Shulou(Shulou.com)06/03 Report--

Many encryption chips of Lingke Xin'an have set up NVM zone. Because of its physical characteristics without power loss and security features such as anti-brute force cracking, many users will use NVM area to store important data. Although the method is simple to use, one technical detail is easy to be ignored. The NVM area has a 100000 erase life or 10-year storage life, so users should allocate it reasonably according to the application scenarios and business logic of their own project to achieve efficient use of the NVM area, as described below.

Problem 1: the logic of updating data is unreasonable.

The write operation of the NVM area is implemented by page, and the write operation should be carried out in page units. For example: some users store multiple sets of data in the same NVM page, but each time they change one set of data, they write to that page, which is not recommended. The correct way is to update multiple groups of data in the page as much as possible, which can effectively reduce the number of sector erasure and prolong the life of the NVM area.

Problem 2: unreasonable use of address division in NVM area

Also because of page-by-page operation, users should align different data groups by page to avoid data cross-page storage. For example: some users put a set of continuous data at the junction of two pages of address, when updating and writing to this group of data, two pages of data are actually written at the same time, even if only 2 bytes of data are written, it will also result in a reduction in the write life of the 1024-byte area (assuming that the target encryption chip's NVM sector size is 512 bytes). This operation is not advocated.

Problem 3: data loss caused by lack of security protection in NVM area

The write operation of the NVM area is completed by three steps: the first step is to read the original data in the target sector, the second step is to erase the data in the target sector, and the third step is to write the modified new data and unmodified original data back to the target sector. Therefore, when the unexpected power outage occurs, the encryption chip just completes the second step of writing the NVM area, and does not complete the third step of writing the NVM area, which will cause irregular data disorder in the target area. Of course, there is also a solution, the next phase of decomposition.

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