Authors:
Maria Chroni
and
Stavros Nikolopoulos
Affiliation:
University of Ioannina, Greece
Keyword(s):
Watermarking Techniques, Text Watermarking Algorithms, PDF Documents, Self-inverting Permutations, Representations of Permutations, Embedding Algorithms, Extracting Algorithms.
Related
Ontology
Subjects/Areas/Topics:
Internet Technology
;
Web Information Systems and Technologies
;
Web Security and Privacy
Abstract:
Portable Document Format (PDF) documents are extensively used over the internet for information exchange and due to the ease of copying and distributing they are susceptible to threats like illegal copying, redistribution, and plagiarism. This work provides to web users copyright protection of their PDF documents by proposing efficient and easily implementable techniques for PDF watermarking; our techniques are based on the ideas of our recently proposed watermarking techniques for software, image, and audio, expanding thus the digital objects that can be efficiently watermarked through the use of self-inverting permutations. In particular, we present various representations of a self-inverting permutation p* namely 1D-representation, 2D-representation, and RPG-representation, and show that theses representations can be efficiently applied to PDF watermarking. Indeed, we first present an audio-based technique for marking a PDF document T by exploiting the 1D-representation of a permu
tation p*, and then, since pages of a PDF document T are 2D objects, we present an image-based algorithm for encoding p* into T by first mapping the elements of p* into a matrix A* and then using the information stored in A* to mark invisibly specific areas of PDF document T. Finally, we describe a graph-based watermarking algorithm for embedding a self-inverting permutation p* into the document structure of a PDF file T by exploiting the RPG-representation of p* and the structure of a PDF document. We have evaluated the embedding and extracting algorithms by testing them on various and different in characteristics PDF documents.
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