Encoding watermark integers as self-inverting permutations

  • Authors:
  • Maria Chroni;Stavros D. Nikolopoulos

  • Affiliations:
  • University of Ioannina;University of Ioannina

  • Venue:
  • Proceedings of the 11th International Conference on Computer Systems and Technologies and Workshop for PhD Students in Computing on International Conference on Computer Systems and Technologies
  • Year:
  • 2010

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Abstract

In a software watermarking environment, several graph theoretic watermark methods use integers as watermark values, where some of these methods encode the watermark integers as reducible permutation graphs (RPG; these are reducible control-flow graphs with a maximum out-degree of two). Since there is a one-to-one correspondence between self-inverting permutations and isomorphic classes of RPGs, for encoding watermark integers most of the watermarking methods use only those permutations that are self-inverting. In this paper we present an efficient algorithm for encoding integers as self-inverting permutations. More precisely, our algorithm takes as input an integer w, computes its binary representation b1b2...bn, and then produces a self-inverting permutation π* in O(n) time. Moreover, we also present an algorithm for decoding a self-inverting permutation; our algorithm takes as input a self-inverting permutation π* produced by the encoding algorithm and returns its corresponding integer w in O(n) time, where n is the length of the input permutation.