CH. XIV] CRYPTOGRAPHS AND CIPHERS 313 



than 100. Accordingly we first try 4, and if that fails try 2. 

 Had no clue of this kind been obtained from the recurrence of 

 a, pair of letters, we should have had to try successively making 

 the key numbers comprise 2, 3, 4, 5, ... digits, but here (and in 

 most messages) a cursory examination suggests the number of 

 digits in the key number. We commence then by assuming 

 provisionally that the key number has 4 digits. Accordingly 

 we must now re-write our message in columns, each of 4 letters 

 giving altogether 4 lines, thus : 



« ■ 9 y j g y p y 



i v a n z b w 

 s u v p s p o 

 v mi v i j i 



If the Gronfeld method was used, the letters in each of these 

 lines were obtained from the corresponding letters in the original 

 message by a simple substitution alphabet. Had the message 

 been long we could probably obtain this alphabet at once by 

 Conrad's Table. Here, however, the message is so short that the 

 Table is not likely to help us decisively, and we must expect 

 to be obliged to try several shifts of the alphabet in each line. 



In the first line y occurs three times, and g twice. Accord- 

 ing to Conrad's Table, the most common letters in English are 

 e, t, a, o, i, n, s, r, h. Probably y stands for one of these and g 

 for another. If y is made to stand successively for each of 

 these, it is equivalent to putting every letter 8 places back- 

 ward, where 6 is successively 20, 5, 24, 10, 16, 11, 6, 7, 17. 

 Similarly, making g stand successively for e, t, a, o, i, n, s, r, h, 

 we have 6 equal to 2, 13, 6, 18, 24, 19, 14, 15, 25. Altogether 

 this gives us 16 systems for the representation of the first line. 

 We might write these out on 16 slips, and provisionally reject any 

 slip in which many unusual letters appear, but obviously, the 

 most probable hypothesis is that where y stands for s, and g 

 for a, both of which changes give 6 = 6, or that where y stands 

 for a, and g for i, both of which changes give = 24: these 

 give for the first line either w, a, s, d, a, s, j, s, or e, i, a, I, 

 i, a, r, a. 



