308 



CRYPTOGBAPHS AND CIPHERS 



[OH. XIV 



enciphered and decoded by non-experts: the St Cyr code fulfils 

 this requirement. 



The St Cyr scheme is essentially the same as Gronfeld's. 

 For instance, in the St Cyr system the key word gibe leads to 

 the same result as the key number 6814 by Gronfeld's method. 

 One advantage of the St Cyr system over that advocated by 

 Gronfeld is that key words are more easily recollected than key 

 numbers. Another advantage comes from the fact that the 

 employment of words is equivalent to using 26 digits instead of 

 10 : thus the key word kings is equivalent to a number whose 

 digits, from left to right, are 11, 9, 14, 7, 19. Messages in this 

 cipher of any considerable length can be read by the same 

 rules as are used to discover the key in Gronfeld's code. 

 To hamper a decipherer I recommend the introduction, as 

 in Gronfeld's method, of a non-significant letter after every 

 with letter. 



The Beaufort Cipher, introduced in the British Navy by 

 Admiral Beaufort in 1857, is of the St Cyr type. Its inventor 

 thought it insoluble, but French writers have shown that no 

 special difficulties occur in the discovery of the key word in the 

 solution, though the analysis is tedious. 



A better system of this kind is the Play/air Cipher. In 

 this 25 cells arranged in the form of a square are filled by the 

 letters of a key word such as Manchester (striking out any 



