## Cryptography

#### Tag: The Great Cipher (Page 1 of 2)

Louis XIV's Great Cipher was unique in its complexity, far far beyond the other ciphers used during the time period. Indeed at the time, by far the most popular type of cipher was the mono alphabetic substitution cipher, yet that is easily deciphered by a good cryptanalyst through the use of frequency analysis.  The Great Cipher was much more than a simple mono alphabetic substitution cipher in that it utilized numbers to represent letters, but on top of this, the numbers didn't just stand for letters they also stood for syallables. Since there was not a 1 to 1 relationship between letters and the cipher alphabet, it was nearly impossible to perform traditional frequency analysis on the cipher text. Furthermore, the cipher was brilliantly created with cipher text indicating to ignore the previous syllable or letter, making it tricky for any decoder to figure out what was part of the cipher and what was simply nonsense.

Perhaps the deciphering of the Great Cipher is even more impressive than the creation of such a complex cipher. The amazing creativity and brilliant thinking that Bazeries had to even consider looking at syllables has to be commended. Furthermore, for him to harp on a repeated phrase and be able to figure out what it meant is incredibly impressive. This also illustrates how amazing the cipher was in that it took Bazeries over three ears to crack it even with his uncanny ability to recognize that it is comprised of syllables.

The first thing The Great Cipher used by Louis XIV did well was not being a monoalphabetic cipher. These ciphers are too susceptible to frequency analysis, making them crackable in a matter of hours at the most. Instead, the Great Cipher is more along the lines of a polyalphabetic cipher. Instead of letters, however, the cipher alphabets are compromised of numbers. But the thing that really makes this cipher a strong one is the fact that these numbers represent single syllables, letters, or even commands instead of just single letters. In doing this, deciphering The Great Cipher would take years.

This cipher took 200 years to decipher due to the odd nature of the cipher. No conventional ciphers substituted numbers for both syllables and letters, as well as having some traps lain within. Due to this, nobody knew how to begin deciphering it. It was only through the efforts of Bazeries that this cipher was eventually cracked. Even so, it took Bazeries 3 whole years to figure out the messages hidden behind the code. He was only able to crack the code as a result of his very out of the box thinking and pure determination. After trying polyalphabetic combinations, which are hard enough to crack on their own due to the pure number of possibilities that exist, and diagraphs, which also took a long time, Bazeries thought to try syllables. It was only after trying many different combinations that he found a single phrase which worked. He then used this word to painstakingly decipher the rest of the text. The pure creativeness of The Great Cipher led to its strength, and the only way it could be decoded was through equal creativity.

I see The Great Cipher is synonymous to the simple monoalphabetic substitution cipher, just on steroids. The concept is the same—one cipher letter or multiple cipher numbers represent a number of plaintext letters. However, what makes the two so different in their difficulty to be cracked lies in the sheer possibility of combinations that could be created from each cipher.

The cipher key was not limited to just one letter replacing another; instead, a few numbers represented syllables. Thus, this opened up a lot more possibilities to stump cryptanalysts.

Before, it was clear in monoalphabetic substitutions that one cipher letter represented one letter of the plaintext. Therefore, we were only faced with a certain amount of different cipher keys to deal with. Even though a completely random monoalphabetic cipher would yield so many possibilities, frequency analysis could easily help decipher it. But now with a cipher with undeterminable characteristics (does "1" represent a letter or does "123" represent one letter? Or a syllable? I'm guessing they did not know how many numbers represented how many letters), patterns that lead to the cracking The Great Cipher become less obvious. There is a multitude of syllables that exist in the French language, making combinations all the greater in amount. This increases the difficulty because although we might see a string of numbers or other patterns, the specific plaintext it refers to—whether it be just one letter or two or three—has much more holes and traps.

In addition, many people might still be familiar with only the mono alphabetic substitution (since cryptology was still developing), so people might have not thought in a “numbers now represents syllables” way just yet. A reason for the people's unfamiliarity would be that since the Great Cipher was made by two people (the Rossignols) who already knew how to crack extremely hard ciphers, their knowledge of the weakness of strong ciphers bolstered their knowledge to build something knew that didn’t fall into the traps of the simple mono alphabetic substitution cipher. As such, because they thought five steps ahead of everyone else. In addition to their death, the Great Cipher remained unsolved for 200 years because the only people smart enough to crack hard ciphers and used the weakness of those to create a new super hard to crack cipher had died. In short, their knowledge of the Great Cipher died along with them until it was unearthed 200 years later.

The father-and-son team of Antoine and Bonaventure Rossignol invented the Great Cipher for the French king Louis XIV to encrypt the empire’s most secret messages, protecting details of his plans, plots and political schemings. While the nature of the Great Cipher was simply an enhanced monoalphabetic cipher with homophones, it seemed implausible that it remained unbreakable for two centuries. However, there were two main factors that led to such a secure cipher.

The most significant one was considered to be the Rossignol’s ingenuity and resourcefulness. Including 587 different numbers, the Great Cipher was obviously not a straightforward substitution cipher. But when Étienne Bazeries, a distinguished cryptanalyst tried to crack it as a homophonic cipher, he failed. He then came up with the idea that each number might represent a digraph, or a pair of letters. Although his efforts to this deciphering approach again yielded nothing, it enlightened him on the possibility that some numbers corresponded to syllables. After a few attempts, he made a breakthrough, with the discovery of “les-en-ne-mi-s” represented by a cluster of numbers (124-22-125-46-345), and thus his idea eventually proved to be right. During that time when cryptography was mainly about encrypting plain alphabets with cipher alphabets, it was creative of the Rossignol to use syllables for the complexity of homophones. More importantly, they had also laid traps for codebreakers, adding numbers which deviously deleted previous numbers instead of representing any meaningful letters or syllables. All their creative encipherment contributed to the strength of its encryption, making it confusing and harder to decipher.

Additionally, after the death of both father and son, the Great Cipher fell into disuse and many details about it were lost; therefore, for those who wanted to break the codes had to start from scratch. Due to its difficulty, only the most prominent cryptanalysts were capable of deciphering it with consistent dedication and patience. As a result, it was no surprise that the Great Cipher was known as one of the strongest ciphers in the history of cryptography.

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.

The Great Cipher used by Louis XIV remained unbroken for 200 years.  What were the factors that led to such a secure cipher?

The Great Cipher, invented by Antoine and Bonaventure Rossignol, was one of the toughest codes to decipher. There are some very important factors to consider when trying to understand why it may have taken so long for someone to crack it. First of all, Antoine got his recognition for deciphering the letter that resulted in a victory for the French. With his work in cryptanalysis he and his son were appointed to the senior positions in the court, so by this time he has already established his reputation as being one of the best cryptanalysts in Europe. His expertise gives him an advantage because he can recognize the weaknesses in ciphers, therefore when he has to create his own, he would know how to make it indecipherable. Of course, this is relative because ciphers can only stay indecipherable for so long before new methods are developed by cryptanalysts to break them. Second, it is usually a weakness to have a long cipher text because it gives the other person a better chance to recognize patterns, however, this cipher had thousands of symbols with only 587 of them being different. This only makes it a lot more difficult for someone to decipher it because it gives them too much information to work with which instead of showing a pattern, creates confusion. Finally, the more time that passes, the harder it is for someone to decipher a text because of lack of contextual clues. When it is the same time period, there is a better chance to crack a cipher text because you would be fully immersed in the linguistics of that society. Since language evolves over time it is best to try to decipher a code as soon as possible. Because of the complexity of the Great Cipher it did take a lot of dedication and persistence for Bazeries to finally crack it after 200 years.

The Great Cipher used by Louis XIV remained unbroken for 200 years.  What were the factors that led to such a secure cipher?

The cipher was pioneered by a father and son duo, most of the specifics to how it exactly worked were known best by these two people. With the death of both father and son, the specifics of the cipher were quickly lost. When there are no people around that know how to use and reproduce the cipher, the motive to crack it is lost. There was some important information enciphered with The Great Cipher, however nobody was actively using it, so resources used to crack ciphers would be diverted to cracking ciphers used at that time. The lack of motive is the smallest reason as to why it took so long to crack; the cipher itself is very elegant and complex. This cipher was not one that took a written word then simply changed letters, it was a completely new way to write down the language. Languages operate with distinct sounds that can be represented by letters, putting two letters together will change the sound. Writing a cipher with syllables in mind will make it more difficult to crack, especially to a cryptanalyst who writes with an alphabetic language (like English). On top of that, The Great Cipher had certain traps put into place that would make certain parts look like gibberish causing cryptanalyst to reevaluate the type of cipher.

In my opinion, a syllabary cipher would be most effective today. This is because most of society is literate and thinks in a similar manner to the way we write, letter for letter, not letter for sound. Using syllables, but re-vamping it with more traps, would confuse people because they are not used to naturally thinking in that manner when writing.

(I double checked some facts here http://en.wikipedia.org/wiki/English_orthography and here http://en.wikipedia.org/wiki/Syllabary)

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The Great Cipher used by Louis XIV remained unbroken for 200 years.  What were the factors that led to such a secure cipher?

The father-son team of Antoine and Bonaventure Rossignol invented The Great Cipher while working closely with Louis XIV as his cryptanalysts. Initially, they were mainly code breakers, but their skill gave them the idea to create a much stronger way to encrypt messages. This idea turned into the Great Cipher. This cipher was very useful for the French and no enemy cryptanalysts were able to crack it. Unfortunately, the Rossignols's death also meant that the Great Cipher's secrets were lost and any archives encoded using it could no longer be read. Although this was inconvenient for the French, the real struggle would be experienced by future generations of code breakers. Eventually letters encrypted by the Great Cipher were passed on to Étienne Bazeries who worked tirelessly to decipher the letters. The high security of the cipher made it nearly impossible to decode.

The first factor that led to this secure cipher was the amount of characters included. 587 different characters immediately made it clear that the it was not a substitution cipher and later, Étienne also discovered it was not a homophonic cipher (a cipher that replaces letters with a proportional number of symbols to how often that letter is used). Later he would also try to decipher it as a digraph (one number represents a pair of letters), but this also was not correct. The grunt work that decoding the Great Cipher must have required is astonishing because the text says each idea could take Étienne multiple months to prove wrong. Eventually, Étienne was struck with the idea that each number represented a whole syllable. After tirelessly working on this idea, he was able to decode 124-22-125-46-345 as meaning "les ennemis". This crucial breakthrough led to Étienne's eventual success despite variations in the cipher and traps laid by the Rossignols. This elaborate cipher truly deserved its name as "The Great Cipher".

The Great Cipher used by Louis XIV implemented a different method of cryptography and ciphering than ever before. The monoalphabetic substitution cipher was too easy to break while the polyalphabetic cipher created by Vigenère took too long to encipher and decode which was not efficient for military operations. The Great Cipher, created by the Rossingols and later cracked by Bazeries, utilized not only letters, but also numbers in the cipher. And the different numbers did not represent letters; they mostly represented syllables. This cipher also included traps. For example, some numbers initiated the deletion of the previous number. Some of the numbers did not represent syllables but single letters. The sophisticated nature of this cipher contributed to its dormancy for two centuries. Yet the ease of deciphering a message ciphered using the Great Cipher was quick enough to be used for military purposes, if the cipher was known. Another characteristic of the Great Cipher that was impressive was that it almost completely paralyzed the use of frequency analysis. Although frequency analysis actually lead to Bazeries cracking of the cipher when he noticed a repeated sequence of numbers. But he then completely guessed what those numbers could mean and he happened to be spot on.

The Great Cipher, used by Louis XIV, was far more complex than any cipher used in the 17th century. It was not simply a substitution cipher nor a homophone cipher. Étienne Bazeries considered that the Great Cipher could be a digraph, which meant that each number represented a pair of letters instead of a single letter. After months of work, Bazeries came to the conclusion that the cipher was not a digraph. He stuck with the concept that each number represented multiple letters, considering that they could possibly represent syllables. After deciphering two words, les ennemis, Bazeries was able to decipher the rest of the text. Another factor that made the Great Cipher so complex was that some of the numbers did not represent single letters nor syllables. Instead these numbers simply deleted the number before them. The Great Cipher was so far beyond its time period that it took centuries for cryptanalysts to catch up and approach the cipher from a different angle.

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