Better approximation for signature size
Better approximation for signature size

Relates to #98.

Yubico/yubico-piv-tool,Yubico/yubico-piv-tool,akgood/yubico-piv-tool,Yubico/yubico-piv-tool,akgood/yubico-piv-tool,akgood/yubico-piv-tool,akgood/yubico-piv-tool