There’s an old saying along the lines of: “If more than one person knows something, it’s no longer a secret.” This point of view was certainly promoted by the Dutch linguist and cryptographer Auguste Kerckhoffs, who is best known today for two essays he published in 1883 in le Journal des Sciences Militaires (Journal of Military Science) entitled La Cryptographie Militaire (Military Cryptography).
The problem arises when multiple people must work together on tasks where they share information while keeping the shared information secure from others. Everything is exacerbated in today’s digital era, where information is created, processed, and stored on humongous computer networks that potentially involve thousands of clients (end-user computers), servers, and storage devices.