trapdoors

Trapdoors are panels or doors that conceal openings in floors, ceilings, or walls. They are designed to be opened to access hidden spaces while remaining inconspicuous when closed. The term is used in several domains, including architecture, stagecraft, and cryptography.

Architectural trapdoors are commonly found in houses and public buildings to access basements, attics, or service spaces. They may be flush with the surrounding surface and operated by hinges, pull handles, or counterweights, and often require safety precautions to prevent accidental opening. In theaters and on film sets, trapdoors are concealed openings in the stage floor that allow performers or props to appear, disappear, or move between levels.

In cryptography, a trapdoor is part of a trapdoor function: a one-way operation that is easy to perform in the forward direction but difficult to reverse without special knowledge. Such functions underpin public-key cryptosystems, where a private key serves as the trapdoor. The term can also describe a hidden mechanism or backdoor that provides unauthorized access to a system, though legitimate security disciplines emphasize controlled and auditable use.