[2] After a period of teaching in schools in the Netherlands and France, he became a professor of German language at the École des Hautes Études Commerciales (Paris)[3] and the École Arago.

[4] He is best known today for his two-part paper published in 1883 in Le Journal des Sciences Militaires (Journal of Military Science) entitled La Cryptographie Militaire (Military Cryptography).

These articles surveyed the then state-of-the-art in military cryptography, and made a plea for considerable improvements in French practice.

It can be understood as the idea that the security of a cryptosystem must depend only on the key, and not on the secrecy of the algorithm used for encryption or any other part of the system.

He published several books on the subject and introduced the movement to France, Spain, and Scandinavia through a series of public lectures.