CryptoDB
Optimally Secure Tweakable Block Ciphers with a Large Tweak from n-bit Block Ciphers
| Authors: |
|
|---|---|
| Download: | |
| Abstract: | We consider the design of a tweakable block cipher from a block cipher whose inputs and outputs are of size n bits. The main goal is to achieve 2n security with a large tweak (i.e., more than n bits). Previously, Mennink at FSE’15 and Wang et al. at Asiacrypt’16 proposed constructions that can achieve 2n security. Yet, these constructions can have a tweak size up to n-bit only. As evident from recent research, a tweakable block cipher with a large tweak is generally helpful as a building block for modes of operation, typical applications including MACs, authenticated encryption, leakage-resistant cryptography and full-disk encryption.We begin with how to design a tweakable block cipher with 2n-bit tweak and n-bit security from two block cipher calls. For this purpose, we do an exhaustive search for tweakable block ciphers with 2n-bit tweaks from two block cipher calls, and show that all of them suffer from birthday-bound attacks. Next, we investigate the possibility to design a tweakable block cipher with 2n-bit tweak and n-bit security from three block cipher calls. We start with some conditions to build such a tweakable block cipher and propose a natural construction, called G̃1, that likely meets them. After inspection, we find a weakness in G̃1 which leads to a birthday-bound attack. Based on G̃1, we then propose another construction, called G̃2, that can avoid this weakness. We finally prove that G̃2 can achieve n-bit security with 2n-bit tweak. |
BibTeX
@article{tosc-2023-33308,
title={Optimally Secure Tweakable Block Ciphers with a Large Tweak from n-bit Block Ciphers},
journal={IACR Transactions on Symmetric Cryptology},
publisher={Ruhr-Universität Bochum},
volume={2023, Issue 2},
pages={47-68},
url={https://tosc.iacr.org/index.php/ToSC/article/view/10977},
doi={10.46586/tosc.v2023.i2.47-68},
author={Yaobin Shen and François-Xavier Standaert},
year=2023
}