# CSCI-100 Introduction to Computing - PowerPoint PPT Presentation

PPT – CSCI-100 Introduction to Computing PowerPoint presentation | free to view - id: 7334ed-NTZlN

The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
Title:

## CSCI-100 Introduction to Computing

Description:

### CSCI-100 Introduction to Computing Privacy & Security Part I Simplified Communications Model - Diagram Encryption Encryption is the coding and scrambling process by ... – PowerPoint PPT presentation

Number of Views:163
Avg rating:3.0/5.0
Slides: 14
Provided by: Michele251
Category:
Tags:
Transcript and Presenter's Notes

Title: CSCI-100 Introduction to Computing

1
CSCI-100 Introduction to Computing
• Privacy Security
• Part I

2
• Simplified Communications Model - Diagram

3
• Encryption
• Encryption is the coding and scrambling process
the intended recipient
• Encryption is needed for electronic commerce
• Encryption Basics
• A readable message is called plaintext
• An encryption algorithm is a formula used to make
• The coded message is called ciphertext

I LOVE YOU
V YBIR LBH
4
• Symmetric key encryption are encryption
techniques that use the same key to encrypt and
decrypt a message
• Strong encryption refers to encryption methods
that are used by banks and military agencies and
are nearly impossible to break

5
• Basic Terminology
• plaintext - the original message
• ciphertext - the coded message
• cipher - algorithm for transforming plaintext to
ciphertext
• key - info used in cipher known only to
• encipher (encrypt) - converting plaintext to
ciphertext
• decipher (decrypt) - recovering ciphertext from
plaintext
• cryptography - study of encryption
principles/methods
• cryptanalysis (codebreaking) - the study of
principles/ methods of deciphering ciphertext
without knowing key
• cryptology - the field of both cryptography and
cryptanalysis

6
• Symmetric Cipher Model

7
• Two requirements for secure use of symmetric
encryption
• a strong encryption algorithm
• a secret key known only to sender / receiver
• Y EK(X)
• X DK(Y)
• Assume encryption algorithm is known
• Implies a secure channel to distribute key

8
(No Transcript)
9
• Classical Substitution Ciphers
• Where letters of plaintext are replaced by other
letters or by numbers or symbols
• Caesar Cipher
• Earliest known substitution cipher
• By Julius Caesar
• First attested use in military affairs
• Replaces each letter by k-th letter on
• Example ( what is k ? )
• meet me after the toga party
• PHHW PH DIWHU WKH WRJD SDUWB

10
• Can define transformation (with k 3) as
• 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
• D E F G H I J K L M N O P Q R S T U V W X Y Z A B
C
• Mathematically give each letter a number
• a b c d e f g h i j k l m
• 0 1 2 3 4 5 6 7 8 9 10 11 12
• n o p q r s t u v w x y Z
• 13 14 15 16 17 18 19 20 21 22 23 24 25
• Then have Caesar cipher as
• Y EK(X) (X k) mod 26
• X DK(Y) (Y k) mod 26
• EXAMPLE Encrypt howdy using key k 5

11
• Cryptanalysis of Caesar Cipher
• Only have 26 possible ciphers
• A maps to A,B,..Z
• Could simply try each in turn
• A brute force search
• Given ciphertext, just try all shifts of letters

12
(No Transcript)
13
• Brute Force Search
• Always possible to simply try every key
• Most basic attack, proportional to key size