A tight security analysis of the FIPS-205 standard (SLH-DSA)

Dai Chi Do; Quoc Toan Nguyen; Phong Quang Trieu; Ba Danh Vu

Paper 2026/632

A tight security analysis of the FIPS-205 standard (SLH-DSA)

Dai Chi Do, Institute of Cryptography Science and Technology

Quoc Toan Nguyen, Institute of Cryptography Science and Technology

Phong Quang Trieu, Institute of Cryptography Science and Technology

Ba Danh Vu, Institute of Cryptography Science and Technology

Abstract

The SPHINCS+ framework, recently standardized by NIST as SLH-DSA (FIPS 205), is a leading stateless hash-based signature scheme for the post-quantum era. Concrete-security evaluation of SPHINCS+ faces a trade-off: tight bounds require a conjectural multi-target decisional second-preimage resistance (SM-DSPR), while fully proven bounds incur substantial looseness. In this paper, we refine the concrete security analysis of SPHINCS+ by eliminating this heuristic reliance. In our approach, we analyze the SM-openPRE and SM-PRE properties instead of relying on SM-DSPR. By utilizing a precise probabilistic simulation technique, we restrict the multi-target tightness degradation exclusively to the maximum number of practically revealed targets rather than the total theoretical targets. When applied to the SLH-DSA parameter sets, our conjecture-free approach bridges the theoretical gap, recovering up to 18 bits of classical security and 9 bits of quantum security compared to the NIST loose evaluation. Our results establish a provable bound for the practical security of SLH-DSA without relying on optimistic multi-target assumptions.

Metadata

Available format(s): PDF
Category: Public-key cryptography
Publication info: Preprint.
Keywords: hash-based signature SPHINCS+
Contact author(s): dodaichi @ hus edu vn
toannq1977 @ gmail com
phongtrieu53 @ gmail com
danhvuba @ gmail com
History: 2026-04-04: approved; 2026-04-01: received; See all versions
Short URL: https://ia.cr/2026/632
License: CC BY

BibTeX

@misc{cryptoeprint:2026/632,
      author = {Dai Chi Do and Quoc Toan Nguyen and Phong Quang Trieu and Ba Danh Vu},
      title = {A tight security analysis of the {FIPS}-205 standard ({SLH}-{DSA})},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/632},
      year = {2026},
      url = {https://eprint.iacr.org/2026/632}
}