Systems and methods for sanitization of multi-level cell (MLC) memory
Inventors
Ray, Biswajit • Milenkovic, Aleksandar • Raquibuzzaman, Md • Buddhanoy, Matchima
Assignees
University of Alabama in Huntsville
Publication Number
US-12307097-B1
Publication Date
2025-05-20
Expiration Date
2043-01-31
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Abstract
A system for performing sanitization of multi-level cell (MLC) memory has a memory controller configured to read and buffer at least a first page of MLC memory that shares MLCs with at least a second page. The memory controller sanitizes the second page by performing at least one write operation to adjust the charge levels in the MLCs so that each bit of the second page is forced to the same value or to a value that mirrors the value of another bit of the same cell. Thus, for multiple pages sharing the same MLCs, the data of at least one page can be sanitized while the data of at least one other page is retained. Such sanitizing can be achieved without having to perform an erase operation, thereby helping to prevent or reduce memory degradation.
Core Innovation
The invention provides systems and methods for sanitizing multi-level cell (MLC) memory by enabling the sanitization of a selected page, such as the least significant bit (LSB) or most significant bit (MSB) page, while retaining the data of another page that shares the same memory cells. A memory controller reads and buffers data from a page to be retained and then performs at least one write operation to force the bits of the page to be sanitized to a value independent of their original data. This write operation adjusts the charge levels within the memory cells, allowing for selective sanitization without an erase operation.
The problem addressed by this invention arises from the architecture of MLC memory, where multiple pages share the same memory cells. Conventional techniques for deleting data often only mark data as invalid instead of removing it, making sensitive data recoverable. Erase operations can only be performed at the block level, not the page level, making it difficult to efficiently and securely sanitize individual pages without affecting other data or degrading the memory.
The core innovation allows the memory controller to sanitize a page by performing targeted write operations that modify only the bits of the target page, such as setting them all to zero or a value derived from another bit in the same cell (for example, the inverse). This methodology makes recovered data on the sanitized page unrecoverable using conventional computer forensic techniques, while leaving other pages sharing the same cells unaffected. This process eliminates the need for block erases and helps prevent memory degradation.
Claims Coverage
The patent claims cover several inventive features relating to the selective sanitization of a page in multi-level cell memory without erasing entire memory blocks. There are multiple independent claims focusing on different aspects of the memory controller's operation and data manipulation processes.
Memory controller sanitizing a page without erasing memory cells
A memory controller is configured to sanitize a second page of MLC memory that shares memory cells with a first page by performing at least one write operation to adjust the charge levels so that, for each memory cell, a bit of the second page is forced to a value independent of its original data, while ensuring that the bit of the first page is retained.
Reading and buffering retained page data before sanitization
The memory controller reads data from the page to be retained and uses this buffered data to perform write operations. The data written to the sanitized page is set to a defined value, such as zero, while the original data of the retained page is preserved in the write process.
Modification of retained page data to generate write data for sanitization
The memory controller is capable of modifying data read from the retained page, for example by inverting it, to generate modified data. This modified data is then used in the write command for sanitizing the page, ensuring the bits of the sanitized page are set independently of their original states.
Selective charge manipulation in shared memory cells
The memory controller performs a sanitization operation by forcing charge into the memory cells to change the target bit in the sanitized page without altering the bit in the retained page, allowing individual page-level sanitization in memory cells shared between pages.
Sanitization method for multi-level cell memory
A method comprising storing first data in a first page and second data in a second page that share MLC memory cells, then sanitizing the second page by performing at least one write operation to alter the bits of the second page independent of their original values, while the first data of the first page is retained.
In summary, the claims are directed to inventive features enabling efficient, selective page sanitization in MLC memory through memory controller operations that adjust charge levels on a per-page basis, using read, buffer, and write commands, modifying or inverting retained page data as needed, all without erasure of memory blocks or loss of retained data.
Stated Advantages
Sanitization is achieved without performing erase operations, thereby helping to prevent or reduce memory degradation.
The technique allows for sanitizing a single page of MLC memory while retaining data in other pages sharing the same memory cells.
Methods can prevent recovery of sanitized data with conventional computer forensic techniques.
The techniques are low cost and compatible with existing memory systems.
Documented Applications
Memory sanitization in devices such as smartphones, mobile devices, tablets, personal digital assistants, personal computers, game consoles, game cartridges, or other devices.
Use in memory systems including memory cards, USB flash drives, and solid-state drives.
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