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If the two match, then the recipientknows the document hasn't been tampered with and that onlythe sender could have created the original message.UNIT 18 Data Security 1I use your public key to turn my message intogibberish. I know that only you can turn thegibberish back into the original message,because only you know your private key. Publickey cryptography also works in reverse - that is,only your public key can decipher your privatekey's encryption.To make a message tamper-proof (providingmessage integrity), the sender runs eachmessage through a message-digest function. Thisfunction within an application produces anumber called a message-authentication code(MAC). The system works because it's almostimpossible for an altered message to have thesame MAC as another message.
Also, you can'ttake a MAC and turn it back into the originalmessage.The software being used for a given exchangeproduces a MAC for a message before it'sencrypted. Next, it encrypts the MAC with thesender's private key. It then encrypts both themessage and the encrypted MAC with therecipient's public key and sends the message.When the recipient gets the message anddecrypts it, they also get an encrypted MAC. Thesoftware takes the message and runs it throughthe same message-digest function that thesender used and creates its own MAC. Then itdecrypts the sender's MAC. If the two are thesame, then the message hasn't been tamperedwith.BRe-read the text to find the answers tothese questions.1 Match the functions in Table 1 with the keysin Table 2.Table 1ato encrypt a message for sendingb to decrypt a received messagecto encrypt the MAC of a messaged to encrypt the MAC of a digital signatureTable 2isender's private keyiitrusted issuer's private keyiiithe recipient's private keyiv the recipient's public key2 Match the terms in Table A with thestatements in Table B.Table AaGibberishbImpostorThe dynamics of the Web dictate that a userauthentication system must exist.
This can bedone using digital certificates.cDecipherA server authenticates itself to a client bysending an unencrypted ASCII-based digitalcertificate. A digital certificate containsinformation about the company operating theserver, including the server's public key. Thedigital certificate is 'signed' by a trusted digitalcertificate issuer, which means that the issuerhas investigated the company operating theserver and believes it to be legitimate. If theclient trusts the issuer, then it can trust theserver. The issuer 'signs' the certificate bygenerating a MAC for it, then encrypts the MACwith the issuer's private key. If the client truststhe issuer, then it already knows the issuer'spublic key.e TenetsThe dynamics and standards of securetransactions will change, but the three basictenets of secure transactions will remain thesame. If you understand the basics, then you'realready three steps ahead of everyone else.[Jeff Downey, 'Power User Tutor', PC Magazine, August 1998]131d MACfTamperTable BiMessage-authentication codeiiPrincipal featuresiiiMeaningless dataiv Person pretending to be someone elsevMake unauthorised changesviConvert to meaningful dataAdditional exercises on page 129UNIT 19Data Security 2STARTERConsider these examples of computer disasters.
How couldyou prevent them or limit their effects? Compare answers withinyour group.12345READINGStudy this table of security measures to protect hardware andsoftware. Which measures would prevent or limit the effects of thedisasters in Task 1?Control Accessto Hardware andSoftware* Lock physical locationsand equipment.* Install a physicalsecurity system.* Monitor access 24hours a day.You open an email attachment which contains a very destructivevirus.Someone guesses your password (the type of car you drive plusthe day and month of your birth) and copies sensitive data.Your hard disk crashes and much of your data is lostpermanently.Someone walks into your computer lab and steals the memorychips from all the PCs.Your backup tapes fail to restore properly.ImplementNetwork Controls* Install firewalls toprotect networks fromexternal and internalattacks.* Password-protectprograms and data withpasswords whichcannot easily becracked.* Monitor username andpassword use - requirechanges to passwordsregularly.* Encrypt data.* Install a callbacksystem.* Use signatureverification orbiometric securitydevices to ensure userauthorisation.Protect againstNatural Disasters* Install uninterruptiblepower supplies andsurge protectors.Find words or phrases in the table which mean:1 copies of changes to files made to reduce the risk of loss ofdata2 software available for a short time on a free trial basis; ifadopted a fee is payable to the author3 cannot be disrupted or cut4 put at risk5 deciphered, worked out6 protect data by putting it in a form only authorised users canunderstand7 a combination of hardware and software to protect networksfrom unauthorised users8 observe and record systematically9 measuring physical characteristics such as distance betweenthe eyes10 at regular intervalsBackup Data andProgramsSeparate andRotate FunctionsProtect againstVirusesMake incrementalbackups, which arecopies of just changesto files, at frequentintervals.If functions areseparate, then two ormore employees wouldneed to conspire tocommit a crime.Use virus protectionprograms.Make full backups,which copy all files,periodically.If functions are rotated,employees would haveless time to developmethods tocompromise a programor system.To protect files fromnatural disasters suchas fire and flood, aswell as from crimesand errors, keepbackups in separatelocations, in fireproofcontainers, under lockand key.Perform periodicaudits.Use only vendorsupplied software orpublic domain orshareware products thatare supplied byservices that guaranteethey are virus-free.134UNIT 19 Data Security 2LANGUAGE WORKCause and effect (2) links using allow and preventWhat is the relationship between theseevents?What is the relationship between theseevents?1 The scanner finds a match for yourfingerprint.2 The keyboard is unlocked.3 You can use the PC.4 The scanner does not find a match for yourfingerprint.5 The keyboard remains locked.6 You cannot use the PC.1 and 2 are cause and effect.
We can linkthem using the methods studied in Unit 18.In addition we can use an if-sentence. Notethat the tenses for both cause and effect arethe same. For example:We can show that 4 and 5 are cause andeffect using the methods studied in Unit 18.We can also use therefore.If the scanner finds a match for yourfingerprint, the keyboard is unlocked.2 allows 3 to happen. We can link 2 and 3using allow or permit.The keyboard is unlocked, allowing/permittingyou to use the PC.The scanner does not find a match for yourfingerprint, therefore the keyboard remainslocked.5 prevents 6 from happening.We can link 5and 6 using prevent or stop.The keyboard remains locked, preventing you(from) using the PC.The keyboard remains locked, stopping you(from) using the PC.Put the verbs in brackets in the correct form in this descriptionof how smart cards work.Smart cards prevent unauthorised users(access) systemsand permit authorised users(have) access to a widerange of facilities.
Some computers have smart card readers(allow) you(buy) things on the Web easily andsafely with digital cash. A smart card can also send data to a readervia an antenna(coil) inside the card. When the cardcomes within range, the reader's radio signal(create) aslight current in the antenna(cause) the card(broadcast) information to the reader which(allow) theuser, for example,(withdraw) money from an ATM or(get) access to a system.UNIT 19 Data Security 2135Decide on the relationship between these events.
Then linkthem using structures from this and earlier units.1Anti-virus programa A user runs anti-virus software.b The software checks files for virus coding.c Coding is matched to a known virus in a virus database.d A message is displayed to the user that a virus has beenfound.e The user removes the virus or deletes the infected file.f The virus cannot spread or cause further damage.2Face recognitiona You approach a high-security network.b Key features of your face are scanned.c The system matches your features to a database record ofauthorised staff.d Your identity is verified.e You can log on.f Your identity is not verified.g You cannot use the system.3Voice recognitiona Computers without keyboards will become more common.bThese computers are voice-activated.c The user wants to log on.d She speaks to the computer.e It matches her voice to a database of voice patterns.f The user has a cold or sore throat.g She can use the system.h Stress and intonation patterns remain the same.136 UNIT 19 Data Security 2PROBLEM-SOLVINGEye scanningHand scanningFig 1Scanning technologyStudy these illustrations for two forms of security scanning.Write your own captions for each of the numbered points.UNIT 19 Data Security 2Backups Work in pairs, A and B.
You each have details of oneform of backup. Explain to your partner how your form of backupworks. Make sure you understand the form of backup your partnerhas. Ask for clarification if anything is unclear.SPEAKINGStudent AStudent BWRITINGYour information is on page 188.Your information is on page 194.Firewalls Study this diagram of a firewalled network system.Write a description of how it operates. You may need to do someresearch on firewalls to supplement the diagram.
Your descriptionshould answer these questions:12345What is its function?What does it consist of?How are the firewalls managed?How does it control outgoing communications?How does it prevent external attack?Web ServerThis management Module.Management ServerHides internal IP addressesand filters network trafficGUI ClientInternetRouterFirewalled gatewayIntranetmanages these Firewall ModulesInternalFirewallDatabaseServerFig 2How a firewall works137Changes networkprotocol andfilters networktrafficthat protect these networks.138 UNIT 19 Data Security 2Backup HSM and Media ChoiceBFind the answers to these questions In thefollowing text1 What factor determines which type ofstorage is used to store a file in an HSMsystem?2 Complete the following table usinginformation from the text.Storage TypeMediaSpeedvery fast withquickest accessspeedopticaloffline3 What happens to data that is not accessedfor a long time?4 How does the system record that a file is innear-line storage?5 What happens when a user tries to access afile in near-line storage?6 What does the reference to a file in offlinestorage contain?7 To whom does the user send a request forthe retrieval of a file from offline storage?8 Name three types of magnetic tapementioned in the text.9 Select the correct answers in the following:a How long can data be stored on tape?i) 6 months ii) 2 years iii) 10 yearsb Hard disks are usually used for whichtype of storage?i) offline ii) online iii) near-linec Tape is normally used for which type ofstorage?i) offline ii) near-line iii) onlined Files are automatically retrieved fromoffline storagei) always ii) sometimes iii) never10 What two factors determine the choice ofstorage media used?11 What items must you remember to maintainwhile data is stored?Near-line and offline storage (often calledHierarchical Storage Management) is the modernway of dealing with current storage needs.
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