Book Cipher

A homophonic substitution cipher that maps each symbol in the plaintext to one or more numbers. This is done by taking a sample of text, numbering each word in the text, and mapping the first letter of each word to its corresponding number. A given plaintext symbol is then enciphered by randomly substituting it with one of its candidate numbers. A sufficiently large sample text should be chosen so that every symbol of the plaintext appears at the start of a word. Otherwise, it will be enciphered as-is.