On the Performance Analysis of SPHINCS⁺ Verification

Abstract

SPHINCS⁺, an updated version of SPHINCS, is a post-quantum hash-based signature scheme submitted to the NIST post-quantum cryptography standardization project. To evaluate its performance, SPHINCS⁺ gives the theoretical number of function calls and the actual runtime of a reference implementation. We show that the theoretical number of function calls for SPHINCS⁺ verification is inconsistent with the runtime and then present the correct number of function calls.