PROM Tamper Protection via Entropy-Based Randomized Read
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Solution Overview
Problem
Conventional approaches to protect programmable read-only memory (PROM) in integrated circuits from tampering are inadequate, as they rely on redundancy and sensors that require calibration values stored in the PROM or software execution, making them vulnerable to attacks.
Innovation Solution
A method involving a randomized read of data from the PROM using an entropy source, such as uninitialized logic with a Linear-Feedback Shift Register (LFSR)-based power-up detector and Alternating Step Generator, to introduce temporal randomness and permutation in data access, ensuring that data is read into registers without dependence on PROM data during initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional approaches use redundancy and sensors to protect PROM sensing, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by making the PROM read operation non-deterministic through temporal randomization. The read address, read timing, and read order are dynamically randomized using an entropy source, preventing attackers from predicting or reproducing attack conditions. This dynamic approach protects reliability without adding redundant hardware components or sensors, thus avoiding increased device complexity.
2Reliability
If sensors are used to detect tampering, then reliability is improved, but ease of operation deteriorates due to calibration requirements
Solution Approach 1:
The patent extracts the tamper protection function from the data storage function. Instead of using sensors that require calibration values stored in PROM, the invention uses the entropy source to generate randomization parameters that are independent of PROM contents. This separation eliminates the need for sensor calibration while maintaining tamper detection capability through non-deterministic read operations.
3Ease of operation
If PROM data is read sequentially in a fixed order, then ease of operation is improved, but reliability deteriorates due to vulnerability to deterministic attacks
Solution Approach 1:
The patent applies dynamics by randomizing the PROM read operation. The read address is selected randomly from the PROM address space, the read timing is randomized with variable delays, and the read order is permuted using a pseudo-random sequence generator. This dynamic randomization maintains operational simplicity from the system's perspective while making the process unpredictable to attackers, thereby improving reliability without complicating the operation.
Solution Approach 2:
The patent introduces an intermediary entropy source that mediates between the deterministic system and the need for randomness. The entropy source generates random numbers that control the read address selection, timing delays, and permutation sequences. This intermediary layer provides the necessary unpredictability for security while keeping the overall system operation simple and manageable.
Data Source
AI summary
Techniques for preventing tampering with programmable read-only memory of an integrated circuit are provided. A method according to these techniques includes performing a randomized read of data stored in the programmable read-only memory based on an input from an entropy source, writing the data to one or more registers of the integrated circuit, and initializing one or more components of the integrated circuit using the data stored in the one or more registers.