Basic Information
A Book code is a cypher that uses a specific, published book as its key. Messages are cyphered by finding the desired word in the key book and then converting that word into a numerical format (for example page/line/word) and then sending that number. The recipient, knowing the format of the cypher, receives the number and finds the relevant word.
This method, whilst slow and, until very recently, completely manual has the advantage that both ends can openly possess and transport the key without much scrutiny (unless the book itself is controversial) and unless one end is caught with a partially encrypted or decrypted message sticking out of the book it can be very difficult to identify which book in a collection is the key. Indeed it may be possible to use several books and identify which one is to serve as key by the start or end of the message. Users also need to be careful that they both have the same edition of the book - different printings may change page and line numbers radically. This may be rectified by using a book with known versification (The Bible is probably the most widely known example of such a book) where giving chapter, verse and word will work.
Sources
Game and Story Use
- Ideal characterisation for scholarly types, some of whom may have the key book by memory - and especially between mentor and apprentice, using a signed copy of the book given as a gift.
- Even a broken book code may be tripped up by the edition thing - for example, the KGB learns that a US agent is using a Bible Code and duly apply the chapter and verse settings to their intercepts. Unfortunately the Americans are using a King James translation and the Soviets an English translation of the Russian Synodal Bible … even when decyphered, the results are… less than clear…
- Likewise, an over confident AI cracking system which gets hold of the wrong book and turns out coincidentally coherent messages that have nothing to do with the original content.
- Ironcially, the use of book code cyphers might be behind rumours of secrets encoded in The Bible and similar famous books.