$\forall$$T$:(Id$\rightarrow$Type), ${\it tab}$:secret{-}table($T$), $k_{1}$, $k_{2}$:$\mathbb{N}$+Atom1. st{-}key{-}match(${\it tab}$;$k_{1}$;$k_{2}$) $\in$ $\mathbb{B}$