Date of Award
Master of Science in Engineering (MSE)
Electrical and Computer Engineering
Flash memories (Computers)--Reliability., Flash memories (Computers)--Security measures., Computer security.
Due to the high bit density and low-cost, NAND flash memory has grown popularity of various consumer electronics over the past decade. NAND flash memory is used as the primary storage medium of smartphones, USB drives, SSD and laptops. To ensure the high bit density and low cost, there is a tradeoff with security and reliability. To expedite the performance of a NAND flash and to mitigate the early wear-out, erase is not performed frequently. As erase is a costly operation that reduces the lifetime of a flash memory cell, a page-level digital sanitization is used to erase data temporarily from a NAND block, which is known as scrubbing. But as a matter of concern, this page level scrubbing based sanitization generates security and privacy issues because of the cell threshold variation due to date retention effect. An adversary can utilize the data retention property to recover the sanitized data. In this thesis, we demonstrate a data recovery procedure from the commercial flash memory chip, sanitized with scrubbing, using partial erase operation. Our result demands the necessity of analog scrubbing and we propose and implement a partial program based analog scrubbing method to make scrubbing based delete data unrecoverable. NAND flash has the full potential to be used as a computing device. For example, NAND flash can be primarily used as a weight storage device for edge computing where power is a big constraint. To use flash memory as a weight storage device, lots of reliability issues need to be addressed. Over time flash memory is changing from its 2D planar structure to a vertically stacked structure. This high-density memory is increasing its bit density with the cost of reliability. We explore the other two major opportunities of NAND flash to enhance the computing reliability issues and big block management issues for high density stacked NAND flash. To exploit these opportunities in improving flash memory reliability in computing and lifetime, we also perform various experiments using the flash memory device. In this thesis, we further (1) explore the reliability issues while NAND flash memory is used as a weight storage device for edge computing and propose a page priority based weight storage method so that the accuracy can be maintained at an acceptable level, and (2) observe the layer-based dependency of BER on high-density NAND flash due to the incoherent erase operation and suggest a new method for big block management to expedite the lifetime of a flash memory. Overall, this thesis depends on the understanding of the basic operations and security vulnerabilities of NAND flash memory through rigorous experimental characterization and proposes new methods to improve the security hole along with reliability issues.
Hasan, Md Mehedi, "Security and privacy threat of scrubbed NAND flash memory and countermeasure" (2020). Theses. 328.