Nagoya University · Computer Science
Professor Akinori Hosoyamada's research lab specializes in quantum cryptanalysis and post-quantum security of symmetric-key primitives. The lab focuses on analyzing the security of widely used cryptographic schemes—such as block ciphers, hash functions, and authenticated encryption—under quantum computing threats, particularly superposition queries. Key research directions include quantum key-recovery attacks, distinguishing attacks on Feistel structures and permutations, and the design of quantum-secure constructions in the idealized model. The lab also investigates the limitations and improvements of existing cryptanalytic techniques like limited birthday distinguishers and meet-in-the-middle attacks in the quantum setting.
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It has been said that security of symmetric key schemes is not so much affected by quantum computers, compared to public key schemes. However, recent works revealed that, in some specific situations, symmetric key schemes are also broken in polynomial time by adversaries with quantum computers. These works contain a quantum distinguishing attack on 3-round Feistel ciphers and a quantum key recovery attack on the Even-Mansour cipher by Kuwakado and Morii, in addition to the quantum forgery attack
Recent results on quantum cryptanalysis show that some symmetric key schemes can be broken in polynomial time even if they are proven to be secure in the classical setting. Liskov, Rivest, and Wagner showed that secure tweakable block ciphers can be constructed from secure block ciphers in the classical setting. However, Kaplan et al. showed that their scheme can be broken by polynomial time quantum superposition attacks, even if underlying block ciphers are quantum-secure. Since then, it remain
Rocca is an authenticated encryption with associated data scheme for beyond 5G/6G systems. It was proposed at FSE 2022/ToSC 2021(2), and the designers make a security claim of achieving 256-bit security against key-recovery and distinguishing attacks, and 128-bit security against forgery attacks (the security claim regarding distinguishing attacks was subsequently weakened in the full version in ePrint 2022/116). A notable aspect of the claim is the gap between the privacy and authenticity secur
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