CHAPTER II

Concealment Devices

Concealment writing may take a host of forms. Perhaps its oldest known application is found in the ancient device of writing a secret message on the shaved head of a slave and dispatching the slave with his communication after his growing hair had covered the writing. Or, if this appears a little incredible, the ancients have left us records of another device considerably more practical: that of writing the secret message on a wooden tablet, covering this with a wax coating, and writing a second message on top of the first.

In the middle ages we meet a development called _puncture cipher_; any piece of printed matter, such as a public proclamation, serves as the vehicle, and the cipher consists simply in punching holes with a pin under certain letters, so that these letters, read in regular order, will convey the desired information. It is said that this kind of concealment writing was resorted to in England at a comparatively recent period, to avoid the payment of postage. Postage on letters was very high, while newspapers were permitted to travel free, and the correspondents sent their messages very handily by punching holes under the letters printed in newspapers. Where the sender of a message may also control the preparation of the printed vehicle, any desired letters can be pointed out by the use of special type forms, misspelled words, accidental gaps, and so on.

But concealment cipher is not necessarily confined to written and printed matter. Ohaver, in his “Solving Cipher Secrets,” demonstrated the conveyance of messages in the shapes and sizes of stones in a garden wall, or in the arrangement of colored candies in a box; and we read, in fiction, of many similar devices, such as a series of knots tied in a string, or beads strung in imitation of the rosary. Again, we hear of cases in which the arrangement of stamps on envelopes is made to represent the terms of a miniature code. All such devices are, of course, combination-cipher rather than pure concealment, since the stones, candies, and so on, must first be made the substitutes for letters or code terms.

A method of pure concealment, said to have been used by Cardinal Richelieu, involved the use of a _grille_. Grilles are made of cardboard, sheet-metal, or other flat material, and are perforated with any desired number, size, and arrangement of openings. The Richelieu grille, of approximately the same size and shape as the paper used for correspondence, could be laid over a sheet of paper so as to reveal only certain portions, and the secret message was written on these. The grille was then removed and the rest of the sheet was filled in with extraneous matter in such a way as to present a seemingly continuous text. The legitimate recipient of this message, having a duplicate grille, simply laid this grille over the sheet of paper, and read his message through the apertures.

Concealment cipher goes by various names, as _null cipher_, _open-letter cipher_, _conventional writing_, _dissimulated writing_, and so on, not always with a difference in meaning, though “conventional writing” does convey somewhat the idea of a tiny code. (In this, casual words have special meanings.)

The name “null cipher” derives from the fact that in any given cryptogram the greater portion of the letters are null, a certain few being significant, and perhaps a few others being significant only in that they act as indicators for finding truly significant letters. To illustrate what is usually meant: Say that your very good friend, Smith, first complains about a radio which he has bought from your neighbor, Johnson, then asks you to take Johnson the following note: “Having trouble about loudspeaker. Believe antenna connected improperly, but do whatever you can.” By reading the final letter of each word, you will find out what Smith actually had to say to Johnson: GET READY TO RUN.

That is the null cipher reduced to its elements, though naturally it can be more skillfully applied. Significant letters may be concealed in an infinite variety of ways. The key, as here, may be their positions in words, or in the text as a whole. It may be their distance from one another, expressed in letters or in inches, or their distance to the left or right of certain other letters (indicators) or of punctuation marks (indicators); and this distance, or position, need not be constant, or regular. Sometimes it is governed by an irregular series of numbers.

Similar devices are applied to whole words. We agree, say, that in whatever communications we send to our accomplice, only the third word of each sentence is to be significant. Desiring to send him the order, STRIKE NOW, we write him as follows: “The building _strike_ is worrying our friends quite a lot. It has _now_ extended to this part of the city.”

A purely concealment cipher may be enveloped in apparent ciphers of other types. The true message is concealed, as usual, in a dummy message, and the whole is enciphered in one of the legitimate systems. It is then hoped that the decryptor, satisfied with having solved the dummy, will look no further. Even more effective would be the device of concealing the message in what appears to be a cryptogram, but is not. It is easy to string letters together in such a way as to make them resemble most convincingly a transposition cryptogram, and in this case it would be hoped that the investigator’s full attention would be given to the hopeless task of decrypting the dummy.

Concerning the decryptment of concealment cipher, we regret to say that cryptanalysis has little help to offer. Fortunately, most of these ciphers depend absolutely on the belief that they will not be recognized as cipher, and once they are so recognized, they present no resistance. In those few cases where the secret message is not at once obvious, it is sometimes useful to arrange the words (or sentences) in columns, or in rows, for a closer inspection.

Figure 2

I N S P E C T D E T A I L S F O R T R I G L E T H A C K N O W L E D G E T H E B O N D S F R O M F E W E L L

We have, for instance, an apparent memorandum in which the awkwardness of the wording, or some other factor, has drawn our attention to the possibility of cipher: “Inspect details for Trigleth — acknowledge the bonds from Fewell.” We arrange these words in column form, aligned by their initials, as in Fig. 2, and the third column promptly gives up the secret message STRIKE NOW.

The words of sentences can, of course, be treated in the same way, and where the alignment from the left gives no results, letters or words can be aligned from the right, or from the center. If columns give no results, diagonals can be inspected, or a zig-zagging line between one column and another.

Experience counts for most, and extensive reading is a vast help. Having seen methods in use, or read the descriptions of methods, we know of some definite thing to look for. Then, too, some of the concealment ciphers have transposition characteristics. This would be the case with the Legrand cipher, which is of the type called “open letter.”

This cipher used a numerical key, which, in turn, was based on a keyword in what seems today a rather odd manner: A keyword CAT, made up of the 3d, 1st, and 20th letters of the alphabet, gives the key 3 1 2 0. Before concealment takes place, a series of word-positions is marked off, and these vacant places are numbered (0 to 9, or 9 to 0), continuing to repeat the ten digits until there are enough of the digits 3, 1, 2, and 0 to accommodate the words of the secret message. This message is then written, word by word, below its digits, beginning with the first digit 3, then going on to find a digit 1, then a digit 2, then a digit 0, then another digit 3, and so on. After the secret message is written into its place, all of the blank positions are filled with connective matter, as in the case of Cardinal Richelieu’s grille-writing. Our later study of transpositions will show approximately how we should go about reading this, once we suspect its use.

So far, we have been considering pure concealment. Many of the classic ciphers, fundamentally of the concealment type, are also substitution ciphers, and their decryptment would follow substitution methods. Of these, perhaps the best known is Bacon’s biliteral cipher, summed up in Fig. 3.

Figure 3

BACON'S BI-LITERAL ALPHABET

A aaaaa IJ abaaa R baaaa B aaaab K abaab S baaab C aaaba L ababa T baaba D aaabb M ababb UV baabb E aabaa N abbaa W babaa F aabab O abbab X babab G aabba P abbba Y babba H aabbb Q abbbb Z babbb

S T R I K E baaab baaba baaaa abaaa abaab aabaa

N O W abbaa abbab babaa

Hold OFf uNtIl you hEar frOm mE agAin. wE May cOMpROmIse.

Lord Bacon’s cipher presupposes that the encipherer may so control the preparation of his published work that he may prescribe the type to be used for each printed letter, and it is claimed that he actually used his cipher for the preservation of historical secrets, including that of his own parentage. Two fonts of type are required, the letters of one font differing (very slightly) from those of the other font. These we may speak of as the _A_-font and the _B_-font, and each letter of the alphabet is given a substitute composed of _A_’s and _B_’s, as shown in full in the figure. Before a message, as STRIKE NOW, can be concealed, it must be expressed in _A_’s and _B_’s, five of these for each of its letters, as shown, so that a message of 9 letters attains a length of 45. For its concealment, we may use any text whatever whose length is 45 letters, for instance, one whose obvious meaning is the contrary of the secret one: “Hold off until you hear from me again. We may compromise.” The first five letters, _HOLDO_, are to represent _S_, the next five, _FFUNT_, are to represent _T_, and so on; and the sole purpose of the _A_’s and _B_’s is to point out the kind of type which must be used in printing the corresponding letters. In the encipherment of the figure, letters taken from the _A_-font are indicated by lower-case and those of the _B_-font by capitals, though it is understood that no such emphatic difference is contemplated in the cipher.

While the average modern person would have no opportunity for employing Lord Bacon’s cipher as described, he has access to an unlimited number of vehicles other than type-difference. Anything, in fact, may serve the purpose, so long as the material is available in two distinguishable forms and in sufficient quantity. Our message of 29 _A_’s and 16 _B_’s could be expressed with a deck of playing cards if aces and face-cards are considered to represent _B_’s. It could assume the form of a fence with 45 palings, in which the _B_-palings are crooked, damaged, or missing. Ohaver once made use of a cartridge belt in which the _A_-loops contained cartridges and the _B_-loops were empty. There is an excellent opportunity here, too, for the compiling of “fake” cryptograms, with _A_-letters and _B_-letters distinguished as vowels and consonants, or by the part of the normal alphabet from which they have been taken.

With a biliteral or binumeral alphabet which requires 26 groups, we cannot have fewer than five characters to the group without making groups of different lengths. But another well-known cipher alphabet, devised by the Abbé Trithème for use in much the same way, is triformed, and thus permits that the group-length be reduced to three. The Trithème (Trithemius; Trittemius) alphabet, expressed in digits 1-2-3, was approximately that shown in Fig. 4.

Figure 4

A TRI-NUMERAL ALPHABET

A 111 J 211 S 311 B 112 K 212 T 312 C 113 L 213 U 313 D 121 M 221 V 321 E 122 N 222 W 322 F 123 O 223 X 323 G 131 P 231 Y 331 H 132 Q 232 Z 332 I 133 R 233 & 333

This alphabet has had many applications, including the use of colored candy previously mentioned. One contributor to Ohaver’s column submitted a cryptogram of the open-letter type in which the digits 1, 2, 3, were indicated in the _number of syllables_ of the successive words. A sentence, “Can you be sure of sufficient assistance from Mayberry?” indicates the digits 1 1 1, 1 1 3, 3 1 3; and, if the alphabet of Fig. 4 is the one in use, represents the letters _A C U_. This is of particular interest in that it is easily done without involving the awkward turns of language that so often betray the concealment cipher. (This same contributor, a Mr. Levine, evolved another cipher, accomplished by an arithmetical process, by which it was possible to make a cryptogram convey two separate messages!)

Many writers have shown alphabets of the biform and triform types applied to open-letter communications by making the significant factor the _number of vowels_ contained in successive words. Thus, the sentence given above yields a series 1, 3, 1, 2, 1, 4, 4, 1, 4. Using a biform alphabet, these are usually considered simply as odd and even; with a triform alphabet, some disposition must be made of numbers larger than 3.

The subject is fascinating, and the literature of cryptography is rich with examples. However, we need not delve further into what, after all, is only the stepchild of a legitimate science. The matter of telegraphic transmission alone will bar these ciphers for most general purposes, or the fact that a cipher once betrayed will never serve again. Then, too, the censorship combats it by cutting out or rearranging or changing words, causing the open letter (or telegram) to convey only the information which it purports to convey.

Concealment cipher has, of course, the unique virtue of being able to convey messages under circumstances which make it seem that no communication has passed, and we have hardly touched upon the fact that the short message, prior to its concealment, may have been a well-enciphered one. But we rather suspect that, for the end desired, invisible inks are more convenient and practical.

1. By PICCOLA.

On peut être Napoleon sans être son ami, mes enfants!

2. By B. NATURAL.

FOR SALE: Spring coats. All fine Scotch serge, for ensembles. Stoat trimmed, fashioned right. Black shirred lining, striped. Effective for brides. Act quickly. - Abraham Batz, 522 Broad, Telephone Exchange 7104-R.

3. By TITOGI.

How about releasing Tony, the gang chief? He don't lie, and is not the true slayer either. Let us be friends. I am all right. Ed Lehr.

4. By TRYIT.

To those friends considering, it is always news, but all filled ciphers disturb happiness with varied answers!

5. By PICCOLA.

Do not send for any supplies before Monday, at earliest. Order once only, as men in charge are feeling sore about your threat to encourage the mutiny at Ford's. - Wilson.

6. By PICCOLA. (Why not, indeed?)

A W I T H A N Y S E N D F O R I T Y O U M U S T B E F E A R T H E C A N H I T T R Y A B O U R E O U T I S E C H I Y O U A N D M Y T I O N C U P C R E A S K T O C A N D Q.