Cryptanalysis of a Generic Class of White-Box Implementations

Abstract

A white-box implementation of a block cipher is a software implementation from which it is difficult for an attacker to extract the cryptographic key. Chow et al. published white-box implementations for AES and DES. These implementations are based on ideas that can be used to derive white-box implementations for other block ciphers as well. In particular, the ideas can be used to derive a white-box implementation for any substitution linear-transformation (SLT) cipher. Although the white-box implementations of AES and DES have been cryptanalyzed, the cryptanalyses published use typical properties of AES and DES. It is therefore an open question whether an SLT cipher exists for which the techniques of Chow et al. result in a secure white-box implementation. In this paper we largely settle this question by presenting an algorithm that is able to extract the key from such an implementation under a mild condition on the diffusion matrix. The condition is, for instance, satisfied by all MDS matrices. Our result can serve as a basis to design block ciphers and to develop white-box techniques that result in secure white-box implementations.