PUF Circuit Partitioning for Secure Key Generation and Testing
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Solution Overview
Problem
Integrated circuits that store secure keys in digital form are vulnerable to invasive attacks and reverse engineering, compromising security as these keys are exposed during manufacturing and can be accessed through external equipment, posing a risk to sensitive information.
Innovation Solution
The implementation of Physically Unclonable Functions (PUFs) generates secure keys during runtime, making them inaccessible through external contacts, while an accessible set of PUF bits is used for analysis to infer properties of the inaccessible set, enhancing security by reducing exposure and replication risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If secure keys are stored in memory and/or fuses in digital form, then the integrated circuit can be provisioned with cryptographic keys for security functions, but the secure keys become vulnerable to discovery through invasive attacks and reverse engineering
Solution Approach 1:
The patent extracts the secure key generation function from traditional storage media (memory/fuses) and implements it through Physically Unclonable Functions (PUFs). The PUF cells generate cryptographic keys dynamically during runtime based on physical characteristics, rather than storing pre-provisioned keys. This extraction removes the vulnerable digital key storage while maintaining the security function.
Solution Approach 2:
The patent replaces the digital/electronic key storage system with a physical system based on PUF cells. These cells utilize inherent physical variations in semiconductor manufacturing to create unique, unclonable physical characteristics that generate cryptographic keys. The substitution transitions from storing digital keys to generating keys through physical property measurements, making invasive attacks ineffective.
2Ease of manufacture
If secure keys are stored in digital form, then key provisioning is straightforward through manufacturing processes, but the keys are exposed to manufacturer's infrastructure and can be accessed during manufacturing
Solution Approach 1:
The PUF cells are self-service in that they automatically generate their unique cryptographic keys based on their inherent physical characteristics during normal operation. No external provisioning process is needed - the physical variations that occur during manufacturing automatically create the security keys. This eliminates the need for manufacturers to handle or store the actual keys, as they are generated autonomously by each device.
Solution Approach 2:
The patent utilizes parameter changes in the physical manufacturing process to create unique PUF characteristics for each device. Small variations in physical parameters (such as transistor dimensions, doping concentrations, or interconnect geometries) that naturally occur during manufacturing are harnessed to generate distinct cryptographic keys. This transforms manufacturing variations from defects into security assets, making each device's keys unique and unclonable.
3Reliability
If PUF cells are made inaccessible to prevent key exposure, then security is enhanced, but testing and validation of the PUF functionality becomes difficult
Solution Approach 1:
The patent segments the PUF system into multiple independent PUF cells or groups of cells. This segmentation allows different portions of the PUF to serve different functions - some cells can be dedicated to security-critical key generation while others can be used for testing and validation. The segmented structure enables selective access to specific cell groups, facilitating testing without compromising the security of the main key generation PUF.
Data Source
AI summary
An integrated circuit substrate of an aspect includes a plurality of exposed electrical contacts. The integrated circuit substrate also includes an inaccessible set of Physically Unclonable Function (PUF) cells to generate an inaccessible set of PUF bits that are not accessible through the exposed electrical contacts. The integrated circuit substrate also includes an accessible set of PUF cells to generate an accessible set of PUF bits that are accessible through the exposed electrical contacts. Other apparatus, methods, and systems are also disclosed.