PUF Memory Shielding for Stable Start-Up
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Solution Overview
Problem
Existing physical unclonable functions (PUFs) face challenges in maintaining the dependency of start-up values on random physical characteristics, leading to instability and errors due to spurious control signals during power-up, which affects the reliability of the digital identifier derived from semiconductor memory elements.
Innovation Solution
The implementation of a semiconductor memory element with a control input that receives shielding during power-up to prevent external control signals from influencing the stable state, ensuring that the memory element settles into a stable state dependent on its random physical characteristics, using a shielding mechanism such as connecting the control input to a reference voltage line to prevent overwrite or activation by spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the memory element is left unshielded during power-up, then the control input can respond to control signals for configuring stable states, but spurious control signals during power-up cause instability and errors in the start-up value
Solution Approach 1:
The shielding mechanism is activated before the memory element is fully powered up to preemptively block spurious control signals from affecting the start-up value. This preliminary protective action prevents harmful signals from interfering with the settling process, ensuring stable and reliable start-up behavior while maintaining control signal responsiveness after power-up completes.
2Reliability
If shielding is applied during power-up, then the dependency on random physical characteristics is maintained, but the control input cannot receive control signals for configuring stable states
Solution Approach 1:
The shielding is applied only during the critical power-up period when the memory element is settling into its start-up value, before configurability is needed. Once power-up is complete and the start-up value is established, the shielding is removed or deactivated, allowing control signals to subsequently configure the memory element into desired stable states. This timing-based approach preserves both the dependency on physical characteristics and the adaptability for configuration.
Solution Approach 2:
The shielding mechanism is made dynamic rather than static, allowing it to be selectively enabled during power-up and disabled during normal operation. This dynamic control enables the system to transition between two states: a protected state during initialization that preserves physical characteristic dependency, and an operational state that allows configurability through control signals.
3Object-generated harmful factors
If the memory element settles based on physical characteristics alone, then the digital identifier is unique and secure, but spurious control signals can overwrite or activate the memory element during settling
Solution Approach 1:
The shielding mechanism acts as an intermediary between the control input and spurious control signals during the critical settling period. It selectively blocks harmful signals while allowing the memory element to settle based on its physical characteristics, thereby preserving the uniqueness and security of the generated digital identifier without exposing the settling process to overwrite or activation by external signals.
Data Source
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AI summary
An electric physical unclonable function (PUF) (100) is provided comprising a semiconductor memory element (110) connectable to a PUF control means for reading content from the memory element and for deriving at least in part from said content a digital identifier, such as a secret key. Upon powering the memory element it settles into one of at least two different stable states. The particular stable state into which the memory element settles is dependent at least in part upon random physical characteristics of the memory element introduced during manufacture of the memory element. Settling of the memory element is further dependent upon a control input (112) of the memory element. The electric physical unclonable function comprises shielding means (142, 144) for shielding, during a time period including the power-up of the memory element and lasting at least until the settling of the memory element, the control input from receiving control signals upon which the particular stable state into which the memory element settles is dependent. In this way, the dependency of the memory element on its physical characteristics is improved, and dependency on possibly irreproducible control signals is reduced.