Editing Running key cipher (section)

== Confusion ==

Because both ciphers classically employed [[novel]]s as part of their key material, many sources confuse the [[book cipher]] and the running key cipher. They are really only very distantly related. The running key cipher is a polyalphabetic substitution, the book cipher is a homophonic substitution. Perhaps the distinction is most clearly made by the fact that a running cipher would work best of all with a book of random numbers, whereas such a book (containing no text) would be useless for a book cipher.