Part 5:Security

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Part 5Security

• Network Security
• (Access Control, Encryption, Firewalls)

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Secure Networks

• Secure network is not an absolute term
• Need to define security policy for organization
• Network security policy cannot be separated from
  security policy for attached computers
• Costs and benefits of security policies must be
  assessed

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Network Security Policy

• Devising a network security policy can be complex
  because a rational policy requires an
  organization to assess the value of information.
  The policy must apply to information stored in
  computers as well as to information traversing a
  network.

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Aspects of Security

• Data integrity
• Data availability
• Data confidentiality
• Privacy

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Responsibility and Control

• Accountability how an audit trail is kept
• Authorization who is responsible for each item
  and how is responsibility delegated to others

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Integrity Mechanisms

• Techniques to ensure integrity
• Parity bits
• Checksums
• CRCs
• These cannot guarantee data integrity (e.g.,
  against intentional change)
• Use of message authentication code (MAC) that
  cannot be broken or forged

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Access Control and Passwords

• Passwords used to control access
• Over a network, passwords susceptible to snooping

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Encryption and Confidentiality

• To ensure confidentiality of a transmitted
  message, use encryption
• Secret key or public key schemes

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Public Key Cryptosystem

• Each processor has private key S and public key
  P
• S is kept secret, and cannot be deduced from P
• P is made available to all processors
• Encryption and decryption with S and P are
  inverse functions P(S(m)) m and S(P(m)) m

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Message Digest

• Digest function maps arbitrary length message m
  to fixed length digest d(m)
• One-way function given d(m), can't find m
• Collision-free infeasible to generate m and m'
  such that d(m) d(m')

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Digital Signature

• To sign message m, sender computes digest d(m)
• Sender computes S(d(m)) and sends along with m
• Receiver computes P(S(d(m))) d(m)
• Receiver computes digest of m and compares with
  result above if match, signature is verified

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Digital Signature
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Internet Firewall

• Protect an organizations computers from internet
  problems (firewall between two structures to
  prevent spread of fire)

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Internet Firewall

• All traffic entering the organization passes
  through the firewall
• All traffic leaving the organization passes
  through the firewall
• The firewall implements the security policy and
  rejects any traffic that doesnt adhere
• The firewall must be immune to security attacks

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Packet Filtering

• Packet filter is embedded in router
• Specify which packets can pass through and which
  should be blocked

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Using Packet Filters to Create a Firewall

• Three components in a firewall
• Packet filter for incoming packets
• Packet filter for outgoing packets
• Secure computer system to run application-layer
  gateways or proxies

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Virtual Private Networks

• Two approaches to building corporate intranet for
  an organization with multiple sites
• Private network connections (confidential)
• Public internet connections (low cost)
• Virtual Private Network
• Achieve both confidentiality and low cost
• Implemented in software

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Virtual Private Network

• VPN software in router at each site gives
  appearance of a private network

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Virtual Private Network

• Obtain internet connection for each site
• Choose router at each site to run VPN software
• Configure VPN software in each router to know
  about the VPN routers at other sites
• VPN software acts as a packet filter next hop
  for outgoing datagram is another VPN router
• Each outgoing datagram is encrypted

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Tunneling

• Desire to encrypt entire datagram so source and
  destination addresses are not visible on Internet
• How can internet routers do proper forwarding?
• Solution VPN software encrypts entire datagram
  and places inside another for transmission
• Called IP-in-IP tunneling (encapsulation)

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Tunneling

• Datagram from computer x at site 1 to computer y
  at site 2
• Router R1 on site 1 encrypts, encapsulates in new
  datagram for transmission to router R2 on site 2

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Other Security Methods
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PGP Pretty Good Privacy

• PGP is a security technology which allows us to
  send email that is authenticated and/or
  encrypted.
• Authentication confirms the identity of the
  sender or a message.
• Encryption scrambles the contents of a message so
  that only the intended recipients can read it.
• Each user of PGP has a public and a private key.
  They are generated in matched pairs a public key
  only ever works with its twin private key.
• A user's public key is not a secret and can be
  distributed widely.
• A user's private key however must be kept secret,
  and is protected by a pass phrase (like a
  password but longer).

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PGP Pretty Good Privacy

• A public key is used in two ways Alice can
  authenticate a signed message from Bob using his
  public key. If the message matches Bob's public
  key then Alice can be sure that the message came
  from Bob.Alice can send a secure message to Bob
  by encrypting the message using Bob's public key.
  The only person who can decrypt the message is
  Bob.
• A private key also has two uses Bob can send an
  authenticated message to Alice by signing it with
  his private key. Since Bob is the only person who
  has his private key (and the pass phrase that
  protects it), Alice knows that if the message
  matches Bob's public key, then it must have been
  sent by Bob.Bob can read a secure message sent
  by Alice by decrypting it with his private key.

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SSL (Secure Sockets Layer)

• The SSL (Secure Sockets Layer) Handshake Protocol
  was developed to provide security and privacy
  over the Internet.
• The SSL protocol runs in a "layer" above TCP/IP
  and below higher-level protocols such as HTTP or
  IMAP.
• The SSL protocol is able to negotiate encryption
  keys as well as authenticate the server before
  data is exchanged by the higher-level
  application.
• The SSL protocol maintains the security and
  integrity of the transmission channel by using
  encryption, authentication and message
  authentication codes.

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HTTPS

• HTTPS stands for Hypertext Transfer Protocol over
  Secure Socket Layer, or HTTP over SSL.
• HTTPS encrypts and decrypts the page requests and
  page information between the client browser and
  the web server using a secure Socket Layer (SSL).
  
• SSL transactions are negotiated by means of a
  keybased encryption algorithm between the client
  and the server.

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IPsec

• Short for IP Security, IPsec is a set of
  protocols developed by the IETF to support secure
  exchange of packets at the IP layer.
• IPsec supports two encryption modes Transport
  and Tunnel.
• Transport mode encrypts only the data portion
  (payload) of each packet, but leaves the header
  untouched.
• The more secure Tunnel mode encrypts both the
  header and the payload. On the receiving side, an
  IPSec-compliant device decrypts each packet.

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SET Secure Electronic Transactions

• Short for Secure Electronic Transaction, a
  standard that will enable secure credit card
  transactions on the Internet.
• SET has been endorsed by virtually all the major
  players in the electronic commerce arena,
  including Microsoft, Netscape, Visa, and
  Mastercard.
• By employing digital signatures, SET will enable
  merchants to verify that buyers are who they
  claim to be.
• It will protect buyers by providing a mechanism
  for their credit card number to be transferred
  directly to the credit card issuer for
  verification and billing without the merchant
  being able to see the number.

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Summary

• Security is desirable but must be defined by an
  organization
• Assess value of information and define a security
  policy
• Aspects to consider include privacy and data
  integrity, availability, and confidentiality

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Summary (continued)

• Mechanisms to provide aspects of security
• Encryption secret and public key cryptosystems
• Firewalls packet filtering
• Virtual private networks
• Use Internet to transfer data among
  organizations sites but ensure that data cannot
  be read by others