A cylinder and key lock mechanism is unlocked when a specific combination of rotation angles of dialer groups, each constituted by one internal dialer disc and by one external dialer ring coupled through teeth, is dialed through rotation of the key having a formed cipher. A security mechanism, being part of the key and driven by the insertion of the key into the cylinder, enables re-programming. When unlocked and with re-programming enabled, re-programming is possible where the inner dialer discs are decoupled from the respective outer dialer rings, the key can be rotated driving only the inner dialer discs and extracted leaving the system in a re-programming configuration. A new key having a different cipher can be inserted and the system exited re-programming with a different coupling between the inner dialer discs and the respective outer dialer rings so that they couple with the new key cipher.