Tuning the Winternitz hash-based digital signature scheme

It is known that, for a given set of parameters, the overall complexity for generating and verifying a signature is constant and independent of the document being signed, for the Winternitz one-time signature scheme (WOTS). These costs are due to the number of chained iterations of a function f. However, the cost for signature generation alone is slightly different from signature verification, and these depend directly on the document. We introduce a new variant for WOTS, which allows the adjustment of these costs, i.e. increase the overall signature generation time in favor of faster verification or vice-versa. We decrease the number of iterations of f by up to half, with regards to the verification procedure, for commonly used values of the Winternitz parameter w. Additionally, our experiments show that these proposals have substantial impact on Merkle-based signature schemes, such as XMSS.