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mbedtls/library/ecdh.c
Janos Follath 52ff8e9387 Fix ECDH secret export for Mongomery curves 
We only switched to little endian for Curve25519, but all Montgomery
curves require little endian byte order.
2019-02-26 16:49:52 +00:00

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/*
* Elliptic curve Diffie-Hellman
*
* Copyright (C) 2006-2015, ARM Limited, 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)
*/
/*
* References:
*
* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
* RFC 4492
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_ECDH_C)
#include "mbedtls/ecdh.h"
#include "mbedtls/platform_util.h"
#include <string.h>
/* Parameter validation macros based on platform_util.h */
#define ECDH_VALIDATE_RET( cond ) \
MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_ECP_BAD_INPUT_DATA )
#define ECDH_VALIDATE( cond ) \
MBEDTLS_INTERNAL_VALIDATE( cond )
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
typedef mbedtls_ecdh_context mbedtls_ecdh_context_mbed;
#endif
static mbedtls_ecp_group_id mbedtls_ecdh_grp_id(
const mbedtls_ecdh_context *ctx )
{
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ctx->grp.id );
#else
return( ctx->grp_id );
#endif
}
#if !defined(MBEDTLS_ECDH_GEN_PUBLIC_ALT)
/*
* Generate public key (restartable version)
*
* Note: this internal function relies on its caller preserving the value of
* the output parameter 'd' across continuation calls. This would not be
* acceptable for a public function but is OK here as we control call sites.
*/
static int ecdh_gen_public_restartable( mbedtls_ecp_group *grp,
mbedtls_mpi *d, mbedtls_ecp_point *Q,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng,
mbedtls_ecp_restart_ctx *rs_ctx )
{
int ret;
/* If multiplication is in progress, we already generated a privkey */
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( rs_ctx == NULL || rs_ctx->rsm == NULL )
#endif
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, d, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul_restartable( grp, Q, d, &grp->G,
f_rng, p_rng, rs_ctx ) );
cleanup:
return( ret );
}
/*
* Generate public key
*/
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 )
{
ECDH_VALIDATE_RET( grp != NULL );
ECDH_VALIDATE_RET( d != NULL );
ECDH_VALIDATE_RET( Q != NULL );
ECDH_VALIDATE_RET( f_rng != NULL );
return( ecdh_gen_public_restartable( grp, d, Q, f_rng, p_rng, NULL ) );
}
#endif /* !MBEDTLS_ECDH_GEN_PUBLIC_ALT */
#if !defined(MBEDTLS_ECDH_COMPUTE_SHARED_ALT)
/*
* Compute shared secret (SEC1 3.3.1)
*/
static int ecdh_compute_shared_restartable( 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,
mbedtls_ecp_restart_ctx *rs_ctx )
{
int ret;
mbedtls_ecp_point P;
mbedtls_ecp_point_init( &P );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul_restartable( grp, &P, d, Q,
f_rng, p_rng, rs_ctx ) );
if( mbedtls_ecp_is_zero( &P ) )
{
ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( z, &P.X ) );
cleanup:
mbedtls_ecp_point_free( &P );
return( ret );
}
/*
* 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 )
{
ECDH_VALIDATE_RET( grp != NULL );
ECDH_VALIDATE_RET( Q != NULL );
ECDH_VALIDATE_RET( d != NULL );
ECDH_VALIDATE_RET( z != NULL );
return( ecdh_compute_shared_restartable( grp, z, Q, d,
f_rng, p_rng, NULL ) );
}
#endif /* !MBEDTLS_ECDH_COMPUTE_SHARED_ALT */
static void ecdh_init_internal( mbedtls_ecdh_context_mbed *ctx )
{
mbedtls_ecp_group_init( &ctx->grp );
mbedtls_mpi_init( &ctx->d );
mbedtls_ecp_point_init( &ctx->Q );
mbedtls_ecp_point_init( &ctx->Qp );
mbedtls_mpi_init( &ctx->z );
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_init( &ctx->rs );
#endif
}
/*
* Initialize context
*/
void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx )
{
ECDH_VALIDATE( ctx != NULL );
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
ecdh_init_internal( ctx );
mbedtls_ecp_point_init( &ctx->Vi );
mbedtls_ecp_point_init( &ctx->Vf );
mbedtls_mpi_init( &ctx->_d );
#else
memset( ctx, 0, sizeof( mbedtls_ecdh_context ) );
ctx->var = MBEDTLS_ECDH_VARIANT_NONE;
#endif
ctx->point_format = MBEDTLS_ECP_PF_UNCOMPRESSED;
#if defined(MBEDTLS_ECP_RESTARTABLE)
ctx->restart_enabled = 0;
#endif
}
static int ecdh_setup_internal( mbedtls_ecdh_context_mbed *ctx,
mbedtls_ecp_group_id grp_id )
{
int ret;
ret = mbedtls_ecp_group_load( &ctx->grp, grp_id );
if( ret != 0 )
{
return( MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE );
}
return( 0 );
}
/*
* Setup context
*/
int mbedtls_ecdh_setup( mbedtls_ecdh_context *ctx, mbedtls_ecp_group_id grp_id )
{
ECDH_VALIDATE_RET( ctx != NULL );
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_setup_internal( ctx, grp_id ) );
#else
switch( grp_id )
{
default:
ctx->point_format = MBEDTLS_ECP_PF_UNCOMPRESSED;
ctx->var = MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0;
ctx->grp_id = grp_id;
ecdh_init_internal( &ctx->ctx.mbed_ecdh );
return( ecdh_setup_internal( &ctx->ctx.mbed_ecdh, grp_id ) );
}
#endif
}
static void ecdh_free_internal( mbedtls_ecdh_context_mbed *ctx )
{
mbedtls_ecp_group_free( &ctx->grp );
mbedtls_mpi_free( &ctx->d );
mbedtls_ecp_point_free( &ctx->Q );
mbedtls_ecp_point_free( &ctx->Qp );
mbedtls_mpi_free( &ctx->z );
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_free( &ctx->rs );
#endif
}
#if defined(MBEDTLS_ECP_RESTARTABLE)
/*
* Enable restartable operations for context
*/
void mbedtls_ecdh_enable_restart( mbedtls_ecdh_context *ctx )
{
ECDH_VALIDATE( ctx != NULL );
ctx->restart_enabled = 1;
}
#endif
/*
* Free context
*/
void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx )
{
if( ctx == NULL )
return;
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
mbedtls_ecp_point_free( &ctx->Vi );
mbedtls_ecp_point_free( &ctx->Vf );
mbedtls_mpi_free( &ctx->_d );
ecdh_free_internal( ctx );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
ecdh_free_internal( &ctx->ctx.mbed_ecdh );
break;
default:
break;
}
ctx->point_format = MBEDTLS_ECP_PF_UNCOMPRESSED;
ctx->var = MBEDTLS_ECDH_VARIANT_NONE;
ctx->grp_id = MBEDTLS_ECP_DP_NONE;
#endif
}
static int ecdh_make_params_internal( mbedtls_ecdh_context_mbed *ctx,
size_t *olen, int point_format,
unsigned char *buf, size_t blen,
int (*f_rng)(void *,
unsigned char *,
size_t),
void *p_rng,
int restart_enabled )
{
int ret;
size_t grp_len, pt_len;
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_ctx *rs_ctx = NULL;
#endif
if( ctx->grp.pbits == 0 )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( restart_enabled )
rs_ctx = &ctx->rs;
#else
(void) restart_enabled;
#endif
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
f_rng, p_rng, rs_ctx ) ) != 0 )
return( ret );
#else
if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q,
f_rng, p_rng ) ) != 0 )
return( ret );
#endif /* MBEDTLS_ECP_RESTARTABLE */
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, point_format,
&pt_len, buf, blen ) ) != 0 )
return( ret );
*olen = grp_len + pt_len;
return( 0 );
}
/*
* 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,
unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int restart_enabled = 0;
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( olen != NULL );
ECDH_VALIDATE_RET( buf != NULL );
ECDH_VALIDATE_RET( f_rng != NULL );
#if defined(MBEDTLS_ECP_RESTARTABLE)
restart_enabled = ctx->restart_enabled;
#else
(void) restart_enabled;
#endif
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_make_params_internal( ctx, olen, ctx->point_format, buf, blen,
f_rng, p_rng, restart_enabled ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_make_params_internal( &ctx->ctx.mbed_ecdh, olen,
ctx->point_format, buf, blen,
f_rng, p_rng,
restart_enabled ) );
default:
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
}
#endif
}
static int ecdh_read_params_internal( mbedtls_ecdh_context_mbed *ctx,
const unsigned char **buf,
const unsigned char *end )
{
return( mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, buf,
end - *buf ) );
}
/*
* Read the ServerKeyExhange parameters (RFC 4492)
* struct {
* ECParameters curve_params;
* ECPoint public;
* } ServerECDHParams;
*/
int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx,
const unsigned char **buf,
const unsigned char *end )
{
int ret;
mbedtls_ecp_group_id grp_id;
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( buf != NULL );
ECDH_VALIDATE_RET( *buf != NULL );
ECDH_VALIDATE_RET( end != NULL );
if( ( ret = mbedtls_ecp_tls_read_group_id( &grp_id, buf, end - *buf ) )
!= 0 )
return( ret );
if( ( ret = mbedtls_ecdh_setup( ctx, grp_id ) ) != 0 )
return( ret );
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_read_params_internal( ctx, buf, end ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_read_params_internal( &ctx->ctx.mbed_ecdh,
buf, end ) );
default:
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
}
#endif
}
static int ecdh_get_params_internal( mbedtls_ecdh_context_mbed *ctx,
const mbedtls_ecp_keypair *key,
mbedtls_ecdh_side side )
{
int 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 );
}
/*
* 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;
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( key != NULL );
ECDH_VALIDATE_RET( side == MBEDTLS_ECDH_OURS ||
side == MBEDTLS_ECDH_THEIRS );
if( mbedtls_ecdh_grp_id( ctx ) == MBEDTLS_ECP_DP_NONE )
{
/* This is the first call to get_params(). Set up the context
* for use with the group. */
if( ( ret = mbedtls_ecdh_setup( ctx, key->grp.id ) ) != 0 )
return( ret );
}
else
{
/* This is not the first call to get_params(). Check that the
* current key's group is the same as the context's, which was set
* from the first key's group. */
if( mbedtls_ecdh_grp_id( ctx ) != key->grp.id )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
}
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_get_params_internal( ctx, key, side ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_get_params_internal( &ctx->ctx.mbed_ecdh,
key, side ) );
default:
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
}
#endif
}
static int ecdh_make_public_internal( mbedtls_ecdh_context_mbed *ctx,
size_t *olen, int point_format,
unsigned char *buf, size_t blen,
int (*f_rng)(void *,
unsigned char *,
size_t),
void *p_rng,
int restart_enabled )
{
int ret;
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_ctx *rs_ctx = NULL;
#endif
if( ctx->grp.pbits == 0 )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( restart_enabled )
rs_ctx = &ctx->rs;
#else
(void) restart_enabled;
#endif
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( ( ret = ecdh_gen_public_restartable( &ctx->grp, &ctx->d, &ctx->Q,
f_rng, p_rng, rs_ctx ) ) != 0 )
return( ret );
#else
if( ( ret = mbedtls_ecdh_gen_public( &ctx->grp, &ctx->d, &ctx->Q,
f_rng, p_rng ) ) != 0 )
return( ret );
#endif /* MBEDTLS_ECP_RESTARTABLE */
return mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, point_format, olen,
buf, blen );
}
/*
* Setup and export the client public value
*/
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 )
{
int restart_enabled = 0;
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( olen != NULL );
ECDH_VALIDATE_RET( buf != NULL );
ECDH_VALIDATE_RET( f_rng != NULL );
#if defined(MBEDTLS_ECP_RESTARTABLE)
restart_enabled = ctx->restart_enabled;
#endif
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_make_public_internal( ctx, olen, ctx->point_format, buf, blen,
f_rng, p_rng, restart_enabled ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_make_public_internal( &ctx->ctx.mbed_ecdh, olen,
ctx->point_format, buf, blen,
f_rng, p_rng,
restart_enabled ) );
default:
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
}
#endif
}
static int ecdh_read_public_internal( mbedtls_ecdh_context_mbed *ctx,
const unsigned char *buf, size_t blen )
{
int ret;
const unsigned char *p = buf;
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 );
}
/*
* Parse and import the client's public value
*/
int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx,
const unsigned char *buf, size_t blen )
{
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( buf != NULL );
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_read_public_internal( ctx, buf, blen ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_read_public_internal( &ctx->ctx.mbed_ecdh,
buf, blen ) );
default:
return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
}
#endif
}
static int ecdh_calc_secret_internal( mbedtls_ecdh_context_mbed *ctx,
size_t *olen, unsigned char *buf,
size_t blen,
int (*f_rng)(void *,
unsigned char *,
size_t),
void *p_rng,
int restart_enabled )
{
int ret;
#if defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_ecp_restart_ctx *rs_ctx = NULL;
#endif
if( ctx == NULL || ctx->grp.pbits == 0 )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( restart_enabled )
rs_ctx = &ctx->rs;
#else
(void) restart_enabled;
#endif
#if defined(MBEDTLS_ECP_RESTARTABLE)
if( ( ret = ecdh_compute_shared_restartable( &ctx->grp, &ctx->z, &ctx->Qp,
&ctx->d, f_rng, p_rng,
rs_ctx ) ) != 0 )
{
return( ret );
}
#else
if( ( ret = mbedtls_ecdh_compute_shared( &ctx->grp, &ctx->z, &ctx->Qp,
&ctx->d, f_rng, p_rng ) ) != 0 )
{
return( ret );
}
#endif /* MBEDTLS_ECP_RESTARTABLE */
if( mbedtls_mpi_size( &ctx->z ) > blen )
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
*olen = ctx->grp.pbits / 8 + ( ( ctx->grp.pbits % 8 ) != 0 );
if( mbedtls_ecp_get_type( &ctx->grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
return mbedtls_mpi_write_binary_le( &ctx->z, buf, *olen );
return mbedtls_mpi_write_binary( &ctx->z, buf, *olen );
}
/*
* 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 )
{
int restart_enabled = 0;
ECDH_VALIDATE_RET( ctx != NULL );
ECDH_VALIDATE_RET( olen != NULL );
ECDH_VALIDATE_RET( buf != NULL );
#if defined(MBEDTLS_ECP_RESTARTABLE)
restart_enabled = ctx->restart_enabled;
#endif
#if defined(MBEDTLS_ECDH_LEGACY_CONTEXT)
return( ecdh_calc_secret_internal( ctx, olen, buf, blen, f_rng, p_rng,
restart_enabled ) );
#else
switch( ctx->var )
{
case MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0:
return( ecdh_calc_secret_internal( &ctx->ctx.mbed_ecdh, olen, buf,
blen, f_rng, p_rng,
restart_enabled ) );
default:
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
}
#endif
}
#endif /* MBEDTLS_ECDH_C */
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