CIS 725
Homework 6
- Do Problem 3.3. in Stallings 3 (a little bit tedious, but gives you a
bit of the flavor of DES).
- Work an example to understand the effects of diffusion: Take a few
sentences from somewhere (book, newspaper, whatever) and encrypt them
using a simple substitution cipher (you can make it up; the details aren't
important). Do a frequency analysis of the resulting ciphertext; list the
the frequencies from least to greatest. Then, add an intermediate step:
use the 'averaging' we talked about in class (which is also in Stallings)
first. Use k=3 (and you can add a copule dummy characters at the end so
that the last couple charactesr in the message get 'averaged' with
something). Then apply the substitution cipher and compute the
frequencies. Describe the differences in a few sentences. Note:
I strongly recommend that you write a bit of code to help you with this!
- Extra Credit: do Problem 3.4 in Stallings.