Cryptography November 14, 2011 1 Intercepting Information Scenario - - PowerPoint PPT Presentation

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cryptography

Cryptography November 14, 2011 1 Intercepting Information Scenario - - PowerPoint PPT Presentation

Oct 23, 2023 111 likes •182 views

Cryptography November 14, 2011 1 Intercepting Information Scenario 1 Wireless broadcasts information using radio signals Any computer on a wireless network CAN listen to any network traffic A computer SHOULD only listen to traffic

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SLIDE 1

Cryptography

November 14, 2011

Intercepting Information Scenario 1

http:/ /www.geeksquad.com/ uploadedImages/ wwwgeeksquadcom/Tools/ Tech_Articles/ going_wireless_1.jpg Wireless broadcasts information using radio signals Any computer on a wireless network CAN listen to any network traffic A computer SHOULD only listen to traffic addressed to it It is impossible to know if anyone is eavesdropping

1 2 Monday, November 14, 2011

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SLIDE 2

Intercepting Information Scenario 2

Spam filter reads a mail message to decide if it is spam What could an unscrupulous person do when he/she writes a spam filter?

Mail server Internet Your laptop

Cryptography

3 4 Monday, November 14, 2011

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SLIDE 3

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext:

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: P

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

5 6 Monday, November 14, 2011

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SLIDE 4

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: PR

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: PRX

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

7 8 Monday, November 14, 2011

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SLIDE 5

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: PRXQ

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: PRXQW

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

9 10 Monday, November 14, 2011

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SLIDE 6

Caesar Cipher Example

Key = 3 Plaintext: Mount Holyoke Ciphertext: PRXQW KROBRNH

PLAINTEXT LETTER M N O P Q R S T U V W X Y CIPHERTEXT LETTER P Q R S T U V W X Y Z A B

General Letter Substitution

Algorithm: Substitute 1 letter for another Key Ciphertext: LUGAU

PLAINTEXT LETTER A B C D E F G H I J K L M CIPHERTEXT LETTER G J A O U N E Z Y P H S T PLAINTEXT LETTER N O P Q R S T U V W X Y Z CIPHERTEXT LETTER V W L M I B D C R K F Q X

11 12 Monday, November 14, 2011