CH. XIV] CRYPTOGRAPHS AND CIPHERS 303 



is usual to send the cipher in groups of five letters, and, before 

 putting it into cipher, to separate the words in the message by 

 letters like j, q, x, z. 



Ciphers of this type suggest themselves naturally to those 

 approaching the subject for the first time, and are commonly 

 made by merely shifting the letters a certain number of places 

 forward. If this is done we may decrease the risk of detection 

 by altering the amount of shifting at short (and preferably 

 irregular) intervals. Thus it may be agreed that if initially we 

 shift every letter one place forward then whenever we come to 

 the letter (say) n we shall shift every letter one more place 

 forward. In this way the cipher changes continually, and is 

 essentially changed to one of the third class ; but even with 

 this improvement it is probable that an expert would decode a 

 fairly long message without much difficulty. 



We can have ciphers for numerals as well as for letters: 

 such ciphers are common in many shops. Any word or sentence 

 containing ten different letters will answer the purpose. Thus, 

 an old tradesman of my acquaintance used the excellent precept 

 Be just Man — the first letter representing 1, the second 2, 

 and so on. In this cipher the price 10/6 would be marked bn/t. 

 This is an instance of a cipher of the first type. 



Second Type of Ciphers. A cipher of the second type is one 

 in which the same letter or word is, in some or all cases, repre- 

 sented by more than one symbol, and this symbol always repre- 

 sents the same letter or word. Such ciphers were uncommon 

 before the Eenaissance, but the fact that to those who held the 

 key they were not more difficult to write or read than ciphers of 

 the first type, while the key was not so easily discovered, led to 

 their common adoption in the seventeenth century. 



A simple instance of such a cipher is given by the use of 

 numerals to denote the letters of the alphabet. Thus a may 

 be represented by 11 or by 37 or by 63, b by 12 or by 38 or 

 by 64, and so on, and finally z by 36 or by 62 or by 88, while 

 we can use 89 or 90 to signify the end of a word and the 

 numbers 91 to 99 to denote words or sentences which con- 

 stantly occur. Of course in practice no one would employ the 



