A key (1) for operating a lock such as a door lock or padlock, includes a grip portion (2) and a cylindrical shank (3). The shank includes an abutment (4) that extends radially to position the key in the lock and transfer driving force from the key to the lock mechanism. The key includes encoding recesses (5) that cooperate with elements for unlocking the lock, such as pins. In cross-section at least part of each encoding recess has a substantially triangular shape with a truncated vertex.