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  1. • Distinguish between data origin authentication and peer entity authentication.

  2. • In the context of secure systems, what is a hash function? Describe the main properties of a hash function. In what way does a hash function differ from an encryption function?

  3. • On what does the strength of a hash function depend?

  4. • What is the significance of a birthday attack on a hash function? Outline how such a birthday attack would proceed.

  5. • Relative to the size of the message digest (hash value), indicate the level of effort that would be required on average for a birthday attack to succeed.

  6. • Which of MD-5 or SHA-1 would you recommend for hash function applications and why?

  7. • What does it mean to sign the hash of a message? Use a diagram to explain how this works, and how the receiver of the message verifies the signature.

  8. • Explain why it is normal practice to authenticate a message by signing the hash of it, rather than signing the entire message.

  9. • Give one difference between a MAC (Message Authentication Code) and a hash function?