Kerckhoffs's principle

Kerckhoffs's principle (axiom, or law) is an idea in cryptography. It was stated by Dutch cryptographer Auguste Kerckhoffs in the 19th century. It is:
Kerckhoffs's principle was more briefly stated by American mathematician Claude Shannon as "the enemy knows the system", that is, "one ought to design systems under the assumption that the enemy will immediately gain full familiarity with them". In that form, it is called Shannon's maxim. It is opposite to the idea of "security through obscurity".
More details.
Some are no longer relevant given the ability of computers to perform complex encryption. The second axiom, Kerckhoffs's principle, is still vitally important.