CRYP_AES_Decrypt forces key mode as CRYP_KEYMODE_NORMAL

[manisht-mwp]

Hello, In stm32u5xx_hal_cryp.c, CRYP_AES_Decrypt() function, it sets the AES_CR_KMOD to be CRYP_KEYMODE_NORMAL. I've set the hcryp->Init.KeyMode = CRYP_KEYMODE_SHARED, but I believe it's not being used.

I believe it should be 'MODIFY_REG(hcryp->Instance->CR, AES_CR_KMOD, hcryp->Init.KeyMode);'

Thanks

[ALABSTM]

Hi @mtamang10,

You point has been forwarded to our development teams. Let's wait for their answer.

With regards,

[ALABSTM]

ST Internal Reference: 191244

[ALABSTM]

Hi @manisht-mwp,

According to our development teams, this is coded this way on purpose. Indeed, as you can see from RM0456, revision 5, there are two cryptographic instances: AES (chapter 49) and SAES (chapter 50).

The first instance, AES, is not intended to share any key. Instead, it is the second instance, SAES, the secure one, that could. Once the SAES instance shared its key with the AES, this latter handles that key as a normal one.

From a functions point-of-view:

• CRYP_AES_Decrypt(), along with HAL_CRYP_Encrypt(), are intended to be used by the AES instance, thus, setting the AES_CR_KMOD to CRYP_KEYMODE_NORMAL.
• HAL_CRYPEx_EncryptSharedKey() and HAL_CRYPEx_DecryptSharedKey(), on the other hand, are intended to be used by the SAES instance.

I hope this makes things clearer. Do not hesitate otherwise.

With regards,