| Figure 138 SLIDE - TYPE I. Plaintext: C U L P E R Z Y X W V T S Q O N M K J I H G F D B A CIPHER: 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..... ══════════════════════════════════════════════════ a b c d e f g h i j k l m n o p ....... Key A: Z Y A X E W V U T S R C Q P O D ....... Key B: A Z B Y F X W V U T S D R Q P E ....... Key C: B A C Z G Y X W V U T E S R Q F ....... ══════════════════════════════════════════════════ SLIDE - TYPE II. Plaintext: 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 CIPHER: C U L P E R Z Y X W V T S Q O N M K J I H G F D B A C U L..... ══════════════════════════════════════════════════ a b c d e f g h i j k l m n o p ....... Key A: A C U L P E R Z Y X W V T S Q O ....... Key B: B A C U L P E R Z Y X W V T S Q ....... Key C: C U L P E R Z Y X W V T S Q O N ....... ══════════════════════════════════════════════════ SLIDE - TYPE III. Plaintext: C U L P E R Z Y X W V T S Q O N M K J I H G F D B A CIPHER: C U L P E R Z Y X W V T S Q O N M K J I H G F D B A C U L..... ══════════════════════════════════════════════════ a b c d e f g h i j k l m n o p ....... Key A: B D A F P G H I J K M U N O Q L ....... Key B: D F B G L H I J K M N C O Q S U ....... Key C: A B C D E F G H I J K L M N O P ....... ══════════════════════════════════════════════════ SLIDE - TYPE IV. Plaintext: D A M S C U B E F G H I J K L N O P Q R T V W X Y Z CIPHER: C U L P E R Z Y X W V T S Q O N M K J I H G F D B A C U L..... ══════════════════════════════════════════════════ a b c d e f g h i j k l m n o p ....... Key A: C R P A Z Y X W V T S Q U O N M ....... Key B: A E L B R Z Y X W V T S C Q O N ....... Key C: U Z E C Y X W V T S Q O L N M K ....... ══════════════════════════════════════════════════ |
alphabets have all been left undisturbed with their primary key-words (CULPEPER, DAMASCUS) and their alphabetical sequences in plain view; in practice, such alphabets ought to be carried through a transposition block, or otherwise made to appear incoherent. Second, the index-letter should never be A (or any other frequent letter) unless the details of encipherment are varied. (We might, for instance, consider that the index-letter is in the sliding alphabet and that keys are in the upper.)
In the Type I slide, the cipher alphabet is in normal order, and “slides against” a mixed plaintext alphabet. In Type II, we find a mixed cipher alphabet “sliding against” the normal one; in Type III, we find this mixed cipher alphabet “sliding against” itself; and in Type IV, we find it “sliding against” another, and different,
| Figure 139 5 10 15 20 25 30 Y V N G K Y E G D P Z E A Y K H S M D Q K K W S J I Q V I O P E I T E A v c I c c c v 35 40 45 50 55 60 K C F K Q J P M L B J X G K C Z D B G N G Q B D Q M E O N K I T c v I T H T H E P E c E c E 65 70 75 80 85 90 X T Y A D D D G J R X R X F W G D A Y T Q S G G C G P B Y O H H I E H A I P H E E v 95 100 105 110 115 120 C L W K C B I C F E Z D G J W K U F K C B U I Z Y B K E K C T H A T H I I c T H A c E A c T H 125 130 135 140 145 150 G K T A O Q C B Y Q U U F Z G G Z Y F N F M J V Z B L Q J U E c H v E c c E E v A 155 160 165 170 175 180 V M M J T A E F V S M E N K Q J E I Z Y A L Q Y R X R X F R v W E v E T c E E W 185 190 195 200 205 210 O U F V S V V V V P K T B K C G O M I K B Q V Z N B I N A O c v c v I E T H E v A c c E A H v 215 220 225 230 235 240 C E V V J F V U Z S B K M K C G P M D T K K Y A D D D Y Z C E c v E A c v T H E v I c H H E H 245 250 255 260 265 270 B T K V S G Q W I T Z D A K P G W B I O N D G R C H P B H U A M v E c T H A T E E v H I H E 275 280 285 290 295 300 G K T Q H G U V Z N Y X M L H F S M D Q K K W Z Q U D A M T E c E c c E v v c I c E c H A 305 310 315 320 325 330 Z D B J O P E U L R Y U G K U Z E U S J Z D B O D R E S I O T H E v E c I T T E T H E E v 335 340 345 R L A B L J R S Z Q Y Q V F L A L E c c c |
mixed alphabet. Every slide, used in any manner, has an equivalent tableau and while tableaux are seldom used, it is very important that we carry in mind a clear picture of their appearance; otherwise we shall find it difficult to understand how slides can be restored with only partial information. The imaginary tableau which is to serve this purpose, using any one of the four slides in the manner specified, is formed as follows: The plaintext alphabet, with letters in exactly the order of the slide, appears at the top. The 26 cipher alphabets, standing below and parallel to the plaintext one, are all seen in exactly the order of the slide, and are shifted, one letter at a time, exactly as the normal alphabet is shifted in the Vigenère tableau. Thus, exactly as in Vigenère, the columns of this imaginary tableau are duplicates of the rows. Keys, if considered, would repeat the first column of such a tableau. This tableau, as mentioned, is imaginary. Should the encipherer or the decipherer actually desire to make use of a tableau in preference to the slide, he would probably prefer one in which both his plaintext alphabet and his key alphabet are running in normal order, so that letters are easier to find. To form this tableau, he would begin by laying out, in normal order, his plaintext alphabet and his key-alphabet, and then lay out his 26 cipher alphabets in the manner explained in connection with the Beaufort alphabets. Each of the four slides of the figure is accompanied by a partial tableau of this kind, and it will be noticed there that we have only one case in which the (secondary) cipher alphabets bear any resemblance to the primary one. This tableau, too, should be well understood, since the cipher alphabets recovered from cryptograms will be like those of the figure.
Of our four slides, only the Type I is radically different from the rest. Since its basic cipher alphabet is not a mixed one, it makes little difference what has been done to its plaintext alphabet. Notice, in the partial tableau which accompanies it, that the difference between one cipher alphabet and another is purely a matter of alphabetical shift (or of “size,” if we wish to replace all of these letters with numbers). Properly speaking, this cipher belongs to the case of the [preceding chapter]; it is presented here largely as a warning of what could happen through misuse of the Type I slide. In the remaining three cases, the sliding alphabet is a mixed one; a series of frequency counts taken from cryptograms cannot be “lined up” unless letters can be placed in the right order before these frequency counts are taken. The “right” order may be the original one of the cipher alphabet, or an equivalent order in which the original letters are taken at a constant interval. In these cases, as with any other periodic cipher, the period is found in the usual way. Individual frequency counts are then taken on the several cipher alphabets, and these are examined in the hope of finding a known alphabetical graph; that is, the graph of some mixed alphabet recovered from previous decryptments — (but notice also the C-alphabet under the Type III slide!). It can also be ascertained whether or not the frequency counts have followed one common graph, whether any two or more have followed one graph, and so on. But when it is found that the frequency counts are those of unknown mixed alphabets, then each alphabet is to be treated by simple substitution methods. Here, the principles will still be those of [Chapter IX], and we will examine, as briefly as possible, the mechanical phases of their application.
Our cryptogram, shown in Fig. 139, is already written into its correct period, 5, with a few substitutions already made, and a few letters noted as vowels or consonants (v-c). With the period determined as 5, and alphabets found to be in an unknown mixed order, our next step is the preparation of a contact sheet (contact chart, contact count) for each one of the five alphabets, the usual form being that shown in Fig. 140. The necessary number of sheets is prepared in advance by writing the normal alphabet through the center, and each is numbered to show what alphabet it represents. It may also carry the numbers of the two contacting alphabets (those in parentheses in the figure). Then, if the cryptogram is properly grouped, so that all first letters of groups belong to alphabet 1, all second letters to alphabet 2, and so on, the putting down of contact letters is very rapid.
Illustrating with alphabet 2: Start with its first letter, V; find V in the prepared alphabet numbered 2; place on its left side the Y of alphabet 1; place on its right side the N of alphabet 3. Pass on to the next letter, E: contacts are Y-G. Pass on to the third letter, another E: contacts are Z-A. And so on to the end of alphabet 2. Each contact chart, of course, will serve also as a frequency count and as a
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