/*
 * %CopyrightBegin%
 *
 * Copyright Ericsson AB 2010-2018. All Rights Reserved.
 *
 * 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.
 *
 * %CopyrightEnd%
 */

#include "ecdh.h"
#include "ec.h"

/*
  (_OthersPublicKey, _MyPrivateKey)
  (_OthersPublicKey, _MyEC_Point)
*/
ERL_NIF_TERM ecdh_compute_key_nif(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
/* (OtherPublicKey, Curve, My) */
{
#if defined(HAVE_EC)
    ERL_NIF_TERM ret;
    unsigned char *p;
    EC_KEY* key = NULL;
    int field_size = 0;
    int i;
    EC_GROUP *group;
    const BIGNUM *priv_key;
    EC_POINT *my_ecpoint = NULL;
    EC_KEY *other_ecdh = NULL;

    if (!get_ec_key(env, argv[1], argv[2], atom_undefined, &key))
	return make_badarg_maybe(env);

    group    = EC_GROUP_dup(EC_KEY_get0_group(key));
    priv_key = EC_KEY_get0_private_key(key);

    if (!term2point(env, argv[0], group, &my_ecpoint)) {
	goto out_err;
    }

    if ((other_ecdh = EC_KEY_new()) == NULL
	|| !EC_KEY_set_group(other_ecdh, group)
	|| !EC_KEY_set_private_key(other_ecdh, priv_key))
	goto out_err;

    field_size = EC_GROUP_get_degree(group);
    if (field_size <= 0)
	goto out_err;

    p = enif_make_new_binary(env, (field_size+7)/8, &ret);
    i = ECDH_compute_key(p, (field_size+7)/8, my_ecpoint, other_ecdh, NULL);

    if (i < 0)
	    goto out_err;
out:
    if (group) EC_GROUP_free(group);
    if (my_ecpoint) EC_POINT_free(my_ecpoint);
    if (other_ecdh) EC_KEY_free(other_ecdh);
    if (key) EC_KEY_free(key);

    return ret;

out_err:
    ret = enif_make_badarg(env);
    goto out;
#else
    return atom_notsup;
#endif
}