Dr Auguste Kerckhoffs (19 January 1835 - 1903) was a Flemish linguist and cryptographer who was professor of languages at the School of Higher Commercial Studies in Paris in the late 19th century.

Kerckhoffs was born in Nuth, Holland, and was baptised as Jean-Guillaume-Hubert-Victor-Françoise-Alexandere-Auguste-Kerckhoffs von Niuewenhof, although he later shortened his name. Kerckhoffs studied at the University of Liège . After a period of teaching in schools in Holland and France, he became a professor of German at the Parisian Ecole des Hautes Etudes Commerciales and Ecole Arago .

He is best known today for a series of two essays he 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. They also included many pieces of practical advice and rules of thumb, including Kerckhoffs' famous six principles of practical cipher design.

Kerckhoffs' second law

Of all his work, the most well-known is the second of his six principles, also known as Kerckhoffs' law: "the security of a cryptosystem must depend only on the key", and not on the secrecy of any other part of the system.

In war, the enemy will have spies, and, in any case, will likely capture and analyse your equipment; hoping to keep that equipment secret is probably futile. In computer security, a determined attacker might be able to run your software under control of a debugger , or probe your hardware in various ways, until he finds out in detail how it works; your security is best managed without relying on the secrecy of those details. Much the same sort of consideration applies in cryptography. Kerckhoffs' law is, in essence, the position that cryptography should be secure even against an opponent who has done such things, or alternatively, that security by obscurity is insufficient in cryptography.

Later work

In 1885, Dr. Kerckhoffs became interested in the constructed language Volapük, and for several years was a leading member of the Volapük movement, and Director of the Academy of Volapük. He published several books on the subject and introduced the movement to France, Spain and Scandinavia through a series of public lectures.

External links

• La Cryptographie Militaire — French original and translations into English