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

2. Recalling
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3. 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
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4. Cryptography Categories
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5. Symmetric Key Symmetric Key Traditional Ciphers Symmetric Key
Modern Round Ciphers
Traditional Ciphers
Simple Modern Cipher
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6. Traditional Ciphers Shift (Caesar) cipher
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7. Questions Traditional Ciphers
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8. 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
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9. Q1: Substitution cipher (Caesar) cont.
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10. 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 M Y 24
B N Z 25
C O 14
D P 15
E Q 16
F R 17
G S 18
H T 19
I U 20
J V 21
K W 22
L X 23
5-Dec-18
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11. 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
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12. Q4: Transposition cipher
The following text was encrypted using the transposition cipher with the following mapping as the key, decrypt the message :
Decrypt
Encrypt
HI SARA I HOPE YOU ARE FINE LOOKING FORWARD TO SEE YOU
Cipher Text:
SAHRIHOAPIOUEAYFIRNEOOEKLGFIONARRDWSETEOUZYZO

13. Q4: Transposition cipher cont.
Answer
HI SARA I HOPE YOU ARE FINE LOOKING FORWARD TO SEE YOU
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14. Q5: Transposition cipher
Encrypt the following message using transposition cipher based on the key shown below:
The message is “SWEET HEART”.
Answer:
WESTHEAREZZT
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