COMP547B Homework set #3



Due Monday March 12th, 2018, 23:59:59

Exercises (from Katz and Lindell’s book)

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Homemade Exercise: non Pseudo-Random Permutation Let F be a pseudo-random family of functions. Let k1 and k2 be two independent random keys. Prove that πk₁k₂(x1,x2) := ⟨ x1⊕Fk₁(x2) , x2⊕Fk₂( x1⊕Fk₁(x2) ) ⟩ is not a pseudo-random permutation family.

Let F be a pseudo-random family of functions. Let k1, k2 and k3 be three independent random keys. Prove that πk₁k₂k₃(x1,x2) := ⟨ x2⊕Fk₂( x1⊕Fk₁(x2) ) , x1⊕Fk₁(x2)⊕Fk₃( x2⊕Fk₂( x1⊕Fk₁(x2) ) ) ⟩

is not a strong pseudo-random permutation family.

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