.-

·-

NATIONAL SECURITY AGENCY 

MECHANIZATION IN SUPPORT 

OF COMINT 

PHASE I 

WARNING· 

THIS DOCUMENT CONTAINS CODEWORD MATERIAL 

TOP SECRET cmJTROl NUit~BER 30:151 4' 

COPY If w.Of 3 f' COP:~S •• • 

PAGE OF ==-PAGES 

Declassified and approved for release by NSA on 08-16-2013 pursuantto E .0. 1352a 

TOP SECRET 
.,,. 

/ / 

\. 

'fOP SE€RE'f FRO'fli 
.. 

.... I.. ..... T0P SE'~R1EAf"EfltOTII 

N~TIONAt SECURlTt AOE~CY 

Washington 25, D. C, 

MECHANIZATION IN SUPPORT 0,. COMINT 

I: Phaee I 

NSA Form 781-ClOS I Jul 52 

Compiled by 

R/D Personnel 

October 1954 

T0P SECRET FR0TII 
~~----- - -

. . .. 

T~BLE OF CONTENTS 

Introduction. • • • • • • • • • • • • • • • • • • • • 

PHASE I 

I. Comint Collection Activities. • • • • • • • • • 

PL 86-36/50 USC 3 

EO 3 . 3 ( h) ( 2 ) 

\fage 

1 

(A) Functional Categories of Intercept Problems 3 

3. Government Communications Service ••• 

4. Military Tactical ••••••••••• 

5. Military Strategic • • • • • • • • • • 

6. Support Communications •••••••• 

II. Operations on Traffic Independent of System • • 

(A) Preliminary Processing .. • • • • • • • • • 1. Logging and Editing Problems • • • • • 

2. Data Conversion Problems • • • • • • • 3. Data Storage and Recovery Problems • • 

(B) Traffic Analysis • • • • • • • • • • • • • 

(c) Textual Analysis • • • • • • • • • • • • • 

III. Diagn~st1c Operations • • • • • • • • • . ~ .. • • 

(A) Search for and Statistical Evaluation of 

Phenomena. • • • • • • • • • • • • • • 

1. .~dentity Problems. • • • • • • • • • • 

2. La.tent Problems. • • • • • • • • • .. • 

(B) Test of Specific HYpotheses. • • • • • • • 

1. Ma.chine Systems. • • • • • • • • • • • 

1 

NSA Form 781-ClOS 1 Jul 52 T()P SEC:RE'f FR()'fH 

g 

6 

6 

10 

10 

11 

12 

12 

13 

14 

15 

15 

16 

17 

18 

18 
··:. .. ...· 

T l.\BLE OF COHTEN'.l.1S 

2. Hand Systems • • • • • • • • • • • • • 

IV. Operations Based on Knowledge ot the 

.General System. • • • • • • • • • • • • • • 2() 

(A) Machine Systems. • • • • • • • • • • • • • 2'0 

1. Analysis of Depths . • • • • • • • • • 20 

a. Depth Search • • • • • • • • • • • 20 

··- b. Depth '!'es ting. • • • • • • • • • • 21 

c. Depth Reading. • • • • • • • • • • 22 

~~ Machine Recovery and Reading • • • • • 22 

3. Decryption .. It • • • • • • • • • • • • 25 

. (B) Hand Systems • • • • • • • • • • • • • • • 25 

l. Additive Eneipherment. • • • • • • • • 25 

2. Exploitation of Statistical 

Phenomena • • • • • • • • • • • • 27 

3. Additional Complex Procedures. • • • • 28 

v. ·support Functions • • . • • • • . - . • • • • • • 30 

, (A) Linguistic and Statistical Aids. • • • • • 30 

(B) Generation ot Crypto-system Data • • • • • 30 

(C) Desk Aids. • • • • • • • • • • • • • • • • 31 

(D) Cryptanalytic Research • • • • • • • • • • 31 

(E) Collateral • • • • • • • • • • • • • • • • 3i 

ii 

NSA Farm 781-ClOS 1 Jul 52 'FOP SE€RET FRO'FII 
' l 

·'·· -.. - to~... , 

t-"f 

INTRODUCTION 

This study is an evaluation of the analytical machine 

and intercept equipment phases of the present Research and 

Development (NSA-30) program in light of the present and 

projected problems of Communications Intelligence. The 

conclusio~s· drawn from this evaluation (should) result in 

a R.esearch and Development program consist~nt with Comint 

mechanization and traffic requirements. 

The study has four phases. The following paragraphs 

serve as an introduction to the first two phases only. 

The present objectives or phases III and IV are included,, 

but may change considerably as phases I and II mature. I 

. Phase I attempts to uncover the a~eas where ~echanization is, or could be, of use to the Comint Effort. In 

phase I no a~tempt is made to evaluate previous or present 

efforts at mechanization in these areas. 

Phase II considers only the areas uncovered in phase 

I, and attempts to give a quantitative estimate of the 

success ot the present effort in each of these areas and 

thus reveal the shortcomings in the present R and D 

program. 

Phase III will consider each of the shortcomings 

·discussed 1n phase II, and will list possible procedures, 

NSA Form 781.ClOS 1 Jul 52 'f6P SECRET FROTH 
,, 

. .. . 

" 

techniques, etc. which can be brought to bear on these 

areas. 

Phase IV will analyze the relative merits or the 

procedures, techniques, etc. set forth in phase III and 

synthesize the results to formulate an R/D program which 

will satisfy COMINT requirements, be within technological 

limitations, and be consistent with agency and government 

policy. 

The collection of the information contained in the 

first two phases of this study was an effort directed by 

R/D personnel. Key personnel from Production have willingly and ably assisted in the actual writing or this reI 

port and in offering pertinent information thru discussions 

and conferences where and when needed. While PROD personnel assisted in 1;he formation of this report, the in1rerpretations contained herein are those formulated by R/D 

personnel. It 1s R/D's hope that these interpretations 

conform with those of the other Offices. 

That ~here are many errors or omission and commission 

in this report should be "a priori" knowledge. The R/D -:. 

Office will be most grateful to persons bringing these 

errors to its attention so·that a more accurate and more 

complete picture may.be obtained. 

2 

NSA Form 781-CIOS I Jul 52 1'0P SE€RE1' FR01'11 . .. .. ~. 
.· 

I. COMINT Collection Activities 

1he COMINT Collection Problem divides into two phases: 

the interception of the various signals discussed below, 

' 

and their f.ubsequent transmission to NSA Headquarters and 

distribution to the interested analysts. 

Sometimes analysts require information about a signal 

over and above that provided by a complete transcription 

thereof. For example,. it may be required th~t an indication of the quality of interception of enciphered 

tr•af'fic be supplied wl th the traffic on a character ... bycharacter or a signal element-by-signal element basis. 

_ .Another requirement is that of providing the analyst a ' . . 

record or time intervals between successively transmitted characters. Still another requirement is the 

inclusion or information which will serve as a means 01~ 

providing transmitter identification and in some cases the 

identification of individual operators. 

These requirements apply generally to severa.1 of the 

intercept situations. 

· (A) Functional Categories of Int~rcept Problems 

The various transmissions of interest: to NSA may 

be broken down into functional categortes. These functional · categol"ies px•ov1de certain degrees or information about 

the ch_aracteristics of the transmissions and thus some 

3. 

'NSA Form 781-ClOS 1 Jul 52 TOP SECRET FRO'fll 
PL 86-36/SO_usc 3605 

EO 3 . 3 ( h) ( 2 ) 

11'lformat1on :regarding the intercept problem. Inte~nal 

networks often create substantial problems in obtaining good intercept sites. 

4 

NSA Form 781-CIOS I Jul 52 T()P SECRE'F FRO'fll 
.· T{)P s@eng~B"fift{)TH ~L 86-36/50 USC 3605 

EO 3 . 3 ( h) ( 2 ) 

3. Government Communications Services 

This classification is used here for internal networks of various government organizations such as 

border guards,, secret police, police, agent transnt1ss1ons. 

and the like. These nets are generally widespread, have 

1ow traffic densities, and ,____~~~~~~~~~~---' 

irregular schedules. 

5 

-

NSA Form 7111-ClOS 1 Ju• 52 TOP SECRET FROTII 
,' 

l . 

4. Military Tactical 

·Military Tactical traffic {somotimes referred to as low-level traffic) is usually intercepted 

and often processed, to some extent, by the ~upporting 

, service COMINT organizations. This material is also 

forwarded to NS~. This traffic is usually low powered, 

and transmitted by simple communication systems with 

irregulaxr schedules. I 

5. Military Strategic PL 86-36/50 USC 3 

EO 3 . 3 ( h) ( 2 ) 

This category consists of high-level . military communications up to the very highest echelon. 

High traffic densities and regular schedules characterize these transmissions. \ 

\\ 

6 .. Support Communications 

This category compr~ses those connn,un1cat1on 

services used to ·support va~ious types of operations. 

These may be either broadcast or point-to-point transmissions. Weather nets and broadcasts, and navigational 

aids and services are examples of support communications. 

6 

NSA Form 781-ClOS 1 Jul 52 
,,,,. 1.. ·" . .. 

These transmissions appear on regular schedules. 

(B) Major Technical Intercept Problems 

1. 

Early 1n 1952, a\ 

' a. Naval Single Channel 

The first problem is to I • 

I This knowledge is required by 

the analyst in his analysis of the traffic. 

b • .....__I __ _____.I 

Here the.problem 1s to achieve good 

quality.1ntercept. 

~L 86-36/50 USC 3 

EO 3 . 3 ( h) ( 2 ) 

• . 

·~1 ~~~~~~~~~ 

7 

NSA Farm 781-ClOS 1 Jul 52 T()P SECRET FR()'fll 
NSA Form 781-ClOS 1 Jul 52 

~ '-" ....... ~T6-PR0TIIPL 86-36/50 USC 3605 

EO 3 . 3 ( h) ( 2 ) 

8 

rroP SEGRET FROTH 
.. , .' 'F0P ~Eft~6f6~R()~ll1 86-36/50 USC 3605 

EQ 3 . 3 ( h) ( 2 ) 

9 

NSA Form 781-ClOS I Jul 52 'f()P SEeRE1' FR61'11 
.• 

T6P ~flt-M16<FR6TII PL 86-36/50 USC 3605 

EO 3 . 3 ( h) ( 2 ) 

' ' 

II. Operations on Traffic Independent of System 

(A) Prelimina~y Processing 

Many operations must be performed on trarr1c 

. 10 

NSA Form 781-ClOS l Jul 52 'f()P SECRErr FRO'FII / 
arriving at NSA prior to its distribution to the users. 

These operations f~ll under the general headings of 

(1) Logging and Editing, (2) Data Conversion and (3) Data 

Storage and Recovery. The operations performed during 

these preliminary processing stages are independent of 

the crypto-system (if any) employed on the traffic by 

the sender prior to transmission. These operations 

performed on the intercepted traffic and the final forms 

and numbers of copies required are governed by the needs 

and desires of the analysts, machines, etc., which must 

further process and analyze the traffic. The problems 

in this area which appear to be amenable to mechanization are as follows: 

1. Logging and Editing Problems 

Generally these problems encompass the 

optimization and mechanization of the logging and edit-

,ing functions which involve the : .. ogging, processing, 

division of page copy into identifiable systems, and 

the deletion of uninformative material. 

Specifically the problems involve the keeping of a record of all traffic and the sections of 

analysts which are responsible 1 the sorting or messages 

in an order pre-determined by a format 1 and recording 

the messages in a log book by hand or by some niachine 

11 

NSA Form 781-ClOS 1 Jul 52 T()P SE€RET FR0'FII 
, .. 

' ' 

process. Duplicate messages are noted at this point and· 

messages are given worksheet numbers. 

The editirig problems include the deletion 

or uninformative material~ reordering of 1nformat1on1 

d1scr1m1nat1on between textual and non-textual groups, 

correction or group length and run-together groups, 

1ndent1f1cat1on or duplicate messages, etc. 

2. Data Conversion Problems 

Traffic arrives at NSA in as many as tour 

ditterent forms: hard copy, perforated paper tape, magnetic tape, and occasior..ally, punched ~a!'ds. Multiple 

copies or copies from which unwanted material is deleted 

may.be required in more than one of these forms. Because of this the general problems of this area center 

about devising procedures and effecting mechanization 

tor converting the original traffic into the various 

desired forms. 

The specific problems involve the prepara~ 

tion ot bard copy where it does not exist, and the preparation of edited versions of these data in punched 

cards, perforated paper tape, and magnetic tape as required as inputs to the various analytic machines. 

3. Data Storage and Recoverz Problem 

The general problem here involves the 

12 ,. 

NSA Fo11n 781-ClOS 1 Jul 52 T6P SECRET FRO:TII ,. ·-;,, 
., t •• 

selection of perma.nent media on which to reproduce all 

had copy received, the storing of information or use to 

the intelligence analyst, ~nd ~he maintenance or files 

containtng all-copy handled. 

Particular problems are: the reproduction 

on' a permanent medium, such as microfilm, and the numbering in the order or-arrival of all had copy traffic; 

the storage and filing of collateral informatlon of use 

to the intelligence analysts; keeping the files current 

by continual addition of both new subjects and new 

information under old subjects; and the immediate recovery of materia+ from storage or files as required. 

(B) Traffic ~nalysis 

Traffic ~nalysis (T/A) is that area of NSA 

primarily concerned with the problems of obtaining 

commun1cat1ons.1ntell1ge~ce from non-textual information. A problem of this area is the reconstruction of 

communication networks which carry communication intel~igence or interest. A second problem involves the 

attempt to determine the "order Qf battlen of the 

communicator, 1.e.; the location and strength of the 

communicator's armed forces and strategic material and 

the identification and location of key personnel. 

The specific problems are those or performing 

the sorting and indexing processes and other clerical 

operations of ·traffic analysis. Large volumes or 

NSA F0rm 781-ClOS 1 Jul 52 1'()P SE€RE'F FRO'fll 
.. . .:. 

traffic must be scanned to unc-0ver frequencies, call signs, 

message serial numbers, transmittal dates and t1~es, page 

and pad numbers, addresses, and operator mistakes. After I , 

studies are made of these results, communication nets are 

reconstructed or modified. 

Techniques which- are applicable in certain situations to network reconstruction, are the recovery by cryptanalytic processes, of call signs (transmitting station 

identification) which have been enciphered. These cryptanalytic processes are similar to some extent to those 

which are applicable to textual analysis. 

(c) Textual Analzsis 

Textual analysis deals.with the problems involved 

in the selection of messages of potential intelligence 

value from the large volume 'of plain text and plain eode 

me$sages handled by NSA. In plain text messages the 

communicators make no attempt to conceal the information 

content. Thus the problem ~.s one of scanning messages 

and selecting those messages which contain certain elements 

as _messages of intelligence value. 

In plain code messages an unenciphered code is 

employed for privacy and brevity. Here the problem is 

es~entially that encountered in the scanning of plain 

text, with some compl1cat1ng and some simplifying factors. 

14 

NSA Form 781-CIDS I Jul 52 'FOP SECRE'F FRO'FII 
, 

'• . T6P ~6FROTH 

The particular proolcmG in this ar~~ are: to 

scan rapidly an extremely large volume of plain text messages to see whether they contain certain words,, addresses, I 

signatures,, etc.; to print out the plain text messages 

conta1~1ng the elements sought for; and to categorize the 

selected messages by subject matter using words,, addresses, 

etc. as the criteria. 

The problems listed above are quite similar to 

some discussed previously. 

For plain code messages the same problems exist 

except that the problems are simpler in that code groups 

are usually uniform in length, but complicated by the fact 

that many codes can appear o~er a communications link. 

A problem unique with plain code messages is the 

automatic decoding ana printing; when the code book is 

known. 

A side problem is one of determining whether a 

secret code or a kriown conunercial code has been employed. 

III. Diagnostic Operations 

.(A) Search for and Stat1st1cal Evaluation of 

Phenomena 

Where messages appear which are neither plain 

. ' 

text nor in some readily'readable enciphering system, we 

must. in the absence of outside information, analyze the 

15 

NSA Form 781-ClOS I Jul 52 
.--------------

text of the messages in order to det~rmine the cryptosystem 

involved. The analyd~s may be of the texts themselves 

{Identity) or upon .derivative fori~ls of the texts (L:-;1.tent). 

I 

The problems of this area enco:upass the procedures in and 

the mechanization of: (1) -Che operations by means of which 

original text is converted to the desired latent form~ 

(2) the diagnostic operations involved in the search for 

and statistical evaluation of phenomena which arise in the 

original or derived text. 

We list the problem3 to be considered under the 

two headings Identity and Latent according to which form 

of text is being considered. 

(l) ;raenti ty Problems 

Here a problem is one of .se~rching for the 

exploit.able intrinsic characteristics of' plain language and 

its encipherments.- Examples are the widely varying frequencies at which the individual letters occur in literal 

text and the cohesion of plain language· as exhibited by 

the rough frequency distribution of pairs o·r letters 

(digraphs)~ triples or letters (trigraphs), etc. Under en-· 

cipherment the intrinsic characteristics of plain language 

are partially or totally destroyed. However, new characteristics may become prominent and these may be employed 

16 

NSA Form 781-ClOS 1 Jul 52 T6P SE€RET FR6TII 
•· T6P S~€BM6-fR6TII 

in the characterization of the enciphering system. An 

example 1s the Enigma machine in which no letter may be enciphered into itself. 

Once a type of message having particular 

characteristics is identified, a problem is to collect all 

messages of that type so that the benefits of a large statistical population may be employed. 

(2) L~tent Problems 

Sometimes a characteristic of cipher text 

is round, not in the text as sent, but in something derived 

from the text. For example, we can assign the numbers from 

1 to 26 to the letters from A to z. A will be considered 

to follow Z, as in a cyclic arrangement. By the use of this 

we introduce a measure of distance between letters of the 

alphabet. We sometimes "difference" the letters in a message by replacing each letter by its assigne1l number and 

then subtracting each assigned number from 1 •.;s predecessor 

in the message. In some cases the distance fz•om a given 

letter to its next occurrence is used to replac~ the letter. 

The problems met in the processing and analysis of Latent text are essentially those of Identity text. 

However, the problem of transforming the original text into 

the desired Latent form and the preparation of the Latent 

data for machine processing exists and is not fully included in the problems of Identity. 

17 

NSA Form 781-CIOS l Jul 52 'f()P SECRE'F FR6TII 
~ • 1' 

(B) Test of Specific Hypotheses 

on hy-pothes1z1ng th•:t enciphering procee·s 

employed in the production or the messages under analye18 1 

more specific tests may be employed to determine the val1di ty ot the original hypothesis. The hypotheses fall 

into two general classes: (1) encipherment was performed 

by a machine system, (2) encipherment was performed by a 

non-machine (hand) system (unencipherea and encipherect ~ 

codes are included here). 

Each eneipherment system produces certain 

distinct and observable characteristics which are discernable message-wise or over a selected group of messages. 

~e problems here concern the mechanization or the tests, 

operations, etc. employed in searching tor and establishing the existence or these observable characteristics. 

1. Machine Systems 

Certain machine systems produce cipher 

text hav~ng marked characteristics. For example, the 

Enigma t11>e machines cannot encipher a letter into itself. 

This phenomenon tends to make Enigma cipher text non-rando11l, in the ·sense that high frequency plain letters tend 

to occur less frequently in cipher text. 

The specific problems here involve the 

processing of varying aJ11S:Wnts of text to ascertain wheth~r 

18 

NSA Farm 781-ClOS 1 Jul 52 T0P SECRET FR0ffll 
,..,.. . .. ' 

,. 

/' 

TOP ~€RWf&eF-R01'11 

charac·terlstics are pres-ent. The proce~ ~ usua~ly includes 

statistical computations. 

2. .!:!and Systems 

Whenever it is believed that a new unenqipher- i.t 

ed code 1s in use, messages employing this code must be separated, from others sent over the same communications link. 

This Qan be done by comparing all groups within the m~ssage 

against' themselves for coincidences to obtain the internal 

"c!Pher"-group repetitions. A. problem here is to perform 

the coincidence tests and obtain the internal "cipher''-

group repetitions. 

When code structu1•es are partially or fully 

known,, all code groups in a message may be compared with the 

known code groups and scored statistically. The problem 

here is to perform the comparisons and do.the statistical 

scor1.ng. 

When codes are enciphered by means of an 

additive pad,, reuses may occur on a different communications 

link at a later time. If an additive pad has been recovered from the first use, other messages may be deciphered with the recovered key and the resulting texts inspected 

as in the first paragraph to see whether it looks like 

either known or unknown unenciphered code. 

Some codes have a "built in" checking feature 

19. 

NSA Form 781-CIOS I Jul 52 TOP SE€RE1' FRO'fll 
. 

' 

~h~p,h ~llows the message receiver to check his text as tc I J 

g;aJ1P:J_es,, lost portions of code groupsj etc. -One 'Such c~ck- ; ' 

:$.~ rea'.tur.e is that t:he last digl t of' the code group 1~ jibe· ' 'I 

m€>1Etu}a~ stim of· the other digits of the.code group. Su~h . ..·· 

chara~~·er1stles can be utilized to identify codes... T"ne 

I problem ~ere is one of finding and exploiting these check- . \.~ 

1rig .r-eatures. 

IV. Operations B~sed on Knowledge cf the General.System 

Encipherment of text is performed by means of a 

machine or hand system. In some cases we are able to 

assume with a high degree of certainty that a particular 

message or set of messages was enciphered (encoded) by 

means of a specific machine or hand system. If we pos3ess 

statistical,, partial or complete knowledge of the variable. 

elements of the system involved, then certain statistical, 

exhaustive,, or.analog attacks may be made to recover the 

messages and some of the remaining unknowns cf' the cryptosystem. 

For convenience we list the problems under two headings: (1) machine systems and (2) hand systems. However,, 

a great deal or overlap exists as will be seen below. 

(A) Machine Systems 

20 

PL 86-36/50 USC 

EO 3.3(h)(2) 

NSA Form 781-ClOS 1 Jul 52 T()P SECRET FR()'FII 
.. •1 •• 

I 

.,,> • 

NSA Form 781-ClOS 1 Jul 52 

TOP S~RiFfifstliR0rrII ~ PL 86-36/50 USC 3605 

EO 3.3(h)(2) 

21 . \ 

'· 

rroP SECRET FRO'fll 
,•J \.'> ,., .;, 

2. Machine .ftecovery ana Seti"Cing 

PL 86-36/50 USC 3605 

E.O 3.3(h)(2) 

Cipher machines are usually set up on two 

bases. The first' is an arrangement or the internal elements 

22 

NSA Form 781-ClOS 1 Jul 52 'fOP SEC:BET FR0'FII 
.: 

of the.machine which may be kept unchanged for a relative,-

ly long period (days, months or even years). This arrangement is call~d th~ internal setting. For example, the 

I 

wiring or the rotors,, the order of rotors, the plugged 

substitution between the keyboard and the input side of a 

rotor maze of the Enigma machine, and the pins on the 

Hagelin wheels fall into this class. 

In addition, there are usually means for starting the machine at some point in its cycle by setting certain marks (usually letters or numbers) on the rotors opposite their respective bench marks. This is called the 

message setting. 

The internal and message settings are considered 

as the variables of the machine. The problem here is to 

recover the internal setting {machine recovery) and the 

PL 86-36/50 USC 3605 

message sett1n$ { sett:lng recovery). EO 3.3(h)(2) 

...._~~~~~~~~~~~~~~~~~~~~~~_J' The Hagelin 

a.nd Enigma offers an example or the former and latter respectively. 

23 

NSA Form 781-ClOS 1 Jul 52 T6P SE€RET FR6TII 
.,• TOP S~6PRO'fll PL 86-36/50 USC 3605 

EO 3 : 3 ( h) ( 2 ) 

··· ... 

A problem which involves a combination of logical and exhaustive trial techniques follows. Let us assume 

that an Enigma machine enciphered the message. Let us 

assume also that we are given a crib (a length of plain 

text corresponding to a certain stretch of cipher text) free 

or garbles. In addition, certain of the internal variables 

are assumed. This narrows the field covered by exhaustive 

trials to the remaining unknmm variables. We also require an analogue to the cipher machine which supplies us 

with the Enigma motion and its internal elements. Then by 

assuming one or more features or each of the ·remaining unknown variables, we employ the crib and machine analogue 

to derive a set of implications. If the implications are 

contradictory, then our original assumptions were inco::-rect. 

We run through the set of possible assumptions and keep only 

those which lead to non-contradictory statements and which 

pass a certain predetermined threshold. 

NSA Form 781-ClOS 1 Jul 52 TOP SE€BE'f FRO'fll 
. ·' T6P S-8t:~D~R6'FII . . 

~ 

The number of problems involved in the attacks 

on machine systems is too large to list here. These problems are listed in Appendix A to Phase I. 

3.. Decryption 

At tlmes, a cryptographic period is completely 

broken, i.e., all the daily settings are recovered, and the 

message settings are recoverable as part of· the message. 

We are then in the same situation as the intended addressee. 

Hence the problem is to decrypt the traffic as i·t·· becomes 

available and print the resulting plain text. However, 

the high deterioration rate or intelligence makes it necessary to perform this decryption and printing as rapidly as 

possible. 

(B) Hand Systems 

1. ~dditlve Encipherment 

PL 86-36/50 USC 3 

EO 3.3(h)(2) 

Successful recove~y of additively enciphered 

messages depends.on the existence of·j 

I Sometimes the key is predictable ,____~~~~~~~~~~~~~~ 

because the text of some known book (like a table of logar1 thms or a novel) i.s used as though it were a sequence of 

symbols. At other times, the symbol sequence is generated 

by a typist striking keys in what he believes to be purely · 

random fashion. The problem is to provide the analyst 

with pairs of groups, one of which has a probability or 

occurring as a fragment of plain text and the other of which 

NSA Form 781-ClOS 1 Jul 52 'FOP SECRE'F FR9TII 
' . 

bas a probability of bP.ing produced as typewriter random.,. 

and paired in such a way that if both had occurred., they 

would have produced a group of the actual cipher text. 

I 

It ~F, desirable that with the pairs of groups, the product 

of their probabi.11 ties of occurrence be also presented. 

Again., the sequence may be generated by a machine built for 

the purpose. Once a large enough sample.is· obtained,, the 

problem is to construct an analogue of the machine so that 

we have a means of generating key similar to the key which 

will be used. This last problem is exactly like the problem or machine recovery. 

The problems of additive analysis fall into 

tour classes. 

(la) The first class of problems deals with system 

discrimination which tries to identify the elements making 

up the enciphering process. Both the steps in the encipherprocess and the enciphering elements are sought. 

(lb) The second class of problems are those of indicator recovery., or identifying and exploiting the decipherment 

information sent in the message such as pad number and 

starting point. 

(le) The third class of problems encompasses the 

search for depths, or the discovery of messages enciphered 

by the same pad. The search for isologs (messages having the 

same plain text but enciphered by different pads made up or 

exploitable additive) is included here. 

NSA Form 781-ClOS 1 Jul 52 T0P SE€1\ET FROTII 
,.-------------- - -

,• 

· (ld) The fourth class of problems are those or exploitation, or the actual recovery of the plain text or 

plain code using methods previously discussed. 

2. Exploitation of Statistical Phenomena 

The case of carelessly generated key which 

was discussed above is subject to attack. In the case of 

the typist discussed above, we can generate key similar to 

that which he produces. We then try 1t out at various positions in a message and examine the resulting decryption to 

see if it looks like plain text. A unique problem here is 

the generation of likely key. The problems of placement of 

key in the message, the decryption of the message employing 

'this k~y, and the recognition of ngood" plain text, have 

been encountered above. 

In another case we have a different phenome~ 

non. Studyii'~g previously recovered key of the system, we 

notice that not all key values occur with equal frequency. 

In this case we say that the distribution of key values is 

statistically rough. Furthermore, we may notice other 

eta'.tisttcal properties which more exactly describe the 

distribution than the mere statement of its roughness. 

Let us say that· some central station using this system 

sends the same message to a number of its outlying stations, 

but enciphers this message with a different pad for each 

27 

NSA Form 781-CIOS I Jul 52 'fOP SE€RE~ FRO'FII 
" TOP SE'~R1F•?PWO'FII 

transmission. The practical reason for this is that recip- . . 

ient station A does not have the same one-time pads as station B or C, nor do B and C hold like pads, because a onetime pad is usually made in only two copies, one for each 

or a pair or correspondents. 

Now we have a sort of reverse "depth", a set 

'of cipher messages in which the texts are identical put the 

key for each is different. This set of messages can be broken 

in the sense that the single plain text and all keys can be 

recovered. T~ affect the solution we assume some plain text 

and derive key. For each messa~e the correct assumption 

should produce key which has the previously noted statistical 

properties. In fact, good assumptions in various portions 

or the text would be consistent and yield better information 

about the statistical nature of key population which in turn 

is used to improve or direct assumptions in other portions 

of the text. 

The problems here include the placement of 

plain text ·in the alignment of mess:iges, the deciphering proc-

; ess to obtain the underlying key, the statistical tests made 

on the key, and the identification of good results. 

3. Additional Procedures 

One case of this is the solution of a columnar transposition. The cryptogra.phy consists of writing a 

message, in the usual left ~o right manner, into a 

28 

NSA Form 781-ClOS 1 Jul 52 'f()P SEERE'F FRO'fll 
,• ,. .• 

rectangular box. Then the colunms of let.ters are written 

out, but the columns are chosen ln a mixed order, not merely 

from left to right. !n cryptanalyzing, we-take advantage or 

our knowledge of language letter frequencies. We assume that 

a certain stretch of message was a single column. Then we 

try other stretch~s of the message as the column which was 

originally to the right of the selected column at the time 

the message was written into the rectangle. In the .correct 

case, the pairs of adjoining letters produced will have plain 

text digraphic properties. Furthermore, since we know the 

statistics or the language, we weight each pair by the probability of occurrence and choose the correct match by the best 

total score. 

Then a third column is added, and our knowledge 

of letter triples forms a basis for scoring, etc. Thus in a 

system of this type the problem is one of storing probability 

weights and data handling to make and score assumed matches 

of stretches of text. 

A second example is the case where it is known 

that additive key was not furnished to the encipherer as 

a one-time tape or reusable tape or pad, but was generated 

by a known complex manual process. Some specific var~able 

or variables of the process are not known. Here it is 

necessary.to duplicate the steps followed by the enciphering clerk, making assumptions about the unkno~m variables. 

Each assumption results in "trial" additive which can be 

NSA Form 781-ClOS 1 Jul 52 'FOP SEEii~'F FRO'FII 
•• , ... ,J~ 

applied to the message text. The result 1 ~alled "pseudo-· 

plain" 1 can be examined to see if it is plain text 1 or has 

the statistical properties of plain text. 

V. Support Functions 

These functions embrace a number of different activities. 

These activities are somewhat general to all cryptanalytic 

work and are not based on any particular traffic or system. 

A. Linguistic and Statistical Aids 

A number of special dictionaries and statistical 

studies based upon various languages of interest are required as aids to cryptanalysts. The dictionaries and 

statistics may be based upon particular traffic decryptions 

or upon general samples of the lar~uage. Dictionaries arranged 

in special ordering (such as ordered alphabetically on last 

letter of the words) may be desired. Frequent revision of 

dictionaries and statistical studies are required. Besides 

linguistic studies large numbers of special mathematical 

and statistical tables are prepared. These have included 

special Poisson1 Binomial and Multinomial tables 1 and others. 

:B. Generation of Crypto-System Data 

It is sometimes desired to proviqe the analyst with 

listings or data pertaining to a particular cipher machine 

system. For example, tables which enable computation or 

cycle distance between specific machine settings 1 and lists 

ot successive settings or a cipher machine. In certain hand 

30 

NSA Form 781-ClOS 1 Jul 52 'FOP SEERE'F FRO'FII 
T6P svr:.TPttJj5 D'-.AJ.t.D .I. ~ReT11 J." 

systems in which the combining of texts is done in several 

steps, tables showing the end results of the several steps 

for various variables may be desired. 

c. Desk Aids 

There are a number of small devices which may be 

provided for the individual cryptanalyst to use directly 

along with his work. These include connnercial adding machines and desk calculators, individual cipher machines, 

analogues of portions of various crypto-processes, tallying 

counters and the like. Such devices may ~e useful, providing that they are actually available to the person while 

working. 

D. C!7ptanalytic Research 

There are times, in the course of current cryptanalysis, during which elements appear which are not subject to regular periodic change, but are such that a 

change in them would obviate current methods of attack. 

Again there are times when information as to new cipher 

machines or systems not in use, but offered for sale, becomes available. In this sort of situation a substantial 

;effort to prepare to solve a problem which may never 

materialize is justified. 

E. Collateral 

Cryptanalysis is not performed in a vacuum. Often 

what helps a~ attack on messages is some notion of what they 

are likely to be about. Sometimes a name recovered from 

31 

NSA Form 781-ClOS 1 Jul S2 T0P SE€RET FRO'fll 
• 

T()P SEeH1ET5'PR6TII 

one message gives ~lues as to the subject matter or 

personal:tties probably referred to elsewhere in the message, or in some related message. Sometimes· direct references to an unread message by date or serial number in the 

messages that are being read helps provide a wedge into 

the ,referenced message. 

Similarly, a "Who's Who" file may furnish :footn9t1:?s 

}' 

to a solved message which will increase the amount of information furnish to an intelligence analyst. 

Extensively cross-indexed files are kept in 

~ operating sections and at higher echelons to furnish aiqs 

of this sort. This type of' information is called "collateral". 

Here we have a large scale data handling problem 

which includes filing, indexing, cross-indexing, looking up,, 

abstracting, etc. 

32 

NSA Form 781-ClOS 1 Jul 52 T()P SECRET FRO'fll 
= -Ji- -?"'' /I I 

' 

' ~I I 

'I 

'' 

. l 

'f()P SE€RE'F FRO'Fli 
/ 

TOP SECRET