The Resilience Model Supporting IIoT System Trustworthiness
the IIoT system behavior is based on the scheme of typical ICS operation shown in Figure 3 12. The IIoT system exists in two contexts, Operational Technology( OT) and Information Technology( IT). The control process exists in the ОТ context while the informational flows controlling how this process goes come from the IT context. Sensors and actuators tie these contexts together.
Let’ s define the formal model for the IIoT system behavior by the subsequent definition of its following components:
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input |
data, |
output |
data |
and |
environment, |
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process definition, and |
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requirements to the IIoT system |
behavior. |
Input data, output data and environment
The set of input variables X = { x 1, … x N } characterizes the input data for the control process( OT), or Process Input.
The set of output variables Y = { y 1, … y M } characterizes the output data for the control process( OT), or Process Output.
The set of variables S IOT describes the system environment. These variables include the values describing the parameters of both the IT and OT context.
S IoT = { s i | i ∈ 1 … l } – environment variables set
∀s i type( s i) = { S OT
S IT
, S IoT = S OT + S IT
The set of variables Ad = { ad i | i ∈ 1 … k } represents the adversary. We consider only the adverse conditions that arise in the IT environment, At ⊆ S IT.
Process definition
As cyber resilience requires some actions on“ adverse conditions, stresses, attacks or compromises on systems that use or are enabled by cyber resources,” there should be a possibility to recognize these conditions, stresses, attacks or compromises. In other words, we assume they are accountable. As they are accountable, the appropriate data describing them may be generated during the process. The data describing security and safety events are usually produced by sensors, for example, on the basis of a watchdog mechanism, detection of attack signatures or passive recognition of the new devices in a network.
Let’ s define D as a set of sensors and actuators data. These data are obtained by applying the functions transforming the OT data to their IT representation:
δ X: X → D x, δ Y: Y → D y, δ IoT: S IoT → D SIoT, D = D x ∪ D y ∪ D SIoT
The control system makes a decision based on data D. In our representation, the sensors and actuators that are the part of the system
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Source: Keith Stouffer, Suzanne Lightman, Victoria Pillitteri, Marshall Abrams, and Adam Hahn. NIST Special Publication 800- 82 Rev. 2. Guide to Industrial Control Systems( ICS) Security. National Institute of Standards and Technology, U. S. Department of Commerce, 2015. https:// doi. org / 10.6028 / NIST. SP. 800-82r2
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