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IntroductionUsing an encryption system requires a set of rules known to the various correspondents. These correspondents must primarily share secret elements, first and foremost the encryption keys. Usually, when using a cipher machine, there are three types of keys:
Notes:
Furthermore, there are other procedural elements that correspondents must share:
Procedures Used During the Spanish Civil WarIntroductionIn 1938, the Nationalist army under General Franco equipped itself with the Kryha v2 cipher machine. A user manual in Spanish was typed and (presumably) distributed to various correspondents. It seems logical to assume that these procedures are inspired by those provided by the Kryha company.
The manualHere is the verbatim translation into English of the manual.
Summary of Instructions for "Kryha" Machines
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The fixed alphabet corresponds to the actual letters of the plaintext.
(We will call this Series I).
The movable alphabet consists of the cipher letters corresponding to
each letter of the fixed alphabet. (We will call this Series II).
The internal wheel of numbered screws contains the holes corresponding
to the internal secret combination. (We will call this Series III).
Series I, II, and III will undergo periodic changes, communicated to
the corresponding personnel by the Central Headquarters (Cuartel General
del Ceneralisimo), indicating the measures to be taken from specific dates.
Initially, all machines will be delivered synchronized for the first
phase of work.
The modifications to Series I and II will determine the order in which
the letters must be placed, reading on the respective circles counter-
clockwise. The modifications to Series III refer to the numbers that must
remain holed.
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ENCRYPTION METHOD
For each dispatch, the starting point must be given. This is determined
by the stopping number of Series III and by the coincidence of a
letter from Series II with one from Series I. (Given precisely in
this order: first by the letter from the moving wheel and then by
the letter from the fixed wheel).
The starting group, consisting of four letters (two for the cipher of
the stopping point in Series III, and the initial coincidence letters), is
given in the dispatch text, inserted in the fourth position of the cryptogram.
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This group must be written according to a pre-established cipher, which
consists of:
1. Look at the stop number, for example, 29 (Series III). If it is
a single digit, simply add a zero before it.
2. Rotate Series II until the initial letter of the day of the week
being encrypted matches the letter X in the fixed alphabet
(Series I). For example, if it is "Jueves" (Thursday), J is front
of the letter X.
3. Look at the letters that correspond to the digits two and nine
of Series I in Series II. In our example, these are O and H,
respectively.
4. Without touching the wheels; that is, we will work in the first
position above. For example, W in M and the corresponding letters
in series II are taken, which are I and Y.
The fourth and orientation group will therefore be, as it should
be written in the office:
OHIY, equivalent to the plaintext group 29 WM
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Series II is rotated until the W in M coincidence is found, and the first
letter of the text is encrypted (in this position), followed by the
subsequent letters, pressing the movement lever fully for each one.
In the office, the held letters are grouped in fours, with the last group
being completed with encrypted Zs.
When converting letters to numbers, three consecutive Ws are encrypted
(W.W.W.). For the reverse step, three encrypted Ns (N.N.N.) will be given.
The value of the number is the one corresponding to the letter in series I.
Encryption is facilitated by breaking the plaintext into groups of four
letters and placing the corresponding cipher letter below each group.
As an extension of the above, we will encrypt the following text using
the machine's delivery combinations and the starting group used as an example:
"ENTERADOS INSTRUCCIONES ENTREGAMOS 6530 FRANCOS."
We will write the plaintext in groups, and below each letter, its
corresponding cipher letter.
Plaintext = ENTE RADO SINS TRUC CION
Ciphertext MPCE MPUR WDKI (") DMUF JKRS
Plaintext = ESEN TREG AMOS WWW6 530N
Ciphertext = OXAE WHJK BFRQ OAUC YXTX
Plaintext = NNFR ANCO SZZZ
Ciphertext = OHMK LTRA IAUG
When writing it in the clean place marked (*), the starting group
OHIY is placed.
DECIPHERING.
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With the initial of the day the telegram (Series II) is encrypted placed
over the X of Series I, the starting group is interpreted and crossed out.
The marked matches are placed in the same position, and in this position,
the first letter of the text is deciphered. Then, by lowering the lever
for each one, the letter from Series II (inner) is replaced in each
position by the corresponding letter from Series I (outer).
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NOTE.
When submitting dispatches for transmission, and in order to avoid
errors, the groups must be typed or handwritten using clear, well-spaced
capital letters.
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IMPORTANT NOTE.
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Any malfunctioning machine must be taken to Central Office with full
security guarantees, where it will be repaired or replaced.
Burgos, December 1938.
-Third Triumphant Year.-
Comments
Number conversionWe use the numerical values associated with the letters to convert number in letter (see below). We also use number conversion for translation of the startup sector. to translate the start sector (29), we use the inner alphabet and two letters: O (24) to translate the 2 (there is no letter associated with 2) and H (9) to translate the 9. So we have OH. Outer alphabet: A=18, B=7, C=20, D=12, E=2, F=00, G=/, H=5, I=10, J=15,K=1, L=8, M=14, N=&, O=0, P=17, Q=3, R=-, S=6, T=16,U=11, V=9, W=0, X=19, Y=13, Z=4. Inner alphabet: A=8, B=20,C=6, D=28, E=11,F=16, G=27, H=9, I=17, J=7, K=18,L=22, M=4, N=15,O=24, P=14, Q=5, R=13, S=25, T=10,U=19, V=26,W=3, X=12, Y=23, Z=21. Indicating system: the day of the weekTo set the starting point of the inner wheel, the day of the week is used (Rotate Series II until the initial letter of the day of the week). Here are the days of the week in Spanish: Lunes (Monday), Martes (Tuesday), Miercoles (Wednesday), Jueves (Thursday), Viernes (Friday), Sabado (Sautrday), Domingo (Sunday). ComplementsFuensenta describes a sealed document, dated February 1941, that contains the new keys and which come from the General State Department.
Data compressionIntroductionMarks (cf. Reference) informs us that the 1925 manual suggests using Kryha as a system for code over-encryption and data compression. Indeed, certain letters (D=12, W=23, N=25, etc.) can encode two digits. Therefore, Kryha can encode numbers from 0 to 25. This allows for a form of compression. Fixed Alphabet: Letters and numeric groups equivalent0(O), 1(K), 2(E), 3(Q), 4(Z), 5(H), 6(S), 7(B), 8(L), 9(V), 10(I), 11(U), 12(D), 13(Y), 14(M), 15(J), 16(T), 17(P), 18(A), 19(X), 20(C), 21(R), 22(G), 23(W), 24(F), 25(N) ExampleConsider the following code:A = 100, B = 101, C=102, D=103, E=104,…, I=109, J=110,K=111,S=119, …, ARM = 124, …, AT = 247, …, CK = 259, …, DAWN = 666, OUR = 221, …, TA = 228, …, WILL = 753 Consider the following clear text: (25 letters) Our armies will attack at dawn. Here is the coded text: (11 groups, 33 letters) 221-124-109-104-119-753-247-228-259-247-666 Equivalent text in Kryha (using the fixed alphabet) : (in whole, 22 letters) 4(Z)-21(R)-12(D)-4(Z)-10(I)-9(V)-10(I)-4(Z)-7(B)-5(H)-3(Q) 24(F)-7(B)-22(G)-8(L)-25(N)-9(V)-24(F)-7(B)-6(S)-6(S)-6(S) Note: if there is a group meaning "Attack at dawn", the compression is obvious. A notable improvementIn 1941, Allied cryptanalysts faced enemy traffic encrypted by the Kryha (from Spain), whose procedures complicated the breaking of the messages. The most significant of the changes in enciphering procedure is that which introduces the element of key interruption into the system. At the end of each word, the letter J (appearing with "-" dash on a single tab) is enciphered as a word-separator. After each such plain-text J the operating lever is depressed twice instead of the usual once. Thus, the first letter of the next word instead of being enciphered at the setting it normally would, is enciphered at the one following it. Note: The methods implemented by the allies to solve the traffic are described by Frode Weierud (link). ReferenceArticles & Books
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