The invention relates to safety paper provided with an authentication for authenticating the paper. In the safety paper according to the invention, the base paper is provided with a structural deviation comprising at least one or some of the following: one or more perforations holes thinner/thicker spots/areas thinner/sparser spots or areas, or colouring agent layers applied onto the base paper. Furthermore, the structural deviation is covered with a coating material layer. The coating material layer covers at least one side of the base paper substantially entirely in such a way that the overall thickness of the paper is primarily constant over the whole area of the paper. However, the coating material of layer has a different thickness at the structural deviations with respect to the other areas of the paper. The invention also relates to a method for manufacturing the safety paper according to the invention.