SOLVING CIPHER SECRETS E d i t e d by M . E . G h a v e r

PRESENTING T H E " M I X E D " DIGRAPH T E S T FOR SOLVING A TRANSPOSITION CIPHER—AND SOLUTIONS TO No. 70 AND T H E BOOKKEEPING CIPHER OF SEPT. 17

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.

T V Y I E T R R O R E H N I A E U D S R l E O N I O R E N A E E O R P T E A L O L T S U H L H Q N O U C A D D C S A A E T D V F U G N N Y C Y I

T h e 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 i n the J u l y 3 , 1926, is­sue. So another method wi l l be presented here, the " mixed " digraph test, based on the fact that the consonant-vowel—CV— and vowel-consonant—VC—digraphs, to­gether, average about sixty-five per cent of all digraphs i n straight Engl ish text. (Note: B y the J a n u a r y 23, 1926, table of ten thousand digraphs, V V = 5 . s % ; C C = 2 9 . 4 % ; C V = 3 2 4 % ; V C = 3 2 . 7 % ; total, 1 0 0 % . )

T h e " 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. F o r example, it points unerringly

to the correct Q U combination in the pres­ent case, as shown below, where series of letters containing Q and V have been matched to bring the QU's together. These test sequences, here consisting of seven let­ters, may be made of anj^ length.

H I CV H L H Q H D L A CV L T L N L V H E CV H S H O CV H E

*ou * Q U * Q U * Q U N D N H N C N G O S V C O L V C O A O N V C U R V C U H V C U D V C U N V C

S 2 2 2

T a k i n g the first of these combinations as most probable, since i t gives a larger and more nearly normal C V - V C count than any of the others, the next step is to find the i n ­terval between the two series of letters H L H . . . and l A E . . .

A n y 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. F o r 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 sim­i lar ly matching other series of letters. B u t they are unnecessary i n this case, as subse­quent articles of the series w i l l show. H o w to use the interval, 3 1 , in the further elim­ination of key lengths wi l l be explained next week.

L a s t week's simple substitution cipher

640 F L Y N N ' S W E E K L Y D E T E C T I V E F I C T I O N

N o . 74 conveyed the message: " J i m : T e l l the boys to meet me at the foot of Canal Street to-morrow night. No one is wise to our plans. B i l l . " T h i s cryptogram should have readily yielded b y taking E I D as the, and then by substituting through such groups as F Y — t o , C Y Y C D — w o owe, E D A A — t e l l , and so on.

Cipher N o . 75 used the subjoined sim­ple adaption of the athbash alphabet—iee September 3 issue. A n interesting method of varying this alphabet by means of key words was illustrated last week i n 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 ( M y e r S t i n e ) , 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. T h e message: " Simplicity is a ready mask for artifice." M r . Stine, you may remem­ber, wanted to test the " seaworthiness " of his " craft ." D i d vou sink it?

A B C D E F G H

I J

K L M

13-31 z 12.21 Y I I . u X 10.01 W g.90 V 8.80 u 7.70 T 6.60 S S-So R 4.40 Q 3.30 P 2.20 O 1.10 N

Store, No. i

.?o.6o S-oo 1.30 2.00 S-oo

11.00 5-70

.21

S30.81

- S I -

M P L -I -C -I T - Y

No. 70 (Charles P . W i n s o r ) , also pub­lished i n the September 17 issue, used the key word L E X I N G T O N in conveying the message: " Transposition ciphers have not received their fair share of the attention of cryptographers." T h e set-up was as follows:

L E X I N G T O N 4 1 9 J 5 2: 8 7 6

H A N S I O N C

O S I P H E

H A V E N O T C E I

I R F A I R E O F T H

A T T E N T

E D T S E

I O N O F C R Y P T O G R A P H E R S

T h e number of letters in this cryptogram, 79, balked elimination of key lengths b y factoring. B u t the cryptogram is not proof against other methods of attack being out­lined in the current series of articles on this type of cipher. L a s t week's suggestion that the word C I P H E R was in the message should have given you a big l i ft .

I n submitting No. 77, this week's s im­ple substitution cipher, M r . Dockhan sug­gests that we have some funny messages for a change. T h i s is a good idea. Decipher M r . Dockham's example, have a good laugh, and fix up a funny one yourself. There is something i n this world besides being altogether serious.

No. 78 is another transposition cipher of the same type as No. 70. A n d finally, No. 79 employs the Vigenere square, or equivalent apparatus, but without a k e y word, the key letters being scattered throughout the message and enciphered with the text. T r y " running down the alphabet " on this cipher. (See November 13, 1926, issue.) A n d then try to fathom M r . Cooke's method of handling his k e y letters.

C I P H E R No. 77 ( J . A . Dockham, Oakland. Cal i f . ) .

U G U G Y U Z I G A T O S U G S U G Z O K O S U G Y U G G I E G P O S U K K A W U D I X U G O V Y K U B U A K I X U G Y A R E O B U G Y N U G S U G U D D I J U G P O I X Y U A G Y O S P U G S H P U G N Y I Y M O W A D D U Z O S E L B M O U B .

C I P H E R No. 78.

O T E N S L I N R T A D O W A A Y T I E T T H A B E

H I E N U C D E M M

C S D A E V T T A S

C I P H E R No. 79 ( W . A . Cooke, Montreal, Quebec, Canada).

H A O G W T Q G P O Z S X V S U J M G G X G B S H O E J X P D R E C N M V Z B W N B P H N J G T I E Y F A S I T Z J Q F Q S P C D

L E T K K F H E T F S H F N T D H N U E

Ciphers Nos. 77 and 78 wi l l be fully ex­plained next week, and No. 79 in three weeks. T r y to solve them, and send in your solutions. W e 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.

10 F W