Sol30 - CHAPTER 30 Cryptography Solutions to Review...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 CHAPTER 30 Cryptography Solutions to Review Questions and Exercises Review Questions 1. Only one key (the shared secret key) is needed for two-way communication. How- ever, for more security, it is recommended that a different key be used for each direction. 2. A shared secret key can only be used between two entities. Alice needs a shared secret key to communicate with Bob and a different shared secret key to communi- cate with John. 3. Each person in the first group needs to have 10 keys to communicate with all peo- ple in the second group. This means we need at least 10 × 10 = 100 keys. Note that the same keys can be used for communication in the reverse direction. However, note that we are not considering the communication between the people in the same group. For this purpose, we would need more keys. 4. Each person needs 9 keys to communicate with the other people. At first glance, it looks like we need 10 × 9 keys. However, if the same key can be used in both directions (from A to B and from B to A), then we need only (10 × 9) / 2 = 45 keys . 5. For two-way communication, 4 keys are needed. Alice needs a private key and a public key; Bob needs a private key and a public key. 6. Alice can use the same pair of keys (private and public) to communicate with both Bob and John. However, if there is a need for two-way communication, Bob and John need to have their own pair of keys. In other words, for two-way communica- tion 6 keys are needed, two for each entity. 7. For two-way communication, the people in the first group need 10 pairs of keys, and the people in the second group need a separate 10 pairs of keys. In other words, for two-way communication 40 keys are needed. 8. Each person in the group needs only one pair of keys (private and public). In other words, 20 keys are needed for two-way communication.
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 Exercises 9.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern