You must give a word count for any question with a maximum word limit.

This question tests your understanding of Block 2 Part 7 (Authentication and introduction to hashing) and Block 3 Part 3.

• a.Consider each of the following situations in turn. For each one, state whether hashing and/or encryption would have an appropriate role and, if they do, explain why they would be used. Write no more than 100 words in total. You may find it useful to do a brief web search for the final scenario, but you should only spend a few minutes on it; an in-depth answer is not expected, and no reference is required.
  • Protecting a private voice call in transit, made using a telecommunication application.
  • Storing passwords in a computer system to allow verification of logon credentials.
  • The communication between the card and the contactless terminal when making a payment using a contactless point of sale (POS) terminal.
• b.Alice has been contacted by Bob, who is seeking her help. He has two files with identical MD5 hashes and does not understand how this could happen. One file is meant to be a download to update his operating system, which he obtained from the manufacturer of his computer. The other was sent to him in an email from a stranger and is an unknown executable file. He is interested to see what the second file does.

He asks Alice how it is possible that two files have the same hash value and if it would be ok for him to try out the unknown executable file. What information and advice should Alice give? (Word limit: 100 words)

• c.Asymmetric encryption is slower than symmetric encryption. However, it has one important advantage. Explain why asymmetric encryption is slower and what its advantage is.