IN last week's installment on solving the type of transposition cipher described in the issues of September 17 and 24, certain key lengths in cipher No. 73—reprinted below—were eliminated by factoring; and certain letter combinations were mentioned as probably occurring in the message.
TVYIE TRROR EHNIA EUDSR lEONI ORENA EEORP TEALO LTSUH LHQNO UCADD CSAAE TDVFU GNNYC YI
The probability of these or other combinations may be tested by examining the digraphs formed by juxtaposing various letter sequences of the cryptogram.
A method for determining this relative "compatability" by digraph frequency has already been given in the July 3, 1926, issue. So another method will be presented here, the "mixed" digraph test, based on the fact that the consonant-vowel—CV— a nd vowel-consonant—VC—digraphs, together, average about sixty-five per cent of all digraphs in straight English text. (Note: By the January 23, 1926, table of ten thousand digraphs, VV=5.s%; CC =29.4%; CV=324%; VC=32.7%; total, 100%.)
The "mixed" test is much more rapid than the "frequency" test, although probably not so accurate. Nevertheless, it is a valuable adjunct to the latter, and is also quite worthy of being used on its own merits. For example, it points unerringly to the correct QU combination in the present case, as shown below, where series of letters containing Q and U have been matched to bring the QU's together. These test sequences, here consisting of seven letters, may be made of any length.
HI cv HL HQ HD LA cv LT LN LV HE cv HS HO cv HE *QU *QU *QU *QU ND NH NC NG OS vc OL vc OA ON vc UR vc UH vc UD vc UN vc —————— —————— —————— —————— 5 2 2 2
Taking the first of these combinations as most probable, since it gives a larger and more nearly normal CV-VC count than any of the others, the next step is to find the interval between the two series of letters HLH . . . and IAE . . .
Any digraph in the column may be selected for this purpose; and in counting the interval, it does not matter which letter of the digraph comes first in the cryptogram. For example, Q is the forty-eighth letter of this cryptogram, and the above U is the seventeenth, giving an interval of thirty-one letters.
Other intervals could be found by similarly matching other series of letters. But they are unnecessary in this case, as subsequent articles of the series will show. How to use the interval, 31, in the further elimination of key lengths will be explained next week.
Last week's simple substitution cipher No. 74 conveyed the message: "Jim: Tell the boys to meet me at the foot of Canal Street to-morrow night. No one is wise to our plans. Bill. "This cryptogram should have readily yielded by taking EID as the, and then by substituting through such groups as FY—to, CY YCD—no one, EDAA—tell, and so on.
Cipher No. 75 used the subjoined simple adaption of the athbash alphabet—see September 3 issue. An interesting method of varying this alphabet by means of key words was illustrated last week in the explanation of cipher No. 71.
A B C D E F G H I J K L M Z Y X W V U T S R Q P O N
No. 69 (Myer Stine), the "bookkeeping cipher," published three weeks ago, used an alphabet of dollars and cents. Application of the system is illustrated by the accompanying decipherment of the first column. The message: "Simplicity is a ready mask for artifice." Mr. Stine, you may remember, wanted to test the "seaworthiness" of his "craft." Did vou sink it?
A 13.31 Z Store No. 1 B 12.21 Y C 11.11 X $0.60 —S D 10.01 W 5.00 I— E 9.90 V 1.30 MP F 8.80 U 2.00 L— G 7.70 T 5.00 I— H 6.60 S 11.00 C— I 5.50 R 5.70 IT J 4.40 Q .21 —Y K 3.30 P —————— L 2.20 O $30.81 M 1.10 N
No. 70 (Charles P. Winsor), also published in the September 17 issue, used the key word LEXINGTON in conveying the message: "Transposition ciphers have not received their fair share of the attention of cryptographers." The set-up was as follows:
L E X I N G T O N 4 1 9 3 5 2 8 7 6 T R A N S P O S I T I O N C I P H E R S H A V E N O T R E C E I V E D T H E I R F A I R S H A R E O F T H E A T T E N T I O N O F C R Y P T O G R A P H E R S
The number of letters in this cryptogram, 79, balked elimination of key lengths by factoring. But the cryptogram is not proof against other methods of attack being outlined in the current series of articles on this type of cipher. Last week's suggestion that the word CIPHER was in the message should have given you a big lift.
In submitting No. 77, this week's simple substitution cipher, Mr. Dockhan suggests that we have some funny messages for a change. This is a good idea. Decipher Mr. Dockham's example, have a good laugh, and fix up a funny one yourself. There is something in this world besides being altogether serious.
No. 78 is another transposition cipher of the same type as No. 70. And finally, No. 79 employs the Vigenère square, or equivalent apparatus, but without a key word, the key letters being scattered throughout the message and enciphered with the text. Try "running down the alphabet" on this cipher. (See November 13, 1926, issue.) And then try to fathom Mr. Cooke's method of handling his key letters.
CIPHER No. 77 (J. A. Dockham, Oakland. Calif.).
UG UGYUZIGATOS UGS UGZOKOS UGY UGGIEGPOS UKKAWUD IX UG OVYKU BUAK IX UGYAREO BUGYN UGS UG UDDIJUGPO IX YUAGYOS PUGSH PUGN YI YMO WADDUZO SELB MOUB.
CIPHER No. 78.
OTENS LINRT ADOWA AYTIE TTHA BE HIENU CDEMM CSDAE VTTAS
CIPHER No. 79 (W. A. Cooke, Montreal, Quebec, Canada).
HAOGW TQGPO ZSXVS UJMGG XGBSH OEJXP DRECN MVZBW NBPHN JGTIE YFASI TZJQF QSPCD LETKK FHETF SHFNT DHNUE
Ciphers Nos. 77 and 78 will be fully explained next week, and No. 79 in three weeks. Try to solve them, and send in your solutions. We would like to see more answers to the more difficult ciphers pouring in..A,re you finding them too hard?
Don't forget, fans, to include translations and explanations with ciphers submitted for publication.