CMOX ECDSA KeyGen Public Key not valid

[Jonas3]

Hi,

I´m trying to implement a simple ECDH test by implementing the functions from the Cryptographic Library V4.2.0.

There are two persons A and B generating a pair of private and public keys. The keys are generated by the cmox_ecdsa_keyGen(...) function.

The curve is BrainpoolP256R1.

When trying to calculate the shared secret with cmox_ecdh(...) the function returns with CMOX_ECC_ERR_INVALID_PUBKEY. 

I´m assuming that the generated public Key is not valid (it´s not placed in the elliptic curve).

What could be the cause?

Thank you!

Here´s my code:

void ECDH_test(void)
{
	//Prepare Time Measurement
	#define CYCCNTENA 0x00000001
  CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;         
  DWT->CTRL |= CYCCNTENA;
	
	/***********************************************************************************************************/
	//Variables
	cmox_ecc_handle_t Ecc_Ctx;
	uint8_t Working_Buffer[2048];
	cmox_ecc_retval_t retval;
	size_t computed_size;
	
	//Choose Random 32 Byte Value for Person A	
	uint8_t RandomA[] =
	{
		0x7e, 0x21, 0x78, 0xf7, 0x1e, 0xb2, 0x4d, 0xda, 0xf8, 0x0d, 0x45, 0x14, 0x63, 0x2e, 0xdd, 0xe0,
		0x22, 0x90, 0x58, 0xaf, 0x1f, 0xb6, 0x00, 0x2e, 0xd8, 0x11, 0xdd, 0xb6, 0x2b, 0xc1, 0xa5, 0x34
	};
	
	//Choose Random 32 Byte Value for Person B	
	uint8_t RandomB[] =
	{
		0x8e, 0xf1, 0x73, 0xf7, 0x1e, 0xb2, 0x4d, 0xda, 0xf8, 0x0d, 0x00, 0x14, 0x63, 0x2e, 0xdd, 0xe0,
		0x22, 0x90, 0x58, 0xaf, 0xee, 0xb6, 0x00, 0x2e, 0xd8, 0x11, 0x11, 0xb6, 0x2b, 0xc1, 0xa5, 0x22
	};

	//Private Keys
	uint8_t Private_KeyA[CMOX_ECC_BPP256R1_PRIVKEY_LEN];
	uint8_t Private_KeyB[CMOX_ECC_BPP256R1_PRIVKEY_LEN];
	
	//Public Keys
	uint8_t Remote_Public_KeyB[CMOX_ECC_BPP256R1_PUBKEY_LEN];
	uint8_t Remote_Public_KeyA[CMOX_ECC_BPP256R1_PUBKEY_LEN];
	
	//Secret
	uint8_t Computed_SecretA[CMOX_ECC_BPP256R1_SECRET_LEN];
	uint8_t Computed_SecretB[CMOX_ECC_BPP256R1_SECRET_LEN];
		
	/***********************************************************************************************************/
	//Start Time Measurement
	timestamp1 = DWT->CYCCNT;
	
	//Reset CRC, then Enable CRC
	HAL_CRC_DeInit(&hcrc);
	cmox_ll_init(NULL);
	
  if (cmox_initialize(NULL) != CMOX_INIT_SUCCESS)
  {
    Error_Handler();
  }
	cmox_ecc_construct(&Ecc_Ctx, CMOX_ECC256_MATH_FUNCS, Working_Buffer, sizeof(Working_Buffer));

	//Generate Key Pair for A									 							 
	retval = cmox_ecdsa_keyGen(&Ecc_Ctx,                                        
														 CMOX_ECC_CURVE_BPP256R1,                          
														 RandomA, sizeof(RandomA),                   
														 Private_KeyA, NULL,     					 								
														 Remote_Public_KeyA, NULL);															 
	if (retval != CMOX_ECC_SUCCESS)
  {
    Error_Handler();
  }

  //Generate Key Pair for B								 							 
	retval = cmox_ecdsa_keyGen(&Ecc_Ctx,                                        
														 CMOX_ECC_CURVE_BPP256R1,                          
														 RandomB, sizeof(RandomA),                   
														 Private_KeyB, NULL,     					 								
														 Remote_Public_KeyB, NULL);	
	if (retval != CMOX_ECC_SUCCESS)
  {
    Error_Handler();
  }														
	

	//A calculates the secret with his own private Key and B´s Public Key													 
	retval = cmox_ecdh(&Ecc_Ctx,                                         
                     CMOX_ECC_CURVE_BPP256R1,                          
                     Private_KeyA, sizeof(Private_KeyA),                
                     Remote_Public_KeyB, sizeof(Remote_Public_KeyB),     					 
                     Computed_SecretA, &computed_size);                 
	if (retval != CMOX_ECC_SUCCESS)
  {
    Error_Handler();
  }
	
	
	/* Cleanup context */
  cmox_ecc_cleanup(&Ecc_Ctx);
	
	/* No more need of cryptographic services, finalize cryptographic library */
  if (cmox_finalize(NULL) != CMOX_INIT_SUCCESS)
  {
    Error_Handler();
  }
										 
	//Stop Time Measurement
  timestamp2 = DWT->CYCCNT;
  runtime = (timestamp2 - timestamp1) / 16000;		
	__NOP();
}

[Jonas3 · Accepted solution]

I found the solution:

The CRC Module won´t reset to the default state by simply calling 

HAL_CRC_DeInit(&hcrc);

You have to call:

	HAL_CRC_DeInit(&hcrc);
	
	__HAL_RCC_CRC_FORCE_RESET();
	__HAL_RCC_CRC_RELEASE_RESET();
  __HAL_RCC_CRC_CLK_ENABLE();