What are the three controls may be put in place to enhance system security?

What are the three controls may be put in place to enhance system security?
Ans: The controls that you might put in place to enhance system security are:
1. Vulnerability avoidance: Controls that are intended to ensure that attacks are unsuccessful. The strategy here is to design the system so that security problems are avoided. For example, sensitive military systems are not connected to public networks so that external access is impossible. You should also think of encryption as a control based on avoidance. Any unauthorized access to encrypted data means that it cannot be read by the attacker. In practice, it is very expensive and time consuming to crack strong encryption.
2. Attack detection and neutralization: Controls that are intended to detect and repel attacks. These controls involve including functionality in a system that monitors its operation and checks for unusual patterns of activity. If these are detected, then action may be taken, such as shutting down parts of the system, restricting access to certain users, etc.
3. Exposure limitation and recovery: Controls that support recovery from problems. These can range from automated backup strategies and information ‘mirroring’ to insurance policies that cover the costs associated with a successful attack on the system.

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What are the three principal threats to the security of a system?

What are the three principal threats to the security of a system?
Ans: In any networked system, there are three main types of security threats:
1. Threats to the confidentiality of the system and its data: These can disclose information to people or programs that are not authorized to have access to that information.
2. Threats to the integrity of the system and its data: These threats can damage or corrupt the software or its data.
3. Threats to the availability of the system and its data: These threats can restrict access to the software or its data for authorized users.

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What is the distinction between a hazard and an accident?

What is the distinction between a hazard and an accident?
Ans: Accident: An unplanned event or sequence of events which results in human death or injury, damage to property, or to the environment. An overdose of insulin is an example of an accident.
Hazard: A condition with the potential for causing or contributing to an accident. A failure of the sensor that measures blood glucose is an example of a hazard.

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What is the most important difference between the two classes of safety critical system?

What is the most important difference between the two classes of safety critical system?
Ans: Safety-critical software falls into two classes:
1. Primary safety-critical software: This is software that is embedded as a controller in a system. Malfunctioning of such software can cause a hardware malfunction, which results in human injury or environmental damage. The insulin pump software, introduced in Chapter 1, is an example of a primary safety-critical system. System failure may lead to user injury.
2. Secondary safety-critical software: This is software that can indirectly result in an injury. An example of such software is a computer-aided engineering design system whose malfunctioning might result in a design fault in the object being designed. This fault may cause injury to people if the designed system malfunctions. Another example of a secondary safety-critical system is the mental health care management system, MHC-PMS. Failure of this system, whereby an unstable patient may not be treated properly, could lead to that patient injuring themselves or others.

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Explain the difference between a system fault and a system failure.

Explain the difference between a system fault and a system failure.
Ans: System fault: A characteristic of a software system that can lead to a system error. The fault is the inclusion of the code to add 1 hour to the time of the last transmission, without a check if the time is greater than or equal to 23.00. System faults do not always result in system errors and system errors do not necessarily result in system failures.
System failure: An event that occurs at some point in time when the system does not deliver a service as expected by its users. No weather data is transmitted because the time is invalid. System reliability and availability problems are mostly caused by system failures.

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Explain how a relatively unreliable system can provide a high level of availability.

Explain how a relatively unreliable system can provide a high level of availability.
Ans: A telephone exchange switch that routes phone calls is an example of a system where availability is more important than reliability. Users expect a dial tone when they pick up a phone, so the system has high availability requirements. If a system fault occurs while a connection is being set up, this is often quickly recoverable. Exchange switches can usually reset the system and retry the connection attempt. This can be done very quickly and phone users may not even notice that a failure has occurred. Furthermore, even if a call is interrupted, the consequences are usually not serious. Therefore, availability rather than reliability is the key dependability requirement for this type of system.

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Briefly define what availability means?

Briefly define what availability means?
Ans: Availability is the probability that a system, at a point in time, will be operational and able to deliver the requested services. A telephone exchange switch that routes phone calls is an example of a system where availability is more important than reliability. Users expect a dial tone when they pick up a phone, so the system has high availability requirements.

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List two other system properties that are sometimes considered to be dependability properties.

List two other system properties that are sometimes considered to be dependability properties.
Ans: 1. Maintainability: As systems are used, new requirements emerge and it is important to maintain the usefulness of a system by changing it to accommodate these new requirements. Maintainable software is software that can be adapted economically to cope with new requirements, and where there is a low probability that making changes will introduce new errors into the system.
2. Survivability: A very important attribute for Internet-based systems is survivability. Survivability is the ability of a system to continue to deliver service whilst under attack and, potentially, whilst part of the system is disabled. Work on survivability focuses on identifying key system components and ensuring that they can deliver a minimal service. Three strategies are used to enhance survivability—resistance to attack, attack recognition, and recovery from the damage caused by an attack.

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What are the four principal dependability properties?

What are the four principal dependability properties?
Ans: There are four principal dependability properties:
1. Availability: Informally, the availability of a system is the probability that it will be up and running and able to deliver useful services to users at any given time.
2. Reliability: Informally, the reliability of a system is the probability, over a given period of time, that the system will correctly deliver services as expected by the user.
3. Safety: Informally, the safety of a system is a judgment of how likely it is that the system will cause damage to people or its environment.
4. Security: Informally, the security of a system is a judgment

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Give three reasons why a system’s dependability is more important than its detailed functionality.

Give three reasons why a system’s dependability is more important than its detailed functionality.
Ans: The dependability of systems is now usually more important than their detailed functionality for the following reasons:
1. System failures affect a large number of people. Many systems include functionality that is rarely used. If this functionality were left out of the system, only a small number of users would be affected. System failures, which affect the availability of a system, potentially affect all users of the system. Failure may mean that normal business is impossible.
2. Users often reject systems that are unreliable, unsafe, or insecure. If users find that a system is unreliable or insecure, they will refuse to use it. Furthermore, they may also refuse to buy or use other products from the same company that produced the unreliable system, because they believe that these products are also likely to be unreliable or insecure.
3. System failure costs may be enormous. For some applications, such as a reactor control system or an aircraft navigation system, the cost of system failure is orders of magnitude greater than the cost of the control system.
4. Undependable systems may cause information loss. Data is very expensive to collect and maintain; it is usually worth much more than the computer system on which it is processed. The cost of recovering lost or corrupt data is usually very high.

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