Name:
Information Assurance: Homework 3
Due September 19, 2007 on compass. Late homeworks will only be accepted until
September 21, 2007 to ensure that answer keys can be posted before the exam.
1. This portion of the homework involves working with AES and DES encryption.
Pull the AES reference library from http://www.cs.uiuc.edu/class/fa07/cs461/aes-
files.zip. This library includes a test AES program which you can augment as
necessary. It also includes a makeKey program which creates a key of the
specified length using the rand() pseudo-random function.
Compile it for your target system. I have tested this program on Windows XP
using cygwin and MSDev and on Linux. Makefiles and project files are included.
Everyone should have access to the csil-linux*.cs.uiuc.edu and the
dcllnx*.ews.uiuc.edu machines.
a. Fetch an encrypted file and a key file from http://www.cs.uiuc.edu/class/fa07/
cs461/hw3-enc.bin and http://www.cs.uiuc.edu/class/fa07/cs461/key07-192.
Decrypt the file using ECB mode. It should result in a plain English file.
Submit the resulting plaintext.
b. Select a file to encrypt using a key in CBC mode. Submit the encrypted file,
key file, and initialization vector file. Indicate the size of the key.
c. Try encrypting your file in ECB mode using different key lengths: 128 bit,
192 bit, and 256 bit keys. Time the performance difference. AES operations
are very fast. You will want to use a high resolution timer such as the
gettimeofday or clock_gettime system calls. In addition, you will probably
need to perform your target measured operation multiple times to have
something that can be measured by the clock granularity. Plus, the I/O time of
the program is likely to be much bigger than the actual encryption time. You
will need to insert your timer calls appropriately to avoid measuring I/O.
Submit a table of the key length and the associated average encrypt time.
d. Repeat part c using DES with its 56 bit key. On Linux the function ecb_crypt
and des_setparity should do the trick. On Windows the base provider for the
Crypto API should provide a DES encryption operation. Add a row to your
table from part c showing the average time for the DES encryption operation.
2. Consider the Diffie-Hellman key exchange algorithm. This public key algorithm
is based on the hard problem of computing discrete logarithms. Assume an
efficient solution for calculating a discrete logarithm was found. How would this
affect the strength of the Diffie-Hellman algorithm? Could it be attacked? How?
3. Work with Gnu Privacy Guard (GPG). You can access GPG from
http://gnupg.org. I have used this on Linux and installed it via
yum on my personal system. It should already be installed on the
University Linux systems. Type “man gpg” to check if it is
