Abstract: The invention relates to a cylindrical lock having a stator with a rotor in said stator having lamellae actuated by a flat key.The rotor comprises floating lamellae capable of moving freely, but to a limited extent, both radially and angularly, and means for guiding the flat key over its entire introduction path into the rotor without any possibility of lateral and radial displacement, this key comprising complementary profiles along its two edges and a tapered end with convex surfaces.