Flat key profile for a lock-key system

The invention relates to a flat key profile for a lock and key system in which a key channel corresponding to the key profile is provided in the lock cylinder. In this case, the key profile of the key shank facing the key back upper profile section and a key face facing the lower profile section, wherein in the lower profile section in a side surface of the key shank a triangular, the center plane of the key shank superior, paracentric profile groove (2) provided on the opposite side surface of the key shank one above or below the opposite paracentric profile groove (2) arranged, triangular profile groove (3; 4) is provided, the arrangement of the paracentric profile groove relative to the opposite profile groove is such that an imaginary line (7), the vertical to the keychain plane from the intersection of the upper or lower leg of the paracentric profile groove with the key side surface to the opposite profile groove extends, to an imaginary line (5) extending from the intersection of the upper or lower leg of the opposite profile groove with the key side surface extends to the paracentric profile groove, a vertical distance (9).