5.3. Key Exchange

Consider the scenario wherein two parties Alice and Bob want to share a secret information (say, a DES key for future correspondence), but it is not possible to communicate this secret by personal contact or by conversing over a secure channel. In other words, Alice and Bob want to arrive at a common secret value by communicating over a public (and hence insecure) channel. A key-exchange or a key-agreement protocol allows Alice and Bob to do so. The protocol should be such that an eavesdropper listening to the conversation between Alice and Bob cannot compute the secret value in feasible time.

Public-key technology is used to design a key-exchange protocol in the following way. Alice generates a key pair (eA, dA) and sends ...

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