Cache Memory Masking for SRAM PUF Aging Mitigation
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Solution Overview
Problem
Conventional SRAM PUFs in cryptographic devices face reliability issues due to silicon aging, particularly NBTI, which affects their performance over time, and require additional memory to store random data to prevent aging, but this is not feasible in cache memory used for cryptographic key storage.
Innovation Solution
A cryptographic device with a cache memory system that uses masking and unmasking operations to vary its content without impacting functionality, allowing start-up data to serve as PUF data without needing additional memory, and incorporates a mask storage and generator to reduce aging effects by changing the mask between uses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SRAM memory is used as PUF to store cryptographic keys, then security against reverse engineering is improved, but the memory cannot be used for other purposes and aging effects still occur
Solution Approach 1:
The cache memory is designed to serve dual purposes: it functions as a standard cache for normal operations and simultaneously serves as a PUF for cryptographic key generation. The same physical memory structure is used for both caching instructions/data and generating secure identifiers, eliminating the need for dedicated PUF hardware while maintaining security.
Solution Approach 2:
The invention merges the cache memory structure with the PUF functionality by using the cache's start-up content as the source of randomness. Instead of separating cache and PUF into different components, the system combines them so that the cache's natural physical variations provide the PUF effect while the cache continues its normal caching function.
2Reliability
If additional memory is allocated to store random data for anti-aging, then aging effects are mitigated, but the amount of available cache memory decreases
Solution Approach 1:
The cache memory serves itself by using its own start-up content as the PUF source. The system does not require external or additional memory resources to generate secure identifiers, as the cache's inherent physical characteristics during power-up provide the necessary randomness. This self-service approach eliminates the need for separate anti-aging memory allocations.
3Reliability
If cache content is kept static for PUF functionality, then PUF reliability is improved, but aging effects accumulate over time
Solution Approach 1:
The system dynamically updates the cache content periodically while maintaining the PUF functionality. By changing the cached data over time, the physical stress on memory cells is distributed and reduced, mitigating aging effects. The PUF reliability is maintained by using the cache's start-up state (which reflects current physical conditions) rather than relying on static historical data.
Data Source
AI summary
An aspect concerns an electronic cryptographic device (100), comprisinga cache memory configured to cache a further memory,a mask storage configured for storing a mask,a mask generator configured to generate the mask and to store the mask in the mask storage,a cache write mechanism configured to write a content of the further memory in the cache memory masked with the mask stored in the mask storage,a cache read mechanism configured to read a content of the cache memory unmasked with the mask stored in the mask storage.