Question $5(8$ points$)$:

Consider a cryptosystem that encrypts a message minM,$M=\{0,1,2\},$ using a shared key $k$ that is

uniformly chosen from the key space kinK,$K=\{0,1,2,3\}.$

$c=$Enc$(k,m)=m+k(mod3),$ and

$m=$Dec$(k,c)=c-k(mod3)$

Is this encryption scheme perfectly secret? Explain your answer.