DRAM Retention-Time PUF for Unpredictable Cryptographic Keys
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Solution Overview
Problem
Existing pseudo-random number generators in cryptographic applications are vulnerable due to predictability if the algorithm and initiation seed are known, making it possible to reproduce the sequence.
Innovation Solution
Implementing a Physically Unclonable Function (PUF) using retention time cell characteristics of dynamic random access memory (DRAM) systems, where specific addresses of bits that experience retention time failures are used to generate a unique and unpredictable PUF or cryptographic key, leveraging the variability in retention times between DRAM cells to create a hardware-based one-way function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pseudo-random number generating algorithm is used, then random numbers can be generated, but the sequence becomes predictable and reproducible if the algorithm and initiation seed are known
Solution Approach 1:
The patent replaces software-based pseudo-random number generation with hardware-based physical phenomenon utilization. Specifically, it uses retention time variations in DRAM cells—a physical characteristic—to generate random numbers, eliminating the predictability inherent in algorithmic approaches while maintaining generation capability.
Solution Approach 2:
The invention leverages inherent physical variations in DRAM cell retention times that naturally occur during normal operation. By utilizing these self-existing physical differences without requiring additional complex hardware or algorithms, the system generates secure random numbers from the device's own operational characteristics.
2Reliability
If PUF is implemented using DRAM retention time characteristics, then unique and unpredictable cryptographic keys are generated, but additional hardware components and operational steps are required
Solution Approach 1:
The patent utilizes existing DRAM cell structures for dual purposes: normal memory storage function and random number generation function. By measuring retention time characteristics of the same DRAM cells used for data storage, the system generates cryptographic keys without requiring completely separate dedicated hardware, thereby reducing overall complexity.
Solution Approach 2:
The invention changes the measurement parameter from standard memory read/write operations to retention time measurement. By monitoring how long charged capacitors maintain their charge state under controlled conditions, the system extracts random information from physical variations in capacitor discharge rates, achieving unpredictability through parameter transformation rather than hardware complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a secure and unpredictable PUF and random number generator, resistant to duplication and prediction, suitable for applications like anti-counterfeiting and supply chain integrity verification, by utilizing the inherent variability in DRAM cell retention times to generate a unique cryptographic key.
Implementation Method 1
a plurality of bits comprising integrated circuits each including a capacitor
Implementation Method 2
stopping bit refresh for a first predetermined time; reading all bits and recording addresses of bits that have experienced bit flip from a first state to a second state
Data Source
AI summary
Methods and apparatuses for implementing a Physically Unclonable Function (PUF) and random number generator capabilities comprising providing a device under test comprising a plurality of bits comprising integrated circuits each including a capacitor; placing the bits in a first state with charge on selected bit capacitors; stopping bit refresh for a first predetermined time; re-enabling refresh for a second predetermined time to read and refresh charge on all bits; reading all bits and recording addresses of bits that have experienced bit flip from a first state to a second state comprising from “1” to “0” state; performing selecting a plurality of said recorded addresses to generate a PUF or cryptographic key; and performing an operation comprising a test or verification operation with said generated information PUF or key. Various hardware elements are also provided as well as machine readable instructions for implementing and controlling aspects of the invention.