Date Added: Sep 2012
In this paper, the authors provide a corrected and generalized version of the scheme presented at SOFSEM'2012 in their paper "Optimizing Segment Based Document Protection" (SOFSEM 2012: Theory and Practice of Computer Science, LNCS 7147, pp. 566-575). They develop techniques for protecting documents with restricted access rights. In these documents so called segments are encrypted. Different segments may be encrypted with different keys so that different user may be given different access rights. Hierarchy of access rights is represented by means of a directed acyclic access graph. The segments are encrypted with keys - where each key corresponds to one node in the access graph.