The History and Mathematics of Codes and Code Breaking

Power of The Great Cipher

There exists a never ending battle in the field of cryptography between those coming up with encryption methods and encrypting messages to those trying to break these ciphers. This back and forth is an ongoing and fairly quick process with each side constantly making advancements. However, the 2nd chapter of Singh discussed "The Great Cipher" which was the cipher used by Louis XIV, which remained unbroken for 200 years. The obvious question is then, what made this particular cipher so difficult and take so long to crack?

There are multiple reasons for this, starting with the complexity of the code itself. The code was comprised of 587 unique numbers with thousands of numbers altogether. This alone makes it very difficult to decipher as if you were assuming these numbers corresponded to letters or a set number of letters, as there would have to be repeated elements of the cipher text corresponding to the same thing in the plain text, which would render frequency analysis practically useless. This leads into the next reason why the cipher was so secure, which is that the numbers corresponded to syllables instead of letters or groups of letters. The majority of the ciphers up till this point revolved around changing something into individual letters, so this not being the case probably threw off many would be deciphers of the text.

Lastly, one of the main reasons this code was so secure is the technology that was available at the time. Nowadays with our computers, excel files, other programs and whatnot it is fairly simple and straightforward to do things such as frequency analysis or substituting in sequences in the cipher text for what we assume it to be in plain text. However, back in the 17th and 18th centuries performing these tasks by hand (especially with a text thousands of characters long) would be an incredibly daunting task. The sheer time commitment it would take to decipher a text of this length would be enormous and this probably discouraged many people from attempting to decipher it.


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  1. Yuthika

    I agree that Louis XVI’ s Great Cipher was very difficult to crack because of its complexity and potential for encryption. One of the topics that Singh did not really elaborate much upon was the ability of those using codes to send phonetic messages that didn’t actually stick with the proper spelling of words, and instead focused more on the pronunciation of words, and encrypted those. For example, if I wanted to encrypt the phrase “cryptography is fun,” I could convert it to a phrase with the same approximate phonetic sound but incorrect spelling (like “kriptografee iz phan”), which would make it increasingly more difficult to crack. It seemed like the only way Louis XIV’s cipher was cracked was through luck and knowledge of context. Cryptanalysis is a mixture of luck, mathematics, and intuition, and without all three of those in copious amounts the Great Cipher could never have been broken. Going back to the idea of phonetic cryptography, it would be interesting to associate the assignment of syllable sounds to letters from languages with phonetic alphabets. For example, most Indian languages have phonetic alphabets, with separate letters for each consonant sound and modifications with extra elements added to those letters for different vowel sounds following those consonant sounds. If those people implementing the Great Cipher had used numbers to encode their plaintext in a similar fashion, it would have been much harder to crack. Perhaps it would still remain a mystery today.

  2. growm

    I agree with "clausen"'s answer to his question as posed in the end of the first paragraph ("what made this particular cipher so difficult and take so long to crack?"). It makes clear sense that the greater the number of permutations the cipher has, the harder it is to crack. Time is not something many people often have in great supply. Without sufficient time (and sometimes resources), a person can want to break a cipher by hand, but be incapable because they simply do not have the time to run thousands of permutations by hand. It also makes perfect sense that some ciphers are breakable only if one has the motivation to attempt to break them. Without motivation, why should someone spend potentially thousands of hours of their life on cracking a message?
    However, as to the concept of the "unbreakable" cipher, as somewhat mentioned in this post, I must say that I don't think any cipher is truly unbreakable. "Unbreakable" sounds too much like "unsinkable," in my opinion. As "clausen" mentions, "The Great Cipher" took two centuries to crack. They must have thought it unbreakable for a time, but eventually the cryptanalysts caught up to the cipher, and they figured out the puzzle. I would therefore ask a "chicken and the egg" question: which pushes the other to develop, the cipher or the analysis? I would argue that as the cipher develops, the analysis tries to catch up. It can seem sometimes that the analysis pushes those developing ciphers to move faster, and this can be true--but the creation of the cipher is what generated the analysis in the first place. This conclusion might seem obvious, but I find it an interesting concept to think about.

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