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A book cipher is a cipher in which the key is some aspect of a book or other piece of text; books being common and widely available in modern times, users of book ciphers take the position that the details of the key is sufficiently well hidden from attackers in practice. This is in some ways an example of security by obscurity. It is typically essential that both correspondents not only have the same book, but the same edition.
Traditionally book ciphers work by replacing words in the plaintext of a message with the location of words from the book being used. In this mode, book ciphers are more properly called codes.
For the book Cipher to work, all parties must know how to read and interpret the code.
A simple way to do this is to exchange numbers for the words to encode. Numbers will represent (PAGE - PARAGRAPH - LINE - and NUMBER OF WORDS IN THE LINE)
Example:
You wish to code the words (meet and Rally Point A tonight 8PM)
You find each of the words in your book and assign the numbers that pin point each word. Lets say the word "Meet" is located on page 62, Paragraph 2, Line 3, and it is the 5th word in the line. Your code for that word should be (62,2,3,5).. You will need something to separate this code with the next. anything you wish to use (besides a number) should work. Letters, symbols, spaces, ...
The process of encryption does take a while. Decrypting takes less time... If you wish to try a challenge. I have encrypted a short message using the Field Manual "INFANTRY RIFLE PLATOON AND SQUAD"
FM 7-8 NO. 7-8
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, DC, 22 April 1992
This FM is downloadable from many sites or email me and I will send you the .zip version of it. If you are up for the challenge, take a look at the next image. I have broken down the paragraphs more like sections. As you can see, some are not even paragraphs, but for this exercise, will be treated as such:
So, you have a page number, paragraph, line number and word placement in the line.
Here is the code:
40,3,3,7 - 40,1,4,6 - 154,5,1,10 - 154,5,3,5 - 186,10,4,1 - 186,10,4,2 - 186,10,4,4 - 194,6,1,11 - 55,10,5,1 - 55,8,3,11 - 80,1,2,6 - 102,4,9,3
There are other ways to add difficulty to this type of encryption. By simply using an obscure book, you add great difficulty to a cryptographers job...
If you decide to take on this challange, PM me the results. I will list the names of folks who got it right and assist those who need help.
This can also be a cool way to practice secure communications by radio. It may be that the very early "Numbers Stations" were book ciphers.... http://en.wikipedia.org/wiki/Numbers_station
Traditionally book ciphers work by replacing words in the plaintext of a message with the location of words from the book being used. In this mode, book ciphers are more properly called codes.
For the book Cipher to work, all parties must know how to read and interpret the code.
A simple way to do this is to exchange numbers for the words to encode. Numbers will represent (PAGE - PARAGRAPH - LINE - and NUMBER OF WORDS IN THE LINE)
Example:
You wish to code the words (meet and Rally Point A tonight 8PM)
You find each of the words in your book and assign the numbers that pin point each word. Lets say the word "Meet" is located on page 62, Paragraph 2, Line 3, and it is the 5th word in the line. Your code for that word should be (62,2,3,5).. You will need something to separate this code with the next. anything you wish to use (besides a number) should work. Letters, symbols, spaces, ...
The process of encryption does take a while. Decrypting takes less time... If you wish to try a challenge. I have encrypted a short message using the Field Manual "INFANTRY RIFLE PLATOON AND SQUAD"
FM 7-8 NO. 7-8
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, DC, 22 April 1992
This FM is downloadable from many sites or email me and I will send you the .zip version of it. If you are up for the challenge, take a look at the next image. I have broken down the paragraphs more like sections. As you can see, some are not even paragraphs, but for this exercise, will be treated as such:
So, you have a page number, paragraph, line number and word placement in the line.
Here is the code:
40,3,3,7 - 40,1,4,6 - 154,5,1,10 - 154,5,3,5 - 186,10,4,1 - 186,10,4,2 - 186,10,4,4 - 194,6,1,11 - 55,10,5,1 - 55,8,3,11 - 80,1,2,6 - 102,4,9,3
There are other ways to add difficulty to this type of encryption. By simply using an obscure book, you add great difficulty to a cryptographers job...
If you decide to take on this challange, PM me the results. I will list the names of folks who got it right and assist those who need help.
This can also be a cool way to practice secure communications by radio. It may be that the very early "Numbers Stations" were book ciphers.... http://en.wikipedia.org/wiki/Numbers_station
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