CH. XIV] CRYPTOGRAPHS AND CIPHERS 293 



only to those possessing the key: the word is also sometimes 

 used to denote the communication made. A simple example 

 is a communication in which every word is spelt backwards. 

 Thus : 



ymene deveileb ot eb gniriter troper noitisop no ssorc daor. 



A cipher may be denned as a manner of writing by characters 

 arbitrarily invented or by an arbitrary use of letters, words, or 

 characters in other than their ordinary sense, intelligible only 

 to those possessing the key: the word is also sometimes used 

 to denote the communication made. A simple example is when 

 each letter is replaced by the one that immediately follows it in 

 the natural order of the alphabet, a being replaced by b, b by c, 

 and so on, and finally z by a. In this cipher the above message 

 would read: 



fofnz cfmjfwfe up cf sfujsjoh sfqpsu qptjujpo po dsptt spbe. 



In both cryptographs and ciphers the essential feature is 

 that the communication may be freely given to all the world 

 though it is unintelligible save to those who possess the key. 

 The key must not be accessible to anyone, and if possible it 

 should be known only to those using the cryptograph or 

 cipher. The art of constructing a cryptograph lies in the 

 concealment of the proper order of the essential letters or 

 words : the art of constructing a cipher lies in concealing what 

 letters or words are represented by the symbols used. 



In an actual communication cipher symbols may be arranged 

 cryptographically, and thus further hinder a reading of the 

 message. Thus the message given above might be put in a 

 cryptographic cipher as 



znfof efwfjmfc pufc hojsjufs uspqfs opjujtpq op ttpsd ebps. 



If the message were written in a foreign language it would 

 further diminish the chance of it being read by a stranger 

 through whose hands it passed. But I may confine myself to 

 messages in English, and for the present to simple cryptographs 

 and ciphers. 



A communication in cryptograph or cipher must be in 



