Kinetis KW2X AES128 CBC and CTR (CCM)

[davidguinn]

I'm using a Kinetis KW21D512 MCU and am porting / implementing our original code from the MC1322X (MC13224).  In the original code, we are using AES 128 CCM to encrypt our data with both a key and a CTR Key.

For the MC1322X code, we use the original Freescale Security Management, which has 2 functions we use:

FuncReturn_t CipherConfigure(cipher_mode_t CipherMode, cipher_key_t *pCipherKey, ctr_value_t *pCtrValue)

FuncReturn_t CipherMsgU8(uint8_t *pu8CipherBuffer, uint8_t u8BufferLength)

But Freescale's Cau API only has a few functions for encrypting data:

cau_aes_set_key

cau_aes_encrypt

So that didn't seem like it had the support we needed.  Looking at the KW2xD_SMAC example, the SecLib.h appears to have more AES128 support(which uses the 2 functions above):

AES_128_CBC_Encrypt

AES_128_CTR

Using these two function, I was able to match the same encryption as the MC1322X code.

So is there a way to tell if it is using the MCU hardware to do the encryption or if it is doing it all in software?

I set the FSL_FEATURE_SOC_CAU_COUNT macro, is that enough to set it up to use the hardware?

Thank you.

[georgecapraru · Accepted solution]

Hi,

The cryptographic module from MC1322X had full AES CCM acceleration.

The FSL_FEATURE_SOC_CAU_COUNT macro is defined in the MCU_features.h header file (ex: MKW24D5_features.h). If it is set to 1, then the MCU has CAU support. You should not modify the value of these defines!

The MKW24D5 has MMCAU which supports the following algorithms: DES, 3DES, AES, MD5, SHA-1, and SHA-256.

The SecLib.h also contains API for AES CCM which in case of MKW24D5 uses part HW part SW. The actual AES encryption is done by the MMCAU module.

Regards,

George