Question: Let E {0, 1} {0,1} {0,1} be a secure blockcipher. Consider the following deterministic MAC scheme ({0, 1), T, V) with the message space

Let E {0, 1} {0,1}" {0,1}" be a secure blockcipher. Consider the following deterministic MAC scheme ({0, 1), T, V) with the message space of messages longer than n bits. The tagging algorithm T is defined as: T(K, M) = E(K, M) || M where M is the first n bits of M and M is the rest. The verification algorithm just re-computes the tagging algorithm. Prove that this MAC is not UF-CMA.

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