Cryptography

The History and Mathematics of Codes and Code Breaking

When Cryptographers Die

There were many strong ciphers that seemed impossible to decipher, but only one has the name "Great Cipher." The Great Cipher stood undecipherable for 200 years. Created by Antoine and Bonaventure Rossignol, it was used by King Louis XIV as a way to keep his secrets hidden, "protect details of his plans, plots, and political schemes." He was impressed by the cipher and the Rossignols' so much he gave the father-son duo offices near his apartments.

What made the Great Cipher so great was the combination of its use of syllables as cipher text in the form of numbers, and the death of both Antoine and Bonaventure. The Great Cipher was secure because it turned basic french syllables into cipher text into numbers, specifically 587 of them. As mentioned before, 200 years went by before it was deciphered. Many people tried their hand at the cipher and ultimately failed, died, or gave up before they could solve it. Along with the death of the Rossignols, there was no one to read the messages. This lead to messages being unreadable for years, thus securing the cipher for years until Etienne Bazeries deciphered the Great Cipher. This still took him a total of 3 years of work of using various techniques. Some of these techniques led to gibberish and complete restarts of his journey. He finally considered the numbers could be syllables, then he found a single word, "les ennemis," from a cluster of numbers that appeared several times. From here he could examine the other parts of cipher texts and decipher them.

The Great Cipher is remembered as one of the most secure ciphers in all of history. The techniques used to decipher it are still used in other deciphering techniques, and it is one of the "forefathers" of today's unsolved ciphers.

Resources on Plagiarism and Academic Integrity

Some resources relevant to our discussion of plagiarism and academic integrity...

The Greatest Cipher

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.

Blog Assignment #5

This summer, I visited the Newseum in Washington, DC, with my kids. The Newseum is a museum focused on the five liberties of the First Amendment to the US Constitution: religion, speech, press, assembly, and petition. One of their current exhibits looks at the FBI's role in fighting crime and terrorism. As my daughters and I were walking through the exhibit, I noticed this display:

For your fifth blog assignment, respond to this display in a post between 200 and 400 words. I'm really curious to know what you make of it, given the discussions we've had in the course about privacy and security.

Please (1) give your post a descriptive title, (2) assign it to the "Student Posts" category, and (3) give it at least three useful tags. Also, (4) try embedding the above photograph in your post. (Click on "Add Media" when you're composing your post to do so.)

Your post is due by 9:00 a.m. on Wednesday, September 27th.

I Don't Really Think There Was Difference

What was the difference?

There was none! The environment that Mary Queen of Scots experienced is quite the same compared to the environment leading up to the development of the Vigenère cipher. In fact, it even states in the book that Vigenère’s publication of Traicté des chiffres happened “ironically… [in] the same year that Thomas Phelippes was breaking the cipher of Mary Queen of Scots.”

Even Mary herself was aware of how insecure the code was. It was just that (1) she could not come up with a better method of encryption and (2) she never questioned if her beloved messenger was a double-agent for Thomas Phelippes which he in fact was.

All of this just goes to show how much of an edge the cryptanalyst had over the cryptographers. No matter how much variation the cryptographers tried to invest into their monoalphabetic, the cryptanalyst could break them easily with one tool — frequency analysis.

However, this was only until Vigenère took the works of three other men to create a cipher that gave the edge back to cryptographers. With it, cryptanalyst would be left to sit hunch-back over their desk for years. It is only a shame however that his amazing cipher would not be appreciated until another two hundred years.

200 Years of Strength

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.

Assume the Worst

Before the Vigenère cipher, a simple monoalphabetic substitution cipher was the most advanced encryption. This is a weak way of coding however, as an encryption is only as strong as the key used to create it, and tools such as frequency analysis make this easy to conquer. Any code could be broken if the person who intercepted it was well acquainted with basic deciphering methods. The best way to protect your secret message was to assume that anyone could intercept and decipher your code. It was a given that before the Vigenère cipher was invented, that no encryption was completely safe. That being said, not many people realized this and truly thought they were keeping their secrets safe. A perfect example of this is Mary Queen of Scots.

Mary Queen of Scots spent her time imprisoned sending encrypted messages back and forth with a conspiracy group. Mary, along with the rest of the group, ignorantly thought that no one was able to crack their "master" encryptions. As a result they talked about many sensitive topics, especially the coup to overthrow the Queen of England. Their false sense of security led to their demise because, in reality, their code was very easy to break. They thought that their code was unbreakable, however, there was no sure way to know how accurate this claim was. Mary downfall was underestimating the environment in which she lived. She assumed that no one would be smart enough to break her code, but as she soon learnt, an encrypted message can be cracked to spill the secrets it contains.

Diffusion of Knowledge and Awareness

In the time of Mary Queen of Scotts, Mary, her conspirators and others trusted the encrypted messages would remain secret, trusted the difficulty of their key, and trusted the inability of others to decipher coded messages. Even though they were not aware that their trust ended in Mary Queen of Scotts death sentence, it was this lack of knowledge and lack of paranoia that allowed this to occur. The environment in Chapter 2 represents that of knowledge and awareness. As people were able to decipher others coded messages it posed the question: who says they can't determine mine? With this increasing awareness of other peoples similar capabilities, this then caused a lack of trust in the system and even deterred from the use of encryption. If an encrypted message was likely to be decrypted by an unknown and unintended recipient, there was not point in writing the message. The ability to decipher others messages also turned into a game. For example, since people did not trust the mail or content of the letters from being discovered, they attempted to write notes in newspapers where at least their identities could remain anonymous. However, cryptanalysts then responded to these messages using the coding system in the previous message. In one instance, a woman aware that her code had been broken warned her recipient through the next newspaper that the code had been broken except she used the same code to relay the message and stated his name. This scenario is humorous as the woman now told the cryptanalysts the recipient's name making the system just as compromised as letters had been. Overall, the new environment caused awareness to increase leading to more caution in transporting private messages, and also led to the yearn to create more difficult coding systems that could not be deciphered easily.

The Great Cipher: Coding in a primitive form

Great Cipher used by Louis XIV was such a successful cipher because it incorporated many types of cryptography, but also "foolproofed" itself by creating almost a ciphertext keyboard. For example, certain numbers created sounds, similar to how computer code can prompt a computer to emit audio. Similarly, certain groups of numbers deleted the previous letter/cluster, like the backspace key of a computer, and how a computer is coded to understand that deleting is the function of the key. I would argue that the Great Cipher was a form of computer code before its time, with the Rossignols being the coders and Louis XIV or any recipient being the computer. Before the Great Cipher, many cryptanalysts were accustomed to assigning one letter with a singular symbol, or group of numbers, but this cipher was so successful because it prompted the reader to emit a syllable, as computer code prompts a computer to perform a very specific behavior rather than reword the code given. It is remarkable to imagine that such a complicated form of cryptography was developed so long ago, because we in some ways still utilize it today. Again, this method connects back to the argument of monarchs controlling the most developed forms of cryptography because of their resources and the content of their messages (Louis XIV could afford to house the Rossingnols). If records were kept, it would be interesting to research whether Antoine and Bonaventure were the first people to develop such a code, and how it relates to modern day technology programming.

The Greatness of the Great Cipher

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.

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