diff options
author | Damien Miller <djm@mindrot.org> | 2003-05-15 10:19:46 +1000 |
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committer | Damien Miller <djm@mindrot.org> | 2003-05-15 10:19:46 +1000 |
commit | 37876e913a069036501086a247ed2ea430cea206 (patch) | |
tree | 8294744f47011c82b63ec0b46f4449ff4f26ec7c /dns.c | |
parent | abbae980e7532da68e7f6aa1da716fb69e7521ad (diff) |
- jakob@cvs.openbsd.org 2003/05/14 18:16:20
[key.c key.h readconf.c readconf.h ssh_config.5 sshconnect.c]
[dns.c dns.h README.dns ssh-keygen.1 ssh-keygen.c]
add experimental support for verifying hos keys using DNS as described
in draft-ietf-secsh-dns-xx.txt. more information in README.dns.
ok markus@ and henning@
Diffstat (limited to 'dns.c')
-rw-r--r-- | dns.c | 293 |
1 files changed, 293 insertions, 0 deletions
@@ -0,0 +1,293 @@ | |||
1 | /* $OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob Exp $ */ | ||
2 | |||
3 | /* | ||
4 | * Copyright (c) 2003 Wesley Griffin. All rights reserved. | ||
5 | * Copyright (c) 2003 Jakob Schlyter. 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 | |||
29 | #include "includes.h" | ||
30 | |||
31 | #ifdef DNS | ||
32 | #include <openssl/bn.h> | ||
33 | #ifdef LWRES | ||
34 | #include <lwres/netdb.h> | ||
35 | #include <dns/result.h> | ||
36 | #else /* LWRES */ | ||
37 | #include <netdb.h> | ||
38 | #endif /* LWRES */ | ||
39 | |||
40 | #include "xmalloc.h" | ||
41 | #include "key.h" | ||
42 | #include "dns.h" | ||
43 | #include "log.h" | ||
44 | #include "uuencode.h" | ||
45 | |||
46 | extern char *__progname; | ||
47 | RCSID("$OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob Exp $"); | ||
48 | |||
49 | #ifndef LWRES | ||
50 | static const char *errset_text[] = { | ||
51 | "success", /* 0 ERRSET_SUCCESS */ | ||
52 | "out of memory", /* 1 ERRSET_NOMEMORY */ | ||
53 | "general failure", /* 2 ERRSET_FAIL */ | ||
54 | "invalid parameter", /* 3 ERRSET_INVAL */ | ||
55 | "name does not exist", /* 4 ERRSET_NONAME */ | ||
56 | "data does not exist", /* 5 ERRSET_NODATA */ | ||
57 | }; | ||
58 | |||
59 | static const char * | ||
60 | dns_result_totext(unsigned int error) | ||
61 | { | ||
62 | switch (error) { | ||
63 | case ERRSET_SUCCESS: | ||
64 | return errset_text[ERRSET_SUCCESS]; | ||
65 | case ERRSET_NOMEMORY: | ||
66 | return errset_text[ERRSET_NOMEMORY]; | ||
67 | case ERRSET_FAIL: | ||
68 | return errset_text[ERRSET_FAIL]; | ||
69 | case ERRSET_INVAL: | ||
70 | return errset_text[ERRSET_INVAL]; | ||
71 | case ERRSET_NONAME: | ||
72 | return errset_text[ERRSET_NONAME]; | ||
73 | case ERRSET_NODATA: | ||
74 | return errset_text[ERRSET_NODATA]; | ||
75 | default: | ||
76 | return "unknown error"; | ||
77 | } | ||
78 | } | ||
79 | #endif /* LWRES */ | ||
80 | |||
81 | |||
82 | /* | ||
83 | * Read SSHFP parameters from key buffer. | ||
84 | */ | ||
85 | static int | ||
86 | dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, | ||
87 | u_char **digest, u_int *digest_len, Key *key) | ||
88 | { | ||
89 | int success = 0; | ||
90 | |||
91 | switch (key->type) { | ||
92 | case KEY_RSA: | ||
93 | *algorithm = SSHFP_KEY_RSA; | ||
94 | break; | ||
95 | case KEY_DSA: | ||
96 | *algorithm = SSHFP_KEY_DSA; | ||
97 | break; | ||
98 | default: | ||
99 | *algorithm = SSHFP_KEY_RESERVED; | ||
100 | } | ||
101 | |||
102 | if (*algorithm) { | ||
103 | *digest_type = SSHFP_HASH_SHA1; | ||
104 | *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); | ||
105 | success = 1; | ||
106 | } else { | ||
107 | *digest_type = SSHFP_HASH_RESERVED; | ||
108 | *digest = NULL; | ||
109 | *digest_len = 0; | ||
110 | success = 0; | ||
111 | } | ||
112 | |||
113 | return success; | ||
114 | } | ||
115 | |||
116 | /* | ||
117 | * Read SSHFP parameters from rdata buffer. | ||
118 | */ | ||
119 | static int | ||
120 | dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, | ||
121 | u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) | ||
122 | { | ||
123 | int success = 0; | ||
124 | |||
125 | *algorithm = SSHFP_KEY_RESERVED; | ||
126 | *digest_type = SSHFP_HASH_RESERVED; | ||
127 | |||
128 | if (rdata_len >= 2) { | ||
129 | *algorithm = rdata[0]; | ||
130 | *digest_type = rdata[1]; | ||
131 | *digest_len = rdata_len - 2; | ||
132 | |||
133 | if (*digest_len > 0) { | ||
134 | *digest = (u_char *) xmalloc(*digest_len); | ||
135 | memcpy(*digest, rdata + 2, *digest_len); | ||
136 | } else { | ||
137 | *digest = NULL; | ||
138 | } | ||
139 | |||
140 | success = 1; | ||
141 | } | ||
142 | |||
143 | return success; | ||
144 | } | ||
145 | |||
146 | |||
147 | /* | ||
148 | * Verify the given hostname, address and host key using DNS. | ||
149 | * Returns 0 if key verifies or -1 if key does NOT verify | ||
150 | */ | ||
151 | int | ||
152 | verify_host_key_dns(const char *hostname, struct sockaddr *address, | ||
153 | Key *hostkey) | ||
154 | { | ||
155 | int counter; | ||
156 | int result; | ||
157 | struct rrsetinfo *fingerprints = NULL; | ||
158 | int failures = 0; | ||
159 | |||
160 | u_int8_t hostkey_algorithm; | ||
161 | u_int8_t hostkey_digest_type; | ||
162 | u_char *hostkey_digest; | ||
163 | u_int hostkey_digest_len; | ||
164 | |||
165 | u_int8_t dnskey_algorithm; | ||
166 | u_int8_t dnskey_digest_type; | ||
167 | u_char *dnskey_digest; | ||
168 | u_int dnskey_digest_len; | ||
169 | |||
170 | |||
171 | debug3("verify_hostkey_dns"); | ||
172 | if (hostkey == NULL) | ||
173 | fatal("No key to look up!"); | ||
174 | |||
175 | result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, | ||
176 | DNS_RDATATYPE_SSHFP, 0, &fingerprints); | ||
177 | if (result) { | ||
178 | verbose("DNS lookup error: %s", dns_result_totext(result)); | ||
179 | return DNS_VERIFY_ERROR; | ||
180 | } | ||
181 | |||
182 | #ifdef DNSSEC | ||
183 | /* Only accept validated answers */ | ||
184 | if (!fingerprints->rri_flags & RRSET_VALIDATED) { | ||
185 | error("Ignored unvalidated fingerprint from DNS."); | ||
186 | return DNS_VERIFY_ERROR; | ||
187 | } | ||
188 | #endif | ||
189 | |||
190 | debug("found %d fingerprints in DNS", fingerprints->rri_nrdatas); | ||
191 | |||
192 | /* Initialize host key parameters */ | ||
193 | if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, | ||
194 | &hostkey_digest, &hostkey_digest_len, hostkey)) { | ||
195 | error("Error calculating host key fingerprint."); | ||
196 | return DNS_VERIFY_ERROR; | ||
197 | } | ||
198 | |||
199 | for (counter = 0 ; counter < fingerprints->rri_nrdatas ; counter++) { | ||
200 | /* | ||
201 | * Extract the key from the answer. Ignore any badly | ||
202 | * formatted fingerprints. | ||
203 | */ | ||
204 | if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, | ||
205 | &dnskey_digest, &dnskey_digest_len, | ||
206 | fingerprints->rri_rdatas[counter].rdi_data, | ||
207 | fingerprints->rri_rdatas[counter].rdi_length)) { | ||
208 | verbose("Error parsing fingerprint from DNS."); | ||
209 | continue; | ||
210 | } | ||
211 | |||
212 | /* Check if the current key is the same as the given key */ | ||
213 | if (hostkey_algorithm == dnskey_algorithm && | ||
214 | hostkey_digest_type == dnskey_digest_type) { | ||
215 | |||
216 | if (hostkey_digest_len == dnskey_digest_len && | ||
217 | memcmp(hostkey_digest, dnskey_digest, | ||
218 | hostkey_digest_len) == 0) { | ||
219 | |||
220 | /* Matching algoritm and digest. */ | ||
221 | freerrset(fingerprints); | ||
222 | #ifdef DNSSEC | ||
223 | debug("matching host key fingerprint found in DNS"); | ||
224 | return DNS_VERIFY_OK; | ||
225 | #else | ||
226 | logit("Matching host key fingerprint found in DNS."); | ||
227 | return DNS_VERIFY_ERROR; | ||
228 | #endif | ||
229 | } else { | ||
230 | /* Correct algorithm but bad digest */ | ||
231 | debug("verify_hostkey_dns: failed"); | ||
232 | failures++; | ||
233 | } | ||
234 | } | ||
235 | } | ||
236 | |||
237 | freerrset(fingerprints); | ||
238 | |||
239 | if (failures) { | ||
240 | error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); | ||
241 | error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @"); | ||
242 | error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); | ||
243 | error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!"); | ||
244 | error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!"); | ||
245 | error("It is also possible that the %s host key has just been changed.", | ||
246 | key_type(hostkey)); | ||
247 | error("Please contact your system administrator."); | ||
248 | return DNS_VERIFY_FAILED; | ||
249 | } | ||
250 | |||
251 | debug("fingerprints found in DNS, but none of them matched"); | ||
252 | |||
253 | return DNS_VERIFY_ERROR; | ||
254 | } | ||
255 | |||
256 | |||
257 | /* | ||
258 | * Export the fingerprint of a key as a DNS resource record | ||
259 | */ | ||
260 | int | ||
261 | export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) | ||
262 | { | ||
263 | u_int8_t rdata_pubkey_algorithm = 0; | ||
264 | u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; | ||
265 | u_char *rdata_digest; | ||
266 | u_int rdata_digest_len; | ||
267 | |||
268 | int i; | ||
269 | int success = 0; | ||
270 | |||
271 | if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, | ||
272 | &rdata_digest, &rdata_digest_len, key)) { | ||
273 | |||
274 | if (generic) | ||
275 | fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, | ||
276 | DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, | ||
277 | rdata_pubkey_algorithm, rdata_digest_type); | ||
278 | else | ||
279 | fprintf(f, "%s IN SSHFP %d %d ", hostname, | ||
280 | rdata_pubkey_algorithm, rdata_digest_type); | ||
281 | |||
282 | for (i = 0; i < rdata_digest_len; i++) | ||
283 | fprintf(f, "%02x", rdata_digest[i]); | ||
284 | fprintf(f, "\n"); | ||
285 | success = 1; | ||
286 | } else { | ||
287 | error("dns_export_rr: unsupported algorithm"); | ||
288 | } | ||
289 | |||
290 | return success; | ||
291 | } | ||
292 | |||
293 | #endif /* DNS */ | ||