International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: New Time-Memory Trade-Offs for Subset Sum -- Improving ISD in Theory and Practice

Andre Esser , Technology Innovation Institute
Floyd Zweydinger , Ruhr University Bochum
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Conference: EUROCRYPT 2023
Abstract: We propose new time-memory trade-offs for the random subset sum problem defined on $(a_1,\ldots,a_n,t)$ over $\Z_{2^n}$. Our trade-offs yield significant running time improvements for every fixed memory limit $M\geq2^{0.091n}$. Furthermore, we interpolate to the running times of the fastest known algorithms when memory is not limited. Technically, our design introduces a pruning strategy to the construction by Becker-Coron-Joux (BCJ) that allows for an exponentially small success probability. We compensate for this reduced probability by multiple randomized executions. Our main improvement stems from the clever reuse of parts of the computation in subsequent executions to reduce the time complexity per iteration. As an application of our construction, we derive the first non-trivial time-memory trade-offs for Information Set Decoding (ISD) algorithms. Our new algorithms improve on previous (implicit) trade-offs asymptotically as well as practically. Moreover, our optimized implementation also improves on \emph{running time}, due to reduced memory access costs. We demonstrate this by obtaining a new record computation in decoding quasi-cyclic codes (QC-3138). Using our newly obtained data points we then extrapolate the hardness of suggested parameter sets for the NIST PQC fourth round candidates McEliece, BIKE and HQC, lowering previous estimates by up to 6 bits and further increasing their reliability.
  title={New Time-Memory Trade-Offs for Subset Sum -- Improving ISD in Theory and Practice},
  author={Andre Esser and Floyd Zweydinger},