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Assessing an Organization's Capability to Implement ... ... Security – PowerPoint PPT presentation

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Title: Security

Reported Security Incidents 1995 2003 Source
Imperative Need for Secure CommunicationCost of
Secure Communication
  • Characteristics of a secure communication
  • Confidentiality
  • Authentication
  • Message Integrity and non-repudiation
  • Availability and Access Control

  • The communicator wants the following to be
  • 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

  • Both sender and receiver should be able to
    confirm identity of other party involved in
  • 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

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

  • 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

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

  • Symmetric Key Cryptography
  • Public Key Cryptography

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
  • Key Distribution Center (KDC)
  • Kerberos

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

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.

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.

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

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.

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).

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

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

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

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

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.

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
  • 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

  • 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

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

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

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.

Public Key Cryptography
  • Example
  • Sender (S) wishes to send a message to Recipient
  • 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.

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

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

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

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
  • 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
  • For a discussion on how to find large prime
    numbers, see http//
  • For example, choose p 5 and q 7

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

Using the RSA AlgorithmCreate Rs Keys
  • Recap p 5, q 7, n 35, z 24, e 5, d
  • 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

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

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

  • 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
  • Message is decrypted using DES key

  • 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
  • However, this implies that S and R must have
    decided upon and exchanged their symmetric key.

  • 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

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.

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 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
  • 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

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.

Availability and Access Control
  • Examples of common attacks
  • Firewalls

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
  • Examples
  • Ping attacks
  • Smurf attack
  • SYN flood attack
  • Distributed Denial of Service attacks

Ping Packets
  • Packets that ask a computer to respond with an
  • Used to see if a computer is still operational in
    a network
  • Ping by computer name
  • Ping
  • Ping by IP address
  • Ping

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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

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.

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
  • 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

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

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
    sites were flooded with DDoS attack for almost
    one day
  • DDoS attack high-level DNS servers on the Internet

  • 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.

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
  • Does not monitor the contents of the packets or
    why they are being transmitted and typically does
    not log the packets for later analysis.

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

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.

Network Address Translation (NAT)
  • Used to shield a private network from outside
  • 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
  • Many organizations combine NAT proxy servers,
    packet filters and application gateways,
    maintaining their online resources in a DMZ

Typical network design using firewalls.
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.

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
  • Uses RSA for public key cryptography
  • S/MIME (Secure Multipurpose Internet Mail
  • PEM (Privacy Enhanced Mail)
  • Secure-HTTP or S-HTTP

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.

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.

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

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.

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.

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

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)

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.

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

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

Wireless Security
  • However WEP has security holes
  • Updates (as of Feb 22, 2005) on wireless security
    check out
  • http//
  • http//
  • http//
  • http//
  • http//

(No Transcript)