AES encryption & UBL

Hi All,

While spending some time on the AES encryption for the binary image, i realized that my application is encrypted fine when using the "UBL_SIGNER" define but there are some problems regarding the generation of the CBC - MAC tag.

If i comment out the "return false" statement ( and essentially i do not compare the CBC-MAC tag) from the following piece of code (from the UBL project), i can see that my encrypted application downloads successfully to the CC2540 SoC and also the application works as expected.

#if UBL_SIGNER
signMode = TRUE; // Now the Signer should encrypt the read back.
#else // A signer must always return FALSE so that usb_msd.c does not save the file name to flash.
if (memcmp(ctrlBlk.signature, sigBuf, KEY_BLENGTH))
#endif
{
//return FALSE;
}
#endif

Can anyone give me a hint on what i might be doing wrong and the calculation of the authentication tags fails each time?

Best regards,

George

one more observation 

It seems there's a bug causing freeze in msd  while optimization set to high
( options -> c/C++ compiler -> optimizations -> level -> high ) 

setting to medium will ease the problem of msd freeze when usb_secure is used 

however, optimization set to medium will exceed the code allowed for UBL , 
disabling MAC signature checking can reduced the code size to fit in the UBL limit 

i do hope there's better work around of course

in "ubl_exec.c" , under function ublAesAuth

#if UBL_SIGNER
HAL_AES_DELAY(); // Delay required for non-DMA AES as RDY bit only goes hi after read out below.

// CBC-MAC generates output on the last block.
for (uint8 cnt = 0; cnt < KEY_BLENGTH; cnt++)
{
sigBuf[cnt] = ENCDO;
}

if (ctrlBlk.allowSignCmd != 0) // If requested to sign this image.
{
ctrlBlk.allowSignCmd = 0;
(void)memcpy(ctrlBlk.signature, sigBuf, KEY_BLENGTH);
UBL_NVM_SET(UBL_ADDR_CTRL, &ctrlBlk, sizeof(aes_ctrl_blk_t));
UBL_NVM_GET(UBL_ADDR_CTRL, &ctrlBlk, sizeof(aes_ctrl_blk_t));
}

signMode = TRUE; // Now the Signer should encrypt the read back.
return FALSE;
#else // A signer must always return FALSE so that usb_msd.c does not save the file name to flash.
if (memcmp(ctrlBlk.signature, sigBuf, KEY_BLENGTH))
#endif
{
// return FALSE;
}
#endif

Just connected uart through USB to uart chipset , with connection of CTS and RTS , finally worked