In software protection we typically have to deal with the white-box attack model. In this model an attacker is assumed to have full access to the software and full control over its execution. The goal of white-box cryptography is to implement cryptographic algorithms in software such that it is hard for an attacker to extract the key by a white-box attack. Chow et al. present white-box implementations for AES and DES. Based on their ideas, white-box implementations can be derived for other block ciphers as well. In the white-box implementations the key of the underlying block cipher is expanded from several bytes to a collection of lookup tables with a total size in the order of hundreds of kilobytes. In this paper we present a technique that uses a white-box implementation to make software tamper resistant. The technique interprets the binary of software code as lookup tables, which are next incorporated into the collection of lookup tables of a white-box implementation. This makes the code tamper resistant as the dual interpretation implies that a change in the code results in an unintentional change in the white-box implementation. We also indicate in the paper that it is difficult for an attacker to make modifications to the white-box implementation such that its original operation is restored.

We derive the guaranteed throughput of a multizone disk that repeatedly handles batches of n requests of constant size. Using this guaranteed throughput in the design of multimedia systems, one can admit more streams or get smaller buffer requirements and guaranteed response times than when an existing lower bound is used. We consider the case that nothing can be assumed about the location of the requests on the disk. Furthermore, we assume that successive batches are handled one after the other, where the n requests in a batch are retrieved using a SCAN-based sweep strategy. We show that we only have to consider two successive batches to determine the guaranteed throughput. Using this, we can compute the guaranteed throughput by determining a maximum-weighted path in a directed acyclic graph in O(z/sub max//sup 3/n/sup 2/) time, where z/sub max/ is the number of zones of the disk.