5 * Author: Tatu Ylonen <ylo@cs.hut.fi>
7 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
10 * Created: Mon Mar 27 01:46:52 1995 ylo
12 * RSA-based authentication. This code determines whether to admit a login
13 * based on RSA authentication. This file also contains functions to check
14 * validity of the host key.
30 #include <openssl/rsa.h>
31 #include <openssl/md5.h>
33 /* Flags that may be set in authorized_keys options. */
34 extern int no_port_forwarding_flag;
35 extern int no_agent_forwarding_flag;
36 extern int no_x11_forwarding_flag;
37 extern int no_pty_flag;
38 extern char *forced_command;
39 extern struct envstring *custom_environment;
42 * Session identifier that is used to bind key exchange and authentication
43 * responses to a particular session.
45 extern unsigned char session_id[16];
48 * The .ssh/authorized_keys file contains public keys, one per line, in the
50 * options bits e n comment
51 * where bits, e and n are decimal numbers,
52 * and comment is any string of characters up to newline. The maximum
53 * length of a line is 8000 characters. See the documentation for a
54 * description of the options.
58 * Performs the RSA authentication challenge-response dialog with the client,
59 * and returns true (non-zero) if the client gave the correct answer to
60 * our challenge; returns zero if the client gives a wrong answer.
64 auth_rsa_challenge_dialog(RSA *pk)
66 BIGNUM *challenge, *encrypted_challenge;
68 unsigned char buf[32], mdbuf[16], response[16];
73 encrypted_challenge = BN_new();
76 /* Generate a random challenge. */
77 BN_rand(challenge, 256, 0, 0);
79 BN_mod(challenge, challenge, pk->n, ctx);
82 /* Encrypt the challenge with the public key. */
83 rsa_public_encrypt(encrypted_challenge, challenge, pk);
85 /* Send the encrypted challenge to the client. */
86 packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
87 packet_put_bignum(encrypted_challenge);
89 BN_clear_free(encrypted_challenge);
92 /* Wait for a response. */
93 packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
94 packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
95 for (i = 0; i < 16; i++)
96 response[i] = packet_get_char();
98 /* The response is MD5 of decrypted challenge plus session id. */
99 len = BN_num_bytes(challenge);
100 if (len <= 0 || len > 32)
101 fatal("auth_rsa_challenge_dialog: bad challenge length %d", len);
103 BN_bn2bin(challenge, buf + 32 - len);
105 MD5_Update(&md, buf, 32);
106 MD5_Update(&md, session_id, 16);
107 MD5_Final(mdbuf, &md);
108 BN_clear_free(challenge);
110 /* Verify that the response is the original challenge. */
111 if (memcmp(response, mdbuf, 16) != 0) {
115 /* Correct answer. */
120 * Performs the RSA authentication dialog with the client. This returns
121 * 0 if the client could not be authenticated, and 1 if authentication was
122 * successful. This may exit if there is a serious protocol violation.
126 auth_rsa(struct passwd *pw, BIGNUM *client_n)
128 extern ServerOptions options;
129 char line[8192], file[1024];
133 unsigned long linenum = 0;
138 /* Temporarily use the user's uid. */
139 temporarily_use_uid(pw->pw_uid);
141 /* The authorized keys. */
142 snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir,
143 SSH_USER_PERMITTED_KEYS);
145 /* Fail quietly if file does not exist */
146 if (stat(file, &st) < 0) {
147 /* Restore the privileged uid. */
151 /* Open the file containing the authorized keys. */
152 f = fopen(file, "r");
154 /* Restore the privileged uid. */
156 packet_send_debug("Could not open %.900s for reading.", file);
157 packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
160 if (options.strict_modes) {
163 /* Check open file in order to avoid open/stat races */
164 if (fstat(fileno(f), &st) < 0 ||
165 (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
166 (st.st_mode & 022) != 0) {
167 snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
168 "bad ownership or modes for '%s'.", pw->pw_name, file);
171 /* Check path to SSH_USER_PERMITTED_KEYS */
173 static const char *check[] = {
174 "", SSH_USER_DIR, NULL
176 for (i = 0; check[i]; i++) {
177 snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]);
178 if (stat(line, &st) < 0 ||
179 (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
180 (st.st_mode & 022) != 0) {
181 snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
182 "bad ownership or modes for '%s'.", pw->pw_name, line);
191 packet_send_debug(buf);
196 /* Flag indicating whether authentication has succeeded. */
204 * Go though the accepted keys, looking for the current key. If
205 * found, perform a challenge-response dialog to verify that the
206 * user really has the corresponding private key.
208 while (fgets(line, sizeof(line), f)) {
214 /* Skip leading whitespace, empty and comment lines. */
215 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
217 if (!*cp || *cp == '\n' || *cp == '#')
221 * Check if there are options for this key, and if so,
222 * save their starting address and skip the option part
223 * for now. If there are no options, set the starting
226 if (*cp < '0' || *cp > '9') {
229 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
230 if (*cp == '\\' && cp[1] == '"')
231 cp++; /* Skip both */
238 /* Parse the key from the line. */
239 if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) {
240 debug("%.100s, line %lu: bad key syntax",
241 SSH_USER_PERMITTED_KEYS, linenum);
242 packet_send_debug("%.100s, line %lu: bad key syntax",
243 SSH_USER_PERMITTED_KEYS, linenum);
246 /* cp now points to the comment part. */
248 /* Check if the we have found the desired key (identified by its modulus). */
249 if (BN_cmp(pk->n, client_n) != 0)
252 /* check the real bits */
253 if (bits != BN_num_bits(pk->n))
254 log("Warning: %s, line %ld: keysize mismatch: "
255 "actual %d vs. announced %d.",
256 file, linenum, BN_num_bits(pk->n), bits);
258 /* We have found the desired key. */
260 /* Perform the challenge-response dialog for this key. */
261 if (!auth_rsa_challenge_dialog(pk)) {
262 /* Wrong response. */
263 verbose("Wrong response to RSA authentication challenge.");
264 packet_send_debug("Wrong response to RSA authentication challenge.");
268 * Correct response. The client has been successfully
269 * authenticated. Note that we have not yet processed the
270 * options; this will be reset if the options cause the
271 * authentication to be rejected.
275 /* RSA part of authentication was accepted. Now process the options. */
277 while (*options && *options != ' ' && *options != '\t') {
278 cp = "no-port-forwarding";
279 if (strncmp(options, cp, strlen(cp)) == 0) {
280 packet_send_debug("Port forwarding disabled.");
281 no_port_forwarding_flag = 1;
282 options += strlen(cp);
285 cp = "no-agent-forwarding";
286 if (strncmp(options, cp, strlen(cp)) == 0) {
287 packet_send_debug("Agent forwarding disabled.");
288 no_agent_forwarding_flag = 1;
289 options += strlen(cp);
292 cp = "no-X11-forwarding";
293 if (strncmp(options, cp, strlen(cp)) == 0) {
294 packet_send_debug("X11 forwarding disabled.");
295 no_x11_forwarding_flag = 1;
296 options += strlen(cp);
300 if (strncmp(options, cp, strlen(cp)) == 0) {
301 packet_send_debug("Pty allocation disabled.");
303 options += strlen(cp);
307 if (strncmp(options, cp, strlen(cp)) == 0) {
309 options += strlen(cp);
310 forced_command = xmalloc(strlen(options) + 1);
315 if (*options == '\\' && options[1] == '"') {
317 forced_command[i++] = '"';
320 forced_command[i++] = *options++;
323 debug("%.100s, line %lu: missing end quote",
324 SSH_USER_PERMITTED_KEYS, linenum);
325 packet_send_debug("%.100s, line %lu: missing end quote",
326 SSH_USER_PERMITTED_KEYS, linenum);
329 forced_command[i] = 0;
330 packet_send_debug("Forced command: %.900s", forced_command);
334 cp = "environment=\"";
335 if (strncmp(options, cp, strlen(cp)) == 0) {
338 struct envstring *new_envstring;
339 options += strlen(cp);
340 s = xmalloc(strlen(options) + 1);
345 if (*options == '\\' && options[1] == '"') {
353 debug("%.100s, line %lu: missing end quote",
354 SSH_USER_PERMITTED_KEYS, linenum);
355 packet_send_debug("%.100s, line %lu: missing end quote",
356 SSH_USER_PERMITTED_KEYS, linenum);
360 packet_send_debug("Adding to environment: %.900s", s);
361 debug("Adding to environment: %.900s", s);
363 new_envstring = xmalloc(sizeof(struct envstring));
364 new_envstring->s = s;
365 new_envstring->next = custom_environment;
366 custom_environment = new_envstring;
370 if (strncmp(options, cp, strlen(cp)) == 0) {
371 char *patterns = xmalloc(strlen(options) + 1);
373 options += strlen(cp);
378 if (*options == '\\' && options[1] == '"') {
383 patterns[i++] = *options++;
386 debug("%.100s, line %lu: missing end quote",
387 SSH_USER_PERMITTED_KEYS, linenum);
388 packet_send_debug("%.100s, line %lu: missing end quote",
389 SSH_USER_PERMITTED_KEYS, linenum);
395 * Deny access if we get a negative
396 * match for the hostname or the ip
397 * or if we get not match at all
399 mname = match_hostname(get_canonical_hostname(),
400 patterns, strlen(patterns));
401 mip = match_hostname(get_remote_ipaddr(),
402 patterns, strlen(patterns));
403 if (mname == -1 || mip == -1 ||
404 (mname != 1 && mip != 1)) {
405 log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).",
406 pw->pw_name, get_canonical_hostname(),
407 get_remote_ipaddr());
408 packet_send_debug("Your host '%.200s' is not permitted to use this key for login.",
409 get_canonical_hostname());
411 /* key invalid for this host, reset flags */
413 no_agent_forwarding_flag = 0;
414 no_port_forwarding_flag = 0;
416 no_x11_forwarding_flag = 0;
417 while (custom_environment) {
418 struct envstring *ce = custom_environment;
419 custom_environment = ce->next;
423 if (forced_command) {
424 xfree(forced_command);
425 forced_command = NULL;
430 /* Host name matches. */
434 log("Bad options in %.100s file, line %lu: %.50s",
435 SSH_USER_PERMITTED_KEYS, linenum, options);
436 packet_send_debug("Bad options in %.100s file, line %lu: %.50s",
437 SSH_USER_PERMITTED_KEYS, linenum, options);
443 * Skip the comma, and move to the next option
444 * (or break out if there are no more).
447 fatal("Bugs in auth-rsa.c option processing.");
448 if (*options == ' ' || *options == '\t')
449 break; /* End of options. */
453 /* Process the next option. */
458 * Break out of the loop if authentication was successful;
459 * otherwise continue searching.
465 /* Restore the privileged uid. */
468 /* Close the file. */
474 packet_send_debug("RSA authentication accepted.");
476 /* Return authentication result. */
477 return authenticated;