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SECURITY i~PROVEMENTS ACCOMPLISHED BY "C" BRANCH IN 1944 

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I Foll~Ywing is a summary of activities designed to improve security of communications in the U. S. Army during 1944. I 

PROCEbunES FOR INCREASING CRYPTOGRAPHIC SECURITY. 

a. I~troduction of new cryptographic systems. 

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ll Literal one-time pads. 2 Aircraft warning service cipher. 3 Radio direction finding cipher. 4 AACS PX codes. ~ Authentication Systems 3, 4, 5. 

b. Modification in method of channel elimins. ti on foi• 

strip systems. PROCEDuRES FOR INCREASING PHYSICAL SECURITY. 

a. E~tablishment of new clearance procedure. 

b. Compilation of file of cryptographic custodians. 

c. Promulgation of rules in document form. 

PROCEDURES FOR INCREASING TRANSMISSION SECURITY. 

a. Expansion of monitoring control and missions. 

b. Standardization of monthly report form. 

c. D~stribution of dissemination charts, reports, e·;c. 

d. Preparation of scripts of training records. 

NEW DEVICES AND MACHINES PLACED IN SERVICE. 

a. Speech equipment AN/GSQ-1( ). 

b. Converter M-325. 

c. Converter M-218( )/u. NEW OR IMPROVED MACHINES IN DEVELOPMENT. 

a. Converter M-294. 

b. Converter M-409. 

c. Speech equipment AN/GSQ-2. 

d. F~csimile equipment AN/GXA-2( ). 

e. Converter attachment AN/GSA-2. 

f. RADCO device. 

MODIFICATIONS OR IMPROVEMENTS IN EXISTING MACHINES. 

a. Modified Converter M-228. 

b. Equipment for one-time tapes. 

c. R~designed parts for Converter M 134-C and Convej'•ter M-2a3. 

ESTABL!SHMENT OF NEW CRYPTONETS. 

a. Cryptonet 37 POA and SWPA using Converter M-228). b. C:ryptonet 38 Worldwide AACS using Converter M-2:~8). 

c. CrJptonet 39 20th Air Force). d. Cfyptonet 40 Jcint Army-Ne.vy). 

e. Cryptonet 41 Persian Gulf Ccmmand). 

f. Cryptonets 97, 98, and 99 (Training cryptonets). 

IMPROVEMENTS IN CRYPTONETS. 

a. Inclusionct' necessary types of systems. 

b. Dtscontinuance of certain Etystems. IMPROVEMENTS IN LIAISON. 

e.. Within Army. (i) Decentralization of accounting, making thea."::;ers 

euboffices of record. 

(2) Assistance given theaters in production of material. 

eclassifi ed and a ursuantto E .0. 1352 
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.~ RE~~~A719a; 

b. With Navy. 

·ill Exchange of holder lists. • 1 2 Establishment of joint Army-Navy cryptonet. 3 Preparation of one-time tapes for Navy. 

c. , Combined operations. (1) Publication of combined documents. 

(a.) Field code. 

(b) Instructions for air-ground nuthentication 

system. (2) Policy permitting use of Converte:r• M-228. 

IMPltOVEMENTS IN OPERATIONAL PROCEDURES. a.'. Utilization of "g" Branch facilities for prodi1cing · cryptographic material. 

b. Forme.tion of lay-out room for multilith stenclls. 

c. New checking procedures. 

d. Addition of new equipment for printing of mat<:lrial. 

SECURITY STUDIES. I 

a. Determination of security limits of cipher IllO.•}hines and 

: ·devices. 

b. Analysis of traf.fic cryptographed in various l~ystems to 

determine weaknesses. 

c. Transmission security analysis of tactical monitoring 

logs. d.. Study of procedure for reporting compromises lLnd 

cryptographic violations. 

e. Study of call signs,, system indicators, and internal 

references. 

f. Study of necessity for paraphrasing cryptographed 

messages which are also transmitted in plain 1.ext over 

1 .classified circuits. 

NEW .OR REVISED PUBLICATIONS. 

a. Systems instructions. 

b. AG and SPSIC letters. 

c. Monthly Informational Document. 

d. Articles and posters in ~.ignal Corps Technical Informatmn 

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REF_._ID: A7Wl.43 ll"\t'i~"'\i-1 ., G •= 

The following discussion amplifies certain points fou•'ld 

in the atove outline. Main paragraph headings below are 

numbered to conform to those of the outline. 

1. PROCEDURES FOR INCREASING CRYPTOGRAPHIC SECURITY. 

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a. Aircraft warning service cipher, radio direction finding cipher, and AACS PX codes were prepared for use by the Air Forces. I 

b. Authorization was granted for three specific authentication 

systems for intra-Army and joint Army-Navy use. 

c. The nev method of channel elimination for strip systems provides a high degree of security by requiring that bott the 

particular channels eliminated and the total number of cr.annels 

eliminated will vary among messages enciphered on the same day. 

2. PROCEDURES FOR INCREASING PHYSICAL SECURITY. I 

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a. By means of an AG letter, procedure was established for 

the investigation f.lnd cles.rLT.nce of telephone company emp:_oyees 

:for duties in connection with automatic encipherine equipment. 

b. A· policy was instituted whereby rules governing :·)hysical 

security of certain cryptographic machines are to be incorporated in cl&asified instruction documents. 

3. PROCEDURES FOR INCREASING TRANSMISSION SECURITY. 

a. Mpnitoring activity was incrc:;.sed to include Pe.c1.fic 

Ocean Areas. European Theater of Operations, United Stctes Army 

Forces in the Middle Eust, and certain areas in and around the 

Mediterranean Theater. In Octocer 1944 direction communication 

channels were established with monitoring stations 1 (Vint Hill 

Farms, ~fo'rrenton, Va. ) , 3 (Miami Beach, Fla.), 9 (Eellrrore, L. I.), 

and 10 (Reseda, C,l.). 

b. A standardized monthly report form (covering violations 

of transmission securitr, remedial action taken, monitoring 

missions assigned, etc.) was adopted. 

c. Charts showing specific violations of radio transmission security~ as found by analysis of monitoring logs, were distributed to.violating units. 

d. Scripts dramatizing actuo.l violations of t.ransn~_ssion 

security were prepared for reproduction as training recordings. 

4. NEW DEVICES AND MACHINES PLACED IN SERVICE. . . 

a. The speech equipment, AN/GSQ-1( ), was received from the 

manufacturers and distributed to several theaters. The equipment 

utilizes code cards, each of which provides security for 15 minutes. 
REF. __ .!~ :A7J.i43 

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b. The Converter M-325 was received from the manufacturer 

and distributed for trial use in certain areas. It is a hand-oper~ted electromechanical device using a reversing rotor 

and three stepping rotors from a set of nine rotors (a set 

consists ,of one reversing rotor and eight stepping rotors). The 

rotors are so de~igned that their wiring may be changed ~t will. 

c. The. Converter M-218( )/u was placed in service at the 

State Dep~rtment. It utilizes a special rotor basket an·i 

plug board rotor, and provides semiautomatic operation er rotographically equal to Converter M-325. 

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5. NEW O!i IMPROVED MACHINES IN DEVELOPMENT. 

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a. Converter M-294, which uses a new type of rotor 1tnd 

rotor bas~et, vas received from the me..nufacturers. 

b. Converter M--409 was developed, and will probably be 

available for service tests sometime in 1945. It. is an nlectromechanica1 machine utilizing the same cryptographic princdples 

as the Converter M-325, but is keyboard operated and ta.po printing. 

c. Moat of the development of speech equipment AN/GfiQ-2 

was accomplishedj the equipment will be service tested in 1945. 

d. F&csimile equipment AN/GXQ-2( ) was developed,, and will 

be ready for use in trial installations in 1945 • • 1 

e. Converter attachment AN/GSA-2 (Auto Converter M-J34-C) 

was teste4, and additional units will probably be procur£d in 

1945. 

f. The RADCO device,, an improved version of SLIDEX,, was 

issued fo~ limited field tests. 

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6. MODIF~CATIONS OR IMPROVEMENTS IN EXISTING MACHINES. 

a. M~dified Converter M-228 was developed; it is provided with a rot'or stepping arrangement different from that of the 

standard converter. When used according to a special procedure,, the Modifi.ed Converter afford non-repeating key operation, and 

is secure enough for radio transmission of TOP SECRET messages. 

b. The new one-time tape system involves an improvem9nt 

over the oid s3stem which used the 131-B-2 subsetJ a receiving transmitter distributor, and one form or another of teletfpe 

equipment. By modifying a receiving transmitter distributor 

(14AB) instead of the 131-B-2 subset,, the same results we.l?e 

accomplishl3d, thus leaving the subset standard. Closely ·~onnected 

to this improvement is the Universal Connection Block,, by means 

of which 1~ is possible to install both a Converter M-228 and . .~ne receiving transmitter distributor for one-time tape o~eration 

tf"'.~~ n a 131-B-2 subset. 

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REF ID: A7:J.&43 

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7. ESTABLISHMENT OF NEW CRYPTONETS. 

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a.: ~ryptonets incorporating Converter M-228 systems 

were established as, for example, Cryptonet 38, which is for use 

in the transmission of weather, flight operational, and administrative trarr1c. I I 

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b. Cryptonet 41 was the first to include Converter M-325. 

c. Three training cryptonets were made up for communication 

between F~rt Monmouth and Camp Crowder. 

8. IMPROVEMENTS IN CRYPTONETS. 

a. The scope of existing and newly created cryptoneGs was 

enlarged to include all necessary types of cryptographic systems. For example, Cryptonet 21 was revised to include one-tim·:l tape, Converter M-134-C, strip, and Converter J-1-209 systems; and plans 

were made for a new cryptonet for Military Attaches and Military Intelligence Liaison Officers to include one-time pad, onet-time 

tape, strip, Convater M-325, and double transposition syatems. 

I • b. The over-all picture of cryptographic systems usod in 

cryptonets has been clarified by the trend toward eliminntion 

of systems which were unnecessary, were little used, or c.:ould 

be comb.ined with other existing systems; for example, tho 

emergency double transposition systems which he.d been prcivided 

ror the world-wide high command cryptonets were eliminatE:d. 

9. IMPROVEMENTS IN LIAISON. 

a. In order to give greater assistance to the theatErs, the 

production of AFCODE, a radiotelephone code developed in AFHQ, 

and the increased production of Converter M-209 were undertaken. • I 

b. Because of the nature of certain COB publications, the burden of publication is thrown on the individual services; 

in thE there has been complete cooperation among the services 

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c. Pe,rmission was granted the British to use Converter M-228 

in combined operations, provided that all maintenance is perrormed by U. s. Army personnel. I 

! I 10. IMPROVEMENTS IN OPERATIONAL PROCEDURES. 

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a. Stencils are now cut by Electromatic typewriters in 

"G" Branch. 

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I b. Ne:w "checking boxes" for use in checking stencils were 

instituted; use of these boxes has renulted in greater ac~uracy. 

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c. The electromechanical counterpart or Converter M-325 I used to a limited extent instead of Converter M-325 itself 

ma.king 26-30 and circuit checks. 

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11. SECURITY STUDIES." 

a. J: ~ethod was developed by which the rotors of Converter 

M-134-C may be reconstructed and traffic read on the ba:~is of 

suffic1ept depth (approximately 10 messages). Several methods 

of solutfon of the Combined Communication Machine were discovered.. :resui ting in a recommendation for a change in lrnnetruction of rotors and in the adoption of a new indica~or 

system. 'T:he wiring and stepping principles of Converte:i" M-294 

were based on specific machine studies. 

b. A study of actual traffic cryptographed in varir)US 

systems resulted in recommendations to improve authorized 

systems and in a drive to replace locally devised insecilre authenti~ation systems, Slidex, aircraft movement codes, etc., 

with secure systems. 

c. Tactical monitoring logs were studied to determlne I violations of transmission security, quality of analysi3 made by the initial examining agency, quality of monito~ing 

,, logs 1 call sign schedules and variations from prescribe 1i 

radio procedure. 

d. The results of a study of procedure for reporting compromi~e and cryptographic violations will be incorpo~ated 

in a reg~stered document. 

e. A preliminary study (with recommendations) was made 

to deter~ne what intelligence can be gleaned from call signs, 

system indicators, and internal message references. 

J2. NEW OR REVISED PUBLICATIONS. 

a. Systems instructions were published as register~d 

d9cuments, as technical manuals, technical bulletins, a 1Ld 

training circulars. 

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b. Effective date lists and current cryptographic tnforma-

' tion were published in the Monthly Informational Docume1Lt.