Tamper Detector Using Dynamic LFSR Parameters
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Solution Overview
Problem
Sophisticated attacks on tamper detection systems, such as injecting foreign signals to simulate detection signals, complicate the detection of unauthorized access and make the installation and programming of tamper detectors more difficult.
Innovation Solution
Incorporating a controller that varies the seed values, generator polynomial, and clock frequency of pseudo-random coded detection signals generated by LFSRs, making it harder for attackers to predict and deduce the seed values and subsequent signal values, and using multiplexers to selectively apply these signals to detection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pseudo-random codes are used for tamper detection, then detection security is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by making the LFSR parameters (seed values and generator polynomial) variable rather than fixed. The controller dynamically changes these parameters based on detected tamper conditions, transforming the detection system from a static to a dynamic configuration. This allows the system to adapt its security parameters in response to attack patterns, maintaining high detection security while managing complexity through programmable adjustment rather than hardware complexity.
Solution Approach 2:
The patent implements parameter changes by modifying the seed values and generator polynomial of the LFSR based on detected tamper conditions. The controller adjusts these parameters dynamically, changing the detection signal characteristics in response to attack detection. This parameter variation approach strengthens the security against prediction attacks while keeping the underlying hardware structure relatively simple, as the complexity is managed through software-controlled parameter changes rather than hardware expansion.
2Measurement precision
If sophisticated tamper countermeasures are implemented, then detection precision is improved, but ease of operation deteriorates
Solution Approach 1:
The patent applies self-service by implementing an automatic tamper detection and response system that operates autonomously without requiring manual intervention. The detector continuously monitors detection circuits, automatically detects tamper conditions, and triggers appropriate responses (such as blocking operations or alerts) without user involvement. This automation maintains high detection precision while improving ease of operation, as the system handles complex detection and response tasks automatically rather than requiring manual configuration or intervention.
Solution Approach 2:
The patent implements feedback by creating a closed-loop system where the detector monitors detection circuit signals, compares them against expected patterns, and adjusts its behavior based on the results. When tamper conditions are detected, the system feeds back control signals to the controller, which then modifies detection parameters or triggers response actions. This feedback mechanism enables the system to maintain high detection precision through continuous adaptation while simplifying operation through automated closed-loop control rather than manual adjustment.
3Ease of manufacture
If fixed LFSR parameters are used, then ease of manufacture is improved, but reliability deteriorates
Solution Approach 1:
The patent applies dynamics by transitioning from fixed to variable LFSR parameters. The controller is designed to dynamically adjust seed values and generator polynomial based on detected tamper conditions, allowing the system to adapt its security parameters in response to attack patterns. This dynamic configuration maintains ease of manufacture through a standardized hardware architecture while significantly improving reliability against prediction attacks, as the changing parameters prevent attackers from successfully cracking fixed codes.
Solution Approach 2:
The patent implements preliminary action by pre-configuring the controller with multiple possible LFSR parameter sets and initialization routines. Before actual tamper detection operations begin, the system is pre-programmed with the capability to switch between different parameter configurations. This preliminary preparation allows the system to maintain ease of manufacture through standardized hardware while improving reliability, as the pre-configured parameter variations are ready to be activated in response to detected attack conditions without requiring complex real-time computation.
Data Source
AI summary
A tamper detector has input and output pins for connection to ends of a tamper detection circuit, and a corresponding set of linear feedback shift registers (LFSRs) timed by clock signals for generating pseudo-random coded detection signals as a function of seed values and of a generator polynomial defined by feedback taps. A comparator compares signals received from the detection circuit with the coded detection signals. A multiplexer provides the coded detection signal selectively from the LFSRs to the output pin and the comparator. A controller varies the seed values for different cycles of values of the pseudo-random coded detection signals. The controller also controls the generator polynomial and a frequency of the clock signals for different cycles of values of the pseudo-random coded detection signals.