© 2009 pearson education, inc. publishing as prentice hall chapter 9 raymond panko’s business...
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© 2009 Pearson Education, Inc. Publishing as Prentice Hall
Chapter 9
Raymond Panko’sBusiness Data Networks and Telecommunications, 7th edition
May only be used by adopters of the book
Security
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-2
Security Requirements
• Authenticity
• Confidentiality
• Integrity
• Non-repudiation
• Availability
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-3
9-1: Security
• A Major Threat
• Intelligent Adversaries– Not just human error to content with
– Adapt to defenses
• Recap from Chapter 1– Authentication
– Cryptography for messages
– Firewalls
– Host hardening
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-4
9-3: Malware
• Malware– A general name for evil software
• Viruses– Pieces of code that attach to other programs
– Virus code executes when infected programs execute
– Infect other programs on the computer
– Spread to other computers by e-mail attachments, IM, peer-to-peer file transfers, etc.
– Antivirus programs are needed to scan arriving files• Also scan for other malware
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-5
9-3: Malware
• Worms
– Stand-alone programs that do not need to attach to other programs
– Can propagate like viruses through e-mail, etc.• This requires human gullibility, which is unreliable
and slow 易受欺騙
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-6
9-3: Malware
• Worms– Vulnerability-enabled worms jump to victim hosts directly
• Can do this because hosts have vulnerabilities
– Vulnerability-enabled worms can spread with amazing speed
– Vendors develop patches for vulnerabilities, but companies often fail or are slow to apply them
InfestedComputer
Computerwith
Vulnerability
寄生
弱點 受害者
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-7
9-3: Malware
• Payloads
– After propagation, viruses and worms execute their payloads
– Payloads erase hard disks or send users to pornography sites if they mistype URLs
– Trojan horses are exploitation programs that disguise themselves as system files
– Spyware Trojans collect sensitive data and send the data it to an attacker
偽裝開採
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-8
9-4: Attacks on Individuals
• Social Engineering– Tricking the victim into doing something against his or her
interests
• Spam– Unsolicited commercial e-mail
• Fraud– Deceiving individuals to get them to do things against their
interests
• Taking the Reader to a Web site with Malware
未經請求的詭計 ; 騙局欺騙
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-9
9-4: Attacks on Individuals
• Credit Card Number Theft– Performed by carders
• Identity theft– Involves collecting enough data to impersonate the victim in
large financial transactions
• Phishing– A sophisticated social engineering attack in which an
authentic-looking e-mail or Web site entices the user to enter his or her username, password, or other sensitive information
網路釣魚
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-10
9-5: Human Break-Ins
• Human Break-Ins
– Viruses and worms rely on one main attack method
– Humans can keep trying different approaches until they succeed
• Hacking
– Hacking is breaking into a computer
– More precisely, hacking is intentionally using a computer resource without authorization or in excess of authorization
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-11
9-5: Human Break-Ins
• Scanning Phase
– Send attack probes to map the network and identify possible victim hosts
– The Nmap program is popular for scanning attacks (Figure 9-6)
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-12
Figure 9-6: Nmap Scanning Output
IP Range to Scan
Type of Scan
Identified Host and
Open Ports
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-13
9-5: Human Break-Ins
• The Break-In
– Uses an exploit—a tailored attack method that is often a program
– Normally exploits a vulnerability on the victim computer
– Often aided by a hacker tool
– The act of breaking in is called the exploit
– The hacker tool is also called an exploit
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-14
9-5: Human Break-Ins
• After the Break-In– The hacker downloads a hacker tool kit to automate
hacking work
– The hacker becomes invisible by deleting log files
– The hacker creates a backdoor (way to get back into the computer)
• Backdoor account—account with a known password and full privileges
• Backdoor program—program to allow reentry; usually Trojanized
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-15
9-5: Human Break-Ins
• After the Break-In– The hacker can then do damage at his or her leisure
• Download a Trojan horse to continue exploiting the computer after the attacker leaves
• Manually give operating system commands to do damage
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-16
9-7: Distributed Denial-of-Service (DDoS) Attack Using Bots
In a distributed denial-of-service attack,the attacker floods the victim computer(or network) with more traffic than the
victim can handle. Legitimate users aredenied service from the unavailable server.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-17
9-7: Distributed Denial-of-Service (DDoS) Attack Using Bots
The attackerinstalls Bot programs
on many PCs.
This is calleda botnet.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-18
9-7: Distributed Denial-of-Service (DDoS) Attack Using Bots
When it istime to attack
the victim,the attackersends attackcommands toall of the Bots.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-19
9-7: Distributed Denial-of-Service (DDoS) Attack Using Bots
The Bots then beginflooding the victim
with attack packets,rendering the victimunavailable to users
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-20
9-8: Bots
Bots can be updatedby their human master
to fix bugs or togive new functionality—for instance, to change
the Bot from a DOSattacker to a spambot.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-21
9-9: Types of Attackers
• Traditional Attackers
– Traditional Hackers• Hackers break into computers• Driven by curiosity, a desire for power, and peer
reputation
– Virus writers
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-22
9-9: Types of Attackers
• Traditional Attackers
– Script kiddies use scripts written by experienced hackers and virus writers
• They have limited knowledge and abilities• But large numbers of script kiddies make them
dangerous
– Disgruntled employees and ex-employees
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-23
9-9: Types of Attackers
• Criminal Attackers
– Most attacks are now made by criminals
– Crime generates funds that criminal attackers need to increase attack sophistication
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-24
9-9: Types of Attackers (Cont.)
• On the Horizon
– Cyberterror attacks by terrorists
– Cyberwar by nations
– Potential for massive attacks
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-25
9-11: Authentication with a Central Authentication Server
1.The supplicant sends its credentials to the verifier.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-26
9-11: Authentication with a Central Authentication Server
2.The verifier passes the credentials to
a central authentication server.
3.The central authentication server
checks the credentials.If the credentials are correct, the
authentication server sends an OK tothe verifier, along with authorizations.
1
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-27
9-11: Authentication with a Central Authentication Server
Central authentication servers bring consistency.
All supplicants are evaluated exactly the same wayno matter what verifiers they connect to.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-28
9-12: Password Authentication
• Passwords– Passwords are strings of
characters
– They are typed to authenticate the use of a username (account) on a computer
• Benefits– Ease of use for users (familiar)
– Inexpensive because they are built into operating systems
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-29
9-12: Password Authentication
• Often Weak (Easy to Crack)
– Word and name passwords are common
– They can be cracked quickly with dictionary attacks
– Hybrid dictionary attacks can crack simple variations, such as “Processing1” almost as fast
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-30
9-12: Password Authentication
• Passwords should be complex– Mix case (A and a), digits (6), and other keyboard
characters ($, #, etc.)
– Can only be cracked with brute force attacks (trying all possibilities)
• Passwords should be long– Eight characters minimum
– Each added character increases the brute force search time by a factor of about 70
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-31
9-12: Password Authentication
• Tell what attack can break it fastest, and tell how difficult it will be for the attacker to guess the password
– swordfish
– Processing1
– SeAtTLe
– R7%t&
– 4h*6tU9$^l
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-32
9-12: Password Authentication
• Other Concerns
– If people are forced to use long and complex passwords, they tend to write them down
– People should use different passwords for different sites• Otherwise, a compromised password will give access
to multiple sites
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-33
9-13: Digital Certificate Authentication
• Public and Private Keys– Each party has both a public key and a
private key
– A party makes its public key available to everybody
– A party keeps its private key secret
• If there are 12 employees, how many private keys will there be?
• How many public keys will there be?
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-34
9-13: Digital Certificate Authentication
• Digital Certificate– Tamper-proof file that gives a
party’s public key
Name: Smith
Public Key: 8m27cj$leo62@lj*^l18dwk...
Other field
…
Tamper Checking Field
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-35
9-13: Digital Certificate Authentication
Calculation Digital Certificate
AuthenticationTest
2.Public key ofthe person
the applicantclaims to be
1.Applicant
does a calculationwith his or her
Private key
3.
Verifier tests the calculation with the public key of theclaimed party (not of the sender)
If the test succeeds, the applicant mustknow the secret private key of the claimed party, which
only the claimed party should know
2
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-36
9-13: Digital Certificate Authentication
• Perspective
– Digital certificate authentication is very strong
– However, it is very expensive because companies must set up the infrastructure for distributing public–private key pairs
– The firm must do the labor of creating, distributing, and installing private keys
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-37
9-14: Biometric Authentication
• Biometric Authentication– Authentication based on bodily measurements
– Promises to eliminate passwords
• Fingerprint Scanning– Dominates biometrics use today
– Simple and inexpensive
– Substantial error rate (misidentification)
– Often can be fooled fairly easily by impostors
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-38
9-14: Biometric Authentication
• Iris Scanners– Scan the iris (colored part of the eye)
– Irises are complex, so iris scanning gives strong authentication
– Expensive
• Face Recognition– Camera: allows analysis of facial structure
– Can be done surreptitiously—that is, without the knowledge or consent of the person being scanned
– Very high error rate and easy to fool
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-39
9-14: Biometric Authentication
• Error and Deception Rates– Error and deception rates are higher than vendors claim
– The effectiveness of biometrics is uncertain
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-40
9-20: Cryptographic Systems
• Cryptographic Systems– Provide security to multi-message dialogues
• At the Beginning of Each Communication Session– The two parties usually mutually authenticate each other
Party A Party B
Initial Authentication
A’s CredentialsTo B
B’s CredentialsTo A
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-41
• Message-by-Message Protection
– After this initial authentication, cryptographic systems provide protection to every message
– Encrypt each message for confidentiality so that eavesdroppers cannot read it
9-20: Cryptographic Systems
Party A Party BMessages Encrypted for Confidentiality
EavesdropperCannot Read Messages
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-42
9-21: Symmetric Key Encryption for Confidentiality
Message“Hello”
Cipher &Key
SymmetricKey
Party AParty B
Network
Encrypted Message
Encryption uses anon-secret cipher
(encryption method )and a secret key
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-43
9-21: Symmetric Key Encryption for Confidentiality
Encrypted Message
SymmetricKey
Party A
Party B
InterceptorNetwork
Interceptor cannot readencrypted messages en route
Encrypted Message
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-44
9-21: Symmetric Key Encryption for Confidentiality
Encrypted Message Message“Hello”
Cipher &Key
SymmetricKey
SameSymmetric
KeyParty A
Party B
InterceptorNetwork
Receiver decrypts the messageusing the same cipher
and the same symmetric key
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-45
Types of Symmetric Key Encryption
DES 3DES AES
Key Length (bits) 56 112 or 168 128, 192, or 256
Strength Weak Strong Strong to Very Strong
Processing Requirements
Moderate High Modest
RAM Requirements Moderate High Modest
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-46
Figure 9-20: Symmetric and Public Key Encryption
Public Key Encryption for Confidentiality
EncryptedMessage
EncryptedMessage
Party A Party B
Encrypt withParty B’s Public Key
Decrypt withParty B’s Private Key
Decrypt withParty A’s Private Key
Encrypt withParty A’s Public Key
Note:Four keys are used to encryptand decrypt in both directions
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-47
9-20: Cryptographic Systems
• Message-by-Message Protection
– Adds an electronic signature to each message
• The electronic signature authenticates the sender
• It also provides message integrity: receiver can tell if a message has been changed in transit
Party A Party BElectronic Signature
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-48
9-20: Cryptographic Systems
• Message-by-Message Protection
– Digital signatures use digital certificate authentication• Very strong authentication, but also very expensive
– HMACs (key-hashed message authentication codes) are less expensive
• They are not quite as secure as digital signatures, but are still quite secure
• The most widely used electronic signature method
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-49
Figure D-7: Digital Signature
SenderReceiver
DS Plaintext
Add Digital Signature to Each MessageProvides Message-by-Message Authentication
Encrypted for Confidentiality
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-50
Figure D-7: Digital Signature: Sender
DS
Plaintext
MD
Hash
Sign (Encrypt) MD withSender’s Private KeySender’s Private Key
To Create the Digital Signature:
1.1. HashHash the plaintext to create the plaintext to createa brief message digesta brief message digest; This is
NOT the digital signature
2. Sign (encrypt) the messagedigest with the sender’s privatesender’s private
keykey to create the digitalSignature
Hash algorithms: MD5, SHA-1http://en.wikipedia.org/wiki/MD5http://en.wikipedia.org/wiki/SHA-1
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-51
Figure D-7: Digital Signature
SenderEncrypts Receiver
Decrypts
Send Plaintext Plus Digital SignatureEncrypted with Symmetric Session Key
DS Plaintext
Transmission
Receiver Decrypts the Message,Getting the Plaintext Plus Digital Signature
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-52
Figure D-7: Digital Signature: Receiver
DSReceived Plaintext
MDMD
1.Hash
2.Decrypt withTrue Party’sPublic Key
3.Are they Equal?
1. Hash the receivedplaintext with the samehashing algorithm the
sender used. This givesthe message digest.
2. Decrypt the digitalsignature with the sender’spublic key. This also should
give the message digest.
3. If the two match, the message is authenticated;The sender has the true
Party’s private key
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-53
Figure D-8: Public Key Deception
Impostor
“I am the True Party.”
“Here is TP’s public key.” (Sends Impostor’s public key)
“Here is authenticationbased on TP’s private key.”
(Really Impostor’s private key)
Decryption of message from Verifierencrypted with Impostor’s public key,
so Impostor can decrypt it
Verifier
Must authenticate True Party.
Believes now has TP’s public key
Believes True Partyis authenticated
based on Impostor’s public key
“True Party,here is a message encrypted
with your public key.”
CriticalDeception
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-54
Digital Certificates
• Digital certificates are electronic documents that give the true party’s name and public key
• Applicants claiming to be the true party have their authentication methods tested by this public key
• If they are not the true party, they cannot use the true party’s private key and so will not be authenticated
• Digital certificates follow the X.509 Standard
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-55
Figure D-10: Roles of Digital Certificates and Digital Signatures in Authentication
• Public key authentication requires both a digital signature and a digital certificate to give the public key needed to test the digital signature
DS Plaintext
Applicant
Verifier
Certificate Authority
DigitalCertificate:True Party’sPublic Key
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-56
Figure D-10: Roles of Digital Certificates and Digital Signatures in Authentication
DigitalSignature
Authentication
Applicant
Verifier
Certificate Authority
DigitalCertificate:True Party’sName andPublic KeyMust be Tested with
True Party’sDigital Certificate
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-57
Figure D-9: Public Key Infrastructure (PKI)
Verifier(Brown)
Certificate AuthorityPKI Server
2.Distribute
PrivateKey
Applicant (Lee)
Verifier(Cheng)
1.Create
Public Key/Private Key
Pair
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-58
Figure D-9: Public Key Infrastructure (PKI)
Verifier(Brown)
Certificate AuthorityPKI Server
4.Certificate
for Lee
Applicant (Lee)
Verifier(Cheng)
3. RequestCertificate
for Lee
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 9-59
Figure D-9: Public Key Infrastructure (PKI)
Verifier(Brown)
Certificate AuthorityPKI Server 6. Request Certificate
Revocation List (CRL)
Applicant (Lee)
5.Certificate
for Lee
Verifier(Cheng)
7. CRL
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