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.

The Even-Goldreich-Micali framework is a generic method for constructing secure digital signature schemes from weaker signature schemes and one-time signature schemes. Several variations are known due to properties demanded on the underlying building blocks. It is in particular interesting when the underlying signature scheme is a so-called F-signature scheme that admits different message spaces for signing and verification. In this paper we overview these variations in the literature and add a new one to the bucket.