Part 4: Explain in a couple of paragraphs how public key encryption can be used to implement a digital signature. Be sure you are very clear on when a private key is used and when a public key is used. Part 5: Generally, a digital signature involves encrypting a cryptographic hash, or digest, generated from the message. Explain why we do not encrypt the message itself. You can answer this question in one sentence. Part 6: For each of the following scenarios below, tell what type of encryption is most appropriate and in a sentence or two explain the reasoning for your choice. 1. Alice wants to send a confidential message to Bill, whom she has never met and who lives in a distant country. 2. Charlie wants to be sure that no one but he can see the financial and medical records he has stored on his computer. 3. David needs a way to check that large computer files stored on corporate servers have not been modified. 4. Eddard uses a "cloud" backup service; he wants to be sure the operators of the service cannot read his files. 5. Frank needs to send a message to George. The message need not be confidential, but George must be assured that it actually came from Frank.