Cryptography

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Firewall Implementation
Web clients
Gateway
R2
R1
Private
Screened
Packet
Packet
inner
subnet
subnet
filtering
filtering
router
router
Web server
Internet
(outside
Private network
firewall)
Flow of network traffic
(inside firewall)
A Web server on a screened subnet firewall
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Firewall Implementation
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Cryptography

• A cryptographic algorithm or cipher is used to
  encrypt and decrypt messages.
• Encrypted message is called ciphertext.
• Cryptographic algorithms use one or more
  variables called keys.
• Keys are very large numbers.

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Cryptographic Algorithms

• Private key cryptography
• one secret key
• ensures confidentiality
• Public key cryptography
• a matched key pair (public private)
• used for authentication
• Hashing Algorithms
• convert message to a digest (unique number)
• ensures integrity

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Digital Signatures

• Combines public key cryptography and hashing
  algorithms.
• message digest is encrypted using public key
  cryptography.
• Can be enhanced using private (secret)
  cryptography to encrypt the message.
• Document is signed encrypted.

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INTRANETS

• Internal private corporate networks.
• Standalone or sit on the secure side of a
  firewall.
• Leverage the public technology on which the Web
  is built.
• Private version of the Internet.

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EXTRANET

• Extends the corporate backbone to outsiders and
  other intranets.
• Uses a VPN that creates secure channel across
  public networks.
• VPN ties a corporation with its suppliers,
  employees, and business partners.
• Automotive Network Exchange (ANX) - an
  IPSec-based VPN connecting auto makers with
  thousands of auto industry suppliers.

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HyperText Markup Language (HTML)

• Web pages are written in HTML that specifies
  general guidelines for display.
• Web browser translates the specification into
  commands for particular hardware.
• HTML uses free-format input HTML can contain
  arbitrary spaces and extra lines.
• HTML instructions are separated from text to be
  displayed using symbols.

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Sections of a HTML Document

• Two main parts - a heading and a body.
• Actual Title
• Additional heading info if needed
• . Text

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HTML Basics

• Paragraph tags are used to determine how to group
  sentences in paragraphs.
• Paragraph 1
• Paragraph 2
• Paragraph 3
• Line break tag
  

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HTML Basics

• Items that correspond to a link are said to be
  anchored. A link begins with the tag , and
  ends with the tag .
• Center
  for CIM
• Browser displays Center for CIM

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HTML Basics

• Numbered (ordered) List
• 1. Item 1
  2. Item 2
  3. Item 3
• 1. Item 1
• 2. Item 2
• 3. Item 3
• Unnumbered (unordered or bulleted) List
• • Item 1
  • Item 2
  • Item 3
• Item 1
• Item 2
• Item 3

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HTML Basics

• Inserting images - the IMG tag.
• An image can appear by itself or adjacent to
  text.
• Alignment

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HTML Basics

• Making images correspond to a selectable link.
• Specifying background color
• displays black background color and image in the
  background

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HTML Basics

• Displaying tables
• ab
• xy
• Specifying multiple links within a single image
• HREF"http//www.okstate.eduCOORDS"108, 5, 219, 49" HREF"http//osu.okstate.
  edu/cocim"