2026-07-22T17:01:19Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:20716 2024-08-29T08:52:52Z ddc:004 open_access

Inverting Step-Reduced SHA-1 and MD5 by Parameterized SAT Solvers Zaikin, Oleg cryptographic hash function MD5 SHA-1 preimage attack SAT Cube-and-Conquer MD5 and SHA-1 are fundamental cryptographic hash functions proposed in 1990s. Given a message of arbitrary finite size, MD5 produces a 128-bit hash in 64 steps, while SHA-1 produces a 160-bit hash in 80 steps. It is computationally infeasible to invert MD5 and SHA-1, i.e. to find a message given a hash. In 2012, 28-step MD5 and 23-step SHA-1 were inverted by CDCL solvers, yet no progress has been made since then. The present paper proposes to construct 31 intermediate inverse problems for any pair of MD5 or SHA-1 steps (i,i+1), such that the first problem is very close to inverting i steps, while the 31st one is almost inverting i+1 steps. We constructed SAT encodings of intermediate problems for MD5 and SHA-1, and tuned a CDCL solver on the simplest of them. Then the tuned solver was used to design a parallel Cube-and-Conquer solver which for the first time inverted 29-step MD5 and 24-step SHA-1. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Oleg Zaikin 2024 Is Part Of LIPIcs, Volume 307, 30th International Conference on Principles and Practice of Constraint Programming (CP 2024) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.CP.2024.31 urn:nbn:de:0030-drops-207165 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CP.2024.31 eng https://creativecommons.org/licenses/by/4.0/legalcode