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443 lines
18 KiB
C
443 lines
18 KiB
C
/**
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* \file ecdh.h
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*
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* \brief This file contains ECDH definitions and functions.
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*
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* The Elliptic Curve Diffie-Hellman (ECDH) protocol is an anonymous
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* key agreement protocol allowing two parties to establish a shared
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* secret over an insecure channel. Each party must have an
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* elliptic-curve public–private key pair.
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*
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* For more information, see <em>NIST SP 800-56A Rev. 2: Recommendation for
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* Pair-Wise Key Establishment Schemes Using Discrete Logarithm
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* Cryptography</em>.
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*/
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/*
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* Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
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* SPDX-License-Identifier: GPL-2.0
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* This file is part of Mbed TLS (https://tls.mbed.org)
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*/
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#ifndef MBEDTLS_ECDH_H
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#define MBEDTLS_ECDH_H
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#if !defined(MBEDTLS_CONFIG_FILE)
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#include "config.h"
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#else
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#include MBEDTLS_CONFIG_FILE
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#endif
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#include "ecp.h"
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/*
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* Use a backward compatible ECDH context.
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*
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* This flag is always enabled for now and future versions might add a
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* configuration option that conditionally undefines this flag.
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* The configuration option in question may have a different name.
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*
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* Features undefining this flag, must have a warning in their description in
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* config.h stating that the feature breaks backward compatibility.
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*/
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#define MBEDTLS_ECDH_LEGACY_CONTEXT
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* Defines the source of the imported EC key.
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*/
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typedef enum
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{
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MBEDTLS_ECDH_OURS, /**< Our key. */
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MBEDTLS_ECDH_THEIRS, /**< The key of the peer. */
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} mbedtls_ecdh_side;
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#if !defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
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/**
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* Defines the ECDH implementation used.
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*
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* Later versions of the library may add new variants, therefore users should
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* not make any assumptions about them.
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*/
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typedef enum
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{
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MBEDTLS_ECDH_VARIANT_NONE = 0, /*!< Implementation not defined. */
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MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0,/*!< The default Mbed TLS implementation */
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} mbedtls_ecdh_variant;
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/**
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* The context used by the default ECDH implementation.
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*
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* Later versions might change the structure of this context, therefore users
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* should not make any assumptions about the structure of
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* mbedtls_ecdh_context_mbed.
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*/
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typedef struct mbedtls_ecdh_context_mbed
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{
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mbedtls_ecp_group grp; /*!< The elliptic curve used. */
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mbedtls_mpi d; /*!< The private key. */
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mbedtls_ecp_point Q; /*!< The public key. */
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mbedtls_ecp_point Qp; /*!< The value of the public key of the peer. */
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mbedtls_mpi z; /*!< The shared secret. */
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#if defined(MBEDTLS_ECP_RESTARTABLE)
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mbedtls_ecp_restart_ctx rs; /*!< The restart context for EC computations. */
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#endif
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} mbedtls_ecdh_context_mbed;
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#endif
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/**
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*
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* \warning Performing multiple operations concurrently on the same
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* ECDSA context is not supported; objects of this type
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* should not be shared between multiple threads.
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* \brief The ECDH context structure.
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*/
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typedef struct mbedtls_ecdh_context
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{
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#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
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mbedtls_ecp_group grp; /*!< The elliptic curve used. */
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mbedtls_mpi d; /*!< The private key. */
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mbedtls_ecp_point Q; /*!< The public key. */
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mbedtls_ecp_point Qp; /*!< The value of the public key of the peer. */
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mbedtls_mpi z; /*!< The shared secret. */
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int point_format; /*!< The format of point export in TLS messages. */
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mbedtls_ecp_point Vi; /*!< The blinding value. */
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mbedtls_ecp_point Vf; /*!< The unblinding value. */
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mbedtls_mpi _d; /*!< The previous \p d. */
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#if defined(MBEDTLS_ECP_RESTARTABLE)
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int restart_enabled; /*!< The flag for restartable mode. */
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mbedtls_ecp_restart_ctx rs; /*!< The restart context for EC computations. */
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#endif /* MBEDTLS_ECP_RESTARTABLE */
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#else
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uint8_t point_format; /*!< The format of point export in TLS messages
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as defined in RFC 4492. */
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mbedtls_ecp_group_id grp_id;/*!< The elliptic curve used. */
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mbedtls_ecdh_variant var; /*!< The ECDH implementation/structure used. */
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union
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{
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mbedtls_ecdh_context_mbed mbed_ecdh;
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} ctx; /*!< Implementation-specific context. The
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context in use is specified by the \c var
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field. */
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#if defined(MBEDTLS_ECP_RESTARTABLE)
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uint8_t restart_enabled; /*!< The flag for restartable mode. Functions of
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an alternative implementation not supporting
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restartable mode must return
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MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED error
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if this flag is set. */
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#endif /* MBEDTLS_ECP_RESTARTABLE */
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#endif /* MBEDTLS_ECDH_LEGACY_CONTEXT */
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}
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mbedtls_ecdh_context;
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/**
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* \brief This function generates an ECDH keypair on an elliptic
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* curve.
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*
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* This function performs the first of two core computations
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* implemented during the ECDH key exchange. The second core
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* computation is performed by mbedtls_ecdh_compute_shared().
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*
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* \see ecp.h
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*
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* \param grp The ECP group to use. This must be initialized and have
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* domain parameters loaded, for example through
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* mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
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* \param d The destination MPI (private key).
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* This must be initialized.
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* \param Q The destination point (public key).
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* This must be initialized.
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* \param f_rng The RNG function to use. This must not be \c NULL.
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* \param p_rng The RNG context to be passed to \p f_rng. This may be
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* \c NULL in case \p f_rng doesn't need a context argument.
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*
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* \return \c 0 on success.
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* \return Another \c MBEDTLS_ERR_ECP_XXX or
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* \c MBEDTLS_MPI_XXX error code on failure.
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*/
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int mbedtls_ecdh_gen_public( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng );
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/**
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* \brief This function computes the shared secret.
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*
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* This function performs the second of two core computations
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* implemented during the ECDH key exchange. The first core
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* computation is performed by mbedtls_ecdh_gen_public().
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*
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* \see ecp.h
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*
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* \note If \p f_rng is not NULL, it is used to implement
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* countermeasures against side-channel attacks.
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* For more information, see mbedtls_ecp_mul().
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*
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* \param grp The ECP group to use. This must be initialized and have
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* domain parameters loaded, for example through
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* mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
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* \param z The destination MPI (shared secret).
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* This must be initialized.
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* \param Q The public key from another party.
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* This must be initialized.
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* \param d Our secret exponent (private key).
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* This must be initialized.
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* \param f_rng The RNG function. This may be \c NULL if randomization
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* of intermediate results during the ECP computations is
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* not needed (discouraged). See the documentation of
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* mbedtls_ecp_mul() for more.
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* \param p_rng The RNG context to be passed to \p f_rng. This may be
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* \c NULL if \p f_rng is \c NULL or doesn't need a
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* context argument.
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*
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* \return \c 0 on success.
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* \return Another \c MBEDTLS_ERR_ECP_XXX or
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* \c MBEDTLS_MPI_XXX error code on failure.
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*/
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int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
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const mbedtls_ecp_point *Q, const mbedtls_mpi *d,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng );
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/**
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* \brief This function initializes an ECDH context.
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*
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* \param ctx The ECDH context to initialize. This must not be \c NULL.
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*/
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void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx );
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/**
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* \brief This function sets up the ECDH context with the information
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* given.
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*
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* This function should be called after mbedtls_ecdh_init() but
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* before mbedtls_ecdh_make_params(). There is no need to call
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* this function before mbedtls_ecdh_read_params().
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*
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* This is the first function used by a TLS server for ECDHE
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* ciphersuites.
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*
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* \param ctx The ECDH context to set up. This must be initialized.
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* \param grp_id The group id of the group to set up the context for.
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*
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* \return \c 0 on success.
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*/
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int mbedtls_ecdh_setup( mbedtls_ecdh_context *ctx,
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mbedtls_ecp_group_id grp_id );
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/**
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* \brief This function frees a context.
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*
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* \param ctx The context to free. This may be \c NULL, in which
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* case this function does nothing. If it is not \c NULL,
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* it must point to an initialized ECDH context.
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*/
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void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx );
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/**
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* \brief This function generates an EC key pair and exports its
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* in the format used in a TLS ServerKeyExchange handshake
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* message.
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*
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* This is the second function used by a TLS server for ECDHE
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* ciphersuites. (It is called after mbedtls_ecdh_setup().)
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*
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* \see ecp.h
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*
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* \param ctx The ECDH context to use. This must be initialized
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* and bound to a group, for example via mbedtls_ecdh_setup().
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* \param olen The address at which to store the number of Bytes written.
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* \param buf The destination buffer. This must be a writable buffer of
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* length \p blen Bytes.
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* \param blen The length of the destination buffer \p buf in Bytes.
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* \param f_rng The RNG function to use. This must not be \c NULL.
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* \param p_rng The RNG context to be passed to \p f_rng. This may be
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* \c NULL in case \p f_rng doesn't need a context argument.
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*
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
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* operations was reached: see \c mbedtls_ecp_set_max_ops().
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* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*/
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int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
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unsigned char *buf, size_t blen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng );
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/**
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* \brief This function parses the ECDHE parameters in a
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* TLS ServerKeyExchange handshake message.
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*
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* \note In a TLS handshake, this is the how the client
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* sets up its ECDHE context from the server's public
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* ECDHE key material.
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*
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* \see ecp.h
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*
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* \param ctx The ECDHE context to use. This must be initialized.
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* \param buf On input, \c *buf must be the start of the input buffer.
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* On output, \c *buf is updated to point to the end of the
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* data that has been read. On success, this is the first byte
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* past the end of the ServerKeyExchange parameters.
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* On error, this is the point at which an error has been
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* detected, which is usually not useful except to debug
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* failures.
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* \param end The end of the input buffer.
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*
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* \return \c 0 on success.
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* \return An \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*
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*/
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int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx,
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const unsigned char **buf,
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const unsigned char *end );
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/**
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* \brief This function sets up an ECDH context from an EC key.
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*
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* It is used by clients and servers in place of the
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* ServerKeyEchange for static ECDH, and imports ECDH
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* parameters from the EC key information of a certificate.
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*
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* \see ecp.h
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*
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* \param ctx The ECDH context to set up. This must be initialized.
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* \param key The EC key to use. This must be initialized.
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* \param side Defines the source of the key. Possible values are:
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* - #MBEDTLS_ECDH_OURS: The key is ours.
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* - #MBEDTLS_ECDH_THEIRS: The key is that of the peer.
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*
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* \return \c 0 on success.
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* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*
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*/
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int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx,
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const mbedtls_ecp_keypair *key,
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mbedtls_ecdh_side side );
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/**
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* \brief This function generates a public key and exports it
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* as a TLS ClientKeyExchange payload.
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*
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* This is the second function used by a TLS client for ECDH(E)
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* ciphersuites.
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*
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* \see ecp.h
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*
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* \param ctx The ECDH context to use. This must be initialized
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* and bound to a group, the latter usually by
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* mbedtls_ecdh_read_params().
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* \param olen The address at which to store the number of Bytes written.
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* This must not be \c NULL.
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* \param buf The destination buffer. This must be a writable buffer
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* of length \p blen Bytes.
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* \param blen The size of the destination buffer \p buf in Bytes.
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* \param f_rng The RNG function to use. This must not be \c NULL.
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* \param p_rng The RNG context to be passed to \p f_rng. This may be
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* \c NULL in case \p f_rng doesn't need a context argument.
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*
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
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* operations was reached: see \c mbedtls_ecp_set_max_ops().
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* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*/
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int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
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unsigned char *buf, size_t blen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng );
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/**
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* \brief This function parses and processes the ECDHE payload of a
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* TLS ClientKeyExchange message.
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*
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* This is the third function used by a TLS server for ECDH(E)
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* ciphersuites. (It is called after mbedtls_ecdh_setup() and
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* mbedtls_ecdh_make_params().)
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*
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* \see ecp.h
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*
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* \param ctx The ECDH context to use. This must be initialized
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* and bound to a group, for example via mbedtls_ecdh_setup().
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* \param buf The pointer to the ClientKeyExchange payload. This must
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* be a readable buffer of length \p blen Bytes.
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* \param blen The length of the input buffer \p buf in Bytes.
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*
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* \return \c 0 on success.
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* \return An \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*/
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int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx,
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const unsigned char *buf, size_t blen );
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/**
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* \brief This function derives and exports the shared secret.
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*
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* This is the last function used by both TLS client
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* and servers.
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*
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* \note If \p f_rng is not NULL, it is used to implement
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* countermeasures against side-channel attacks.
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* For more information, see mbedtls_ecp_mul().
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*
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* \see ecp.h
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* \param ctx The ECDH context to use. This must be initialized
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* and have its own private key generated and the peer's
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* public key imported.
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* \param olen The address at which to store the total number of
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* Bytes written on success. This must not be \c NULL.
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* \param buf The buffer to write the generated shared key to. This
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* must be a writable buffer of size \p blen Bytes.
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* \param blen The length of the destination buffer \p buf in Bytes.
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* \param f_rng The RNG function, for blinding purposes. This may
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* b \c NULL if blinding isn't needed.
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* \param p_rng The RNG context. This may be \c NULL if \p f_rng
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* doesn't need a context argument.
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*
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* \return \c 0 on success.
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* \return #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
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* operations was reached: see \c mbedtls_ecp_set_max_ops().
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* \return Another \c MBEDTLS_ERR_ECP_XXX error code on failure.
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*/
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int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
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unsigned char *buf, size_t blen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng );
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#if defined(MBEDTLS_ECP_RESTARTABLE)
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/**
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* \brief This function enables restartable EC computations for this
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* context. (Default: disabled.)
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*
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* \see \c mbedtls_ecp_set_max_ops()
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*
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* \note It is not possible to safely disable restartable
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* computations once enabled, except by free-ing the context,
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* which cancels possible in-progress operations.
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*
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* \param ctx The ECDH context to use. This must be initialized.
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*/
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void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx );
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#endif /* MBEDTLS_ECP_RESTARTABLE */
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#ifdef __cplusplus
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}
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#endif
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#endif /* ecdh.h */
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