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The Bagelin - Gretener Cipher TeleprinterThe Hagelin - Gretener cipher teleprinter is an apparatus· s~mjlar , 

to the standard teletype machme, operating ~n the start-stop principle, 

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. which. accanplishes automatic encipherment of electrical impulses on line. 

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Messages ·at both ends of a conuminications link appear in plain text or 

unenciphered form. The principal feature of the machme is the key-generating 

unit; this unit may be used·with ~eleprinters employing the inten'lational or 

Ba.udot five-element code, or with the ETK-teleprinter., a machine invented by 

Gretener using a fourteen-element code. In the latter machine, each plaintext symbol (letter or rmmeral) is printed by forming a combination of one 

to five signs seleeted from a set of fourteen available elements. These 

fourteen elemants are coaxially arranged in th~ printing part of the 

mechanism and are selected according to the particular plain-text character 

key which is depressed. In the cipher unit devised by Hagelin and Gretener, the 

generation of key under the fourteen-element code introduces a number of 

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eombina tions whi~h is considerably greater than is possible with the Baud.ot fiveelement code. Thus, _after the plain-text character (one to five elements) has 

been added to the keying character (one to fourteen element's), according to the 

' .. non-Vernam rule for combining markS and spaces, the resulting cipher character 

~be composed of one to fourteen elements in iJ-4 or 161 384_ndnus tv.o 

possible combinations. Of these, only about forty are readable symbols (letters _,,,_~ ..... 

and numerals); the remainder are not readable and, if produced in printed for , 

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' would appear as meaningless characters. Like the teleprinter, the key genera ng ~ ;' 

mechanism operates on the start-stop principle. Through one revolution or th ' i~\ ·~ c:;':z 

~-~ i~\ control shaft, the teleprinter and key generator run synchron~uslyi the 

-.....J ~ __.. teleprinter_ producing the printing impulses (at its 0\'111 ter~) and the i 0 ~; 

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generator emitting the keymg impulses; both signals are combined on the '....:; g~ :s =; 

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fourteen levels and transmitted as an enciphered signal over a line o~ by radi ~ 0 g ~ 

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Decipherment and plain-text printing take place through similar apparatu~ at th 

receiving station. In the particular embodime~t shovn for use of tl"e fourteenelement code, the machine operates on the neutral or single current system 

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(current or no current), in contrast to the polar system, in which there is constant 

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Declassified and approved for release by NSA on 11-17-2014 pursuant to E .0. 1352a 
REF ID:A4148847 

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flow of current, during both marking and spacing in~ervals, but in opposite 

directions~. 

The generation of cipher key for this machine is accomplished through the 

~dium or fourteen condensers•· These condensers are part of a circuit ~onsisting 

·~r a ch.D.in of •fourteen polal\ity reverse~, the chance operation of which ,determine 

V(hethe:t~ a condenser· is to be charged or ,not.. Eo.ch condenser leads to one segment 1 • • 

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of th~ distributor1 ,where the charge (or no charge) is taken off in sequence by 

the rotating brush and carried to the ·mixing circuit:. Here the ~ipher key .~ 

impulses are added to the plain text. impulses in the ~nventional manner to form 

the enciphered signal; T~ unit which randomly determines the condensers to be 

charged includes fourteen variable pin rotors of different sizes. (As shown in 

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the descripti~e write-up provided by the compaf\V,, these wheel hav~ I 

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29;,- 31; 321 341 371 381 YJ 1 . 411 421 431 44; 451 461 and 47 positions, and are 

not prime-sized to' each Qther.) The pins, which can be slid axially by hand, 

project from the sides or the rotor, just below the periphe,ry, either to the 

left ~- to the righti Each pin rotor and ratchet to move to rotor forward by one 

pin division. If.; however, an armature has been lowered by an energized control 

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magnet, depending on the positioning of its make and break contact by an active 

pin~ then. a blocking effect takes place, and the pin rotor is not permitted to I , 

adJance~ ,:/ 

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.','."·The cipher circuit now consi~t:s of a/chain of fourt~en polarity reversers, 

thJ' ac,tion of each of which is dep1endent on the influence of a right hand rotor )- ( 

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./f~. oil contact A. Inserted betrveen ea.ch two polarity ~versers 1 a condenser is 

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fz'oujYit into connection with tho positive ·or negative branch of the polarity 

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. {' re,erser chain through the action of contaQt Q. All C<?ndensers are connected on 

!:•1;, ' 't ' / " one/side in series and to the negative pole of the input. These ~ondensers may ;; I 1/ I ' ' 

~feh~refore become charged or not. Whether condenser_ No. l is charged depends on 

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the po.sition .of its related contacts A and C. flhether condenser No. 4 is I . . , 

~harged depends on the P'esitions of the first four contacts A and No 4 contact .c. ,1 ,{ \ 

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REF ID:A4148847 

'l;'he inp~ to the chain or polarity reversers takes place through a rotary 

feed switch. The cha.in of polarity reversers _must not form a closed-circuit 

and is ther<:fore broken at irregular intervals and at different points in the 

circuit by means of a. rotary separator switbh. Both rotary switches are mounted 

on the same shaft as the variable pj.n rotors; the switches rotate in opposite 

directions with relation to each other. The irregular stepping 0£ the rotacy 

switches is dependent on separate control magnets, which, in turn, are co9trolled 

by variable pin rot0r contacts B.. The descriptive writ&-up on this version of the 

ma.chine does not specifically identify these.contacts, but it is evident that they 

may be any of those among the four teen ava.iL"l.ble contacts, used ·eitre r singly 

or in a mUltipJ..e arrangE?ment. A separate polarity reverser, through which 

i!.l'®~~.snt is introduced into the r.nverser cha.in, ie controlled through a relay 

by one of the variable pin rotors (not specifically identified) whose ,control 

ma.gnet is constantly without cu.1,rent. Th~ rotor therefore 'becomes a fast wheel, 

stepping each time a key is struck, and prevents a. condition in which all the 

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variable pin ~otors stand still, i.eG• all the control Jna.f!llets are energized. 

If 0 for example, at a .given setting, the rotar.v teed switch is at 

p0larity reverser No. 21 and the rotary seperator switch has broken the circuit 

between polarity reversers Nos. 7 and s, th~n condens.er No. 7 will receive its 

cha1!g9 (or no charge) through the lead-in po~ity reverser and reversers 

Nos. 21 31 41 5161. and 7 and No. 7 eontact C. ·u, when the next character is 

stl"Uok., the feed switch stands still while the separator f?Witch adVances one step 

. (so that the separation of the chain of polarity raversers is between reversers 

r~os .6 and 7) 1 t.hen the charge of condenser No. 7 ~ after the next key is struck,. I . 

/de~ends upon the lead-in polarity reverser and reversers Nos. i,14,13,.12,111.10, 

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/ / ~i~ and 7. In this Wa::J /1 the charge of any condenser is dependent on a , constantly 

_:~hanging number and a constantly changing configuration. of rotor pins. 

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" . . ~ As the sixleen wheels are aligned· at the start of a message, the condensers 

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\,will become charged or not, accord:ing to the particular configuration of pins 

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and.their effect on the various single and double make and-break contacts. During 

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the single revolution of the cont1•ol , shaft of the cipher unit 1 while one message 

character is being enciphered a.J;ld transntj.tted1 the advance of the variable pin , •.'it; 

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rotors must. take pl.ace simultaneously. Th~ latter movement will result .in a l I' , ' , , 

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change of positions of the contacts A, B., C. In order that,,· despit,e the change, 

the condenser charges may remain constant during a complete revolution :Of the 

collector brush on the control shaft, all condensers are cut off from the va.ria~ie 

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pin rotor contacts C by a set of cam contacts shortly before the start and are 

connected up again shortly before the stop. The condensers thereby store their 

charges for a sufficient .interval. \ 

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Additional variation fIJJ.13 be introduced into the cryptographic circuit by 

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arranging for the· f'ollowing change$ of wiring: 

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In another variation of the circuit, which imposes some major changes 

in the wiring, the write-up discusses a plan that eliminates t~e two rotar.v 

switches (reed and separator.) and the hand-set permutation switch that 

interchanges the control magnets. The remaining three pe:nnutation 

switches now have twenty-eight divisions, with their internal wiring 

changeable by.plugging. Two of these switches, those for interchanging the . . . - order of the contacts C and the order of the condensers, are mounted on the ' r 

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shaft with the variable pin rotors and are subject to irregular stepping by 

having their control magnets come under the influence of pre-selected contacts B.· 

The, third permutation switch, for interchanging the polarity reversers, is set 

only by hand and the remains fixed thereafter. The input rOf the .feed 

voltages into the chain of polarity reversers now occurs at four arbitrarily 

selected points. From time to time at the feed inlet, the chain of 

polarity reversers is separated by cutting off the interchangeable leads. 

(The method for accomplishing this separation is no t clear, since the 

·write-up states that the separator switch is eliminated in this version 

of the machine.} In this way, there arise tour,distinct chains of 

polarity-reverser switch at esch switch position. The jack and plug 

connections of the fourteen control magnets as well as the connections 

of the control maiJiets of the tw:>- rotary permutation sVJitches with their 

reia.ted contacts B are made by hand at the time that the keying elements are 

set.up in the machine. .No permutation switch is provided tor this purpose.· 

to guarnatee a constantly-changing configuration of pins, the fourteenth 

contact B -is controlled by a variable pin ~otor whose control magnet is 

permanently 'without current,' i.e., this wheel always steps. 

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