An encryption scheme for limited k-time access to digital media

Digital content needs to be protected against piracy yet readily accessible to the user. Furthermore, the digital content may come with a proper use license which concerns how the content may be used by the purchaser/user. In this paper we describe a method fir protecting digital content from piracy where the "proper use license" is a k-time license. This license says that the digital content may be used/accessed at most k times. To protect the digital content from piracy or misuse we provide an application that will decrypt and re-encrypt the content according to our k-time encryption scheme. Since secret keys must reside on the user\´s system, we heighten the level of security by hiding secret keys in the heuristic solutions of NP-hard problems and by extending the security with some other well known methods.