Integrated Monotonic Counter Using Ring Oscillators for Secure NVM
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Solution Overview
Problem
Conventional counters in electronic systems require a large number of programmable fuses to store counter values, leading to space inefficiency and compromising system security if not properly protected.
Innovation Solution
A non-volatile monotonic counter is integrated with the processing unit on the same semiconductor die, using signal generating circuits and ring oscillators to generate counter values that are retained across power cycles and incremented only as a function of time, enhancing security by reducing vulnerability to attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional counters use a large number of programmable fuses to store counter values, then counter value storage capacity is improved, but space efficiency deteriorates
Solution Approach 1:
The patent replaces the mechanical/fuse-based storage system with an electrical/electronic system using ring oscillators and signal transition counting. Instead of using physical fuses to store counter values, the invention uses the number of signal transitions generated by ring oscillators to represent counter values, eliminating the need for large arrays of programmable fuses and significantly reducing space requirements.
Solution Approach 2:
The invention changes the fundamental parameter used for counter value representation from physical fuse states to signal transition counts. By measuring the number of transitions in signals generated by ring oscillators over a predetermined time period, the system encodes counter values in temporal/frequency domain rather than spatial domain, achieving the same storage capacity with much smaller physical footprint.
2Ease of operation
If counter values are stored in conventional counters, then counter functionality is achieved, but system security deteriorates due to vulnerability to power cycle attacks and spoofing
Solution Approach 1:
The patent implements preliminary action by continuously generating signals through ring oscillators and accumulating transition counts before any read operation occurs. The counter value is not stored in a vulnerable register but is continuously being generated and updated in the background, ensuring that when a read is performed, the value reflects the true elapsed time without being susceptible to power cycle attacks or spoofing attempts.
Solution Approach 2:
The ring oscillator-based counter is self-service in that it continuously generates its own timing signals and automatically updates its count value without external intervention. The system uses its own internal oscillation to measure time elapsed, making it autonomous and resistant to external attacks. The counter serves itself by using the physical properties of the ring oscillator to generate and maintain accurate time measurements.
Data Source
AI summary
Some embodiments include a counter having a first generator to generate signals having different frequencies, and a second generator to generate counter values of the counter. Each of the counter values may be based at least in part on a number of transitions of a respective signal among the signals. Other embodiments are described.