SOLVING CIPHER SECRETS Edited by M. E. Ghaver FOR THE FIRST TIME HERE, THE SOLUTION OF A NUMBER OF CRYPTO• GRAMS IS EXPLAINED-ALSO A TIP ABOUT THE RADIO CONTEST CIPHER FTENTIMES a cryptogram In this article for the first time we will may be so short that—de• actually consider the solution of a number pending, of course, on the of cryptograms. The cipher selected for relative complexity of the this purpose is one of the numerous variants cipher — its solution be• of the famous Vigenere alphabetic square, comes a difficult matter, being that given by John Wilkins—after• if not altogether an impossibility. ward Bishop of Chester—on pages 72 to 76, In such cases decipherment can often be inclusive, of his " Mercury, or the Secret materially simplified if a number of cryp• and Swift Messenger," an early work on tograms in the same key are available. cryptography published in London in 1641, With one exception, noted below, all the This form of the cipher uses the same methods so far discussed in this department type of alphabet as its famous original, and have depended upon the analysis of a sin• is identical in its results, but holds one ad• gle cryptogram. vantage, at least, over it, in that instead of In some instances single cryptogram requiring a ready-made table of the whole methods may be used with a number of number of alphabets, it employs a special messages, the added effectiveness being due table, formed of just those alphabets se• to the increased bulk of material. On the lected by the key word. other hand, some of these multiple message For example, if the key word TRY be methods are peculiarly adapted to a number agreed upon, the table will consist of three of cryptograms, not being applicable to the alphabets, one beginning with each letter of resolution of a single example. the key. The alphabets used by Wilkins A certain insight into multiple crypto• consist of but twenty-four letters, / and V gram methods has already been afforded being omitted. For in the English alphabet readers of FLYNN'S WEEKLY in the issue of of that time the letters / and / were used July 3, where a method was given applicable interchangeably, as were also U and V. to the solution of a number of transposition Here, however, the full twenty-six letter cryptograms in the same key. alphabet is employed. (Message alphabet) A B C D E F G 11 I J K L M N 0 F Q R S T U V W X Y Z T TUVWXYZABCDEFGHI JKLMNOPQRS R RSTUVWXYZABCDEFGHI J KLMNOPQ Y YZABCDEFGHIJKLMNOPQRSTUVWX (Cipher alphabets) 794 SOLVING CIPHER SECRETS 795 Now, to encipher any message, as the quired—after each cipher letter, taking care short example given at (b), write a letter to preserve the columnar arrangement, the of the key above each letter of the message, cryptogram itself constituting the first col• taking both in their order, and repeating umn. The letters forming any word of the key as the length of the message may the message will then appear in a single col• require, as shown at (a): umn, under the key letter by which it was enciphered. (a) Key: TRYT RY TR YTRY (Key) (b) Message; MEET ME AT ONCE (c) Cipher: FVCM DC TK MGTC Z YXWVUT SRQ P... (d) Regrouped: FVCMD CTKMG TC F GHl J KLMNOPQ... X Y Z .4 B C D /; F G H I . The key letter above each text letter ,iow X VZABCDA; FGHI... M NOPQRSr UVWX... indicates the alphabet in which it is to be D EFGHIJK LA/. .. enciphered. For example, the first letter of VWXYZABCDA'. .. Y Z B C D E . the message, M, is to be enciphered in the R S V U V W X . , . HIJKLMNOP... T alphabet, its substitute in that alphabet G n I j K L M .V O . being F, which is accordingly placed below VWXYZABCD. X YZABCD£'F . , . M in line (c). Similarly, the second letter, E, of the Of course, if a whole line of the crypto message becomes V in the R alphabet. The gram is enciphered in the same alphabet, third letter, also an E, becomes C in the or if normal word divisions are observed, y alphabet; and so on. The cryptogram decipherment by the above method is still for MEET ME AT ONCE, with the key easier. TRY, is thus FVCM DC TK MGTC, as Now that the reader is acquainted with shown at (c). the system, it is well to produce the cryp• As described by Wilkins, the normal word tograms he is expected to decipher. To in• divisions are observed in the cryptogram. crease the interest, these cryptograms have In the present day, however, the customary been made the captured correspondence of procedure would be to regroup the letters, a supposed hand of kidnapers. preferably by fives, as shown at (d). In these cryptograms, the key letter has In passing, it must be mentioned that been changed with each text letter; also, ex• Wilkins also suggests the use of mixed cepting that a twenty-six letter alphabet alphabets in this cipher instead of the has been used, and normal word divisions straight A-to-Z arrangement, and the have not been ohsdrved, the cipher is other• change of key letter with each word or line wise exactly like that described by Wilkins. instead of with each letter. The resolution Here ape our cryptograms, six of them, of mixed alphabets will he taken up later. numbered for reference. /J 20 -y so ss (1) JOPTE CGENS NTFDF PPGZD THBTM WXCCD JXPU. (2) OSYIV CHXIV NUQFZ XPOFP TFUCI SGTPH M. (3) LOETS MUTYE KHGII VVKTFN GPNLW. (4) YSBPX SNPMS HQQMN DVVYR QIHIU OJPTH GTPH. (•;) CLEGG DVSVK MHRUY FAICI PJIKl ELNKM KVVW. (6) TVYJJ SAHVV AZRVE VFTFT -SFRRR KVM. But both the other devices could easily he Now, since this is supposed to be a series solved by " running down the alphabet." of cryptograms in unknown cipher, it can• Suppose, for example, that the key letter not be assumed that they are in the same he changed with each word, thus: key. Possibly a number of different ciphers have been employed. Again they may be (a) Key: TTTT RR YY TTTT in the same system, hut with different keys. (b) Message : MEET ME AT ONCE (c) Cipher: FXXM DV YR HGVX Consequently, before any two or more of (d) Regrouped: FXXMD VYRHG VX the above cryptograms can he combined • To solve this, it is only necessary to write for solution, it is necessary to know that the alphabet—all twenty-six letters if re• they are in identical ciphers. 796 FLYNN'S WEEKLY If the reader desires he can try each gram. Thus, the group PT occurs at the cryptogram individually by the transposi• third letter of cryptogram No. i; at the tion test given in the September 4 issue of twentieth letter of No. 2; and at the twenty^ FLYNN'S WEEKLY. These tests will elimi• eighth letter of No. 4. The reader may nate the transposition cipher, and allow us easily check them. to consider the possibility of substitution Were there enough recurrent groups in ciphers. each cryptogram, they could he tested by In this latter class, the substitutes may the Kasiski method in the usual manner, consist of one, two, three, or more charac• See FLYNN'S WEEKLY for August 7, 1926. ters. The present cryptograms consist of Here all such groups happen to he acci• 34, 31, 25, 34, 35, and 28 letters, respec• dentals, which are of no value by the above tively. Some of these numbers are not method. evenly divisible by 2, 3, 4 . and con• The Kasiski principle, however, is not sequently we can assume—unless substi• limited in its application merely to a single tutes of mixed lengths have been used— cryptogram. It can be used just as well that at least some of the cryptograms are with any number of cryptograms, the re• of the straight letter-for-letter substitution current groups of which can be treated ex• type. actly as if they occurred in a single speci• Messages enciphered in the same key will men. To illustrate this, suppose that we often have similar predominating characters examine the groups found in both No. i or groups of characters. For instance, that and No. 2. cyptograms Nos. 5 and 6 both contain a Groups (2) Intervals large number of V's might be pointed out (il Factors PT 20 as significant. 3 17 17 TF 12 21 9 3-9 Predominant groups, however, will re• FP IS 19 4 2-4 ceive the bulk of attention here. And to XP 32 16 16 2-4-8-16 save our readers a few hours of merely rou• tine work, a complete table of all the re• It will he seen that the intervals current groups in all six of the present cryp• figured here exactly as if the recurrent tograms is herewith appended. groups occurred at their respective numeri• cal places in one and the same cryptogram, (1) (2) (3) (4) (s) (6)_ PT 20 28 — instead of two. The largest predominating 3 — — SN 10 — — 6 — — factor is 4, which suggests a fixed period TF 12 21 18 — — 18 cipher using four alphabets. By this sup• FP IS 19 — — — position PT and TF become accidental re• TH 21 — — — 29 current groups. At least, we may progress XP —16 — — — — with that assumption. IV — 4-9 — — — — CI — 24 — — 19 — The supposed natural or periodic groups, GTPH — 27 — 31 — — FP and XP, however, might have resulted HG 12 30 — from using different keys of the same length, DV — — 16 —6 — — but with certain characters ~ in common.