In mechanical steering columns, a physical steel shaft locks the steering wheel to the rack and pinion. In steer-by-wire, that physical link is replaced by electronic actuators and digital bus packets. If an adversary tampers with steering commands while cruising at 120 km/h, the consequence is fatal. This article provides a comprehensive walkthrough of conducting a compliant ISO/SAE 21434 Threat Analysis and Risk Assessment (TARA) on a steer-by-wire ECU.
An attack tree breaks down the ultimate adversarial goal ('Inject Unintended Steering Angle') into logical branches: Sub-goal 1: Pivot through compromised cellular T-Box; Sub-goal 2: Bypass central gateway firewall; Sub-goal 3: Forfeit SecOC message counter authentication. By calculating the feasibility score of each intermediate branch, engineers prove mathematically that achieving the root objective requires exceeding the maximum feasibility threshold of the vehicle's Cybersecurity Assurance Level.