Tag: traps

The Complexity of the Great Cipher

On September 19, 2012

Antoine and Bonaventure Rossignol created the Great Cipher of Louis XIV and made it so complex that it took over 200 years to decipher. Generation after generation attempted to crack the cipher, yet no progress was made. The Rossignol’s both died, which terminated the ciphers use, as well as cutting off any potential collaboration with the creators and knowledge of exact details that could have been useful to the hundreds of codebreakers that tried to uncover the mystery. It was not until Commandant Etienne Bazeries came along and spent three years of his life working on deciphering letters of Louis XIV that the code was finally solved. Bazeries knew that it was not a substitution cipher, as there were 587 different numbers instead of the usual 26 different numbers. To Bazeries’ dismay, the cipher was also not a homophonic cipher, which was a possibility he entertained for months.

His final attempt proved to be worth it after all. The main factor that made this cipher so secure was the fact that each number represented a whole syllable, not a pair of letters. Bazeries finally got on a roll, guessing the remaining letters of an unfinished word, which enabled him to recognize other syllables. Another major deceiving factor in the Great Cipher was the traps that the Rossignols inserted; some numbers occasionally deleted previous numbers instead of standing for another syllable. The combination of the traps, the vague numbers, and the inability to collaborate with the Rossignols created an extremely secure and virtually unbreakable cipher.

The Great Decipherment

By herbstts

On September 18, 2012

In Student Posts

The Great Cipher, invented by the Rossignol family, was such a difficult cipher to crack because of two important factors. First the details and use of it was lost one the Rossignols died, which meant hat cryptanalyst had to start from scratch without knowing anything about how the cipher was created besides what they assume based on what other ciphers looked like during the same time period as Louis XIV. The other significant factor that made the Great Cipher so powerful is the fact that it was not a simple single letter substitution cipher but actually a double letter substitution with a twist: instead of substituting letters, it instead substituted syllables. This greatly complicated the cipher because there an incredibly large number of ways in which to rearrange and cipher syllables, and if there is now starting point at which to begin deciphering the Great Cipher, then it becomes infinitely harder to crack the Great Cipher as opposed to a simple single letter substitution cipher. While these things combine to make it difficult to crack the Great Cipher; the inclusion of traps, such as numbers to delete the previous syllables, made it difficult to tell whether or not a postulated key to the cipher is correct until the traps are detected and accounted for. The combination of having no information about the formation of the Great Cipher as well as the unique substitution it uses as well as traps to trick cryptanalysts all combined to make it unbroken for 200 years after it was created despite the effort of many intelligent cryptologists.