mbedtls/library/ecdh.c

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/*
* Elliptic curve Diffie-Hellman
*
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* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
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*
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* This file is part of mbed TLS (https://tls.mbed.org)
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*
* 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.
*/
/*
* References:
*
* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
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* RFC 4492
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*/
#if !defined(MBEDTLS_CONFIG_FILE)
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#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
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#if defined(MBEDTLS_ECDH_C)
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#include "mbedtls/ecdh.h"
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#include <string.h>
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/*
* Generate public key: simple wrapper around mbedtls_ecp_gen_keypair
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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),
void *p_rng )
{
return mbedtls_ecp_gen_keypair( grp, d, Q, f_rng, p_rng );
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}
/*
* Compute shared secret (SEC1 3.3.1)
*/
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 )
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{
int ret;
mbedtls_ecp_point P;
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mbedtls_ecp_point_init( &P );
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/*
* Make sure Q is a valid pubkey before using it
*/
MBEDTLS_MPI_CHK( mbedtls_ecp_check_pubkey( grp, Q ) );
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MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, &P, d, Q, f_rng, p_rng ) );
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if( mbedtls_ecp_is_zero( &P ) )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
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MBEDTLS_MPI_CHK( mbedtls_mpi_copy( z, &P.X ) );
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cleanup:
mbedtls_ecp_point_free( &P );
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return( ret );
}
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/*
* Initialize context
*/
void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx )
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{
memset( ctx, 0, sizeof( mbedtls_ecdh_context ) );
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}
/*
* Free context
*/
void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx )
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{
if( ctx == NULL )
return;
mbedtls_ecp_group_free( &ctx->grp );
mbedtls_ecp_point_free( &ctx->Q );
mbedtls_ecp_point_free( &ctx->Qp );
mbedtls_ecp_point_free( &ctx->Vi );
mbedtls_ecp_point_free( &ctx->Vf );
mbedtls_mpi_free( &ctx->d );
mbedtls_mpi_free( &ctx->z );
mbedtls_mpi_free( &ctx->_d );
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}
/*
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* Setup and write the ServerKeyExhange parameters (RFC 4492)
* struct {
* ECParameters curve_params;
* ECPoint public;
* } ServerECDHParams;
*/
int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
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unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
size_t grp_len, pt_len;
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if( ctx == NULL || ctx->grp.pbits == 0 )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) )
!= 0 )
return( ret );
if( ( ret = mbedtls_ecp_tls_write_group( &ctx->grp, &grp_len, buf, blen ) )
!= 0 )
return( ret );
buf += grp_len;
blen -= grp_len;
if( ( ret = mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format,
&pt_len, buf, blen ) ) != 0 )
return( ret );
*olen = grp_len + pt_len;
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return( 0 );
}
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/*
* Read the ServerKeyExhange parameters (RFC 4492)
* struct {
* ECParameters curve_params;
* ECPoint public;
* } ServerECDHParams;
*/
int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx,
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const unsigned char **buf, const unsigned char *end )
{
int ret;
if( ( ret = mbedtls_ecp_tls_read_group( &ctx->grp, buf, end - *buf ) ) != 0 )
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return( ret );
if( ( ret = mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, buf, end - *buf ) )
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!= 0 )
return( ret );
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return( 0 );
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}
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/*
* Get parameters from a keypair
*/
int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key,
mbedtls_ecdh_side side )
{
int ret;
if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 )
return( ret );
/* If it's not our key, just import the public part as Qp */
if( side == MBEDTLS_ECDH_THEIRS )
return( mbedtls_ecp_copy( &ctx->Qp, &key->Q ) );
/* Our key: import public (as Q) and private parts */
if( side != MBEDTLS_ECDH_OURS )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
if( ( ret = mbedtls_ecp_copy( &ctx->Q, &key->Q ) ) != 0 ||
( ret = mbedtls_mpi_copy( &ctx->d, &key->d ) ) != 0 )
return( ret );
return( 0 );
}
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/*
* Setup and export the client public value
*/
int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
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unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
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if( ctx == NULL || ctx->grp.pbits == 0 )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) )
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!= 0 )
return( ret );
return mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format,
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olen, buf, blen );
}
/*
* Parse and import the client's public value
*/
int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx,
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const unsigned char *buf, size_t blen )
{
int ret;
const unsigned char *p = buf;
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if( ctx == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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if( ( ret = mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, &p, blen ) ) != 0 )
return( ret );
if( (size_t)( p - buf ) != blen )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
return( 0 );
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}
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/*
* Derive and export the shared secret
*/
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 )
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{
int ret;
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if( ctx == NULL )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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if( ( ret = mbedtls_ecdh_compute_shared( &ctx->grp, &ctx->z, &ctx->Qp, &ctx->d,
f_rng, p_rng ) ) != 0 )
{
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return( ret );
}
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if( mbedtls_mpi_size( &ctx->z ) > blen )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
*olen = ctx->grp.pbits / 8 + ( ( ctx->grp.pbits % 8 ) != 0 );
return mbedtls_mpi_write_binary( &ctx->z, buf, *olen );
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}
#endif /* MBEDTLS_ECDH_C */