Auguste Kerckhoffs (19 January 1835 – 9 August 1903) was a Dutch linguist and cryptographer who was professor of languages at the École des Hautes Études Commerciales in Paris in the late 19th century. The best-known is the second of his six principles, also known as Kerckhoffs's principle. 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 any other part of the system.