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/**
* \file ecdh.h
*
* \brief This file contains ECDH definitions and functions.
*
* The Elliptic Curve Diffie-Hellman (ECDH) protocol is an anonymous
* key agreement protocol allowing two parties to establish a shared
* secret over an insecure channel. Each party must have an
* elliptic-curve public–private key pair.
*
* For more information, see <em>NIST SP 800-56A Rev. 2: Recommendation for
* Pair-Wise Key Establishment Schemes Using Discrete Logarithm
* Cryptography</em>.
*/
/*
* Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
* 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.
*
* This file is part of Mbed TLS (https://tls.mbed.org)
*/
#ifndef MBEDTLS_ECDH_H
#define MBEDTLS_ECDH_H
#include "ecp.h"
#ifdef __cplusplus
extern "C" {
#endif
/**
* Defines the source of the imported EC key.
*/
typedef enum
{
MBEDTLS_ECDH_OURS, /**< Our key. */
MBEDTLS_ECDH_THEIRS, /**< The key of the peer. */
} mbedtls_ecdh_side;
/**
*
* \warning Performing multiple operations concurrently on the same
* ECDSA context is not supported; objects of this type
* should not be shared between multiple threads.
* \brief The ECDH context structure.
*/
typedef struct mbedtls_ecdh_context
{
mbedtls_ecp_group grp; /*!< The elliptic curve used. */
mbedtls_mpi d; /*!< The private key. */
mbedtls_ecp_point Q; /*!< The public key. */
mbedtls_ecp_point Qp; /*!< The value of the public key of the peer. */
mbedtls_mpi z; /*!< The shared secret. */
int point_format; /*!< The format of point export in TLS messages. */
mbedtls_ecp_point Vi; /*!< The blinding value. */
mbedtls_ecp_point Vf; /*!< The unblinding value. */
mbedtls_mpi _d; /*!< The previous \p d. */
#if defined(MBEDTLS_ECP_RESTARTABLE)
int restart_enabled; /*!< The flag for restartable mode. */
mbedtls_ecp_restart_ctx rs; /*!< The restart context for EC computations. */
#endif
}
mbedtls_ecdh_context;
/**
* \brief This function generates an ECDH keypair on an elliptic
* curve.
*
* This function performs the first of two core computations
* implemented during the ECDH key exchange. The second core
* computation is performed by mbedtls_ecdh_compute_shared().
*
* \see ecp.h
*
* \param grp The ECP group.
* \param d The destination MPI (private key).
* \param Q The destination point (public key).
* \param f_rng The RNG function.
* \param p_rng The RNG context.
*
* \return \c 0 on success.
* \return Another \c MBEDTLS_ERR_ECP_XXX or
* \c MBEDTLS_MPI_XXX error code on failure.
*/
int mbedtls_ecdh_gen_public( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief This function computes the shared secret.
*
* This function performs the second of two core computations
* implemented during the ECDH key exchange. The first core
* computation is performed by mbedtls_ecdh_gen_public().
*
* \see ecp.h
*
* \note If \p f_rng is not NULL, it is used to implement
* countermeasures against side-channel attacks.
* For more information, see mbedtls_ecp_mul().
*
* \param grp The ECP group.
* \param z The destination MPI (shared secret).
* \param Q The public key from another party.
* \param d Our secret exponent (private key).
* \param f_rng The RNG function.
* \param p_rng The RNG context.
*
* \return \c 0 on success.
* \return Another \c MBEDTLS_ERR_ECP_XXX or
* \c MBEDTLS_MPI_XXX error code on failure.
*/
int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
const mbedtls_ecp_point *Q, const mbedtls_mpi *d,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief This function initializes an ECDH context.
*
* \param ctx The ECDH context to initialize.
*/
void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx );
/**
* \brief This function frees a context.
*
* \param ctx The context to free.
*/
void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx );
/**
* \brief This function generates a public key and a TLS
* ServerKeyExchange payload.
*
* This is the first function used by a TLS server for ECDHE
* ciphersuites.
*
* \note This function assumes that the ECP group (grp) of the
* \p ctx context has already been properly set,
* for example, using mbedtls_ecp_group_load().
*
* \see ecp.h
*
* \param ctx The ECDH context.
* \param olen The number of characters written.
* \param buf The destination buffer.
* \param blen The length of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
* operations was reached: see \c mbedtls_ecp_set_max_ops().
* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
*/
int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief This function parses and processes a TLS ServerKeyExhange
* payload.
*
* This is the first function used by a TLS client for ECDHE
* ciphersuites.
*
* \see ecp.h
*
* \param ctx The ECDH context.
* \param buf The pointer to the start of the input buffer.
* \param end The address for one Byte past the end of the buffer.
*
* \return \c 0 on success.
* \return An \c MBEDTLS_ERR_ECP_XXX error code on failure.
*
*/
int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx,
const unsigned char **buf, const unsigned char *end );
/**
* \brief This function sets up an ECDH context from an EC key.
*
* It is used by clients and servers in place of the
* ServerKeyEchange for static ECDH, and imports ECDH
* parameters from the EC key information of a certificate.
*
* \see ecp.h
*
* \param ctx The ECDH context to set up.
* \param key The EC key to use.
* \param side Defines the source of the key: 1: Our key, or
* 0: The key of the peer.
*
* \return \c 0 on success.
* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
*
*/
int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key,
mbedtls_ecdh_side side );
/**
* \brief This function generates a public key and a TLS
* ClientKeyExchange payload.
*
* This is the second function used by a TLS client for ECDH(E)
* ciphersuites.
*
* \see ecp.h
*
* \param ctx The ECDH context.
* \param olen The number of Bytes written.
* \param buf The destination buffer.
* \param blen The size of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
* operations was reached: see \c mbedtls_ecp_set_max_ops().
* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
*/
int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief This function parses and processes a TLS ClientKeyExchange
* payload.
*
* This is the second function used by a TLS server for ECDH(E)
* ciphersuites.
*
* \see ecp.h
*
* \param ctx The ECDH context.
* \param buf The start of the input buffer.
* \param blen The length of the input buffer.
*
* \return \c 0 on success.
* \return An \c MBEDTLS_ERR_ECP_XXX error code on failure.
*/
int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx,
const unsigned char *buf, size_t blen );
/**
* \brief This function derives and exports the shared secret.
*
* This is the last function used by both TLS client
* and servers.
*
* \note If \p f_rng is not NULL, it is used to implement
* countermeasures against side-channel attacks.
* For more information, see mbedtls_ecp_mul().
*
* \see ecp.h
*
* \param ctx The ECDH context.
* \param olen The number of Bytes written.
* \param buf The destination buffer.
* \param blen The length of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG context.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
* operations was reached: see \c mbedtls_ecp_set_max_ops().
* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
*/
int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#if defined(MBEDTLS_ECP_RESTARTABLE)
/**
* \brief This function enables restartable EC computations for this
* context. (Default: disabled.)
*
* \see \c mbedtls_ecp_set_max_ops()
*
* \note It is not possible to safely disable restartable
* computations once enabled, except by free-ing the context,
* which cancels possible in-progress operations.
*
* \param ctx The ECDH context.
*/
void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx );
#endif /* MBEDTLS_ECP_RESTARTABLE */
#ifdef __cplusplus
}
#endif
#endif /* ecdh.h */