HOP-1 and HOP-2: New Re-keying Schemes for Symmetric Ciphers

Re-keying is one of the most effective techniques to protect symmetric ciphers against side-channel attacks. Since its introduction, numerous re-keying schemes have been developed. This paper proposes two new index-based re-keying schemes, HOP-1 and HOP-2, which are variants of Kocher's re-keying scheme. Specifically, through tree-based analysis of Kocher's re-keying scheme, we identify strategies to minimize key repetition in Kocher's approach. We compare HOP-1 and HOP-2 with existing re-keying schemes and evaluate their application to two leakage-resilient authenticated encryption schemes, highlighting their effectiveness relative to these other re-keying schemes.