1.a) Describe the high level steps involved for decryption using a Feistel cipher.

b) Modify the pseudo code provided in the lecture notes that describe encryption using a Feistel network to do decryption. You need to actually rewrite the code. Use different font colors and comments to highlight the areas of the code you have changed.

c) What are some benefit(s) of a Feistel structure?

2.Recall the 3DES encryption logic is: C = E (K3, D(K2,E(K1, P)))
Where:
E = Encryption
D = Decryption
Kn= Key n
P = Plain text
C = Cipher text

Write the symbolic logic for the 3DES decryption. Describe the logic in a few sentences.

3.Assuming an initial implementation of your encryption system was done using DES. What issues would need to be addressed if you decide to upgrade to the 3DES algorithm? There are several issues to consider.

4.Your manager is considering purchasing a message authentication system. She is considering 3 different systems. One system uses MD5 hashing, another uses SHA1 hashing and the other system uses a brand new hashing algorithm called VSH (Very Smooth Hash). You have been asked to prepare an executive summary (i.e. clear and concise) that describes the attributes of each algorithm and the pros and cons. What would your recommendation be?

5. How would you protect the passwords on your system using some of the mechanisms we have studied? Discuss implementation strategies and explain your decisions.