CSCI-235 Micro-Computers in Science

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CSCI-235Micro-Computers in Science

• Privacy Security

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• Simplified Communications Model - Diagram

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• 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
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• 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

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• 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

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• Symmetric Cipher Model

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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)

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• 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