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I have the following homework question that im not sure about.
Alice and bob are going to use the diffie-hellman key agreement protocol to agree on a key for use in AES. Explain briefly why they would need to use digital signatures and why they cannot use Message Authentication Codes (MACs) instead.
I find the question a bit hard to understand, im aware that MACs require a shared secret key to compute the MAC so this would have to be done first but am not sure why digital signatures need to be used ?