+/*
+ ecdh.c -- Diffie-Hellman key exchange handling
+ Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>
+
+ 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.
+*/
+
+#include "system.h"
+#include "utils.h"
+#include "xalloc.h"
+
+#include <openssl/err.h>
+#include <openssl/ec.h>
+#include <openssl/obj_mac.h>
+
+#include "ecdh.h"
+#include "logger.h"
+
+EC_GROUP *secp256k1 = NULL;
+EC_GROUP *secp384r1 = NULL;
+EC_GROUP *secp521r1 = NULL;
+
+// TODO: proper KDF
+static void *kdf(const void *in, size_t inlen, void *out, size_t *outlen) {
+ memcpy(out, in, inlen);
+ *outlen = inlen;
+ return out;
+}
+
+bool ecdh_generate_public(ecdh_t *ecdh, void *pubkey) {
+ if(!secp521r1)
+ secp521r1 = EC_GROUP_new_by_curve_name(NID_secp521r1);
+
+ *ecdh = EC_KEY_new_by_curve_name(NID_secp521r1);
+ if(!EC_KEY_generate_key(*ecdh)) {
+ logger(LOG_ERR, "Generating EC key failed: %s", ERR_error_string(ERR_get_error(), NULL));
+ abort();
+ }
+
+ const EC_POINT *point = EC_KEY_get0_public_key(*ecdh);
+ if(!point) {
+ logger(LOG_ERR, "Getting public key failed: %s", ERR_error_string(ERR_get_error(), NULL));
+ abort();
+ }
+
+ size_t result = EC_POINT_point2oct(secp521r1, point, POINT_CONVERSION_COMPRESSED, pubkey, ECDH_SIZE, NULL);
+ if(!result) {
+ logger(LOG_ERR, "Converting EC_POINT to binary failed: %s", ERR_error_string(ERR_get_error(), NULL));
+ abort();
+ }
+
+ return true;
+}
+
+bool ecdh_compute_shared(ecdh_t *ecdh, const void *pubkey, void *shared) {
+ EC_POINT *point = EC_POINT_new(secp521r1);
+
+ int result = EC_POINT_oct2point(secp521r1, point, pubkey, ECDH_SIZE, NULL);
+ if(!point) {
+ logger(LOG_ERR, "Converting binary to EC_POINT failed: %s", ERR_error_string(ERR_get_error(), NULL));
+ abort();
+ }
+
+ result = ECDH_compute_key(shared, ECDH_SIZE, point, *ecdh, kdf);
+ EC_POINT_free(point);
+ EC_KEY_free(*ecdh);
+ *ecdh = NULL;
+
+ if(!result) {
+ logger(LOG_ERR, "Computing Elliptic Curve Diffie-Hellman shared key failed: %s", ERR_error_string(ERR_get_error(), NULL));
+ return false;
+ }
+
+ return true;
+}