Lecture 2: Overview (cont)

modified from slides of Lawrie Brown

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Key Security Concepts

Confidentiality

• preserving authorized restrictions on information access and disclosure.

• including means for protecting personal privacy and proprietary information

Integrity

• guarding against improper information modification or destruction,

• including ensuring information nonrepudiation and authenticity

Availability

• ensuring timely and reliable access to and use of information

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Computer Security Terminology• Adversary (threat agent) - An entity that attacks, or is

a threat to, a system.• Attack - An assault on system security that derives

from an intelligent threat; a deliberate attempt to evade security services and violate security policy of a system.

• Countermeasure - An action, device, procedure, or technique that reduces a threat, a vulnerability, or an attack by eliminating or preventing it, by minimizing the harm it can cause, or by discovering and reporting it so that corrective action can be taken.

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Computer Security Terminology

• Risk - An expectation of loss expressed as the probability that a particular threat will exploit a particular vulnerability with a particular harmful result.

• Security Policy - A set of rules and practices that specify how a system or org provides security services to protect sensitive and critical system resources.

• System Resource (Asset) - Data; a service provided by a system; a system capability; an item of system equipment; a facility that houses system operations and equipment.

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Computer Security Terminology

• Threat - A potential for violation of security, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm.

• Vulnerability - Flaw or weakness in a system's design, implementation, or operation and management that could be exploited to violate the system's security policy.

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Security Concepts and Relationships

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Vulnerabilities, Threats and Attacks

• vulnerabilities– leaky (loss of confidentiality)– corrupted (loss of integrity)– unavailable or very slow (loss of availability)

• threats– capable of exploiting vulnerabilities– represent potential security harm

• attacks (threats carried out)– passive or active attempt to alter/affect system resources– insider or outsider

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Countermeasuresmeans used to deal

with security attacks

may introduce new vulnerabilities

Residual vulnerabilities may

remaingoal is to minimize

residual level of risk to the assets

• prevent• detect• recover

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Threat Consequences• Unauthorized disclosure is a threat to confidentiality

• Exposure: This can be deliberate or be the result of a human, hardware, or software error

• Interception: unauthorized access to data

• Inference: e.g., traffic analysis or use of limited access to get detailed information

• Intrusion: unauthorized access to sensitive data

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Threat Consequences• Deception is a threat to either system or data

integrity• Masquerade: e.g., Trojan horse; or an attempt

by an unauthorized user to gain access to a system by posing as an authorized user

• Falsification: altering or replacing of valid data or the introduction of false data

• Repudiation: denial of sending, receiving or possessing the data.

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Threat Consequences• Disruption is a threat to availability or system

integrity• Incapacitation: a result of physical destruction

of or damage to system hardware• Corruption: system resources or services

function in an unintended manner; unauthorized modification

• Obstruction: e.g. overload the system or interfere with communications

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Threat Consequences• Usurpation is a threat to system integrity.

• Misappropriation: e.g., theft of service, distributed denial of service attack

• Misuse: security functions can be disabled or thwarted

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Scope of Computer Security

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Computer and Network Assets

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Passive and Active Attacks• Passive attacks attempt to learn or make use of information

from the system but does not affect system resources• eavesdropping/monitoring transmissions• difficult to detect• emphasis is on prevention rather than detection• two types:

– message contents– traffic analysis

• Active attacks involve modification of the data stream• goal is to detect them and then recover• four categories:

– masquerade– replay– modification of messages– denial of service

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Security Functional Requirementscomputer security technical measures

• access control• identification &

authentication; • system &

communication protection

• system & information integrity

management controls and procedures

• awareness & training• audit & accountability• certification,

accreditation, & security assessments

• contingency planning• maintenance• physical &

environmental protection

• planning• personnel security• risk assessment• systems & services

acquisition

overlap computer security technical

measures and management controls

• configuration management

• incident response• media protection

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• assuring a communication is from the source that it claims to be from

• interference by a third party masquerading as one of the two legitimate parties

• Peer Entity Authentication– corroboration of the identity

of a peer entity – confidence that an entity is

not performing • a masquerade or • an unauthorized replay

AuthenticationService

Data Origin Authentication corroboration of the source of

a data supports applications where

there are no prior interactions

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• limit and control the access to host systems and applications

• each entity trying to gain access must first be identified, or authenticated

Access ControlService

NonrepudiationService

prevents either sender or receiver from denying a transmitted message

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• protection of transmitted data from passive attacks

• Protects user data transmitted over a period of time

– connection confidentiality

– connectionless confidentiality

– selective-field confidentiality

– protects the traffic flow from analysis

– traffic-flow confidentiality

Data Confidentiality

Service

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• can apply to a stream of messages, a single message, or selected fields within a message

• with and without recovery

• connectionless integrity service – provides protection against

message modification only

• connection-oriented integrity service – assures that messages are

received as sent• no duplication, insertion

modification, reordering, or replays

Data IntegrityService

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• a service that protects a system to ensure its availability– being accessible and

usable upon demand by an authorized system entity

• a variety of attacks can result in the loss of or reduction in availability

• some of these attacks are amenable to authentication and encryption

• some attacks require a physical action to prevent or recover from loss of availability

• depends on proper management and control of system resources

AvailabilityService

Security Mechanism• Feature designed to

– Prevent attackers from violating security policy– Detect attackers’ violation of security policy– Recover, continue to function correctly even if attack

succeeds.

• No single mechanism that will support all services– Authentication, authorization, availability,

confidentiality, integrity, non-repudiation22

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Security Trends

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Security Technologies

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Computer Security Strategy

Specification & policy

what is the security scheme supposed to do?

Implementation & mechanisms

how does it do it?

Correctness & assurance

does it really work?

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Security Policy• formal statement of rules and practices that

specify or regulate security services• factors to consider:

– value of the protected assets– vulnerabilities of the system– potential threats and the likelihood of attacks

• trade-offs to consider:– ease of use versus security– cost of security versus cost of failure and recovery

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Security Implementation

prevention

detection

recovery

response

complementary courses of

action

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Assurance and Evaluation• assurance

– the degree of confidence one has that the security measures work as intended

– both system design and implementation

• evaluation– process of examining a system with respect to

certain criteria– involves testing and formal analytic or

mathematical techniques

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Answers to Questions• 1 - The protection afforded to an automated information system in

order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications).

• 3 - Passive attacks have to do with eavesdropping on, or monitoring, transmissions. Electronic mail, file transfers, and client/server exchanges are examples of transmissions that can be monitored.

Active attacks include the modification of transmitted data and attempts to gain unauthorized access to computer systems.

• 4 - Passive attacks: release of message contents and traffic analysis. Active attacks: masquerade, replay, modification of messages, and denial of service.

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Answers to Questions• 5 - Authentication: The assurance that the communicating

entity is the one that it claims to beAccess control: The prevention of unauthorized use of a resourceData confidentiality: The protection of data from unauthorized disclosureData integrity: The assurance that data received are exactly as sent by an authorized entityNonrepudiation: Provides protection against denial by one of the entities involved in a communication. Availability service: Resource being accessible/usable by an authorized system entity