Operation

With the ENIGMA I first three, starting from 1939 five different rollers, were available which were durchnummeriert with Roman numbers (I, II, III, IV and V). The user selected three of the five rollers after default of a secret key table, which planned changing attitudes for each day, and used these after arrangement prescribed in the daily keying element under the heading "„roller situation the "“.

The table represented the valid in each case daily keying elements, which were changed around midnight for a complete month. Down exemplarily only three monthly days are represented, whereby, as at that time usual, which are sorted days descending. This permits it to the encoder, "„used "“codes of the past days to cut off and destroy.

Day UKW roller situation of Ringstellung --- Plug connections --- 31 B I IV III 16 26 08 AD CN ET FLAT STEEL BAR GI JV KZ PU QY WX 30 B II V I 18 24 11 BN DZ EP FX GT HW IY OU QV R-S 29 B III I IV 01 17 22 AH BL CX DI IT FIBER PLASTIC GU NP OQ TY 

Example of the 31. the monthly: UKW B, roller situation of I IV III meant, as Umkehrwalze is to be selected the roller B. Rolls I is left (as slow rotor), to use roller IV in the center and roller III right (as fast rotor). The rings, which are appropriate at the outside and which disalignment between the internal wiring of the rollers and the letter determine, to which the transfer takes place on the next roller, are on the 16. , 26. and/or 8. To adjust letter of the alphabet, thus to P, Z and H.

The Ringstellung was often registered (like here) numerically and not alphabetically to probably prevent in order mistakes with the other partial keys. As an assistance for the operator inside a conversion table is attached in the frame cover of the ENIGMA.

 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 

Finally the double-pole socket contacts with appropriate double-pole cables, attached at the front plate, are to be wired. Usually exactly ten cables were plugged in. The upper in each case socket of a pair of sockets has a somewhat larger diameter than the lower, so that the plugs can be put only into an orientation. Thus the desired electrical crossover and thus the permutation of the two letters are surely reached. Six letters remain ungesteckert. (This firm rule of the Six self steckered letters was for the code breakers an assistance.)

In order to reduce the danger of guessing from keys to, by the German places some rules for the list of the key tables were invented. Like that it was forbidden that a roller situation, which was used on one monthly day already repeated itself on another monthly day. Also a roller could never be on two following each other monthly days in the same place in the Walzensatz. A third rule should prevent a guessing of obvious plug combinations. Like that it was forbidden that two letters following each other in the alphabet were gesteckert with one another. (Also this the code breakers used to their favour and called it Consecutive plug knock out.)

All these regulations caused the opposite, i.e. an attenuation of the coding. They led to a facilitation of work for the code breakers, that could in particular exclude more key combinations due to the rules mentioned with the progressing of a monthly ever.

After attitude of roller situation, Ringstellung and plug connections the operator closes the flap attached above the Walzensatzes and the front flap. The latter causes a firm pressing of the plugs in slightly and a safe contacting (as well as a protection from spying the key). Now the user still the three (rotary) rollers must into a defined initial position, called the basic position, turns, and the ENIGMA is ready for the coding.

Radiogram

In order to guarantee that not all radiograms of a key net with identical keys are coded, which would make the texts open to attack were prescribed, to adjust for each saying an individual basic position (saying key) of the three rollers. The exact procedures for this changed occasionally and were not homogeneous also with all units. In approximately it ran off according to the following pattern, if for example the following plain language were to be conveyed:

"„The supreme command of the armed forces communicates: Aachen is saved. The threat could be turned away and the rescue of the city against 18:00 clock be guaranteed by bundled employment of the auxiliary workers. "“

Since the ENIGMA can code only capital letters and no numbers or punctuation marks and also no free character knows, must be prepared accordingly represented above the plain language before the coding with the ENIGMA first. Punctuation marks are replaced through "„X "“, included names in "„J "“and written out numbers ziffernweise. Furthermore it was usual to replace (except with names) "„CH "“through "„Q "“and to divide the text afterwards in pentads. One receives thus the following plain language prepared for the coding:

TO DASOB ERKOM MANDO DERWE HRMAQ TGIBT BEKAN NTXJA ACHEN JISTG ERETT ETXDU RQGEB UENDE LTENE INSAT ZDERH ILFSK RAEFT EKONN TEDIE BEDRO HUNGA BGEWE NDETU NDDIE RETTU NGDER CITY AGAINST XEINS XAQTX NULLX NULLX UHRSI QERGE PLACE TWERD ENX 

The encoder adjusted its ENIGMA I like further above described after the daily keying element for example for the 31. the monthly (roller situation of B I IV III, Ringstellung 16 26 08 and plug connections AD CN ET flat steel bar GI JV KZ PU QY WX). He invents now a coincidental basic position, for example "„QWE "“and adjusts the three rollers in such a way that exactly these three letters in the windows become visible. Now he invents a coincidental saying key, likewise from three letters, for example "„RTZ "“. These it codes with its ENIGMA and observes, how successively the lamps light up "„EEC "“. In such a way coded saying key it communicates to the receiver as well as the coincidentally selected basic position as indicator as well as the time and the number of letters of the text in the preamble (head) of the radiogram openly.

Furthermore it selects for this day valid group of knowing, which consists of three letters from a table of group of knowing still another, for example "„OWN "“. The group of knowing serves the receiver of the message to recognize that the message is really intended for it and also authorized can be decoded. The group of knowing is supplemented by the sender around two coincidentally selected "„filling letters "“, for example "„XY "“, and placed in front unencrypted as the first pentad the Geheimtext.

The encoder adjusts now the three rollers of its ENIGMA to the saying key selected by him "„RTZ "“and codes the above plain language. Together with the preamble and the group of knowing the following radiogram results:

Head: 22:20 - 198 - QWE EEC 

 XYOWN LJPQH SVDWC LYXZQ FXHIU VWDJO BJNZX RCWEO TVNAC FDAIQ FYCLF DGJBH WVMFY NWVHF KWZWA OASZY SCMRW BVWWT RBLGR XNNDF ZRGZL FHWFG FUVAG BDTXV DWMCV CEGEN BLOWI KBSCG EKAPD XMJRW QNHOT WWEIG LUIHF FPQWZ WCREY PACKY AQZDM ZWLJN INYYY RGA 

Head and Geheimtext are transmitted as Morsezeichen and taken up by the receiver. This examines as the first whether the number of letters (198) is correct and the saying became to receive Then it looks at the first pentad, ignores themselves the first two letters and sees "„OWN "“. It looks this group of knowing discovered there into its table of group of knowing, and can now be safe that the saying is intended for it and it can decode it. Its ENIGMA is already concerning roller situation, Ringstellung and plug connections according to also it admitted daily keying elements identically to that the sender adjusted. Still the correct basic position is missing to it. This information receives it from the indicator "„QWE EEC "“in the preamble, which it interprets as follows: Adjust the rollers to the basic position "„QWE "“and grope then "„EEC "“. Now he can observe, how successively the lamps light up "„RTZ "“with its ENIGMA. This is the saying key which can be adjusted.

It turns now the rollers on the new basic position "„RTZ "“and begins, the Geheimtext, begun with the second pentad "„LJPQH "“to enter into its ENIGMA. Now successively the lamps light up, and which appears the following text:

dasoberkommandoderwehrmaqtgibtbekanntxjaachenjistg erettetxdurqgebuendelteneinsatzderhilfskraeftekonn tediebedrohungabgewendetunddierettungderstadtgegen xeinsxaqtxnullxnullxuhrsiqergestelltwerdenx 

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