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1/* $OpenBSD: mac.c,v 1.37 2025/09/05 10:01:35 dtucker Exp $ */
2/*
3 * Copyright (c) 2001 Markus Friedl. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include <sys/types.h>
27
28#include <stdio.h>
29#include <stdlib.h>
30#include <string.h>
31
32#include "digest.h"
33#include "hmac.h"
34#include "umac.h"
35#include "mac.h"
36#include "misc.h"
37#include "ssherr.h"
38#include "sshbuf.h"
39
40#define SSH_DIGEST 1 /* SSH_DIGEST_XXX */
41#define SSH_UMAC 2 /* UMAC (not integrated with OpenSSL) */
42#define SSH_UMAC128 3
43
44struct macalg {
45 char *name;
46 int type;
47 int alg;
48 int truncatebits; /* truncate digest if != 0 */
49 int key_len; /* just for UMAC */
50 int len; /* just for UMAC */
51 int etm; /* Encrypt-then-MAC */
52};
53
54static const struct macalg macs[] = {
55 /* Encrypt-and-MAC (encrypt-and-authenticate) variants */
56 { "hmac-sha1", SSH_DIGEST, SSH_DIGEST_SHA1, 0, 0, 0, 0 },
57 { "hmac-sha1-96", SSH_DIGEST, SSH_DIGEST_SHA1, 96, 0, 0, 0 },
58 { "hmac-sha2-256", SSH_DIGEST, SSH_DIGEST_SHA256, 0, 0, 0, 0 },
59 { "hmac-sha2-512", SSH_DIGEST, SSH_DIGEST_SHA512, 0, 0, 0, 0 },
60 { "hmac-md5", SSH_DIGEST, SSH_DIGEST_MD5, 0, 0, 0, 0 },
61 { "hmac-md5-96", SSH_DIGEST, SSH_DIGEST_MD5, 96, 0, 0, 0 },
62 { "umac-64@openssh.com", SSH_UMAC, 0, 0, 128, 64, 0 },
63 { "umac-128@openssh.com", SSH_UMAC128, 0, 0, 128, 128, 0 },
64
65 /* Encrypt-then-MAC variants */
66 { "hmac-sha1-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_SHA1, 0, 0, 0, 1 },
67 { "hmac-sha1-96-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_SHA1, 96, 0, 0, 1 },
68 { "hmac-sha2-256-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_SHA256, 0, 0, 0, 1 },
69 { "hmac-sha2-512-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_SHA512, 0, 0, 0, 1 },
70 { "hmac-md5-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_MD5, 0, 0, 0, 1 },
71 { "hmac-md5-96-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_MD5, 96, 0, 0, 1 },
72 { "umac-64-etm@openssh.com", SSH_UMAC, 0, 0, 128, 64, 1 },
73 { "umac-128-etm@openssh.com", SSH_UMAC128, 0, 0, 128, 128, 1 },
74
75 { NULL, 0, 0, 0, 0, 0, 0 }
76};
77
78/* Returns a list of supported MACs separated by the specified char. */
79char *
80mac_alg_list(char sep)
81{
82 char *ret = NULL;
83 const struct macalg *m;
84 char sep_str[2] = {sep, '\0'};
85
86 for (m = macs; m->name != NULL; m++)
87 xextendf(&ret, sep_str, "%s", m->name);
88
89 return ret;
90}
91
92static int
93mac_setup_by_alg(struct sshmac *mac, const struct macalg *macalg)
94{
95 mac->type = macalg->type;
96 if (mac->type == SSH_DIGEST) {
97 if ((mac->hmac_ctx = ssh_hmac_start(macalg->alg)) == NULL)
98 return SSH_ERR_ALLOC_FAIL;
99 mac->key_len = mac->mac_len = ssh_hmac_bytes(macalg->alg);
100 } else {
101 mac->mac_len = macalg->len / 8;
102 mac->key_len = macalg->key_len / 8;
103 mac->umac_ctx = NULL;
104 }
105 if (macalg->truncatebits != 0)
106 mac->mac_len = macalg->truncatebits / 8;
107 mac->etm = macalg->etm;
108 return 0;
109}
110
111int
112mac_setup(struct sshmac *mac, char *name)
113{
114 const struct macalg *m;
115
116 for (m = macs; m->name != NULL; m++) {
117 if (strcmp(name, m->name) != 0)
118 continue;
119 if (mac != NULL)
120 return mac_setup_by_alg(mac, m);
121 return 0;
122 }
123 return SSH_ERR_INVALID_ARGUMENT;
124}
125
126int
127mac_init(struct sshmac *mac)
128{
129 if (mac->key == NULL)
130 return SSH_ERR_INVALID_ARGUMENT;
131 switch (mac->type) {
132 case SSH_DIGEST:
133 if (mac->hmac_ctx == NULL ||
134 ssh_hmac_init(mac->hmac_ctx, mac->key, mac->key_len) < 0)
135 return SSH_ERR_INVALID_ARGUMENT;
136 return 0;
137 case SSH_UMAC:
138 if ((mac->umac_ctx = umac_new(mac->key)) == NULL)
139 return SSH_ERR_ALLOC_FAIL;
140 return 0;
141 case SSH_UMAC128:
142 if ((mac->umac_ctx = umac128_new(mac->key)) == NULL)
143 return SSH_ERR_ALLOC_FAIL;
144 return 0;
145 default:
146 return SSH_ERR_INVALID_ARGUMENT;
147 }
148}
149
150int
151mac_compute(struct sshmac *mac, u_int32_t seqno,
152 const u_char *data, int datalen,
153 u_char *digest, size_t dlen)
154{
155 static union {
156 u_char m[SSH_DIGEST_MAX_LENGTH];
157 u_int64_t for_align;
158 } u;
159 u_char b[4];
160 u_char nonce[8];
161
162 if (mac->mac_len > sizeof(u))
163 return SSH_ERR_INTERNAL_ERROR;
164
165 switch (mac->type) {
166 case SSH_DIGEST:
167 put_u32(b, seqno);
168 /* reset HMAC context */
169 if (ssh_hmac_init(mac->hmac_ctx, NULL, 0) < 0 ||
170 ssh_hmac_update(mac->hmac_ctx, b, sizeof(b)) < 0 ||
171 ssh_hmac_update(mac->hmac_ctx, data, datalen) < 0 ||
172 ssh_hmac_final(mac->hmac_ctx, u.m, sizeof(u.m)) < 0)
173 return SSH_ERR_LIBCRYPTO_ERROR;
174 break;
175 case SSH_UMAC:
176 POKE_U64(nonce, seqno);
177 umac_update(mac->umac_ctx, data, datalen);
178 umac_final(mac->umac_ctx, u.m, nonce);
179 break;
180 case SSH_UMAC128:
181 put_u64(nonce, seqno);
182 umac128_update(mac->umac_ctx, data, datalen);
183 umac128_final(mac->umac_ctx, u.m, nonce);
184 break;
185 default:
186 return SSH_ERR_INVALID_ARGUMENT;
187 }
188 if (digest != NULL) {
189 if (dlen > mac->mac_len)
190 dlen = mac->mac_len;
191 memcpy(digest, u.m, dlen);
192 }
193 return 0;
194}
195
196int
197mac_check(struct sshmac *mac, u_int32_t seqno,
198 const u_char *data, size_t dlen,
199 const u_char *theirmac, size_t mlen)
200{
201 u_char ourmac[SSH_DIGEST_MAX_LENGTH];
202 int r;
203
204 if (mac->mac_len > mlen)
205 return SSH_ERR_INVALID_ARGUMENT;
206 if ((r = mac_compute(mac, seqno, data, dlen,
207 ourmac, sizeof(ourmac))) != 0)
208 return r;
209 if (timingsafe_bcmp(ourmac, theirmac, mac->mac_len) != 0)
210 return SSH_ERR_MAC_INVALID;
211 return 0;
212}
213
214void
215mac_clear(struct sshmac *mac)
216{
217 if (mac->type == SSH_UMAC) {
218 if (mac->umac_ctx != NULL)
219 umac_delete(mac->umac_ctx);
220 } else if (mac->type == SSH_UMAC128) {
221 if (mac->umac_ctx != NULL)
222 umac128_delete(mac->umac_ctx);
223 } else if (mac->hmac_ctx != NULL)
224 ssh_hmac_free(mac->hmac_ctx);
225 mac->hmac_ctx = NULL;
226 mac->umac_ctx = NULL;
227}
228
229/* XXX copied from ciphers_valid */
230#define MAC_SEP ","
231int
232mac_valid(const char *names)
233{
234 char *maclist, *cp, *p;
235
236 if (names == NULL || strcmp(names, "") == 0)
237 return 0;
238 if ((maclist = cp = strdup(names)) == NULL)
239 return 0;
240 for ((p = strsep(&cp, MAC_SEP)); p && *p != '\0';
241 (p = strsep(&cp, MAC_SEP))) {
242 if (mac_setup(NULL, p) < 0) {
243 free(maclist);
244 return 0;
245 }
246 }
247 free(maclist);
248 return 1;
249}