Name:
TEST 1
CSCE 522 – Fall 2002
September 25, 2002
Name:
Major
SSN (last 4 digits):
Answer the following questions. Be brief and precise, please.
You have 1 hour 15 minutes to finish the exam.
1. 14 points
Explain how Diffie-Hellman works. What is the man-in-the-middle attack against DiffieHellman?
2. 6 points
What is column cipher? Briefly explain how can it be broken.
1
Name:
3. 15 points
Briefly explain DES (key, plaintext and cipher size, main steps of DES)? Outline one cycle of
DES.
4. (5 points)
Briefly show how RSA provide confidentiality?
2
Name:
III. Think! (40 points)
Undergraduate students!!! Answer only question 1 or question 2 in this section but not both!
Question 3 need to be answered by everybody.
1. 15 points
 Assume an attacker has random pairs of (P,C), that is plaintext messages and matching
ciphertext messages. What is the meet-in-the middle attack with DES double encryption? (5)
P
E
K1
E
K2
D
D
K2
K1
C

Explain how DES electronic code book (ECB) works. (5)

Is DES in ECB mode vulnerable for meet-in-the middle attack? Why or why not? (5)
3
Name:
2. 15 points
Show how secret-key cryptosystem may provide message authenticity (to a third party) using a
trusted server.
4
Name:
----------------------------------------------------------------------------------------------------------(BONUS QUESTION)
5 points
Show how hash function could be used to prove that the message content, sent from S to R,
encrypted by R’s public-key (confidentiality) has not been damaged (modified) during
transmission.
5