Student_Solution_Chap_10

Student_Solution_Cha - CHAPTER 10 Symmetric-Key Cryptography(Solution to Odd-Numbered Problems Review Questions 1 Symmetric-key cryptography is

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

View Full Document Right Arrow Icon
1 CHAPTER 10 Symmetric-Key Cryptography (Solution to Odd-Numbered Problems) Review Questions 1. Symmetric-key cryptography is based on sharing secrecy; asymmetric-key cryp- tography is based on personal secrecy. 3. In cryptography, a trapdoor is a secret with which Bob can use a feasible algorithm to decrypt the ciphertext. If Eve does not know the trapdoor, she needs to use an algorithm which is normally infeasible. 5. RSA uses two exponents, e and d , where e is public and d is private. Alice calcu- lates C = P e mod n to create ciphertext C from plaintext P; Bob uses P = C d mod n to retrieve the plaintext sent by Alice. a. The one-way function is the C = P e mod n. Given P and e , it is easy to calculate C; given C and e , it difficult to calculate P if n is very large. b. The trapdoor in this system is the value of d , which enables Bob to use P = C d mod n. c. The public key is the tuple ( e , n ). The private key is d. d. The security of RSA mainly depend on the factorization of n . If n is very large, and the value of e and d are chosen properly, the system is secure. 7. ElGamal is based on discrete logarithm problem. The plaintext is masked with e 1 rd to create the ciphertext. Part of the mask is created by Bob and become public; the other part is created by Alice. a. The one-way function is C = mask (P). Given P and the mask, it is easy to cal- culate the C; given C is difficult to unmask P. b. The trapdoor is the value of d that enables Bob to unmask C. c. The public key is ( e 1 , e 2 and n ). The private key is d . d. The security of ElGamal depends on two points; p should be very large and Alice needs to select a new r for each encryption.
Background image of page 1

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

View Full DocumentRight Arrow Icon
2 9. An elliptic curve is an equation in two variables similar to the equations used to calculate the length of a curve in the circumference of an ellipse. Elliptic curves with points belonging to the groups GF(
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/22/2012 for the course CSE 5345 taught by Professor Youngheliu during the Spring '12 term at UT Arlington.

Page1 / 6

Student_Solution_Cha - CHAPTER 10 Symmetric-Key Cryptography(Solution to Odd-Numbered Problems Review Questions 1 Symmetric-key cryptography is

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online