Improving the Security and Efficiency of Block Ciphers based on LS-Designs

Abstract : LS-designs are a family of bitslice ciphers aiming at efficient masked implementations against side-channel analysis. This paper discusses their security against invariant subspace attacks, and describes an alternative family of eXtended LS-designs (XLS-designs), that enables additional options to prevent such attacks. LS-and XLS-designs provide a large family of ciphers from which efficient implementations can be obtained, possibly enhanced with countermeasures against physical attacks. We argue that they are interesting primitives in order to discuss the general question of " how simple can block ciphers be? " .