Semiconductor Memory Flag for Confidential Data Protection
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Solution Overview
Problem
Existing semiconductor memory devices face challenges in protecting confidential information stored in NAND flash memory from unauthorized rewriting, as ROM fuse parameters can be rewritten, allowing attackers to bypass erase restrictions on confidential information areas.
Innovation Solution
Implementing a semiconductor memory device with a confidential information area and a set flag, where the flag determines whether data can be erased or written, and using ROM fuse parameters with different values before and after writing confidential information to restrict access and prevent unauthorized changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ROM fuse parameters are used to restrict access to confidential information area, then security protection is improved, but the parameters can be rewritten by attackers allowing bypass of erase restrictions
Solution Approach 1:
The memory device is divided into a confidential information area and a non-confidential area, with the confidential information area further segmented into a data region and a flag region. This segmentation allows independent control of the flag parameter to prevent unauthorized rewriting while maintaining security protection.
Solution Approach 2:
A flag parameter is set in advance in the flag region before confidential information is stored in the data region. This preliminary action establishes a protective state that prevents subsequent unauthorized erasing or rewriting operations on the confidential information.
2Ease of manufacture
If confidential information area is made writable for testing before shipment, then manufacturing flexibility is improved, but security protection deteriorates allowing unauthorized changes after shipment
Solution Approach 1:
The flag parameter dynamically changes state from an initial value (allowing writing/erasing during manufacturing and testing) to a protected value (preventing unauthorized operations after shipment). This dynamic transition enables both manufacturing flexibility and post-shipment security protection.
Solution Approach 2:
The flag parameter transitions between different states: initially set to permit writing and erasing during manufacturing/testing, then changed to a protected state that prevents unauthorized operations. This parameter change mechanism resolves the contradiction between manufacturing flexibility and security protection.
Data Source
AI summary
A semiconductor memory device includes a memory which comprises a confidential information area storing confidential information and a flag. A controller reads the flag from the memory when instructed to erase or write data in the confidential information area, determines whether the flag is set, erases or writes data in the confidential information area when the flag is clear, and abandons a process requested by an erase or write instruction when the flag is set. An authenticator uses data in the confidential information area to execute an operation for authentication. A management information area may store management information for associated pages. The flag may include a bit string and a complementary bit string to improve reliability of the flag. The confidential information area may store dummy data when the memory is used for uses other than an application with an authentication function, so no problem arises using a normal controller.