a. Barack often sends funny jokes to Hillary. He does not care about confidentia

Question

a. Barack often sends funny jokes to Hillary. He does not care about confidentiality of these messages but wants to get credit for the jokes and prevent Bill from claiming authorship of or modifying them. How can this be achieved using public-key cryptography? b. As public-key cryptography is computationally intensive and drains the battery of Barack's device, he comes up with an alternative approach. First, he shares a secret key k with Hillary but not with Bill. Next, together with a joke x, he sends over the value d = h x), where h is a cryptographic hash function. Does value d provide assurance to Hillary that Barack is the author of x and that x was not modified by Bill? Justify your answer

Explanation / Answer

a. Cryptography provides confidentiality, integrity & authenticity is mainly used to protect any information that is transmitted between networks.

To Prevent bill from taking authorship of the jokes that Barack sends to Hillary, the below steps must be followed:

b. The computed value d is the Message Authentication Code (MAC). This mainly gives Hillary the assurance that Barack himself is the author of the jokes.

The Message Authentication Code is calculated based on the joke x. Since Cryptographic Hash functions are one-way, it is not easy for Bill to extract the key k from d. Even if Bill modifies the joke, it is impossible for Bill to compute the Message Authentication Code. Therefors, Hillary can be assured that the joke was not modified by Bill.

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