Network security-1195284736736860-4
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Network security-1195284736736860-4 Network security-1195284736736860-4 Presentation Transcript

  • Chapter 13Network Security 1
  • Chapt er Thir t een - Net wor k Secur it yIntroductionWhile computer systems today have some of the best securitysystems ever, they are more vulnerable than ever before.This vulnerability stems from the world-wide access tocomputer systems via the Internet.Computer and network security comes in many forms,including encryption algorithms, access to facilities, digitalsignatures, and using fingerprints and face scans as passwords. 2
  • Chapt er Thir t een - Net wor k Secur it yViruses and WormsA computer virus is a small program that alters the way acomputer operates and often does various types of damage bydeleting and corrupting data and program files, or by alteringoperating system components, so that computer operation isimpaired or even halted.Many different types of viruses, such as parasitic, boot sector,stealth, polymorphic, and macro. 3
  • Chapt er Thir t een - Net wor k Secur it yViruses and WormsA computer worm is a program that copies itself from onesystem to another over a network, without the assistance of ahuman being.Worms usually propagate themselves by transferring fromcomputer to computer via e-mail.Typically, a virus or a worm is transported as a Trojan horse—in other words, hiding inside a harmless-looking piece of codesuch as an e-mail or an application macro. 4
  • Chapt er Thir t een - Net wor k Secur it yStandard System AttacksTwo leading forms of attacks the last few years:1. Exploiting known operating system vulnerabilities2. Exploiting known vulnerabilities in application softwareFor both of these, software company issues a patch.Patch may fix it, or introduce even more holes.Either way, bad guys find new holes and exploit. 5
  • Chapt er Thir t een - Net wor k Secur it yStandard System AttacksA very common way to attack vulnerability is via an e-mailattachment. You open the attachment and you launch the virus.Second common way to attack is to simply scan your computerports while you are connected to the Internet (either dial-up ornon-dial-up). If you have an open port, hacker will downloadmalicious software to your machine. 6
  • Chapt er Thir t een - Net wor k Secur it yOther Standard System AttacksDenial of service attacks, or distributed denial of serviceattacks, bombard a computer site with so many messages thatthe site is incapable of answering valid request.In e-mail bombing, a user sends an excessive amount ofunwanted e-mail to someone.Smurfing is a nasty technique in which a program attacks anetwork by exploiting IP broadcast addressing operations.Ping storm is a condition in which the Internet Ping program isused to send a flood of packets to a server. 7
  • Chapt er Thir t een - Net wor k Secur it y 8
  • Chapt er Thir t een - Net wor k Secur it yOther Standard System AttacksSpoofing is when a user creates a packet that appears to besomething else or from someone else.Trojan Horse is a malicious piece of code hidden inside aseemingly harmless piece of code.Stealing, guessing, and intercepting passwords is also a triedand true form of attack. 9
  • Chapt er Thir t een - Net wor k Secur it yPhysical ProtectionProtection from environmental damage such as floods,earthquakes, and heat.Physical security such as locking rooms, locking downcomputers, keyboards, and other devices.Electrical protection from power surges.Noise protection from placing computers away from devicesthat generate electromagnetic interference. 10
  • Chapt er Thir t een - Net wor k Secur it yPhysical Protection - SurveillanceProper placement of security cameras can deter theft andvandalism.Cameras can also provide a record of activities.Intrusion detection is a field of study in which specialists try toprevent intrusion and try to determine if a computer system hasbeen violated.A honeypot is an indirect form of surveillance. Networkpersonnel create a trap, watching for unscrupulous activity 11
  • Chapt er Thir t een - Net wor k Secur it yControlling AccessDeciding who has access to what.Limiting time of day access.Limiting day of week access.Limiting access from a location, such as not allowing a user touse a remote login during certain periods or any time. 12
  • Chapt er Thir t een - Net wor k Secur it y 13
  • Chapt er Thir t een - Net wor k Secur it yPasswords and ID SystemsPasswords are the most common form of security and the mostabused.Simple rules help support safe passwords, including:• Change your password often.• Pick a good, random password (minimum 8 characters, mixedsymbols).• Don’t share passwords or write them down.• Don’t select names and familiar objects as passwords. 14
  • Chapt er Thir t een - Net wor k Secur it y 15
  • Chapt er Thir t een - Net wor k Secur it yPasswords and ID SystemsMany new forms of “passwords” are emerging (biometrics):• Fingerprints• Face prints• Retina scans and iris scans• Voice prints• Ear prints 16
  • Chapt er Thir t een - Net wor k Secur it yAccess RightsTwo basic questions to access right: who and how?Who do you give access right to? No one, group of users,entire set of users?How does a user or group of users have access? Read, write,delete, print, copy, execute?Most network operating systems have a powerful system forassigning access rights. 17
  • Chapt er Thir t een - Net wor k Secur it y 18
  • Chapt er Thir t een - Net wor k Secur it yAuditingCreating a computer or paper audit can help detect wrongdoing.Auditing can also be used as a deterrent.Many network operating systems allow the administrator toaudit most types of transactions.Many types of criminals have been caught because ofcomputer-based audits. 19
  • Chapt er Thir t een - Net wor k Secur it y 20
  • Chapt er Thir t een - Net wor k Secur it yBasic Encryption and DecryptionCryptography is the study of creating and using encryption anddecryption techniques.Plaintext is the the data that before any encryption has beenperformed.Ciphertext is the data after encryption has been performed.The key is the unique piece of information that is used to createciphertext and decrypt the ciphertext back into plaintext. 21
  • Chapt er Thir t een - Net wor k Secur it y 22
  • Chapt er Thir t een - Net wor k Secur it yMonoalphabetic Substitution-basedCiphersMonoalphabetic substitution-based ciphers replace a characteror characters with a different character or characters, basedupon some key.Replacing: abcdefghijklmnopqrstuvwxyzWith: POIUYTREWQLKJHGFDSAMNBVCXZThe message: how about lunch at noonencodes into EGVPO GNMKN HIEPM HGGH 23
  • Chapt er Thir t een - Net wor k Secur it yPolyalphabetic Substitution-based CiphersSimilar to monoalphabetic ciphers except multiple alphabeticstrings are used to encode the plaintext.For example, a matrix of strings, 26 rows by 26 characters orcolumns can be used.A key such as COMPUTERSCIENCE is placed repeatedlyover the plaintext.COMPUTERSCIENCECOMPUTERSCIENCECOMPUTERthisclassondatacommunicationsisthebest 24
  • Chapt er Thir t een - Net wor k Secur it yPolyalphabetic Substitution-based CiphersTo encode the message, take the first letter of the plaintext, t,and the corresponding key character immediately above it, C.Go to row C column t in the 26x26 matrix and retrieve theciphertext character V.Continue with the other characters in the plaintext. 25
  • Chapt er Thir t een - Net wor k Secur it yTransposition-based CiphersIn a transposition-based cipher, the order the plaintext is notpreserved.As a simple example, select a key such as COMPUTER.Number the letters of the word COMPUTER in the order theyappear in the alphabet.1 4 3 5 8 7 2 6C O M P U T E R 26
  • Chapt er Thir t een - Net wor k Secur it yTransposition-based CiphersNow take the plaintext message and write it under the key.1 4 3 5 8 7 2 6C O M P U T E Rt h i s i s t he b e s t c l as s i h a v e ev e r t a k e n 27
  • Chapt er Thir t een - Net wor k Secur it yTransposition-based CiphersThen read the ciphertext down the columns, starting with thecolumn numbered 1, followed by column number 2.TESVTLEEIEIRHBSESSHTHAENSCVKITAA 28
  • Chapt er Thir t een - Net wor k Secur it yPublic Key CryptographyVery powerful encryption technique in which two keys areused: the first key (the public key) encrypts the message whilethe second key (the private key) decrypts the message.Not possible to deduce one key from the other.Not possible to break the code given the public key.If you want someone to send you secure data, give them yourpublic key, you keep the private key.Secure sockets layer on the Internet is a common example ofpublic key cryptography. 29
  • Chapt er Thir t een - Net wor k Secur it yData Encryption StandardCreated in 1977 and in operation into the 1990s, the dataencryption standard took a 64-bit block of data and subjected itto 16 levels of encryption.The choice of encryption performed at each of the 16 levelsdepends on the 56-bit key applied.Even though 56 bits provides over 72 quadrillion combinations,a system using this standard has been cracked (in 1998 byElectronic Frontier Foundation in 3 days). 30
  • Chapt er Thir t een - Net wor k Secur it y 31
  • Chapt er Thir t een - Net wor k Secur it yTriple-DESA more powerful data encryption standard.Data is encrypted using DES three times: the first time by thefirst key, the second time by a second key, and the third time bythe first key again. (Can also have 3 unique keys.)While virtually unbreakable, triple-DES is CPU intensive.With more smart cards, cell phones, and PDAs, a faster (andsmaller) piece of code is highly desirable. 32
  • Chapt er Thir t een - Net wor k Secur it yAdvanced Encryption Standard (AES)Selected by the U.S. government to replace DES.National Institute of Standards and Technology selected thealgorithm Rijndael (pronounced rain-doll) in October 2000 asthe basis for AES.AES has more elegant mathematical formulas, requires onlyone pass, and was designed to be fast, unbreakable, and able tosupport even the smallest computing device. 33
  • Chapt er Thir t een - Net wor k Secur it yAdvanced Encryption Standard (AES)Key size of AES: 128, 192, or 256 bitsEstimated time to crack (assuming a machine could crack aDES key in 1 second) : 149 trillion yearsVery fast execution with very good use of resourcesAES should be widely implemented by 2004 34
  • Chapt er Thir t een - Net wor k Secur it yDigital SignaturesDocument to be signed is sent through a complex mathematicalcomputation that generates a hash.Hash is encoded with the owner’s private key then stored.To prove future ownership, stored hash is decoded using theowner’s public key and that hash is compared with a currenthash of the document.If the two hashes agree, the document belongs to the owner.The U.S. has just approved legislation to accept digitally signeddocuments as legal proof. 35
  • Chapt er Thir t een - Net wor k Secur it yPublic Key InfrastructureThe combination of encryption techniques, software, andservices that involves all the necessary pieces to support digitalcertificates, certificate authorities, and public key generation,storage, and management.A certificate, or digital certificate, is an electronic document,similar to a passport, that establishes your credentials when youare performing transactions. 36
  • Chapt er Thir t een - Net wor k Secur it yPublic Key InfrastructureA digital certificate contains your name, serial number,expiration dates, copy of your public key, and digital signatureof certificate-issuing authority.Certificates are usually kept in a registry so other users maycheck them for authenticity. 37
  • Chapt er Thir t een - Net wor k Secur it yPublic Key InfrastructureCertificates are issued by a certificate authority (CA). A CA iseither specialized software on a company network or a trustedthird party.Let’s say you want to order something over the Internet. Theweb site wants to make sure you are legit, so the web serverrequests your browser to sign the order with your private key(obtained from your certificate). 38
  • Chapt er Thir t een - Net wor k Secur it yPublic Key InfrastructureThe web server then requests your certificate from the thirdparty CA, validates that certificate by verifying third party’ssignature, then uses that certificate to validate the signature onyour order.The user can do the same procedure to make sure the webserver is not a bogus operation.A certificate revocation list is used to “deactivate” a user’scertificate. 39
  • Chapt er Thir t een - Net wor k Secur it yPublic Key InfrastructureApplications that could benefit from PKI:• World Wide Web transactions• Virtual private networks• Electronic mail• Client-server applications• Banking transactions 40
  • Chapt er Thir t een - Net wor k Secur it ySteganographyThe art and science of hiding information inside other,seemingly ordinary messages or documents.Unlike sending an encrypted message, you do not know whensteganography is hiding a secret message within a document.Examples include creating a watermark over an image or taking“random” pixels from an image and replacing them with thehidden data. 41
  • Chapt er Thir t een - Net wor k Secur it ySecuring CommunicationsSo far we have examined standard system attacks, physicalprotection, controlling access, and securing data. Now let’sexamine securing communications.One way to secure the transfer of data is to scramble the signalas it is being transmitted. This is called spread spectrumtechnology. 42
  • Chapt er Thir t een - Net wor k Secur it yGuarding Against VirusesSignature-based scanners look for particular virus patterns orsignatures and alert the user.Terminate-and-stay-resident programs run in the backgroundconstantly watching for viruses and their actions.Multi-level generic scanning is a combination of antivirustechniques including intelligent checksum analysis and expertsystem analysis. 43
  • Chapt er Thir t een - Net wor k Secur it yFirewallsA system or combination of systems that supports an accesscontrol policy between two networks.A firewall can limit the types of transactions that enter asystem, as well as the types of transactions that leave a system.Firewalls can be programmed to stop certain types or ranges ofIP addresses, as well as certain types of TCP port numbers(applications). 44
  • Chapt er Thir t een - Net wor k Secur it yFirewallsA packet filter firewall is essentially a router that has beenprogrammed to filter out or allow to pass certain IP addressesor TCP port numbers.A proxy server is a more advanced firewall that acts as adoorman into a corporate network. Any external transactionthat request something from the corporate network must enterthrough the proxy server.Proxy servers are more advanced but make external accessesslower. 45
  • Chapt er Thir t een - Net wor k Secur it y 46
  • Chapt er Thir t een - Net wor k Secur it y 47
  • Chapt er Thir t een - Net wor k Secur it yWireless SecurityHow do you make a wireless LAN secure?WEP (Wired Equivalency Protocol) was the first securityprotocol used with wireless LANs. It had weak 40-bit statickeys and was too easy to break.WPA (Wi-Fi Protected Access) replaced WEP. Majorimprovement including dynamic key encryption and mutualauthentication for wireless clients. 48
  • Chapt er Thir t een - Net wor k Secur it yWireless SecurityBoth of these should eventually give way to a new protocolcreated by the IEEE - IEEE 802.11i.802.11i allows the keys, the encryption algorithms, andnegotiation to be dynamically assigned.Also, AES encryption based on the Rijndael algorithm with128-, 192-, or 256-bit keys is incorporated. 49
  • Chapt er Thir t een - Net wor k Secur it ySecurity Policy Design IssuesWhat is the company’s desired level of security?How much money is the company willing to invest in security?If the company is serious about restricting access through anInternet link, what about restricting access through all otherentry ways?The company must have a well-designed security policy. 50
  • Chapt er Thir t een - Net wor k Secur it yNetwork Security In Action: MakingWireless LANs SecureRecall Hannah the network administrator from Chapters Seven,Eight, and Nine? Now her company wants to add a wirelessLAN to their system and make it secure.She needs to protect herself from war drivers.Should she use WEP?What about Cisco’s LEAP (Lightweight ExtensibleAuthentication Protocol)? 51
  • Chapt er Thir t een - Net wor k Secur it yNetwork Security In Action: MakingWireless LANs SecureWhat about WPA? It is relatively new. Is the software andhardware all compatible with WPA?If she decides to use WPA, where does she have to install theWPA software? In the user’s laptop? At the wireless accesspoint? At the network server? All the above? 52