Abstract: A cylinder lock with a key, the lock having a plug with at least one hole intersecting the keyway. The hole is provided with two shoulders, one whereof lies further outward, the other one lying further inward with respect to the surface of the plug. An auxiliary tumbler is accommodated in the hole and comprises an auxiliary pin, an auxiliary complementary pin and a spring acting by expansion between the auxiliary pin and complementary pin. The tumbler can assume an elongated configuration, wherein the pin and the complementary pin are mutually spaced and axially offset angularly with respect to each other, or a shortened configuration, wherein they are aligned in mutual abutment without axially offset. The key has an elastic element adapted to cooperate with the auxiliary tumbler to allow, with the key inserted, compression thereof to the shortened configuration and disengagement from the notch and rotation of the plug.