Random Numbers

Abstract

The discussion on pages 67 and 88 makes it clear that the use of random keys can lead to encryption with absolute security. When a long, random key is used, the Vigenère method (and also other polyalphabetic ciphers) produces ciphertext with a uniform distribution of letters. The only way to decipher such ciphertext, even if the encryption method is known, is to try all possible keys. This, however, is impractical even with the help of a fast computer. Even if a very fast computer can generate the plaintexts for all the possible keys in a reasonable amount of time, a person would still have to go over each plaintext to see whether it makes sense. The computer may be programmed to check each plaintext as it is being generated and reject it if it looks random or if it consists mostly of phrases that are not in the dictionary. Such an automatic check, however, would still leave too many plaintexts for a human to examine.