Homework #2
J. H. Wang
Oct. 26, 2016
Homework #2
• Chap.3:
– Review questions 3.3, 3.7
– Problems 3.1, 3.14(a), 3.20
• Due: two weeks (Nov. 9, 2016)
• Chap. 3
– Review question 3.3: What is a one-way hash
function? How is it different from message
authentication code?
– Review question 3.7: Differentiate between public-key
cryptosystem and symmetric encryption algorithm.
– Problem 3.1: Consider a 32-bit hash function
defined as the concatenation of two 16-bit
functions: XOR and RXOR, which are defined in
Section 3.2 as “two simple hash functions.”
(a) Will this checksum detect all errors caused by
an odd number of error bits? Explain.
(b) Will this checksum detect all errors caused by
an even number of error bits? If not, characterize
the error patterns that will cause the checksum to
fail.
(c) Comment on the effectiveness of this function
for use as a hash function for authentication.
– 3.14: Perform encryption and decryption using
the RSA algorithm (Figure 3.10) for the
following:
(a) p=3; q=11, e=7; M=2.
Hint: Decryption is not as hard as you think;
use some finesse.
– 3.20: Suppose Bob uses the RSA
cryptosystem with a very large modulus n for
which the factorization cannot be found in a
reasonable amount of time. Suppose Alice
sends a message to Bob by representing
each alphabetic character as an integer
between 0 and 25 (A->0, …, Z->25), and then
encrypting each number separately using
RSA with large e and large n. Is this method
secure? If not, describe the most efficient
attack against this encryption method.
Homework Submission
• For hand-written exercises, please hand in
your homework in class (paper version)
Thanks for Your Attention!