HW 6, Non-Text Questions

1. How can symmetric encryption, public key encryption and hash functions be combined to create digital signatures? Give and example that provides confidentiality, integrity, authentication, and non-repudiation. Please limit your discussion to a half-page.
2. Describe the security implications of the following:
   1. E_k(M)||H(M)
   2. M||E_k(H(M))
   3. E_k(j)||E_j(M)||H(M+j)
   Would you use these? Why or why not?
3. A contest is being run in which participants must choose from a set of gifts and may only receive gifts from that set if they win. There are only a limited set of elements that you must choose from, but you do not wish to disclose your choices to others and you must choose these elements before you will know if you will receive them. Create a scheme using a hash function that will allow you to prove what your choices were after you find out if you won.
4. Explain Birthday Attacks.
5. Explain the Kerberos Authentication Protocol.