Princess Nora Bint Abdul Rahman University

Princess Nora Bint Abdul Rahman University College of Computer and Information Systems Network and Data Communication Department Information Security (NET 311) Sheet#1 (Symmetric Key Encryption)

Student Name: Student ID Section No

Question 1: A. Encrypt the following message using transposition cipher based on the key shown below:

The message is “SWEET HEART”. Answer: ______

B. Alice wants to encrypt a message to Bob by using the shift cipher algorithm “Caesar cipher” and the key= 20. The plaintext = “QUIZ”. A 00 M 12 Y 24 B 01 N 13 Z 25 C 02 O 14 D 03 P 15 E 04 Q 16 F 05 R 17 G 06 S 18 H 07 T 19 I 08 U 20 J 09 V 21 K 10 W 22 L 11 X 23

( Hint: you may need to use the table in previous question)

Answer: ______Princess Nora Bint Abdul Rahman University College of Computer and Information Systems Network and Data Communication Department Information Security (NET 311) Sheet#1 (Symmetric Key Encryption) Princess Nora Bint Abdul Rahman University College of Computer and Information Systems Network and Data Communication Department Information Security (NET 311) Sheet#1 (Symmetric Key Encryption) Question 2: The following ciphertext was generated using a simple substitution algorithm:

53‡‡†305))6*;4826)4‡.)4‡);806*;48†8¶60))85;;]8*;:‡*8†83 (88)5*†;46(;88*96*?;8)*‡(;485);5*†2:*‡(;4956*2(5*—4)8¶8* ;4069285);)6†8)4‡‡;1(‡9;48081;8:8‡1;48†85;4)485†528806*81 (‡9;48;(88;4(‡?34;48)4‡;161;:188;‡?;

Hints: 1. In English, the most frequently occurring letter is E. Also, e is often appears in pairs (e.g., meet, speed, seen, been, agree, etc.).Try to find a character in the ciphertext that decodes to E. Answer: ______2. The most common word in English is “the.” Use this fact to guess the characters that stand for t and h. Answer: ______3. Is this encryption algorithm classified as monoalphabetic cipher or polyalphabetic cipher? And how did that help you decrypting the text? Answer: ______4. BONUS: Decipher the rest of the message by deducing additional words. Warning: The resulting message is in English but may not make much sense on a first reading. Answer: ______Princess Nora Bint Abdul Rahman University College of Computer and Information Systems Network and Data Communication Department Information Security (NET 311) Sheet#1 (Symmetric Key Encryption) ______Princess Nora Bint Abdul Rahman University College of Computer and Information Systems Network and Data Communication Department Information Security (NET 311) Sheet#1 (Symmetric Key Encryption) Question 3: A. In DES, if M = 0000 2000 8000 0000 ( Hex), Find the IP(M).

IP(M)=………………………………………………………………………………….. ( Hex)

B. Using the S-box shown below, What is the output if the input was: 011011

Answer: ______

GOOD LUCK