NET 311D Information Security

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Presentation transcript:

NET 311D Information Security Networks and Communication Systems Department TA. Anfal AlHazzaa TUTORIAL 1 (Traditional Ciphers “Character-oriented”)

Recalling Networks and Communication Systems Department

Example Networks and Communication Systems Department Plaintext : original message before being transformed. Ciphertext : The message after transformation (coded). Cipher : algorithm for transforming plaintext to ciphertext Key : information used in cipher known only to sender/receiver Encrypt : converting plaintext to ciphertext Decrypt: recovering ciphertext from plaintext Cryptography : study of encryption principles/methods Cryptanalysis (codebreaking) - study of principles/ methods of decrypting ciphertext without knowing key Networks and Communication Systems Department

Cryptography Categories Networks and Communication Systems Department

Symmetric Key Symmetric Key Traditional Ciphers Symmetric Key Modern Round Ciphers Traditional Ciphers Simple Modern Cipher Networks and Communication Systems Department

Traditional Ciphers Shift (Caesar) cipher Networks and Communication Systems Department

Questions Traditional Ciphers Networks and Communication Systems Department

Q1: Substitution cipher (Caesar) Encrypt the following texts using the shift (Caesar) cipher with the keys in brackets: “Welcome” (Key=10) GOVMYWO “Open the door” (Key=5) TUJS YMJ ITTW GOVMYWO TUJS YMJ ITTW Networks and Communication Systems Department

Q1: Substitution cipher (Caesar) cont. Networks and Communication Systems Department

Q2: Substitution cipher (Caesar) Alice wants to encrypt a message to Bob by using the shift cipher algorithm “Caesar cipher” and the key= 20. The plaintext = “QUIZ”. ( Hint: you may need to use the table) Answer: KOCT 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 5-Dec-18 Networks and Communication Systems Department

Q3: Substitution cipher (Monoalphbetic) Use the following table as the key to encrypt the following texts using the substitution cypher: “Announce it tomorrow” EVVRYVZH BF FRDRWWRX - “DO IT” - JR BF A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Networks and Communication Systems Department

Q4: Transposition cipher The following text was encrypted using the transposition cipher with the following mapping as the key, decrypt the message : 1 2 3 4 5 Decrypt Encrypt HI SARA I HOPE YOU ARE FINE LOOKING FORWARD TO SEE YOU Cipher Text: SAHRIHOAPIOUEAYFIRNEOOEKLGFIONARRDWSETEOUZYZO

Q4: Transposition cipher cont. Answer HI SARA I HOPE YOU ARE FINE LOOKING FORWARD TO SEE YOU Networks and Communication Systems Department

Q5: Transposition cipher Encrypt the following message using transposition cipher based on the key shown below: The message is “SWEET HEART”. Answer: WESTHEAREZZT Networks and Communication Systems Department