Those who follow some of my other projects know that I'm a nut for treasure hunts. More the making of them then the doing of them. This is one of the many tools that I use to put together a treasure hunt.
What is a book cypher? Also called an Ottendorf cypher, the book cypher is a series of numbers that are used with a known piece of text to hide a message in plain sight. This works really well if two people have the same book and the series of numbers are sent back and fourth to each other.
The simplest version is a single piece of text like say an article in the news paper or a bronze monument with a bit of text. Three numbers are used to indicate a single letter. The first number is the line of the text from top to bottom. The second number is the word in that line of text and lastly the final number is the letter in that word.
In some of my treasure hunts I need to point the participants to a certain book and page. This happens when the page of text that I have chosen doesn't contain the letters that I need or I want to be extra evil and complex and have the code spread over more than one page of text. Enter the Dewy decimal system. For those of us who had library science in school, the Dewey Decimal System is a way that the library numbers books for rapid location. These numbers are usually labeled right on the spine of a book in a library. I use these numbers to identify a book inside a library that the participants need to locate to decipher the code. Another way to identify a book if you are creating a treasure hunt for another location is to use the ISBN or International Standard Book Number. This number identifies a specific book. If there was an update to the book then it gets a new number. This way if you are in California and your participants are in Florida you can reference that book and know that you are both using the same book.
When I use a book and spread the code over multiple pages I add a fourth number to the code. Page number, then line, then word, then letter in that word.
One of my recent finds is to get a inexpensive book of word searches. Yes those wonderful grids of letter that have all manners of random letters all in a block. They make perfect book cypher material. The best part is if you have a book of them you have no problem getting the letters that you need to code your message. If you want you can tear out an individual page and hide it in a location and have a code based on it.
Lastly the newest way that I have applied the book cypher is to a memorial wall of bricks. Here in our town we have a large veterans memorial that contains hundreds of bricks that have three lines of text on each one. The name of the vet, rank and service, and years of service. Like the multi-page book cypher more numbers are needed to get the letter. Starting from the top left of the wall the first number is the line of the brick from the top down. The second number is the brick in that line. Third number is the line on that brick. Fourth number is the word on that line. and the final number is the letter in that word. A word of caution here. After you have created your code have someone else translate it. I created a large code that somewhere along the line I was off by one brick and it messed the entire code up making me have to give up the answer to move the treasure hunt along. Make very sure you are accurate when creating this code. There are other way that you can combine codes to make this simple code more complex or simple. Know your audience. If you are making with a group of ten year olds in mind, remember that if they don't make some manner of progress in a short time frustration sets in a the fun is sucked out of the entire adventure. If you are making for a high school / collage age (my favorite age range) then you can bring on the evil and make it as complex as you want.
Good luck in your adventure