Successful Systems of Secret Writing
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
.
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
.
| A B C | J K L | S T U |
| D E F | M N O | V W X |
| G H I | P Q R | Y Z |
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.”
| a y p e i e |
| c e p |
| h r i |
| r m l s v |
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.
| A | B | C | D | E | F | G | H | |
|---|---|---|---|---|---|---|---|---|
| A | a | d | g | k | n | q | t | x |
| B | b | e | h | l | o | r | uv | y |
| C | c | f | ij | m | p | s | w | z |
Fig. 4.—The “two-letter” cipher.
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | a | b | c | d | e |
| 2 | f | g | h | i | j |
| 3 | k | l | m | n | o |
| 4 | p | q | r | s | t |
| 5 | uv | w | x | y | z |
Fig. 5.—The Nihilist code.