11.2 a. Consider the Davies and Price hash code scheme described in Section 11.4 and assume that DES is used as the encryption algorithm: Hi = Hi-1⊕ E(Mi, Hi-1) Recall the complementarity property of DES (Problem 3.14): If Y = E(K, X), then Y′ = E(K′, X′). Use this property to show how a message consisting of blocks M1, M2,c, MN can be altered without altering its hash code. b. Show that a similar attack will succeed against the scheme proposed in [MEYE88]: Hi = Mi⊕ E(Hi-1, Mi) | |
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