Manual for the Solution of Military Ciphers

by Parker Hitt

Graphic Frequency Tables

Frequency of occurrence in 200 letters of text.

French

A	16	1111111111111111
B	2	11
C	6	111111
D	10	1111111111
E	39	111111111111111111111111111111111111111
F	2	11
G	1	1
H	1	1
I	13	1111111111111
J	1	1
K
L	10	1111111111
M	6	111111
N	16	1111111111111111
O	11	11111111111
P	6	111111
Q	2	11
R	15	111111111111111
S	13	1111111111111
T	13	1111111111111
U	12	111111111111
V	4	1111
W
X	1	1
Y
Z

Italian

A	23	11111111111111111111111
B	1	1
C	9	111111111
D	6	111111
E	25	1111111111111111111111111
F	2	11
G	3	111
H	1	1
I	23	11111111111111111111111
L	14	11111111111111
M	6	111111
N	13	1111111111111
O	19	1111111111111111111
P	6	111111
Q
R	13	1111111111111
S	10	1111111111
T	12	111111111111
U	6	111111
V	4	1111
X
Y
Z	2	11

German

A	10	1111111111
B	4	1111
C	6	111111
D	10	1111111111
E	32	11111111111111111111111111111111
F	4	1111
G	8	11111111
H	8	11111111
I	16	1111111111111111
J
K	2	11
L	6	111111
M	4	1111
N	24	111111111111111111111111
O	6	111111
P	2	11
Q
R	14	11111111111111
S	11	11111111111
T	12	111111111111
U	10	1111111111
V	2	11
W	3	111
X
Y
Z	3	111

Portuguese

A	28	1111111111111111111111111111
B	1	1
C	7	1111111
D	8	11111111
E	28	1111111111111111111111111111
F	2	11
G	2	11
H	2	11
I	12	111111111111
J	1	1
L	6	111111
M	9	111111111
N	10	1111111111
O	22	1111111111111111111111
P	6	111111
Q	3	111
R	13	1111111111111
S	18	111111111111111111
T	9	111111111
U	9	111111111
V	3	111
X
Y
Z	1	1

---

[1] Occurrence rare, usually in proper names. [↑]

Chapter III

Technique of Cipher Examination

In time of active operations it is important that captured or intercepted cipher messages reach the examining office with the least possible delay. The text of messages, captured at a distance from the examining office, should be sent to the office by telegraph or telephone, the original messages being forwarded to the office as soon thereafter as possible.

The preamble, “place from,” date, address and signature, give most important clues as to the language of the cipher, the cipher method probably used, and even the subject matter of the message. If the whole of a telegraphic or radio message is in cipher, it is highly probable that the preamble, “place from,” etc., are in an operators’ cipher and are distinct from the body of the message. As these operators’ ciphers are necessarily simple, an attempt should always be made to discover, by methods of analysis to be set forth later, the exact extent of the operator’s cipher and then to decipher the parts of the messages enciphered with it.

In military messages, we almost invariably find the language of the text to be that of the nation to which the military force belongs. The language of the text of the message of secret agents is, however, another matter and, in dealing with such messages, we should use all available evidence, both external and internal, before deciding finally on the language used. Whenever a frequency table can be prepared, such a table will give the best evidence for this purpose.

All work in enciphering and deciphering messages and in copying ciphers should be done with capital letters. There is much less chance of error when working with capitals and, with little practice, it is just about as fast. An additional safeguard is to use black ink or pencil for the plain text and colored ink or pencil for the cipher. A separate color may be used for the key when necessary.

The following blank form is suggested as convenient for keeping a record of a cipher under examination. It should accompany the cipher through the examining process and should be filled in as the facts are determined. This record, the original cipher and all notes of work done during the examination, should be filed together when the examination is completed, whether the cipher has been solved or not. It may be that other ciphers solved later will give clues to the solution of such unsolved ciphers.

The first column of this blank should be filled out from data furnished by the officer obtaining the cipher from the enemy. A general order, emphasizing the importance of promptly forwarding captured or intercepted ciphers to an examining office, could specify that a brief report embodying this data should be forwarded with each cipher.

The second column of the blank should be filled out progressively as the work proceeds. The office number should be a serial one, the first cipher examined being No. 1. The date and hour of receipt at examining office will be a check as to the time required to transmit it from place of capture. The spaces “From,” “At,” “To,” “At,” “Date,” are for the information concerning sender and addressee of the cipher and are to be obtained from the message. In case an operators’ cipher has been used, these parts of the message will have to be deciphered before the blanks can be filled in.

Intelligence Section, General Staff
1st FieldArmy
----------- ----------- Place, Date
Record ofCipher Examination
This cipher obtainedby ----------- ----------- at ----------- ----------- on ----------- ----------- (date) (hour) How being transmitted when obtained. (Underscore meansused and enter data on sending and receiving stations). Sending Station Receiving Station Radio Telephone Telegraph Buzzer Helio Lantern Flag Cyclist from to Foot Messenger from ,, to ,, Mtd. Messenger from ,, to ,, How obtained. (Underscore means used). Captured beforedelivery to addressee. Captured after delivery to addressee.Intercepted, not received by addressee. Copied, but received byaddressee. Remarks:		Office No. ----------- Received ----------- ----------- (Date) (Hour) From ----------- At ----------- To ----------- At ----------- Date ----------- Probable language of text ----------- Class Transposition ----------- ----------- Substitution ----------- ----------- Case ----------- Remarks: Solution completed --------- ---------- (date) (hour) Language of text ----------- Key, (if determined) ----------- ----------- Type ----------- FileNo. ----------- ----------- ----------- Examiner.

The probable language of the text is assumed from the preceding data and, if necessary, from internal evidence. Thus a cipher from a Mexican source and not containing K or W is probably in Spanish.

The class and case are determined by the rules laid down later. The space for remarks is to permit notation of any special features. When the solution is completed, the date and hour are noted, the language of text and key (if determined) are entered and a type number, to identify it with other ciphers prepared by the same method (but not necessarily the same key), is given to it. The file number is for convenience in filing and in preparation of a card index.

The process of examination in an office with one examiner, one stenographer and one clerk, might be as follows: On receipt of a captured cipher with accompanying report, the stenographer makes four copies of the cipher on the typewriter. The clerk and stenographer then check the work. The stenographer then proceeds to fill out the first column and first two lines of the second column of the record blank from the report of the capturing officer, keeping the original cipher and two copies with the record. He may also fill out the first seven lines of the second column, if this data is on the captured cipher in plain text. In the meantime the clerk is counting and setting down the whole number of letters of the cipher and the occurrence of AEIOU, LNRST, and JKQXZ, while the examining officer is looking over the cipher for possible recurring groups of letters and underlining them when found.

This work being completed, the examining officer is in a position, ordinarily, to decide on the class of the cipher and he may have found something in his examination which will lead him to the case under the class. The clerk in this preliminary count should keep track of the total occurrence of each of the fifteen check letters and not of the three groups given above. This takes a little longer but when done, the data for fifteen letters of the alphabet for a frequency table is completed, leaving only eleven other letters, and in Spanish, but nine, to be counted, in case it is necessary to prepare a frequency table.

If the examining officer decides the cipher to be of the transposition class, no further work with frequency tables is necessary. The clerk should proceed to count and set down the number of vowels in each line and column and the examining officer should look for any occurrence of the letter Q and try to connect it with U and another vowel. The stenographer may be set to work putting the cipher into rectangles of different dimensions. The clerk’s work gives data for possible rearrangement, for if the vowels are much out of proportion at any point, they must be connected with the proper proportion of consonants as a first step in rearrangement. Work with transposition ciphers must necessarily include much of the fit and try method. The details of this work are taken up later.

If a cipher seems to be a substitution cipher, the examining officer should look over the frequency of occurrence of each of the fifteen letters counted. If some letters (it is of no importance at present which ones) occur much more frequently than others and some occur rarely or not at all, we may safely decide on Case [4], [5] or [6] and let the clerk proceed to finish the frequency table for the message. On the other hand, if all the fifteen letters examined occur with somewhere near the same frequency—for example, the most common letter occurring not over three or four times as often as the least common letter—we may at once eliminate the first three cases and let the clerk proceed to examine the cipher for recurring pairs and groups, counting the intervening letters, so that the examining officer may decide whether [Case 7], or some more complicated case, should be chosen.

If something more complicated than [Case 7] has been used and other ciphers are on hand awaiting examination, the cipher should go into the unsolved file to be worked on when other work permits, unless the contents of the cipher are believed to be very important. Every opportunity should be taken to clean up the unsolved file and, whenever a message is solved, the methods should be tried, if applicable, to everything remaining in the file.

The first few days or weeks after the establishment of an examining office will be the most trying time. When solved ciphers begin to pile up, the methods of the enemy will be more and more apparent and it will often be possible to determine the method from knowledge of the name of the sender and receiver.

When a cipher has been solved, the solution should be prepared in triplicate and given the serial number of the cipher. Any parts which are not clear, through errors in enciphering or in transmission, should be underlined or otherwise made conspicuous, so that the head of the Intelligence Section may note them and, possibly, from other sources, supply the deficiency.

One of the copies of the cipher and report of examination, with a copy of the solution, should be turned over at once to the head of the Intelligence Section or to the Chief of Staff. The other copies of the solution should be filed with the original cipher, the report of examination, and all work done on the cipher.

Periodically, say once a week or even daily at the beginning of active operations, there should be an interchange between all examining offices of solved messages involving new methods used by the enemy. All the examining offices will thus be kept in touch. It may also be possible to assign certain hostile radio stations to each examining office to prevent duplication of work.

Chapter IV

Classes of Ciphers

There are, in general, two classes of ciphers. These are the transposition cipher and the substitution cipher.

Substitution ciphers may be made up of substituted letters, numerals, conventional signs or combinations of all three; and furthermore, for a single letter of the original text there may be substituted a single letter, numeral or sign or two or more of each, or a whole word or group of figures, combination of conventional signs, or combinations of all three of these elements. Thus substitution ciphers may vary from those of extreme simplicity to those whose complication defies any ordinary method of analysis and whose solution requires the possession of long messages and much time and study. Fortunately the more difficult substitution ciphers are rarely used for military purposes, on account of the time and care required for enciphering and deciphering.

Transposition ciphers are limited to the characters of the original text. These characters are rearranged singly, according to some predetermined method or key (monoliteral transposition), or whole words are similarly rearranged (route cipher).

There may also be a combination of transposition and substitution methods in enciphering a message but in this case it will fall into the substitution class on first determination and after solution as a substitution cipher it must be handled as a transposition cipher. Examples of this case will be given.

We may also find transposition or substitution methods applied to words taken from a code book, or to numbers which represent these words. Thus cipher methods blend into code work, for a code is, after all, only a specialized substitution cipher.

We can now lay down the rules for determining whether any given cipher belongs to the substitution class or to the transposition class.

Count the number of letters in the message, the number of vowels, AEIOU, the number of the consonants, LNRST, and the number of the consonants, JKQXZ.

If the text is English and the cipher is a transposition cipher, this proportion will hold; vowels AEIOU constitute 40% of the whole; consonants LNRST, 30% and consonants JKQXZ, 3%.

If the text be Spanish the proportions for a transposition cipher will be: vowels AEIOU 45%, consonants LNRST, 30%; consonants JKQXZ, 2%.

If these proportions do not hold within 5%, one way or the other, the cipher is certainly a substitution cipher. Note, however, that often the end of a message is filled with letters like K, X, Z to complete cipher words and it is best to neglect the last word or words in making a count. Also, if the cipher be a long one, this determination can safely be made by taking 100 or 200 consecutive letters of the message, either from the beginning or, if nulls at the beginning are suspected, from the interior of the message.

The distinction between the route cipher (transposition) and the substitution cipher where whole words are substituted for letters of the original text, must be made on the basis of the words actually used. It is better to consider such a message as a route cipher when the words used appear to have some consecutive meaning bearing on the situation at hand. A substitution cipher of this variety would only be used for transmission of a short message of great importance and secrecy, and then the chances are that certain words corresponding to A, E, N, O and T would appear with such frequency as to point at once to the fact that a substitution cipher was used. Watch the initial or terminal letters in such a cipher; they may spell the message.

In general, the determination of class by proportion of vowels, common consonants and rare consonants may be safely followed. We will now proceed to the examination of the more common varieties of each class of cipher.

Chapter V

Examination of Transposition Ciphers

After having decided that a cipher belongs to the transposition class, it remains to decide on the variety of cipher used. As, by definition, a transposition cipher consists wholly of characters of the original message, rearranged according to some law, we may, in general, say that such a cipher offers fewer difficulties in solution than a substitution cipher. A transposition cipher is like a picture puzzle; the parts are all there and the solution merely involves their correct arrangement.

Case 1.—Geometrical ciphers. This case includes all ciphers in which a certain number of the characters are chosen so that they will form a square or rectangle of predetermined dimensions; and then these characters are arranged according to a geometrical design.

Taking the message:

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

of twenty-four letters and assuming a rectangle of six letters horizontally, and four letters vertically, we may have:

(a) Simple Horizontal:

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

(b) Simple Vertical:

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

(c) Alternate Horizontal:

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

(d) Alternate Vertical:

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

(e) Simple Diagonal:

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

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

(f) Alternate Diagonal:

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

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

(g) Spiral, clockwise:

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

(h) Spiral, counter clockwise:

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

It is simply a matter of inspection to read a message in a cipher of this type, once the dimensions of the rectangles have been determined. We place the whole or a portion of the message in such rectangles and read horizontally, vertically and diagonally forward and backward. Parts of words will at once be apparent and the whole message is soon deciphered. Two examples will show the process.

Message

ILVGIOIAEITSRNMANHMNG

This message contains eight vowels or 38% out of twenty-one letters, and the letters LNRST occur 7 times or 33%, the letters XQJKZ not appearing. It is therefore a transposition cipher. Twenty-one letters immediately suggest seven columns of three letters each or three columns of seven letters each. Trying the former we have:

I L V G I O I

A E I T S R N

M A N H M N G

and reading down each column in succession ([Case 1-b]) reveals the message to be “I am leaving this morning.”

Message

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

There are 120 letters in this message with 57 vowels or 47% vowels, and the letters LNRST occur 31 times or 26% of the whole.

Non-occurrence of K and W and vowel proportion leads us to the assumption that it is a transposition cipher of a Spanish text. The factors of 120 are 5 × 3 × 2 × 2 × 2. We may then have one rectangle of 4 × 30 or one of 5 × 24 or two of 5 × 12, or three of 5 × 8, or four of 5 × 6, or five of 3 × 8, or ten of 3 × 4, or twenty of 3 × 2. The message being in a rectangle of 4 × 30, we can inspect it as it stands and this is clearly not the arrangement if it be a geometrical transposition cipher at all. It is best however to try the largest possible rectangles first so we will put it in the form 5 × 24, thus:

M

S

I

B

R

O

R

S

E

E

V

U

E

E

M

C

O

R

E

R

E

L

I

D

E

T

O

E

P

Q

E

N

R

E

R

N

S

E

R

Y

E

C

O

L

L

E

R

E

U

S

P

L

U

R

C

E

L

O

A

J

A

E

H

U

H

P

F

A

S

O

N

N

O

A

A

E

P

I

U

A

P

P

E

A

C

U

Q

A

R

U

O

P

O

E

I

I

R

R

M

I

A

F

D

A

A

R

Q

U

B

O

Z

A

E

G

E

R

S

F

S

X

Here an inspection shows this to be Case [1-f], alternate diagonal, and the text to be “ME SITUO SOBRE PARRAL PORQUE ME PRESENCIA FUE REVELADA POR U”; here the sense breaks but note that U is the twelfth letter of the line and continue as if the rectangle were 5 × 12 and we have “NA PAREJA QU.” Now inspect the second rectangle of 5 × 12 in the same way and the sense continues “E SE ME ACERCO Y HUBO QUE RECHAZAR POR EL FUEGO ALLI ESRERO ORDENES FINISX”.

The practical way of examining a cipher of this type is to have several men prepare rectangles of different dimensions, using the letters of the cipher in the order received. The rectangles can be inspected very rapidly when once prepared. Note that the dimensions of any rectangle will rarely be such as to contain more than fifty letters, on account of the necessity of filling up a rectangle with nulls if the number of letters of the message is just a little greater than a multiple of the rectangle. Also large rectangles give, for all but the diagonal method, whole words in a line or column and these are easily noted.

The following ciphers come under Case 1:

Case 1-i.—The rail fence cipher, useful as an operators’ cipher but permits of no variation and is therefore read almost as easily as straight text when the method is known. The message:

HOSTILE CAVALRY HAS RETIRED

is written:

O T L C V L Y A R T R D

H S I E A A R H S E I E

and is sent:

OTLCV LYART RDHSI EAARH SEIEX

Case 1-j.

Message

S S O H S	T P F O R	I E E A E
T Q N E T	F A I X E	G L F D R
A U L R N	O S R X L	H A T R O

To solve this cipher, read down the columns in this order 8, 1, 15, 2, 14, 3, 13, 4, 12, etc. A variation is to arrange the cipher so the columns are read upwards. Another is to arrange the ciphers so the columns are read alternately upward and downward. The factors of the number of letters in this case give the shape of the rectangle as usual.

It will be seen that there are a great number of possible transposition ciphers that come under Case 1 but practically all of them are useless from a military standpoint because they do not depend on a key which can be readily and frequently changed. However such ciphers constantly crop up in cipher examination, being used for special communication between parties who consider the regular military ciphers too complicated. Thus some of these expedients have been used.

Reversed Writing.—(Special case of Case [1-a]).

LEAVING TONIGHT is enciphered THGINOT GNIVAEL or it may be reversed by words, thus GNIVAEL THGINOT or by groups of five letters, thus IVAEL NOTGN XTHGI.

Vertical Writing.—(Special case of Case [1-b]). Same message is enciphered,

LT
EO
AN
VI	and is sent, LTEOA NVIIG NHGTX.
IG
NH
GT

Case 2.—This case includes all transposition ciphers in which lines and columns of the text are rearranged according to some key word or key number. There are many varieties of this case but their solution usually is arrived at through the methods suggested for Case 1, that is, arrangement into appropriate rectangles and examination of lines and columns for words or syllables. Rearrangement of columns or lines follows until the solution is completed.

Case 2-a.

Message

HIIGF	TNGHI	NTCVN	IEIOT	CYIFY	LHAEA	ESNBA	EEEEN
RWGBN	YDELR	OAESG	RNEBO	VNLDA	ICAOA	LCNDT	IRGVA
CDOIE	SEREC	DVPEI	AFIFL	RINEH	ETT

There are 108 letters in this message and examination shows it to be a transposition cipher, English text. The number of letters, 108, immediately suggests a rectangle of 12 × 9 or 9 × 12 letters. Put into this form we have:

Vowels H I I G F T N G H I N T 3 C V N I E I O T C Y I F 5 Y L H A E A E S N B A E 6 E E E N R W G B N Y D E 4 L R O A E S G R N E B O 5 V N L D A I C A O A L C 5 N D T I R G V A C D O I 4 E S E R E C D V P E I A 6 F I F L R I N E H E T T 4	Vowels H I I G F T N G H 2 I N T C V N I E I 4 O T C Y I F Y L H 2 A E A E S N B A E 6 E E E N R W G B N 3 Y D E L R O A E S 4 G R N E B O V N L 2 D A I C A O A L C 5 N D T I R G V A C 2 D O I E S E R E C 5 D V P E I A F I F 4 L R I N E H E T T 3
	Vowels
H I I G F T N G H I N T	3
C V N I E I O T C Y I F	5
Y L H A E A E S N B A E	6
E E E N R W G B N Y D E	4
L R O A E S G R N E B O	5
V N L D A I C A O A L C	5
N D T I R G V A C D O I	4
E S E R E C D V P E I A	6
F I F L R I N E H E T T	4
	Vowels
H I I G F T N G H	2
I N T C V N I E I	4
O T C Y I F Y L H	2
A E A E S N B A E	6
E E E N R W G B N	3
Y D E L R O A E S	4
G R N E B O V N L	2
D A I C A O A L C	5
N D T I R G V A C	2
D O I E S E R E C	5
D V P E I A F I F	4
L R I N E H E T T	3

The vowel count of the lines shows the first arrangement to be the more likely. We will now number the columns and try pairing off certain ones which in no line would give impossible combinations of letters.

1	2	3	4	5	6	7	8	9	10	11	12
H	I	I	G	F	T	N	G	H	I	N	T
C	V	N	I	E	I	O	T	C	Y	I	F
Y	L	H	A	E	A	E	S	N	B	A	E
E	E	E	N	R	W	G	B	N	Y	D	E
L	R	O	A	E	S	G	R	N	E	B	O
V	N	L	D	A	I	C	A	O	A	L	C
N	D	T	I	R	G	V	A	C	D	O	I
E	S	E	R	E	C	D	V	P	E	I	A
F	I	F	L	R	I	N	E	H	E	T	T

These combinations appear among others:

1	6	2	4	5	2
H	T	I	G	F	I
C	I	V	I	E	V
Y	A	L	A	E	L
E	W	E	N	R	E
L	S	R	A	E	R
V	I	N	D	A	N
N	G	D	I	R	D
E	C	S	R	E	S
F	I	I	L	R	I

The word FIGHT stares at us from the first line; let us arrange the columns thus:

5	2	4	1	6	3
F	I	G	H	T	I
E	V	I	C	I	N
E	L	A	Y	A	H
R	E	N	E	W	E
E	R	A	L	S	O
A	N	D	V	I	L
R	D	I	N	G	T
E	S	R	E	C	E
R	I	L	F	I	F

We have the words FIGHTI(NG), VICIN(ITY), RENEWE(D), ANDVIL(LA), RDINGT(O), RECE(IVED). With this to go on, we must choose column 11 as the next one and then in order, columns 8, 10, 7, 12, 9. But note that the order 11, 8, 10, 7, 12, 9, is the same as the order 5, 2, 4, 1, 6, 3. The message was written in twelve columns and the columns have been transposed in that order. We may, although it is entirely unnecessary, speculate on the key word used. It was probably

M E X I C O

4 2 6 3 1 5

meaning that the 4th column of the plain text was transferred in enciphering so it became our 1st, the 2d column remained the 2d; the 6th column became our 3d, etc.

Actually, this cipher was solved because the word VILLA was suspected and all the necessary letters were found in line six of the arrangement in twelve columns. The order 1, 6, 3, 11, 8 was tried and gave this result.

1	6	3	11	8
H	T	I	N	G
C	I	N	I	T
Y	A	H	A	S
E	W	E	D	B
L	S	O	B	R
V	I	L	L	A
N	G	T	O	A
E	C	E	I	V
F	I	F	T	E

The remainder of the solution followed the lines already laid down and, naturally, offered no difficulties, in view of the large number of connected syllables available.

Case 2-b.

Message

SLCOF	WEETN	EBRDO	ORVYM	FFEDI
NMTEC	ROIAR	PERHO	ESETS	RFBHL
TENAH	OPTAU	SOMTL	RTETT	ASCBH
NIODC	RENEN	AAPRD	LACYE	ECIIE
SGUFN

This is a transposition cipher, English text, and contains 105 letters. The factors of 105 are 5 × 3 × 7 so that we must investigate the following rectangles; 5 × 21, 15 × 7, three of 5 × 7, five of 3 × 7 and seven of 5 × 3.

21 × 5 Vowels S L C O F W E E T N E B R D O O R V Y M F 6 F E D I N M T E C R O I A R P E R H O E S 9 E T S R F B H L T E N A H O P T A U S O M 7 T L R T E T T A S C B H N I O D C R E N E 6 N A A P R D L A C Y E E C I I E S G U F N 9 Vowels 1 2 1 2 1 0 1 4 0 1 3 3 1 3 3 3 1 1 3 2 1 The vowel count of the columns of the rectangle 5 × 21 is verysatisfactory. Let us consider it as three blocks of 5 × 7 each,since we must do this ultimately, and make a vowel count of columns forthese blocks.

5 × 21 Vowels S L C O F 1 W E E T N 2 E B R D O 2 O R V Y M 1 F F E D I 2 N M T E C 1 R O I A R 3 P E R H O 2 E S E T S 2 R F B H L 0 T E N A H 2 O P T A U 3 S O M T L 1 R T E T T 1 A S C B H 1 N I O D C 2 R E N E N 2 A A P R D 2 L A C Y E 2 E C I I E 4 S G U F N 1 Vowels 7 9 8 7 6

	Column
	1	2	3	4	5
Vowels, 1st block	2	2	3	2	2
Vowels, 2d block	2	3	2	2	2
Vowels, 3d block	3	4	3	2	2

This is also excellent, so we will try three blocks 5 × 7 and see if rearrangement of horizontal lines will give results reading the columns vertically.

1	S L C O F	P E R H O	A S C B H
2	W E E T N	E S E T S	N I O D C
3	E B R D O	R F B H L	R E N E N
4	O R V Y M	T E N A H	A A P R D
5	F F E D I	O P T A U	L A C Y E
6	N M T E C	S O M T L	E C I I E
7	R O I A R	R T E T T	S G U F N

Among other combinations are:

3	E B R D O	R F B H L	R E N E N
2	W E E T N	E S E T S	N I O D C
1	S L C O F	P E R H O	A S C B H
5	F F E D I	O P T A U	L A C Y E
7	R O I A R	R T E T T	S G U F N

The addition of line 6 above line 3 and line 4 below line 7 will complete this cipher. The successive columns should be read downward.

Case 2-c. In this case, both lines and columns are rearranged by means of a key word or key words. The method of solution is the same as Case 2-a and 2-b except that the lines must be rearranged after the columns have been correctly arranged, or in some cases, vice versa. This cipher is not infrequently met with because it seems to offer safety by use of two key words and by the great but only apparent complexity of the method.

Message

WVGAE	EGENL	TFTOH	TEIEF	RBTSE
INENG	ONWRM	GXIXN	GOITN	ROMRO
ESPAL	HNEAC	UDNNH	DERME

This is a transposition cipher, English text and the number of letters, 70, leads us to try rectangles of 10 × 7 and 7 × 10.

	Vowels		Vowels
W V G A E E G E N L	4	W V G A E E G	3
T F T O H T E I E F	3	E N L T F T O	2
R B T S E I N E N G	3	H T E I E F R	3
O N W R M G X I X N	2	B T S E I N E	3
G O I T N R O M R O	4	N G O N W R M	1
E S P A L H N E A C	4	G X I X N G O	2
U D N N H D E R M E	3	I T N R O M R	2
		O E S P A L H	3
		N E A C U D N	3
		N H D E R M E	2

The first form looks the more likely from the vowel count. We proceed to number the columns and lines and try rearrangement of columns so as to obtain possible letter combinations from every line.

	1	2	3	4	5	6	7	8	9	10
1	W	V	G	A	E	E	G	E	N	L
2	T	F	T	O	H	T	E	I	E	F
3	R	B	T	S	E	I	N	E	N	G
4	O	N	W	R	M	G	X	I	X	N
5	G	O	I	T	N	R	O	M	R	O
6	E	S	P	A	L	H	N	E	A	C
7	U	D	N	N	H	D	E	R	M	E

Among other combinations we have these:

	3	5	1	4	2	8	10	6	9	7
1	G	E	W	A	V	E	L	E	N	G
2	T	H	T	O	F	I	F	T	E	E
3	T	E	R	S	B	E	G	I	N	N
4	W	M	O	R	N	I	N	G	X	X
5	I	N	G	T	O	M	O	R	R	O
6	P	L	E	A	S	E	C	H	A	N
7	N	H	U	N	D	R	E	D	M	E

A very casual inspection of the lines shows that they should be rearranged in order 6, 1, 2, 7, 3, 5, 4, as follows:

	3	5	1	4	2	8	10	6	9	7
6	P	L	E	A	S	E	C	H	A	N
1	G	E	W	A	V	E	L	E	N	G
2	T	H	T	O	F	I	F	T	E	E
7	N	H	U	N	D	R	E	D	M	E
3	T	E	R	S	B	E	G	I	N	N
5	I	N	G	T	O	M	O	R	R	O
4	W	M	O	R	N	I	N	G	X	X

Although of no particular importance, it may be stated that the column key in this case was GRAND and the line key was CENTRAL, both used as in enciphering [Case 2-a].

Case 3. Route ciphers. In this case, whole words of the message are transposed according to some of the methods of Case 1 or 2 or their equivalents. The route cipher is little used at present. Its development and use during the Civil War was caused by the inability of the telegraphers of that day to handle regular cipher matter correctly and rapidly. It was, even in those days, frankly only a delaying cipher and, to be of any value, had to be filled with meaningless words to conceal the message proper. An example from the Signal Book will suffice to show the general character of route ciphers. To one familiar with monoliteral transposition ciphers, even the best of route ciphers offers but little difficulty.

“To encipher the message ‘MOVE DAYLIGHT. ENEMY APPROACHING FROM NORTH. PRISONERS SAY STRENGTH ONE HUNDRED THOUSAND. MEET HIM AS PLANNED.’ arrange as follows:

MOVE	STRENGTH	PLANNED	SAY
DAYLIGHT	ONE	AS	PRISONERS
ENEMY	HUNDRED	HIM	NORTH
APPROACHING	THOUSAND	MEET	FROM

Here the route is down the first column, up the fourth, down the second and up the third.”

This cipher was often complicated by the introduction of nulls for every fifth word. Thus the above message might be sent:

MOVE STRENGTH PLANNED SAY NEVER DAYLIGHT ONE AS PRISONERS LEAVING ENEMY HUNDRED HIM NORTH UNCHANGED APPROACHING THOUSAND MEET FROM COME.

The words in italics are nulls and not a part of the message and the receiver eliminates them before arranging his message in columns to get the sense of it.

As an additional complication, it was customary for each correspondent to have a dictionary or code in which the names of all prominent generals and places and many of the prominent verbs,—as to march, to sail, to encamp, to attack, to retreat,—were represented by other words.

A route cipher using the code words of the War Department code might have some advantages over the method of enciphering code messages as prescribed in that Code.