Now như the opposite problem: using an encryption algorithm to construct a oneway hash function. Như using RSA with a known key. Then process a message consisting of a sequence of blocks to as follows: Encrypt the first block, XOR the result with the second block and encrypt again, etc. Show mà this scheme is not secure by Solving the problem sau. Given a two-block message B1, B2, and the its hash
RSAH (B1, B2) = RSA (RSA (B1) + B2)
Given an arbitrary block C1, C2 compared mà choose .Thus, the hash function does not Satisfy weak collision resistance.
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