Analog Circuit Trojan Detection Using PTL Watermark Nodes
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Solution Overview
Problem
Existing methods for detecting malicious circuits (Trojans) in analog circuits are costly, destructive, and inefficient, particularly due to their small size and the continuous nature of signal values, making them hard to detect in large circuits.
Innovation Solution
A Trojan detection system uses neural networks to identify insensitive nodes in analog circuits, inserts watermark circuits at these nodes, and connects them to a watermark output pin, allowing voltage changes caused by Trojans to be observed at the output pin, using pass transistor logic (PTL) and cascaded differential amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If physical analysis techniques (SEM or focused ion beam) are used to detect malicious circuits, then detection capability is improved, but cost increases and the process becomes destructive
Solution Approach 1:
The patent applies preliminary action by inserting watermark circuits into the analog circuit design before fabrication. These watermarks are placed at strategically selected insensitive nodes where Trojans are likely to be inserted. The watermark circuits remain dormant during normal operation but can be activated later to detect Trojans non-destructively, avoiding the need for costly and destructive post-fabrication physical analysis techniques.
Solution Approach 2:
The patent uses watermark circuits as intermediaries to detect Trojans. Instead of directly applying destructive physical analysis techniques to the suspect circuit, the watermark circuits serve as mediator elements that can reveal the presence of Trojans through electrical measurements. This intermediary approach enables non-destructive detection and eliminates the need for expensive SEM or focused ion beam equipment.
2Measurement precision
If watermark circuits are inserted at insensitive nodes, then Trojan detection capability is improved, but circuit complexity increases
Solution Approach 1:
The patent applies local quality by selectively inserting watermark circuits only at specific insensitive nodes within the analog circuit, rather than throughout the entire circuit. The neural network identifies which nodes are most susceptible to Trojan insertion, and watermarks are placed only at those locations. This localized approach provides effective Trojan detection while minimizing the addition of circuit complexity compared to comprehensive watermarking.
Solution Approach 2:
The patent uses partial action by implementing watermark circuits at a subset of critical nodes rather than all possible nodes. The neural network identifies the most vulnerable insensitive nodes, and watermarks are inserted only at those locations. This partial watermarking strategy provides sufficient Trojan detection capability while avoiding the excessive circuit complexity that would result from comprehensive watermarking of all nodes.
3Reliability
If the analog circuit is monitored continuously for Trojan activity, then detection reliability is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic action by designing the watermark circuits to be activated only when needed for Trojan detection, rather than continuously monitoring the circuit. The watermarks can be triggered on-demand or periodically to check for Trojan presence. This approach maintains high detection reliability when activation occurs while consuming minimal power during normal circuit operation when the watermarks are dormant.
Solution Approach 2:
The watermark circuits are designed to be self-service elements that can detect Trojans without requiring continuous external monitoring or control. Once inserted, the watermarks autonomously monitor their local circuit nodes and can signal Trojan presence through their output. This self-service capability provides reliable detection while minimizing power consumption, as the watermarks only consume significant power when actually detecting or signaling a Trojan event.
Data Source
AI summary
A Trojan detection system places watermark circuits within an analog circuit design that allow the system to observe a node within an analog circuit under test (CUT) that is otherwise not observable. The watermark circuit can be a pass transistor logic (PTL)-based connection between the node and a readable output pin (i.e., a “watermark output pin”). In particular, the watermark circuits can be inserted at a node where a Trojan is likely to be inserted; thus, the watermarks provide a manner for observing changes (e.g., voltage changes) caused by a malicious modification to an analog circuit. The detection system can identify potential locations (nodes) in the CUT where a Trojan may be inserted using one or more neural networks. The detection system can then insert watermark circuits connected to the identified locations.