Cryptanalysis of White-Box DES Implementations with Arbitrary External Encodings

Abstract. At DRM 2002, Chow et al. [4] presented a method for implementing the DES block cipher such that it becomes hard to extract the embedded secret key in a white-box attack context. In such a context, an attacker has full access to the implementation and its execution environment. In order to provide an extra level of security, an implementation shielded with external encodings was introduced by Chow et al. and improved by Link and Neumann [10]. In this paper, we present an algorithm to extract the secret key from such white-box DES implementations. The cryptanalysis is a differential attack on obfuscated rounds, and works regardless of the shielding external encodings that are applied. The cryptanalysis has a average time complexity of 214 and a negligible space complexity. Keywords. White-Box Cryptography, Obfuscation, DES, Data Encryption Standard, Cryptanalysis

• Type: Conference
• Year: 2007
• Where: SACRYPT
• Authors: Brecht Wyseur, Wil Michiels, Paul Gorissen, Bart Preneel
• Keywords: Chow Et, External Encodings, SACRYPT 2007, Secret Key