Text Watermarking against Ownership Rights Violation

The paper describes an approach to natural language watermarking and hashing based on semantic structures. In our method we are interested in the linguistic semantic phenomenon of presupposition. Presupposition is implicit information that is taken for granted by the reader and establishes common ground between the author´s and reader´s situational knowledge; it is a semantic component of certain linguistic expressions (lexical items and syntactic constructions called presupposition triggers, 100 in total). The same sentence can be used with or without presupposition, provided that all the relations between discourse referents are preserved. 3 types of transformations are employed: triggers removal, triggers synonymic replacements and introducing triggers where there were none. The key is formed as a hash table containing information about the original text, the number of transformed sentences and the triggers on which the transformations were based. This method is resilient against data loss and data altering attacks.