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  1. • What are the two main advantages and two main limitations of public key encryption compared with symmetric encryption?

  2. • Draw a diagram to show how a single message can be both encrypted and authenticated using public key encryption

  3. • Many communications systems use a combination of public key encryption and symmetric encryption. Why is this the case, and how does it work?

  4. • Explain why the security of RSA depends on the difficulty of factoring large numbers

  5. • Using the following key generation parameter values chosen for an RSA system: p = 17, q = 7, e = 13 Find the values of the private key components, d and n. Encrypt the message which is 11100001 in binary using this RSA system.

  6. • What is the purpose of the Diffie-Hellmann public key technique? Briefly describe it.

  7. • Prove that Diffie-Hellman works – i.e. that the secret keys calculated by both sides of the communication are identical.

  8. • In what situation does Elliptic Curve Cryptography perform better than RSA?

  9. • Discuss the significance of key size in cryptography? In your answer, comment on both symmetric and public key encryption.