Security and EthicsLecture #10

Department of Computer Science and TechnologyUniversity of Bedfordshire

Written by David Goodwin,based on the lecture series of Dayou Li

and the book Understanding Operating Systems 4thed.by I.M.Flynn and A.McIver McHoes (2006).

Operating Systems, 2012

Security andEthicsRole of OS in security

I OS has access to every part of the system.

I Vulnerability at OS level opens up the entire system toattack.

I The more complex and powerful the OS, the more likelyit is to have vulnerability to attack.

I System administrators must be on guard to their OSwith all available defences against attack and possiblefailures.

I OS role in security relates to system survivability,protection, backup and recovery.

Security andEthicsSystem survivability

I The capability to fulfil its mission, in a timely manner,in the presence of attacks, failures and accidents

I Key propertiesI Resistance to attacksI Recognition of attacks and resulting damagesI Recovery of essential services after an attackI Adaptation of system defence mechanisms to mitigate

future attacks

Security andEthicsStrategies for survivability

I Resistance to attackI strategies for repelling attacks

I AuthenticationI Access controlsI EncryptionI Message filteringI System diversificationI Functional isolation

Security andEthicsStrategies for survivability

I Recognition of attacks and damagesI Strategies for detecting attacks and evaluating damages

I Intrusion detectionI Integrity checking

Security andEthicsStrategies for survivability

I Recovery of essential and full services after an attackI Strategies for limiting damages and restoring

compromised information or functionality, maintainingor restoring essential services within mission timeconstraints, restoring full services

I Redundant componentsI Data replicationI System back up and restorationI Contingency planning

Security andEthicsStrategies for survivability

I Adaptation and evolution to reduce effectiveness offuture attacks

I Strategies for improving system survivability based onknowledge gained from intrusions

I Intrusion recognition patterns

Security andEthicsLevel of protection

configuration ease of protection relative risk vulnerability

single computer high low compromisedwithout email or passowrds,internet virusesLAN without medium medium sniffers, spoofinginternet (+viruses, passwords)LAN with low high Email, web services,internet FTP, Telnet

(+sniffers,spoofing,passwords, viruses)

Security andEthicsBackup and recovery

I Layered backup schedule – back up weekly entiresystem and daily only files changed on the day

I Copies saved for 3-6 months on a safe off-site location

I Backup becomes significant when a virus infects thecomputer – eradication software can be run anddamaged files reloaded (though changes have to beregenerated)

I Safe off-site backup crucial to disaster recovery such aswater, fire, malfunctioning sever, corrupted archivalmedia and intrusion from unauthorised users

I Policies and procedures and regular user training areessential

Security andEthicsSecurity breaches

I Unintentional intrusionsI Intentional attacks

I Denial of services attacksI Making services not available (e.g. over the Internet)I BrowsingI Directory or data in memory / disk from previous

process / fileI Wire tappingI Listening / collecting information (e.g. passwords for

later access) bypassing authenticationI Repeated trials (guessing authentic passwords)I Trap doors (including backdoor passwords)I Unspecified and undocumented entry points to systemsI Trash collection / dumpster diving

Security andEthicsViruses and worms (1)

I VirusI a small program that alters the way a computer operates

without the permission or knowledge of the userI Self-executing – often placing its own code in the path

of anotherI Self-replicating – accomplished by copying itself from an

infected file to a clean fileI Targeting certain OS exploiting known vulnerability in

the system software – hence important to correctlyupdate the OS with patches

Security andEthicsViruses and worms (2)

I Types of virusI File infector

Normally resident in memory and infect executive filesin the OS

I Boot sectorInfect the boot sector (disks and hard drives) when thecomputer is booted up (powered on)

I Master boot recordInfect the boot record of a disk saving a legitimate copyof the master boot record in a different location on thevolume

I MultipartiteInfect both boot record and program files makingespecially difficult to repair

I MacroInfect data files such as word processing and spreadsheet

Security andEthicsViruses and worms (3)

I WormsI Memory-resident program that copies from one system

to the next without requiring the aid of an infectedprogram file

I Immediate result – slower processing of legitimate workas the worm siphons off processing time and memoryspace

I Particularly destructive on networksI Morris Worm – the first widely destructive worm

infected more than 6000 systems over several days in1988. It was installed from a university computer andspread overnight to hundreds of other universities.

Security andEthicsViruses and worms (4)

I Trojan HorsesI A virus disguised as a legitimate / harmless programI Sometimes carries within itself the means to allow the

program creator to secretly access the user systemI Replaces the standard login with an identical fake login

to capture the keystrokesI The user sees a login prompt and types in user IDI The user sees a password prompt and type in passwordI The rogue program records user ID and password and

send a typical login failure message to the user, andreturns to legitimate program

I Now the user see the legitimate login and types in userID

I The user then sees the legitimate password prompt andtypes in password

I Finally the user gains access, unaware that the ID andpassword were stored by the rogue program

Security andEthicsViruses and worms (5)

I BombsI A logic bomb is a destructive program with a fuse –

triggering event (e.g. keystroke or Internet connection).I A logic bomb often spreads unnoticed throughout a

network until a predetermined event when it goes offand does the damage.

I A time bomb is triggered by a specific time such as aday of the year.

I Example –Michaelangelo discovered in 1991 was designed toexecute on the birthday of Michaelangelo (6 March1475) when a computer is booted up. It overwrote thefirst 17 sectors on heads 0-3 of the first 256 tracks ofthe disk making subsequent boot difficult.

Security andEthicsViruses and worms (6)

I Blended threatsI Combines characteristics of other attacksI Harms the affected systemI Spread to other systems using multiple methodsI Attacks other systems from multiple pointsI Propagates without human interventionI Exploits vulnerabilities of target systems

Security andEthicsVirus and worms (7)

I Antivirus software is capable of repairing files infectedwith a virus but it is generally unable to repair worms.

Security andEthicsSystem protection

I Vulnerabilities – file downloads, email exchange,vulnerable firewalls, improperly configure Internetconnections

I Regularly running antivirus software (preventive anddiagnostic)

I Using up-to-date firewalls

I Authorised individual access only

I Using encryption where necessary

Security andEthicsAntivirus software

website organisationcsrc.nist.gov Computer Security Division of the National

Institute of Standards and Technologywww.cert.org CERT Co-ordination Centrewww.ciac.org U.S. DOE Computer Incident Advisory Capabilitywww.macfee.com McFee, Inc.www.sans.org SANS Institutewww.symantec.com Symantec Corp.www.us-cert.gov U.S. Computer Emergency Readiness Team

Security andEthicsFirewalls (1)

I FirewallA set of hardware and/or software to protect systems bydisguising its IP address from outsiders who have noauthorised access or ask for information about it

I Typical tasksI Log activities that access the InternetI Maintain access control based on sender / receiver’s IP

address / services requestedI Hide the internal network from unauthorised usersI Verify that virus protection is installed and enforcedI Perform authentication based on the source of request

from the Internet

Security andEthicsFirewalls (2)

I Fundamental mechanismsI Packet filtering

The firewall reviews the header information for comingand outgoing Internet packets to verify that the sourceaddress, destination address and protocol are correct.

I Proxy serverIt hides important network information from outsidersby making the network server invisible.

Security andEthicsAuthentication

I Verification that an individual trying to access a systemis authorised to do so

I Kerberos – a network authentication protocol developedas part of the Athena project at MIT

I For password encryption for network security, Kerberosprovides strong authentication (using strongcryptography – the science of coding messages) forclient/server applications

I Free open-source implementation available atwww.mit.edu/kerberos/

Security andEthicsEncryption

I The most extreme protection for sensitive data

I Data put in a secret code

I Total network encryption – all communications withinthe systems are encrypted

I Partial encryption – may be used between the entry andexit points of a network, or other vulnerable parts

I Storage encryption – information stored in an encryptedform and decrypted when it is used

I Increased system overhead

I The key must be kept securely for decryption

Security andEthicsPassword management (1)

I PasswordI Most basic technique, needing careful user training,

forgettable, unlikely to be changed frequently,commonly shared, considered bothersome, etc.

I Password constructionI Stored in encrypted form for security reasonI Contains a combination of characters and numbers –

minimum length, use of misspelled words / joint bits ofphrases, certain pattern on keyboard, acronyms, etc.

I Password alternativesI Smart cardI Biometrics – face, fingerprints, iris, etc.

Security andEthicsPassword management (2)

I Dictionary attackI It is a method to break encrypted passwords, requiring a

copy of the encrypted password file and the encryptionalgorithm.

I Social engineeringI Looking in and around the user desktop for a written

reminder, trying the user logon ID as the password,searching logon scripts, and even telephoning friendsand co-workers to learn the names of a user’s familymembers, pets, hobbies, etc.

I PhishingI Intruder pretends to be a legitimate entry to ask unwary

users to confirm their personal and/or financialinformation via the Internet, email or telephone.

Security andEthicsEthics (1)

I Ethical behaviour – be good and do good.

I IEEE and ACM issued a standard of ethics for theglobal computing community in 1992.

I Unauthorised users can have severe consequencesI Illegally copied softwareI Plagiarism / unauthorised copying of copyrighted workI Eavesdropping on email, data or voice communicationsI Cracking / hacking to gain access another system and

monitor or change dataI Unethical use of technology – unauthorised access to

private/protected computer systems or electronicinformation (murky area of law though)

Security andEthicsEthics (2)

I Education of ethical behaviourI Publish polices that clearly state actions that should

and should not be conductedI Run regular seminars on subject including real-life case

historiesI Conduct open discussions of ethical questions (e.g. it is

ok to read someone else’s email or is it ok for someoneelse to read your email?)

I Useful information on Ethics and Professional Conductfrom ACM at www.acm.org