LM-DAE: Low-Memory Deterministic Authenticated Encryption for 128-bit Security

Abstract

This paper proposes a new lightweight deterministic authenticated encryption (DAE) scheme providing 128-bit security. Lightweight DAE schemes are practically important because resource-restricted devices sometimes cannot afford to manage a nonce properly. For this purpose, we first design a new mode LM-DAE that has a minimal state size and uses a tweakable block cipher (TBC). The design can be implemented with low memory and is advantageous in threshold implementations (TI) as a side-channel attack countermeasure. LM-DAE further reduces the implementation cost by eliminating the inverse tweak schedule needed in the previous TBC-based DAE modes. LM-DAE is proven to be indistinguishable from an ideal DAE up to the O(2ⁿ) query complexity for the block size n. To achieve 128-bit security, an underlying TBC must handle a 128-bit block, 128-bit key, and 128+4-bit tweak, where the 4-bit tweak comes from the domain separation. To satisfy this requirement, we extend SKINNY-128-256 with an additional 4-bit tweak, by applying the elastic-tweak proposed by Chakraborti et al. We evaluate the hardware performances of the proposed scheme with and without TI. Our LM-DAE implementation achieves 3,717 gates, roughly 15% fewer than state-of-the-art nonce-based schemes, thanks to removing the inverse tweak schedule.