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.