CEN 559
Selected Topics in Computer Engineering
Instructor: Dr. Mostafa Dahshan
Second Semester 1428/1429 – Spring 2008
Homework 4
1. Construct a Playfair matrix with the key “largest”.
2. Using this Playfair matrix:
M F H I/J K
U N O P
Q
Z V W X Y
E L A R
G
D S T
B
C
Encrypt this message:
Must see you over Cadogan West. Coming at once.
3. The following message was encrypted twice using 7x4 transposition matrix with key:
4261735:
PLEDNHOIRRKAAUSITPYAVFSHIRDG
Find the original message.
4. How many possible keys does the Playfair cipher have? Ignore the fact that some keys
might produce identical encryption results. Express your answer as an approximate power
of 2. Explain your answer.
5. In Feistel cipher, show that RD2 = LE14 and LD2 = RE14.