Industrial Internet Security Framework v 1.0 | Page 18

Security Framework

3: Key System Characteristics Enabling Trustworthiness

guidance documents 1 require that the software used in safety-critical systems is rigorously
validated and verified using, for example, full branch-coverage testing or even formal methods
to uncover security issues. Rigorous software development practices can help developers identify
and eliminate potential safety issues and security vulnerabilities.

3.4

RELIABILITY

Reliability is the ability of a system or component to perform its required functions under stated
conditions for a specified period of time.
Reliability and availability are related. Reliability is the fraction of actual availability over
scheduled availability, as affected by scheduled maintenance, updates, repairs and backups.
These reduce availability, but they do not reduce reliability if properly scheduled. Reliability
reflects how much a company can count on a system working when it's scheduled and expected
to be working.
Assurance of reliability requires detailed understanding of the operational environment, the
system’s composition and how it was engineered and pre-fielded to establish the likelihood of
failure. The parameters, configuration settings and physical attributes are needed for each
element. Verification activities that tested whether the planned values for these were
imp