Towards Imperceptible Natural Language Watermarking for German

Watermarking natural language is still a challenge in the domain of digital watermarking. Here, only the textual information must be used as a cover. No format changes or modified illustrations are accepted. Still, natural language watermarking (NLW) has some important applications, especially in leakage tracking, where a small set of individually marked copies of a confidently text is distributed. Properties of watermarking schemes such as imperceptibility, blindness or adaptability to non-English languages are of importance here. In order to address these three simultaneously, we present a blind NLW scheme, consisting of four independent embedding methods, which operate on the phonetical, morphological, lexical and syntactical layer of German texts. An evaluation based on 1,645 assessments provided by 131 test persons reveals promising results.