Paper 2026/938 Original: eprint.iacr.org/2026/938 ↗

Storing Less in-the-Head: An Area-Efficient Hardware Architecture for SDitH-v2

Abstract

In 2022, the National Institute of Standards and Technology (NIST) initiated a second call for post-quantum digital signature proposals to broaden algorithmic diversity beyond the already standardized schemes based on structured lattices and hashes. While five out of the 14 second-round entries were built on the MPC-in-the-Head paradigm, only two advanced into the recently announced third round. Despite their theoretical appeal, available results on their implementation costs imply a reduced applicability to resource-constrained embedded devices. In this work we analyze one of the remaining candidates, the revised second version of the Syndrome Decoding in the Head (SDitH) signature scheme based on the VOLE-in-the-Head framework, and showcase that these issues are not inherent to the family of algorithms. We propose an area-efficient hardware design including highly optimized variants of both Batch Line Commitment (BLC) and Polynomial Interactive Oracle Proof (PIOP) routines. As a result, we reduce memory requirements by a factor of 22 to 52 compared to the approach of the reference implementation and by a factor of 40 to 88 compared to the previous hardware implementation of SDitH-v1, while still achieving competitive runtimes. To the best of our knowledge, this yields the most compact hardware implementation of any MPCitH or code-based signature primitive, with our algorithmic improvements directly transferable to software designs. During our analysis, we additionally determined nine significant discrepancies between specification and reference implementation of SDitH-v2, with a subset breaking test vector compatibility. Beyond addressing these issues, we suggest specification changes to further reduce resource usage on embedded targets without compromising security assumptions.