Paper 2025/1314

THF: Designing Low-Latency Tweakable Block Ciphers

Abstract

We introduce the $\textsf{Three-Hash Framework}$ ($\textsf{THF}$), a new instantiation of the $\textsf{LRW+}$ paradigm that employs three hash functions to process tweak inputs. We prove that $\textsf{THF}$ achieves beyond-birthday-bound security under standard assumptions. By extending the general practical cryptanalysis framework to the multiple-tweak setting, we further demonstrate that $\textsf{THF}$ offers balanced resistance to both single- and multiple-tweak attacks, thereby enabling the potential for lower latency compared to existing constructions. Building on this framework, we design $\texttt{Blink}$, a family of tweakable block ciphers optimized for ultra-low latency. $\texttt{Blink}$ features logarithmic-depth Toeplitz-based hashing, which ensures efficient diffusion and scalability with varying tweak lengths. Our cryptanalysis shows that $\texttt{Blink}$ achieves strong security with fewer rounds, while hardware evaluations confirm its superior latency performance. Notably, $\texttt{Blink}$ maintains comparable latency even when the tweak length is doubled, underscoring the scalability advantage of $\textsf{THF}$.