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1 | /* $OpenBSD: ssh-rsa.c,v 1.39 2006/08/03 03:34:42 deraadt Exp $ */ | |
2 | /* | |
3 | * Copyright (c) 2000, 2003 Markus Friedl <markus@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 "includes.h" | |
19 | ||
20 | #include <sys/types.h> | |
21 | ||
22 | #include <openssl/evp.h> | |
23 | #include <openssl/err.h> | |
24 | ||
25 | #include <stdarg.h> | |
26 | #include <string.h> | |
27 | ||
28 | #include "xmalloc.h" | |
29 | #include "log.h" | |
30 | #include "buffer.h" | |
31 | #include "key.h" | |
32 | #include "compat.h" | |
33 | #include "ssh.h" | |
34 | ||
35 | static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *); | |
36 | ||
37 | /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */ | |
38 | int | |
39 | ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp, | |
40 | const u_char *data, u_int datalen) | |
41 | { | |
42 | const EVP_MD *evp_md; | |
43 | EVP_MD_CTX md; | |
44 | u_char digest[EVP_MAX_MD_SIZE], *sig; | |
45 | u_int slen, dlen, len; | |
46 | int ok, nid; | |
47 | Buffer b; | |
48 | ||
49 | if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) { | |
50 | error("ssh_rsa_sign: no RSA key"); | |
51 | return -1; | |
52 | } | |
53 | nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; | |
54 | if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { | |
55 | error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid); | |
56 | return -1; | |
57 | } | |
58 | EVP_DigestInit(&md, evp_md); | |
59 | EVP_DigestUpdate(&md, data, datalen); | |
60 | EVP_DigestFinal(&md, digest, &dlen); | |
61 | ||
62 | slen = RSA_size(key->rsa); | |
63 | sig = xmalloc(slen); | |
64 | ||
65 | ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa); | |
66 | memset(digest, 'd', sizeof(digest)); | |
67 | ||
68 | if (ok != 1) { | |
69 | int ecode = ERR_get_error(); | |
70 | ||
71 | error("ssh_rsa_sign: RSA_sign failed: %s", | |
72 | ERR_error_string(ecode, NULL)); | |
73 | xfree(sig); | |
74 | return -1; | |
75 | } | |
76 | if (len < slen) { | |
77 | u_int diff = slen - len; | |
78 | debug("slen %u > len %u", slen, len); | |
79 | memmove(sig + diff, sig, len); | |
80 | memset(sig, 0, diff); | |
81 | } else if (len > slen) { | |
82 | error("ssh_rsa_sign: slen %u slen2 %u", slen, len); | |
83 | xfree(sig); | |
84 | return -1; | |
85 | } | |
86 | /* encode signature */ | |
87 | buffer_init(&b); | |
88 | buffer_put_cstring(&b, "ssh-rsa"); | |
89 | buffer_put_string(&b, sig, slen); | |
90 | len = buffer_len(&b); | |
91 | if (lenp != NULL) | |
92 | *lenp = len; | |
93 | if (sigp != NULL) { | |
94 | *sigp = xmalloc(len); | |
95 | memcpy(*sigp, buffer_ptr(&b), len); | |
96 | } | |
97 | buffer_free(&b); | |
98 | memset(sig, 's', slen); | |
99 | xfree(sig); | |
100 | ||
101 | return 0; | |
102 | } | |
103 | ||
104 | int | |
105 | ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen, | |
106 | const u_char *data, u_int datalen) | |
107 | { | |
108 | Buffer b; | |
109 | const EVP_MD *evp_md; | |
110 | EVP_MD_CTX md; | |
111 | char *ktype; | |
112 | u_char digest[EVP_MAX_MD_SIZE], *sigblob; | |
113 | u_int len, dlen, modlen; | |
114 | int rlen, ret, nid; | |
115 | ||
116 | if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) { | |
117 | error("ssh_rsa_verify: no RSA key"); | |
118 | return -1; | |
119 | } | |
120 | if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { | |
121 | error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits", | |
122 | BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); | |
123 | return -1; | |
124 | } | |
125 | buffer_init(&b); | |
126 | buffer_append(&b, signature, signaturelen); | |
127 | ktype = buffer_get_string(&b, NULL); | |
128 | if (strcmp("ssh-rsa", ktype) != 0) { | |
129 | error("ssh_rsa_verify: cannot handle type %s", ktype); | |
130 | buffer_free(&b); | |
131 | xfree(ktype); | |
132 | return -1; | |
133 | } | |
134 | xfree(ktype); | |
135 | sigblob = buffer_get_string(&b, &len); | |
136 | rlen = buffer_len(&b); | |
137 | buffer_free(&b); | |
138 | if (rlen != 0) { | |
139 | error("ssh_rsa_verify: remaining bytes in signature %d", rlen); | |
140 | xfree(sigblob); | |
141 | return -1; | |
142 | } | |
143 | /* RSA_verify expects a signature of RSA_size */ | |
144 | modlen = RSA_size(key->rsa); | |
145 | if (len > modlen) { | |
146 | error("ssh_rsa_verify: len %u > modlen %u", len, modlen); | |
147 | xfree(sigblob); | |
148 | return -1; | |
149 | } else if (len < modlen) { | |
150 | u_int diff = modlen - len; | |
151 | debug("ssh_rsa_verify: add padding: modlen %u > len %u", | |
152 | modlen, len); | |
153 | sigblob = xrealloc(sigblob, 1, modlen); | |
154 | memmove(sigblob + diff, sigblob, len); | |
155 | memset(sigblob, 0, diff); | |
156 | len = modlen; | |
157 | } | |
158 | nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; | |
159 | if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { | |
160 | error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid); | |
161 | xfree(sigblob); | |
162 | return -1; | |
163 | } | |
164 | EVP_DigestInit(&md, evp_md); | |
165 | EVP_DigestUpdate(&md, data, datalen); | |
166 | EVP_DigestFinal(&md, digest, &dlen); | |
167 | ||
168 | ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa); | |
169 | memset(digest, 'd', sizeof(digest)); | |
170 | memset(sigblob, 's', len); | |
171 | xfree(sigblob); | |
172 | debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : ""); | |
173 | return ret; | |
174 | } | |
175 | ||
176 | /* | |
177 | * See: | |
178 | * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/ | |
179 | * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn | |
180 | */ | |
181 | /* | |
182 | * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) | |
183 | * oiw(14) secsig(3) algorithms(2) 26 } | |
184 | */ | |
185 | static const u_char id_sha1[] = { | |
186 | 0x30, 0x21, /* type Sequence, length 0x21 (33) */ | |
187 | 0x30, 0x09, /* type Sequence, length 0x09 */ | |
188 | 0x06, 0x05, /* type OID, length 0x05 */ | |
189 | 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */ | |
190 | 0x05, 0x00, /* NULL */ | |
191 | 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */ | |
192 | }; | |
193 | /* | |
194 | * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) | |
195 | * rsadsi(113549) digestAlgorithm(2) 5 } | |
196 | */ | |
197 | static const u_char id_md5[] = { | |
198 | 0x30, 0x20, /* type Sequence, length 0x20 (32) */ | |
199 | 0x30, 0x0c, /* type Sequence, length 0x09 */ | |
200 | 0x06, 0x08, /* type OID, length 0x05 */ | |
201 | 0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */ | |
202 | 0x05, 0x00, /* NULL */ | |
203 | 0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */ | |
204 | }; | |
205 | ||
206 | static int | |
207 | openssh_RSA_verify(int type, u_char *hash, u_int hashlen, | |
208 | u_char *sigbuf, u_int siglen, RSA *rsa) | |
209 | { | |
210 | u_int ret, rsasize, oidlen = 0, hlen = 0; | |
211 | int len; | |
212 | const u_char *oid = NULL; | |
213 | u_char *decrypted = NULL; | |
214 | ||
215 | ret = 0; | |
216 | switch (type) { | |
217 | case NID_sha1: | |
218 | oid = id_sha1; | |
219 | oidlen = sizeof(id_sha1); | |
220 | hlen = 20; | |
221 | break; | |
222 | case NID_md5: | |
223 | oid = id_md5; | |
224 | oidlen = sizeof(id_md5); | |
225 | hlen = 16; | |
226 | break; | |
227 | default: | |
228 | goto done; | |
229 | } | |
230 | if (hashlen != hlen) { | |
231 | error("bad hashlen"); | |
232 | goto done; | |
233 | } | |
234 | rsasize = RSA_size(rsa); | |
235 | if (siglen == 0 || siglen > rsasize) { | |
236 | error("bad siglen"); | |
237 | goto done; | |
238 | } | |
239 | decrypted = xmalloc(rsasize); | |
240 | if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa, | |
241 | RSA_PKCS1_PADDING)) < 0) { | |
242 | error("RSA_public_decrypt failed: %s", | |
243 | ERR_error_string(ERR_get_error(), NULL)); | |
244 | goto done; | |
245 | } | |
246 | if (len < 0 || (u_int)len != hlen + oidlen) { | |
247 | error("bad decrypted len: %d != %d + %d", len, hlen, oidlen); | |
248 | goto done; | |
249 | } | |
250 | if (memcmp(decrypted, oid, oidlen) != 0) { | |
251 | error("oid mismatch"); | |
252 | goto done; | |
253 | } | |
254 | if (memcmp(decrypted + oidlen, hash, hlen) != 0) { | |
255 | error("hash mismatch"); | |
256 | goto done; | |
257 | } | |
258 | ret = 1; | |
259 | done: | |
260 | if (decrypted) | |
261 | xfree(decrypted); | |
262 | return ret; | |
263 | } |