344 lines
9.5 KiB
C
344 lines
9.5 KiB
C
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/*
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* Elliptic curve Diffie-Hellman
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*
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* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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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/*
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* References:
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*
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* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
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* RFC 4492
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*/
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#if !defined(MBEDTLS_CONFIG_FILE)
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#include "mbedtls/config.h"
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#else
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#include MBEDTLS_CONFIG_FILE
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#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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#if defined(MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED)
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#include "mbedtls/ed25519.h"
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#endif /* MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED */
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#if defined(MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED)
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/*
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* Swap given bytes
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*/
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static void swap(unsigned char *a, unsigned char *b) {
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unsigned char t = *a; *a = *b; *b = t;
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}
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/*
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* Reverse bytes in range [first, last)
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*/
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static void reverse_bytes(unsigned char *first, unsigned char *last) {
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while ((first!=last)&&(first!=--last)) {
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swap (first,last);
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++first;
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}
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}
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#endif /* MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED */
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#if defined(MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED)
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/*
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* Compute shared secret on the Curve25519 curve
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*/
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static int mbedtls_ecdh_compute_shared_curve25519( 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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int ret;
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unsigned char shared_key[MBEDTLS_ED25519_DH_LEN];
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unsigned char public_key[MBEDTLS_ED25519_KEY_LEN];
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unsigned char private_key[MBEDTLS_ED25519_KEY_LEN];
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(void) f_rng;
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(void) p_rng;
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if( grp->id != MBEDTLS_ECP_DP_CURVE25519 )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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// Q -> Q(BE) -> Q(LE)
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MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &Q->X, public_key, MBEDTLS_ED25519_KEY_LEN ) );
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reverse_bytes( public_key, public_key + MBEDTLS_ED25519_KEY_LEN );
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// d -> d(BE) -> d(LE)
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MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, private_key, MBEDTLS_ED25519_KEY_LEN ) );
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reverse_bytes( private_key, private_key + MBEDTLS_ED25519_KEY_LEN );
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// compute shared secret
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if( mbedtls_curve25519_key_exchange( shared_key, public_key, private_key ) )
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{
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ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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goto cleanup;
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}
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// z(LE) -> z(BE) -> z
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reverse_bytes( shared_key, shared_key + MBEDTLS_ED25519_DH_LEN );
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MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( z, shared_key, MBEDTLS_ED25519_DH_LEN ) );
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cleanup:
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return( ret );
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}
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#endif /* MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED */
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/*
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* Generate public key: simple wrapper around mbedtls_ecp_gen_keypair
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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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return mbedtls_ecp_gen_keypair( grp, d, Q, f_rng, p_rng );
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}
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/*
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* Compute shared secret (SEC1 3.3.1)
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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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int ret;
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mbedtls_ecp_point P;
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if( grp == NULL )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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#if defined(MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED)
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/*
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* Use custom optimization
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*/
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if( grp->id == MBEDTLS_ECP_DP_CURVE25519 )
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return mbedtls_ecdh_compute_shared_curve25519(grp, z, Q, d, f_rng, p_rng);
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#endif /* MBEDTLS_ECDH_CURVE25519_OVER_ED25519_ENABLED */
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mbedtls_ecp_point_init( &P );
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/*
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* Make sure Q is a valid pubkey before using it
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*/
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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 ) )
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{
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ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
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goto cleanup;
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}
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MBEDTLS_MPI_CHK( mbedtls_mpi_copy( z, &P.X ) );
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cleanup:
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mbedtls_ecp_point_free( &P );
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return( ret );
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}
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/*
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* Initialize context
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*/
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void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx )
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{
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memset( ctx, 0, sizeof( mbedtls_ecdh_context ) );
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}
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/*
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* Free 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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if( ctx == NULL )
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return;
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mbedtls_ecp_group_free( &ctx->grp );
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mbedtls_ecp_point_free( &ctx->Q );
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mbedtls_ecp_point_free( &ctx->Qp );
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mbedtls_ecp_point_free( &ctx->Vi );
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mbedtls_ecp_point_free( &ctx->Vf );
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mbedtls_mpi_free( &ctx->d );
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mbedtls_mpi_free( &ctx->z );
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mbedtls_mpi_free( &ctx->_d );
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}
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/*
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* Setup and write the ServerKeyExhange parameters (RFC 4492)
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* struct {
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* ECParameters curve_params;
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* ECPoint public;
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* } ServerECDHParams;
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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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int ret;
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size_t grp_len, pt_len;
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if( ctx == NULL || ctx->grp.pbits == 0 )
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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 )
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return( ret );
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if( ( ret = mbedtls_ecp_tls_write_group( &ctx->grp, &grp_len, buf, blen ) )
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!= 0 )
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return( ret );
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buf += grp_len;
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blen -= grp_len;
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if( ( ret = mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format,
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&pt_len, buf, blen ) ) != 0 )
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return( ret );
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*olen = grp_len + pt_len;
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return( 0 );
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}
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/*
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* Read the ServerKeyExhange parameters (RFC 4492)
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* struct {
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* ECParameters curve_params;
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* ECPoint public;
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* } ServerECDHParams;
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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, const unsigned char *end )
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{
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int ret;
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if( ( ret = mbedtls_ecp_tls_read_group( &ctx->grp, buf, end - *buf ) ) != 0 )
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return( ret );
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if( ( ret = mbedtls_ecp_tls_read_point( &ctx->grp, &ctx->Qp, buf, end - *buf ) )
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!= 0 )
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return( ret );
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return( 0 );
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}
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/*
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* Get parameters from a keypair
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*/
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int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key,
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mbedtls_ecdh_side side )
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{
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int ret;
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if( ( ret = mbedtls_ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 )
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return( ret );
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/* If it's not our key, just import the public part as Qp */
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if( side == MBEDTLS_ECDH_THEIRS )
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return( mbedtls_ecp_copy( &ctx->Qp, &key->Q ) );
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/* Our key: import public (as Q) and private parts */
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if( side != MBEDTLS_ECDH_OURS )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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if( ( ret = mbedtls_ecp_copy( &ctx->Q, &key->Q ) ) != 0 ||
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( ret = mbedtls_mpi_copy( &ctx->d, &key->d ) ) != 0 )
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return( ret );
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return( 0 );
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}
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/*
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* Setup and export the client public value
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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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int ret;
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if( ctx == NULL || ctx->grp.pbits == 0 )
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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 )
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return( ret );
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return mbedtls_ecp_tls_write_point( &ctx->grp, &ctx->Q, ctx->point_format,
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olen, buf, blen );
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}
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/*
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* Parse and import the client's public value
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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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int ret;
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const unsigned char *p = buf;
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if( ctx == NULL )
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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 )
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return( ret );
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if( (size_t)( p - buf ) != blen )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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return( 0 );
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}
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/*
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* Derive and export the shared secret
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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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{
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int ret;
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if( ctx == NULL )
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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,
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f_rng, p_rng ) ) != 0 )
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{
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return( ret );
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}
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if( mbedtls_mpi_size( &ctx->z ) > blen )
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return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
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*olen = ctx->grp.pbits / 8 + ( ( ctx->grp.pbits % 8 ) != 0 );
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return mbedtls_mpi_write_binary( &ctx->z, buf, *olen );
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}
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#endif /* MBEDTLS_ECDH_C */
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