1 /* $OpenBSD: ssh-ecdsa-sk.c,v 1.5 2019/11/26 03:04:27 djm Exp $ */
2 /*
3 * Copyright (c) 2000 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
5 * Copyright (c) 2019 Google Inc. 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 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 /* #define DEBUG_SK 1 */
29
30 #include "includes.h"
31
32 #include <sys/types.h>
33
34 #ifdef WITH_OPENSSL
35 #include <openssl/bn.h>
36 #include <openssl/ec.h>
37 #include <openssl/ecdsa.h>
38 #include <openssl/evp.h>
39 #endif
40
41 #include <string.h>
42 #include <stdio.h> /* needed for DEBUG_SK only */
43
44 #include "openbsd-compat/openssl-compat.h"
45
46 #include "sshbuf.h"
47 #include "ssherr.h"
48 #include "digest.h"
49 #define SSHKEY_INTERNAL
50 #include "sshkey.h"
51
52 /* ARGSUSED */
53 int
ssh_ecdsa_sk_verify(const struct sshkey * key,const u_char * signature,size_t signaturelen,const u_char * data,size_t datalen,u_int compat,struct sshkey_sig_details ** detailsp)54 ssh_ecdsa_sk_verify(const struct sshkey *key,
55 const u_char *signature, size_t signaturelen,
56 const u_char *data, size_t datalen, u_int compat,
57 struct sshkey_sig_details **detailsp)
58 {
59 #ifdef OPENSSL_HAS_ECC
60 ECDSA_SIG *sig = NULL;
61 BIGNUM *sig_r = NULL, *sig_s = NULL;
62 u_char sig_flags;
63 u_char msghash[32], apphash[32], sighash[32];
64 u_int sig_counter;
65 int ret = SSH_ERR_INTERNAL_ERROR;
66 struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
67 char *ktype = NULL;
68 struct sshkey_sig_details *details = NULL;
69 #ifdef DEBUG_SK
70 char *tmp = NULL;
71 #endif
72
73 if (detailsp != NULL)
74 *detailsp = NULL;
75 if (key == NULL || key->ecdsa == NULL ||
76 sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
77 signature == NULL || signaturelen == 0)
78 return SSH_ERR_INVALID_ARGUMENT;
79
80 if (key->ecdsa_nid != NID_X9_62_prime256v1)
81 return SSH_ERR_INTERNAL_ERROR;
82
83 /* fetch signature */
84 if ((b = sshbuf_from(signature, signaturelen)) == NULL)
85 return SSH_ERR_ALLOC_FAIL;
86 if (sshbuf_get_cstring(b, &ktype, NULL) != 0 ||
87 sshbuf_froms(b, &sigbuf) != 0 ||
88 sshbuf_get_u8(b, &sig_flags) != 0 ||
89 sshbuf_get_u32(b, &sig_counter) != 0) {
90 ret = SSH_ERR_INVALID_FORMAT;
91 goto out;
92 }
93 if (strcmp(sshkey_ssh_name_plain(key), ktype) != 0) {
94 ret = SSH_ERR_KEY_TYPE_MISMATCH;
95 goto out;
96 }
97 if (sshbuf_len(b) != 0) {
98 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
99 goto out;
100 }
101
102 /* parse signature */
103 if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
104 sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
105 ret = SSH_ERR_INVALID_FORMAT;
106 goto out;
107 }
108 if ((sig = ECDSA_SIG_new()) == NULL) {
109 ret = SSH_ERR_ALLOC_FAIL;
110 goto out;
111 }
112 if (!ECDSA_SIG_set0(sig, sig_r, sig_s)) {
113 ret = SSH_ERR_LIBCRYPTO_ERROR;
114 goto out;
115 }
116 #ifdef DEBUG_SK
117 fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
118 /* sshbuf_dump_data(data, datalen, stderr); */
119 fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
120 free(tmp);
121 fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
122 free(tmp);
123 fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
124 __func__, sig_flags, sig_counter);
125 #endif
126 sig_r = sig_s = NULL; /* transferred */
127
128 if (sshbuf_len(sigbuf) != 0) {
129 ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
130 goto out;
131 }
132
133 /* Reconstruct data that was supposedly signed */
134 if ((original_signed = sshbuf_new()) == NULL) {
135 ret = SSH_ERR_ALLOC_FAIL;
136 goto out;
137 }
138 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, datalen,
139 msghash, sizeof(msghash))) != 0)
140 goto out;
141 /* Application value is hashed before signature */
142 if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
143 strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
144 goto out;
145 #ifdef DEBUG_SK
146 fprintf(stderr, "%s: hashed application:\n", __func__);
147 sshbuf_dump_data(apphash, sizeof(apphash), stderr);
148 fprintf(stderr, "%s: hashed message:\n", __func__);
149 sshbuf_dump_data(msghash, sizeof(msghash), stderr);
150 #endif
151 if ((ret = sshbuf_put(original_signed,
152 apphash, sizeof(apphash))) != 0 ||
153 (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
154 (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
155 (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
156 goto out;
157 /* Signature is over H(original_signed) */
158 if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
159 sighash, sizeof(sighash))) != 0)
160 goto out;
161 if ((details = calloc(1, sizeof(*details))) == NULL) {
162 ret = SSH_ERR_ALLOC_FAIL;
163 goto out;
164 }
165 details->sk_counter = sig_counter;
166 details->sk_flags = sig_flags;
167 #ifdef DEBUG_SK
168 fprintf(stderr, "%s: signed buf:\n", __func__);
169 sshbuf_dump(original_signed, stderr);
170 fprintf(stderr, "%s: signed hash:\n", __func__);
171 sshbuf_dump_data(sighash, sizeof(sighash), stderr);
172 #endif
173
174 /* Verify it */
175 switch (ECDSA_do_verify(sighash, sizeof(sighash), sig, key->ecdsa)) {
176 case 1:
177 ret = 0;
178 break;
179 case 0:
180 ret = SSH_ERR_SIGNATURE_INVALID;
181 goto out;
182 default:
183 ret = SSH_ERR_LIBCRYPTO_ERROR;
184 goto out;
185 }
186 /* success */
187 if (detailsp != NULL) {
188 *detailsp = details;
189 details = NULL;
190 }
191 out:
192 explicit_bzero(&sig_flags, sizeof(sig_flags));
193 explicit_bzero(&sig_counter, sizeof(sig_counter));
194 explicit_bzero(msghash, sizeof(msghash));
195 explicit_bzero(sighash, sizeof(msghash));
196 explicit_bzero(apphash, sizeof(apphash));
197 sshkey_sig_details_free(details);
198 sshbuf_free(original_signed);
199 sshbuf_free(sigbuf);
200 sshbuf_free(b);
201 ECDSA_SIG_free(sig);
202 BN_clear_free(sig_r);
203 BN_clear_free(sig_s);
204 free(ktype);
205 return ret;
206 #else
207 return SSH_ERR_INTERNAL_ERROR;
208 #endif
209 }
210