Critical Path Replica Circuit for Tamper Detection in SoCs
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Solution Overview
Problem
System-on-Chips (SoCs) in secure embedded systems face challenges in detecting and protecting against tamper events caused by changes in operating voltage, temperature, or frequency, which can lead to operational failures and leakage of sensitive information.
Innovation Solution
A critical path replica (CPR) circuit is used to duplicate critical paths in SoCs, detecting deviations in voltage, temperature, or frequency by mimicking the critical path and failing before the actual design, thereby triggering tamper response mechanisms such as chip reset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a critical path replica circuit is implemented to detect tamper events, then detection capability is improved, but device complexity increases
Solution Approach 1:
The patent implements a critical path replica (CPR) circuit that duplicates the timing characteristics of the actual critical path in the SoC. This copy detects tamper events by comparing its operation against expected behavior, enabling voltage, temperature, and frequency detection without requiring separate sensing circuits for each parameter.
Solution Approach 2:
The CPR circuit serves multiple detection functions simultaneously - it detects voltage tamper, temperature tamper, and frequency tamper through a single unified mechanism. This multi-functional approach improves reliability across multiple environmental parameters while avoiding the complexity of implementing separate detection circuits for each parameter.
2Loss of time
If the CPR circuit is designed to fail ahead of actual design, then detection timing is improved, but manufacturing precision requirements increase
Solution Approach 1:
The CPR circuit is intentionally designed with conservative timing margins that cause it to fail before the actual critical path under tamper conditions. This preliminary failure mode enables early detection of environmental deviations before they affect the main design, providing advance warning of potential security breaches.
Solution Approach 2:
The patent controls the timing parameters of the CPR circuit to create a deliberate margin between the replica's critical path and the actual design's critical path. By adjusting delay elements and timing characteristics during design, the CPR is ensured to exhibit failures at threshold values that precede actual design failures, achieving early detection without requiring excessive manufacturing precision.
Data Source
AI summary
A system for detecting tamper events in a digital circuit by having a Critical Path Replica (CPR) circuit operable in parallel with the circuit being monitored, and adjusted to generate a timing violation if the operating parameters of the circuit change to be outside the normal operating parameters. The critical path replica circuit is adjusted to generate a timing violation before the actual circuit being monitored fails due to the changed operating parameters.