Switching Blindings with a View Towards IDEA

Cryptographic algorithms implemented on smart-cards must be protected against side-channel attacks. Some encryption schemes and hash functions like IDEA, RC6, MD5, SHA-1 alternate various arithmetic and boolean operations, each of them requiring a different kind of blinding. Hence the maskings have to be changed frequently. How to switch reasonably between standard arithmetic masking and boolean masking was shown in [2], [3], [5] and [9]. In this paper we propose more space-efficient table-based conversion methods. Furthermore, we deal with some non-standard arithmetic operations, namely arithmetic modulo 2 +1 for some k ∈ IN and a special multiplication used by IDEA.