Security

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Security
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Reported Security Incidents 1995 2003 Source
http//www.cert.org/present/cert-overview-trends/m
odule-1.pdf
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Imperative Need for Secure CommunicationCost of
downtime
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Secure Communication

• Characteristics of a secure communication
• Confidentiality
• Authentication
• Message Integrity and non-repudiation
• Availability and Access Control

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Confidentiality

• The communicator wants the following to be
  confidential
• The fact that the communication is occurring
• Timing of communication
• Frequency of communication
• Confidentiality often relies on cryptographic
  techniques for encrypting/ decrypting data using
  one or more keys to encrypt/decrypt data

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Authentication

• Both sender and receiver should be able to
  confirm identity of other party involved in
  communication
• Confirm that the other party is indeed who/what
  they claim to be
• Authentication relies on authentication
  techniques, several of which rely on
  cryptographic techniques

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Message Integrity and Non-Repudiation

• Message integrity
• Content of communication is not altered
  maliciously or by accident
• Relies on cryptographic techniques
• Non-repudiation
• Not denying what was communicated

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Availability

• Can communication occur in first place?
• Hackers preventing infrastructure from being used
  by legitimate users e.g., viruses, DoS attacks
• Detect breaches and respond to attacks

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Access Control

• Entities allowed to gain access to resources only
  if they have the appropriate access rights (e.g.,
  login ID, passwords, biometric devices)
• Facilitated by firewalls, which provide access
  control based on a per-packet basis, and on a
  per-service basis.
• Provide a degree of isolation and protection from
  those outside of ones network

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Cryptography

• Symmetric Key Cryptography
• Public Key Cryptography

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Symmetric Key Cryptography

• Symmetric Key Cryptography
• Caesar Cipher
• Monoalphabetic Cipher
• Polyalphabetic Cipher
• Data Encryption Standard (DES)
• Triple DES (3DES)
• Advanced Encryption Standard (AES)
• Trusted Intermediaries for symmetric key
  distribution
• Key Distribution Center (KDC)
• Kerberos

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Basic Terminology

• Plain Text
• Original data not disguised
• Cipher (Encrypted) Text
• Disguised data looks unintelligible to intruder
• Data disguised using encryption algorithm
• Key
• A string of s or characters used as input to
  encryption algorithm to disguise plain text
• Symmetric Key Both parties use same key to
  encrypt and decrypt text

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Symmetric Key Cryptography

• Caesar Cipher
• Each letter in plaintext is substituted with
  letter that is K letters later
• Wrap around is allowed (i.e., z followed by
  letter a)
• If K 3, a in plaintext becomes d in cipher text
• b in plaintext becomes e in cipher text
• Example Decrypt the following using a Caesar
  Cipher of K 3 Assume wrap around is allowed.
  
• L JP J JHHN

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Symmetric Key Cryptography

• Data Encryption Standard (DES)
• Published in 1977, and updated in 1993
• For commercial and non-classified U.S. Govt. use
• Encodes plaintext using 56-bit key
• Objective Scramble data and key so that every
  bit of the cipher text depends on every bit of
  the data and every bit of the key
• Algorithm Complex (beyond the scope of the
  course) Decryption works by reversing the
  algorithms operations.

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How well does DES work?

• DES challenge contest
• Launched in 1997 by RSA Data Security Inc. -- A
  network security company
• Encrypted strong cryptography makes the world a
  safer place using a 56-bit DES.
• Winning team took 4 months to decode.
• Used volunteers throughout the Internet to
  systematically explore key space.
• Claimed 10K cash prize after testing only a
  quarter of the key space (about 18 quadrillion
  keys)

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How well does DES work?

• In 1999, RSA launched another DES challenge.
• Message was decrypted in little over 22 hours by
  a network of volunteers and a special purpose
  computer called Deep Crack.
• Claimed 250 K cash prize.

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Symmetric Key Cryptography

• Triple DES (3 DES)
• If 56-bit DES is considered to be insecure, one
  can simply run the algorithm multiple times,
  using a different key each time
• DES run three times (with a different 56-bit key
  each time DES is run).

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Symmetric Key Cryptography

• Advanced Encryption Standard (AES)
• NIST in Nov 2001 announced successor to DES.
• AES is also a symmetric key algorithm that
  processes data in 128-bit blocks
• AES can operate with 128-bit keys, 192-bit keys,
  and 256-bit keys

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Trusted Intermediaries

• Disadvantage of Symmetric Key Cryptography
• 2 communicating parties have to agree upon their
  secret key ahead of time in a secure manner.
• Since sender and receiver do not meet face to
  face in the networking world , they need a
  trusted intermediary
• Trusted Intermediaries
• Key Distribution Center
• Kerberos

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Key Distribution Center (KDC)

• A server that shares a different secret
  symmetric key with each registered user.
• KDC knows the secret key of each user, and each
  user can communicate securely with KDC using this
  key.

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Example Using KDC

• Assume Sender (S) and Recipient (R) use KDC for
  their communication.
• Assume Ss secret key known to S and KDC is
  KS-KDC
• Assume Rs secret key known to R and KDC is
  KR-KDC.

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Example Using KDC

• Using key, S sends a message to KDC saying that S
  wants to communicate with R. We denote this
  message as MS-KDC(S, R).
• KDC decrypts MS-KDC(S, R)
• KDC generates a random number key KSR, which is
  to be used as symmetric key by S and R during
  their communication.

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Example Using KDC contd

• KDC sends S the key KSR, and a pair of values X
  and KSR encrypted using Rs key. We denote this
  message sent back to S by KDC as
• MKDC-S(KSR, MKDC-R(X, KSR)).
• S decrypts message and extracts symmetric key
  KSR. S extracts and forwards MKDC-R(X, KSR) to R
• Note that S cannot decrypt MKDC-R(X, KSR)
• R decrypts MKDC-R(X, KSR) and uses KSR as
  symmetric key to converse with S
• R and S communicate using symmetric key KSR

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Kerberos

• Developed by MIT
• Very similar to KDC
• Has additional functions such as
• Time stamp for validity of nonce KSR.
• Has information about which users have access
  privileges to which services on which network
  servers.

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Public Key CryptographyOverview

• Define concept of Public and Private keys
• Demonstrate RSA Algorithm
• Review Authentication Protocols (ap)
• Exchanging Public Keys
• Person in the middle-attack

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Introduction - Public Key Cryptography

• Use public key cryptography so that two parties
  can communicate using encryption/decryption
  without using a shared secret key.
• Key maintenance is difficult
• Public key cryptography
• A radically different and marvelously elegant
  approach towards encryption/decryption
• Also used for authentication and digital
  signatures

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Basic Idea of Public Key Cryptography

• Each participant has a private key (known only to
  the participant) and a public key.
• Public key is made available to others
• Could be posted even on a website which is
  accessible by the rest of the world.
• Public key of recipient is used by sender to
  encrypt message.
• Recipient decrypts message using recipients
  private key.

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Public Key Cryptography

• Example
• Sender (S) wishes to send a message to Recipient
  (R)
• S fetches Rs public key.
• S uses Rs public key to encrypt message
• S sends encrypted message to R.
• R decrypts cipher text with Rs private key.

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RSA Algorithm

• Named after its founders, Ron Rivest, Adi Shamir,
  and Leonard Adleman
• Has become almost synonymous with public key
  cryptography

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Using the RSA Algorithm

• Rs public key is denoted as KR and the private
  key is denoted as KR-.
• These keys are chosen such that
• KR- (KR (m)) KR (KR- (m)) m
• S will encrypt a plain text message, m, using
  public key KR and send it to R

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Using the RSA Algorithm

• To encrypt the message, S uses Rs public key and
  determines the cipher text, c as
• c me mod n
• To decrypt the message, R uses Rs private key
  and determines the plain text, m as
• m cd mod n

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Using the RSA AlgorithmCreate Rs Keys

• Choose two large prime numbers, p and q.
• The larger the values, the more difficult it is
  to break RSA, and the longer it takes to
  encode/decode.
• It is recommended that the product of p and q be
  on the order of 1024 bits for corporate use and
  768 bits for use with less valuable
  information.
• For a discussion on how to find large prime
  numbers, see http//www.utm.edu/research/primes/pr
  ove/).
• For example, choose p 5 and q 7

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Using the RSA AlgorithmCreate Rs Keys

• Compute n pq 35
• Compute z (p-1)(q-1) (4)(6) 24
• Choose a number, e, less than n, which has no
  common factors (other than 1) with z.
• R chooses e 5
• Find a number, d, such that ed-1 is exactly
  divisible (that is, with no remainder) by z.
• d 29
• Note (ed-1) (5x29 -1) (145-1) 144
• 144 is exactly divisible by z 24

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Using the RSA AlgorithmCreate Rs Keys

• Recap p 5, q 7, n 35, z 24, e 5, d
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• Rs public key is given by
• KR (n, e) (35, 5)
• Rs private key is given by
• KR- (n, d) (35, 29)
• Example
• Interpret each letter in the English alphabet as
  a number between 1 and 26. That is, a 1, b
  2, , z 26.
• S will send message love to R

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Using the RSA AlgorithmEncrypt Message using KR
(n, e) (35, 5)
Plaintext letter m (numeric representation) m e c me mod n
l 12 248832 17
o 15 759375 15
v 22 5153632 22
e 5 3125 10

• S will send 17152210 to R

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Using the RSA AlgorithmEncrypt Message using KR-
(n, d) (35, 29)
Cipher text cd m cd mod n msg
17 481968572106750915091411825223071697 12 l
15 12783403948858939111232757568359375 15 o
22 851643319086537701956194499721106030592 22 v
10 100000000000000000000000000000 5 e

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RSA and DES/AES

• RSA is a complex algorithm and uses concepts from
  number theory.
• DES is at least 100 times faster than RSA.
• In practice, RSA is often used in combination
  with DES or AES.
• Message is encrypted using DES key
• S encrypts DES key with Rs public key
• R decrypts and obtains DES key with Rs private
  key.
• Message is decrypted using DES key

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Authentication

• ap 4.0 (symmetric)
• S announces to R, I am S
• R sends a plaintext nonce ( n) to S.
• Note nonce is a one time value that is specific
  to that communication session
• S resends same nonce back to R but this time
  nonce is encrypted with symmetric key used by S
  and R.
• R decrypts nonce using symmetric key. If
  decrypted nonce equals the nonce sent to S
  earlier (i.e. decrypted nonce n) , then S is
  authenticated.
• However, this implies that S and R must have
  decided upon and exchanged their symmetric key.

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Authentication

• ap 5.0 (public/private)
• S announces to R, I am S
• R sends a plaintext nonce ( n) to S
• S resends same nonce back to R but this time
  nonce is encrypted with Ss private key.
• R decrypts nonce using Ss public key. If
  decrypted nonce equals the nonce sent to S
  earlier (i.e. decrypted nonce n) , then S is
  authenticated.

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Exchanging Public Keys

• Why should public key be publicly available?
• Wouldnt it be better for S and R to exchange
  their respective public keys via e-mail, after
  authenticating each other?
• Possibility of person in the middle attack.
  

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Person in the Middle Attack

• S transmits, I am S
• T eavesdrops.
• R sends a nonce n.
• T intercepts nonce, and sends R encrypted nonce
  (encrypted using Ts private key).
• R sends a message to S asking for Ss public key.
  
• T intercepts message, and sends Ts public key to
  R.
• R decrypts nonce with Ts public key (thinking
  that he is using Ss public key), and
  inadvertently authenticates T.

• While R is encrypting new data using Ts public
  key, T is busy posing as R to S. In
  particular
• T transmits Rs nonce to S
• S transmits encrypted nonce (encrypted using Ss
  private key).
• T intercepts encrypted nonce, and asks S for her
  public key.
• S sends her public key

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Person in the Middle Attack contd

• R sends encrypted data (encrypted using Ts
  public key)
• T decrypts using her private key, and finds out
  Rs plain text.
• T encrypts Rs plain text using Ss public key.
• T transmits encrypted text to S.
• S decrypts using her private key, and finds out
  Rs plain text.
• S and R presume that they have had a secure
  communication. They are ignorant of the fact
  that T has intercepted and decrypted all messages.

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Availability and Access Control

• Examples of common attacks
• Firewalls

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Examples of some attacks

• Denial of Service attacks
• Hacker attempts to disrupt the network by
  flooding the network with messages so that the
  network cannot process messages from legitimate
  users
• Examples
• Ping attacks
• Smurf attack
• SYN flood attack
• Distributed Denial of Service attacks

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Ping Packets

• Packets that ask a computer to respond with an
  acknowledgement
• Used to see if a computer is still operational in
  a network
• Ping by computer name
• Ping bus.orst.edu
• Ping by IP address
• Ping 128.193.76.73

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TCP header Packet s (Sequence s)

• Assume a file has 500,000 bytes
• Assume TCP breaks this file into packets, where
  each packet size is 1000 bytes
• Each packet is given a packet
• The packet for a packet is the number of the
  first byte in that packet.
• The packet of first packet would be 1
• The packet of next packet would be 1001
• The packet of third packet would be 2002 and so
  on

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TCP Acknowledgement

• Assume S transmits to R
• R acknowledges receipt of Ss message, by
  specifying an acknowledgment .
• The ACK sent by R is the packet of the next
  packet that R is expecting from S.
• Example
• After S sends first packet, R sends an
  acknowledgment to S by specifying ACK 1001.
• After S sends second packet, R acknowledges by
  specifying ACK 2001.

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SYN Flood Attack

• Nature of attack
• Attacker (client) sends a TCP SYN (Synchronize
  Sequence/Packet Number) request to server.
• The server responds by sending a TCP SYN/ACK
  packet.
• The attacker does not respond resulting in
  half-open session using up server resources.
• The attacker sends a flood of such TCP SYN
  requests without responding.
• Requests from other legitimate clients are unable
  to reach the server due to multiple half-open
  sessions

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Distributed DoS (DDos) attack

• In a DDoS attack, a hacker first gains control of
  hundreds/thousands of computers (slaves).
• Plants software referred to as DDoS agent on each
  of the slaves
• Hacker then uses software referred to as DDoS
  handler (master) to control the agents (slaves)
• Attacker launches attacks from all the slaves and
  it is difficult to trace hacker

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High Profile Victims of DDoS

• Yahoo, eBay, Amazon, Microsoft and eTrade
  websites have been rendered inaccessible to
  legitimate visitors after being flooded with
  traffic from hundreds of hijacked system
• www.msn.com www.expedia.com www.carpoint.com
  sites were flooded with DDoS attack for almost
  one day
• DDoS attack high-level DNS servers on the Internet

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Firewalls

• Firewalls are used to prevent intruders on the
  Internet from making unauthorized access and
  denial of service attacks to your network.
• Examines packets flowing into and out of the
  organizations network (usually via the Internet
  or corporate Intranet), restricting access to
  that network.
• Two main types of firewalls are packet level
  firewalls and application-level firewalls.

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Packet-level Firewall

• Examines the source and destination address of
  packets that pass through it
• Only allowing packets that have acceptable
  addresses to pass.
• Since each packet is examined separately, the
  firewall cant understand what the senders goal
  is.
• Does not monitor the contents of the packets or
  why they are being transmitted and typically does
  not log the packets for later analysis.

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Packet-level Firewall contd

• In general, addresses are typically examined at
  the transport layer (TCP Port ID) and network
  layer (IP address)
• Example 1 Dont allow Telnet (Dest. Port ID 23
  not allowed)
• Example 2 Dont allow packets from Internet on
  an Intranet (Source IP has to be that of a device
  in the intranet)
• May be vulnerable to IP spoofing
• Accomplished by changing the source address on
  incoming packets from their real address to an
  address inside the organizations network.
• Packet-level firewalls have strengthened their
  security since the first cases of IP spoofing
  (Dec 1994).
• Example Some firewalls automatically delete any
  packets arriving from the Internet that have
  internal source addresses

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Application-Level Firewalls

• Acts as an intermediate host computer, separating
  a private network from the rest of the Internet,
  but it works on specific applications, such as
  Web site access.
• Application gateway acts as an intermediary
  between the outside client making the request and
  the destination server responding to that
  request, hiding individual computers on the
  network behind the firewall.
• Because of the increased complexity of what they
  do, application level firewalls require more
  processing power than packet filters which can
  impact network performance.

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Network Address Translation (NAT)

• Used to shield a private network from outside
  interference.
• An NAT proxy server uses an address table,
  translating network addresses inside the
  organization into aliases for use on the
  Internet. So, internal IP addresses remain
  hidden.
• Many organizations combine NAT proxy servers,
  packet filters and application gateways,
  maintaining their online resources in a DMZ
  network

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Typical network design using firewalls.
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Security in many layers

• 5 layer model
• Application Layer
• Transport Layer
• Network Layer
• Data Link Layer
• Physical Layer
• Each layer can have its own security protocols.

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Security at Application Layer

• Secure E-mail
• PGP (Pretty Good Privacy)
• e-mail encryption scheme that has become a de
  facto standard.
• Uses MD5 or SHA for message digest/fingerprints.
  
• Uses CAST, 3DES, IDEA for symmetric key
  cryptography
• Uses RSA for public key cryptography
• S/MIME (Secure Multipurpose Internet Mail
  Extensions)
• PEM (Privacy Enhanced Mail)
• Secure-HTTP or S-HTTP

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Secure E-mail using PGP

• When PGP is installed, software creates a private
  key and public key for user.
• Public key is posted on the website.
• Private key is protected using a password.
• Password has to be entered every time user
  accesses private key.

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Security at Application Layer

• SET (Secure Electronic Transactions)
• Developed by MasterCard and VISA in 1997
• Developed to provide protection from electronic
  payment fraud.
• SET uses DES for Symmetric Key Cryptography and
  RSA for key exchange.

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Security at Transport LayerSSL Secure Socket
Layer

• Developed to provide data encryption and
  authentication between a Web client and a Web
  server.
• Client and server perform handshake and negotiate
  cryptographic technique to be used.
• Client and server authenticate each other
• Encrypted session progresses after handshake is
  completed.
• SSL is typically applied at the transport layer
• Implies that SSL is not limited to one
  application
• Can be applied to Web, e-mail, HTTP applications
  etc.

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SSL (Continued)

• SSL was not developed for payment transactions.
• Assume Bob makes a purchase from ABC Incorporated
  over SSL
• ABCs certificate issued by CA does not indicate
  whether ABC Incorporated is authorized to accept
  payment card purchases nor if the company is a
  reliable merchant.
• Similarly, ABC Incorporated has no assurance that
  Bob is authorized to make a payment card purchase
  
• May result in stolen credit card transactions,
  customer repudiation of purchased goods.

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Network Layer SecurityIPSecurity IPSec

• IPSec is a suite of protocols that provide
  security at the network layer.
• Complex suite of protocols
• IPSec would encrypt all parts of the packet
  including user data at application layer, TCP
  header and IP header.
• Implies that all data sent by hosts e-mail, Web
  pages etc., would be hidden from Intruder.

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IPSec (Continued)

• 2 key protocols in the IPSec suite are
• Authentication Header (AH) protocol
• provides source authentication and data integrity
  but not confidentiality
• Encapsulation Security Payload (ESP) protocol
• provides authentication, data integrity and
  confidentiality.

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IPSec (Continued)

• Before sending secure packets, source and
  destination handshake and create a one-way
  (simplex) network-layer logical connection
  known as Security Association (SA).
• SA is uniquely identified by
• Security protocol (AH or ESP) identifier
• Source IP address for simplex connection
• A 32-bit connection identifier called the
  Security Parameter Index (SPI)

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SA and Key Management

• IKE (Internet Key Exchange) algorithm is the
  default key management protocol for IPsec.
• ISKMP (Internet Security Association and Key
  Management Protocol) defines procedures for
  establishing and tearing down SAs.

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Security in IEEE 802.11Wireless Network

• Security Standards are not as advanced in
  wireless environment
• Since Fall 2004, mobile phones are being attacked
• Started in Phillipines and has reached U.S.
• Virus drains your phone battery

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Wireless Security

• WEP (Wired Equivalent Privacy) protocol provides
• Authentication
• Encryption between a host and a wireless access
  point (WAP)
• Using symmetric key approach
• No key management algorithm
• Authentication carried out using ap4.0

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Wireless Security

• However WEP has security holes
• Updates (as of Feb 22, 2005) on wireless security
  check out
• http//msnbc.msn.com/id/6998751/
• http//www.nature.com/news/2005/050221/full/050221
  -6.html
• http//www.iss.net/wireless/
• http//www.practicallynetworked.com/tools/wireless
  _articles_security.htm
• http//www.research.ibm.com/gsal/wsa/

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