Jens Palsberg, Sowmya Krishnaswamy, Minseok Kwon, Di Ma & Qiuyun Shao
Purdue University
USA

There are at least four U.S. patents on software watermarking, and an idea for further advancing the state of the art was presented in 1999 by Collberg and Thomborsen. 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 reports on practical experience with this technique.

We have implemented and experimented with a watermarking system for Java based on the ideas of Collberg and Thomborsen. Our experiments show that watermarking 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 implementation is not designed to resists all possible attacks; to do that it should be combined with other protection techniques such as obfuscation and tamperproofing.

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