Blind Side Channel on the Elephant LFSR

Abstract

: Elephant is a finalist to the NIST lightweight cryptography competition. In this paper, the first theoretical blind side channel attack against the authenticated encryption algorithm Elephant is presented. More precisely, we are targetting the LFSR-based counter used internally. LFSRs are classic functions used in symmetric cryptography. In the case of Elephant, retrieving the initial state of the LFSR is equivalent to retrieving the encryption key. The paper ends by the study of different ways to tweak the design of Elephant to mitigate our attack.