CPE 401/601 Computer Communication Networks

Spring 2011

Homework 2 : Security

Due on Wednesday, Apr 20 at 1:00 pm

The following problems are from the text book (Kurose and Ross, 5th edition):

Chapter 8:

R1 : What are the differences between message confidentiality and message integrity? Can you have one without the other? Justify your answer.

R3 : From a service perspective, what are the main differences between symmetric key and public key crypto systems?

P2 : Show that Trudy's known-plaintext attack, in which she knows the (ciphertext, plaintext) translation for seven letters, reduces the number of possible substitutions to be checked by approximately 10^9.

P5 : Consider the block cipher in Figure 8.5. For a given "key" Alice and Bob would need to keep eight tables, each 8 bits by 8 bits. For Alice and Bob to store all eight tables, how many bits of storage are necessary? How does this number compare with the number of bits required for a full table 64-bit block cipher?

P8 : Consider RSA with p=5 and q=11.

a - What are n and z values?
b - Is e=3 an acceptable value, why?
c - Find d given e=3.
d - Encrypt message 8 using (n,e) values.

Chapter 9:

R6: What is an important difference between a request-response message and a trap message in SNMP?

P3: What is ASN.1 object identifier for the RMON protocol (see Figure 9.3)?

P8: Consider Figure 9.9. What would be the BER encoding of {weight, 160} {lastname, "Dario"}?


Submitting your files

Submission of your homework is via WebCT. You must submit all the required files in a single document containing your answers.