This works studies the use of the AES block-cipher for Picnic-style signatures, which work in the multiparty-computation-in-the-head model. It applies advancements to arithmetic circuits for the computation of the AES S-box over multiparty computation in the preprocessing model to obtain an improvement of signature sizes of 40\% on average compared to using binary circuits for AES-128, AES-192 and AES-256 in combination with previous techniques. This work also discusses other methods for the computation of the S-box and provides insights into the reaches and limits of the multiparty-computation-in-the-head paradigm.