A key that controls a lock with a cylindrical plug, the key having a shank the body of which has an external, rounded surface and forms a hollow, partially enclosed profile. The external rounded surface is shaped for turning the key in the lock cavity of the lock, while at least in the end part of the lateral section of the shank, an open cavity is created for inserting an arm of the validating lever of the lock. At least a part of the shank is U-shaped or V-shaped fitted with at least one open coding track and/or at least one coding channel with a shaped coding surface.

A key for controlling a lock with a cylindrical plug, where the body of its shank (10) is at least in a part of its length formed by a hollow, partially enclosed profile, the external rounded surface of which (16) is shaped for turning the key in the lock cavity, while at least in the end part (12) of the lateral section of the shank (10), an open cavity is created for inserting an arm of the validating lever (5) of the lock. At least a part of the shank (10) is created in the U- or V-shape, while in at least one such part of the shank (10), the bottom and/or the wall of the inner and outer arch of the shank (10) is fitted with at least one open coding track (9) and/or at least one coding channel (18) with a shaped coding surface. The lock for validating the key contains at least one cylindrical plug (1) rotatable in its housing (2), where in the plug body (1), a sprung sidebar (3) of the lock is situated in its outer longitudinal groove, pushed to the inner surface of the housing (2). The sidebar (3) is adapted for inserting into the turning validating levers (5) that are arranged in a row in the longitudinal axis of the plug (1) on the pivot in the plug (1) and they are located in the lateral slots (6) along the plug's (1) length. These validating levers (5) are in case of incorrect coding of the key (11) in a blocked functional state in a position preventing the inserting of the sidebar (3) into the groove (23) in the plug (1), and thus the turning of the plug (1) inside the housing (2) of the lock, while in the unblocked state in case of correct coding of the key (11), they are in the functional position allowing for the movement of the sidebar (3) in the direction into the groove (23) in the plug (1) and thus the turning of the plug (1) inside the housing (2) of the lock. The validating levers (5) at least partially protrude into the cavity of the key (11), by which they allow for achieving contact between the validating levers (5) and code carriers, which are the coding tracks (9) or channels (18) in the key (11).