300 CRYPTOGRAPHS AND CIPHERS [CH. XIV 



over the line A (which is the second line of the first score) thus 

 leaving only the top and bottom of the piece of paper visible, 

 it will be found to read Conceal yourself, your foes look for you. 

 I have seen what purports to be the original, but of the truth 

 of the anecdote I know nothing, and the desirability of con- 

 cealing himself must have been so patent that it was hardly 

 necessary to communicate it by a cryptograph. 



Ciphers. I proceed next to some of the more common types 

 of ciphers. It is immaterial whether we employ special char- 

 acters to denote the various letters; or whether we use the 

 letters in a non-natural sense, such as the letter z for a, the 

 letter y for b, and so on. In the former case it is desirable to 

 use symbols, for instance, musical notes, which are not likely to 

 attract special notice. Geometrical figures have also been used 

 for the same purpose. It is not even necessary to employ 

 written signs. Natural objects have often been used, as in a 

 necklace of beads, or a bouquet of flowers, where the different 

 shaped or coloured beads or different flowers stand for different 

 letters or words. An even more subtle form of disguising the 

 cipher is to make the different distances between consecutive 

 knots or beads indicate the different letters. Of all such 

 systems we may say that a careful scrutiny shows that different 

 symbols are being used, and as soon as the various symbols are 

 distinguished one from the other no additional complication 

 is introduced, while for practical purposes they give more 

 trouble to the sender and the recipient than those written 

 in symbols in current use. Accordingly I confine myself 

 to ciphers written by the use of the current letters and 

 numerals. There are four types of ciphers. 



First Type of Ciphers. Simple Substitution Alphabets. A 

 cipher of the first type is one in which the same letter or word 

 is always represented by the same symbol, and this symbol 

 always represents the same letter or word. 



Perhaps the simplest illustration of a cipher of this type 

 is to employ one language, written as far as practical in the 

 alphabet of another language. It is said that during the 

 Indian Mutiny messages in English, but written in Greek 



