Let F be a pseudorandom function, and G a pseudorandom generator with expansion factor n $+1.$ Assume

two definitions of an encryption scheme as bellow, and for each one state if the scheme is a$)$ secure against an

eavesdropper, and b$)$ CPA$-$secure$.$ In each case, the shared key is a random k in $\{0,1\}$

n$.$

$1.$ To encrypt m in $\{0,1\}$

n$+1$ choose uniform r in $\{0,1\}$

n and ouput the ciphtertext $$r$,$ G$($r$)$ m$.$

$2.$ To encrypt m in $\{0,1\}$

n$,$ output the ciphertext m $$ Fk$(0$n$).$