1 /* $OpenBSD: sshconnect1.c,v 1.70 2006/11/06 21:25:28 markus Exp $ */
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 * Code to connect to a remote host, and to perform the client side of the
7 * login (authentication) dialog.
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".
18 #include <sys/types.h>
19 #include <sys/socket.h>
21 #include <openssl/bn.h>
22 #include <openssl/md5.h>
44 #include "sshconnect.h"
51 /* Session id for the current session. */
52 u_char session_id[16];
53 u_int supported_authentications = 0;
55 extern Options options;
56 extern char *__progname;
59 * Checks if the user has an authentication agent, and if so, tries to
60 * authenticate using the agent.
63 try_agent_authentication(void)
67 AuthenticationConnection *auth;
73 /* Get connection to the agent. */
74 auth = ssh_get_authentication_connection();
78 if ((challenge = BN_new()) == NULL)
79 fatal("try_agent_authentication: BN_new failed");
80 /* Loop through identities served by the agent. */
81 for (key = ssh_get_first_identity(auth, &comment, 1);
83 key = ssh_get_next_identity(auth, &comment, 1)) {
85 /* Try this identity. */
86 debug("Trying RSA authentication via agent with '%.100s'", comment);
89 /* Tell the server that we are willing to authenticate using this key. */
90 packet_start(SSH_CMSG_AUTH_RSA);
91 packet_put_bignum(key->rsa->n);
95 /* Wait for server's response. */
98 /* The server sends failure if it doesn't like our key or
99 does not support RSA authentication. */
100 if (type == SSH_SMSG_FAILURE) {
101 debug("Server refused our key.");
105 /* Otherwise it should have sent a challenge. */
106 if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
107 packet_disconnect("Protocol error during RSA authentication: %d",
110 packet_get_bignum(challenge);
113 debug("Received RSA challenge from server.");
115 /* Ask the agent to decrypt the challenge. */
116 if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
118 * The agent failed to authenticate this identifier
119 * although it advertised it supports this. Just
120 * return a wrong value.
122 logit("Authentication agent failed to decrypt challenge.");
123 memset(response, 0, sizeof(response));
126 debug("Sending response to RSA challenge.");
128 /* Send the decrypted challenge back to the server. */
129 packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
130 for (i = 0; i < 16; i++)
131 packet_put_char(response[i]);
135 /* Wait for response from the server. */
136 type = packet_read();
138 /* The server returns success if it accepted the authentication. */
139 if (type == SSH_SMSG_SUCCESS) {
140 ssh_close_authentication_connection(auth);
141 BN_clear_free(challenge);
142 debug("RSA authentication accepted by server.");
145 /* Otherwise it should return failure. */
146 if (type != SSH_SMSG_FAILURE)
147 packet_disconnect("Protocol error waiting RSA auth response: %d",
150 ssh_close_authentication_connection(auth);
151 BN_clear_free(challenge);
152 debug("RSA authentication using agent refused.");
157 * Computes the proper response to a RSA challenge, and sends the response to
161 respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
163 u_char buf[32], response[16];
167 /* Decrypt the challenge using the private key. */
168 /* XXX think about Bleichenbacher, too */
169 if (rsa_private_decrypt(challenge, challenge, prv) <= 0)
171 "respond_to_rsa_challenge: rsa_private_decrypt failed");
173 /* Compute the response. */
174 /* The response is MD5 of decrypted challenge plus session id. */
175 len = BN_num_bytes(challenge);
176 if (len <= 0 || (u_int)len > sizeof(buf))
178 "respond_to_rsa_challenge: bad challenge length %d", len);
180 memset(buf, 0, sizeof(buf));
181 BN_bn2bin(challenge, buf + sizeof(buf) - len);
183 MD5_Update(&md, buf, 32);
184 MD5_Update(&md, session_id, 16);
185 MD5_Final(response, &md);
187 debug("Sending response to host key RSA challenge.");
189 /* Send the response back to the server. */
190 packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
191 for (i = 0; i < 16; i++)
192 packet_put_char(response[i]);
196 memset(buf, 0, sizeof(buf));
197 memset(response, 0, sizeof(response));
198 memset(&md, 0, sizeof(md));
202 * Checks if the user has authentication file, and if so, tries to authenticate
206 try_rsa_authentication(int idx)
209 Key *public, *private;
210 char buf[300], *passphrase, *comment, *authfile;
211 int i, perm_ok = 1, type, quit;
213 public = options.identity_keys[idx];
214 authfile = options.identity_files[idx];
215 comment = xstrdup(authfile);
217 debug("Trying RSA authentication with key '%.100s'", comment);
219 /* Tell the server that we are willing to authenticate using this key. */
220 packet_start(SSH_CMSG_AUTH_RSA);
221 packet_put_bignum(public->rsa->n);
225 /* Wait for server's response. */
226 type = packet_read();
229 * The server responds with failure if it doesn't like our key or
230 * doesn't support RSA authentication.
232 if (type == SSH_SMSG_FAILURE) {
233 debug("Server refused our key.");
237 /* Otherwise, the server should respond with a challenge. */
238 if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
239 packet_disconnect("Protocol error during RSA authentication: %d", type);
241 /* Get the challenge from the packet. */
242 if ((challenge = BN_new()) == NULL)
243 fatal("try_rsa_authentication: BN_new failed");
244 packet_get_bignum(challenge);
247 debug("Received RSA challenge from server.");
250 * If the key is not stored in external hardware, we have to
251 * load the private key. Try first with empty passphrase; if it
252 * fails, ask for a passphrase.
254 if (public->flags & KEY_FLAG_EXT)
257 private = key_load_private_type(KEY_RSA1, authfile, "", NULL,
259 if (private == NULL && !options.batch_mode && perm_ok) {
260 snprintf(buf, sizeof(buf),
261 "Enter passphrase for RSA key '%.100s': ", comment);
262 for (i = 0; i < options.number_of_password_prompts; i++) {
263 passphrase = read_passphrase(buf, 0);
264 if (strcmp(passphrase, "") != 0) {
265 private = key_load_private_type(KEY_RSA1,
266 authfile, passphrase, NULL, NULL);
269 debug2("no passphrase given, try next key");
272 memset(passphrase, 0, strlen(passphrase));
274 if (private != NULL || quit)
276 debug2("bad passphrase given, try again...");
279 /* We no longer need the comment. */
282 if (private == NULL) {
283 if (!options.batch_mode && perm_ok)
284 error("Bad passphrase.");
286 /* Send a dummy response packet to avoid protocol error. */
287 packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
288 for (i = 0; i < 16; i++)
293 /* Expect the server to reject it... */
294 packet_read_expect(SSH_SMSG_FAILURE);
295 BN_clear_free(challenge);
299 /* Compute and send a response to the challenge. */
300 respond_to_rsa_challenge(challenge, private->rsa);
302 /* Destroy the private key unless it in external hardware. */
303 if (!(private->flags & KEY_FLAG_EXT))
306 /* We no longer need the challenge. */
307 BN_clear_free(challenge);
309 /* Wait for response from the server. */
310 type = packet_read();
311 if (type == SSH_SMSG_SUCCESS) {
312 debug("RSA authentication accepted by server.");
315 if (type != SSH_SMSG_FAILURE)
316 packet_disconnect("Protocol error waiting RSA auth response: %d", type);
317 debug("RSA authentication refused.");
322 * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
323 * authentication and RSA host authentication.
326 try_rhosts_rsa_authentication(const char *local_user, Key * host_key)
331 debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");
333 /* Tell the server that we are willing to authenticate using this key. */
334 packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
335 packet_put_cstring(local_user);
336 packet_put_int(BN_num_bits(host_key->rsa->n));
337 packet_put_bignum(host_key->rsa->e);
338 packet_put_bignum(host_key->rsa->n);
342 /* Wait for server's response. */
343 type = packet_read();
345 /* The server responds with failure if it doesn't admit our
346 .rhosts authentication or doesn't know our host key. */
347 if (type == SSH_SMSG_FAILURE) {
348 debug("Server refused our rhosts authentication or host key.");
351 /* Otherwise, the server should respond with a challenge. */
352 if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
353 packet_disconnect("Protocol error during RSA authentication: %d", type);
355 /* Get the challenge from the packet. */
356 if ((challenge = BN_new()) == NULL)
357 fatal("try_rhosts_rsa_authentication: BN_new failed");
358 packet_get_bignum(challenge);
361 debug("Received RSA challenge for host key from server.");
363 /* Compute a response to the challenge. */
364 respond_to_rsa_challenge(challenge, host_key->rsa);
366 /* We no longer need the challenge. */
367 BN_clear_free(challenge);
369 /* Wait for response from the server. */
370 type = packet_read();
371 if (type == SSH_SMSG_SUCCESS) {
372 debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
375 if (type != SSH_SMSG_FAILURE)
376 packet_disconnect("Protocol error waiting RSA auth response: %d", type);
377 debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
382 * Tries to authenticate with any string-based challenge/response system.
383 * Note that the client code is not tied to s/key or TIS.
386 try_challenge_response_authentication(void)
391 char *challenge, *response;
393 debug("Doing challenge response authentication.");
395 for (i = 0; i < options.number_of_password_prompts; i++) {
396 /* request a challenge */
397 packet_start(SSH_CMSG_AUTH_TIS);
401 type = packet_read();
402 if (type != SSH_SMSG_FAILURE &&
403 type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
404 packet_disconnect("Protocol error: got %d in response "
405 "to SSH_CMSG_AUTH_TIS", type);
407 if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
408 debug("No challenge.");
411 challenge = packet_get_string(&clen);
413 snprintf(prompt, sizeof prompt, "%s%s", challenge,
414 strchr(challenge, '\n') ? "" : "\nResponse: ");
417 error("Permission denied, please try again.");
418 if (options.cipher == SSH_CIPHER_NONE)
419 logit("WARNING: Encryption is disabled! "
420 "Response will be transmitted in clear text.");
421 response = read_passphrase(prompt, 0);
422 if (strcmp(response, "") == 0) {
426 packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
427 ssh_put_password(response);
428 memset(response, 0, strlen(response));
432 type = packet_read();
433 if (type == SSH_SMSG_SUCCESS)
435 if (type != SSH_SMSG_FAILURE)
436 packet_disconnect("Protocol error: got %d in response "
437 "to SSH_CMSG_AUTH_TIS_RESPONSE", type);
444 * Tries to authenticate with plain passwd authentication.
447 try_password_authentication(char *prompt)
452 debug("Doing password authentication.");
453 if (options.cipher == SSH_CIPHER_NONE)
454 logit("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
455 for (i = 0; i < options.number_of_password_prompts; i++) {
457 error("Permission denied, please try again.");
458 password = read_passphrase(prompt, 0);
459 packet_start(SSH_CMSG_AUTH_PASSWORD);
460 ssh_put_password(password);
461 memset(password, 0, strlen(password));
466 type = packet_read();
467 if (type == SSH_SMSG_SUCCESS)
469 if (type != SSH_SMSG_FAILURE)
470 packet_disconnect("Protocol error: got %d in response to passwd auth", type);
480 ssh_kex(char *host, struct sockaddr *hostaddr)
484 Key *host_key, *server_key;
486 int ssh_cipher_default = SSH_CIPHER_3DES;
487 u_char session_key[SSH_SESSION_KEY_LENGTH];
489 u_int supported_ciphers;
490 u_int server_flags, client_flags;
493 debug("Waiting for server public key.");
495 /* Wait for a public key packet from the server. */
496 packet_read_expect(SSH_SMSG_PUBLIC_KEY);
498 /* Get cookie from the packet. */
499 for (i = 0; i < 8; i++)
500 cookie[i] = packet_get_char();
502 /* Get the public key. */
503 server_key = key_new(KEY_RSA1);
504 bits = packet_get_int();
505 packet_get_bignum(server_key->rsa->e);
506 packet_get_bignum(server_key->rsa->n);
508 rbits = BN_num_bits(server_key->rsa->n);
510 logit("Warning: Server lies about size of server public key: "
511 "actual size is %d bits vs. announced %d.", rbits, bits);
512 logit("Warning: This may be due to an old implementation of ssh.");
514 /* Get the host key. */
515 host_key = key_new(KEY_RSA1);
516 bits = packet_get_int();
517 packet_get_bignum(host_key->rsa->e);
518 packet_get_bignum(host_key->rsa->n);
520 rbits = BN_num_bits(host_key->rsa->n);
522 logit("Warning: Server lies about size of server host key: "
523 "actual size is %d bits vs. announced %d.", rbits, bits);
524 logit("Warning: This may be due to an old implementation of ssh.");
527 /* Get protocol flags. */
528 server_flags = packet_get_int();
529 packet_set_protocol_flags(server_flags);
531 supported_ciphers = packet_get_int();
532 supported_authentications = packet_get_int();
535 debug("Received server public key (%d bits) and host key (%d bits).",
536 BN_num_bits(server_key->rsa->n), BN_num_bits(host_key->rsa->n));
538 if (verify_host_key(host, hostaddr, host_key) == -1)
539 fatal("Host key verification failed.");
541 client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
543 derive_ssh1_session_id(host_key->rsa->n, server_key->rsa->n, cookie, session_id);
545 /* Generate a session key. */
549 * Generate an encryption key for the session. The key is a 256 bit
550 * random number, interpreted as a 32-byte key, with the least
551 * significant 8 bits being the first byte of the key.
553 for (i = 0; i < 32; i++) {
556 session_key[i] = rnd & 0xff;
561 * According to the protocol spec, the first byte of the session key
562 * is the highest byte of the integer. The session key is xored with
563 * the first 16 bytes of the session id.
565 if ((key = BN_new()) == NULL)
566 fatal("ssh_kex: BN_new failed");
567 if (BN_set_word(key, 0) == 0)
568 fatal("ssh_kex: BN_set_word failed");
569 for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
570 if (BN_lshift(key, key, 8) == 0)
571 fatal("ssh_kex: BN_lshift failed");
573 if (BN_add_word(key, session_key[i] ^ session_id[i])
575 fatal("ssh_kex: BN_add_word failed");
577 if (BN_add_word(key, session_key[i]) == 0)
578 fatal("ssh_kex: BN_add_word failed");
583 * Encrypt the integer using the public key and host key of the
584 * server (key with smaller modulus first).
586 if (BN_cmp(server_key->rsa->n, host_key->rsa->n) < 0) {
587 /* Public key has smaller modulus. */
588 if (BN_num_bits(host_key->rsa->n) <
589 BN_num_bits(server_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
590 fatal("respond_to_rsa_challenge: host_key %d < server_key %d + "
591 "SSH_KEY_BITS_RESERVED %d",
592 BN_num_bits(host_key->rsa->n),
593 BN_num_bits(server_key->rsa->n),
594 SSH_KEY_BITS_RESERVED);
596 rsa_public_encrypt(key, key, server_key->rsa);
597 rsa_public_encrypt(key, key, host_key->rsa);
599 /* Host key has smaller modulus (or they are equal). */
600 if (BN_num_bits(server_key->rsa->n) <
601 BN_num_bits(host_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
602 fatal("respond_to_rsa_challenge: server_key %d < host_key %d + "
603 "SSH_KEY_BITS_RESERVED %d",
604 BN_num_bits(server_key->rsa->n),
605 BN_num_bits(host_key->rsa->n),
606 SSH_KEY_BITS_RESERVED);
608 rsa_public_encrypt(key, key, host_key->rsa);
609 rsa_public_encrypt(key, key, server_key->rsa);
612 /* Destroy the public keys since we no longer need them. */
613 key_free(server_key);
616 if (options.cipher == SSH_CIPHER_NOT_SET) {
617 if (cipher_mask_ssh1(1) & supported_ciphers & (1 << ssh_cipher_default))
618 options.cipher = ssh_cipher_default;
619 } else if (options.cipher == SSH_CIPHER_INVALID ||
620 !(cipher_mask_ssh1(1) & (1 << options.cipher))) {
621 logit("No valid SSH1 cipher, using %.100s instead.",
622 cipher_name(ssh_cipher_default));
623 options.cipher = ssh_cipher_default;
625 /* Check that the selected cipher is supported. */
626 if (!(supported_ciphers & (1 << options.cipher)))
627 fatal("Selected cipher type %.100s not supported by server.",
628 cipher_name(options.cipher));
630 debug("Encryption type: %.100s", cipher_name(options.cipher));
632 /* Send the encrypted session key to the server. */
633 packet_start(SSH_CMSG_SESSION_KEY);
634 packet_put_char(options.cipher);
636 /* Send the cookie back to the server. */
637 for (i = 0; i < 8; i++)
638 packet_put_char(cookie[i]);
640 /* Send and destroy the encrypted encryption key integer. */
641 packet_put_bignum(key);
644 /* Send protocol flags. */
645 packet_put_int(client_flags);
647 /* Send the packet now. */
651 debug("Sent encrypted session key.");
653 /* Set the encryption key. */
654 packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options.cipher);
656 /* We will no longer need the session key here. Destroy any extra copies. */
657 memset(session_key, 0, sizeof(session_key));
660 * Expect a success message from the server. Note that this message
661 * will be received in encrypted form.
663 packet_read_expect(SSH_SMSG_SUCCESS);
665 debug("Received encrypted confirmation.");
672 ssh_userauth1(const char *local_user, const char *server_user, char *host,
673 Sensitive *sensitive)
677 if (supported_authentications == 0)
678 fatal("ssh_userauth1: server supports no auth methods");
680 /* Send the name of the user to log in as on the server. */
681 packet_start(SSH_CMSG_USER);
682 packet_put_cstring(server_user);
687 * The server should respond with success if no authentication is
688 * needed (the user has no password). Otherwise the server responds
691 type = packet_read();
693 /* check whether the connection was accepted without authentication. */
694 if (type == SSH_SMSG_SUCCESS)
696 if (type != SSH_SMSG_FAILURE)
697 packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER", type);
700 * Try .rhosts or /etc/hosts.equiv authentication with RSA host
703 if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
704 options.rhosts_rsa_authentication) {
705 for (i = 0; i < sensitive->nkeys; i++) {
706 if (sensitive->keys[i] != NULL &&
707 sensitive->keys[i]->type == KEY_RSA1 &&
708 try_rhosts_rsa_authentication(local_user,
713 /* Try RSA authentication if the server supports it. */
714 if ((supported_authentications & (1 << SSH_AUTH_RSA)) &&
715 options.rsa_authentication) {
717 * Try RSA authentication using the authentication agent. The
718 * agent is tried first because no passphrase is needed for
719 * it, whereas identity files may require passphrases.
721 if (try_agent_authentication())
724 /* Try RSA authentication for each identity. */
725 for (i = 0; i < options.num_identity_files; i++)
726 if (options.identity_keys[i] != NULL &&
727 options.identity_keys[i]->type == KEY_RSA1 &&
728 try_rsa_authentication(i))
731 /* Try challenge response authentication if the server supports it. */
732 if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
733 options.challenge_response_authentication && !options.batch_mode) {
734 if (try_challenge_response_authentication())
737 /* Try password authentication if the server supports it. */
738 if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
739 options.password_authentication && !options.batch_mode) {
742 snprintf(prompt, sizeof(prompt), "%.30s@%.128s's password: ",
744 if (try_password_authentication(prompt))
747 /* All authentication methods have failed. Exit with an error message. */
748 fatal("Permission denied.");
752 return; /* need statement after label */