/**
* \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: GPL-2.0
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
* This file is part of Mbed TLS (https://tls.mbed.org)
*/
#ifndef MBEDTLS_ECDH_H
#define MBEDTLS_ECDH_H
#if !defined(MBEDTLS_CONFIG_FILE)
#include "config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#include "ecp.h"
/*
* Use a backward compatible ECDH context.
*
* This flag is always enabled for now and future versions might add a
* configuration option that conditionally undefines this flag.
* The configuration option in question may have a different name.
*
* Features undefining this flag, must have a warning in their description in
* config.h stating that the feature breaks backward compatibility.
*/
#define MBEDTLS_ECDH_LEGACY_CONTEXT
#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;
#if !defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
/**
* Defines the ECDH implementation used.
*
* Later versions of the library may add new variants, therefore users should
* not make any assumptions about them.
*/
typedef enum
{
MBEDTLS_ECDH_VARIANT_NONE = 0, /*!< Implementation not defined. */
MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0,/*!< The default Mbed TLS implementation */
} mbedtls_ecdh_variant;
/**
* The context used by the default ECDH implementation.
*
* Later versions might change the structure of this context, therefore users
* should not make any assumptions about the structure of
* mbedtls_ecdh_context_mbed.
*/
typedef struct mbedtls_ecdh_context_mbed
{
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. */
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_ctx rs; /*!< The restart context for EC computations. */
#endif
} mbedtls_ecdh_context_mbed;
#endif
/**
*
* \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
{
#if defined(MBEDTLS_ECDH_LEGACY_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_ECP_RESTARTABLE */
#else
uint8_t point_format; /*!< The format of point export in TLS messages
as defined in RFC 4492. */
mbedtls_ecp_group_id grp_id;/*!< The elliptic curve used. */
mbedtls_ecdh_variant var; /*!< The ECDH implementation/structure used. */
union
{
mbedtls_ecdh_context_mbed mbed_ecdh;
} ctx; /*!< Implementation-specific context. The
context in use is specified by the \c var
field. */
#if defined(MBEDTLS_ECP_RESTARTABLE)
uint8_t restart_enabled; /*!< The flag for restartable mode. Functions of
an alternative implementation not supporting
restartable mode must return
MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED error
if this flag is set. */
#endif /* MBEDTLS_ECP_RESTARTABLE */
#endif /* MBEDTLS_ECDH_LEGACY_CONTEXT */
}
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 to use. This must be initialized and have
* domain parameters loaded, for example through
* mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
* \param d The destination MPI (private key).
* This must be initialized.
* \param Q The destination point (public key).
* This must be initialized.
* \param f_rng The RNG function to use. This must not be \c NULL.
* \param p_rng The RNG context to be passed to \p f_rng. This may be
* \c NULL in case \p f_rng doesn't need a context argument.
*
* \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 to use. This must be initialized and have
* domain parameters loaded, for example through
* mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
* \param z The destination MPI (shared secret).
* This must be initialized.
* \param Q The public key from another party.
* This must be initialized.
* \param d Our secret exponent (private key).
* This must be initialized.
* \param f_rng The RNG function. This may be \c NULL if randomization
* of intermediate results during the ECP computations is
* not needed (discouraged). See the documentation of
* mbedtls_ecp_mul() for more.
* \param p_rng The RNG context to be passed to \p f_rng. This may be
* \c NULL if \p f_rng is \c NULL or doesn't need a
* context argument.
*
* \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. This must not be \c NULL.
*/
void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx );
/**
* \brief This function sets up the ECDH context with the information
* given.
*
* This function should be called after mbedtls_ecdh_init() but
* before mbedtls_ecdh_make_params(). There is no need to call
* this function before mbedtls_ecdh_read_params().
*
* This is the first function used by a TLS server for ECDHE
* ciphersuites.
*
* \param ctx The ECDH context to set up. This must be initialized.
* \param grp_id The group id of the group to set up the context for.
*
* \return \c 0 on success.
*/
int mbedtls_ecdh_setup( mbedtls_ecdh_context *ctx,
mbedtls_ecp_group_id grp_id );
/**
* \brief This function frees a context.
*
* \param ctx The context to free. This may be \c NULL, in which
* case this function does nothing. If it is not \c NULL,
* it must point to an initialized ECDH context.
*/
void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx );
/**
* \brief This function generates an EC key pair and exports its
* in the format used in a TLS ServerKeyExchange handshake
* message.
*
* This is the second function used by a TLS server for ECDHE
* ciphersuites. (It is called after mbedtls_ecdh_setup().)
*
* \see ecp.h
*
* \param ctx The ECDH context to use. This must be initialized
* and bound to a group, for example via mbedtls_ecdh_setup().
* \param olen The address at which to store the number of Bytes written.
* \param buf The destination buffer. This must be a writable buffer of
* length \p blen Bytes.
* \param blen The length of the destination buffer \p buf in Bytes.
* \param f_rng The RNG function to use. This must not be \c NULL.
* \param p_rng The RNG context to be passed to \p f_rng. This may be
* \c NULL in case \p f_rng doesn't need a context argument.
*
* \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 the ECDHE parameters in a
* TLS ServerKeyExchange handshake message.
*
* \note In a TLS handshake, this is the how the client
* sets up its ECDHE context from the server's public
* ECDHE key material.
*
* \see ecp.h
*
* \param ctx The ECDHE context to use. This must be initialized.
* \param buf On input, \c *buf must be the start of the input buffer.
* On output, \c *buf is updated to point to the end of the
* data that has been read. On success, this is the first byte
* past the end of the ServerKeyExchange parameters.
* On error, this is the point at which an error has been
* detected, which is usually not useful except to debug
* failures.
* \param end The end of the input 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. This must be initialized.
* \param key The EC key to use. This must be initialized.
* \param side Defines the source of the key. Possible values are:
* - #MBEDTLS_ECDH_OURS: The key is ours.
* - #MBEDTLS_ECDH_THEIRS: The key is that 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 exports it
* as 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 to use. This must be initialized
* and bound to a group, the latter usually by
* mbedtls_ecdh_read_params().
* \param olen The address at which to store the number of Bytes written.
* This must not be \c NULL.
* \param buf The destination buffer. This must be a writable buffer
* of length \p blen Bytes.
* \param blen The size of the destination buffer \p buf in Bytes.
* \param f_rng The RNG function to use. This must not be \c NULL.
* \param p_rng The RNG context to be passed to \p f_rng. This may be
* \c NULL in case \p f_rng doesn't need a context argument.
*
* \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 the ECDHE payload of a
* TLS ClientKeyExchange message.
*
* This is the third function used by a TLS server for ECDH(E)
* ciphersuites. (It is called after mbedtls_ecdh_setup() and
* mbedtls_ecdh_make_params().)
*
* \see ecp.h
*
* \param ctx The ECDH context to use. This must be initialized
* and bound to a group, for example via mbedtls_ecdh_setup().
* \param buf The pointer to the ClientKeyExchange payload. This must
* be a readable buffer of length \p blen Bytes.
* \param blen The length of the input buffer \p buf in Bytes.
*
* \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 to use. This must be initialized
* and have its own private key generated and the peer's
* public key imported.
* \param olen The address at which to store the total number of
* Bytes written on success. This must not be \c NULL.
* \param buf The buffer to write the generated shared key to. This
* must be a writable buffer of size \p blen Bytes.
* \param blen The length of the destination buffer \p buf in Bytes.
* \param f_rng The RNG function, for blinding purposes. This may
* b \c NULL if blinding isn't needed.
* \param p_rng The RNG context. This may be \c NULL if \p f_rng
* doesn't need a context argument.
*
* \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 to use. This must be initialized.
*/
void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx );
#endif /* MBEDTLS_ECP_RESTARTABLE */
#ifdef __cplusplus
}
#endif
#endif /* ecdh.h */