The Great Cipher used by King Louis XIV was an extremely strong cipher for several reasons. First, the cipher text included 587 different numbers. This magnitude of possible decipherments was the first line of defense. Additionally, because multiple cipher types had been created by the time the Great Cipher was implemented, there were many more possibilities for the encryption than just the simple monoalphabetic cipher. However, the Rossignols chose not to use any previously created ciphers, vouching instead to devise their own. This creativity further complicated the matter of decipherment. Because the Great Cipher substituted numbers for syllables, any letter-based frequency analysis was useless. This major difference was probably the biggest reason why the cipher stayed unbroken for so long. Once discovering the substitution for syllables, the hard work of decipherment was still far from completion. The next stumbling block came in the form of inconsistency. Some of the numbers stood not for syllables, but for individual letters. Finally, the Rossignols laid “traps”, as Singh refers to them, within the cipher itself. One such example is a number which deletes the previous number. Combining all the individual parts of the Great Cipher results in a code which is devilishly difficult to decipher. Considering all the intricacies of the Great Cipher, it is little wonder that it remained a mystery for two centuries.
Tag: Louis XIV
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.
