Watermarking Essential Data Structures for Copyright Protection

Software watermarking is a new research area that aims at providing copyright protection for commercial software. It minimizes software piracy by hiding copyright signatures inside the program code or its runtime state. Prior proposals hide the watermarks in dummy data structures, e.g., linked lists and graphs that are created during the execution of the hosting software for this reason. This makes it vulnerable to subtractive attacks, because the attacker can remove the data structure without altering the operation or the semantic of the software program. In this regard, we argue that hiding watermarks in one or more data structures that are used by the program would make the watermark more robust because removing the watermark would alter the semantic and the operations of the underlying software. However, the challenge is that the insertion of the watermark should have a minimal effect on the operations and performance of the data structure. This paper proposes a novel method for watermarking R-tree data structure and its variants. The proposed watermarking scheme takes advantage of the redundancy in the way the entries within R-tree nodes are ordered. R-trees do not require ordering the entries in a specific way. Node entries are re-ordered in a way to map the watermark. The new order is calculated relative to a “secret” initial order, known only to the software owner, using a technique based on a numbering system that uses variable radix and factorial base. The addition of the watermark in the R-tree data structure neither affects the performance nor increases the size of the R-tree. The paper provides a threat model and analysis to show that the watermarked R-trees are robust and can withstand various types of attacks.