Abstract. Invertibility attack is a hostile measure to breach watermarking systems. In this paper, a novel watermarking protocol using a one-way hash function and a check of random watermarks is proposed in order to combat invertibility attacks. The described technique can be used in conjunction with any watermarking algorithm, no matter it is kept secret or made public, without resorting to a third party jury as required by some previous approaches. By introducing a set of reference sequences, segmentation of the digital information and iterative computation of watermarks, the protocol is further enhanced so that it can resist more sophisticated types of attack based on forging an illegitimate detector.