proposal: Add method to move a given DH group to the front

This way a responder (like strongSwan) selecting a proposal first and
then checking if the KE payload matches sees the peer's preferred group
first.

src/libstrongswan/crypto/proposal/proposal.c

@@ -1,8 +1,8 @@
 /*
- * Copyright (C) 2008-2016 Tobias Brunner
+ * Copyright (C) 2008-2018 Tobias Brunner
  * Copyright (C) 2006-2010 Martin Willi
  * Copyright (C) 2013-2015 Andreas Steffen
- * Hochschule fuer Technik Rapperswil
+ * HSR Hochschule fuer Technik Rapperswil
  *
  * 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
@@ -171,6 +171,36 @@ METHOD(proposal_t, has_dh_group, bool,
 	return found;
 }
 
+METHOD(proposal_t, promote_dh_group, bool,
+	private_proposal_t *this, diffie_hellman_group_t group)
+{
+	enumerator_t *enumerator;
+	entry_t *entry;
+	bool found = FALSE;
+
+	enumerator = array_create_enumerator(this->transforms);
+	while (enumerator->enumerate(enumerator, &entry))
+	{
+		if (entry->type == DIFFIE_HELLMAN_GROUP &&
+			entry->alg == group)
+		{
+			array_remove_at(this->transforms, enumerator);
+			found = TRUE;
+		}
+	}
+	enumerator->destroy(enumerator);
+
+	if (found)
+	{
+		entry_t entry = {
+			.type = DIFFIE_HELLMAN_GROUP,
+			.alg = group,
+		};
+		array_insert(this->transforms, ARRAY_HEAD, &entry);
+	}
+	return found;
+}
+
 METHOD(proposal_t, strip_dh, void,
 	private_proposal_t *this, diffie_hellman_group_t keep)
 {
@@ -716,6 +746,7 @@ proposal_t *proposal_create(protocol_id_t protocol, u_int number)
 			.create_enumerator = _create_enumerator,
 			.get_algorithm = _get_algorithm,
 			.has_dh_group = _has_dh_group,
+			.promote_dh_group = _promote_dh_group,
 			.strip_dh = _strip_dh,
 			.select = _select_proposal,
 			.get_protocol = _get_protocol,

src/libstrongswan/crypto/proposal/proposal.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009-2016 Tobias Brunner
+ * Copyright (C) 2009-2018 Tobias Brunner
  * Copyright (C) 2006 Martin Willi
  * HSR Hochschule fuer Technik Rapperswil
  *
@@ -108,7 +108,16 @@ struct proposal_t {
 	 * @param group			group to check for
 	 * @return				TRUE if algorithm included
 	 */
-	bool (*has_dh_group) (proposal_t *this, diffie_hellman_group_t group);
+	bool (*has_dh_group)(proposal_t *this, diffie_hellman_group_t group);
+
+	/**
+	 * Move the given DH group to the front of the list if it was contained in
+	 * the proposal.
+	 *
+	 * @param group			group to promote
+	 * @return				TRUE if algorithm included
+	 */
+	bool (*promote_dh_group)(proposal_t *this, diffie_hellman_group_t group);
 
 	/**
 	 * Strip DH groups from proposal to use it without PFS.

src/libstrongswan/tests/suites/test_proposal.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2016 Tobias Brunner
+ * Copyright (C) 2016-2018 Tobias Brunner
  * HSR Hochschule fuer Technik Rapperswil
  *
  * This program is free software; you can redistribute it and/or modify it
@@ -57,21 +57,27 @@ static struct {
 	{ PROTO_AH,  "sha256-esn-noesn", "AH:HMAC_SHA2_256_128/EXT_SEQ/NO_EXT_SEQ" },
 };
 
-START_TEST(test_create_from_string)
+static void assert_proposal_eq(proposal_t *proposal, char *expected)
 {
-	proposal_t *proposal;
 	char str[BUF_LEN];
 
-	proposal = proposal_create_from_string(create_data[_i].proto,
+	if (!expected)
-										   create_data[_i].proposal);
-	if (!create_data[_i].expected)
 	{
 		ck_assert(!proposal);
 		return;
 	}
 	snprintf(str, sizeof(str), "%P", proposal);
-	ck_assert_str_eq(create_data[_i].expected, str);
+	ck_assert_str_eq(expected, str);
-	proposal->destroy(proposal);
+}
+
+START_TEST(test_create_from_string)
+{
+	proposal_t *proposal;
+
+	proposal = proposal_create_from_string(create_data[_i].proto,
+										   create_data[_i].proposal);
+	assert_proposal_eq(proposal, create_data[_i].expected);
+	DESTROY_IF(proposal);
 }
 END_TEST
 
@@ -151,6 +157,43 @@ START_TEST(test_select_spi)
 }
 END_TEST
 
+START_TEST(test_promote_dh_group)
+{
+	proposal_t *proposal;
+
+	proposal = proposal_create_from_string(PROTO_IKE,
+										   "aes128-sha256-modp3072-ecp256");
+	ck_assert(proposal->promote_dh_group(proposal, ECP_256_BIT));
+	assert_proposal_eq(proposal, "IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/ECP_256/MODP_3072");
+	proposal->destroy(proposal);
+}
+END_TEST
+
+START_TEST(test_promote_dh_group_already_front)
+{
+	proposal_t *proposal;
+
+	proposal = proposal_create_from_string(PROTO_IKE,
+										   "aes128-sha256-modp3072-ecp256");
+	ck_assert(proposal->promote_dh_group(proposal, MODP_3072_BIT));
+	assert_proposal_eq(proposal, "IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_3072/ECP_256");
+	proposal->destroy(proposal);
+}
+END_TEST
+
+START_TEST(test_promote_dh_group_not_contained)
+{
+	proposal_t *proposal;
+
+	proposal = proposal_create_from_string(PROTO_IKE,
+										   "aes128-sha256-modp3072-ecp256");
+
+	ck_assert(!proposal->promote_dh_group(proposal, MODP_2048_BIT));
+	assert_proposal_eq(proposal, "IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_3072/ECP_256");
+	proposal->destroy(proposal);
+}
+END_TEST
+
 Suite *proposal_suite_create()
 {
 	Suite *s;
@@ -167,5 +210,11 @@ Suite *proposal_suite_create()
 	tcase_add_test(tc, test_select_spi);
 	suite_add_tcase(s, tc);
 
+	tc = tcase_create("promote_dh_group");
+	tcase_add_test(tc, test_promote_dh_group);
+	tcase_add_test(tc, test_promote_dh_group_already_front);
+	tcase_add_test(tc, test_promote_dh_group_not_contained);
+	suite_add_tcase(s, tc);
+
 	return s;
 }