BlueNRG-LP: API for AES decryption?

[BLEuser]

The chip has an API for the AES encryption HW, but I cannot find any access option to the AES decryption HW.

[Sebastien DENOUAL]

Hi @BLEuser​ ,

It exists a specific API for this :

tBleStatus hci_le_encrypt(uint8_t Key[16],

             uint8_t Plaintext_Data[16],

             uint8_t Encrypted_Data[16]);

This API can be used to request controller to encrypt Plaintext_Data iusing the Key given in the command

 *    and returns the Encrypted_Data to the Host

Here below is a copy/past of a code example where data is encrypted using AES engine with hci_le_encrypt and then decrypted with sw decryption using crypo lib.

Particular attention must be paid to the endianness: hci_le_encrypt uses data in little endian format, while cryptolib uses big endian format.

uint8_t key_le[16] = {0x0f,0x0e,0x0d,0x0c,0x0b,0x0a,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01,0x00};

uint8_t key_be[16];

uint8_t plaintext_data_le[16] = {0x0f,0x0e,0x0d,0x0c,0x0b,0x0a,0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x02,0x01,0x00};

uint8_t plaintext_data_be[16];

uint8_t encrypted_data_le[16];

uint8_t encrypted_data_be[16];

int32_t length;

int32_t ret_val;

AESECBctx_stt AESECBctx;

AESECBctx.mKeySize = CRL_AES128_KEY;

AESECBctx.mFlags = E_SK_DEFAULT;

hci_le_encrypt(key_le, plaintext_data_le, encrypted_data_le);

for(int i = 0; i < 16; i++)

{

key_be[i] = key_le[15 - i];

}

for(int i = 0; i < 16; i++)

{

plaintext_data_be[i] = plaintext_data_le[15-i];

}

for(int i = 0; i < 16; i++)

{

encrypted_data_be[i] = encrypted_data_le[15-i];

}

for(int i = 0; i < sizeof(encrypted_data_le); i++)

printf("%02X ",encrypted_data_be[i]);

printf("\n");

ret_val = AES_ECB_Decrypt_Init(&AESECBctx, key_be, NULL);

if(ret_val != AES_SUCCESS)

{

printf("AES_ECB_Decrypt_Init 0x%02X\n",ret_val);

while(1);

}

ret_val = AES_ECB_Decrypt_Append(&AESECBctx, encrypted_data_be, sizeof(encrypted_data_be), plaintext_data_be, &length);

if(ret_val != AES_SUCCESS)

{

printf("AES_ECB_Decrypt_Append 0x%02X\n",ret_val);

while(1);

}

for(int i = 0; i < sizeof(plaintext_data_be); i++)

printf("%02X ",plaintext_data_be[i]);

printf("\n");

ret_val = AES_ECB_Decrypt_Finish(&AESECBctx, plaintext_data_be, &length);

if(ret_val != AES_SUCCESS)

{

printf("AES_ECB_Decrypt_Finish 0x%02X\n",ret_val);

while(1);

}

Hope it helps.

Regards,

Sebastien.