2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * Created: Fri Mar 17 17:09:28 1995 ylo
6 * This program is the ssh daemon. It listens for connections from clients, and
7 * performs authentication, executes use commands or shell, and forwards
8 * information to/from the application to the user client over an encrypted
9 * connection. This can also handle forwarding of X11, TCP/IP, and authentication
14 RCSID("$OpenBSD: sshd.c,v 1.96 2000/03/28 21:15:45 markus Exp $");
29 # include <openssl/dh.h>
30 # include <openssl/bn.h>
31 # include <openssl/hmac.h>
32 # include <openssl/dsa.h>
33 # include <openssl/rsa.h>
38 # include <ssl/hmac.h>
49 int allow_severity = LOG_INFO;
50 int deny_severity = LOG_WARNING;
57 /* Server configuration options. */
58 ServerOptions options;
60 /* Name of the server configuration file. */
61 char *config_file_name = SERVER_CONFIG_FILE;
64 * Flag indicating whether IPv4 or IPv6. This can be set on the command line.
65 * Default value is AF_UNSPEC means both IPv4 and IPv6.
68 int IPv4or6 = AF_INET;
70 int IPv4or6 = AF_UNSPEC;
74 * Debug mode flag. This can be set on the command line. If debug
75 * mode is enabled, extra debugging output will be sent to the system
76 * log, the daemon will not go to background, and will exit after processing
77 * the first connection.
81 /* Flag indicating that the daemon is being started from inetd. */
84 /* debug goes to stderr unless inetd_flag is set */
87 /* argv[0] without path. */
90 /* Saved arguments to main(). */
94 * The sockets that the server is listening; this is used in the SIGHUP
97 #define MAX_LISTEN_SOCKS 16
98 int listen_socks[MAX_LISTEN_SOCKS];
99 int num_listen_socks = 0;
102 * the client's version string, passed by sshd2 in compat mode. if != NULL,
103 * sshd will skip the version-number exchange
105 char *client_version_string = NULL;
106 char *server_version_string = NULL;
109 * Any really sensitive data in the application is contained in this
110 * structure. The idea is that this structure could be locked into memory so
111 * that the pages do not get written into swap. However, there are some
112 * problems. The private key contains BIGNUMs, and we do not (in principle)
113 * have access to the internals of them, and locking just the structure is
114 * not very useful. Currently, memory locking is not implemented.
117 RSA *private_key; /* Private part of server key. */
118 RSA *host_key; /* Private part of host key. */
122 * Flag indicating whether the current session key has been used. This flag
123 * is set whenever the key is used, and cleared when the key is regenerated.
127 /* This is set to true when SIGHUP is received. */
128 int received_sighup = 0;
130 /* Public side of the server key. This value is regenerated regularly with
134 /* session identifier, used by RSA-auth */
135 unsigned char session_id[16];
137 /* Prototypes for various functions defined later in this file. */
141 * Close all listening sockets
144 close_listen_socks(void)
147 for (i = 0; i < num_listen_socks; i++)
148 close(listen_socks[i]);
149 num_listen_socks = -1;
153 * Signal handler for SIGHUP. Sshd execs itself when it receives SIGHUP;
154 * the effect is to reread the configuration file (and to regenerate
158 sighup_handler(int sig)
161 signal(SIGHUP, sighup_handler);
165 * Called from the main program after receiving SIGHUP.
166 * Restarts the server.
171 log("Received SIGHUP; restarting.");
172 close_listen_socks();
173 execv(saved_argv[0], saved_argv);
174 log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno));
179 * Generic signal handler for terminating signals in the master daemon.
180 * These close the listen socket; not closing it seems to cause "Address
181 * already in use" problems on some machines, which is inconvenient.
184 sigterm_handler(int sig)
186 log("Received signal %d; terminating.", sig);
187 close_listen_socks();
192 * SIGCHLD handler. This is called whenever a child dies. This will then
193 * reap any zombies left by exited c.
196 main_sigchld_handler(int sig)
198 int save_errno = errno;
201 while (waitpid(-1, &status, WNOHANG) > 0)
204 signal(SIGCHLD, main_sigchld_handler);
209 * Signal handler for the alarm after the login grace period has expired.
212 grace_alarm_handler(int sig)
214 /* Close the connection. */
217 /* Log error and exit. */
218 fatal("Timeout before authentication for %s.", get_remote_ipaddr());
222 * Signal handler for the key regeneration alarm. Note that this
223 * alarm only occurs in the daemon waiting for connections, and it does not
224 * do anything with the private key or random state before forking.
225 * Thus there should be no concurrency control/asynchronous execution
229 key_regeneration_alarm(int sig)
231 int save_errno = errno;
233 /* Check if we should generate a new key. */
235 /* This should really be done in the background. */
236 log("Generating new %d bit RSA key.", options.server_key_bits);
238 if (sensitive_data.private_key != NULL)
239 RSA_free(sensitive_data.private_key);
240 sensitive_data.private_key = RSA_new();
242 if (public_key != NULL)
243 RSA_free(public_key);
244 public_key = RSA_new();
246 rsa_generate_key(sensitive_data.private_key, public_key,
247 options.server_key_bits);
250 log("RSA key generation complete.");
252 /* Reschedule the alarm. */
253 signal(SIGALRM, key_regeneration_alarm);
254 alarm(options.key_regeneration_time);
259 sshd_exchange_identification(int sock_in, int sock_out)
262 int remote_major, remote_minor;
264 char buf[256]; /* Must not be larger than remote_version. */
265 char remote_version[256]; /* Must be at least as big as buf. */
267 snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
268 PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION);
269 server_version_string = xstrdup(buf);
271 if (client_version_string == NULL) {
272 /* Send our protocol version identification. */
273 if (atomicio(write, sock_out, server_version_string, strlen(server_version_string))
274 != strlen(server_version_string)) {
275 log("Could not write ident string to %s.", get_remote_ipaddr());
279 /* Read other side\'s version identification. */
280 for (i = 0; i < sizeof(buf) - 1; i++) {
281 if (read(sock_in, &buf[i], 1) != 1) {
282 log("Did not receive ident string from %s.", get_remote_ipaddr());
285 if (buf[i] == '\r') {
289 /*break; XXX eat \r */
291 if (buf[i] == '\n') {
297 buf[sizeof(buf) - 1] = 0;
298 client_version_string = xstrdup(buf);
302 * Check that the versions match. In future this might accept
303 * several versions and set appropriate flags to handle them.
305 if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n",
306 &remote_major, &remote_minor, remote_version) != 3) {
307 s = "Protocol mismatch.\n";
308 (void) atomicio(write, sock_out, s, strlen(s));
311 log("Bad protocol version identification '%.100s' from %s",
312 client_version_string, get_remote_ipaddr());
315 debug("Client protocol version %d.%d; client software version %.100s",
316 remote_major, remote_minor, remote_version);
318 switch(remote_major) {
320 if (remote_minor < 3) {
321 packet_disconnect("Your ssh version is too old and"
322 "is no longer supported. Please install a newer version.");
323 } else if (remote_minor == 3) {
324 /* note that this disables agent-forwarding */
329 s = "Protocol major versions differ.\n";
330 (void) atomicio(write, sock_out, s, strlen(s));
333 log("Protocol major versions differ for %s: %d vs. %d",
334 get_remote_ipaddr(), PROTOCOL_MAJOR, remote_major);
341 * Main program for the daemon.
344 main(int ac, char **av)
348 int opt, sock_in = 0, sock_out = 0, newsock, i, fdsetsz, pid, on = 1;
352 struct sockaddr_storage from;
353 const char *remote_ip;
357 struct linger linger;
359 char ntop[NI_MAXHOST], strport[NI_MAXSERV];
360 int listen_sock, maxfd;
364 if (strchr(av[0], '/'))
365 av0 = strrchr(av[0], '/') + 1;
369 /* Initialize configuration options to their default values. */
370 initialize_server_options(&options);
372 /* Parse command-line arguments. */
373 while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ46")) != EOF) {
382 config_file_name = optarg;
386 options.log_level = SYSLOG_LEVEL_DEBUG;
395 options.log_level = SYSLOG_LEVEL_QUIET;
398 options.server_key_bits = atoi(optarg);
401 options.ports_from_cmdline = 1;
402 if (options.num_ports >= MAX_PORTS)
403 fatal("too many ports.\n");
404 options.ports[options.num_ports++] = atoi(optarg);
407 options.login_grace_time = atoi(optarg);
410 options.key_regeneration_time = atoi(optarg);
413 options.host_key_file = optarg;
416 client_version_string = optarg;
417 /* only makes sense with inetd_flag, i.e. no listen() */
422 fprintf(stderr, "sshd version %s\n", SSH_VERSION);
423 fprintf(stderr, "Usage: %s [options]\n", av0);
424 fprintf(stderr, "Options:\n");
425 fprintf(stderr, " -f file Configuration file (default %s)\n", SERVER_CONFIG_FILE);
426 fprintf(stderr, " -d Debugging mode\n");
427 fprintf(stderr, " -i Started from inetd\n");
428 fprintf(stderr, " -q Quiet (no logging)\n");
429 fprintf(stderr, " -p port Listen on the specified port (default: 22)\n");
430 fprintf(stderr, " -k seconds Regenerate server key every this many seconds (default: 3600)\n");
431 fprintf(stderr, " -g seconds Grace period for authentication (default: 300)\n");
432 fprintf(stderr, " -b bits Size of server RSA key (default: 768 bits)\n");
433 fprintf(stderr, " -h file File from which to read host key (default: %s)\n",
435 fprintf(stderr, " -4 Use IPv4 only\n");
436 fprintf(stderr, " -6 Use IPv6 only\n");
442 * Force logging to stderr until we have loaded the private host
443 * key (unless started from inetd)
446 options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
447 options.log_facility == -1 ? SYSLOG_FACILITY_AUTH : options.log_facility,
450 /* check if RSA support exists */
451 if (rsa_alive() == 0) {
453 printf("sshd: no RSA support in libssl and libcrypto -- exiting. See ssl(8)\n");
454 log("no RSA support in libssl and libcrypto -- exiting. See ssl(8)");
457 /* Read server configuration options from the configuration file. */
458 read_server_config(&options, config_file_name);
460 /* Fill in default values for those options not explicitly set. */
461 fill_default_server_options(&options);
463 /* Check certain values for sanity. */
464 if (options.server_key_bits < 512 ||
465 options.server_key_bits > 32768) {
466 fprintf(stderr, "Bad server key size.\n");
469 /* Check that there are no remaining arguments. */
471 fprintf(stderr, "Extra argument %s.\n", av[optind]);
475 debug("sshd version %.100s", SSH_VERSION);
477 sensitive_data.host_key = RSA_new();
479 /* Load the host key. It must have empty passphrase. */
480 if (!load_private_key(options.host_key_file, "",
481 sensitive_data.host_key, &comment)) {
482 error("Could not load host key: %.200s: %.100s",
483 options.host_key_file, strerror(errno));
488 /* Initialize the log (it is reinitialized below in case we
490 if (debug_flag && !inetd_flag)
492 log_init(av0, options.log_level, options.log_facility, log_stderr);
494 /* If not in debugging mode, and not started from inetd,
495 disconnect from the controlling terminal, and fork. The
496 original process exits. */
497 if (!debug_flag && !inetd_flag) {
500 #endif /* TIOCNOTTY */
501 if (daemon(0, 0) < 0)
502 fatal("daemon() failed: %.200s", strerror(errno));
504 /* Disconnect from the controlling tty. */
506 fd = open("/dev/tty", O_RDWR | O_NOCTTY);
508 (void) ioctl(fd, TIOCNOTTY, NULL);
511 #endif /* TIOCNOTTY */
513 /* Reinitialize the log (because of the fork above). */
514 log_init(av0, options.log_level, options.log_facility, log_stderr);
516 /* Check that server and host key lengths differ sufficiently.
517 This is necessary to make double encryption work with rsaref.
518 Oh, I hate software patents. I dont know if this can go? Niels */
519 if (options.server_key_bits >
520 BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED &&
521 options.server_key_bits <
522 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
523 options.server_key_bits =
524 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED;
525 debug("Forcing server key to %d bits to make it differ from host key.",
526 options.server_key_bits);
528 /* Do not display messages to stdout in RSA code. */
531 /* Initialize the random number generator. */
534 /* Chdir to the root directory so that the current disk can be
535 unmounted if desired. */
538 /* Start listening for a socket, unless started from inetd. */
541 s1 = dup(0); /* Make sure descriptors 0, 1, and 2 are in use. */
545 /* We intentionally do not close the descriptors 0, 1, and 2
546 as our code for setting the descriptors won\'t work
547 if ttyfd happens to be one of those. */
548 debug("inetd sockets after dupping: %d, %d", sock_in, sock_out);
550 public_key = RSA_new();
551 sensitive_data.private_key = RSA_new();
553 log("Generating %d bit RSA key.", options.server_key_bits);
554 rsa_generate_key(sensitive_data.private_key, public_key,
555 options.server_key_bits);
557 log("RSA key generation complete.");
559 for (ai = options.listen_addrs; ai; ai = ai->ai_next) {
560 if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
562 if (num_listen_socks >= MAX_LISTEN_SOCKS)
563 fatal("Too many listen sockets. "
564 "Enlarge MAX_LISTEN_SOCKS");
565 if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
566 ntop, sizeof(ntop), strport, sizeof(strport),
567 NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
568 error("getnameinfo failed");
571 /* Create socket for listening. */
572 listen_sock = socket(ai->ai_family, SOCK_STREAM, 0);
573 if (listen_sock < 0) {
574 /* kernel may not support ipv6 */
575 verbose("socket: %.100s", strerror(errno));
578 if (fcntl(listen_sock, F_SETFL, O_NONBLOCK) < 0) {
579 error("listen_sock O_NONBLOCK: %s", strerror(errno));
584 * Set socket options. We try to make the port
585 * reusable and have it close as fast as possible
586 * without waiting in unnecessary wait states on
589 setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR,
590 (void *) &on, sizeof(on));
593 setsockopt(listen_sock, SOL_SOCKET, SO_LINGER,
594 (void *) &linger, sizeof(linger));
596 debug("Bind to port %s on %s.", strport, ntop);
598 /* Bind the socket to the desired port. */
599 if ((bind(listen_sock, ai->ai_addr, ai->ai_addrlen) < 0) &&
601 error("Bind to port %s on %s failed: %.200s.",
602 strport, ntop, strerror(errno));
606 listen_socks[num_listen_socks] = listen_sock;
609 /* Start listening on the port. */
610 log("Server listening on %s port %s.", ntop, strport);
611 if (listen(listen_sock, 5) < 0)
612 fatal("listen: %.100s", strerror(errno));
615 freeaddrinfo(options.listen_addrs);
617 if (!num_listen_socks)
618 fatal("Cannot bind any address.");
622 * Record our pid in /etc/sshd_pid to make it easier
623 * to kill the correct sshd. We don\'t want to do
624 * this before the bind above because the bind will
625 * fail if there already is a daemon, and this will
626 * overwrite any old pid in the file.
628 f = fopen(SSH_DAEMON_PID_FILE, "w");
630 fprintf(f, "%u\n", (unsigned int) getpid());
635 public_key = RSA_new();
636 sensitive_data.private_key = RSA_new();
638 log("Generating %d bit RSA key.", options.server_key_bits);
639 rsa_generate_key(sensitive_data.private_key, public_key,
640 options.server_key_bits);
642 log("RSA key generation complete.");
644 /* Schedule server key regeneration alarm. */
645 signal(SIGALRM, key_regeneration_alarm);
646 alarm(options.key_regeneration_time);
648 /* Arrange to restart on SIGHUP. The handler needs listen_sock. */
649 signal(SIGHUP, sighup_handler);
650 signal(SIGTERM, sigterm_handler);
651 signal(SIGQUIT, sigterm_handler);
653 /* Arrange SIGCHLD to be caught. */
654 signal(SIGCHLD, main_sigchld_handler);
656 /* setup fd set for listen */
658 for (i = 0; i < num_listen_socks; i++)
659 if (listen_socks[i] > maxfd)
660 maxfd = listen_socks[i];
661 fdsetsz = howmany(maxfd, NFDBITS) * sizeof(fd_mask);
662 fdset = (fd_set *)xmalloc(fdsetsz);
665 * Stay listening for connections until the system crashes or
666 * the daemon is killed with a signal.
671 /* Wait in select until there is a connection. */
672 memset(fdset, 0, fdsetsz);
673 for (i = 0; i < num_listen_socks; i++)
674 FD_SET(listen_socks[i], fdset);
675 if (select(maxfd + 1, fdset, NULL, NULL, NULL) < 0) {
677 error("select: %.100s", strerror(errno));
680 for (i = 0; i < num_listen_socks; i++) {
681 if (!FD_ISSET(listen_socks[i], fdset))
683 fromlen = sizeof(from);
684 newsock = accept(listen_socks[i], (struct sockaddr *)&from,
687 if (errno != EINTR && errno != EWOULDBLOCK)
688 error("accept: %.100s", strerror(errno));
691 if (fcntl(newsock, F_SETFL, 0) < 0) {
692 error("newsock del O_NONBLOCK: %s", strerror(errno));
696 * Got connection. Fork a child to handle it, unless
697 * we are in debugging mode.
701 * In debugging mode. Close the listening
702 * socket, and start processing the
703 * connection without forking.
705 debug("Server will not fork when running in debugging mode.");
706 close_listen_socks();
713 * Normal production daemon. Fork, and have
714 * the child process the connection. The
715 * parent continues listening.
717 if ((pid = fork()) == 0) {
719 * Child. Close the listening socket, and start using the
720 * accepted socket. Reinitialize logging (since our pid has
721 * changed). We break out of the loop to handle the connection.
723 close_listen_socks();
726 log_init(av0, options.log_level, options.log_facility, log_stderr);
731 /* Parent. Stay in the loop. */
733 error("fork: %.100s", strerror(errno));
735 debug("Forked child %d.", pid);
737 /* Mark that the key has been used (it was "given" to the child). */
742 /* Close the new socket (the child is now taking care of it). */
744 } /* for (i = 0; i < num_listen_socks; i++) */
745 /* child process check (or debug mode) */
746 if (num_listen_socks < 0)
751 /* This is the child processing a new connection. */
754 * Disable the key regeneration alarm. We will not regenerate the
755 * key since we are no longer in a position to give it to anyone. We
756 * will not restart on SIGHUP since it no longer makes sense.
759 signal(SIGALRM, SIG_DFL);
760 signal(SIGHUP, SIG_DFL);
761 signal(SIGTERM, SIG_DFL);
762 signal(SIGQUIT, SIG_DFL);
763 signal(SIGCHLD, SIG_DFL);
766 * Set socket options for the connection. We want the socket to
767 * close as fast as possible without waiting for anything. If the
768 * connection is not a socket, these will do nothing.
770 /* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
773 setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));
776 * Register our connection. This turns encryption off because we do
779 packet_set_connection(sock_in, sock_out);
781 remote_port = get_remote_port();
782 remote_ip = get_remote_ipaddr();
784 /* Check whether logins are denied from this host. */
786 /* XXX LIBWRAP noes not know about IPv6 */
788 struct request_info req;
790 request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL);
793 if (!hosts_access(&req)) {
798 /*XXX IPv6 verbose("Connection from %.500s port %d", eval_client(&req), remote_port); */
801 /* Log the connection. */
802 verbose("Connection from %.500s port %d", remote_ip, remote_port);
805 * We don\'t want to listen forever unless the other side
806 * successfully authenticates itself. So we set up an alarm which is
807 * cleared after successful authentication. A limit of zero
808 * indicates no limit. Note that we don\'t set the alarm in debugging
809 * mode; it is just annoying to have the server exit just when you
810 * are about to discover the bug.
812 signal(SIGALRM, grace_alarm_handler);
814 alarm(options.login_grace_time);
816 sshd_exchange_identification(sock_in, sock_out);
818 * Check that the connection comes from a privileged port. Rhosts-
819 * and Rhosts-RSA-Authentication only make sense from priviledged
820 * programs. Of course, if the intruder has root access on his local
821 * machine, he can connect from any port. So do not use these
822 * authentication methods from machines that you do not trust.
824 if (remote_port >= IPPORT_RESERVED ||
825 remote_port < IPPORT_RESERVED / 2) {
826 options.rhosts_authentication = 0;
827 options.rhosts_rsa_authentication = 0;
830 if (!packet_connection_is_ipv4() &&
831 options.kerberos_authentication) {
832 debug("Kerberos Authentication disabled, only available for IPv4.");
833 options.kerberos_authentication = 0;
837 packet_set_nonblocking();
839 /* perform the key exchange */
841 /* authenticate user and start session */
845 /* Cleanup user's ticket cache file. */
846 if (options.kerberos_ticket_cleanup)
850 /* The connection has been terminated. */
851 verbose("Closing connection to %.100s", remote_ip);
869 BIGNUM *session_key_int;
870 unsigned char session_key[SSH_SESSION_KEY_LENGTH];
871 unsigned char cookie[8];
872 unsigned int cipher_type, auth_mask, protocol_flags;
876 * Generate check bytes that the client must send back in the user
877 * packet in order for it to be accepted; this is used to defy ip
878 * spoofing attacks. Note that this only works against somebody
879 * doing IP spoofing from a remote machine; any machine on the local
880 * network can still see outgoing packets and catch the random
881 * cookie. This only affects rhosts authentication, and this is one
882 * of the reasons why it is inherently insecure.
884 for (i = 0; i < 8; i++) {
887 cookie[i] = rand & 0xff;
892 * Send our public key. We include in the packet 64 bits of random
893 * data that must be matched in the reply in order to prevent IP
896 packet_start(SSH_SMSG_PUBLIC_KEY);
897 for (i = 0; i < 8; i++)
898 packet_put_char(cookie[i]);
900 /* Store our public server RSA key. */
901 packet_put_int(BN_num_bits(public_key->n));
902 packet_put_bignum(public_key->e);
903 packet_put_bignum(public_key->n);
905 /* Store our public host RSA key. */
906 packet_put_int(BN_num_bits(sensitive_data.host_key->n));
907 packet_put_bignum(sensitive_data.host_key->e);
908 packet_put_bignum(sensitive_data.host_key->n);
910 /* Put protocol flags. */
911 packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN);
913 /* Declare which ciphers we support. */
914 packet_put_int(cipher_mask());
916 /* Declare supported authentication types. */
918 if (options.rhosts_authentication)
919 auth_mask |= 1 << SSH_AUTH_RHOSTS;
920 if (options.rhosts_rsa_authentication)
921 auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA;
922 if (options.rsa_authentication)
923 auth_mask |= 1 << SSH_AUTH_RSA;
925 if (options.kerberos_authentication)
926 auth_mask |= 1 << SSH_AUTH_KERBEROS;
929 if (options.kerberos_tgt_passing)
930 auth_mask |= 1 << SSH_PASS_KERBEROS_TGT;
931 if (options.afs_token_passing)
932 auth_mask |= 1 << SSH_PASS_AFS_TOKEN;
935 if (options.skey_authentication == 1)
936 auth_mask |= 1 << SSH_AUTH_TIS;
938 if (options.password_authentication)
939 auth_mask |= 1 << SSH_AUTH_PASSWORD;
940 packet_put_int(auth_mask);
942 /* Send the packet and wait for it to be sent. */
946 debug("Sent %d bit public key and %d bit host key.",
947 BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n));
949 /* Read clients reply (cipher type and session key). */
950 packet_read_expect(&plen, SSH_CMSG_SESSION_KEY);
952 /* Get cipher type and check whether we accept this. */
953 cipher_type = packet_get_char();
955 if (!(cipher_mask() & (1 << cipher_type)))
956 packet_disconnect("Warning: client selects unsupported cipher.");
958 /* Get check bytes from the packet. These must match those we
959 sent earlier with the public key packet. */
960 for (i = 0; i < 8; i++)
961 if (cookie[i] != packet_get_char())
962 packet_disconnect("IP Spoofing check bytes do not match.");
964 debug("Encryption type: %.200s", cipher_name(cipher_type));
966 /* Get the encrypted integer. */
967 session_key_int = BN_new();
968 packet_get_bignum(session_key_int, &slen);
970 protocol_flags = packet_get_int();
971 packet_set_protocol_flags(protocol_flags);
973 packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY);
976 * Decrypt it using our private server key and private host key (key
977 * with larger modulus first).
979 if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
980 /* Private key has bigger modulus. */
981 if (BN_num_bits(sensitive_data.private_key->n) <
982 BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
983 fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
985 BN_num_bits(sensitive_data.private_key->n),
986 BN_num_bits(sensitive_data.host_key->n),
987 SSH_KEY_BITS_RESERVED);
989 rsa_private_decrypt(session_key_int, session_key_int,
990 sensitive_data.private_key);
991 rsa_private_decrypt(session_key_int, session_key_int,
992 sensitive_data.host_key);
994 /* Host key has bigger modulus (or they are equal). */
995 if (BN_num_bits(sensitive_data.host_key->n) <
996 BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) {
997 fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d",
999 BN_num_bits(sensitive_data.host_key->n),
1000 BN_num_bits(sensitive_data.private_key->n),
1001 SSH_KEY_BITS_RESERVED);
1003 rsa_private_decrypt(session_key_int, session_key_int,
1004 sensitive_data.host_key);
1005 rsa_private_decrypt(session_key_int, session_key_int,
1006 sensitive_data.private_key);
1009 compute_session_id(session_id, cookie,
1010 sensitive_data.host_key->n,
1011 sensitive_data.private_key->n);
1013 /* Destroy the private and public keys. They will no longer be needed. */
1014 RSA_free(public_key);
1015 RSA_free(sensitive_data.private_key);
1016 RSA_free(sensitive_data.host_key);
1019 * Extract session key from the decrypted integer. The key is in the
1020 * least significant 256 bits of the integer; the first byte of the
1021 * key is in the highest bits.
1023 BN_mask_bits(session_key_int, sizeof(session_key) * 8);
1024 len = BN_num_bytes(session_key_int);
1025 if (len < 0 || len > sizeof(session_key))
1026 fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
1027 get_remote_ipaddr(),
1028 len, sizeof(session_key));
1029 memset(session_key, 0, sizeof(session_key));
1030 BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);
1032 /* Destroy the decrypted integer. It is no longer needed. */
1033 BN_clear_free(session_key_int);
1035 /* Xor the first 16 bytes of the session key with the session id. */
1036 for (i = 0; i < 16; i++)
1037 session_key[i] ^= session_id[i];
1039 /* Set the session key. From this on all communications will be encrypted. */
1040 packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);
1042 /* Destroy our copy of the session key. It is no longer needed. */
1043 memset(session_key, 0, sizeof(session_key));
1045 debug("Received session key; encryption turned on.");
1047 /* Send an acknowledgement packet. Note that this packet is sent encrypted. */
1048 packet_start(SSH_SMSG_SUCCESS);
1050 packet_write_wait();