Paper 2026/824

Better Usability: Leakage-Resistant AEADs from Single-length Blockciphers

Abstract

Existing leakage-resistant AEADs are rarely compatible with {\it single-length key} blockciphers (BCs), i.e., blockciphers with key-length equaling block-length. We present UEDTDM and UEDTMX, two single-length key BC-based leakage-resistant AEAD constructions. Both of them are one-pass with rate $1/4$, use ``partially fixed-key'' BC to maximize {\it practical} efficiency, and gather the strongest level of Grade-3 leakage-resistance (a terminology due to Bellizia et al., CRYPTO 2020) with a satisfactory black-box security bound. Their concrete security bounds are comparable with state-of-the-art construction TEDT of Berti et al. (TCHES 2020). Assuming that the underlying MJH hash has $(n-2\log_2n)$-bit collision security, they achieve $(n-2\log_2n)$-bit CIML2 and black-box CCA security, and approximately $n/2$-bit CCAmL2 security. Even more, they achieve birthday-bound context-committing security. To prove these claims, we introduce a framework UEDT that generalizes and expands the usability of the EDT construction of Berti et al. (ToSC 2017), prove unified provable security results, and then derive concrete bounds for the two instances, UEDTDM and UEDTMX. This framework may be of independent interest. We also demonstrate the performance advantage of our algorithms, especially in software. On x86 architectures where the AES-NI instructions are supported, our algorithms are twice faster than the closest competitor; LR-BC-3 (Bronchain et al., TCHES 2021). In addition, the ability to use the efficient MJH hash function and to reduce the amount of rekeying makes the algorithms faster across multiple platforms, as well.

Note: The full version of the paper, including CCAmL2 related definitions and formal proofs.