What is the benefit of HMAC over simple constructions such as appending the shared secret key (i.e., H(m||K) where "m" is the message and "K" is a shared secret key)?

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HMAC supports more hash functions (e.g., MD5, SHA1)

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H(m||K) is vulnerable to a length-extension attack

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It is faster

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The simple construct H(m||K) allows an attacker to pre-compute message pairs for a birthday collision - HMAC does not

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What is the benefit of HMAC over simple constructions such as appending the shar...

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