University of Virginia, Department of Computer Science
CS588: Cryptology - Principles and Applications, Fall 2001

Manifest: Wednesday 3 October 2001
Assignments Due
Wednesday, 10 OctoberProblem Set 3
Wednesday, 17 OctoberNo Class
Wednesday, 24 OctoberMidterm

MBC Chapter 18 has some "sketches" of protocols. We will explore several of these protocols in more detail in later classes.
A Private Matchmaking Protocol, Kan Zhang and Roger Needham. Optional, but useful if you are trying Challenge #2.

Quiz Answers
  1. Here is the RSA algorithm, with some pieces missing. Fill in the blanks:
    1. Pick 2 large secret primes, p and q.
    2. Let n = pq [blank 1]
    3. Choose e and d so: ed ≡ 1 mod (p - 1) (q - 1) [blank 2]
    4. Encryption function (public): E(M) = Me mod n.
    5. Decryption function (private): D(C) = Cd mod n [blank 3]

  2. What is the private key?
    d or (d, n). To do decryption, we need to know d and n. No one else can know d. The public key is (e, n). Note that p and q must be kept secret, but are not part of the private key (we don't need them to decrypt). They should be destroyed after computing d.
  3. What is the range of M that can be reliably transmitted using RSA?
    0..n-1. We are transmitting Me mod n, so we could not transmit more than n different messages without having two messages map to the same ciphertext.


CS 655 University of Virginia
Department of Computer Science
CS 588: Cryptology - Principles and Applications
David Evans