Welcome to the resource topic for 2023/1808
Title:
Small Stretch Problem of the DCT Scheme and How to Fix it
Authors: Yuchao Chen, Tingting Guo, Lei Hu, Lina Shang, Shuping Mao, Peng Wang
Abstract:DCT is a beyond-birthday-bound~(BBB) deterministic authenticated encryption~(DAE) mode proposed by Forler et al. in ACISP 2016, ensuring integrity by redundancy. The instantiation scheme of DCT employs the BRW polynomial, which is more efficient than the usual polynomial function in GCM by reducing half of the multiplication operations. However, we show that DCT suffers from a small stretch problem similar to GCM. When the stretch length \tau is small, choosing a special m-block message, we can reduce the number of queries required by a successful forgery to \mathcal{O}(2^{\tau}/m). We emphasize that this attack efficiently balances space and time complexity, but does not contradict the security bounds of DCT. Finally, we propose an improved scheme named Robust DCT~(RDCT) with a minor change to DCT, which improves the security when \tau is small and makes it resist the above attack.
ePrint: https://eprint.iacr.org/2023/1808
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