eec 688/788 secure and dependable computing lecture 2 wenbing zhao department of electrical and...

EEC 688/788EEC 688/788Secure and Dependable Secure and Dependable ComputingComputing

Lecture 2Lecture 2

Wenbing ZhaoWenbing ZhaoDepartment of Electrical and Computer EngineeringDepartment of Electrical and Computer Engineering

Cleveland State UniversityCleveland State University

[email protected]@ieee.org

04/18/2304/18/23EEC688/788: Secure & Dependable EEC688/788: Secure & Dependable

ComputingComputing Wenbing ZhaoWenbing Zhao

OutlineOutline Basic terminology Dependability concepts

Attributes Fault, error, and failure Approaches to achieving dependability

Security concepts Attributes Vulnerabilities, threats, attacks, and controls

Computer Security: Art and Science, by Matt Bishop, Addison-Wesley Professional, 2002 http://my.safaribooksonline.com/book/networking/security/0201440997

Security in Computing, 4th Edition By Charles P. Pfleeger, Shari Lawrence Pfleeger http://proquest.safaribooksonline.com/0132390779



TerminologyTerminology A system is an entity that interacts with

other entities, i.e., other systems, including hardware, software, humans, and the physical world with its natural phenomena

These other systems are the environment of the given system

The system boundary is the common frontier between the system and its environment

A system may consists of one or more components, such as nodes or processes

System

Environment

System Boundary



TerminologyTerminology State: determines the status of the system

A system may be recovered to where it was before a failure if its state was captured and survives the failure

Service delivered by a system: work done that benefits its users User/Client: another system that interacts with the former Function of a system: what the system is intended to do (Functional) Specification: description of the system function Correct service: when the delivered service implements the system

function



Dependability and its Dependability and its AttributesAttributes Dependability refers to the ability of a distributed system

to provide correct services to its users despite various threats to the system such as undetected software defects, hardware failures, and malicious attacks

A dependable system has the following attributes Availability: a measure of the readiness of the system Reliability: a measure of the system’s capability of providing correct

services continuously for a period of time Integrity: the capability of the system to protect its state from being

compromised due to various threats Maintainability: the capability of the system to evolve after it is deployed Safety: when the system fails, it does not cause catastrophic

consequences



Quantitative Dependability Quantitative Dependability MeasuresMeasures Availability - a measure of the readiness of the system

It is the probability of being operational at a given instant of time A 0.999999 availability means that the system is not operational

at most one hour in a million hours A system with high availability may in fact fail. However, failure

frequency and recovery time should be small enough to achieve the desired availability

Soft real-time systems such as telephone switching and airline reservation require high availability



Quantitative Dependability Quantitative Dependability MeasuresMeasures Reliability - a measure of continuous delivery of correct service.

It is the probability of surviving (potentially despite failures) over an interval of time

May also be evaluated as time to failure For example, the reliability requirement might be stated as a

0.999999 availability for a 10-hour mission. In other words, the probability of failure during the mission may be at most 10-6

Hard real-time systems such as flight control and process control demand high reliability, in which a failure could mean loss of life



Fault, Error, and FailureFault, Error, and Failure The adjudged or hypothesized cause of an error is called a fault An error is a manifestation of a fault in a system, in which the logical

state of an element differs from its intended value A service failure occurs if the error propagates to the service

interface and causes the service delivered by the system to deviate from correct service

The failure of a component causes a permanent or transient fault in the system that contains the component

Service failure of a system causes a permanent or transient external fault for the other system(s) that receive service from the given system



FaultFault Faults can arise during all stages in a computer system's

evolution - specification, design, development, manufacturing, assembly, and installation - and throughout its operational life

Most faults that occur before full system deployment are discovered through testing and eliminated

Faults that are not removed can reduce a system's dependability when it is in the field

A fault can be classified by its duration, nature of output, and correlation to other faults (and many other criteria)



Fault Types - Based on DurationFault Types - Based on Duration

Permanent faults are caused by irreversible device/software failures within a component due to damage, fatigue, or improper manufacturing, or bad design and implementation Permanent software faults are also called Bohrbugs Easier to detect

Transient/intermittent faults are triggered by environmental disturbances or incorrect design Transient software faults are also referred to as Heisenbugs Study shows that Heisenbugs are the majority software faults Harder to detect



Fault Types - Based on Nature of Fault Types - Based on Nature of OutputOutput

Malicious fault: The fault that causes a unit to behave arbitrarily or malicious. Also referred to as Byzantine fault A sensor sending conflicting outputs to different processors Compromised software system that attempts to cause service

failure Non-malicious faults: the opposite of malicious faults

Faults that are not caused with malicious intention Faults that exhibit themselves consistently to all observers, e.g.,

fail-stop A fail-stop system simply stops executing once it fails

Malicious faults are much harder to detect than non-malicious faults

Wenbing ZhaoWenbing Zhao

Fault Types - Based on Fault Types - Based on CorrelationCorrelation Components fault may be independent of one

another or correlated A fault is said to be independent if it does not

directly or indirectly cause another fault Faults are said to be correlated if they are related.

Faults could be correlated due to physical or electrical coupling of components

Correlated faults are more difficult to detect than independent faults


ComputingComputing



Approaches to Achieving Approaches to Achieving DependabilityDependability Fault Avoidance - how to prevent, by construction,

the fault occurrence or introduction Fault Removal - how to minimize, by verification,

the presence of faults Fault Tolerance - how to provide, by redundancy, a

service complying with the specification in spite of faults

Fault Forecasting - how to estimate, by evaluation, the presence, the creation, and the consequence of faults



Computer Security and its Computer Security and its AttributesAttributes

Computer security is synonymous to the following three attributes: Confidentiality: computer-related assets are accessed only by

authorized parties. Confidentiality is sometimes called secrecy or privacy

Integrity: assets can be modified only by authorized parties or only in authorized ways

Availability: assets are accessible to authorized parties at appropriate times



ConfidentialityConfidentiality Confidentiality is the concealment of information

Conceal the content of the information Conceal the very existence of information

The need for keeping information secret arises from the government and the industry Enforce “need to know” principle

Achieve confidentiality: access control mechanisms Cryptography: users without the cryptographic key cannot access

unscrambled information Other access control mechanisms may conceal the mere

existence of data, such as Steganography



IntegrityIntegrity Integrity refers to the trustworthiness of information, usually

phrased in terms of preventing improper or unauthorized change Data integrity: the content of the information Origin integrity: the source of the data, i.e., authentication

Integrity mechanisms: Prevention mechanisms:

Blocking any unauthorized attempts to change the data Blocking any attempts to change the data in unauthorized ways

Detection mechanisms: report that the data’s integrity is no longer trustworthy Analyze system events to detect problems Analyze the data itself to see if required or expected constraints still hold



Working with Confidentiality & Working with Confidentiality & IntegrityIntegrity With confidentiality, the data is either compromised

or it is not With integrity, both the correctness and the

trustworthiness of the data must be considered Origin of the data How well the data was protected before it arrived at the

current machine How well the data is protected on the current machine

Evaluating integrity is often very difficult



AvailabilityAvailability Availability refers to the ability to use the information

desired An aspect of reliability Also an aspect of system design: an unavailable system is at

least as bad as no system at all Why availability is relevant to security?

Someone may deliberately arrange to deny access to data or to a service by making it unavailable

Denial of service attacks: attempts to block availability It is very difficulty to detect denial of service attacks

Must determine if the unusual access patterns are attributable to deliberate manipulation of resources or of environment (i.e., an atypical event)



AvailabilityAvailability The security community is just beginning to understand what

availability implies and how to ensure it A small, centralized control of access is fundamental to

preserving confidentiality and integrity, but it is not clear that a single access control point can enforce availability

Much of computer security's past success has focused on confidentiality and integrity; full implementation of availability is security's next great challenge



Relationship of Security Relationship of Security GoalsGoals A secure system must meet all three requirements The challenge is how to find the right balance among

the goals, which often conflict For example, it is easy to preserve a particular object's

confidentiality in a secure system simply by preventing everyone from reading that object

However, this system is not secure, because it does not meet the requirement of availability for proper access

=> There must be a balance between confidentiality and availability



Relationship of Security Relationship of Security GoalsGoals



Vulnerabilities, Threats, Attacks, & Vulnerabilities, Threats, Attacks, & ControlsControls

A vulnerability is a weakness in the security system A threat to a computing system is a set of

circumstances that has the potential to cause loss or harm

A human who exploits a vulnerability perpetrates an attack on the system.

How do we address these problems? We use a control as a protective measure A control is an action, device, procedure, or technique that

removes or reduces a vulnerability A threat is blocked by control of a vulnerability



Threats, Vulnerabilities, and Threats, Vulnerabilities, and ControlsControls



Type of ThreatsType of Threats An interception means that some unauthorized

party has gained access to an asset In an interruption, an asset of the system becomes

lost, unavailable, or unusable If an unauthorized party not only accesses but

tampers with an asset, the threat is a modification An unauthorized party might create a fabrication of

counterfeit objects on a computing system



Type of ThreatsType of Threats



Threats: Threats: Methods, Opportunity, and Methods, Opportunity, and MotiveMotive

A malicious attacker must have three things: Method: the skills, knowledge, tools, and other

things with which to launch an attack Opportunity: the time and access to accomplish

the attack Motive: a reason to want to perform this attack

against this system

04/18/2304/18/23 EEC688: Secure & Dependable ComputingEEC688: Secure & Dependable Computing Wenbing ZhaoWenbing Zhao

Methods of Defense Methods of Defense Harm occurs when a threat is realized against a

vulnerability To protect against harm, we can neutralize the threat,

close the vulnerability, or both The possibility for harm to occur is called risk


Methods of Defense Methods of Defense We can deal with harm in several ways. We can seek

to Prevent it, by blocking the attack or closing the vulnerability Deter it, by making the attack harder, but not impossible Deflect it, by making another target more attractive (or this

one less so) Detect it, either as it happens or some time after the fact Recover from its effects

Intrusion tolerance is also a form of recovery because it enables the system to continue operating correctly despite attacks


Methods of Defense Methods of Defense –– Multiple Multiple ControlsControls


Countermeasures / ControlsCountermeasures / Controls Encryption

Scrambling process Software controls

Internal program controls, OS controls, development controls

Hardware controls hardware or smart card implementations of encryption

Policies and Procedures Example: change password periodically

Physical Controls Example: Locks on doors, guards at entry points

eec 688/788 secure and dependable computing lecture 2 wenbing zhao department of electrical and...

Documents

dependable system

given system

distributed system

system reliability

system function slide

dependable computing

attributes dependability

com0132390779 slide