IN REPLY 

REFER TO 

REF ID :.2211_4 ... •• 

WP&T Div. WAR DEPART~NT·· -CONfl.DENTIAL 

• • •• 1 

:"· 

MEMORANDUM TO: 

OFFICE OF THE CHIEF SIGNAL-OFFICER 

· WASHINGTON 

January.20, 1933 

Major.- Hugh Mitchell,- Off:i:~er-in-Charge, . Research ~ ·Development Division •. 

.. 

Attached hereto is a preliminary report, in duplicate, 

on Signal Corps Converter, Type M-134, which will ~e 0£ interest . 

. to you and to. the Signal Corps Laboratories at Fort Monmouth·~ 

}

1

11.ULi 

S. B. Akin; 

·Maj or, Signal Corps • 

Attached: . Report in.dupl •. 

· · · · · · · · · · : · · · · .. · ·c0Pr'·1at~,,.1 ~ . . ·. . . . .• . . . . . .· .. · . . . . .. : . . . t >_L v l fl I 

Peclassified· and approved. for release by NSA on 11-20-2013 .:pursuant to E.O. 1-352ff . . · · ~--dil... 
REF .ID~22114 ,., CONFIDENTIAL 

PRELIMINARY REPOm' ON SIGNAL CORPS CONVERTER, TYPE M-134 

1. A test of the cipher machine disclosed the following: 

.!!:• Speed. 

(1) 'J'.he··m~mum mechanical speed of the· machine, determined 

. . . 

by depressing the same key repeatedly arid as rapidly as_po~sible, 

is 33 depress~o:ils pe~ minute. ·. 

(2) The maximum speed of encipherment or decipherment by 

an ._operator·-w-o~I?-ng as rapidly as possible for a short length .. ~\. .J· 

- .. "'C'i1C;·":" .::-"'=:~"' 

time, approximately- five minutes, is .30 letters per minute. J.\' ',~ 

-:}<-, .. _./,:,,/:·· 

(.3) The average speed of encipherment or decip..°llel'J9.@Ii~kb.Y 

. . : } '1~•t'' 

an -operator working in a methodical manner for a f~~j.:"ong ·. .;;"\_ {; 

period, appro:X:imately .30 minutes, is 25 letters PEhil mhftite. This 

average is based upon the actual . encipherm!Pl,t ~-Jlcipberment or 

. . J -~-, . . 1066 five-letter gr~ps, equivalent ~.app~9.i£i-.iiately 6POO letters •. 

. . . ~ \_ J . ·. (4) Comparative speed tests wt.th CipMer Device M-94 and . \ 

with the Division Field Code, using p~rti"ons of the same text as . \ 

abo-re, showed that the cipher machine :(~ approximately twice as . . \ . 

fast as the M-94 deirice, but no t-aster than the,.J>ivision Field 

. . j''~J, .. ~l::: . ~~..#if~. Code. ·;~_ =r ,;,.'ff . ,;:i· ·. 

. . . . :/"1' . 'v.. .. ~r . '.7-

· c-s> Further ~'+~on the subjec.~~p· speed will be found .. ~.., ~ ~/ ./" -~~~ . 

under parag;°'s.w 2 a.--~~l' d. , incl,.. · >l.~- . ~~: ?-:_, - J - ~-/ii~~~ 

b. Reliabilitv •. ,'":,./ \. ~.t\. - ~ ~ .~~/ . Iri _;,gener~···i t mq be sF. _.Ybli;\ the machine is .quite re~iable 

. ·. i ,,../"" .. .-· !""I;. "\,.)./ \ 

in oper~~-imf1 ·bi.it the f d1_~!_~.pg mec~ical failures were note~ during 

the test~ ·· = ... 

. (~)- When the keyboard keys are allowed. to come up slowly-

·aft.er depressing, the cipher wheel occasionally fails to rotate :, .· . . ~ . 

and orient itself to its next correct position. ~his failure seems 

~ . 

to be CE!JlSed by faulty·action of' the tape-stepping mechanism, and 

renders all -subsequent text incorrect. In normal operation of the 

keyboai-d, however, t:P.is failure does not appear • 

. _, 
REF ID :IJIR22114 

.... • 

(2) Arter the machine_has been in operation £or about 

an hour, the clutch governing the stopping of the cipher wheel 

sometimes fails to operate. The cause of this was·not determined~ 

(3) Unless the perforations· in the keytape are accurately 

placed with respect to the pins 0£ the keytape transmitter, there 

will be occasions.when the tr~smitter·pins will be set·up for a 

permutation either not represented on the cipher wheel, or not 

correct with respect to t.'ie tape. When this happens the cipher 

-~ 

wheel ~, ~ in the first case,~not stop revolving, and in the .... 

second case,~stop at an incorrect position. f1h.ile the first 

case happened many times during the test, the second either did 

not happen, or· if it did, remained unnoticed, as it invoives 

only a.single-letter error • 

.2.. Security. . Theoretically, the machine can be used to produce cryptograms 

that. are absolutely indecipherable without possession of the key-

. . 

tape. This method of operation would require the use of a keytape 

representing a random-mixed sequence coincident in length with the 

total: length of the traffic to be enciphered. Such a method would 

obviously involve "great difficulties in practice with regard to 

the production, distribUtion and manipulation of keytapes among 

. . 

the offices or organi~ations provided with the machines. If several offices use the same keytape and the latter is employed repeatedly, even with different initial points for different messages, an ac~ation of traffic that is solvable without possession of the keytape would undoubtedl.y result,· and the system · 

would not be aaf'e for"use between the higher headquarters where 

communications secrecy for more than a few hours must be maintained. "To circumvent these difficulties.a fairly simple modification in construction can be made, as outlined below in par-

~raph · 2 .!.• 

. . 

· ... 

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REF ID:if22114 .... CONFIDENTIAL 

2. The foregoing facts lead_ to the following discussion: 

!:• If a printing mechanism were added to the machine, the speed 

of operation would undoubt~dly be increased,. but to what extent cannot 

be ·stated. Certainq it would not be very great because most of the 

time lost in present operation is due to the necessity for w8.iting 

(a variable length of time in each c~se) until the clpher wheel has 

stepped to the prope~ position. This delay ~ould.still intervene 

even if the entire operation from depression of a key ~o printing Qf · 

the ·char~cter were automatic, because it.is an inherent feature of-the 

present cipher mechanism. 

B.• If a printing mechanism is added, :f'ul.l advantage ought to be 

taken of such a feature by freeing it, if possible, of limitations 

·imposed by the cipher mechanism. By so doing the speed of operation 

could be increased to double or triple the present speed in enciphering 

or.deciphering • 

. . !.•· The.present sp~ed limitation is imposed by the fact that the 

cipher wheel mu~ be displaced through irregular angular distances and 

brought to a stop at a preclse spot. Although it might be possible to 

increase the speed of this displacement, it would be accomplished most 

probabIY at the ~~ense of (1). certainty of· operation .and (2) a much 

. . 

increased.wear and te~·on the starting-stopping mechanism, with consequent lack of continued serviceability. 

· g,. It appears necessary to modify the machine so.as to bring about 

.·, 

by some simple, practical means a degree of cryptographic- security impossible to obtain with the present model without the difficulties of tape . . 

production and distribution, as set forth in paragraph l £.• The following 

scheme is the one which seems to offer the most promise. 

g,. If there ·is inserted in the set of 26 circuits leading from the 

keyboard to the left-hand-fixed· contacts of the cipher wheel a set of· 

·five cipher whee1s 0£ the Hebern type., then the same keytape of length 

sufficient· to encipher a message of ·average_ length could be employed 

- 3 CONFIDENTIAL 
REF. ID :/ii)22114 

... CONFIDENTIAL 

repeatedly to encipher different messages, providing the set-up of the 

Hebern wheels were changed for each message. Each message would contain an indicator girlng the complete key set-up. Means similar to 

be . that used in the present Hebern lamp_ machine would hav~ to_jprovida:ito 

take care of the enciphering-deciphering equivalency. This is accomplished by means .of a screw which juxtaposes two sets of 26.contacts 

for enciphering and two other.sets of 26 contacts for deciphering, as 

per diagram ij attached to en~losure. The addition of this modification . . 

. . 

would make the m&CL1iine somewhat larger and heavier, but still not beyond the limits of what is feasible in a ·machine for use in regimental 

and higher headquarters. 

l• Inasmuch .as· it seems advisable· to modify the· machine in 

·respect to both -speed-· and cryptographic. security, serious consideration 

should be given to the·possibil~ties of the scheme out.lined in the 

attached description and accompanying photostat of a system bearing 

much resemblan.ce to the present development but whiCh, it is believed, 

offers much greater advantages t~ati does the present model. It is believed that not only could the newly proposed system be operated as 

£ast as a typist could manipulate a keyboard, but also the degree of 

cryptographic security afforded by the use of but one, relatively short 

keytape by all .communicants over a ?eriod of many d~s would be sufficient ·for communications exchanged between even the highest headquarters. 

3. The following recommendations ai:e made: 

~· That the present mQ~~l-be given a thorough t~st for ~peed, .. . \- . 

: ) 

ruggedness and reliability ·by submitting it to an organization such as 

OT t\...~ .~"t" s~"'a.I Co-~a'"'~ ,. ' . the 5lst Signa1 Batta1ion~at Fort Monmouth,· end that report thereo£ be 

I 

made as promptly as possible .• · 

_e •. That the development of a printing 'attachment should proceed . ' . 

:· .. · .. with out ·_deley, since. this attachment woul~ .b'~ the same for the present 

model as for. ·any propos~d new machine. 

. -- .. 4 ,,_-:. 
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REF IO:jj22114 

.. CONFIDENTIAL 

.£.• That the Laboratories give further consideration to the 

possibility of increasing the speed of the present model end, if 

practicable, increa_se the speed ,to_ twice the present ·speed. . .. . 

d. That if the latter turns out.~(:). be practicahle of achieving, . . 

then the present· model.be modified in ·accor~ce with the ·ideas outlined in· paragraph 2 fil·· but if' ~t turns out to be 'impracticable or 

impossibl.e of achieving; then consideration should be given to the . . 

development of.the scheme outlined ~n-the"attacb.ed description. 

Attached: 

Description. 

. .... ·.- .. _.. 

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