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CS 472
Network and Systems Security
Fall 2009
Midterm Exam
Time 2 & 1/2 hours
Open Book & Notes

 

 

Name:                                  

Unix Login:   

 

 

Each Question is 10 points

Question 1:

The crypto program of assignment #1 is used to encrypt files.

The syntax of this program is:

% crypto key plainfile cipherfile.

Assume you got hold of a cipherfile and  find out that the content of the file is all 0s.

How you interpret this?

 

Question 2:

XOR is a very important ingredient in symmetric encryption techniques.

Why is that?

 

 

 

 

 

 

Give two examples of symmetric encryption techniques that use XOR and refer to  the specific steps of these techniques where the XOR is actually used.

 

 

 

 

Question 3:

The traditional combination lock, T, requires three turns between 1 and 40.

Assume that you have the option of buying new weaker combination locks, W that requires two turns between numbers 0 and 9.

W is weaker than T by X%.

What is the value of X?

Question 4:

Almost all encryption algorithms use the concepts of permutation..

How many bits are required to store the permutation table to map  8-bit blocks to other arbitrary 8-bit blocks?

Question 5:

Assume that Bob  and Alice  share a secret K . (e.g., by meeting at Starbucks in Chicago J)

Describe two methods by which Alice can authenticate Bob using the shared secret K.

 

 

 

 

 

 

 

Question 6:

UNIX stores the hash of a random salt and the user password.

What is the security value of this salt?

 

     


Question 7:

Consider In the following openssl commands:

 

%  openssl   genrsa    -out  rsaprivatekey.pem    -des3    1024

 

 

What is the  meaning of the option  –des3  ?

 

 

 

What is the value of 1024 represents?

 

 

 

 

When using this command in class, what is the specific password that Dr. wahab have used?

 

 

 

 

 

 

 

 

 

 

% openssl  rsautl  -encrypt   -pubin -inkey   rsapublickey.pem -in   file1   -out  file2

 

What is the size limit imposed on file1 and why?

Question 8:

Show the result, in HEX, of the 1st  octet out of the S-Boxes  of the 1st round of DES   to encrypt one data block of all 0s using a key of all 0s. 

 

 

 

 

 

 

 

 

 

 

Question 9:

Show the result, in HEX, of the 1st  octet of the 1st round of AES-128   to encrypt one data block of all 1s using a key of all 0s. 

Question 10:

Here is a description of a Silly Encryption Algorithm (SEA):  

·        The algorithm has  a single round.

·        The input data block size and the encryption key lengths are one octet.

·        Just  XOR  the input data block with the encryption key.

 

Use the SEA algorithm to encrypt the message:  “F0F0” using the CBC chaining.

Assume the IV is “FF” and the encryption key is “FF”.