Writing Key in OP Byte

bsuthar · ‎2025-10-17

Hello Team,

I want to store encryption Key - 4 byte into Option Byte OR any other memory Except in-built Flash Memory.

Is it possible to write in Option Memory ?

If not what could be the other option ?

TDK · ‎2025-10-17

There are no spare addresses in option bytes for this.

The usual method for doing this is writing them to the last page of FLASH. If you don't want to do that, you'll need to use an external memory chip.

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mƎALLEm · ‎2025-10-17

Hello,

I think you can store only two bytes in the option bytes in STM32F3. (By the way you didn't mention the exact part number you are using)

The only possibility in your case (4 bytes) is to use the RTC backup registers where you need an external battery.

I'm not in favor to save the keys in an external memory as it may "breach" the security by sniffing the communication between the chips ;).

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