Chapter XII — Multiple-Alphabet Ciphers — The Vigenère — Elementary Cryptanalysis by Helen Fouché Gaines

Chapter XII Multiple-Alphabet Ciphers — The Vigenère

The theory of polyalphabetical substitution is as follows: The encipherer has at his disposal several simple substitution alphabets, usually 26. He uses one such alphabet to encipher only one letter; for the next letter, he may use another cipher alphabet; for the third letter, a third alphabet; and so on, until some preconcerted plan has been followed out. The earliest known ciphers of this kind, the Porta (1563) and the Vigenère (1586), made use of a chart, or tableau, on which all of the available cipher alphabets were written out in full one below another. The Gronsfeld cipher (1655) used a purely mental encipherment plan; but the Beaufort ciphers, arriving two hundred years later (1857), again made use of a tableau, and something of the same idea survives in the use of strips; that is, a set of long narrow cards, each card carrying a simple substitution key. Slides, however, must have been in use near the time of Beaufort, since the best-known of the slide-ciphers, the Saint-Cyr, was being taught in 1880 at the French military school from which it takes its name. As to cipher disks, these appear to have been known even in Porta’s time, and have passed through many complications, though it has not been a great many years since a very simple disk was in use in our own army. (A drawing of the United States Army Cipher Disk may be seen in Webster’s New International Dictionary.)

To know thoroughly any one of these ciphers is to understand the fundamental principles of all, and we are going to base our studies chiefly upon the Vigenère, most perfect of the simpler types, and the basis upon which others have been founded. Fig. 85 shows, in full, the Vigenère tableau, or “alphabet square.” The alphabet standing horizontally across the top of this figure is the plaintext alphabet, and serves for the whole tableau. Below this, and parallel to it, are the 26 “Caesar” alphabets, the first one being a duplicate of the plaintext alphabet, while the remaining 25 have been shifted, one letter at a time, until the last one begins with Z. These are the 26 available cipher alphabets, and each one is named according to its first letter, which is also spoken of as its key. Thus, the key-letter A points out the A-alphabet; the key-letter B points out the B-alphabet, and so on. The alphabet standing vertically on the left side of the tableau is merely a list of these key-letters, and so is called the key-alphabet. Except where cipher machines are employed, the ordinary plan of encipherment does not make use of the full 26 available cipher alphabets; only a few of these are used, and these few are taken always in a given rotation, so that the cipher becomes periodic. If the rotation includes, say, twelve of the cipher alphabets (whether or not these are all different), the cryptograms are said to have a period of 12. (The word “cycle” is also used in this connection.) Since each letter of the normal alphabet is the key to one of the Vigenère cipher alphabets, the encipherer, wishing to make use of several different cipher alphabets, is able to remember their sequence by means of a key-word, in which each letter will point out one particular cipher alphabet. If today’s key-word is BED, only three cipher alphabets will be used, the B-alphabet, the E-alphabet, and the D-alphabet, and the cryptograms will all have a period of 3. But if, tomorrow, the key-word is changed to CONSTANTINOPLE, the complete rotation will include fourteen alphabets, and the cryptograms will have a period of 14.

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

A 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
B 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 A
C C D E F G H I J K L M N O P Q R S T U V W X Y Z A B
D D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
E E F G H I J K L M N O P Q R S T U V W X Y Z A B C D
F F G H I J K L M N O P Q R S T U V W X Y Z A B C D E
G G H I J K L M N O P Q R S T U V W X Y Z A B C D E F
H H I J K L M N O P Q R S T U V W X Y Z A B C D E F G
I I J K L M N O P Q R S T U V W X Y Z A B C D E F G H
J J K L M N O P Q R S T U V W X Y Z A B C D E F G H I
K K L M N O P Q R S T U V W X Y Z A B C D E F G H I J
L L M N O P Q R S T U V W X Y Z A B C D E F G H I J K
M M N O P Q R S T U V W X Y Z A B C D E F G H I J K L
N N O P Q R S T U V W X Y Z A B C D E F G H I J K L M
O O P Q R S T U V W X Y Z A B C D E F G H I J K L M N
P P Q R S T U V W X Y Z A B C D E F G H I J K L M N O
Q Q R S T U V W X Y Z A B C D E F G H I J K L M N O P
R R S T U V W X Y Z A B C D E F G H I J K L M N O P Q
S S T U V W X Y Z A B C D E F G H I J K L M N O P Q R
T T U V W X Y Z A B C D E F G H I J K L M N O P Q R S
U U V W X Y Z A B C D E F G H I J K L M N O P Q R S T
V V W X Y Z A B C D E F G H I J K L M N O P Q R S T U
W W X Y Z A B C D E F G H I J K L M N O P Q R S T U V
X X Y Z A B C D E F G H I J K L M N O P Q R S T U V W
Y Y Z A B C D E F G H I J K L M N O P Q R S T U V W X
Z Z 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

To make use of a cipher alphabet, say the B-alphabet, we may lay a ruler across the tableau in such a way that this one alphabet is pointed out. Then, to encipher any letter, as S, we may find this letter, S, in the plaintext alphabet at the top, and trace down its column as far as the B-alphabet which is being pointed out by the ruler; we find that the substitute, in this alphabet, is T. Or, wishing to decipher T, we find this letter in the B-alphabet and trace upward to the plaintext alphabet in order to find that its original is S. While the foregoing explains the principle, it has not been expressed in the usual language. Where we have mentioned the use of the B-alphabet, it is much commoner to hear that a certain letter has been enciphered or deciphered “with key-letter B,” and the usual description of the encipherment will be somewhat as follows: To encipher S by B, find S in the plaintext alphabet, find B in the key-alphabet, and use the substitute which is found at the intersection of the S-column with the B-row. Or: To decipher T by B, first find the key-letter B, trace horizontally to the right as far as the cipher-letter T, then trace upward to its original, S. This, we believe, is the original description, as explained by Blaise de Vigenère himself, and the original encipherment plan was that indicated in Fig. 86. The message of this figure is SEND SUPPLIES TO MORLEY’S STATION. The key-word, BED, has been repeated often enough to pair one

Figure 86

Original Method of VIGENÈRE

Encipherment

Key:

E D B E D B E D B E D B

E D B E D B

Message:

S U P P L I E S T O M O

R L E Y S S

Cipher:

W X Q T O J I V U S P P

V O F C V T

Figure 87

Modern Enciphernent

B E D B E D

B E D

S E N D S U

P P L

T I Q E W X

Q T O

I E S T O M

O R L

J I V U S P

P V O

E Y S S T A

T I O

F C V T X D

U M R

15 20

O J

I V U S P P V O F C

V T X

D U

X X

key-letter with each text-letter, and these pairs are handled one at a time: S is enciphered by B, E is enciphered by E, N is enciphered by D, and so on, following the original description.

The modern method would be that of Fig. 87. Knowing that a great many letters are going to be enciphered by B, a great many others by E, and a great many others by D, and having no wish to preserve word-divisions, we begin by writing our plaintext into three columns (or by grouping it conveniently), and then encipher at a single writing all of those letters which are to be enciphered by any one same key-letter. That is, we apply one cipher alphabet at a time, as first explained. The modern practice will also require that the cryptogram be taken off in five-letter groups, and that the final group be made complete. This is another of those cases in which the decryptor will number his letters, as shown in the figure. The student who has not previously met the Vigenère cipher is urged to perform the two operations of encipherment and decipherment and thus familiarize himself with the use of a tableau; it is possible that in most of his subsequent reading he will find explanations based on the “columns” and “rows” of a “tableau,” when, as a matter of fact, no tableau has been used. To understand how this might be, suppose we take a look now at the Saint-Cyr cipher.

In Fig. 88, we have the principle of the sliding device by means of which this encipherment is accomplished. The Saint-Cyr slide is very easily prepared of cardboard, or of any other flexible and fairly strong material, but may also be prepared of wood, or may be set up for any temporary purpose on two strips of paper. Its details, also, may be varied to suit the operator’s own convenience. As shown, however, the upper and single alphabet, which is the plaintext one, is written on a card, and slots will be cut in this card at two points: Just below and to the left of A; and just below and to the right of Z. This plaintext alphabet is considered stationary.

            Figure 88
            THE SAINT-CYR SLIDE
        ┌─────────────────────────────────────────────────────┐
        │ 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 │
┌───────┴┬───────────────────────────────────────────────────┬┴────────────
│ 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 A B C D│E F G H I J.. └───────┬┴───────────────────────────────────────────────────┴┬─────────────┘
        └─────────────────────────────────────────────────────┘ (To Y.)

The lower and double alphabet, which is to furnish all of the substitutes, is written on a long narrow strip, the two ends of which may be inserted into the slots of the other card. This strip, or slide, may then be moved back and forth at will. However prepared, the spacing must be uniform throughout both alphabets. The Saint-Cyr cipher also makes use of a key-word in which each letter is the key to a cipher alphabet, and which is applied exactly as in Fig. 86 or Fig. 87. To apply the key-letter B, we adjust the slide in such a way that the B of the sliding alphabet will stand directly beneath A of the stationary one. This gives us exactly the same set-up which we used in Chapter IX for cases of simple substitution; that is, we have a plaintext alphabet with a cipher alphabet standing just below it; each plaintext letter is standing directly above its substitute, and each substitute directly beneath its original. The cipher alphabet just referred to, in which key-letter B, found in the sliding alphabet, is standing directly below the index-letter, A, found in the stationary alphabet, is identical with the B-alphabet of the Vigenère tableau, and is even called by the same name. Should we move the sliding alphabet, so as to place key-letter C directly beneath index-letter A, we reproduce the C-alphabet of the Vigenère cipher, again called by the same name. In the figure, we have the E-alphabet in position, with key-letter E standing directly beneath index-letter A. And since the sliding alphabet may be placed in 26 different positions, each time reproducing one of the Vigenère cipher alphabets, having the same key and the same name, it appears that our Saint-Cyr “cipher” is merely a duplication of the Vigenère. The chances are, then, that even though we call our cipher by its original name, and even make references to its tableau, our actual work of encipherment and decipherment will have been accomplished by means of the more convenient and rapid Saint-Cyr slide. But where a slide is possible, a cipher disk is also possible, and many will prefer to use the disk.

To prepare one of these, we might proceed as follows: First, cut out from cardboard (or other desired material) a pair of disks, one smaller than the other. Divide the peripheries of both disks into 26 equal segments, and write the 26 letters of the alphabet in a circle around both of the peripheries, causing both alphabets to run in the same direction. Place the smaller disk on top of the larger; and, finally, stick a drawing pin through the exact center of both disks, to serve as a pivot. The smaller disk may now be rotated to 26 different positions, so that any desired key-letter can be caused to stand beside index-letter A of the outer disk, and will place in position the cipher alphabet of which it is the key. The use of this revolving alphabet in place of a sliding one does away with the necessity for doubling its length.

Now let us examine carefully Fig. 89, with its two examples of decipherment. At (a) of this figure, a short cryptogram fragment, beginning T I Q...., is being deciphered with the original key-word, BED, and is bringing out the message, SEND SUPPLIES..... This, of course, is to be expected of any cipher. But at (b), it is this message fragment, SEND SUPPLIES, which is acting as a trial key; exactly the same process is being used as if applying the true key, and this decipherment is bringing out the original key, repeating over and over. The Vigenère cipher, then, works equally well in reverse, and in this respect it differs from some of its kindred ciphers. To understand this peculiarity, we have merely to consider the tableau. Concerning this we have said that the horizontal alphabet which stands across the top is the plaintext alphabet, and that the vertical one at the left is merely a list of keys. Suppose we decide to look at it the other way round, and say that the vertical alphabet at the left is the plaintext one, and that all 26 of the cipher alphabets are standing on end with their key-letters at the top, so that the horizontal alphabet, written across the top, is merely a list of these keys. Will there be any difference in the encipherment? Might the slide, also, be prepared in a vertical position? Does it make any difference in the results whether we encipher plaintext SEN by key BED, or encipher plaintext BED by key SEN?

One road to decryptment, then, is clearly indicated. If we have a probable word, we may use this word exactly as if it were the key, and, if it is actually present, it will bring out the true key. Or, if we have no probable word, we may try probable sequences, or make use of the trigram list. Here, however, we have two separate cases: The simplest, in which the probable word is long enough to bring out the key-word repeating; and the most difficult, in which the sequence, or probable word, is very short, and will bring out only a short fragment of the key-word.

The simpler case is readily explained. We have, say, a cryptogram beginning U S Z H L W D B P B G G F S..., in which we suspect the presence of the word SUPPLIES. We decipher the first eight letters, using this probable word as a trial key, and obtain a jumbled series of letters C Y K S A O Z J, which is not satisfactory.

		Figure	89
(a)	Deciphering with the	KEY:
	Key:	B E D B E	D	B	E	D	B	E	D.......
	CRYPTOGRAM:	T I Q E W	X	Q	T	O	J	I	V.......
	Plaintext:	S E N D S	U	P	P	L	I	E	S.......
(b)	Deciphering with the	MESSAGE:
	Trial Key:	S E N D S	U	P	P	L	I	E	S.......
	CRYPTOGRAM:	T I Q E W	X	Q	T	O	J	I	V.......
	True Key:	B E D B E	D	B	E	D	B	E	D.......

We leave off the first cryptogram-letter, U, and decipher the next eight, obtaining another jumbled series of letters A F S W L V X X. We start again at the third letter, then at the fourth letter, and still there is no information. But at the fifth trial, beginning at the fifth cryptogram-letter, we obtain a series T C O M E T C O, and this is satisfactory, not necessarily because we have recognized the word COMET, though this, of course, is a very desirable happening, but because the last three letters, T C O, are repeating the first three. The series is beginning over. The student should practice doing this, using both the tableau and the slide (or disk), until he is sure that he understands the process. The exact details of his work are immaterial; if he is sure that his key will be a recognizable word, it will be satisfactory to make decipherments directly on the cryptogram, erasing as he goes. Sometimes, however, the key is incoherent, or apparently so, and a jumbled series like C Y K S A O Z J might actually be the correct key; for this reason, it is well to follow a routine of some kind which will preserve all of the decipherments. One such plan is illustrated in Fig. 90.

Here, the cryptogram, or a substantial portion of it, would be written across a sheet of quadrille paper, and the probable word would be written at one side, where each of its letters will govern one row of decipherments. The first letter, S in the figure, has been used to decipher the whole row of cryptogram-letters, giving every possible key-letter which can produce S. The second letter, U, has been used to decipher them all again (except the very first letter; we do not expect a word UPPLIES). The third letter, P, has been used to decipher them all a third time; and soon. The resulting rows of decipherment include all key-letters which could have produced S, then U, then P, and so on. To read them consecutively, beginning at any cryptogram letter, start immediately below that letter, and read diagonally downward to the right. The first diagonal gives key CYK..., the second gives AFS..., and so on to the fifth diagonal, showing the key as T C O M E T C O. (If it is desired that these possible keys should come out standing in a horizontal position, then the decipherments may be made diagonally.) F. R. Carter, the originator of this scheme, does not necessarily make all of the decipherments which are included in the figure. He begins with the assumption that his key will be a recognizable word; having deciphered in full the first three rows, he abandons all of those diagonals which cannot develop into words. If, in the end, he is forced to conclude that his key was incoherent, no decipherments have been erased; he may still go back and develop the rest of his diagonals, in the hope that one will begin repeating.

The more difficult of our two cases, that in which we have no probable words other than the, and, which, that, have, but, etc., can follow exactly the routine

	Figure 90
Deciphering with	the Probable Word	SUPPLIES	- Routine of F.R.CARTER
Cryptogram fragment:....	U S Z H L W	D B P	B G G F S.........
Probable word: S	C A H P T/ E	L J X	J O O N A.........
U	Y F N R C/	J H V	H M M L Y.........
P	K S W H	O/ M A	M R R Q D.........
P	S W H	O M/ A	M R R Q D.........
L	A L	S Q E/	Q V V U H.........
I	O	V T H	T//Y Y X K.........
E		Z X L	X C//C B O.........
S			O//
			(Key: COMET)

outlined in Fig. 90; but in this case there must be two separate work-sheets. Here, it is usually better to forget words and start at once with the list of normally frequent trigrams, THE, AND, THA, ENT, ION, TIO, etc. The key-fragments which are deciphered by these will be very short, and very numerous; a great many of them will be very good usable sequences, and perhaps the correct key-sequence will not look quite so inviting as others which are incorrect. It becomes necessary, then, to have a second work-sheet on which we may take these fragments one by one and try them as keys. If any one of them is a fragment of the original key, it must bring out fragments of plaintext, and must bring them out at some regular interval. If the scheme of Fig. 90 is the one preferred, the second work-sheet may be prepared exactly like the first, and used in the same way. The only difference is as follows: On the first work-sheet, where the figure shows the word SUPPLIES, a supposed trigram (THE, AND, etc.) will have been used to bring out supposed key-fragments; on the second work-sheet, one of these supposed key-fragments will have been used. These new rows of decipherment may then be examined to find out whether any of the new diagonals contain apparent plaintext fragments, and, if so, whether these occur at a regular interval.

For this kind of work, however, Ohaver has offered us another routine which requires somewhat more preparation than Carter’s but which is well worth the extra trouble, especially if it be remembered that a trigram-search is never necessary except with the shortest of cryptograms. For the longer cryptograms, we have easier methods. Ohaver’s plan can be examined in Fig. 91.

The cryptogram, shown at the top of this figure, contains 26 letters; therefore, remembering that each letter, except the final two, may begin a cipher-trigram, it contains 24 trigrams. The preparation of the two work-sheets requires that these 24 cipher-trigrams be written out in full on both sheets. This work should be done in ink, or on the typewriter. Then, too, for a reason which will be explained in a moment, it is well that the first of these work-sheets be prepared with a great deal of space, say seven or eight lines, between its rows of trigrams. Now, considering the first work-sheet, shown at (a) of the figure: The upper row shows the 24 cipher-trigrams as originally written out. We have been working down the trigram list, using every normally frequent trigram as a trial key, and have failed to find THE, AND, THA, or ENT, which means that we have done quite a lot of tedious work. We have now reached the normally frequent trigram ION, and this we have

Figure 91

N F

V E O L N V M R N G Q F H H R N H I R V F E

(a) Trial Sheet No. 1ION LNF NFV

FVE

VEO

EOL

OLN

LNV

NVM

VMR

MRN

RNG

NGQ

AZS

FRI

XHR NQB WAY GXA DZI FHZ NYE EDA JZT

FSD

GQF

QFH

FHH HHR HRN RNH NHI HIR IRV RVF VFE

FEB

YCS

IRU

XTU ZTE ZDA JZU FTV ZUE ADI JHS NRR

XQO

(b) Trial Sheet No. 2EDA LNF NFV

FVE

VEO

EOL

OLN

LNV

NVM

VMR

MRN

RNG

NGQ

HKF

JCV

BSE RBO ALL KIN HKV JSM RJR ION NKG

JDQ

GQF

QFH

FHH HHR HRN RNH NHI HIR IRV RVF VFE

FEB

CNF

MCH

BEH DER DON NKH JEI DFR EOV NSF RCE

BBB

D A E D A E D A E D A E D A E D

L N

V E

L N

M R

G Q

H H

N H

R V

I N.. A L L.. I O N.. B E H.. D F R.. A Y

(TION?) (FRIDAY?)

applied as a trial key, assuming one by one that each of the 24 trigrams represents ION. We have, then, 24 decipherments on the second row, and any one of these 24 deciphered trigrams might be a fragment of the original key. However, it is natural to assume that a trigram FRI or WAY is more likely than one such as XHR or NQB, and those fragments which look like usable sequences have been underscored in the figure. These are to be tested first. At (b), we have the other work-sheet, the upper row, as before, showing the 24 possible cipher-trigrams. Here, we have already failed in our tests for key-fragments FRI, WAY, DZI, NYE, which means that we have done some more tedious work, and we have now arrived at the possible key-fragment EDA. If this sequence, EDA, is actually a portion of the original key, it must not only bring out fragments of a plaintext message, but must bring them out at some constant distance apart. The point at which we found this is the tenth trigram, and here it may be advisable to remind that this begins at the tenth cryptogram letter; that is, every trigram presents only one new letter, so that to find a completely different trigram in either direction, we must count backward or forward a distance of three trigrams.

Beginning, then, at the tenth trigram, and examining every third trigram in both directions, we find that our key-fragment has given us the following decipherments: HKF, RBO, HKV, ION, CNF, DER, JEI, NSF. These are largely incoherent; but, in addition, it must not be overlooked that on the continuously-written cryptogram, these would be consecutive, giving us a message H K F R B O... Applied at interval 3, then, our key-fragment EDA, will not decipher us a message; therefore, the period of this cryptogram, using this key, cannot be 3.

To examine for the possibility of a period 4, we start again with our tenth trigram, and examine every fourth decipherment in both directions; our series, this time, is JCV, KIN, ION, MCH, NKH, NSF. Most of these are usable, and the first one might be due to nulls, initials, and so on; but here again we have the reminder that with each trigram representing only one new letter, these are almost consecutive, starting at the second cryptogram letter, so that our message, with each fourth letter missing, will be as follows: * J C V * K I N * I O N.... Unless we can think of some letters which would fill these gaps and provide plaintext, our period is not 4.

Trying again, however, beginning at the tenth trigram and examining each fifth decipherment, we find something more satisfactory: ALL, ION, BEH, DFR. If these are correct, the period is 5. At (c), we have gone back to the continuously-written cryptogram in order to try these in their places; and since a period 5 would mean that each of the letters E D A is used regularly to encipher each fifth letter, we are able to include two shorter decipherments at the two ends of the cryptogram. The next step in logical order is to try deciphering T in front of ION, since the trigram TIO would have been the next one on our trigram list. This brings out key-letter C, which, if correct, will decipher correctly at each interval 5, and which extends our key-letters to C E D A. We can see, too, that this is not the beginning of the word; the sequence we have is D A * C E. In the given example, it is not difficult, also, to guess a probable word, FRIDAY. Now, having twice called attention to the fact that the trigram-search can grow quite tedious, we hasten to point out that it need not be made more so by deciphering each trigram individually. If your trial key is THE, set your slide at the T-alphabet (or point this out on the tableau), and decipher every first letter on the sheet. Then set the H-alphabet in position, and decipher every second letter on the sheet. Finally, set the E-alphabet in position and decipher all of the remaining letters.

The foregoing few paragraphs have illustrated the worst case in almost its worst form, but will show the principle. Now let us consider this work in a much more usual case. As mentioned earlier, the first of the two work-sheets will be prepared with a great deal of space between the rows of trigrams. The full number of decipherments will be made for the first trigram THE, but not erased. Just below these, a second row of decipherments will be made for AND, and these, too, will be left standing. (THA can be omitted.) A third row of decipherments is made for ENT, a fourth row for ION, and so on down the list, until there are six or eight rows of possible key-fragments. These are all examined and compared with one another, in the hope of finding duplications. Perhaps THE and AND have both brought out a key-fragment EDA, or one has brought out CED and the other EDA, having ED in common. It is far from unusual, in some of these cases, to find a whole series of these overlapping key-fragments, for instance, CON, ONS, NST. This will explain why many persons consider the trigram-search the simplest and most direct way of attacking a Vigenère cryptogram.

For the benefit of the novice, we end the chapter at this point in order that he may have some practice. Example 104 comprises a thrilling serial with all the trimmings, gripping and original title, smashing climax, and a brave hero, John Miller. The key to the title is STRANGE. Part I repeats a word found in the title; part II repeats a word of part I; and somewhere are the trigrams NOT, CON, YET, ING, TEN, THE. We have heard, too, that an amateur encipherer will occasionally encipher the nulls which he adds in his final group. Example 105 is easily investigated through short common words. As to the remaining examples, while it is true that they can be attacked by the trigram method, the student will probably prefer to leave them until he has seen the methods outlined in Chapters XIV and ^XV.

104. By PICCOLA. (For trigram practice. A new key for each fragment).

Title of Serial: S L K R N T K W W Z S N V T W T I A A I I X X

Part I: R I G Z V Z K I U O M H J L B W F P K S R Z T R H E

T W

O S W I O S G Q I I. Part II: H H T X T N E O L V R M T U L C L

P X

T Y R X K U K B U W U O J Z H X M Z K H. Part III: S Y Z Y R T

F U

K C U S I I R Q U X W U F K C J N R L Q N F O K V X M P U O N

J A

J H V O P. Part IV: X B V P Y S X C J J Y U R X O T S P I N Y

L U

A V M X M M F C I B S T I T O O T B R O.

105. By PICCOLA. (For investigation of short words. - Still Vigenère!)

V Y I D J G I E J S N V R J H J F J D B G E K O W U Y A R F F

Z W

V O K U X R P G R J U O E K M R B U Y S U H Q W J L J G C

W H

G I

106. By NEON. (Any repeated trigram is worth watching!)

P Q X E J F V E G Y M N Y N Y I U F R D S G V R I L P S G Z T

E S

R K N Y I G P E R W G R R N D L O J N T Y I D X O T Y C I P C

E V

E S G O I R L I S I R Z Q E U C G L T C I X H Y I X H E L E K

J E

P X I E Y R R S L H D L I F Y G P R J G S D I C E.

107. By THE ADMIRAL. (Numbers are always possible!)

L V P R V S F P T Y J S P H L F R C E U S B O S Z P H J F Z N

O A

K T T V V Z C F R J X C C T P W W R H K E W Y U K W G L N U X

C T

X W G E R F R Z N V Z O W F J W Q Z N U K W Y O E W M P A I.

108. By NEON. (This cryptogram, circulated in April, 1935, caused great

consternation

among

solvers.

you

see

any

reason

why?)

T W G J C N I U J X C S L S K K B N V G W I P S U Q I U J A U

J U

H B E V J V M A O H G G L T P D G L E Y S S L A F I M J S W Q

U M

N N F L V H I U I Z D Q K V Y R T W H I M R F E U K P N O V Y

K E

N V Q N O T.

109. By PICCOLA.

A X S E H G O I W W F O I A L G E M Q W E E N B W R E I K L S

Z Z

X L G A H V P Z K L D L G G D W T C M H Q D J N W K E H M V V

B M

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