In cryptography, Kerckhoffs’s principle (also called Kerckhoffs’s Desiderata, Kerckhoffs’s assumption, axiom, or law) was stated by Auguste Kerckhoffs in the 19th century: A cryptosystem should be secure even if everything about the system, except the key, is public knowledge.
Kerckhoffs’s principle was reformulated (perhaps independently) by Claude Shannon as “The enemy knows the system.” In that form, it is called Shannon’s maxim. In contrast to “security through obscurity,” it is widely embraced by cryptographers.
Kerckhoffs’s principle on Wikipedia.
