts nonropeated however it would be oxceedingly difficult and time consuming to htinl dle by unaided matchiMn It would help considerably if the original frequency location of each element in the scramble could be deotermined This night be accomplished by the methods described in Section 5 HI aeteroining the code for multiplication or phase reversal systems can be accomplished quite readily if the code is repeated at sufficiently short intervals In the one systen which was Met in Project 0-4 3 Preliminary Report Mlo 18 the code wave was repeated 100 times per second In this case the soranbled signal could be applied to the vertical plates of az cecillosoope with the horizontal sweep synchronized with the code cycle It ic obvious that every time -he coding wave passes throuEgh zero the soranbled signal also passes through zero re- It has been found experisentally that if only the crossovers of the coding wave are reproduced the speech will be intelligibly decoded The decoding wave need not be the reciprooal of the coding wave It can be like the one drawn in at the right in the photograph It is only necessary therefore to generate a wave having its crossovers at the indicated points and reverse the phase of the scranbled signal of these points H2 HS Level modulations by theaselves are but with they other might systems very well used not in private combination in be an attempt to foil the matching of speech patterns The level modulations themselves however need not be solved cryptographically mudt be set into this machine perhaps in the The scrambled asterform of a punched tape al must then be re produced and fed into the enahane maintaining proper sanchronism between the reproducing and decoding systems Obviously this is a very formidable job 31 There appears to be no method either cryptographic or noacryptogrehio for breakins the noise masking abod if the noise is predistorted random and suffiocietly high in level Thee requirements to really ask the speech however make the technical difficulties for system operation very great and it is unlikely that this method can be used over radio channels Cracking this system therefore becomes a matter Project of solving the noise distorting systea lines these along experience no had C43 has here are some alternative possibiliIn the ties which uy apply in special gues case of nonrepeated code TDS for instance the process of matching variable area patterns has actually restored the speech in reproducible form Variable area patterns can be played back just like the sound trackhs used with motion pietures A playback neine of this type is describ4d in Preliminary Report fo 18 The re- 1l K2 18 14 Scraebled veeoder channels can theoretically be solved by matching Actually u mentioaed in Section osoillograns 4 above this procedure is very difficult because the channels look so much alike aranged elements are moutned on a strip of adhesive and scanned With a light slit and photocell Considerable noise is caused by the Joints between the separate elements but this could be largely elizinated by a specially designed squelch circuit perhaps controlled by a separate light bean and photocell to out off the output wherever a joint is passing under the scanning been The first attempt to use this decoding method was unsuccessful as discussed in Preliminary Report go 28 However there is nothing basically wrong with the method it asi- Ll L2 1 Channel mixing systems woald be exceedingly difficult to handle cryptographically if a sufficient number of channels Were involved so that non-crytographic methods were inapplicable The only possible method of atSince tack appears to be matchinj spectrograms however about 25 percent of normal speech consists of pauses many of the switch pointA will occur in these pauses and it will therefore be difficult to establish continuity by matching 7 Deternination of the Message ply needs better execution than it received in the first attempt TVe objective of deecodin work is usually not to determine the codes used but to lean the intelligence which was tranmitted under these codes In the case of repeated code systems the procedure for obtaiting intelligence is obvious once the ode has been determined by the methods outlined above It is only necessory to set this code into a mAchine similar to that used at the receiving end of the system being eonitored and listen directly to the transmitted speech If the naterial has been recorded while the code was being deternined the recorded material con in general be decoded in the a ne way __ If the solution of the coding system requires speotrogran rather than variable area patterns it is still theoretically possible to A playback maplay back the rearranged pieces chine for spectrograms is described in Preliainary Report No 17 This first model requires a negative transparency of the spectrograms to be scanned by a light slit and photocell with a multi-frequenoy light chopper interposed ahead of the photocell Again the method is basically sound The experimental machine described in the report needs considerable improvement before it will yield adequate quality for the purpose described above in order to overcome the deult aue ytejitb gradation of quality caused by the joints by slight nisplaoements of the elements by epillover at the boundaries etc Jurthermore in order to get good patterns for matching the signal must be subjected to a very high degree of onspression which distorts both the time and the frequency distribution of energy It may be necessary to make one kind of pattern for matchiu and another kind for playing back as wae done with the variable area patterns described in Preliminary Report No 26 In the once of nonrepeate od e eyete is the determination of the code sequenceegaaino leaves us in general a long way from the deterObviously all the nination of the message material must be recorded in scrambled form It is aeoossary during the process to establish time reference points in the scramble perhaps by superposing clicks or spurts of tone during the recordine process and referring the code sequences to these points A doeoding aaohine must be available such as the one described in Preliminary Report INo 18 which is adaptable to a variety of coding system The code sequence 54 -1Zk 7_T7 -- _ As a final alternative it is possible to learn to read speech speatrograu by visual inspection Theoretically therefore the rearranged speotrograns might yield the mesage direotly Fere acain however the boundary distortion will increase the difficulty of reading the ptterns It has also been found that the beat patterns for matching are not the best for reading and it aax be necessary to make two ' 55 sets of patterns However since spectrograas have been continually improving the possibility of visually deterzining-th3 intelligence froa rearranged spectrograzs zust be listed as a aditinot poseibilityy ana one which ifit is feaalble is the zoat general of all methods since the basic procedure is the same for all of the sorambling methods which can be handled in this manner PAC TCAL EVAiUATION OF PRIVACY SYSTEMS The material in the foregoing chapters is intended to be useful not only for possible In the oase of repeated code systems the craoking time determined in the above way interception and decoding of scrambled meseesges but also to aid in the production of new privacy systems and to estimate the degree of security which we might expect to obtain from these or other systems Uxperience has 1hown that there is a strong tendency to underestimate the security or military value of a given privacy system as soon as laboratory studies have indicated that the system can be cracked In this chapter therefore an attempt will be made to point out the great difference between what might be termed theoretical or laboratory evaluation and practical or field evaluation In order to balance the effect of the previous chapters this one is written from the standpoint not of the man interested in decoding a system but of the man interested in getting a practical privacy system into use in the field substantially represents the total decoding time because as mentioned previously this code oan be set into a receiving machimn and the message obtained directly Some additional time might be added however for determining what was said during the time that the oode was being determined The procedure outlined above is very 1 Orackina Time The objective of a laboratory study of a privacy system is to obtain somekind of qusatitative measure of the time or effort required to decode the system The questions are How long does it take to determine the code and how much equipment and how many people are required In general the procedure is to acquire a pair of actual models of the system under scrutiny ThI coding and decoding processes are studied in detail possibly with the aid of nathematical analysls to determine whether there are anyweakmesm or any oharacteristios of the coding process of which advantuge miGht be taken to assist in the oraohina process Possibly a noncryptographio method will be found to apply In this case the oraoking time reduces substantially to zero If nonoryptographio methods are not applicable awilable cryptographic 'ools and methods are brought to bear Usually a new scrambling ayetoe will require modifications or ohbn es in the existing tools or techniques Possibly the basic methods can be improved for use against this particular system or possibly new methods can be devised Presumably after all this development work the project personnel will have become skilled in the art of decoding this particular system The oraoking time can then be determined quantitatively perhaps with estimates as to how far this nay be reduced by further skill well illustrated in the series of Preliminary Reports covering the development of cracking methods for the repeated cori TDS system They include rnathematical analysis Fos 3 and 6 the 1 and development of a new decoding tool eos 7 and the reduction of the docodiag technique 14 In the case of the maLlto a routine 11o tiplication system the ohronoloical steps are all listed in one report No 18 Too often the cracking time as determined above is quoted without qualification to describe the security of a system It is of course usually understood that the use of this figure involves the following usumptions 1 that the enemy kows all about the eoding system 2 that he is equipped with an adequate supply of the machines our own models may still be far from the production stage 3 that he has developed the same decoding tools and techniques that we have some of our tools may be entirely new and secret 4 he is equipped with an adequate supply of the decoding tools 5 he has trained men in their use and 6 he is in a position to receive a good signal free of interforense Such aesuaptions certainly represent an extreme possibility Experience has shown that there is a strong tendency to forget just how extreme a condition such assumptions represent Bren if the assumptions are valid there are still other factors which affect the military value of a privacy system as will be diecussed in a subsequent section 2 Nonreneated Code Systems If the code is hanged periodically it may be necessary to have several decoding teams working in parallel in order to keep up with the transmitted material as was mentioned in the previous chapter The number of teams whioh will be required depends on the relation I j between the intervals of the code changes and the cracking tine No particular difficulty presents itself in expressing the decodin offort under these conditions in term o ___ hours The evaluation is complicated however by the necessity for additional equipment not only for decoding but for recoriing the product of the number of steps on the vidual wheels Such schees should be dofstinuished from truly nonrepeating codes because wherever cyclic processes are used they are subject to analysis This is a matter pertinent to the field of cryptanalysia and will not be discussed here In general it may be said that the difficulty of solving such long cycles is not determined by the total length but rather by the length of the individual suboycles In the cue of nonrepeaGed code s97teow the cracking time for any given portion of a message will in general be Iona compared to the duration of that portion of the message Zvery portion of the message must be cracked individually ad the decoding effort can be ampressed as a ratio of decoding time to message time This ratio may be 1 0Q0 or 100 000 to 1 that is each second of nmssage will take 1 000 Gonversely it or 100 000 seconds to decode would require 1 000 or 100 000 teams to keep up with the messags as they are spoken Systems designed to produce a long code sequence usually contain provision for readjusting or realigning certain elements periodically or from day to day Assuwing that we kncw all about the system except the momentary settings estimates can usually be made of the length of tim and the number of people it would take to determine the unknown settings by anslysing a given sample of the cod sequence The analyst requires a kncwledge of the code for a long sequence of soraubled speeoh before he can begin the work aimed at determining the unknown setting Es must obtain and solve a suffi- This kind of evaluation is somewhat unsatisfactory because the length of tine it will take the enemy to determine the intellipece in a particular sentence which might carry milltar information will depend on whether or not he im at the moment working on this sentence or whether he is wasting his tivA decoding previous material which might contain no information of value to his It ha in fact been proposed that the seaurity of such high-privacy systems could be materimlly enhanced by keeping the circuit 100 per cent busy with all kinds of material possibly even from recordings making certain that the eaey has no way of determining when the circuit is being used for passing important information As in the ease of noa repeated code systems it seems a bit unrealistic in evaluating such a system to assume that the ineny will seBise upon the few seconds of message time which are important and to compute the length of time it will take him to decode that portion of the s8 Code Analysis 1any schemes have been proposed for generating everohanging codes by a combination of short cycles geared together in such a way that the number of elements in the cycle is the product of the number of elements in the individual cycles One scheme is to use odd ratios such as 99 to 100 so that the code cycle will not repeat until the smaller wheel has %ad 100 revolutions In other words there are 9 900 steps in the code cycle before it repeats Another scheme is the cycloneter type in which one wheel rotates one step for each revolution of another wheel Again the total cycle is indi- ciently long sample of the scramble by the methods outlined in the previous chapters and then analyzs this sequence to obtain the settinge Too frequently the evaluation of a coding system is based on the analysing tim alone whereas tho time required for solving or unscrambling a long sequence of scrambled speech nay be overwhelsingly greater than the analyting time In fact if there is no way of solving the code sequence from the soraable alone then the analyst can contribute nothing and the system is still secret regardless of any inherent weakness of the cyclic coding system e EvaIuation The continuously changing military situations of modern warfare require rapid means of communication in order that the required military actions can be taken Obviously a perfectly seouoe speech privacy system is of no military value if it requires so much time for encoding and decoding that it slows up the conunaeation system to the point where appropriate steps cannot be taken when needed Obviously also a oraoking system is of no value if it is too slow to permit counter measures to be taken according to the intercepted intelligence or certain purposes 15 minutes or even 5 minutes cracking time is much too slow Where this is true a privacy system giving 15 minutes or 5 minutes privaoy is just as good as one with an hour's security This is important because systems able time aza equipment to intercepting and deoodina them which afford a few xinuzea of privacy uan be produced in portable form whereas those pro- vidin loner privacy at the present cannot itigAdvantae iht als be taken of te etkno h Avnaemgtas element of surprise consider also the equipment and train- Suppose we suddenly introduce in the field a low-grade privacy syetem in large quantities 11ow long would it take before the enei diagnosed the systea developed a decodin method manufactured receiving sets ed personnel required for decoding intercepted 0oounicationa As a specific exaaple the small TD unit required about Uo minutes for decoding but it required a van-load of highly speoialized equipment as described in Prolimimary Report No 24 Suppose the small portable TDS unit were used in mazy planes and tanks and other mobile equipment that required som privacy Suppose also that different codes were used distributed these where neeaed and organised end trained personnel to use then Until he has done theoe things the units provide complete seorec7y different kind of systen night then be introduced which would again prorido aeorecy within different groups of units and that the for a tim codes were changed at some reasonable interval Would it be worth the enemy's while to provide enough decoding equipnent and enough traid m sidrto It ta intended in the foreoin to point out that there are other onsiderations in the evaluaticn of privaey systeas than the tire it takes a highly speoialised group such as the personnel of C-43 to decode the system under the ideal conditions of a laboratory The decoding time alone is so often quoted because it is the only element which tan be described quantitatively While there is always theoretical agreezent about the existence of the other considerations apparently they cannot be pointed out too often or too stronaly of the proper type and also deooding equipment personnel to follov these units around and de- code their neseages If it is not worth his while then units rated as low in privacy W provide high grade privacy under such conditions Obviously the foregoing does not apply if the unite are used to convey wessegs between the hiaher echelons of command In such cases the meseages have a longer term significance to the enemy and he can u'ford to devote consider- ___________ __ C 4 - - - - y - - S I I I liii II it K 4 K I 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I - I A 2 - ii 4 U A - I I 4 1 w C iLl 'Ii' IiII 1111111 iljJj 1 77 I U S 11111 jF A - 13 1 I - -1 GBP ii i U 4 4 K ji i f i 1if' I J 111 1 I U jlj 4 I'j i I ii jIII I If lit 3 t4 II iji 4i jJ a i 13-5-3'11 Vvk J i 81 m 1o the none In eyoto- no tho motions illustration Int a bond or noise hon been edded to innrooeo the minoy Ono bolt 0 the highest of the tutu- from bonds into which the ohonnel one divided hoo been filled with them noioo In tho upper opootrogren this noise no atoedy Ind 111 the lower one it no turned on and off about 4 than per second note thot although tho noiao no introduced into only one oubhond 1t oppooro 1n or the four oidohonde 1n the above ptterno 11113 ohms that In run each oldohond con- telno components no eooh oub hond - I 77 14 '35 Figure 57 - Time Division Hultiplox lith Eloisa Channel I IIJ I 1% fl-Iii II 4 iIHII I II g1 3 38 niacin 8 95am I an 33 3 3 8383523391533343 Egg-nagging gg aga j l agaa ggug a kigugaa gg II Ki 3ill Qr 11 J 1 44 4 It Ii 1 11 Id 585 Emigm gamers SE mm 88mm Kit 3 n t ifif KJ vz 11ML phi-51 45 4 27 137 gingham m5 mascara 535 an Eu no 83 3350 8 53m lasagna- aqua lain-Egon Eh gg ggian nua sauna-ungain- 104 ink-chug gouging-Aug a igi uigog Eggsgihogiaoi aa 1 1 Ilifl f1 140-A U 4O O h ajA 0 4 13 144 Oh 1114-1 i 0a l 47 i 1 4 g IN o 3 4 can Macaw-5519 you ush 93 th r aunt-5 8 ugi i uSPg-gu ag nagging-8355 52 pol-In IB-gagl ilgl cleavages- 3 i 3 55H33i 1 55 gg u 38 Aug-nagging gugan g lzg u og-o g a iinua ou 51 11 13 31 1111 an FrJu Ha 7 1 13% if 91 7 f 93 93 Human I 8 chum gai q nh g g luh 5 qu causal ag a azgg ngauuga 3 5 11 italu- p ul1 4 s 4 23 5 1 1 1 11 43 I I inch r3 1 JF W4 H 1 W at st ELMH mu uf u TW 1-i - in fit E 1 filL ii n I jsiX I I IiiI ii I j J j t 1ii 1K Er 1 95 it I hi n I Iii j1Ri ' A ii P11 i'a wn - Ix u h Ai' 7 pr - All 1 The upper'apeotrogranlahoaa a continuous noiae lithlaeuaral enrda or'eyllahlee shoeing through the harmonica ahoaa that of the noiae ia ahauti llcatlaa Examination or the eignal aith an oeoilloecope ahoaa that the nod-e oonaiata of abort pulaea about 10 ailli- aecoode apart These can he removed hl a blanking circuit - The lower epectrogran aha-a a not the as the one ahoea eithout tho pol-ea the outstanding characterintic an in the sample aha-e in an alnoet coaplete lack of the structure of now-a1 ape-ch llao the energy ia distributed name or leaa evenly near the ireqpenoy range for each eomd or ayllahle There are no characteristic areaa There axe no regular houndariee either vertical or horizontal the aeqnenoe of eorda and epacea looks nomeal in the apectrograa and hen the annual cadence of speech to the ear These charactewiatica axe to he eapaoted1Ihan the scrambling ayetaa operatae on the nave Iona directly In thin particular system the speech was anltipliad by a coding'aaee the latter repeated 100 tiaea per aecond aith a pulse bet-eon each cycle It in obvious that a hiahu egree of eynohxonie- 1- required to-reoove the cod- ing nave at the receiving end ahich astounta for the high frequenqy of the pol-ea It may he noted that phase reearaal at a sufficiently high and irregular'rate to achieve privacy in also eaaentially a multiplication pron-ea except that the coding'aara haa no valnaa other than pine and alone unity or each a ayateanaoold be expected to look like the above- figure 65 - multiplication 32mm rttr l 1 A b 51 n 15 r n 1 H3555 Santa Ola I 3 Pam___ - --- -- - - ___________________ _______________ I I 1 ilJf if I I I II I It 1 44J Ii ' kl i j El i1 mi- a0j hi I 1A a 9 1111III 11111 a -'- - - - - _____ -- __ ----- 1 0 I I 9 2 7 2131 D aII LIP bg auakul a glad Ill - Pillarvyouugsigg lvga hb ggo gs-gang 7 rr_ 777 Irv-1 J gagging-BE gigs-Egg 39 53% Fguggngag alight Ii an He m4 may nun 5 1 A 14 -4 14 1- 4 1 N - A w 4 I Ni I' 44-- - 4 4 If I 4 ui Ow 44i -14 14 0 a A 10 9 po - 4 4 A -4 103 a A PC Q 04a NONCRYPTOGRAPHIC DloCODIoD IoTBODS Diagram Used by Zisousaion 1 Captured set or junctional Equivalent a 2 bytyen findinto lze stop Program - - got Simpoale Condtion Cozproxalse Deood iz Uethods a Interadiate Condition b Listen to Portion of Frequenoy Band o Listen Part Time d Limlter Peak Chopper Compressor e Reotifir f superposition a Approxiatm CMe by Trial SPoi l Uood Code by Reooding h is Direotional Discriminator 3 Automatio Deooding a Total Energy b 0 Energy Yerqumnoy Dietri utioe PitOh Change Corrector do Wobble Corrector o Code Wave Generator f as tTO Parallel Autozaria Inharmonio Detector 33 38 27 yes 28 and 29 'es Yes 30 ABsC 31 AB and 32 33 Yes yes 34 Yen No 38 37 35 yes 37 U and 37 No ITO 37 38 ITO 38 No 39 3o 39 34 34 34 35 35 Se ITo 2105 AT1- r ser 29345 TITLE- Final Report - Part I - Speech Privacy Systems - Interception Diagnosis Decoding Evaluation u AUTHOR Sj Koenig W ORIGINATING AGENCY Bell Telephone Labs Inc New York N Y PUBLISHED BY Office of Scientific Research and Development NDRC Div 13 ICC 0 5 SATIl Oct '44 ABSTRACT Secr CSIWOY L AN4JA Eng U S ASU None 0410 Ao-SS NO None 4 rIStUSTIASFON I 4573A '1'1 1photos tables diagrs The results of three years' experience in diagnosing decoding and evaluating speech privacy systems are summarized Speechprivacy systems may be used in connection with radio telephone systems or wire systems but radio interception problems only are discussed The decoding techniques described apply to wire as well as to radio communications The sound spectrograph is described including its history method of operation and capabilities It analyzes speech in terms of its three basic dimensions frequency amplitude and time and portrays the analysis in the form of spectrograms Basic speech scrambling methods are also explained in which the original speech is transmitted with its parts modified displaced or Interchanged Cryptanalysis and cryptography which apply to telegraph types of communication are also described DIVISION Electronics t SECTION Communications $ '-- J SUBJECT HEADINGS _ Communication systems Secret 23992 87 Decoders 28877 -A A 2 0 CAL INDEX 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