A method of text watermarking using presuppositions

Vybornova, Olga [UCL] Macq, Benoît [UCL]

We propose a method for watermarking texts of arbitrary length using natural-language semantic structures. For the key of our approach we use the linguistic semantic phenomenon of presuppositions. Presupposition is the implicit information considered as well-known or which readers of the text are supposed to treat as well-known; this information is a semantic component of certain linguistic expressions (lexical items and syntactical constructions called presupposition triggers). The same sentence can be used with or without presupposition, or with a different presupposition trigger, provided that all the relations between subjects, objects and other discourse referents are preserved - such transformations will not change the meaning of the sentence. We define the distinct rules for presupposition identification for each trigger and regular transformation rules for using/non-using the presupposition in a given sentence (one bit per sentence in this case). Isolated sentences can carry the proposed watermarks. However, the longer is the text, the more efficient is the watermark. The proposed approach is resilient to main types of random transformations, like passivization, topicalization, extraposition, preposing, etc. The web of resolved presupposed information in the text will hold the watermark of the text (e.g. integrity watermark, or prove of ownership), introducing "secret ordering" into the text structure to make it resilient to "data loss" attacks and "data altering" attacks.