Colliding Message Pairs for 23 and 24-step SHA-512
Somitra Kumar Sanadhya, Palash Sarkar

TL;DR
This paper presents new collision attacks on 23 and 24-step SHA-512, providing the first colliding message pair for 24-step and significantly reducing attack complexities.
Contribution
It introduces the first colliding message pair for 24-step SHA-512 and improves attack complexities using a differential path from prior research.
Findings
First colliding message pair for 24-step SHA-512
Reduced attack complexities to $2^{16.5}$ and $2^{34.5}$ calls
Attacks based on differential path by Sanadhya and Sarkar
Abstract
Recently, Indesteege et al. [1] had described attacks against 23 and 24-step SHA-512 at SAC '08. Their attacks are based on the differential path by Nikolic and Biryukov [2]. The reported complexities are and calls to the respective step reduced SHA-512 hash function. They provided colliding message pairs for 23-step SHA-512 but did not provide a colliding message pair for 24-step SHA-512. In this note we provide a colliding message pair for 23-step SHA-512 and the first colliding message pair for 24-step SHA-512. Our attacks use the differential path first described by Sanadhya and Sarkar at ACISP '08 [3]. The complexities of our attacks are and calls to the respective step reduced SHA-512 hash function. Complete details of the attacks will be provided in an extended version of this note.
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Taxonomy
TopicsCryptographic Implementations and Security · Coding theory and cryptography
