The phase of Context Definition includes the modeling of the "Target of Evaluation" (TOE), also referred as the Item (acc. to ISO 21434) using system modeling in SysML, the identification of Assets, their Security Attributes and involved Stakeholders.
Create a system model or import one from any of the supported external SysML tools; using an existing safety architecture is also a valid starting point
Consider every element that is contained in the architecture as a "Candidate Asset". Mark it as an Asset if the loss of any of its security attributes may lead to the violation of any of the stakeholder objectives.
Define security attributes for each identified Asset. Use a predefined set of attributes for example based on the CIA triad, or your company project template, or customize the attributes for your project if required.
Model Stakeholders and their relationships to Assets. Define their security objectives and level of risk they are willing to accept. Use a predefined set of objectives, for example defined by HEAVENS [1] or customize the objectives for your project if required.
Besides the pure system modeling and the assignment of security attributed, an arbitrary number of external documents can be added to enrich the context definition. Once the context is established, potential threats can be derived from the TOE.
Sample high level system architecture as the Target of Evaluation (TOE)