How to compute (externaly) AES CTR data block that can be decrypt by OTFDEC on STM32U585 ?

[Aurelien1]

Hi,

I would like to test OTFDEC on STM32U585 to use it inside a custom BOOTLOADER.

For my test, I use online website to compute AES CTR on this plaintext data "azertyuioqsdfghj" with the key 0x01020304050607081112131421222324 (I discuss IV further).

I set the data directly in source code and run my application. It write the data in HyperFlash at address 0x70001000. In addition, the I use OTFDEC to display decrypt value.

My issue is that I cannot recover the plaintext Data.

What is the IV for OTFDEC (I set NONCE and version to 0)?

I think I have an issue with IV but I am not sure.

Can someone give me an example with an external tool to create cryptic data?

Can someone explain me how OTFDEC works?

What is the IV really used If I configure OTFDEC to start at 0x70001000 address (with nonce and version set to 0)?

Thanks a lot for helping me.

Have a good day.

Aurélien

[Mohamed Aymen HZAMI]

Hello @Aurelien​ and welcome to the community,

What do you mean by IV for OTFDEC?

You can have a look on this application note to learn more about the OTFDEC

You can follow the OTFDEC configuration from this example from the STM32U5 Firmware

Project path: "STM32Cube_FW_U5_V1.1.0\Projects\B-U585I-IOT02A\Examples\OTFDEC\OTFDEC_Data_Decrypt"

Mohamed Aymen