I managed to solve the issue, I did the following steps:

ecc_point *point = wc_ecc_new_point();
mp_read_unsigned_bin(point->x, xPoint, 32);
mp_read_unsigned_bin(point->y, yPoint, 32);
mp_set(point->z, 1);
wc_ecc_shared_secret_gen(&privateKey, point, sharedSecret, &sharedSecretSize);

And this sharedSecret I send back to the softdevice of the nordic chip.

Thanks you very much for the support.

Hi Kaleb,

thanks for the answer. We are working with a Nordic chip and need to implement the Bluetooth Low Energy Security Encryped connection and we are working on a microcontroller.

With the wolfSSL we are generating the private and public key of our side:

          WC_RNG rng;
          ecc_key priv;
          result = wc_InitRng(&rng);
          result = wc_ecc_init(&priv);
          result = wc_ecc_set_curve(&priv, 32, ECC_SECP256R1);
          result = wc_ecc_make_key(&rng, 32, &priv); // make public/private key pair

now we receive a "BLE_GAP_EVT_LESC_DHKEY_REQUEST" from the nordic softdevice from the peer, in this event-case we need to calculate the agreed secret and send this secret back.
The format of the received data is a x,y (32bit value each) of the ECC keys. But as far as I understand the

result = wc_DhAgree();

needs a p and q value.
Is the 'wc_ecc_shared_secret_gen' not the solution better function? But then what to use for the z-value? 1?

I think this little last calculation is missing and when we have this, the Bluetooth connection is encrypted, so I do not think that the other approach makes more sense. Or probably you can short describe which steps are necessary to reach the goal there.

Thank you again for the support and kind Regards
Lorenz

Hello everybody,

I am stuck with the calculation of a DHKey (P256 for a Bluetooth LE security connection).
I have a public key (x,y) from the peer and a private key from my own. Now I need to calculate a DHKey.

When I call the 'wc_ecc_shared_secret' I get a result -3, but here I do not know how to generate a public key out of the x and y values. Is this approach the correct one?

Can somebody give my a hint?

Thank you very much for the support.