mp_to_fixlen_octets
CHECK_MPI_OK( mp_to_fixlen_octets(&Qx, pointQ->data + 1,
CHECK_MPI_OK( mp_to_fixlen_octets(&Qy, pointQ->data + 1 + len,
CHECK_MPI_OK( mp_to_fixlen_octets(&privKeyVal, privKeyBytes, len) );
CHECK_MPI_OK( mp_to_fixlen_octets(&r, signature->data, olen) );
CHECK_MPI_OK( mp_to_fixlen_octets(&s, signature->data + olen, olen) );
mp_err mp_to_fixlen_octets(const mp_int *mp, unsigned char *str, mp_size len);