How to use eFuse BLK3 in flash?

[GerryTitan]

Hello,

I am trying to figure out the best approach for using eFuse BLK3 in an application, for example as a 256-bit key. I see from the eFuse manager docs that there are functions such as esp_efuse_read_block and esp_efuse_write_block, but everything else I've read in the docs seems to suggest that eFuse keys are completely inaccessible to software once they are set. I have also tried accessing BLK3 from flash using esp_efuse_read_block, but it seems to always return an empty string (or rather an empty void pointer). So what are the best practices for using BLK3, obviously without compromising security?

Thanks in advance.

[WiFive]

eFuse keys are completely inaccessible to software once they are set.

That is true if they are read protected and if they are not read protected they can be read by SW or over UART. So it is useful for an immutable key store but not a secret key store.