16. What was the algorithm allegedly used by Ensei Tankado in the Digital Fortress encryption program?
From Quiz Dan Brown - "Digital Fortress"
Answer:
Rotating cleartext function
From the book:
"The notion of a rotating cleartext function was first put forth in an obscure, 1987 paper by a Hungarian mathematician, Josef Harne. Because brute-force computers broke codes by examining cleartext for identifiable word patterns, Harne proposed an encryption algorithm that, in addition to encrypting, shifted decrypted cleartext over a time variant. In theory, the perpetual mutation would ensure that the attacking computer would never locate recognisable word patterns and thus never know when it had found the proper key. The concept was somewhat like the idea of colonising Mars-fathomable on an intellectual level, but, at present, well beyond human ability."
However, this is not possible. See http://becomingparanoid.com/2006/03/13/digital-fortress-what-dan-brown-got-wrong/ for more information. PS: I'm a Mathematics graduate so I sort of understand these things.