Imperfect variant of one$-$time pad$]$ Consider a variant of the one$-$time pad with

the key space K $=\{0,1\}$n $\backslash 0$n $,$ i$.$e$.,$ the key space consists of all the n$-$bit strings except for

the all$-$zero string $($and the message space is unchanged: M $=\{0,1\}$n $).$