Cecil Henry Bullivant

From the earliest times secret writing has been considered no less an art than a necessity. Innumerable have been the systems invented and the means employed to insure the secrecy of messages and instructions. Yet in the passage of time by far the greater number of these methods of cipher has become obsolete and practically useless, failing in most cases to comply with the three great necessities which Bacon declared to be indispensable to all ciphers and cryptograms: (1) Easy of reading and writing; (2) difficult of solution; and (3) void of suspicion.

Ciphers may be generally divided into two branches—code ciphers and letter ciphers. The first of these terms refers to systems so arranged that one group of characters represents several words or sentences, whilst the other term designates those cryptograms where each letter in every word has its corresponding symbol.

As letter ciphers are the more usual, and certainly the handier of the two classes, examples are given of some systems which have been successfully used at different times and for different purposes.

The simplest of all methods, and, for that matter, the easiest to be detected, consists in having an arbitrary list of numbers, one of which shall represent each letter in the alphabet—e.g., A appears as 4, B as 8, C as 12, &c.

This plan can be varied by substituting letters for the numbers, and having each letter of the alphabet represented by another letter—e.g., A being substituted by G, B by L, C by Q, and so on; but the disadvantages attending these very simple ciphers are so great that for a message of any real importance the system is useless.

In the same way the expedient of reversing the alphabet and making A represented by Z, B by Y, C by X, is too simple and generally known to require further description.

One of the easiest and earliest ciphers is shown in Fig. 1. This is written in the following manner: The “bounding” lines in which the desired letters are contained are drawn and the position of the letter in them indicated by a dot. Taking, for example, Fig. 1, A would be one dot, B two, and C three dots inscribed inside the two lines forming the angle. Thus the word CIPHER would be written C I P H E R.

At this point it might be remarked that in all the examples here given the letters are arranged in their simplest order—that of alphabetical sequence; whereas, for practical purposes, they can be arranged in any form desired, the more complicated the better. To illustrate this Fig. 2 shows another arrangement of the letters, by using which the same word would appear C I P H E R.

Fig. 1.—One of the earliest ciphers.

d j v	a o w	e p u
h l s	b m r	i y
g k t	c q x	f n z

Fig. 2.—Another arrangement of
cipher shown in Fig. 1.

An example of another simple cipher created merely by the transposition of letters is shown in Fig. 3, which can be read by taking the first letter of the first line, the last letter of the last line, the last letter of the first line, and the first letter of the last, then the last letter of the first line, the penultimate letter of the last, and so on. When the letters in Fig. 3 are properly transposed they will be found to read “A very simple cipher.”

Fig. 3.—Transposition of
letters cipher.

Lord Bacon invented a cipher composed of two letters only, which, although confusing to the uninitiated, is somewhat too cumbersome for any general use. Supposing the two letters decided upon to be A and B, they are grouped into series of five and employed in the following manner: The first letter in the alphabet, A, is represented by AAAAA, B becomes AAAAB, C appears as AAABA, D as AABAA. Using this combination, the same word “cipher” would be written AAABA, BBAAA, BBBBB, AABBA, ABAAA, BBBAB.

Amongst the easy ciphers must be mentioned that shown in Fig. 4, which is used thus: In the center block of small type you find the letters of the word you wish to write in cipher. Suppose it to be TO-MORROW. Now in the vertical column at the side you find that the letter on a line with “t” is A, whilst the letter at the top of the vertical column is G. Therefore the cipher letters for “t” are AG. The next letter, “o,” is on a line with B and under E, so the cipher letters are BE. In a similar way “m” becomes CD, and, proceeding with the remaining letters in the same fashion, we obtain the whole word written in cipher thus: AG, BE, CD, BE, BF, BF, BE, CG.

Russian Nihilist Code

An adaptation of the last-mentioned system is shown in Fig. 5, where the letters at the side and top are replaced by numerals. This method is very much in use amongst the Russian Nihilists, who would therefore write the sentence “Plot discovered” as follows: 41, 32, 35, 45; 14, 24, 44, 13, 35, 51, 15, 43, 15, 14.

This, again, can be very much complicated by multiplying each number by the position held by the letter in the word. Thus in the sentence just put into cipher, P is the first letter in the word “plot,” L is the second, O the third, T the fourth, whilst in the next word D is the first, I the second, &c. You therefore multiply the ciphers in the first word by 1, 2, 3, 4 respectively, and deal similarly with those of the second word. The sentence thus treated would appear—41, 64, 105, 180; 14, 48, 132, 52, 175, 306, 105, 344, 135, 140.

To read this the system must be reversed, and each number divided by its position in the word.

A useful form of musical cipher is shown in Fig. 6, which explains itself. In using this system it is usual to separate the different words by dividing the notes into bars, as can be seen from a glance at Fig. 7. Here it will be noticed that only crotchets and minims are used for ciphers, whilst the other notes introduced have no significance, only serving the purpose of confusing whoever has sufficient curiosity to pry into the message. Therefore, discordant as the passage may sound to the wrong person, it probably makes very sweet music to whoever has ears and eyes to understand its meaning.

Before proceeding to more complicated ciphers, that known as the fractional may be mentioned. This is a very simple method, and easily learned. The letters of the alphabet are divided into groups of five as shown in Fig. 8, each group being marked successively up to five, and each letter in the group treated in the same way. The numerator is used to designate the group to which the letter belongs, whilst the denominator shows the individual letter in that group.

Fig. 8.—The fractional cipher.

Adopting this method the word CIPHER therefore appears as in Fig. 9. As numerals above 5 do not appear in this cipher any more than does the figure 0, they can be added at will to complicate the appearance of the cryptogram, as shown in Fig. 10, where the same word is shown with the addition of meaningless numerals.

The Sphinx

Now to turn to more scientifically constructed ciphers, such as have been employed by various Governments in correspondence with their ambassadors and secret servants.

The Sphinx Cipher, shown in Fig. 11, is based upon a key-word of six or seven letters, previously arranged by the parties concerned A key-alphabet is written in full at the top of the plan, and against each letter of the key-word a complete alphabet is written as shown in the figure.

Fig. 11.—A Government cipher, called the “Sphinx.”

Suppose that the key-word chosen is BALFOUR, and that the message to be sent is WAR DECLARED LEAVE NOW, the key-word is then applied to the message thus:—

You then find in the top row the first letter of your message, which is W, and you see that the letter on a line with B and under W is X, which will be the first letter of your cipher. You then find A above and A by the side, which will give you C. You then find R above, and in the L horizontal column is its equivalent U. Proceeding thus with your message you arrive at the cipher, which reads: XCU HJISBTHH QKHWG QSB.

To read this it is only necessary to write the key-word under the cipher and reverse the proceeding.

An ingenious cipher, used by the War Office of a well-known Continental Power, is partially shown in Fig. 12.

On two adjacent sides of a square entire alphabets are written, commencing at any letter (in the figure they begin at K in one and S in the other). Against each letter of the perpendicular alphabet the entire twenty-six letters are written horizontally, beginning with A and continuing in order. Leaving the first of these horizontal alphabets simple, against the remaining twenty-five, small alphabets are written as you will see in the figure, which shows the plain alphabets and five letters so treated.

Fig. 12.—Another Government cipher—still in use.

The cipher is used in this way. The letters in each word of the message are divided into couples. These couples are found in the doubled alphabets in the center of the cipher scheme, and the key letters at the side and top show the actual cipher equivalent.

Suppose it is desired to put into this cipher the words CABLE CODE. Dividing the letters into couples CA, BL, E. CO, DE are obtained. Finding the combination CA it is simple to ascertain that the index letters are TM, which is therefore the cipher. BL is EL, whilst the remaining letter E from the top alphabet is found to be SO. Treating the word CODE in the same way the ciphers prove to be HM, XN, and therefore the message is transmitted thus: TMELSO HMXN.

So far an idea has been given of the systems of cipher from the simplest methods to the most complicated of political cryptograms. Although the actual details are necessarily hidden, it may be assumed as a positive fact that the most secret political ciphers now in use by civilized Governments are but adaptations of one or other of the methods described.