Let F be a pseudorandom function and G be a pseudorandom generator with expansion factor ℓ(n)… 1 answer below »

Let F be a pseudorandom function and G be a pseudorandom generator with expansion factor ℓ(n) = n+ 1. For each of the following encryption schemes, state whether the scheme has indistinguishable encryptions in the presence of an eavesdropper and whether it is CPA-secure. (In each case, the shared key is a uniform k ∈ {0, 1}n.) Explain your answer.

(a) To encrypt m ∈ {0, 1}n+1, choose uniform r ∈ {0, 1} n and output the ciphertext hr, G(r) ⊕ mi.

(b) To encrypt m ∈ {0, 1}n, output the ciphertext m ⊕ Fk(0n).

(c) To encrypt m ∈ {0, 1}2n, parse m as m1||m2 with |m1| = |m2|, then choose uniform r ∈ {0, 1}n and send hr, m1⊕Fk(r), m2⊕Fk(r+1)}.

 

 

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