Mbed OS Reference | ecp_helper.h Source File

 /*
  * Copyright (c) 2022, Nuvoton Technology Corporation
  *
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 #ifndef ECP_HELPER_H
 #define ECP_HELPER_H
 
 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif
 
 #include "mbedtls/bignum.h"
 
 /**
  * \brief           Check if MPI has been normalized
  *
  * \param N         Input MPI which is to check
  * \param P         Prime modulus
  *
  * \return          0 if not normalized,
  *                  1 if normalized
  */
 #define ECP_HELPER_MPI_IS_NORM(N, P)                          \
     ((mbedtls_mpi_cmp_int(&N, 0) >= 0) && (mbedtls_mpi_cmp_mpi(&N, &P) < 0))
 
 /**
  * \brief           Normalize MPI if it is not normalized yet
  *
  * \param R         Holds pointer to normalized MPI (N1 or N2)
  * \param N1        Input MPI which is to normalize
  * \param N2        Output MPI which holds normalized N1 if N1 is not normalized yet
  * \param P         Prime modulus
  */
 #define ECP_HELPER_MPI_NORM(R, N1, N2, P)                     \
     do {                                                            \
         if (ECP_HELPER_MPI_IS_NORM(N1, P)) {                  \
             *R = &N1;                                               \
         } else {                                                    \
             MBEDTLS_MPI_CHK(mbedtls_mpi_mod_mpi(&N2, &N1, &P));     \
             *R = &N2;                                               \
         }                                                           \
     } while(0)
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /**
  * \brief           This function deduces y coordinate from x coordinate
  *                  for a ECP point expressed in compact representation.
  *
  * \param grp       The ECP group to be exported.
  *                  This must be initialized and have group parameters
  *                  set, for example through mbedtls_ecp_group_load().
  * \param y         Deduced y coordinate which is smaller. The other would be
  *                  \p grp->P - \p y. \p y must point to an initialized MPI.
  *
  * \return          \c 0 on success.
  * \return          #MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if \p grp does not
  *                  designate a Curve25519 or Curve448 curve.
  * \return          Another negative error code on other kinds of failure.
  */
 int ecp_helper_deduce_y(const mbedtls_ecp_group *grp,
                         mbedtls_mpi *y,
                         const mbedtls_mpi *x);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif /* ECP_HELPER_H */
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