On the effectiveness of meta-detection for countering oracle attacks in watermarking
We evaluate the performance of smart metadetection as a way to combat oracle attacks in watermarking. In a recent work, we have shown that few queries are sufficient for a simple metadetector (namely, a metadetector based on the closeness of queries to the watermark detection boundary) to detect an oracle attack. A limitation of our prior analysis is the assumption that all the queries correspond to either honest users or malicious ones. In this paper, we address a more realistic scenario in which honest queries are interspersed with queries derived from an oracle attack. By focusing on this more general situation, we evaluate the performance of the metadetection and derive conditions under which powerful testing is possible.