Book Code

Another way to disguise messages is to use specific words in a common book or essay. Individual words can be identified by page, line and word number separated by periods. For example, using this book we have, ( NOTE: Works for printed copy only.)

That is, we find on the fifth page of this book the third line and the tenth word is “earliest.” You should verify this. In our system, we will agree to disregard headings, blank lines, and figures. Here are some more examples to check.

For this secret code, it is important that both the sender and receiver have the exact same book, which is used as the key. Common books for this type of secret code are lasting works like the U.S. Declaration of Independence, a classic novel, or even a textbook or dictionary of the same edition.

Of course, your agreed upon book should contain most of the words in your message. If a word is missing, you can reword your message or create a way to disguise the missing words.

9.7.1 13.2.7 39.4.4 2.9.6

change your book often

This secret code is sometimes referred as the Arnold Cipher as it was used by Benedict Arnold in the American Revolutionary War.

Benedict Arnold

A similar cipher is called a Beale Cipher, where words in a book are numbered in order. The first letter in each numbered word is used to spell out the message.

Mission 15: Decipher the book coded message using this book (printed version) as the key.

12.4.5 42.3.5 2.8.7

Mission 16: Encode the message using the next page (42) as the key.

cryptography is your advantage

The End!
Previous series post: — Vigenère Cipher

Link to Mission Answers
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