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STM32L083 AES peripheral

alanmonu12
Associate

Hi community!

Currently, I am using a MCU STM32L083 and I am trying to implement a bootloader. The firmware to be updated is encrypted with a AES-128 algorithm. 

The firmware is encrypted one time with a unique key for each divice and a second time for the model of the device. 

Is it possible to use two different keys?

Basically I need to use key1 to descrypt a block of data and then use key2 on that block to get the plain text.

 

Thank you in advance.

Alan.

2 REPLIES 2
tjaekel
Senior III

Isn't similar to do a ZIP on a ZIP file? (even in terms of ZIP there is not really a further compression)
Why not?: you can encrypt the same file again and again, with different keys.

Just do the opposite to decrypt, with different keys, on different "stages".

Where is the "problem"?

Hi tjaekel!

The problem comes when I try to decrpy the second "step"

CRYP_HandleTypeDef hcryp_unique;
CRYP_HandleTypeDef hcryp_model;

hcryp_unique.Instance = AES;
hcryp_unique.Init.DataType = CRYP_DATATYPE_8B;
hcryp_unique.Init.pKey = (uint8_t *)unique_key;
hcryp_unique.Init.pInitVect = (uint8_t *)iv;

HAL_CRYP_Init(&hcryp_unique);

hcryp_model.Instance = AES;
hcryp_model.Init.DataType = CRYP_DATATYPE_8B;
hcryp_model.Init.pKey = (uint8_t *)model_key;
hcryp_model.Init.pInitVect = (uint8_t *)iv2;

HAL_CRYP_Init(&hcryp_model);

int result = HAL_CRYP_AESCBC_Decrypt(&hcryp_unique, storage_page, 256, plain, 10000);
result = HAL_CRYP_AESCBC_Decrypt(&hcryp_model, plain, 256, plain2, 10000);

"result" is equals 1 after the sencond time a call HAL_CRYP_AESCBC_Decrypt function. The keys and IVs are correct.