Let Gen, Enc, Dec$)$ be an encryption scheme that has indistinguishable encryptions

against an eavesdropper. Prove that the following encryption scheme is also secure against

an eavesdropper.

$En{c}_k^{\text{'}}(m)\frac{?}{b}=ar(En{c}_k(m))$

The following questions are meant to guide you through the proof. If you feel that you do

not need them, you can just provide the full proof at the end.