2.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 was invited by the father-and-son team of Antonine and Bonavenure Rossignol. They had a great amount of experience in the field of cipher and, after serving Louis XIV, had precious resource.

Since they spent so much time on enciphering and deciphering, they should know the most advanced technology to break the cipher at that time, which helped them improve the strength of the code they made. Thus they can improve the way they enciphered the message and made sure that no one could break the cipher and get the message with current technology. This cipher was so strong that it remained unbroken for 200 years after the death of them and the lose of the way to break the cipher.

I just remember the first blog I wrote. It was said that we could break the cipher with our knowledge even though breaking the cipher need the knowledge in the fields of mathematics, linguistics and statistics.  But now I thought the cipher has already developed to a so high level that only the experts in the field of cipher could took part in the work of cipher.