CSCI-235 Micro-Computers in Science - PowerPoint PPT Presentation

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CSCI-235 Micro-Computers in Science

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Title: CSCI-235 Micro-Computers in Science


1
CSCI-235Micro-Computers in Science
  • Privacy Security

2
  • Simplified Communications Model - Diagram

3
  • Encryption
  • Encryption is the coding and scrambling process
    by which a message is made unreadable except by
    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
    plaintext unreadable
  • 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
    sender/receiver
  • 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
  • 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

9
  • 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

10
  • 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

11
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12
  • Privacy in Cyberspace
  • Privacy refers to an individuals ability to
    restrict the collection, use, and sale of
    confidential personal information
  • The Internet is eroding privacy through the
    selling of information collected through Web
    sites
  • Few laws regulate selling personal information

13
  • Cookies
  • Cookies are small text files that are written to
    an individuals hard drive whenever a Web site is
    visited
  • File is sent back to the server each time you
    visit that site
  • Stores preferences, allowing Web site to be
    customized
  • Stores passwords, allowing you to visit multiple
    pages within the site without logging in to each
    one
  • Tracks surfing habits, targeting you for specific
    types of advertisements
  • Legitimate purposes of cookies include recording
    information for future use. Example retail sites
    using shopping carts
  • Questionable practices include banner ad
    companies tracking a users browsing actions and
    placing banner ads on Web sites based on those
    actions

14
  • Hacker
  • Someone who attempts to gain access to computer
    systems illegally
  • Hacker noun (see Raymond, 1991)
  • A person who enjoys learning the details of
    computer systems and how to stretch their
    capabilities as opposed to the most users of
    computers, who prefer to learn only the minimum
    amount necessary
  • One who programs enthusiastically or who enjoys
    programming rather than just theorizing about
    programming

15
  • First Network Hack (Telephone)
  • John Draper (AKA Capn Crunch)
  • 1970s
  • Free long distance calls using a whistle found in
    a cereal box
  • Whistle emits the same frequency as ATT long
    lines to indicate a line was ready to route a new
    call (2600 Hz)

16
  • Flaw
  • ATT took cost cutting measures
  • The signaling and voice used the same circuit
  • This flaw made the system vulnerable to anybody
    that can generate 2600 Hz
  • Solution
  • Now signaling takes place on a separate path from
    the one you talk on
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