Cryptology ePrint Archive: Report 2021/292

Quantum Collision Attacks on Reduced SHA-256 and SHA-512

Akinori Hosoyamada and Yu Sasaki

Abstract: In this paper, we study dedicated quantum collision attacks on SHA-256 and SHA-512 for the first time. The attacks reach 38 and 39 steps, respectively, which significantly improve the classical attacks for 31 and 27 steps. Both attacks adopt the framework of the previous work that converts many semi-free-start collisions into a 2-block collision, and are faster than the generic attack in the cost metric of time-space tradeoff. We observe that the number of required semi-free-start collisions can be reduced in the quantum setting, which allows us to convert the previous classical 38 and 39 step semi-free-start collisions into a collision. The idea behind our attacks is simple and will also be applicable to other cryptographic hash functions.

Category / Keywords: secret-key cryptography / hash function, SHA-256, SHA-512, collision attack, quantum attack, conversion from semi-free-start collisions

Original Publication (with major differences): IACR-CRYPTO-2021

Date: received 5 Mar 2021, last revised 25 Jun 2021

Contact author: akinori hosoyamada bh at hco ntt co jp

Available format(s): PDF | BibTeX Citation

Note: Minor revision. Some errors in Section 7 are corrected. Complexity analysis is slightly changed.

Version: 20210625:091010 (All versions of this report)

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