Provided is a locking system having a key and a lock cylinder. The lock cylinder has a cylinder core journalled in a housing and having a keyway for inserting the key. A plurality of tumblers actuable by the key and an additional blocking element movably arranged in a guide passage of the cylinder core project into the keyway, said additional blocking element being displaceable obliquely or transversely to the direction of insertion of the key. The additional blocking element is made for cooperation with a counter-element arranged at the key blade with a key introduced up to the maximum insertion depth. The counter-element is in this respect arranged in a groove or recess starting from the key tip and extending in the longitudinal direction of the key blade.