1 /*
2  * Copyright (c) 2022, 2023 Omar Polo <op@openbsd.org>
3  * Copyright (c) 2014 Reyk Floeter <reyk@openbsd.org>
4  *
5  * Permission to use, copy, modify, and distribute this software for any
6  * purpose with or without fee is hereby granted, provided that the above
7  * copyright notice and this permission notice appear in all copies.
8  *
9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16  */
17 
18 #include <ctype.h>
19 #include <err.h>
20 #include <errno.h>
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <time.h>
25 #include <unistd.h>
26 
27 #include <openssl/evp.h>
28 #include <openssl/hmac.h>
29 
30 #ifndef __OpenBSD__
31 # define pledge(a, b) (0)
32 #endif
33 
34 #ifndef __dead
35 # define __dead __attribute__((noreturn))
36 #endif
37 
38 #if defined(__FreeBSD__) || defined(__NetBSD__)
39 # include <sys/endian.h>
40 #elif defined(__APPLE__)
41 # include <machine/endian.h>
42 # include <libkern/OSByteOrder.h>
43 # define htobe64(x) OSSwapHostToBigInt64(x)
44 # define be32toh(x) OSSwapBigToHostInt32(x)
45 #else
46 # include <endian.h>
47 #endif
48 
49 static __dead void
50 usage(void)
51 {
52 	fprintf(stderr, "usage: %s\n", getprogname());
53 	exit(1);
54 }
55 
56 static int
57 b32c(unsigned char c)
58 {
59 	if (c >= 'A' && c <= 'Z')
60 		return (c - 'A');
61 	if (c >= '2' && c <= '7')
62 		return (c - '2' + 26);
63 	errno = EINVAL;
64 	return (-1);
65 }
66 
67 static size_t
68 b32decode(const char *s, char *q, size_t qlen)
69 {
70 	int	 i, val[8];
71 	char	*t = q;
72 
73 	while (*s != '\0') {
74 		memset(val, 0, sizeof(val));
75 		for (i = 0; i < 8; ++i) {
76 			if (*s == '\0')
77 				break;
78 			if ((val[i] = b32c(*s)) == -1)
79 				return (0);
80 			s++;
81 		}
82 
83 		if (qlen < 5) {
84 			errno = ENOSPC;
85 			return (0);
86 		}
87 		qlen -= 5;
88 
89 		*q++ = (val[0] << 3) | (val[1] >> 2);
90 		*q++ = ((val[1] & 0x03) << 6) | (val[2] << 1) | (val[3] >> 4);
91 		*q++ = ((val[3] & 0x0F) << 4) | (val[4] >> 1);
92 		*q++ = ((val[4] & 0x01) << 7) | (val[5] << 2) | (val[6] >> 3);
93 		*q++ = ((val[6] & 0x07) << 5) | val[7];
94 	}
95 
96 	return (q - t);
97 }
98 
99 /* adapted from httpd(8) */
100 static char *
101 url_decode(char *url, char *dst)
102 {
103 	char		*p, *q;
104 	char		 hex[3];
105 	unsigned long	 x;
106 
107 	hex[2] = '\0';
108 	p = url;
109 	q = dst;
110 
111 	while (*p != '\0') {
112 		if (*p != '%') {
113 			*q++ = *p++;
114 			continue;
115 		}
116 
117 		if (!isxdigit((unsigned char)p[1]) ||
118 		    !isxdigit((unsigned char)p[2]))
119 			return (NULL);
120 
121 		hex[0] = p[1];
122 		hex[1] = p[2];
123 
124 		/*
125 		 * We don't have to validate "hex" because it is
126 		 * guaranteed to include two hex chars followed by nul.
127 		 */
128 		x = strtoul(hex, NULL, 16);
129 		*q++ = (char)x;
130 		p += 3;
131 	}
132 	*q = '\0';
133 	return (url);
134 }
135 
136 static int
137 uri2secret(char *s)
138 {
139 	char		*q, *t, *f, *secret = NULL;
140 
141 	if ((q = strchr(s, '?')) == NULL)
142 		return (-1);
143 
144 	t = q + 1;
145 	while ((f = strsep(&t, "&")) != NULL) {
146 		if (!strncmp(f, "secret=", 7))
147 			secret = f + 7;
148 	}
149 
150 	if (secret == NULL)
151 		return (-1);
152 	if (url_decode(secret, s) == NULL)
153 		errx(1, "failed to percent-decode the secret");
154 	return (0);
155 }
156 
157 int
158 main(int argc, char **argv)
159 {
160 	char		 buf[1024];
161 	size_t		 buflen;
162 	unsigned char	 md[EVP_MAX_MD_SIZE];
163 	unsigned int	 mdlen;
164 	char		*s, *q, *line = NULL;
165 	size_t		 linesize = 0;
166 	ssize_t		 linelen;
167 	uint64_t	 ct;
168 	uint32_t	 hash;
169 	uint8_t		 off;
170 	int		 ch;
171 
172 	if (pledge("stdio", NULL) == -1)
173 		err(1, "pledge");
174 
175 	while ((ch = getopt(argc, argv, "")) != -1) {
176 		switch (ch) {
177 		default:
178 			usage();
179 		}
180 	}
181 	argc -= optind;
182 	argv += optind;
183 
184 	if (argc != 0)
185 		usage();
186 
187 	linelen = getline(&line, &linesize, stdin);
188 	if (linelen == -1) {
189 		if (ferror(stdin))
190 			err(1, "getline");
191 		errx(1, "no secret provided");
192 	}
193 	for (s = q = line; *s != '\0'; ++s) {
194 		if (isspace((unsigned char)*s)) {
195 			linelen--;
196 			continue;
197 		}
198 		*q++ = *s;
199 	}
200 	*q = '\0';
201 	if (linelen < 1)
202 		errx(1, "no secret provided");
203 
204 	if (!strncmp(line, "otpauth://", 10) && uri2secret(line) == -1)
205 		errx(1, "failed to decode otpauth URI");
206 
207 	if ((buflen = b32decode(line, buf, sizeof(buf))) == 0)
208 		err(1, "can't base32 decode the secret");
209 
210 	ct = htobe64(time(NULL) / 30);
211 
212 	HMAC(EVP_sha1(), buf, buflen, (unsigned char *)&ct, sizeof(ct),
213 	    md, &mdlen);
214 
215 	off = md[mdlen - 1] & 0x0F;
216 
217 	memcpy(&hash, md + off, sizeof(hash));
218 	hash = be32toh(hash);
219 	printf("%06d\n", (hash & 0x7FFFFFFF) % 1000000);
220 
221 	free(line);
222 	return (0);
223 }