Sommerville-Software-Engineering-10ed

13.4 ■ Secure systems design 389
Denial-of-service attacks
Denial-of-service attacks attempt to bring down a networked system by bombarding it with a huge number of
service requests, usually from hundreds of attacking systems. These place a load on the system for which it was
not designed and they exclude legitimate requests for system service. Consequently, the system may become
unavailable either because it crashes with the heavy load or has to be taken offline by system managers to stop
the flow of requests.
http://software-engineering-book.com/web/denial-of-service/
13.4.1 Design risk assessment
Security risk assessment during requirements engineering identifies a set of highlevel
security requirements for a system. However, as the system is designed and
implemented, architectural and technology decisions made during the system design
process influence the security of a system. These decisions generate new design
requirements and may mean that existing requirements have to change.
System design and the assessment of design-related risks are interleaved processes
(Figure 13.10). Preliminary design decisions are made, and the risks associated
with these decisions are assessed. This assessment may lead to new requirements
to mitigate the risks that have been identified or design changes to reduce these risks.
As the system design evolves and is developed in more detail, the risks are reassessed
and the results are fed back to the system designers. The design risk assessment
process ends when the design is complete and the remaining risks are acceptable.
When assessing risks during design and implementation, you have more information
about what needs to be protected, and you also will know something about the
vulnerabilities in the system. Some of these vulnerabilities will be inherent in the
design choices made. For example, an inherent vulnerability in password-based
authentication is that an authorized user reveals their password to an unauthorized
user. So, if password-based authentication is used, the risk assessment process may
suggest new requirements to mitigate the risk. For example, there may be a requirement
for multifactor authentication where users must authenticate themselves using
some personal knowledge as well as a password.
Technology
choices
System
requirements
System
design
Architectural
design
Design risk
assessment
Figure 13.10 Interleaved
design and risk
assessment
Design assets
Design and
requirements
changes