Ciphers. Consider a cipher such that for each secret key $\{0,1{\}}^n$ the resulting function $E_k$ is a randomly chosen bijection $E_k$:$\{0,1\}\{0,1{\}}^n.$ Can

such a cipher be implemented efficiently in a real$-$world application, i$.$e$.,$ in time and space polynomial in $n?$

a$)$ No

b$)$ Yes