Maryllian Cipher

The Maryllian Cipher is a classic code system, also known as "The Maryllian", invented by Michael "Emdash" Maryllian (1841 - 1924) in June 1860.

System Summary

A vector-based code, counting characters from one single center letter which is defined in the header (or prefix) of the code data itself. In this manner, many - but not unlimited - possibilities for one letter substitution exist, making the code more difficult to break.

Code Details

"The Maryllian" at work

Encoding

1. Select a book
2. Select a page
3. Find a letter in or near the middle of the page
4. Determine the exact position of this letter (Page number, paragraph number, line number, letter number (position of the letter in the selected line)
5. write down this position as header
6. Repeat
   1. look on the page for the letter you want to encode
   2. count the distance of this letter to the central letter, in characters, not counting blanks. The resulting number will be prefixed as negative when the letter to encode is to be found before the central letter.
   3. write down this number as cipher number (encoded letter)
7. until all letters of your original text are encoded

During encoding, Maryllian recommends to look for multiple occurrences of the same letter, so that an "e" could be represented in many numbers, preferrably positive and negative, to confuse unauthorized decoders.

Decoding

1. Take the book which was defined as code base
2. Use the header data of the code to find the central letter
3. Repeat
   1. count the distance from the central letter according to the code number, in characters, not counting blanks. The resulting letter will be the deciphered letter. If the code number is negative, go left, otherwise right.
   2. write down this letter as deciphered letter (decoded letter)
4. until all code number of your code text are decoded

Possible Mishaps

What happens during encoding if a letter to encode is not on the page? In this case, Maryllian recommends to take a "similar" letter which will "blend in" depending on the context.

Example

7,3,10,37
15,69,-127,-244,12,168,234,378,-187

Systematic Weaknesses of the code

1. Both parties have to have exactly the same edition of the book
2. The counting of letters is a slow and error-prone method (this weakness vanishes with the use of modern computers, which were not accessible by the inventor)
3. Even using different numbers for the same letter, the overall distribution of alternatives is limited to the occurrences of these letters on the page

Contemporary Critic

Most code experts of its time criticized "The Maryllian" as "painful slow to work with" and impractical compared even to other book-based codes. On the other hand, the respected Peter Foyle (of the "Deep-night code follies" fame) saved the reputation of the system by calculating the 0-threshold efficiency resulting in high values because the complete mapping of the letters could take place on one single page instead of a whole book, thus making it more easy to transport and use in warlike situations.

History

According to John Miselstone's "Complex Cryptography" the Maryllian Cipher was considered as unbreakable in 1872. Actually, at this time the breakability of things was measured in H/i² (Horkenbargle per square inch) so the usual methods couldn't be applied completely. Later the Horkenbargle index was changed to standard pressure.
It is not clear whether "The Maryllian" was used during the civil war.