Paper 2026/2142

$\mathsf{PRAWNS}$: Threshold Hash-Based Signatures from Threshold PRFs

Abstract

We propose an efficient threshold mechanism that is well suited for certain hash-based signatures. Our proposal has a number of compelling features: • The final signature assembled from a quorum of signature shares has the same format as a non-threshold hash-based signature. In particular, the verifier is unaware that the signer is thresholdized. Moreover, we can add and remove parties and change the threshold without changing the public key. • Our framework can be used to thresholdize one-time signature schemes, such as Winternitz, and a few-time schemes, such as XMSS, HORS, FORS, and PORS+FP. • The public key and the signatures reveal nothing about the number of parties $n$ or the threshold $t$. • An instantiation of our framework scales well to a large number of parties $n$ and a large threshold $t$. One limitation of the framework is that it does not support an efficient distributed key generation protocol (DKG). Another limitation is that the framework does not directly apply to SLH-DSA. It is primarily designed for the Winternitz, XMSS, and FORS schemes.