, and welcome again.

This time we will discuss a story and a cipher. Firstly, the cipher.

This cipher is called Book Cipher, because the 'key' in this case is a book. (Actually, some aspect of book)

Few ways in which the encryption is done using a book cipher are as follows:

each word in plaintext, replaced by a word-number from the book.
each letter in plaintext, replaced by a letter/word-number.
each word in plaintext, replaced by a page number!

Famous keys are usually the famous or widely available publications like: bible! dictionary! american constitution! etc.

EXAMPLE:
The ciphertext: 1,2,3,6 will correspond to the plaintext: WITH; if the key is a document/book beginning with the text given below:
"When in the course of human events, ..."
Actually, the numbers 1,2,3,6 correspond to different words in the text; and on picking the first letters of those words, one gets the plaintext back. For reference:

When(1) in(2) the(3) course(4) of(5) human(6) events(7) ... 

Book ciphers are very popular in the general media, and can be seen in many novels, short stories and movies - from Sherlock Holmes' Valley of Fears to films like National Treasure. But the real cases, real stories associated with book ciphers have fascinated people more.

While even today, the book ciphers are easily found deployed in the mystery challenge of Cicada 3301, an anonymous Internet Cryptography contest held every year; a more famous story is of the "Beale Cipher".

The story originate from a pamphlet published in 1885 called "The Beale Papers". It contained three ciphertexts, one of which, when decrypted, stated the location of a buried treasure of gold, silver and jewels worth over 50 million US$. According to the story associated, these ciphers were handed to an innkeeper by a person known as "Thomas Cipher", who had hidden in it the details and location of the treasure in these ciphers. The innkeeper himself was unable to decrypt any of the three ciphers, and on his deathbed, handed them to his reliable friend, who himself, took years to decrypt only the second of the cipher (using "Declaration of Independence" as the 'key' document - see the 'demo'). The rest of the two ciphers remain unbroken till date!

Since their publishing the ciphers have attracted huge attention - some tried to break them but failed, some even claimed it a hoax - nonetheless, the concept of book cipher indeed became immortal in the memories of time.

Next we will discuss how a message can be 'concealed' within another message, also called, 'Steganography'.
Bye till then.
:-)

Post-8 Ended.