OTP Random Bitcell Using Dual Programmed Elements Against Cloning
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Solution Overview
Problem
Random numbers generated using One Time Programmable (OTP) devices are vulnerable to detection and replication due to discernable states, which compromises security applications.
Innovation Solution
A random number generator employs at least two programmed OTP elements within a single bitcell to generate a random bit value, making it difficult to physically inspect and predict the bit value, thereby enhancing security by utilizing the difference in electrical characteristics of the OTP elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OTP devices are used to store random numbers, then random number generation is achieved, but the random numbers become vulnerable to detection and replication through physical analysis
Solution Approach 1:
The patent applies asymmetry by programming both OTP elements to the same indistinguishable state (e.g., both programmed or both unprogrammed), eliminating the symmetric distinguishable states that made previous systems vulnerable. This asymmetric approach ensures that physical inspection cannot reveal the random bit value, as both elements appear identical under SEM analysis regardless of their actual logical states.
Solution Approach 2:
The patent changes the parameter of OTP element states from distinguishable (programmed vs. unprogrammed) to indistinguishable (both programmed or both unprogrammed). By transitioning to a parameter regime where both elements share the same physical state, the system achieves security against physical analysis while maintaining random number generation capability through the indistinguishability of the elements.
2Reliability
If OTP device states are made discernable for verification, then device functionality is confirmed, but the random numbers become easily replicated
Solution Approach 1:
The patent uses asymmetry to create a verification mechanism that does not rely on discernable physical states. By programming both OTP elements to the same state, the system verifies functionality through electrical characteristic comparison rather than physical inspection, thereby preventing replication while maintaining verification capability.
3Ease of operation
If simple physical inspection methods like SEM are used, then device analysis is simplified, but security is compromised due to discernable OTP states
Solution Approach 1:
The patent maintains inspection simplicity while improving security by ensuring both OTP elements are in the same physical state (asymmetric approach). This allows simple physical inspection methods like SEM to confirm device integrity without revealing sensitive information, as the indistinguishable states prevent security compromise even under inspection.
Data Source
AI summary
A random number generator includes a first one time programmable (OTP) element and a second OTP element. The first OTP element and second OTP element have a first distribution of probable values for an electrical characteristic when unprogrammed and a second distribution of probable values when programmed. A programming circuit applies a programming signal to the first OTP element and to the second OTP element that causes the first OTP element to switch from being unprogrammed to being programmed and having a first value for its electrical characteristic and the second OTP element to switch from being unprogrammed to being programmed and having a second value for its electrical characteristic. A sense amplifier provides an output signal at a first logic state when the first value exceeds the second value and at a second logic state when the second value exceeds the first value.