/*
 *  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/mbedtls_config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_ECDH_C)

#include "mbedtls/ecdh.h"

#include <string.h>

/*
 * Generate public key: simple wrapper around mbedtls_ecp_gen_keypair
 */
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)
{
    return mbedtls_ecp_gen_keypair(grp, d, Q, f_rng, p_rng);
}

/*
 * 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)
{
    int ret;
    mbedtls_ecp_point P;

    mbedtls_ecp_point_init(&P);

    /*
     * Make sure Q is a valid pubkey before using it
     */
    MBEDTLS_MPI_CHK(mbedtls_ecp_check_pubkey(grp, Q));

    MBEDTLS_MPI_CHK(mbedtls_ecp_mul(grp, &P, d, Q, f_rng, p_rng));

    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);
}

/*
 * Initialize context
 */
void mbedtls_ecdh_init(mbedtls_ecdh_context *ctx)
{
    memset(ctx, 0, sizeof(mbedtls_ecdh_context));
}

/*
 * Free context
 */
void mbedtls_ecdh_free(mbedtls_ecdh_context *ctx)
{
    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);
}

/*
 * 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 ret;
    size_t grp_len, pt_len;

    if (ctx == NULL || ctx->grp.pbits == 0) {
        return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
    }

    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;
    return (0);
}

/*
 * 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;

    if ((ret = mbedtls_ecp_tls_read_group(&ctx->grp, buf, end - *buf)) != 0) {
        return (ret);
    }

    if ((ret = mbedtls_ecp_tls_read_point(&ctx->grp, &ctx->Qp, buf, end - *buf))
        != 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;

    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);
}

/*
 * 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 ret;

    if (ctx == NULL || ctx->grp.pbits == 0) {
        return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
    }

    if ((ret = mbedtls_ecdh_gen_public(&ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng))
        != 0) {
        return (ret);
    }

    return mbedtls_ecp_tls_write_point(&ctx->grp, &ctx->Q, ctx->point_format,
                                       olen, buf, blen);
}

/*
 * Parse and import the client's public value
 */
int mbedtls_ecdh_read_public(mbedtls_ecdh_context *ctx,
                             const unsigned char *buf, size_t blen)
{
    int ret;
    const unsigned char *p = buf;

    if (ctx == NULL) {
        return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
    }

    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);
}

/*
 * 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 ret;

    if (ctx == NULL) {
        return (MBEDTLS_ERR_ECP_BAD_INPUT_DATA);
    }

    if ((ret = mbedtls_ecdh_compute_shared(&ctx->grp, &ctx->z, &ctx->Qp, &ctx->d,
                                           f_rng, p_rng)) != 0) {
        return (ret);
    }

    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);
}

#endif /* MBEDTLS_ECDH_C */