]>
Commit | Line | Data |
---|---|---|
8efc0c15 | 1 | /* |
5260325f | 2 | * Author: Tatu Ylonen <ylo@cs.hut.fi> |
5260325f | 3 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
4 | * All rights reserved | |
5260325f | 5 | * RSA-based authentication. This code determines whether to admit a login |
6 | * based on RSA authentication. This file also contains functions to check | |
7 | * validity of the host key. | |
6ae2364d | 8 | * |
bcbf86ec | 9 | * As far as I am concerned, the code I have written for this software |
10 | * can be used freely for any purpose. Any derived versions of this | |
11 | * software must be clearly marked as such, and if the derived work is | |
12 | * incompatible with the protocol description in the RFC file, it must be | |
13 | * called by a name other than "ssh" or "Secure Shell". | |
5260325f | 14 | */ |
8efc0c15 | 15 | |
16 | #include "includes.h" | |
4095f623 | 17 | |
18 | #include <sys/types.h> | |
19 | #include <sys/stat.h> | |
42f11eb2 | 20 | |
21 | #include <openssl/rsa.h> | |
22 | #include <openssl/md5.h> | |
8efc0c15 | 23 | |
24 | #include "rsa.h" | |
25 | #include "packet.h" | |
26 | #include "xmalloc.h" | |
42f11eb2 | 27 | #include "ssh1.h" |
8efc0c15 | 28 | #include "uidswap.h" |
4fe2af09 | 29 | #include "match.h" |
38c295d6 | 30 | #include "auth-options.h" |
42f11eb2 | 31 | #include "pathnames.h" |
32 | #include "log.h" | |
33 | #include "servconf.h" | |
34 | #include "auth.h" | |
46df736f | 35 | #include "hostfile.h" |
1853d1ef | 36 | #include "monitor_wrap.h" |
82b00264 | 37 | #include "ssh.h" |
41feb690 | 38 | #include "misc.h" |
94ec8c6b | 39 | |
40 | /* import */ | |
41 | extern ServerOptions options; | |
42 | ||
aa3378df | 43 | /* |
44 | * Session identifier that is used to bind key exchange and authentication | |
45 | * responses to a particular session. | |
46 | */ | |
1e3b8b07 | 47 | extern u_char session_id[16]; |
8efc0c15 | 48 | |
aa3378df | 49 | /* |
50 | * The .ssh/authorized_keys file contains public keys, one per line, in the | |
51 | * following format: | |
52 | * options bits e n comment | |
53 | * where bits, e and n are decimal numbers, | |
54 | * and comment is any string of characters up to newline. The maximum | |
ea067773 | 55 | * length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a |
aa3378df | 56 | * description of the options. |
57 | */ | |
8efc0c15 | 58 | |
1853d1ef | 59 | BIGNUM * |
46f1eece | 60 | auth_rsa_generate_challenge(Key *key) |
61 | { | |
62 | BIGNUM *challenge; | |
63 | BN_CTX *ctx; | |
64 | ||
65 | if ((challenge = BN_new()) == NULL) | |
66 | fatal("auth_rsa_generate_challenge: BN_new() failed"); | |
67 | /* Generate a random challenge. */ | |
68 | BN_rand(challenge, 256, 0, 0); | |
69 | if ((ctx = BN_CTX_new()) == NULL) | |
70 | fatal("auth_rsa_generate_challenge: BN_CTX_new() failed"); | |
71 | BN_mod(challenge, challenge, key->rsa->n, ctx); | |
72 | BN_CTX_free(ctx); | |
73 | ||
74 | return challenge; | |
75 | } | |
76 | ||
1853d1ef | 77 | int |
46f1eece | 78 | auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16]) |
79 | { | |
80 | u_char buf[32], mdbuf[16]; | |
81 | MD5_CTX md; | |
82 | int len; | |
83 | ||
52103b10 | 84 | /* don't allow short keys */ |
82b00264 | 85 | if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { |
b7ced7d1 | 86 | error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits", |
87 | BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); | |
52103b10 | 88 | return (0); |
89 | } | |
90 | ||
46f1eece | 91 | /* The response is MD5 of decrypted challenge plus session id. */ |
92 | len = BN_num_bytes(challenge); | |
93 | if (len <= 0 || len > 32) | |
94 | fatal("auth_rsa_verify_response: bad challenge length %d", len); | |
95 | memset(buf, 0, 32); | |
96 | BN_bn2bin(challenge, buf + 32 - len); | |
97 | MD5_Init(&md); | |
98 | MD5_Update(&md, buf, 32); | |
99 | MD5_Update(&md, session_id, 16); | |
100 | MD5_Final(mdbuf, &md); | |
101 | ||
102 | /* Verify that the response is the original challenge. */ | |
103 | if (memcmp(response, mdbuf, 16) != 0) { | |
104 | /* Wrong answer. */ | |
105 | return (0); | |
106 | } | |
107 | /* Correct answer. */ | |
108 | return (1); | |
109 | } | |
110 | ||
aa3378df | 111 | /* |
112 | * Performs the RSA authentication challenge-response dialog with the client, | |
113 | * and returns true (non-zero) if the client gave the correct answer to | |
114 | * our challenge; returns zero if the client gives a wrong answer. | |
115 | */ | |
8efc0c15 | 116 | |
117 | int | |
46f1eece | 118 | auth_rsa_challenge_dialog(Key *key) |
8efc0c15 | 119 | { |
c8d54615 | 120 | BIGNUM *challenge, *encrypted_challenge; |
46f1eece | 121 | u_char response[16]; |
122 | int i, success; | |
5260325f | 123 | |
b775c6f2 | 124 | if ((encrypted_challenge = BN_new()) == NULL) |
125 | fatal("auth_rsa_challenge_dialog: BN_new() failed"); | |
5260325f | 126 | |
1853d1ef | 127 | challenge = PRIVSEP(auth_rsa_generate_challenge(key)); |
5260325f | 128 | |
5260325f | 129 | /* Encrypt the challenge with the public key. */ |
46f1eece | 130 | rsa_public_encrypt(encrypted_challenge, challenge, key->rsa); |
5260325f | 131 | |
132 | /* Send the encrypted challenge to the client. */ | |
133 | packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); | |
134 | packet_put_bignum(encrypted_challenge); | |
135 | packet_send(); | |
c8d54615 | 136 | BN_clear_free(encrypted_challenge); |
5260325f | 137 | packet_write_wait(); |
138 | ||
c8d54615 | 139 | /* Wait for a response. */ |
54a5250f | 140 | packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE); |
c8d54615 | 141 | for (i = 0; i < 16; i++) |
142 | response[i] = packet_get_char(); | |
95500969 | 143 | packet_check_eom(); |
c8d54615 | 144 | |
1853d1ef | 145 | success = PRIVSEP(auth_rsa_verify_response(key, challenge, response)); |
5260325f | 146 | BN_clear_free(challenge); |
46f1eece | 147 | return (success); |
8efc0c15 | 148 | } |
149 | ||
aa3378df | 150 | /* |
46f1eece | 151 | * check if there's user key matching client_n, |
152 | * return key if login is allowed, NULL otherwise | |
aa3378df | 153 | */ |
8efc0c15 | 154 | |
1853d1ef | 155 | int |
46f1eece | 156 | auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey) |
8efc0c15 | 157 | { |
ea067773 | 158 | char line[SSH_MAX_PUBKEY_BYTES], *file; |
1853d1ef | 159 | int allowed = 0; |
1e3b8b07 | 160 | u_int bits; |
5260325f | 161 | FILE *f; |
1e3b8b07 | 162 | u_long linenum = 0; |
5260325f | 163 | struct stat st; |
46df736f | 164 | Key *key; |
94ec8c6b | 165 | |
5260325f | 166 | /* Temporarily use the user's uid. */ |
63bd8c36 | 167 | temporarily_use_uid(pw); |
5260325f | 168 | |
169 | /* The authorized keys. */ | |
c8445989 | 170 | file = authorized_keys_file(pw); |
171 | debug("trying public RSA key file %s", file); | |
5260325f | 172 | |
173 | /* Fail quietly if file does not exist */ | |
174 | if (stat(file, &st) < 0) { | |
175 | /* Restore the privileged uid. */ | |
176 | restore_uid(); | |
c8445989 | 177 | xfree(file); |
159897f3 | 178 | return (0); |
8efc0c15 | 179 | } |
5260325f | 180 | /* Open the file containing the authorized keys. */ |
181 | f = fopen(file, "r"); | |
182 | if (!f) { | |
183 | /* Restore the privileged uid. */ | |
184 | restore_uid(); | |
c8445989 | 185 | xfree(file); |
159897f3 | 186 | return (0); |
8efc0c15 | 187 | } |
c8445989 | 188 | if (options.strict_modes && |
6978866a | 189 | secure_filename(f, file, pw, line, sizeof(line)) != 0) { |
c8445989 | 190 | xfree(file); |
191 | fclose(f); | |
bbe88b6d | 192 | logit("Authentication refused: %s", line); |
c8445989 | 193 | restore_uid(); |
159897f3 | 194 | return (0); |
5260325f | 195 | } |
46f1eece | 196 | |
197 | /* Flag indicating whether the key is allowed. */ | |
198 | allowed = 0; | |
5260325f | 199 | |
46df736f | 200 | key = key_new(KEY_RSA1); |
5260325f | 201 | |
aa3378df | 202 | /* |
203 | * Go though the accepted keys, looking for the current key. If | |
204 | * found, perform a challenge-response dialog to verify that the | |
205 | * user really has the corresponding private key. | |
206 | */ | |
ea067773 | 207 | while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { |
5260325f | 208 | char *cp; |
ca75d7de | 209 | char *key_options; |
2ceb8101 | 210 | int keybits; |
5260325f | 211 | |
aa3378df | 212 | /* Skip leading whitespace, empty and comment lines. */ |
213 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) | |
214 | ; | |
5260325f | 215 | if (!*cp || *cp == '\n' || *cp == '#') |
216 | continue; | |
217 | ||
aa3378df | 218 | /* |
219 | * Check if there are options for this key, and if so, | |
220 | * save their starting address and skip the option part | |
221 | * for now. If there are no options, set the starting | |
222 | * address to NULL. | |
223 | */ | |
5260325f | 224 | if (*cp < '0' || *cp > '9') { |
225 | int quoted = 0; | |
ca75d7de | 226 | key_options = cp; |
5260325f | 227 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { |
228 | if (*cp == '\\' && cp[1] == '"') | |
229 | cp++; /* Skip both */ | |
230 | else if (*cp == '"') | |
231 | quoted = !quoted; | |
8efc0c15 | 232 | } |
5260325f | 233 | } else |
ca75d7de | 234 | key_options = NULL; |
5260325f | 235 | |
236 | /* Parse the key from the line. */ | |
46df736f | 237 | if (hostfile_read_key(&cp, &bits, key) == 0) { |
96a7b0cc | 238 | debug("%.100s, line %lu: non ssh1 key syntax", |
42f11eb2 | 239 | file, linenum); |
5260325f | 240 | continue; |
8efc0c15 | 241 | } |
5260325f | 242 | /* cp now points to the comment part. */ |
243 | ||
5260325f | 244 | /* Check if the we have found the desired key (identified by its modulus). */ |
46df736f | 245 | if (BN_cmp(key->rsa->n, client_n) != 0) |
aa3378df | 246 | continue; |
5260325f | 247 | |
57112b5a | 248 | /* check the real bits */ |
2ceb8101 | 249 | keybits = BN_num_bits(key->rsa->n); |
250 | if (keybits < 0 || bits != (u_int)keybits) | |
bbe88b6d | 251 | logit("Warning: %s, line %lu: keysize mismatch: " |
57112b5a | 252 | "actual %d vs. announced %d.", |
46df736f | 253 | file, linenum, BN_num_bits(key->rsa->n), bits); |
57112b5a | 254 | |
5260325f | 255 | /* We have found the desired key. */ |
d343d900 | 256 | /* |
257 | * If our options do not allow this key to be used, | |
258 | * do not send challenge. | |
259 | */ | |
ca75d7de | 260 | if (!auth_parse_options(pw, key_options, file, linenum)) |
d343d900 | 261 | continue; |
5260325f | 262 | |
46f1eece | 263 | /* break out, this key is allowed */ |
264 | allowed = 1; | |
33de75a3 | 265 | break; |
8efc0c15 | 266 | } |
267 | ||
5260325f | 268 | /* Restore the privileged uid. */ |
269 | restore_uid(); | |
8efc0c15 | 270 | |
5260325f | 271 | /* Close the file. */ |
c8445989 | 272 | xfree(file); |
5260325f | 273 | fclose(f); |
8efc0c15 | 274 | |
46f1eece | 275 | /* return key if allowed */ |
276 | if (allowed && rkey != NULL) | |
277 | *rkey = key; | |
94ec8c6b | 278 | else |
46f1eece | 279 | key_free(key); |
280 | return (allowed); | |
281 | } | |
282 | ||
283 | /* | |
284 | * Performs the RSA authentication dialog with the client. This returns | |
285 | * 0 if the client could not be authenticated, and 1 if authentication was | |
286 | * successful. This may exit if there is a serious protocol violation. | |
287 | */ | |
288 | int | |
fdaef11e | 289 | auth_rsa(Authctxt *authctxt, BIGNUM *client_n) |
46f1eece | 290 | { |
291 | Key *key; | |
292 | char *fp; | |
fdaef11e | 293 | struct passwd *pw = authctxt->pw; |
46f1eece | 294 | |
295 | /* no user given */ | |
fdaef11e | 296 | if (!authctxt->valid) |
46f1eece | 297 | return 0; |
298 | ||
1853d1ef | 299 | if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) { |
94ec8c6b | 300 | auth_clear_options(); |
46f1eece | 301 | return (0); |
302 | } | |
303 | ||
304 | /* Perform the challenge-response dialog for this key. */ | |
305 | if (!auth_rsa_challenge_dialog(key)) { | |
306 | /* Wrong response. */ | |
307 | verbose("Wrong response to RSA authentication challenge."); | |
308 | packet_send_debug("Wrong response to RSA authentication challenge."); | |
309 | /* | |
310 | * Break out of the loop. Otherwise we might send | |
311 | * another challenge and break the protocol. | |
312 | */ | |
313 | key_free(key); | |
314 | return (0); | |
315 | } | |
316 | /* | |
317 | * Correct response. The client has been successfully | |
318 | * authenticated. Note that we have not yet processed the | |
319 | * options; this will be reset if the options cause the | |
320 | * authentication to be rejected. | |
321 | */ | |
322 | fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); | |
323 | verbose("Found matching %s key: %s", | |
324 | key_type(key), fp); | |
325 | xfree(fp); | |
326 | key_free(key); | |
8efc0c15 | 327 | |
46f1eece | 328 | packet_send_debug("RSA authentication accepted."); |
329 | return (1); | |
8efc0c15 | 330 | } |