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Future deprecation notice
=========================

We plan on retiring more legacy cryptography in a near-future
release, specifically:

 * Refusing all RSA keys smaller than 1024 bits (the current minimum
   is 768 bits)

This list reflects our current intentions, but please check the final
release notes for future releases.

Potentially-incompatible changes
================================

This release disables a number of legacy cryptographic algorithms
by default in ssh:

 * Several ciphers blowfish-cbc, cast128-cbc, all arcfour variants
   and the rijndael-cbc aliases for AES.

 * MD5-based and truncated HMAC algorithms.

These algorithms are already disabled by default in sshd.

Changes since OpenSSH 7.1p2
===========================

This is primarily a bugfix release.

Security
--------

 * ssh(1), sshd(8): remove unfinished and unused roaming code (was
   already forcibly disabled in OpenSSH 7.1p2).

 * ssh(1): eliminate fallback from untrusted X11 forwarding to
   trusted forwarding when the X server disables the SECURITY
   extension.

 * ssh(1), sshd(8): increase the minimum modulus size supported for
   diffie-hellman-group-exchange to 2048 bits.

 * sshd(8): pre-auth sandboxing is now enabled by default (previous
   releases enabled it for new installations via sshd_config).

New Features
------------

 * all: add support for RSA signatures using SHA-256/512 hash
   algorithms based on draft-rsa-dsa-sha2-256-03.txt and
   draft-ssh-ext-info-04.txt.

 * ssh(1): Add an AddKeysToAgent client option which can be set to
   'yes', 'no', 'ask', or 'confirm', and defaults to 'no'.  When
   enabled, a private key that is used during authentication will be
   added to ssh-agent if it is running (with confirmation enabled if
   set to 'confirm').

 * sshd(8): add a new authorized_keys option "restrict" that includes
   all current and future key restrictions (no-*-forwarding, etc.).
   Also add permissive versions of the existing restrictions, e.g.
   "no-pty" -> "pty". This simplifies the task of setting up
   restricted keys and ensures they are maximally-restricted,
   regardless of any permissions we might implement in the future.

 * ssh(1): add ssh_config CertificateFile option to explicitly list
   certificates. bz#2436

 * ssh-keygen(1): allow ssh-keygen to change the key comment for all
   supported formats.

 * ssh-keygen(1): allow fingerprinting from standard input, e.g.
   "ssh-keygen -lf -"

 * ssh-keygen(1): allow fingerprinting multiple public keys in a
   file, e.g. "ssh-keygen -lf ~/.ssh/authorized_keys" bz#1319

 * sshd(8): support "none" as an argument for sshd_config
   Foreground and ChrootDirectory. Useful inside Match blocks to
   override a global default. bz#2486

 * ssh-keygen(1): support multiple certificates (one per line) and
   reading from standard input (using "-f -") for "ssh-keygen -L"

 * ssh-keyscan(1): add "ssh-keyscan -c ..." flag to allow fetching
   certificates instead of plain keys.

 * ssh(1): better handle anchored FQDNs (e.g. 'cvs.openbsd.org.') in
   hostname canonicalisation - treat them as already canonical and
   remove the trailing '.' before matching ssh_config.

Bugfixes
--------

 * sftp(1): existing destination directories should not terminate
   recursive uploads (regression in openssh 6.8) bz#2528

 * ssh(1), sshd(8): correctly send back SSH2_MSG_UNIMPLEMENTED
   replies to unexpected messages during key exchange. bz#2949

 * ssh(1): refuse attempts to set ConnectionAttempts=0, which does
   not make sense and would cause ssh to print an uninitialised stack
   variable. bz#2500

 * ssh(1): fix errors when attempting to connect to scoped IPv6
   addresses with hostname canonicalisation enabled.

 * sshd_config(5): list a couple more options usable in Match blocks.
   bz#2489

 * sshd(8): fix "PubkeyAcceptedKeyTypes +..." inside a Match block.

 * ssh(1): expand tilde characters in filenames passed to -i options
   before checking whether or not the identity file exists. Avoids
   confusion for cases where shell doesn't expand (e.g. "-i ~/file"
   vs. "-i~/file"). bz#2481

 * ssh(1): do not prepend "exec" to the shell command run by "Match
   exec" in a config file, which could cause some commands to fail
   in certain environments. bz#2471

 * ssh-keyscan(1): fix output for multiple hosts/addrs on one line
   when host hashing or a non standard port is in use bz#2479

 * sshd(8): skip "Could not chdir to home directory" message when
   ChrootDirectory is active. bz#2485

 * ssh(1): include PubkeyAcceptedKeyTypes in ssh -G config dump.

 * sshd(8): avoid changing TunnelForwarding device flags if they are
   already what is needed; makes it possible to use tun/tap
   networking as non-root user if device permissions and interface
   flags are pre-established

 * ssh(1), sshd(8): RekeyLimits could be exceeded by one packet.
   bz#2521

 * ssh(1): fix multiplexing master failure to notice client exit.

 * ssh(1), ssh-agent(1): avoid fatal() for PKCS11 tokens that present
   empty key IDs. bz#1773

 * sshd(8): avoid printf of NULL argument. bz#2535

 * ssh(1), sshd(8): allow RekeyLimits larger than 4GB. bz#2521

 * ssh-keygen(1): sshd(8): fix several bugs in (unused) KRL signature
   support.

 * ssh(1), sshd(8): fix connections with peers that use the key
   exchange guess feature of the protocol. bz#2515

 * sshd(8): include remote port number in log messages. bz#2503

 * ssh(1): don't try to load SSHv1 private key when compiled without
   SSHv1 support. bz#2505

 * ssh-agent(1), ssh(1): fix incorrect error messages during key
   loading and signing errors. bz#2507

 * ssh-keygen(1): don't leave empty temporary files when performing
   known_hosts file edits when known_hosts doesn't exist.

 * sshd(8): correct packet format for tcpip-forward replies for
   requests that don't allocate a port bz#2509

 * ssh(1), sshd(8): fix possible hang on closed output. bz#2469

 * ssh(1): expand %i in ControlPath to UID. bz#2449

 * ssh(1), sshd(8): fix return type of openssh_RSA_verify. bz#2460

 * ssh(1), sshd(8): fix some option parsing memory leaks. bz#2182

 * ssh(1): add a some debug output before DNS resolution; it's a
   place where ssh could previously silently stall in cases of
   unresponsive DNS servers. bz#2433

 * ssh(1): remove spurious newline in visual hostkey. bz#2686

 * ssh(1): fix printing (ssh -G ...) of HostKeyAlgorithms=+...

 * ssh(1): fix expansion of HostkeyAlgorithms=+...

Documentation
-------------

 * ssh_config(5), sshd_config(5): update default algorithm lists to
   match current reality. bz#2527

 * ssh(1): mention -Q key-plain and -Q key-cert query options.
   bz#2455

 * sshd_config(8): more clearly describe what AuthorizedKeysFile=none
   does.

 * ssh_config(5): better document ExitOnForwardFailure. bz#2444

 * sshd(5): mention internal DH-GEX fallback groups in manual.
   bz#2302

 * sshd_config(5): better description for MaxSessions option.
   bz#2531

Portability
-----------

 * ssh(1), sftp-server(8), ssh-agent(1), sshd(8): Support Illumos/
   Solaris fine-grained privileges. Including a pre-auth privsep
   sandbox and several pledge() emulations. bz#2511

 * Renovate redhat/openssh.spec, removing deprecated options and
   syntax.

 * configure: allow --without-ssl-engine with --without-openssl

 * sshd(8): fix multiple authentication using S/Key. bz#2502

 * sshd(8): read back from libcrypto RAND_* before dropping
   privileges.  Avoids sandboxing violations with BoringSSL.

 * Fix name collision with system-provided glob(3) functions.
   bz#2463

 * Adapt Makefile to use ssh-keygen -A when generating host keys.
   bz#2459

 * configure: correct default value for --with-ssh1 bz#2457

 * configure: better detection of _res symbol bz#2259

 * support getrandom() syscall on Linux

/* $OpenBSD: sshconnect.c,v 1.271 2016/01/14 22:56:56 markus Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Code to connect to a remote host, and to perform the client side of the
 * login (authentication) dialog.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include <sys/param.h>	/* roundup */
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <netinet/in.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <paths.h>
#include <signal.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "xmalloc.h"
#include "ssh.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "uidswap.h"
#include "compat.h"
#include "key.h"
#include "sshconnect.h"
#include "hostfile.h"
#include "log.h"
#include "misc.h"
#include "readconf.h"
#include "atomicio.h"
#include "dns.h"
#include "monitor_fdpass.h"
#include "ssh2.h"
#include "version.h"
#include "authfile.h"
#include "ssherr.h"
#include "authfd.h"

char *client_version_string = NULL;
char *server_version_string = NULL;
Key *previous_host_key = NULL;

static int matching_host_key_dns = 0;

static pid_t proxy_command_pid = 0;

/* import */
extern Options options;
extern char *__progname;
extern uid_t original_real_uid;
extern uid_t original_effective_uid;

static int show_other_keys(struct hostkeys *, Key *);
static void warn_changed_key(Key *);

/* Expand a proxy command */
static char *
expand_proxy_command(const char *proxy_command, const char *user,
    const char *host, int port)
{
	char *tmp, *ret, strport[NI_MAXSERV];

	snprintf(strport, sizeof strport, "%d", port);
	xasprintf(&tmp, "exec %s", proxy_command);
	ret = percent_expand(tmp, "h", host, "p", strport,
	    "r", options.user, (char *)NULL);
	free(tmp);
	return ret;
}

/*
 * Connect to the given ssh server using a proxy command that passes a
 * a connected fd back to us.
 */
static int
ssh_proxy_fdpass_connect(const char *host, u_short port,
    const char *proxy_command)
{
	char *command_string;
	int sp[2], sock;
	pid_t pid;
	char *shell;

	if ((shell = getenv("SHELL")) == NULL)
		shell = _PATH_BSHELL;

	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) < 0)
		fatal("Could not create socketpair to communicate with "
		    "proxy dialer: %.100s", strerror(errno));

	command_string = expand_proxy_command(proxy_command, options.user,
	    host, port);
	debug("Executing proxy dialer command: %.500s", command_string);

	/* Fork and execute the proxy command. */
	if ((pid = fork()) == 0) {
		char *argv[10];

		/* Child.  Permanently give up superuser privileges. */
		permanently_drop_suid(original_real_uid);

		close(sp[1]);
		/* Redirect stdin and stdout. */
		if (sp[0] != 0) {
			if (dup2(sp[0], 0) < 0)
				perror("dup2 stdin");
		}
		if (sp[0] != 1) {
			if (dup2(sp[0], 1) < 0)
				perror("dup2 stdout");
		}
		if (sp[0] >= 2)
			close(sp[0]);

		/*
		 * Stderr is left as it is so that error messages get
		 * printed on the user's terminal.
		 */
		argv[0] = shell;
		argv[1] = "-c";
		argv[2] = command_string;
		argv[3] = NULL;

		/*
		 * Execute the proxy command.
		 * Note that we gave up any extra privileges above.
		 */
		execv(argv[0], argv);
		perror(argv[0]);
		exit(1);
	}
	/* Parent. */
	if (pid < 0)
		fatal("fork failed: %.100s", strerror(errno));
	close(sp[0]);
	free(command_string);

	if ((sock = mm_receive_fd(sp[1])) == -1)
		fatal("proxy dialer did not pass back a connection");
	close(sp[1]);

	while (waitpid(pid, NULL, 0) == -1)
		if (errno != EINTR)
			fatal("Couldn't wait for child: %s", strerror(errno));

	/* Set the connection file descriptors. */
	packet_set_connection(sock, sock);

	return 0;
}

/*
 * Connect to the given ssh server using a proxy command.
 */
static int
ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
{
	char *command_string;
	int pin[2], pout[2];
	pid_t pid;
	char *shell;

	if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
		shell = _PATH_BSHELL;

	/* Create pipes for communicating with the proxy. */
	if (pipe(pin) < 0 || pipe(pout) < 0)
		fatal("Could not create pipes to communicate with the proxy: %.100s",
		    strerror(errno));

	command_string = expand_proxy_command(proxy_command, options.user,
	    host, port);
	debug("Executing proxy command: %.500s", command_string);

	/* Fork and execute the proxy command. */
	if ((pid = fork()) == 0) {
		char *argv[10];

		/* Child.  Permanently give up superuser privileges. */
		permanently_drop_suid(original_real_uid);

		/* Redirect stdin and stdout. */
		close(pin[1]);
		if (pin[0] != 0) {
			if (dup2(pin[0], 0) < 0)
				perror("dup2 stdin");
			close(pin[0]);
		}
		close(pout[0]);
		if (dup2(pout[1], 1) < 0)
			perror("dup2 stdout");
		/* Cannot be 1 because pin allocated two descriptors. */
		close(pout[1]);

		/* Stderr is left as it is so that error messages get
		   printed on the user's terminal. */
		argv[0] = shell;
		argv[1] = "-c";
		argv[2] = command_string;
		argv[3] = NULL;

		/* Execute the proxy command.  Note that we gave up any
		   extra privileges above. */
		signal(SIGPIPE, SIG_DFL);
		execv(argv[0], argv);
		perror(argv[0]);
		exit(1);
	}
	/* Parent. */
	if (pid < 0)
		fatal("fork failed: %.100s", strerror(errno));
	else
		proxy_command_pid = pid; /* save pid to clean up later */

	/* Close child side of the descriptors. */
	close(pin[0]);
	close(pout[1]);

	/* Free the command name. */
	free(command_string);

	/* Set the connection file descriptors. */
	packet_set_connection(pout[0], pin[1]);

	/* Indicate OK return */
	return 0;
}

void
ssh_kill_proxy_command(void)
{
	/*
	 * Send SIGHUP to proxy command if used. We don't wait() in
	 * case it hangs and instead rely on init to reap the child
	 */
	if (proxy_command_pid > 1)
		kill(proxy_command_pid, SIGHUP);
}

/*
 * Creates a (possibly privileged) socket for use as the ssh connection.
 */
static int
ssh_create_socket(int privileged, struct addrinfo *ai)
{
	int sock, r, gaierr;
	struct addrinfo hints, *res = NULL;

	sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
	if (sock < 0) {
		error("socket: %s", strerror(errno));
		return -1;
	}
	fcntl(sock, F_SETFD, FD_CLOEXEC);

	/* Bind the socket to an alternative local IP address */
	if (options.bind_address == NULL && !privileged)
		return sock;

	if (options.bind_address) {
		memset(&hints, 0, sizeof(hints));
		hints.ai_family = ai->ai_family;
		hints.ai_socktype = ai->ai_socktype;
		hints.ai_protocol = ai->ai_protocol;
		hints.ai_flags = AI_PASSIVE;
		gaierr = getaddrinfo(options.bind_address, NULL, &hints, &res);
		if (gaierr) {
			error("getaddrinfo: %s: %s", options.bind_address,
			    ssh_gai_strerror(gaierr));
			close(sock);
			return -1;
		}
	}
	/*
	 * If we are running as root and want to connect to a privileged
	 * port, bind our own socket to a privileged port.
	 */
	if (privileged) {
		PRIV_START;
		r = bindresvport_sa(sock, res ? res->ai_addr : NULL);
		PRIV_END;
		if (r < 0) {
			error("bindresvport_sa: af=%d %s", ai->ai_family,
			    strerror(errno));
			goto fail;
		}
	} else {
		if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
			error("bind: %s: %s", options.bind_address,
			    strerror(errno));
 fail:
			close(sock);
			freeaddrinfo(res);
			return -1;
		}
	}
	if (res != NULL)
		freeaddrinfo(res);
	return sock;
}

static int
timeout_connect(int sockfd, const struct sockaddr *serv_addr,
    socklen_t addrlen, int *timeoutp)
{
	fd_set *fdset;
	struct timeval tv, t_start;
	socklen_t optlen;
	int optval, rc, result = -1;

	gettimeofday(&t_start, NULL);

	if (*timeoutp <= 0) {
		result = connect(sockfd, serv_addr, addrlen);
		goto done;
	}

	set_nonblock(sockfd);
	rc = connect(sockfd, serv_addr, addrlen);
	if (rc == 0) {
		unset_nonblock(sockfd);
		result = 0;
		goto done;
	}
	if (errno != EINPROGRESS) {
		result = -1;
		goto done;
	}

	fdset = xcalloc(howmany(sockfd + 1, NFDBITS),
	    sizeof(fd_mask));
	FD_SET(sockfd, fdset);
	ms_to_timeval(&tv, *timeoutp);

	for (;;) {
		rc = select(sockfd + 1, NULL, fdset, NULL, &tv);
		if (rc != -1 || errno != EINTR)
			break;
	}

	switch (rc) {
	case 0:
		/* Timed out */
		errno = ETIMEDOUT;
		break;
	case -1:
		/* Select error */
		debug("select: %s", strerror(errno));
		break;
	case 1:
		/* Completed or failed */
		optval = 0;
		optlen = sizeof(optval);
		if (getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &optval,
		    &optlen) == -1) {
			debug("getsockopt: %s", strerror(errno));
			break;
		}
		if (optval != 0) {
			errno = optval;
			break;
		}
		result = 0;
		unset_nonblock(sockfd);
		break;
	default:
		/* Should not occur */
		fatal("Bogus return (%d) from select()", rc);
	}

	free(fdset);

 done:
 	if (result == 0 && *timeoutp > 0) {
		ms_subtract_diff(&t_start, timeoutp);
		if (*timeoutp <= 0) {
			errno = ETIMEDOUT;
			result = -1;
		}
	}

	return (result);
}

/*
 * Opens a TCP/IP connection to the remote server on the given host.
 * The address of the remote host will be returned in hostaddr.
 * If port is 0, the default port will be used.  If needpriv is true,
 * a privileged port will be allocated to make the connection.
 * This requires super-user privileges if needpriv is true.
 * Connection_attempts specifies the maximum number of tries (one per
 * second).  If proxy_command is non-NULL, it specifies the command (with %h
 * and %p substituted for host and port, respectively) to use to contact
 * the daemon.
 */
static int
ssh_connect_direct(const char *host, struct addrinfo *aitop,
    struct sockaddr_storage *hostaddr, u_short port, int family,
    int connection_attempts, int *timeout_ms, int want_keepalive, int needpriv)
{
	int on = 1;
	int sock = -1, attempt;
	char ntop[NI_MAXHOST], strport[NI_MAXSERV];
	struct addrinfo *ai;

	debug2("%s: needpriv %d", __func__, needpriv);
	memset(ntop, 0, sizeof(ntop));
	memset(strport, 0, sizeof(strport));

	for (attempt = 0; attempt < connection_attempts; attempt++) {
		if (attempt > 0) {
			/* Sleep a moment before retrying. */
			sleep(1);
			debug("Trying again...");
		}
		/*
		 * Loop through addresses for this host, and try each one in
		 * sequence until the connection succeeds.
		 */
		for (ai = aitop; ai; ai = ai->ai_next) {
			if (ai->ai_family != AF_INET &&
			    ai->ai_family != AF_INET6)
				continue;
			if (getnameinfo(ai->ai_addr, ai->ai_addrlen,
			    ntop, sizeof(ntop), strport, sizeof(strport),
			    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
				error("%s: getnameinfo failed", __func__);
				continue;
			}
			debug("Connecting to %.200s [%.100s] port %s.",
				host, ntop, strport);

			/* Create a socket for connecting. */
			sock = ssh_create_socket(needpriv, ai);
			if (sock < 0)
				/* Any error is already output */
				continue;

			if (timeout_connect(sock, ai->ai_addr, ai->ai_addrlen,
			    timeout_ms) >= 0) {
				/* Successful connection. */
				memcpy(hostaddr, ai->ai_addr, ai->ai_addrlen);
				break;
			} else {
				debug("connect to address %s port %s: %s",
				    ntop, strport, strerror(errno));
				close(sock);
				sock = -1;
			}
		}
		if (sock != -1)
			break;	/* Successful connection. */
	}

	/* Return failure if we didn't get a successful connection. */
	if (sock == -1) {
		error("ssh: connect to host %s port %s: %s",
		    host, strport, strerror(errno));
		return (-1);
	}

	debug("Connection established.");

	/* Set SO_KEEPALIVE if requested. */
	if (want_keepalive &&
	    setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
	    sizeof(on)) < 0)
		error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));

	/* Set the connection. */
	packet_set_connection(sock, sock);

	return 0;
}

int
ssh_connect(const char *host, struct addrinfo *addrs,
    struct sockaddr_storage *hostaddr, u_short port, int family,
    int connection_attempts, int *timeout_ms, int want_keepalive, int needpriv)
{
	if (options.proxy_command == NULL) {
		return ssh_connect_direct(host, addrs, hostaddr, port, family,
		    connection_attempts, timeout_ms, want_keepalive, needpriv);
	} else if (strcmp(options.proxy_command, "-") == 0) {
		packet_set_connection(STDIN_FILENO, STDOUT_FILENO);
		return 0; /* Always succeeds */
	} else if (options.proxy_use_fdpass) {
		return ssh_proxy_fdpass_connect(host, port,
		    options.proxy_command);
	}
	return ssh_proxy_connect(host, port, options.proxy_command);
}

static void
send_client_banner(int connection_out, int minor1)
{
	/* Send our own protocol version identification. */
	if (compat20) {
		xasprintf(&client_version_string, "SSH-%d.%d-%.100s\r\n",
		    PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION);
	} else {
		xasprintf(&client_version_string, "SSH-%d.%d-%.100s\n",
		    PROTOCOL_MAJOR_1, minor1, SSH_VERSION);
	}
	if (atomicio(vwrite, connection_out, client_version_string,
	    strlen(client_version_string)) != strlen(client_version_string))
		fatal("write: %.100s", strerror(errno));
	chop(client_version_string);
	debug("Local version string %.100s", client_version_string);
}

/*
 * Waits for the server identification string, and sends our own
 * identification string.
 */
void
ssh_exchange_identification(int timeout_ms)
{
	char buf[256], remote_version[256];	/* must be same size! */
	int remote_major, remote_minor, mismatch;
	int connection_in = packet_get_connection_in();
	int connection_out = packet_get_connection_out();
	int minor1 = PROTOCOL_MINOR_1, client_banner_sent = 0;
	u_int i, n;
	size_t len;
	int fdsetsz, remaining, rc;
	struct timeval t_start, t_remaining;
	fd_set *fdset;

	fdsetsz = howmany(connection_in + 1, NFDBITS) * sizeof(fd_mask);
	fdset = xcalloc(1, fdsetsz);

	/*
	 * If we are SSH2-only then we can send the banner immediately and
	 * save a round-trip.
	 */
	if (options.protocol == SSH_PROTO_2) {
		enable_compat20();
		send_client_banner(connection_out, 0);
		client_banner_sent = 1;
	}

	/* Read other side's version identification. */
	remaining = timeout_ms;
	for (n = 0;;) {
		for (i = 0; i < sizeof(buf) - 1; i++) {
			if (timeout_ms > 0) {
				gettimeofday(&t_start, NULL);
				ms_to_timeval(&t_remaining, remaining);
				FD_SET(connection_in, fdset);
				rc = select(connection_in + 1, fdset, NULL,
				    fdset, &t_remaining);
				ms_subtract_diff(&t_start, &remaining);
				if (rc == 0 || remaining <= 0)
					fatal("Connection timed out during "
					    "banner exchange");
				if (rc == -1) {
					if (errno == EINTR)
						continue;
					fatal("ssh_exchange_identification: "
					    "select: %s", strerror(errno));
				}
			}

			len = atomicio(read, connection_in, &buf[i], 1);

			if (len != 1 && errno == EPIPE)
				fatal("ssh_exchange_identification: "
				    "Connection closed by remote host");
			else if (len != 1)
				fatal("ssh_exchange_identification: "
				    "read: %.100s", strerror(errno));
			if (buf[i] == '\r') {
				buf[i] = '\n';
				buf[i + 1] = 0;
				continue;		/**XXX wait for \n */
			}
			if (buf[i] == '\n') {
				buf[i + 1] = 0;
				break;
			}
			if (++n > 65536)
				fatal("ssh_exchange_identification: "
				    "No banner received");
		}
		buf[sizeof(buf) - 1] = 0;
		if (strncmp(buf, "SSH-", 4) == 0)
			break;
		debug("ssh_exchange_identification: %s", buf);
	}
	server_version_string = xstrdup(buf);
	free(fdset);

	/*
	 * Check that the versions match.  In future this might accept
	 * several versions and set appropriate flags to handle them.
	 */
	if (sscanf(server_version_string, "SSH-%d.%d-%[^\n]\n",
	    &remote_major, &remote_minor, remote_version) != 3)
		fatal("Bad remote protocol version identification: '%.100s'", buf);
	debug("Remote protocol version %d.%d, remote software version %.100s",
	    remote_major, remote_minor, remote_version);

	active_state->compat = compat_datafellows(remote_version);
	mismatch = 0;

	switch (remote_major) {
	case 1:
		if (remote_minor == 99 &&
		    (options.protocol & SSH_PROTO_2) &&
		    !(options.protocol & SSH_PROTO_1_PREFERRED)) {
			enable_compat20();
			break;
		}
		if (!(options.protocol & SSH_PROTO_1)) {
			mismatch = 1;
			break;
		}
		if (remote_minor < 3) {
			fatal("Remote machine has too old SSH software version.");
		} else if (remote_minor == 3 || remote_minor == 4) {
			/* We speak 1.3, too. */
			enable_compat13();
			minor1 = 3;
			if (options.forward_agent) {
				logit("Agent forwarding disabled for protocol 1.3");
				options.forward_agent = 0;
			}
		}
		break;
	case 2:
		if (options.protocol & SSH_PROTO_2) {
			enable_compat20();
			break;
		}
		/* FALLTHROUGH */
	default:
		mismatch = 1;
		break;
	}
	if (mismatch)
		fatal("Protocol major versions differ: %d vs. %d",
		    (options.protocol & SSH_PROTO_2) ? PROTOCOL_MAJOR_2 : PROTOCOL_MAJOR_1,
		    remote_major);
	if ((datafellows & SSH_BUG_DERIVEKEY) != 0)
		fatal("Server version \"%.100s\" uses unsafe key agreement; "
		    "refusing connection", remote_version);
	if ((datafellows & SSH_BUG_RSASIGMD5) != 0)
		logit("Server version \"%.100s\" uses unsafe RSA signature "
		    "scheme; disabling use of RSA keys", remote_version);
	if (!client_banner_sent)
		send_client_banner(connection_out, minor1);
	chop(server_version_string);
}

/* defaults to 'no' */
static int
confirm(const char *prompt)
{
	const char *msg, *again = "Please type 'yes' or 'no': ";
	char *p;
	int ret = -1;

	if (options.batch_mode)
		return 0;
	for (msg = prompt;;msg = again) {
		p = read_passphrase(msg, RP_ECHO);
		if (p == NULL ||
		    (p[0] == '\0') || (p[0] == '\n') ||
		    strncasecmp(p, "no", 2) == 0)
			ret = 0;
		if (p && strncasecmp(p, "yes", 3) == 0)
			ret = 1;
		free(p);
		if (ret != -1)
			return ret;
	}
}

static int
check_host_cert(const char *host, const Key *host_key)
{
	const char *reason;

	if (key_cert_check_authority(host_key, 1, 0, host, &reason) != 0) {
		error("%s", reason);
		return 0;
	}
	if (buffer_len(host_key->cert->critical) != 0) {
		error("Certificate for %s contains unsupported "
		    "critical options(s)", host);
		return 0;
	}
	return 1;
}

static int
sockaddr_is_local(struct sockaddr *hostaddr)
{
	switch (hostaddr->sa_family) {
	case AF_INET:
		return (ntohl(((struct sockaddr_in *)hostaddr)->
		    sin_addr.s_addr) >> 24) == IN_LOOPBACKNET;
	case AF_INET6:
		return IN6_IS_ADDR_LOOPBACK(
		    &(((struct sockaddr_in6 *)hostaddr)->sin6_addr));
	default:
		return 0;
	}
}

/*
 * Prepare the hostname and ip address strings that are used to lookup
 * host keys in known_hosts files. These may have a port number appended.
 */
void
get_hostfile_hostname_ipaddr(char *hostname, struct sockaddr *hostaddr,
    u_short port, char **hostfile_hostname, char **hostfile_ipaddr)
{
	char ntop[NI_MAXHOST];

	/*
	 * We don't have the remote ip-address for connections
	 * using a proxy command
	 */
	if (hostfile_ipaddr != NULL) {
		if (options.proxy_command == NULL) {
			if (getnameinfo(hostaddr, hostaddr->sa_len,
			    ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST) != 0)
			fatal("%s: getnameinfo failed", __func__);
			*hostfile_ipaddr = put_host_port(ntop, port);
		} else {
			*hostfile_ipaddr = xstrdup("<no hostip for proxy "
			    "command>");
		}
	}

	/*
	 * Allow the user to record the key under a different name or
	 * differentiate a non-standard port.  This is useful for ssh
	 * tunneling over forwarded connections or if you run multiple
	 * sshd's on different ports on the same machine.
	 */
	if (hostfile_hostname != NULL) {
		if (options.host_key_alias != NULL) {
			*hostfile_hostname = xstrdup(options.host_key_alias);
			debug("using hostkeyalias: %s", *hostfile_hostname);
		} else {
			*hostfile_hostname = put_host_port(hostname, port);
		}
	}
}

/*
 * check whether the supplied host key is valid, return -1 if the key
 * is not valid. user_hostfile[0] will not be updated if 'readonly' is true.
 */
#define RDRW	0
#define RDONLY	1
#define ROQUIET	2
static int
check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
    Key *host_key, int readonly,
    char **user_hostfiles, u_int num_user_hostfiles,
    char **system_hostfiles, u_int num_system_hostfiles)
{
	HostStatus host_status;
	HostStatus ip_status;
	Key *raw_key = NULL;
	char *ip = NULL, *host = NULL;
	char hostline[1000], *hostp, *fp, *ra;
	char msg[1024];
	const char *type;
	const struct hostkey_entry *host_found, *ip_found;
	int len, cancelled_forwarding = 0;
	int local = sockaddr_is_local(hostaddr);
	int r, want_cert = key_is_cert(host_key), host_ip_differ = 0;
	int hostkey_trusted = 0; /* Known or explicitly accepted by user */
	struct hostkeys *host_hostkeys, *ip_hostkeys;
	u_int i;

	/*
	 * Force accepting of the host key for loopback/localhost. The
	 * problem is that if the home directory is NFS-mounted to multiple
	 * machines, localhost will refer to a different machine in each of
	 * them, and the user will get bogus HOST_CHANGED warnings.  This
	 * essentially disables host authentication for localhost; however,
	 * this is probably not a real problem.
	 */
	if (options.no_host_authentication_for_localhost == 1 && local &&
	    options.host_key_alias == NULL) {
		debug("Forcing accepting of host key for "
		    "loopback/localhost.");
		return 0;
	}

	/*
	 * Prepare the hostname and address strings used for hostkey lookup.
	 * In some cases, these will have a port number appended.
	 */
	get_hostfile_hostname_ipaddr(hostname, hostaddr, port, &host, &ip);

	/*
	 * Turn off check_host_ip if the connection is to localhost, via proxy
	 * command or if we don't have a hostname to compare with
	 */
	if (options.check_host_ip && (local ||
	    strcmp(hostname, ip) == 0 || options.proxy_command != NULL))
		options.check_host_ip = 0;

	host_hostkeys = init_hostkeys();
	for (i = 0; i < num_user_hostfiles; i++)
		load_hostkeys(host_hostkeys, host, user_hostfiles[i]);
	for (i = 0; i < num_system_hostfiles; i++)
		load_hostkeys(host_hostkeys, host, system_hostfiles[i]);

	ip_hostkeys = NULL;
	if (!want_cert && options.check_host_ip) {
		ip_hostkeys = init_hostkeys();
		for (i = 0; i < num_user_hostfiles; i++)
			load_hostkeys(ip_hostkeys, ip, user_hostfiles[i]);
		for (i = 0; i < num_system_hostfiles; i++)
			load_hostkeys(ip_hostkeys, ip, system_hostfiles[i]);
	}

 retry:
	/* Reload these as they may have changed on cert->key downgrade */
	want_cert = key_is_cert(host_key);
	type = key_type(host_key);

	/*
	 * Check if the host key is present in the user's list of known
	 * hosts or in the systemwide list.
	 */
	host_status = check_key_in_hostkeys(host_hostkeys, host_key,
	    &host_found);

	/*
	 * Also perform check for the ip address, skip the check if we are
	 * localhost, looking for a certificate, or the hostname was an ip
	 * address to begin with.
	 */
	if (!want_cert && ip_hostkeys != NULL) {
		ip_status = check_key_in_hostkeys(ip_hostkeys, host_key,
		    &ip_found);
		if (host_status == HOST_CHANGED &&
		    (ip_status != HOST_CHANGED || 
		    (ip_found != NULL &&
		    !key_equal(ip_found->key, host_found->key))))
			host_ip_differ = 1;
	} else
		ip_status = host_status;

	switch (host_status) {
	case HOST_OK:
		/* The host is known and the key matches. */
		debug("Host '%.200s' is known and matches the %s host %s.",
		    host, type, want_cert ? "certificate" : "key");
		debug("Found %s in %s:%lu", want_cert ? "CA key" : "key",
		    host_found->file, host_found->line);
		if (want_cert && !check_host_cert(hostname, host_key))
			goto fail;
		if (options.check_host_ip && ip_status == HOST_NEW) {
			if (readonly || want_cert)
				logit("%s host key for IP address "
				    "'%.128s' not in list of known hosts.",
				    type, ip);
			else if (!add_host_to_hostfile(user_hostfiles[0], ip,
			    host_key, options.hash_known_hosts))
				logit("Failed to add the %s host key for IP "
				    "address '%.128s' to the list of known "
				    "hosts (%.500s).", type, ip,
				    user_hostfiles[0]);
			else
				logit("Warning: Permanently added the %s host "
				    "key for IP address '%.128s' to the list "
				    "of known hosts.", type, ip);
		} else if (options.visual_host_key) {
			fp = sshkey_fingerprint(host_key,
			    options.fingerprint_hash, SSH_FP_DEFAULT);
			ra = sshkey_fingerprint(host_key,
			    options.fingerprint_hash, SSH_FP_RANDOMART);
			if (fp == NULL || ra == NULL)
				fatal("%s: sshkey_fingerprint fail", __func__);
			logit("Host key fingerprint is %s\n%s", fp, ra);
			free(ra);
			free(fp);
		}
		hostkey_trusted = 1;
		break;
	case HOST_NEW:
		if (options.host_key_alias == NULL && port != 0 &&
		    port != SSH_DEFAULT_PORT) {
			debug("checking without port identifier");
			if (check_host_key(hostname, hostaddr, 0, host_key,
			    ROQUIET, user_hostfiles, num_user_hostfiles,
			    system_hostfiles, num_system_hostfiles) == 0) {
				debug("found matching key w/out port");
				break;
			}
		}
		if (readonly || want_cert)
			goto fail;
		/* The host is new. */
		if (options.strict_host_key_checking == 1) {
			/*
			 * User has requested strict host key checking.  We
			 * will not add the host key automatically.  The only
			 * alternative left is to abort.
			 */
			error("No %s host key is known for %.200s and you "
			    "have requested strict checking.", type, host);
			goto fail;
		} else if (options.strict_host_key_checking == 2) {
			char msg1[1024], msg2[1024];

			if (show_other_keys(host_hostkeys, host_key))
				snprintf(msg1, sizeof(msg1),
				    "\nbut keys of different type are already"
				    " known for this host.");
			else
				snprintf(msg1, sizeof(msg1), ".");
			/* The default */
			fp = sshkey_fingerprint(host_key,
			    options.fingerprint_hash, SSH_FP_DEFAULT);
			ra = sshkey_fingerprint(host_key,
			    options.fingerprint_hash, SSH_FP_RANDOMART);
			if (fp == NULL || ra == NULL)
				fatal("%s: sshkey_fingerprint fail", __func__);
			msg2[0] = '\0';
			if (options.verify_host_key_dns) {
				if (matching_host_key_dns)
					snprintf(msg2, sizeof(msg2),
					    "Matching host key fingerprint"
					    " found in DNS.\n");
				else
					snprintf(msg2, sizeof(msg2),
					    "No matching host key fingerprint"
					    " found in DNS.\n");
			}
			snprintf(msg, sizeof(msg),
			    "The authenticity of host '%.200s (%s)' can't be "
			    "established%s\n"
			    "%s key fingerprint is %s.%s%s\n%s"
			    "Are you sure you want to continue connecting "
			    "(yes/no)? ",
			    host, ip, msg1, type, fp,
			    options.visual_host_key ? "\n" : "",
			    options.visual_host_key ? ra : "",
			    msg2);
			free(ra);
			free(fp);
			if (!confirm(msg))
				goto fail;
			hostkey_trusted = 1; /* user explicitly confirmed */
		}
		/*
		 * If not in strict mode, add the key automatically to the
		 * local known_hosts file.
		 */
		if (options.check_host_ip && ip_status == HOST_NEW) {
			snprintf(hostline, sizeof(hostline), "%s,%s", host, ip);
			hostp = hostline;
			if (options.hash_known_hosts) {
				/* Add hash of host and IP separately */
				r = add_host_to_hostfile(user_hostfiles[0],
				    host, host_key, options.hash_known_hosts) &&
				    add_host_to_hostfile(user_hostfiles[0], ip,
				    host_key, options.hash_known_hosts);
			} else {
				/* Add unhashed "host,ip" */
				r = add_host_to_hostfile(user_hostfiles[0],
				    hostline, host_key,
				    options.hash_known_hosts);
			}
		} else {
			r = add_host_to_hostfile(user_hostfiles[0], host,
			    host_key, options.hash_known_hosts);
			hostp = host;
		}

		if (!r)
			logit("Failed to add the host to the list of known "
			    "hosts (%.500s).", user_hostfiles[0]);
		else
			logit("Warning: Permanently added '%.200s' (%s) to the "
			    "list of known hosts.", hostp, type);
		break;
	case HOST_REVOKED:
		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
		error("@       WARNING: REVOKED HOST KEY DETECTED!               @");
		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
		error("The %s host key for %s is marked as revoked.", type, host);
		error("This could mean that a stolen key is being used to");
		error("impersonate this host.");

		/*
		 * If strict host key checking is in use, the user will have
		 * to edit the key manually and we can only abort.
		 */
		if (options.strict_host_key_checking) {
			error("%s host key for %.200s was revoked and you have "
			    "requested strict checking.", type, host);
			goto fail;
		}
		goto continue_unsafe;

	case HOST_CHANGED:
		if (want_cert) {
			/*
			 * This is only a debug() since it is valid to have
			 * CAs with wildcard DNS matches that don't match
			 * all hosts that one might visit.
			 */
			debug("Host certificate authority does not "
			    "match %s in %s:%lu", CA_MARKER,
			    host_found->file, host_found->line);
			goto fail;
		}
		if (readonly == ROQUIET)
			goto fail;
		if (options.check_host_ip && host_ip_differ) {
			char *key_msg;
			if (ip_status == HOST_NEW)
				key_msg = "is unknown";
			else if (ip_status == HOST_OK)
				key_msg = "is unchanged";
			else
				key_msg = "has a different value";
			error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
			error("@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @");
			error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
			error("The %s host key for %s has changed,", type, host);
			error("and the key for the corresponding IP address %s", ip);
			error("%s. This could either mean that", key_msg);
			error("DNS SPOOFING is happening or the IP address for the host");
			error("and its host key have changed at the same time.");
			if (ip_status != HOST_NEW)
				error("Offending key for IP in %s:%lu",
				    ip_found->file, ip_found->line);
		}
		/* The host key has changed. */
		warn_changed_key(host_key);
		error("Add correct host key in %.100s to get rid of this message.",
		    user_hostfiles[0]);
		error("Offending %s key in %s:%lu", key_type(host_found->key),
		    host_found->file, host_found->line);

		/*
		 * If strict host key checking is in use, the user will have
		 * to edit the key manually and we can only abort.
		 */
		if (options.strict_host_key_checking) {
			error("%s host key for %.200s has changed and you have "
			    "requested strict checking.", type, host);
			goto fail;
		}

 continue_unsafe:
		/*
		 * If strict host key checking has not been requested, allow
		 * the connection but without MITM-able authentication or
		 * forwarding.
		 */
		if (options.password_authentication) {
			error("Password authentication is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.password_authentication = 0;
			cancelled_forwarding = 1;
		}
		if (options.kbd_interactive_authentication) {
			error("Keyboard-interactive authentication is disabled"
			    " to avoid man-in-the-middle attacks.");
			options.kbd_interactive_authentication = 0;
			options.challenge_response_authentication = 0;
			cancelled_forwarding = 1;
		}
		if (options.challenge_response_authentication) {
			error("Challenge/response authentication is disabled"
			    " to avoid man-in-the-middle attacks.");
			options.challenge_response_authentication = 0;
			cancelled_forwarding = 1;
		}
		if (options.forward_agent) {
			error("Agent forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.forward_agent = 0;
			cancelled_forwarding = 1;
		}
		if (options.forward_x11) {
			error("X11 forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.forward_x11 = 0;
			cancelled_forwarding = 1;
		}
		if (options.num_local_forwards > 0 ||
		    options.num_remote_forwards > 0) {
			error("Port forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.num_local_forwards =
			    options.num_remote_forwards = 0;
			cancelled_forwarding = 1;
		}
		if (options.tun_open != SSH_TUNMODE_NO) {
			error("Tunnel forwarding is disabled to avoid "
			    "man-in-the-middle attacks.");
			options.tun_open = SSH_TUNMODE_NO;
			cancelled_forwarding = 1;
		}
		if (options.exit_on_forward_failure && cancelled_forwarding)
			fatal("Error: forwarding disabled due to host key "
			    "check failure");
		
		/*
		 * XXX Should permit the user to change to use the new id.
		 * This could be done by converting the host key to an
		 * identifying sentence, tell that the host identifies itself
		 * by that sentence, and ask the user if he/she wishes to
		 * accept the authentication.
		 */
		break;
	case HOST_FOUND:
		fatal("internal error");
		break;
	}

	if (options.check_host_ip && host_status != HOST_CHANGED &&
	    ip_status == HOST_CHANGED) {
		snprintf(msg, sizeof(msg),
		    "Warning: the %s host key for '%.200s' "
		    "differs from the key for the IP address '%.128s'"
		    "\nOffending key for IP in %s:%lu",
		    type, host, ip, ip_found->file, ip_found->line);
		if (host_status == HOST_OK) {
			len = strlen(msg);
			snprintf(msg + len, sizeof(msg) - len,
			    "\nMatching host key in %s:%lu",
			    host_found->file, host_found->line);
		}
		if (options.strict_host_key_checking == 1) {
			logit("%s", msg);
			error("Exiting, you have requested strict checking.");
			goto fail;
		} else if (options.strict_host_key_checking == 2) {
			strlcat(msg, "\nAre you sure you want "
			    "to continue connecting (yes/no)? ", sizeof(msg));
			if (!confirm(msg))
				goto fail;
		} else {
			logit("%s", msg);
		}
	}

	if (!hostkey_trusted && options.update_hostkeys) {
		debug("%s: hostkey not known or explicitly trusted: "
		    "disabling UpdateHostkeys", __func__);
		options.update_hostkeys = 0;
	}

	free(ip);
	free(host);
	if (host_hostkeys != NULL)
		free_hostkeys(host_hostkeys);
	if (ip_hostkeys != NULL)
		free_hostkeys(ip_hostkeys);
	return 0;

fail:
	if (want_cert && host_status != HOST_REVOKED) {
		/*
		 * No matching certificate. Downgrade cert to raw key and
		 * search normally.
		 */
		debug("No matching CA found. Retry with plain key");
		raw_key = key_from_private(host_key);
		if (key_drop_cert(raw_key) != 0)
			fatal("Couldn't drop certificate");
		host_key = raw_key;
		goto retry;
	}
	if (raw_key != NULL)
		key_free(raw_key);
	free(ip);
	free(host);
	if (host_hostkeys != NULL)
		free_hostkeys(host_hostkeys);
	if (ip_hostkeys != NULL)
		free_hostkeys(ip_hostkeys);
	return -1;
}

/* returns 0 if key verifies or -1 if key does NOT verify */
int
verify_host_key(char *host, struct sockaddr *hostaddr, Key *host_key)
{
	u_int i;
	int r = -1, flags = 0;
	char valid[64], *fp = NULL, *cafp = NULL;
	struct sshkey *plain = NULL;

	if ((fp = sshkey_fingerprint(host_key,
	    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
		error("%s: fingerprint host key: %s", __func__, ssh_err(r));
		r = -1;
		goto out;
	}

	if (sshkey_is_cert(host_key)) {
		if ((cafp = sshkey_fingerprint(host_key->cert->signature_key,
		    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
			error("%s: fingerprint CA key: %s",
			    __func__, ssh_err(r));
			r = -1;
			goto out;
		}
		sshkey_format_cert_validity(host_key->cert,
		    valid, sizeof(valid));
		debug("Server host certificate: %s %s, serial %llu "
		    "ID \"%s\" CA %s %s valid %s",
		    sshkey_ssh_name(host_key), fp,
		    (unsigned long long)host_key->cert->serial,
		    host_key->cert->key_id,
		    sshkey_ssh_name(host_key->cert->signature_key), cafp,
		    valid);
		for (i = 0; i < host_key->cert->nprincipals; i++) {
			debug2("Server host certificate hostname: %s",
			    host_key->cert->principals[i]);
		}
	} else {
		debug("Server host key: %s %s", compat20 ?
		    sshkey_ssh_name(host_key) : sshkey_type(host_key), fp);
	}

	if (sshkey_equal(previous_host_key, host_key)) {
		debug2("%s: server host key %s %s matches cached key",
		    __func__, sshkey_type(host_key), fp);
		r = 0;
		goto out;
	}

	/* Check in RevokedHostKeys file if specified */
	if (options.revoked_host_keys != NULL) {
		r = sshkey_check_revoked(host_key, options.revoked_host_keys);
		switch (r) {
		case 0:
			break; /* not revoked */
		case SSH_ERR_KEY_REVOKED:
			error("Host key %s %s revoked by file %s",
			    sshkey_type(host_key), fp,
			    options.revoked_host_keys);
			r = -1;
			goto out;
		default:
			error("Error checking host key %s %s in "
			    "revoked keys file %s: %s", sshkey_type(host_key),
			    fp, options.revoked_host_keys, ssh_err(r));
			r = -1;
			goto out;
		}
	}

	if (options.verify_host_key_dns) {
		/*
		 * XXX certs are not yet supported for DNS, so downgrade
		 * them and try the plain key.
		 */
		if ((r = sshkey_from_private(host_key, &plain)) != 0)
			goto out;
		if (sshkey_is_cert(plain))
			sshkey_drop_cert(plain);
		if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) {
			if (flags & DNS_VERIFY_FOUND) {
				if (options.verify_host_key_dns == 1 &&
				    flags & DNS_VERIFY_MATCH &&
				    flags & DNS_VERIFY_SECURE) {
					r = 0;
					goto out;
				}
				if (flags & DNS_VERIFY_MATCH) {
					matching_host_key_dns = 1;
				} else {
					warn_changed_key(plain);
					error("Update the SSHFP RR in DNS "
					    "with the new host key to get rid "
					    "of this message.");
				}
			}
		}
	}
	r = check_host_key(host, hostaddr, options.port, host_key, RDRW,
	    options.user_hostfiles, options.num_user_hostfiles,
	    options.system_hostfiles, options.num_system_hostfiles);

out:
	sshkey_free(plain);
	free(fp);
	free(cafp);
	if (r == 0 && host_key != NULL) {
		key_free(previous_host_key);
		previous_host_key = key_from_private(host_key);
	}

	return r;
}

/*
 * Starts a dialog with the server, and authenticates the current user on the
 * server.  This does not need any extra privileges.  The basic connection
 * to the server must already have been established before this is called.
 * If login fails, this function prints an error and never returns.
 * This function does not require super-user privileges.
 */
void
ssh_login(Sensitive *sensitive, const char *orighost,
    struct sockaddr *hostaddr, u_short port, struct passwd *pw, int timeout_ms)
{
	char *host;
	char *server_user, *local_user;

	local_user = xstrdup(pw->pw_name);
	server_user = options.user ? options.user : local_user;

	/* Convert the user-supplied hostname into all lowercase. */
	host = xstrdup(orighost);
	lowercase(host);

	/* Exchange protocol version identification strings with the server. */
	ssh_exchange_identification(timeout_ms);

	/* Put the connection into non-blocking mode. */
	packet_set_nonblocking();

	/* key exchange */
	/* authenticate user */
	debug("Authenticating to %s:%d as '%s'", host, port, server_user);
	if (compat20) {
		ssh_kex2(host, hostaddr, port);
		ssh_userauth2(local_user, server_user, host, sensitive);
	} else {
#ifdef WITH_SSH1
		ssh_kex(host, hostaddr);
		ssh_userauth1(local_user, server_user, host, sensitive);
#else
		fatal("ssh1 is not supported");
#endif
	}
	free(local_user);
}

void
ssh_put_password(char *password)
{
	int size;
	char *padded;

	if (datafellows & SSH_BUG_PASSWORDPAD) {
		packet_put_cstring(password);
		return;
	}
	size = roundup(strlen(password) + 1, 32);
	padded = xcalloc(1, size);
	strlcpy(padded, password, size);
	packet_put_string(padded, size);
	explicit_bzero(padded, size);
	free(padded);
}

/* print all known host keys for a given host, but skip keys of given type */
static int
show_other_keys(struct hostkeys *hostkeys, Key *key)
{
	int type[] = {
		KEY_RSA1,
		KEY_RSA,
		KEY_DSA,
		KEY_ECDSA,
		KEY_ED25519,
		-1
	};
	int i, ret = 0;
	char *fp, *ra;
	const struct hostkey_entry *found;

	for (i = 0; type[i] != -1; i++) {
		if (type[i] == key->type)
			continue;
		if (!lookup_key_in_hostkeys_by_type(hostkeys, type[i], &found))
			continue;
		fp = sshkey_fingerprint(found->key,
		    options.fingerprint_hash, SSH_FP_DEFAULT);
		ra = sshkey_fingerprint(found->key,
		    options.fingerprint_hash, SSH_FP_RANDOMART);
		if (fp == NULL || ra == NULL)
			fatal("%s: sshkey_fingerprint fail", __func__);
		logit("WARNING: %s key found for host %s\n"
		    "in %s:%lu\n"
		    "%s key fingerprint %s.",
		    key_type(found->key),
		    found->host, found->file, found->line,
		    key_type(found->key), fp);
		if (options.visual_host_key)
			logit("%s", ra);
		free(ra);
		free(fp);
		ret = 1;
	}
	return ret;
}

static void
warn_changed_key(Key *host_key)
{
	char *fp;

	fp = sshkey_fingerprint(host_key, options.fingerprint_hash,
	    SSH_FP_DEFAULT);
	if (fp == NULL)
		fatal("%s: sshkey_fingerprint fail", __func__);

	error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
	error("@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @");
	error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
	error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
	error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
	error("It is also possible that a host key has just been changed.");
	error("The fingerprint for the %s key sent by the remote host is\n%s.",
	    key_type(host_key), fp);
	error("Please contact your system administrator.");

	free(fp);
}

/*
 * Execute a local command
 */
int
ssh_local_cmd(const char *args)
{
	char *shell;
	pid_t pid;
	int status;
	void (*osighand)(int);

	if (!options.permit_local_command ||
	    args == NULL || !*args)
		return (1);

	if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
		shell = _PATH_BSHELL;

	osighand = signal(SIGCHLD, SIG_DFL);
	pid = fork();
	if (pid == 0) {
		signal(SIGPIPE, SIG_DFL);
		debug3("Executing %s -c \"%s\"", shell, args);
		execl(shell, shell, "-c", args, (char *)NULL);
		error("Couldn't execute %s -c \"%s\": %s",
		    shell, args, strerror(errno));
		_exit(1);
	} else if (pid == -1)
		fatal("fork failed: %.100s", strerror(errno));
	while (waitpid(pid, &status, 0) == -1)
		if (errno != EINTR)
			fatal("Couldn't wait for child: %s", strerror(errno));
	signal(SIGCHLD, osighand);

	if (!WIFEXITED(status))
		return (1);

	return (WEXITSTATUS(status));
}

void
maybe_add_key_to_agent(char *authfile, Key *private, char *comment,
    char *passphrase)
{
	int auth_sock = -1, r;

	if (options.add_keys_to_agent == 0)
		return;

	if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) {
		debug3("no authentication agent, not adding key");
		return;
	}

	if (options.add_keys_to_agent == 2 &&
	    !ask_permission("Add key %s (%s) to agent?", authfile, comment)) {
		debug3("user denied adding this key");
		return;
	}

	if ((r = ssh_add_identity_constrained(auth_sock, private, comment, 0,
	    (options.add_keys_to_agent == 3))) == 0)
		debug("identity added to agent: %s", authfile);
	else
		debug("could not add identity to agent: %s (%d)", authfile, r);
}