1/*	$NetBSD: wg-keygen.c,v 1.1 2020/08/20 21:28:02 riastradh Exp $	*/
2
3/*
4 * Copyright (C) Ryota Ozaki <ozaki.ryota@gmail.com>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the project nor the names of its contributors
16 *    may be used to endorse or promote products derived from this software
17 *    without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33__RCSID("$NetBSD: wg-keygen.c,v 1.1 2020/08/20 21:28:02 riastradh Exp $");
34
35#include <stdio.h>
36#include <stdlib.h>
37#include <err.h>
38#include <resolv.h>
39#include <string.h>
40
41#define KEY_LEN			32
42#define KEY_BASE64_LEN		44
43
44__dead static void
45usage(void)
46{
47	const char *progname = getprogname();
48
49	fprintf(stderr, "Usage:\n");
50	fprintf(stderr, "\t%s       : Generate a private key\n", progname);
51	fprintf(stderr, "\t%s --pub : Generate a public key from a private key via stdin\n", progname);
52	fprintf(stderr, "\t%s --psk : Generate a pre-shared key\n", progname);
53
54	exit(EXIT_FAILURE);
55}
56
57/* Mimic crypto/external/bsd/openssh/dist/kexc25519.c */
58#define CURVE25519_SIZE	32
59extern int crypto_scalarmult_curve25519(uint8_t [CURVE25519_SIZE],
60    const uint8_t [CURVE25519_SIZE], const uint8_t [CURVE25519_SIZE]);
61
62static void
63gen_pubkey(uint8_t key[CURVE25519_SIZE], uint8_t pubkey[CURVE25519_SIZE])
64{
65	static const uint8_t basepoint[CURVE25519_SIZE] = {9};
66
67	crypto_scalarmult_curve25519(pubkey, key, basepoint);
68}
69
70static void
71normalize_key(uint8_t key[KEY_LEN])
72{
73
74	/* Mimic the official implementation, wg */
75	key[0] &= 248;
76	key[31] &= 127;
77	key[31] |= 64;
78}
79
80static char *
81base64(uint8_t key[KEY_LEN])
82{
83	static char key_b64[KEY_BASE64_LEN + 1];
84	int error;
85
86	error = b64_ntop(key, KEY_LEN, key_b64, KEY_BASE64_LEN + 1);
87	if (error == -1)
88		errx(EXIT_FAILURE, "b64_ntop failed");
89	key_b64[KEY_BASE64_LEN] = '\0'; /* just in case */
90
91	return key_b64;
92}
93
94int
95main(int argc, char *argv[])
96{
97	uint8_t key[KEY_LEN];
98
99	if (!(argc == 1 || argc == 2))
100		usage();
101
102	if (argc == 1) {
103		arc4random_buf(key, KEY_LEN);
104		normalize_key(key);
105		printf("%s\n", base64(key));
106		return 0;
107	}
108
109	if (strcmp(argv[1], "--psk") == 0) {
110		arc4random_buf(key, KEY_LEN);
111		printf("%s\n", base64(key));
112		return 0;
113	}
114
115	if (strcmp(argv[1], "--pub") == 0) {
116		char key_b64[KEY_BASE64_LEN + 1];
117		int ret;
118		char *retc;
119		uint8_t pubkey[KEY_LEN];
120
121		retc = fgets(key_b64, KEY_BASE64_LEN + 1, stdin);
122		if (retc == NULL)
123			err(EXIT_FAILURE, "fgets");
124		key_b64[KEY_BASE64_LEN] = '\0';
125		if (strlen(key_b64) != KEY_BASE64_LEN)
126			errx(EXIT_FAILURE, "Invalid length of a private key");
127		ret = b64_pton(key_b64, key, KEY_LEN);
128		if (ret == -1)
129			errx(EXIT_FAILURE, "b64_pton failed");
130		gen_pubkey(key, pubkey);
131		printf("%s\n", base64(pubkey));
132		return 0;
133	}
134
135	usage();
136}
137