Chapter 1Chapter 1OverviewOverview

The art of war teaches us to rely not on the The art of war teaches us to rely not on the likelihood of the enemy's not coming, but likelihood of the enemy's not coming, but on our own readiness to receive him; not on on our own readiness to receive him; not on the chance of his not attacking, but rather the chance of his not attacking, but rather on the fact that we have made our position on the fact that we have made our position unassailable. unassailable.

——The Art of War, The Art of War, Sun TzuSun Tzu

BackgroundBackground

Information SecurityInformation Security requirements have changed requirements have changed in recent timesin recent times

traditionally provided by physical and traditionally provided by physical and administrative mechanismsadministrative mechanisms

computer use requires computer use requires automated tools to protect automated tools to protect files and other stored informationfiles and other stored information

use of networks and communications links use of networks and communications links requires measures to protect data during requires measures to protect data during transmissiontransmission

DefinitionsDefinitions

Computer SecurityComputer Security - - generic name for the generic name for the collection of tools designed to protect data collection of tools designed to protect data and to thwart hackersand to thwart hackers

Network SecurityNetwork Security - - measures to protect measures to protect data during their transmissiondata during their transmission

Internet SecurityInternet Security - - measures to protect measures to protect data during their transmission over a data during their transmission over a collection of interconnected networkscollection of interconnected networks

A secure(dependable) system is a A secure(dependable) system is a robust system that exhibits: robust system that exhibits:

secrecy(privacy or confidentiality) secrecy(privacy or confidentiality) integrity integrity reliability reliability availability availability non repudiation non repudiation

Security Loopholes: Security Loopholes:

Trojan Horse: the programs that appear to Trojan Horse: the programs that appear to be benign or even useful to users. be benign or even useful to users.

Virus: the programs that multiply themselveVirus: the programs that multiply themselves throughout the network. s throughout the network.

Worm: the programs that copy and compile Worm: the programs that copy and compile themselves on remote systems, not modify otthemselves on remote systems, not modify other programs - denial of service. her programs - denial of service.

Common security threats: Common security threats:

Natural disaster: 15%Natural disaster: 15%

Human disaster: 85%Human disaster: 85%

interruption(loss of data, denial of service) - avainterruption(loss of data, denial of service) - availability ilability

interception - secrecy interception - secrecy modification - integrity modification - integrity fabrication - integrity fabrication - integrity

Security threat sources: Security threat sources:

unintentional system or user faults - fault-tounintentional system or user faults - fault-tolerant mechanisms lerant mechanisms

external intruders - authentication verificatiexternal intruders - authentication verification on

internal intruders - authorization validation internal intruders - authorization validation

系統安全的系統安全的威脅威脅

發生原因發生情形

軟、硬體的技術問題 使用者本身

無心之過 硬體損害、程式設計不良、

系統當機。

密碼遺忘、洩露、人為疏失

不當操作、濫用資源。

蓄意破壞 密碼破解、病毒、特洛依

木馬、竊聽、偽造資訊。

網路駭客、內部職員故意

破壞。

系統品質與安全系統品質與安全

兩者需求互相衝突兩者需求互相衝突系統品質系統品質

–容易使用性容易使用性–即時性即時性–傳輸量傳輸量–簡單性簡單性

系統品質與安全系統品質與安全

網 路 安 全 性無 最高低 中 高

低

高

平衡點

系統安全的等級標準系統安全的等級標準

A等級 B等級 C等級 D等級

C1 Dn . . . . . . . . . . . . . .D1

DOSWindows NT

Services, Mechanisms, AttacksServices, Mechanisms, Attacks

need systematic way to define requirementsneed systematic way to define requirements consider three aspects of information consider three aspects of information

security:security:• security attacksecurity attack• security mechanismsecurity mechanism• security servicesecurity service

Security ServiceSecurity Service

• is something that enhances the security of the is something that enhances the security of the data processing systems and the information data processing systems and the information transfers of an organizationtransfers of an organization

• intended to counter security attacksintended to counter security attacks• make use of one or more security mechanisms make use of one or more security mechanisms

to provide the serviceto provide the service

Security MechanismSecurity Mechanism

a mechanism that is designed to detect, a mechanism that is designed to detect, prevent, or recover from a security attackprevent, or recover from a security attack

no single mechanism that will support all no single mechanism that will support all functions requiredfunctions required

however however one particular element underlies one particular element underlies many of the security mechanisms in use: many of the security mechanisms in use: cryptographic techniquescryptographic techniques

Security AttackSecurity Attack

any action that compromises the security of any action that compromises the security of information owned by an organizationinformation owned by an organization

information security is about how to information security is about how to prevent attacks, or failing that, to detect prevent attacks, or failing that, to detect attacks on information-based systemsattacks on information-based systems

have a wide range of attackshave a wide range of attacks can focus of generic types of attackscan focus of generic types of attacks note: often note: often threatthreat & & attackattack mean same mean same

OSI ITU-T X.800 Security ServicesOSI ITU-T X.800 Security Services

X.800 defines it as: a service provided by a X.800 defines it as: a service provided by a protocol layer of communicating open protocol layer of communicating open systems, which ensures adequate security of systems, which ensures adequate security of the systems or of data transfersthe systems or of data transfers

RFC 2828 defines it as: a processing or RFC 2828 defines it as: a processing or communication service provided by a system communication service provided by a system to give a specific kind of protection to to give a specific kind of protection to system resourcessystem resources

X.800 defines it in 5 major categoriesX.800 defines it in 5 major categories

OSI ITU-T X.800 Security ServicesOSI ITU-T X.800 Security Services

AuthenticationAuthentication - - assurance that the assurance that the communicating entity is the one claimedcommunicating entity is the one claimed

Access ControlAccess Control - - prevention of the unauthorized prevention of the unauthorized use of a resourceuse of a resource

Data ConfidentialityData Confidentiality – –protection of data from protection of data from unauthorized disclosureunauthorized disclosure

Data IntegrityData Integrity - - assurance that data received is as assurance that data received is as sent by an authorized entitysent by an authorized entity

Non-RepudiationNon-Repudiation - - protection against denial by protection against denial by one of the parties in a communicationone of the parties in a communication

Security Mechanisms (X.800)Security Mechanisms (X.800)

specific security mechanisms:specific security mechanisms:• encipherment, digital signatures, access encipherment, digital signatures, access

controls, data integrity, authentication controls, data integrity, authentication exchange, traffic padding, routing control, exchange, traffic padding, routing control, notarizationnotarization

pervasive security mechanisms:pervasive security mechanisms:• trusted functionality, security labels, event trusted functionality, security labels, event

detection, security audit trails, security detection, security audit trails, security recoveryrecovery

X.800 X.800 Classify Security Attacks asClassify Security Attacks as

passive attackspassive attacks - - eavesdropping on, or monitoring eavesdropping on, or monitoring of, transmissions to:of, transmissions to:• obtain message contents, orobtain message contents, or

• monitor traffic flowsmonitor traffic flows

active attacksactive attacks – modification of data stream to: – modification of data stream to:• masquerade of one entity as some othermasquerade of one entity as some other

• replay previous messagesreplay previous messages

• modify messages in transitmodify messages in transit

• denial of servicedenial of service

Model for Network SecurityModel for Network Security

Model for Network SecurityModel for Network Security

using this model requires us to: using this model requires us to: • design a suitable algorithm for the security design a suitable algorithm for the security

transformation transformation • generate the secret information (keys) used by generate the secret information (keys) used by

the algorithm the algorithm • develop methods to distribute and share the develop methods to distribute and share the

secret information secret information • specify a protocol enabling the principals to specify a protocol enabling the principals to

use the transformation and secret information use the transformation and secret information for a security service for a security service

Model for Network Access SecurityModel for Network Access Security

Model for Network Access SecurityModel for Network Access Security

using this model requires us to: using this model requires us to: • select appropriate gatekeeper functions to select appropriate gatekeeper functions to

identify users identify users • implement security controls to ensure only implement security controls to ensure only

authorised users access designated information authorised users access designated information or resources or resources

Approaches to protect a system from Approaches to protect a system from intrusion:intrusion:

Encryption of data Authentication Authorization Auditing Training Firewall & Intrusion Detection System Virus detection &Virus detection & Anti-virusAnti-virus