Experience with software watermarking

There are at least four U.S. patents on software wa-termarking, and an idea for further advancing the state of the art was presented in 1999 by Collberg and Thom-borsen. The new idea is to embed a watermark in dynamic data structures, thereby protecting against many program-transformation attacks. Until now there have been no re-ports on practical experience with this technique. We have implemented and experimented with a water-marking system for Java based on the ideas of Collberg and Thomborsen. Our experiments show that watermark-ing can be done efficiently with moderate increases in code size, execution times, and heap-space usage, while making the watermarked code resilient to a variety of program-transformation attacks. For a particular representation of watermarks, the time to retrieve a watermark is on the order of one minute per megabyte of heap space. Our implemen-tation is not designed to resists all possible attacks; to do that it should be combined with other protection techniques such as obfuscation and tamperproofing