Misuse Cases: Use Cases with Hostile Intent Presented by: Frank Xu Gannon University

Objectives Understand what misuse cases are Understand applications of misuse cases ▫eliciting requirements ▫eliciting exceptions ▫developing test cases

Use Cases Individual use case describes ▫how a particular actor(agent) interacts with the system to achieve a result of value to the specific actor. The set of all use cases together describes ▫the complete behavior of the system. A use-case model ▫provide graphical overview of actors, use cases, and their dependency.

Drive the car Park the car Lock the car

Misuse Cases The scenarios in which such 'negative' agents attempt to defeat the system under design

Misuse Case Misuse cases are negative use cases Actor is a hostile agent

Applications of Misuse Cases Eliciting functional requirements Eliciting nonfunctional requirements Eliciting exceptions Developing test cases

Eliciting Functional requirements

Eliciting Functional Requirements

Eliciting Non-functional Requirements “The car shall be constructed to the intrusion resistance defined in STD ”

Eliciting Safety Requirements Misuse Cases are not limited to eliciting Security Requirements, or threats from human agents. A negative agent such as bad weather can be represented as a misuse case  Drivers may lose control of their cars if the road is covered in ice or wet leaves  The weather as an agent 'intending' to make the car skid.

Eliciting Safety Requirements

Eliciting “-ility” Requirements Nonfunctional Requirements Negative agents ReliabilityHuman error, storms, design errors, interference on telecommunication links Maintainability and PortabilityInflexible design, incompatible platform UsabilityPoorly designed the user interface

Eliciting Exceptions An exception is an undesired event that could cause a system to fail. ▫“What could they do to make this go wrong?” ▫Divided by 0 Handling such exception lead to resumption of normal operations, or lead to a safe shutdown. ▫GE locomotive – satellite signal transmitting vs. weather

Eliciting Test Cases

Products of use/misuse-case analysis that can contribute to effective test planning include ▫ Specific failure modes (for real-time, embedded, and safety related systems) ▫ Security threats model (for distributed commercial and government systems) ▫Exception-handling scenarios (always useful, often directly translating to test scripts)

Key points Misuse Case models are a promising approach for ▫Eliciting functional requirements ▫Eliciting various non-functional requirements, such as for security, safety, etc ▫Identifying threats to system operation ▫Identifying ways of neutralizing those threats

Reference I. Alexander, "Misuse Cases: Use Cases with Hostile Intent," IEEE Software, vol. 20, no. 1, pp , Jan/Feb, 2003.

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