CPSC557 Assignment 2 Answer Key
نویسنده
چکیده
Answer Consider the case where the initial value is H0 and M ′ = M1‖M2‖ . . . ‖MN . Let the notation H1(M1, I) denote the first iteration of the hash function using message block M1 and initial value I. H1(M1, H0) = EM1(H0)⊕H0 H1(M1, H0) = EM1(H0)⊕H0 by complementary Property of DES H1(M1, H0) = EM1(H0)⊕H0 = H1(M1,H0) A⊕B = A⊕B ∀A,B Thus H1(H0,M1) yields the same result as H1(H0,M1). In addition, for i = 2 to N the same Hi are produced for H(M,H0) and H(M ′, H0) because H1 is the same and M & M ′ are identical after the first block. Thus they produce the same hash HN . Therefore M,H0 and M ,H0 have the same hash code (i.e., a weak collision has been produced).
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