openssh/sshconnect2.c

/* $OpenBSD: sshconnect2.c,v 1.356 2022/02/01 23:32:51 djm Exp $ */
/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 * Copyright (c) 2008 Damien Miller.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <netdb.h>
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <unistd.h>
#if defined(HAVE_STRNVIS) && defined(HAVE_VIS_H) && !defined(BROKEN_STRNVIS)
#include <vis.h>
#endif

#include "openbsd-compat/sys-queue.h"

#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "sshbuf.h"
#include "packet.h"
#include "compat.h"
#include "cipher.h"
#include "sshkey.h"
#include "kex.h"
#include "myproposal.h"
#include "sshconnect.h"
#include "authfile.h"
#include "dh.h"
#include "authfd.h"
#include "log.h"
#include "misc.h"
#include "readconf.h"
#include "match.h"
#include "dispatch.h"
#include "canohost.h"
#include "msg.h"
#include "pathnames.h"
#include "uidswap.h"
#include "hostfile.h"
#include "ssherr.h"
#include "utf8.h"
#include "ssh-sk.h"
#include "sk-api.h"

#ifdef GSSAPI
#include "ssh-gss.h"
#endif

/* import */
extern char *client_version_string;
extern char *server_version_string;
extern Options options;

/*
 * SSH2 key exchange
 */

static char *xxx_host;
static struct sockaddr *xxx_hostaddr;
static const struct ssh_conn_info *xxx_conn_info;

static int
verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh)
{
	if (verify_host_key(xxx_host, xxx_hostaddr, hostkey,
	    xxx_conn_info) == -1)
		fatal("Host key verification failed.");
	return 0;
}

/* Returns the first item from a comma-separated algorithm list */
static char *
first_alg(const char *algs)
{
	char *ret, *cp;

	ret = xstrdup(algs);
	if ((cp = strchr(ret, ',')) != NULL)
		*cp = '\0';
	return ret;
}

static char *
order_hostkeyalgs(char *host, struct sockaddr *hostaddr, u_short port,
    const struct ssh_conn_info *cinfo)
{
	char *oavail = NULL, *avail = NULL, *first = NULL, *last = NULL;
	char *alg = NULL, *hostname = NULL, *ret = NULL, *best = NULL;
	size_t maxlen;
	struct hostkeys *hostkeys = NULL;
	int ktype;
	u_int i;

	/* Find all hostkeys for this hostname */
	get_hostfile_hostname_ipaddr(host, hostaddr, port, &hostname, NULL);
	hostkeys = init_hostkeys();
	for (i = 0; i < options.num_user_hostfiles; i++)
		load_hostkeys(hostkeys, hostname, options.user_hostfiles[i], 0);
	for (i = 0; i < options.num_system_hostfiles; i++) {
		load_hostkeys(hostkeys, hostname,
		    options.system_hostfiles[i], 0);
	}
	if (options.known_hosts_command != NULL) {
		load_hostkeys_command(hostkeys, options.known_hosts_command,
		    "ORDER", cinfo, NULL, host);
	}
	/*
	 * If a plain public key exists that matches the type of the best
	 * preference HostkeyAlgorithms, then use the whole list as is.
	 * Note that we ignore whether the best preference algorithm is a
	 * certificate type, as sshconnect.c will downgrade certs to
	 * plain keys if necessary.
	 */
	best = first_alg(options.hostkeyalgorithms);
	if (lookup_key_in_hostkeys_by_type(hostkeys,
	    sshkey_type_plain(sshkey_type_from_name(best)),
	    sshkey_ecdsa_nid_from_name(best), NULL)) {
		debug3_f("have matching best-preference key type %s, "
		    "using HostkeyAlgorithms verbatim", best);
		ret = xstrdup(options.hostkeyalgorithms);
		goto out;
	}

	/*
	 * Otherwise, prefer the host key algorithms that match known keys
	 * while keeping the ordering of HostkeyAlgorithms as much as possible.
	 */
	oavail = avail = xstrdup(options.hostkeyalgorithms);
	maxlen = strlen(avail) + 1;
	first = xmalloc(maxlen);
	last = xmalloc(maxlen);
	*first = *last = '\0';

#define ALG_APPEND(to, from) \
	do { \
		if (*to != '\0') \
			strlcat(to, ",", maxlen); \
		strlcat(to, from, maxlen); \
	} while (0)

	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
			fatal_f("unknown alg %s", alg);
		/*
		 * If we have a @cert-authority marker in known_hosts then
		 * prefer all certificate algorithms.
		 */
		if (sshkey_type_is_cert(ktype) &&
		    lookup_marker_in_hostkeys(hostkeys, MRK_CA)) {
			ALG_APPEND(first, alg);
			continue;
		}
		/* If the key appears in known_hosts then prefer it */
		if (lookup_key_in_hostkeys_by_type(hostkeys,
		    sshkey_type_plain(ktype),
		    sshkey_ecdsa_nid_from_name(alg), NULL)) {
			ALG_APPEND(first, alg);
			continue;
		}
		/* Otherwise, put it last */
		ALG_APPEND(last, alg);
	}
#undef ALG_APPEND
	xasprintf(&ret, "%s%s%s", first,
	    (*first == '\0' || *last == '\0') ? "" : ",", last);
	if (*first != '\0')
		debug3_f("prefer hostkeyalgs: %s", first);
	else
		debug3_f("no algorithms matched; accept original");
 out:
	free(best);
	free(first);
	free(last);
	free(hostname);
	free(oavail);
	free_hostkeys(hostkeys);

	return ret;
}

void
ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port,
    const struct ssh_conn_info *cinfo)
{
	char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
	char *s, *all_key;
	int r, use_known_hosts_order = 0;

	xxx_host = host;
	xxx_hostaddr = hostaddr;
	xxx_conn_info = cinfo;

	/*
	 * If the user has not specified HostkeyAlgorithms, or has only
	 * appended or removed algorithms from that list then prefer algorithms
	 * that are in the list that are supported by known_hosts keys.
	 */
	if (options.hostkeyalgorithms == NULL ||
	    options.hostkeyalgorithms[0] == '-' ||
	    options.hostkeyalgorithms[0] == '+')
		use_known_hosts_order = 1;

	/* Expand or fill in HostkeyAlgorithms */
	all_key = sshkey_alg_list(0, 0, 1, ',');
	if ((r = kex_assemble_names(&options.hostkeyalgorithms,
	    kex_default_pk_alg(), all_key)) != 0)
		fatal_fr(r, "kex_assemble_namelist");
	free(all_key);

	if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL)
		fatal_f("kex_names_cat");
	myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(ssh, s);
	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
	    compat_cipher_proposal(ssh, options.ciphers);
	myproposal[PROPOSAL_ENC_ALGS_STOC] =
	    compat_cipher_proposal(ssh, options.ciphers);
	myproposal[PROPOSAL_COMP_ALGS_CTOS] =
	    myproposal[PROPOSAL_COMP_ALGS_STOC] =
	    (char *)compression_alg_list(options.compression);
	myproposal[PROPOSAL_MAC_ALGS_CTOS] =
	    myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;
	if (use_known_hosts_order) {
		/* Query known_hosts and prefer algorithms that appear there */
		myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
		    compat_pkalg_proposal(ssh,
		    order_hostkeyalgs(host, hostaddr, port, cinfo));
	} else {
		/* Use specified HostkeyAlgorithms exactly */
		myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
		    compat_pkalg_proposal(ssh, options.hostkeyalgorithms);
	}

	if (options.rekey_limit || options.rekey_interval)
		ssh_packet_set_rekey_limits(ssh, options.rekey_limit,
		    options.rekey_interval);

	/* start key exchange */
	if ((r = kex_setup(ssh, myproposal)) != 0)
		fatal_r(r, "kex_setup");
#ifdef WITH_OPENSSL
	ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
	ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
	ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
	ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
	ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
	ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
	ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
# ifdef OPENSSL_HAS_ECC
	ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
# endif
#endif
	ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
	ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
	ssh->kex->verify_host_key=&verify_host_key_callback;

	ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &ssh->kex->done);

	/* remove ext-info from the KEX proposals for rekeying */
	myproposal[PROPOSAL_KEX_ALGS] =
	    compat_kex_proposal(ssh, options.kex_algorithms);
	if ((r = kex_prop2buf(ssh->kex->my, myproposal)) != 0)
		fatal_r(r, "kex_prop2buf");

#ifdef DEBUG_KEXDH
	/* send 1st encrypted/maced/compressed message */
	if ((r = sshpkt_start(ssh, SSH2_MSG_IGNORE)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, "markus")) != 0 ||
	    (r = sshpkt_send(ssh)) != 0 ||
	    (r = ssh_packet_write_wait(ssh)) != 0)
		fatal_fr(r, "send packet");
#endif
}

/*
 * Authenticate user
 */

typedef struct cauthctxt Authctxt;
typedef struct cauthmethod Authmethod;
typedef struct identity Identity;
typedef struct idlist Idlist;

struct identity {
	TAILQ_ENTRY(identity) next;
	int	agent_fd;		/* >=0 if agent supports key */
	struct sshkey	*key;		/* public/private key */
	char	*filename;		/* comment for agent-only keys */
	int	tried;
	int	isprivate;		/* key points to the private key */
	int	userprovided;
};
TAILQ_HEAD(idlist, identity);

struct cauthctxt {
	const char *server_user;
	const char *local_user;
	const char *host;
	const char *service;
	struct cauthmethod *method;
	sig_atomic_t success;
	char *authlist;
#ifdef GSSAPI
	/* gssapi */
	gss_OID_set gss_supported_mechs;
	u_int mech_tried;
#endif
	/* pubkey */
	struct idlist keys;
	int agent_fd;
	/* hostbased */
	Sensitive *sensitive;
	char *oktypes, *ktypes;
	const char *active_ktype;
	/* kbd-interactive */
	int info_req_seen;
	int attempt_kbdint;
	/* password */
	int attempt_passwd;
	/* generic */
	void *methoddata;
};

struct cauthmethod {
	char	*name;		/* string to compare against server's list */
	int	(*userauth)(struct ssh *ssh);
	void	(*cleanup)(struct ssh *ssh);
	int	*enabled;	/* flag in option struct that enables method */
	int	*batch_flag;	/* flag in option struct that disables method */
};

static int input_userauth_service_accept(int, u_int32_t, struct ssh *);
static int input_userauth_ext_info(int, u_int32_t, struct ssh *);
static int input_userauth_success(int, u_int32_t, struct ssh *);
static int input_userauth_failure(int, u_int32_t, struct ssh *);
static int input_userauth_banner(int, u_int32_t, struct ssh *);
static int input_userauth_error(int, u_int32_t, struct ssh *);
static int input_userauth_info_req(int, u_int32_t, struct ssh *);
static int input_userauth_pk_ok(int, u_int32_t, struct ssh *);
static int input_userauth_passwd_changereq(int, u_int32_t, struct ssh *);

static int userauth_none(struct ssh *);
static int userauth_pubkey(struct ssh *);
static int userauth_passwd(struct ssh *);
static int userauth_kbdint(struct ssh *);
static int userauth_hostbased(struct ssh *);

#ifdef GSSAPI
static int userauth_gssapi(struct ssh *);
static void userauth_gssapi_cleanup(struct ssh *);
static int input_gssapi_response(int type, u_int32_t, struct ssh *);
static int input_gssapi_token(int type, u_int32_t, struct ssh *);
static int input_gssapi_error(int, u_int32_t, struct ssh *);
static int input_gssapi_errtok(int, u_int32_t, struct ssh *);
#endif

void	userauth(struct ssh *, char *);

static void pubkey_cleanup(struct ssh *);
static int sign_and_send_pubkey(struct ssh *ssh, Identity *);
static void pubkey_prepare(struct ssh *, Authctxt *);
static void pubkey_reset(Authctxt *);
static struct sshkey *load_identity_file(Identity *);

static Authmethod *authmethod_get(char *authlist);
static Authmethod *authmethod_lookup(const char *name);
static char *authmethods_get(void);

Authmethod authmethods[] = {
#ifdef GSSAPI
	{"gssapi-with-mic",
		userauth_gssapi,
		userauth_gssapi_cleanup,
		&options.gss_authentication,
		NULL},
#endif
	{"hostbased",
		userauth_hostbased,
		NULL,
		&options.hostbased_authentication,
		NULL},
	{"publickey",
		userauth_pubkey,
		NULL,
		&options.pubkey_authentication,
		NULL},
	{"keyboard-interactive",
		userauth_kbdint,
		NULL,
		&options.kbd_interactive_authentication,
		&options.batch_mode},
	{"password",
		userauth_passwd,
		NULL,
		&options.password_authentication,
		&options.batch_mode},
	{"none",
		userauth_none,
		NULL,
		NULL,
		NULL},
	{NULL, NULL, NULL, NULL, NULL}
};

void
ssh_userauth2(struct ssh *ssh, const char *local_user,
    const char *server_user, char *host, Sensitive *sensitive)
{
	Authctxt authctxt;
	int r;

	if (options.preferred_authentications == NULL)
		options.preferred_authentications = authmethods_get();

	/* setup authentication context */
	memset(&authctxt, 0, sizeof(authctxt));
	authctxt.server_user = server_user;
	authctxt.local_user = local_user;
	authctxt.host = host;
	authctxt.service = "ssh-connection";		/* service name */
	authctxt.success = 0;
	authctxt.method = authmethod_lookup("none");
	authctxt.authlist = NULL;
	authctxt.methoddata = NULL;
	authctxt.sensitive = sensitive;
	authctxt.active_ktype = authctxt.oktypes = authctxt.ktypes = NULL;
	authctxt.info_req_seen = 0;
	authctxt.attempt_kbdint = 0;
	authctxt.attempt_passwd = 0;
#if GSSAPI
	authctxt.gss_supported_mechs = NULL;
	authctxt.mech_tried = 0;
#endif
	authctxt.agent_fd = -1;
	pubkey_prepare(ssh, &authctxt);
	if (authctxt.method == NULL) {
		fatal_f("internal error: cannot send userauth none request");
	}

	if ((r = sshpkt_start(ssh, SSH2_MSG_SERVICE_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, "ssh-userauth")) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");

	ssh->authctxt = &authctxt;
	ssh_dispatch_init(ssh, &input_userauth_error);
	ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &input_userauth_ext_info);
	ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_ACCEPT, &input_userauth_service_accept);
	ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt.success);	/* loop until success */
	pubkey_cleanup(ssh);
	ssh->authctxt = NULL;

	ssh_dispatch_range(ssh, SSH2_MSG_USERAUTH_MIN, SSH2_MSG_USERAUTH_MAX, NULL);

	if (!authctxt.success)
		fatal("Authentication failed.");
	if (ssh_packet_connection_is_on_socket(ssh)) {
		verbose("Authenticated to %s ([%s]:%d) using \"%s\".", host,
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
		    authctxt.method->name);
	} else {
		verbose("Authenticated to %s (via proxy) using \"%s\".", host,
		    authctxt.method->name);
	}
}

/* ARGSUSED */
static int
input_userauth_service_accept(int type, u_int32_t seq, struct ssh *ssh)
{
	int r;

	if (ssh_packet_remaining(ssh) > 0) {
		char *reply;

		if ((r = sshpkt_get_cstring(ssh, &reply, NULL)) != 0)
			goto out;
		debug2("service_accept: %s", reply);
		free(reply);
	} else {
		debug2("buggy server: service_accept w/o service");
	}
	if ((r = sshpkt_get_end(ssh)) != 0)
		goto out;
	debug("SSH2_MSG_SERVICE_ACCEPT received");

	/* initial userauth request */
	userauth_none(ssh);

	ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &input_userauth_error);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_SUCCESS, &input_userauth_success);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_FAILURE, &input_userauth_failure);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_BANNER, &input_userauth_banner);
	r = 0;
 out:
	return r;
}

/* ARGSUSED */
static int
input_userauth_ext_info(int type, u_int32_t seqnr, struct ssh *ssh)
{
	return kex_input_ext_info(type, seqnr, ssh);
}

void
userauth(struct ssh *ssh, char *authlist)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;

	if (authctxt->method != NULL && authctxt->method->cleanup != NULL)
		authctxt->method->cleanup(ssh);

	free(authctxt->methoddata);
	authctxt->methoddata = NULL;
	if (authlist == NULL) {
		authlist = authctxt->authlist;
	} else {
		free(authctxt->authlist);
		authctxt->authlist = authlist;
	}
	for (;;) {
		Authmethod *method = authmethod_get(authlist);
		if (method == NULL)
			fatal("%s@%s: Permission denied (%s).",
			    authctxt->server_user, authctxt->host, authlist);
		authctxt->method = method;

		/* reset the per method handler */
		ssh_dispatch_range(ssh, SSH2_MSG_USERAUTH_PER_METHOD_MIN,
		    SSH2_MSG_USERAUTH_PER_METHOD_MAX, NULL);

		/* and try new method */
		if (method->userauth(ssh) != 0) {
			debug2("we sent a %s packet, wait for reply", method->name);
			break;
		} else {
			debug2("we did not send a packet, disable method");
			method->enabled = NULL;
		}
	}
}

/* ARGSUSED */
static int
input_userauth_error(int type, u_int32_t seq, struct ssh *ssh)
{
	fatal_f("bad message during authentication: type %d", type);
	return 0;
}

/* ARGSUSED */
static int
input_userauth_banner(int type, u_int32_t seq, struct ssh *ssh)
{
	char *msg = NULL;
	size_t len;
	int r;

	debug3_f("entering");
	if ((r = sshpkt_get_cstring(ssh, &msg, &len)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, NULL, NULL)) != 0)
		goto out;
	if (len > 0 && options.log_level >= SYSLOG_LEVEL_INFO)
		fmprintf(stderr, "%s", msg);
	r = 0;
 out:
	free(msg);
	return r;
}

/* ARGSUSED */
static int
input_userauth_success(int type, u_int32_t seq, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;

	if (authctxt == NULL)
		fatal_f("no authentication context");
	free(authctxt->authlist);
	authctxt->authlist = NULL;
	if (authctxt->method != NULL && authctxt->method->cleanup != NULL)
		authctxt->method->cleanup(ssh);
	free(authctxt->methoddata);
	authctxt->methoddata = NULL;
	authctxt->success = 1;			/* break out */
	return 0;
}

#if 0
static int
input_userauth_success_unexpected(int type, u_int32_t seq, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;

	if (authctxt == NULL)
		fatal_f("no authentication context");

	fatal("Unexpected authentication success during %s.",
	    authctxt->method->name);
	return 0;
}
#endif

/* ARGSUSED */
static int
input_userauth_failure(int type, u_int32_t seq, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	char *authlist = NULL;
	u_char partial;

	if (authctxt == NULL)
		fatal("input_userauth_failure: no authentication context");

	if (sshpkt_get_cstring(ssh, &authlist, NULL) != 0 ||
	    sshpkt_get_u8(ssh, &partial) != 0 ||
	    sshpkt_get_end(ssh) != 0)
		goto out;

	if (partial != 0) {
		verbose("Authenticated using \"%s\" with partial success.",
		    authctxt->method->name);
		/* reset state */
		pubkey_reset(authctxt);
	}
	debug("Authentications that can continue: %s", authlist);

	userauth(ssh, authlist);
	authlist = NULL;
 out:
	free(authlist);
	return 0;
}

/*
 * Format an identity for logging including filename, key type, fingerprint
 * and location (agent, etc.). Caller must free.
 */
static char *
format_identity(Identity *id)
{
	char *fp = NULL, *ret = NULL;
	const char *note = "";

	if (id->key != NULL) {
		fp = sshkey_fingerprint(id->key, options.fingerprint_hash,
		    SSH_FP_DEFAULT);
	}
	if (id->key) {
		if ((id->key->flags & SSHKEY_FLAG_EXT) != 0)
			note = " token";
		else if (sshkey_is_sk(id->key))
			note = " authenticator";
	}
	xasprintf(&ret, "%s %s%s%s%s%s%s",
	    id->filename,
	    id->key ? sshkey_type(id->key) : "", id->key ? " " : "",
	    fp ? fp : "",
	    id->userprovided ? " explicit" : "", note,
	    id->agent_fd != -1 ? " agent" : "");
	free(fp);
	return ret;
}

/* ARGSUSED */
static int
input_userauth_pk_ok(int type, u_int32_t seq, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	struct sshkey *key = NULL;
	Identity *id = NULL;
	int pktype, found = 0, sent = 0;
	size_t blen;
	char *pkalg = NULL, *fp = NULL, *ident = NULL;
	u_char *pkblob = NULL;
	int r;

	if (authctxt == NULL)
		fatal("input_userauth_pk_ok: no authentication context");

	if ((r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0)
		goto done;

	if ((pktype = sshkey_type_from_name(pkalg)) == KEY_UNSPEC) {
		debug_f("server sent unknown pkalg %s", pkalg);
		goto done;
	}
	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
		debug_r(r, "no key from blob. pkalg %s", pkalg);
		goto done;
	}
	if (key->type != pktype) {
		error("input_userauth_pk_ok: type mismatch "
		    "for decoded key (received %d, expected %d)",
		    key->type, pktype);
		goto done;
	}

	/*
	 * search keys in the reverse order, because last candidate has been
	 * moved to the end of the queue.  this also avoids confusion by
	 * duplicate keys
	 */
	TAILQ_FOREACH_REVERSE(id, &authctxt->keys, idlist, next) {
		if (sshkey_equal(key, id->key)) {
			found = 1;
			break;
		}
	}
	if (!found || id == NULL) {
		fp = sshkey_fingerprint(key, options.fingerprint_hash,
		    SSH_FP_DEFAULT);
		error_f("server replied with unknown key: %s %s",
		    sshkey_type(key), fp == NULL ? "<ERROR>" : fp);
		goto done;
	}
	ident = format_identity(id);
	debug("Server accepts key: %s", ident);
	sent = sign_and_send_pubkey(ssh, id);
	r = 0;
 done:
	sshkey_free(key);
	free(ident);
	free(fp);
	free(pkalg);
	free(pkblob);

	/* try another method if we did not send a packet */
	if (r == 0 && sent == 0)
		userauth(ssh, NULL);
	return r;
}

#ifdef GSSAPI
static int
userauth_gssapi(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	Gssctxt *gssctxt = NULL;
	OM_uint32 min;
	int r, ok = 0;
	gss_OID mech = NULL;

	/* Try one GSSAPI method at a time, rather than sending them all at
	 * once. */

	if (authctxt->gss_supported_mechs == NULL)
		gss_indicate_mechs(&min, &authctxt->gss_supported_mechs);

	/* Check to see whether the mechanism is usable before we offer it */
	while (authctxt->mech_tried < authctxt->gss_supported_mechs->count &&
	    !ok) {
		mech = &authctxt->gss_supported_mechs->
		    elements[authctxt->mech_tried];
		/* My DER encoding requires length<128 */
		if (mech->length < 128 && ssh_gssapi_check_mechanism(&gssctxt,
		    mech, authctxt->host)) {
			ok = 1; /* Mechanism works */
		} else {
			authctxt->mech_tried++;
		}
	}

	if (!ok || mech == NULL)
		return 0;

	authctxt->methoddata=(void *)gssctxt;

	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_u32(ssh, 1)) != 0 ||
	    (r = sshpkt_put_u32(ssh, (mech->length) + 2)) != 0 ||
	    (r = sshpkt_put_u8(ssh, SSH_GSS_OIDTYPE)) != 0 ||
	    (r = sshpkt_put_u8(ssh, mech->length)) != 0 ||
	    (r = sshpkt_put(ssh, mech->elements, mech->length)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");

	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_RESPONSE, &input_gssapi_response);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERROR, &input_gssapi_error);
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);

	authctxt->mech_tried++; /* Move along to next candidate */

	return 1;
}

static void
userauth_gssapi_cleanup(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	Gssctxt *gssctxt = (Gssctxt *)authctxt->methoddata;

	ssh_gssapi_delete_ctx(&gssctxt);
	authctxt->methoddata = NULL;

	free(authctxt->gss_supported_mechs);
	authctxt->gss_supported_mechs = NULL;
}

static OM_uint32
process_gssapi_token(struct ssh *ssh, gss_buffer_t recv_tok)
{
	Authctxt *authctxt = ssh->authctxt;
	Gssctxt *gssctxt = authctxt->methoddata;
	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
	gss_buffer_desc mic = GSS_C_EMPTY_BUFFER;
	gss_buffer_desc gssbuf;
	OM_uint32 status, ms, flags;
	int r;

	status = ssh_gssapi_init_ctx(gssctxt, options.gss_deleg_creds,
	    recv_tok, &send_tok, &flags);

	if (send_tok.length > 0) {
		u_char type = GSS_ERROR(status) ?
		    SSH2_MSG_USERAUTH_GSSAPI_ERRTOK :
		    SSH2_MSG_USERAUTH_GSSAPI_TOKEN;

		if ((r = sshpkt_start(ssh, type)) != 0 ||
		    (r = sshpkt_put_string(ssh, send_tok.value,
		    send_tok.length)) != 0 ||
		    (r = sshpkt_send(ssh)) != 0)
			fatal_fr(r, "send %u packet", type);

		gss_release_buffer(&ms, &send_tok);
	}

	if (status == GSS_S_COMPLETE) {
		/* send either complete or MIC, depending on mechanism */
		if (!(flags & GSS_C_INTEG_FLAG)) {
			if ((r = sshpkt_start(ssh,
			    SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE)) != 0 ||
			    (r = sshpkt_send(ssh)) != 0)
				fatal_fr(r, "send completion");
		} else {
			struct sshbuf *b;

			if ((b = sshbuf_new()) == NULL)
				fatal_f("sshbuf_new failed");
			ssh_gssapi_buildmic(b, authctxt->server_user,
			    authctxt->service, "gssapi-with-mic",
			    ssh->kex->session_id);

			if ((gssbuf.value = sshbuf_mutable_ptr(b)) == NULL)
				fatal_f("sshbuf_mutable_ptr failed");
			gssbuf.length = sshbuf_len(b);

			status = ssh_gssapi_sign(gssctxt, &gssbuf, &mic);

			if (!GSS_ERROR(status)) {
				if ((r = sshpkt_start(ssh,
				    SSH2_MSG_USERAUTH_GSSAPI_MIC)) != 0 ||
				    (r = sshpkt_put_string(ssh, mic.value,
				    mic.length)) != 0 ||
				    (r = sshpkt_send(ssh)) != 0)
					fatal_fr(r, "send MIC");
			}

			sshbuf_free(b);
			gss_release_buffer(&ms, &mic);
		}
	}

	return status;
}

/* ARGSUSED */
static int
input_gssapi_response(int type, u_int32_t plen, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	Gssctxt *gssctxt;
	size_t oidlen;
	u_char *oidv = NULL;
	int r;

	if (authctxt == NULL)
		fatal("input_gssapi_response: no authentication context");
	gssctxt = authctxt->methoddata;

	/* Setup our OID */
	if ((r = sshpkt_get_string(ssh, &oidv, &oidlen)) != 0)
		goto done;

	if (oidlen <= 2 ||
	    oidv[0] != SSH_GSS_OIDTYPE ||
	    oidv[1] != oidlen - 2) {
		debug("Badly encoded mechanism OID received");
		userauth(ssh, NULL);
		goto ok;
	}

	if (!ssh_gssapi_check_oid(gssctxt, oidv + 2, oidlen - 2))
		fatal("Server returned different OID than expected");

	if ((r = sshpkt_get_end(ssh)) != 0)
		goto done;

	if (GSS_ERROR(process_gssapi_token(ssh, GSS_C_NO_BUFFER))) {
		/* Start again with next method on list */
		debug("Trying to start again");
		userauth(ssh, NULL);
		goto ok;
	}
 ok:
	r = 0;
 done:
	free(oidv);
	return r;
}

/* ARGSUSED */
static int
input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	gss_buffer_desc recv_tok;
	u_char *p = NULL;
	size_t len;
	OM_uint32 status;
	int r;

	if (authctxt == NULL)
		fatal("input_gssapi_response: no authentication context");

	if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0)
		goto out;

	recv_tok.value = p;
	recv_tok.length = len;
	status = process_gssapi_token(ssh, &recv_tok);

	/* Start again with the next method in the list */
	if (GSS_ERROR(status)) {
		userauth(ssh, NULL);
		/* ok */
	}
	r = 0;
 out:
	free(p);
	return r;
}

/* ARGSUSED */
static int
input_gssapi_errtok(int type, u_int32_t plen, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	Gssctxt *gssctxt;
	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
	gss_buffer_desc recv_tok;
	OM_uint32 ms;
	u_char *p = NULL;
	size_t len;
	int r;

	if (authctxt == NULL)
		fatal("input_gssapi_response: no authentication context");
	gssctxt = authctxt->methoddata;

	if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
	    (r = sshpkt_get_end(ssh)) != 0) {
		free(p);
		return r;
	}

	/* Stick it into GSSAPI and see what it says */
	recv_tok.value = p;
	recv_tok.length = len;
	(void)ssh_gssapi_init_ctx(gssctxt, options.gss_deleg_creds,
	    &recv_tok, &send_tok, NULL);
	free(p);
	gss_release_buffer(&ms, &send_tok);

	/* Server will be returning a failed packet after this one */
	return 0;
}

/* ARGSUSED */
static int
input_gssapi_error(int type, u_int32_t plen, struct ssh *ssh)
{
	char *msg = NULL;
	char *lang = NULL;
	int r;

	if ((r = sshpkt_get_u32(ssh, NULL)) != 0 ||	/* maj */
	    (r = sshpkt_get_u32(ssh, NULL)) != 0 ||	/* min */
	    (r = sshpkt_get_cstring(ssh, &msg, NULL)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &lang, NULL)) != 0)
		goto out;
	r = sshpkt_get_end(ssh);
	debug("Server GSSAPI Error:\n%s", msg);
 out:
	free(msg);
	free(lang);
	return r;
}
#endif /* GSSAPI */

static int
userauth_none(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	int r;

	/* initial userauth request */
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");
	return 1;
}

static int
userauth_passwd(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	char *password, *prompt = NULL;
	const char *host = options.host_key_alias ?  options.host_key_alias :
	    authctxt->host;
	int r;

	if (authctxt->attempt_passwd++ >= options.number_of_password_prompts)
		return 0;

	if (authctxt->attempt_passwd != 1)
		error("Permission denied, please try again.");

	xasprintf(&prompt, "%s@%s's password: ", authctxt->server_user, host);
	password = read_passphrase(prompt, 0);
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_u8(ssh, 0)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, password)) != 0 ||
	    (r = sshpkt_add_padding(ssh, 64)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");

	free(prompt);
	if (password != NULL)
		freezero(password, strlen(password));

	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ,
	    &input_userauth_passwd_changereq);

	return 1;
}

/*
 * parse PASSWD_CHANGEREQ, prompt user and send SSH2_MSG_USERAUTH_REQUEST
 */
/* ARGSUSED */
static int
input_userauth_passwd_changereq(int type, u_int32_t seqnr, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	char *info = NULL, *lang = NULL, *password = NULL, *retype = NULL;
	char prompt[256];
	const char *host;
	int r;

	debug2("input_userauth_passwd_changereq");

	if (authctxt == NULL)
		fatal("input_userauth_passwd_changereq: "
		    "no authentication context");
	host = options.host_key_alias ? options.host_key_alias : authctxt->host;

	if ((r = sshpkt_get_cstring(ssh, &info, NULL)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &lang, NULL)) != 0)
		goto out;
	if (strlen(info) > 0)
		logit("%s", info);
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_u8(ssh, 1)) != 0)	/* additional info */
		goto out;

	snprintf(prompt, sizeof(prompt),
	    "Enter %.30s@%.128s's old password: ",
	    authctxt->server_user, host);
	password = read_passphrase(prompt, 0);
	if ((r = sshpkt_put_cstring(ssh, password)) != 0)
		goto out;

	freezero(password, strlen(password));
	password = NULL;
	while (password == NULL) {
		snprintf(prompt, sizeof(prompt),
		    "Enter %.30s@%.128s's new password: ",
		    authctxt->server_user, host);
		password = read_passphrase(prompt, RP_ALLOW_EOF);
		if (password == NULL) {
			/* bail out */
			r = 0;
			goto out;
		}
		snprintf(prompt, sizeof(prompt),
		    "Retype %.30s@%.128s's new password: ",
		    authctxt->server_user, host);
		retype = read_passphrase(prompt, 0);
		if (strcmp(password, retype) != 0) {
			freezero(password, strlen(password));
			logit("Mismatch; try again, EOF to quit.");
			password = NULL;
		}
		freezero(retype, strlen(retype));
	}
	if ((r = sshpkt_put_cstring(ssh, password)) != 0 ||
	    (r = sshpkt_add_padding(ssh, 64)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		goto out;

	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ,
	    &input_userauth_passwd_changereq);
	r = 0;
 out:
	if (password)
		freezero(password, strlen(password));
	free(info);
	free(lang);
	return r;
}

/*
 * Select an algorithm for publickey signatures.
 * Returns algorithm (caller must free) or NULL if no mutual algorithm found.
 *
 * Call with ssh==NULL to ignore server-sig-algs extension list and
 * only attempt with the key's base signature type.
 */
static char *
key_sig_algorithm(struct ssh *ssh, const struct sshkey *key)
{
	char *allowed, *oallowed, *cp, *tmp, *alg = NULL;
	const char *server_sig_algs;

	/*
	 * The signature algorithm will only differ from the key algorithm
	 * for RSA keys/certs and when the server advertises support for
	 * newer (SHA2) algorithms.
	 */
	if (ssh == NULL || ssh->kex->server_sig_algs == NULL ||
	    (key->type != KEY_RSA && key->type != KEY_RSA_CERT) ||
	    (key->type == KEY_RSA_CERT && (ssh->compat & SSH_BUG_SIGTYPE))) {
		/* Filter base key signature alg against our configuration */
		return match_list(sshkey_ssh_name(key),
		    options.pubkey_accepted_algos, NULL);
	}

	/*
	 * Workaround OpenSSH 7.4 bug: this version supports RSA/SHA-2 but
	 * fails to advertise it via SSH2_MSG_EXT_INFO.
	 */
	server_sig_algs = ssh->kex->server_sig_algs;
	if (key->type == KEY_RSA && (ssh->compat & SSH_BUG_SIGTYPE74))
		server_sig_algs = "rsa-sha2-256,rsa-sha2-512";

	/*
	 * For RSA keys/certs, since these might have a different sig type:
	 * find the first entry in PubkeyAcceptedAlgorithms of the right type
	 * that also appears in the supported signature algorithms list from
	 * the server.
	 */
	oallowed = allowed = xstrdup(options.pubkey_accepted_algos);
	while ((cp = strsep(&allowed, ",")) != NULL) {
		if (sshkey_type_from_name(cp) != key->type)
			continue;
		tmp = match_list(sshkey_sigalg_by_name(cp),
		    server_sig_algs, NULL);
		if (tmp != NULL)
			alg = xstrdup(cp);
		free(tmp);
		if (alg != NULL)
			break;
	}
	free(oallowed);
	return alg;
}

static int
identity_sign(struct identity *id, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen, u_int compat, const char *alg)
{
	struct sshkey *sign_key = NULL, *prv = NULL;
	int retried = 0, r = SSH_ERR_INTERNAL_ERROR;
	struct notifier_ctx *notifier = NULL;
	char *fp = NULL, *pin = NULL, *prompt = NULL;

	*sigp = NULL;
	*lenp = 0;

	/* The agent supports this key. */
	if (id->key != NULL && id->agent_fd != -1) {
		return ssh_agent_sign(id->agent_fd, id->key, sigp, lenp,
		    data, datalen, alg, compat);
	}

	/*
	 * We have already loaded the private key or the private key is
	 * stored in external hardware.
	 */
	if (id->key != NULL &&
	    (id->isprivate || (id->key->flags & SSHKEY_FLAG_EXT))) {
		sign_key = id->key;
	} else {
		/* Load the private key from the file. */
		if ((prv = load_identity_file(id)) == NULL)
			return SSH_ERR_KEY_NOT_FOUND;
		if (id->key != NULL && !sshkey_equal_public(prv, id->key)) {
			error_f("private key %s contents do not match public",
			    id->filename);
			r = SSH_ERR_KEY_NOT_FOUND;
			goto out;
		}
		sign_key = prv;
		if (sshkey_is_sk(sign_key)) {
			if ((sign_key->sk_flags &
			    SSH_SK_USER_VERIFICATION_REQD)) {
 retry_pin:
				xasprintf(&prompt, "Enter PIN for %s key %s: ",
				    sshkey_type(sign_key), id->filename);
				pin = read_passphrase(prompt, 0);
			}
			if ((sign_key->sk_flags & SSH_SK_USER_PRESENCE_REQD)) {
				/* XXX should batch mode just skip these? */
				if ((fp = sshkey_fingerprint(sign_key,
				    options.fingerprint_hash,
				    SSH_FP_DEFAULT)) == NULL)
					fatal_f("fingerprint failed");
				notifier = notify_start(options.batch_mode,
				    "Confirm user presence for key %s %s",
				    sshkey_type(sign_key), fp);
				free(fp);
			}
		}
	}
	if ((r = sshkey_sign(sign_key, sigp, lenp, data, datalen,
	    alg, options.sk_provider, pin, compat)) != 0) {
		debug_fr(r, "sshkey_sign");
		if (pin == NULL && !retried && sshkey_is_sk(sign_key) &&
		    r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
			notify_complete(notifier, NULL);
			notifier = NULL;
			retried = 1;
			goto retry_pin;
		}
		goto out;
	}

	/*
	 * PKCS#11 tokens may not support all signature algorithms,
	 * so check what we get back.
	 */
	if ((r = sshkey_check_sigtype(*sigp, *lenp, alg)) != 0) {
		debug_fr(r, "sshkey_check_sigtype");
		goto out;
	}
	/* success */
	r = 0;
 out:
	free(prompt);
	if (pin != NULL)
		freezero(pin, strlen(pin));
	notify_complete(notifier, r == 0 ? "User presence confirmed" : NULL);
	sshkey_free(prv);
	return r;
}

static int
id_filename_matches(Identity *id, Identity *private_id)
{
	static const char * const suffixes[] = { ".pub", "-cert.pub", NULL };
	size_t len = strlen(id->filename), plen = strlen(private_id->filename);
	size_t i, slen;

	if (strcmp(id->filename, private_id->filename) == 0)
		return 1;
	for (i = 0; suffixes[i]; i++) {
		slen = strlen(suffixes[i]);
		if (len > slen && plen == len - slen &&
		    strcmp(id->filename + (len - slen), suffixes[i]) == 0 &&
		    memcmp(id->filename, private_id->filename, plen) == 0)
			return 1;
	}
	return 0;
}

static int
sign_and_send_pubkey(struct ssh *ssh, Identity *id)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	struct sshbuf *b = NULL;
	Identity *private_id, *sign_id = NULL;
	u_char *signature = NULL;
	size_t slen = 0, skip = 0;
	int r, fallback_sigtype, sent = 0;
	char *alg = NULL, *fp = NULL;
	const char *loc = "", *method = "publickey";
	int hostbound = 0;

	/* prefer host-bound pubkey signatures if supported by server */
	if ((ssh->kex->flags & KEX_HAS_PUBKEY_HOSTBOUND) != 0 &&
	    (options.pubkey_authentication & SSH_PUBKEY_AUTH_HBOUND) != 0) {
		hostbound = 1;
		method = "publickey-hostbound-v00@openssh.com";
	}

	if ((fp = sshkey_fingerprint(id->key, options.fingerprint_hash,
	    SSH_FP_DEFAULT)) == NULL)
		return 0;

	debug3_f("using %s with %s %s", method, sshkey_type(id->key), fp);

	/*
	 * If the key is an certificate, try to find a matching private key
	 * and use it to complete the signature.
	 * If no such private key exists, fall back to trying the certificate
	 * key itself in case it has a private half already loaded.
	 * This will try to set sign_id to the private key that will perform
	 * the signature.
	 */
	if (sshkey_is_cert(id->key)) {
		TAILQ_FOREACH(private_id, &authctxt->keys, next) {
			if (sshkey_equal_public(id->key, private_id->key) &&
			    id->key->type != private_id->key->type) {
				sign_id = private_id;
				break;
			}
		}
		/*
		 * Exact key matches are preferred, but also allow
		 * filename matches for non-PKCS#11/agent keys that
		 * didn't load public keys. This supports the case
		 * of keeping just a private key file and public
		 * certificate on disk.
		 */
		if (sign_id == NULL &&
		    !id->isprivate && id->agent_fd == -1 &&
		    (id->key->flags & SSHKEY_FLAG_EXT) == 0) {
			TAILQ_FOREACH(private_id, &authctxt->keys, next) {
				if (private_id->key == NULL &&
				    id_filename_matches(id, private_id)) {
					sign_id = private_id;
					break;
				}
			}
		}
		if (sign_id != NULL) {
			debug2_f("using private key \"%s\"%s for "
			    "certificate", sign_id->filename,
			    sign_id->agent_fd != -1 ? " from agent" : "");
		} else {
			debug_f("no separate private key for certificate "
			    "\"%s\"", id->filename);
		}
	}

	/*
	 * If the above didn't select another identity to do the signing
	 * then default to the one we started with.
	 */
	if (sign_id == NULL)
		sign_id = id;

	/* assemble and sign data */
	for (fallback_sigtype = 0; fallback_sigtype <= 1; fallback_sigtype++) {
		free(alg);
		slen = 0;
		signature = NULL;
		if ((alg = key_sig_algorithm(fallback_sigtype ? NULL : ssh,
		    id->key)) == NULL) {
			error_f("no mutual signature supported");
			goto out;
		}
		debug3_f("signing using %s %s", alg, fp);

		sshbuf_free(b);
		if ((b = sshbuf_new()) == NULL)
			fatal_f("sshbuf_new failed");
		if (ssh->compat & SSH_OLD_SESSIONID) {
			if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0)
				fatal_fr(r, "sshbuf_putb");
		} else {
			if ((r = sshbuf_put_stringb(b,
			    ssh->kex->session_id)) != 0)
				fatal_fr(r, "sshbuf_put_stringb");
		}
		skip = sshbuf_len(b);
		if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
		    (r = sshbuf_put_cstring(b, authctxt->server_user)) != 0 ||
		    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
		    (r = sshbuf_put_cstring(b, method)) != 0 ||
		    (r = sshbuf_put_u8(b, 1)) != 0 ||
		    (r = sshbuf_put_cstring(b, alg)) != 0 ||
		    (r = sshkey_puts(id->key, b)) != 0) {
			fatal_fr(r, "assemble signed data");
		}
		if (hostbound) {
			if (ssh->kex->initial_hostkey == NULL) {
				fatal_f("internal error: initial hostkey "
				    "not recorded");
			}
			if ((r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0)
				fatal_fr(r, "assemble %s hostkey", method);
		}
		/* generate signature */
		r = identity_sign(sign_id, &signature, &slen,
		    sshbuf_ptr(b), sshbuf_len(b), ssh->compat, alg);
		if (r == 0)
			break;
		else if (r == SSH_ERR_KEY_NOT_FOUND)
			goto out; /* soft failure */
		else if (r == SSH_ERR_SIGN_ALG_UNSUPPORTED &&
		    !fallback_sigtype) {
			if (sign_id->agent_fd != -1)
				loc = "agent ";
			else if ((sign_id->key->flags & SSHKEY_FLAG_EXT) != 0)
				loc = "token ";
			logit("%skey %s %s returned incorrect signature type",
			    loc, sshkey_type(id->key), fp);
			continue;
		}
		error_fr(r, "signing failed for %s \"%s\"%s",
		    sshkey_type(sign_id->key), sign_id->filename,
		    id->agent_fd != -1 ? " from agent" : "");
		goto out;
	}
	if (slen == 0 || signature == NULL) /* shouldn't happen */
		fatal_f("no signature");

	/* append signature */
	if ((r = sshbuf_put_string(b, signature, slen)) != 0)
		fatal_fr(r, "append signature");

#ifdef DEBUG_PK
	sshbuf_dump(b, stderr);
#endif
	/* skip session id and packet type */
	if ((r = sshbuf_consume(b, skip + 1)) != 0)
		fatal_fr(r, "consume");

	/* put remaining data from buffer into packet */
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_putb(ssh, b)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "enqueue request");

	/* success */
	sent = 1;

 out:
	free(fp);
	free(alg);
	sshbuf_free(b);
	freezero(signature, slen);
	return sent;
}

static int
send_pubkey_test(struct ssh *ssh, Identity *id)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	u_char *blob = NULL;
	char *alg = NULL;
	size_t bloblen;
	u_int have_sig = 0;
	int sent = 0, r;

	if ((alg = key_sig_algorithm(ssh, id->key)) == NULL) {
		debug_f("no mutual signature algorithm");
		goto out;
	}

	if ((r = sshkey_to_blob(id->key, &blob, &bloblen)) != 0) {
		/* we cannot handle this key */
		debug3_f("cannot handle key");
		goto out;
	}
	/* register callback for USERAUTH_PK_OK message */
	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_PK_OK, &input_userauth_pk_ok);

	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_u8(ssh, have_sig)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, alg)) != 0 ||
	    (r = sshpkt_put_string(ssh, blob, bloblen)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");
	sent = 1;

 out:
	free(alg);
	free(blob);
	return sent;
}

static struct sshkey *
load_identity_file(Identity *id)
{
	struct sshkey *private = NULL;
	char prompt[300], *passphrase, *comment;
	int r, quit = 0, i;
	struct stat st;

	if (stat(id->filename, &st) == -1) {
		do_log2(id->userprovided ?
		    SYSLOG_LEVEL_INFO : SYSLOG_LEVEL_DEBUG3,
		    "no such identity: %s: %s", id->filename, strerror(errno));
		return NULL;
	}
	snprintf(prompt, sizeof prompt,
	    "Enter passphrase for key '%.100s': ", id->filename);
	for (i = 0; i <= options.number_of_password_prompts; i++) {
		if (i == 0)
			passphrase = "";
		else {
			passphrase = read_passphrase(prompt, 0);
			if (*passphrase == '\0') {
				debug2("no passphrase given, try next key");
				free(passphrase);
				break;
			}
		}
		switch ((r = sshkey_load_private_type(KEY_UNSPEC, id->filename,
		    passphrase, &private, &comment))) {
		case 0:
			break;
		case SSH_ERR_KEY_WRONG_PASSPHRASE:
			if (options.batch_mode) {
				quit = 1;
				break;
			}
			if (i != 0)
				debug2("bad passphrase given, try again...");
			break;
		case SSH_ERR_SYSTEM_ERROR:
			if (errno == ENOENT) {
				debug2_r(r, "Load key \"%s\"", id->filename);
				quit = 1;
				break;
			}
			/* FALLTHROUGH */
		default:
			error_r(r, "Load key \"%s\"", id->filename);
			quit = 1;
			break;
		}
		if (private != NULL && sshkey_is_sk(private) &&
		    options.sk_provider == NULL) {
			debug("key \"%s\" is an authenticator-hosted key, "
			    "but no provider specified", id->filename);
			sshkey_free(private);
			private = NULL;
			quit = 1;
		}
		if (!quit && private != NULL && id->agent_fd == -1 &&
		    !(id->key && id->isprivate))
			maybe_add_key_to_agent(id->filename, private, comment,
			    passphrase);
		if (i > 0)
			freezero(passphrase, strlen(passphrase));
		free(comment);
		if (private != NULL || quit)
			break;
	}
	return private;
}

static int
key_type_allowed_by_config(struct sshkey *key)
{
	if (match_pattern_list(sshkey_ssh_name(key),
	    options.pubkey_accepted_algos, 0) == 1)
		return 1;

	/* RSA keys/certs might be allowed by alternate signature types */
	switch (key->type) {
	case KEY_RSA:
		if (match_pattern_list("rsa-sha2-512",
		    options.pubkey_accepted_algos, 0) == 1)
			return 1;
		if (match_pattern_list("rsa-sha2-256",
		    options.pubkey_accepted_algos, 0) == 1)
			return 1;
		break;
	case KEY_RSA_CERT:
		if (match_pattern_list("rsa-sha2-512-cert-v01@openssh.com",
		    options.pubkey_accepted_algos, 0) == 1)
			return 1;
		if (match_pattern_list("rsa-sha2-256-cert-v01@openssh.com",
		    options.pubkey_accepted_algos, 0) == 1)
			return 1;
		break;
	}
	return 0;
}

/* obtain a list of keys from the agent */
static int
get_agent_identities(struct ssh *ssh, int *agent_fdp,
    struct ssh_identitylist **idlistp)
{
	int r, agent_fd;
	struct ssh_identitylist *idlist;

	if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) {
		if (r != SSH_ERR_AGENT_NOT_PRESENT)
			debug_fr(r, "ssh_get_authentication_socket");
		return r;
	}
	if ((r = ssh_agent_bind_hostkey(agent_fd, ssh->kex->initial_hostkey,
	    ssh->kex->session_id, ssh->kex->initial_sig, 0)) == 0)
		debug_f("bound agent to hostkey");
	else
		debug2_fr(r, "ssh_agent_bind_hostkey");

	if ((r = ssh_fetch_identitylist(agent_fd, &idlist)) != 0) {
		debug_fr(r, "ssh_fetch_identitylist");
		close(agent_fd);
		return r;
	}
	/* success */
	*agent_fdp = agent_fd;
	*idlistp = idlist;
	debug_f("agent returned %zu keys", idlist->nkeys);
	return 0;
}

/*
 * try keys in the following order:
 *	1. certificates listed in the config file
 *	2. other input certificates
 *	3. agent keys that are found in the config file
 *	4. other agent keys
 *	5. keys that are only listed in the config file
 */
static void
pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
{
	struct identity *id, *id2, *tmp;
	struct idlist agent, files, *preferred;
	struct sshkey *key;
	int agent_fd = -1, i, r, found;
	size_t j;
	struct ssh_identitylist *idlist;
	char *ident;

	TAILQ_INIT(&agent);	/* keys from the agent */
	TAILQ_INIT(&files);	/* keys from the config file */
	preferred = &authctxt->keys;
	TAILQ_INIT(preferred);	/* preferred order of keys */

	/* list of keys stored in the filesystem and PKCS#11 */
	for (i = 0; i < options.num_identity_files; i++) {
		key = options.identity_keys[i];
		if (key && key->cert &&
		    key->cert->type != SSH2_CERT_TYPE_USER) {
			debug_f("ignoring certificate %s: not a user "
			    "certificate", options.identity_files[i]);
			continue;
		}
		if (key && sshkey_is_sk(key) && options.sk_provider == NULL) {
			debug_f("ignoring authenticator-hosted key %s as no "
			    "SecurityKeyProvider has been specified",
			    options.identity_files[i]);
			continue;
		}
		options.identity_keys[i] = NULL;
		id = xcalloc(1, sizeof(*id));
		id->agent_fd = -1;
		id->key = key;
		id->filename = xstrdup(options.identity_files[i]);
		id->userprovided = options.identity_file_userprovided[i];
		TAILQ_INSERT_TAIL(&files, id, next);
	}
	/* list of certificates specified by user */
	for (i = 0; i < options.num_certificate_files; i++) {
		key = options.certificates[i];
		if (!sshkey_is_cert(key) || key->cert == NULL ||
		    key->cert->type != SSH2_CERT_TYPE_USER) {
			debug_f("ignoring certificate %s: not a user "
			    "certificate", options.identity_files[i]);
			continue;
		}
		if (key && sshkey_is_sk(key) && options.sk_provider == NULL) {
			debug_f("ignoring authenticator-hosted key "
			    "certificate %s as no "
			    "SecurityKeyProvider has been specified",
			    options.identity_files[i]);
			continue;
		}
		id = xcalloc(1, sizeof(*id));
		id->agent_fd = -1;
		id->key = key;
		id->filename = xstrdup(options.certificate_files[i]);
		id->userprovided = options.certificate_file_userprovided[i];
		TAILQ_INSERT_TAIL(preferred, id, next);
	}
	/* list of keys supported by the agent */
	if ((r = get_agent_identities(ssh, &agent_fd, &idlist)) == 0) {
		for (j = 0; j < idlist->nkeys; j++) {
			found = 0;
			TAILQ_FOREACH(id, &files, next) {
				/*
				 * agent keys from the config file are
				 * preferred
				 */
				if (sshkey_equal(idlist->keys[j], id->key)) {
					TAILQ_REMOVE(&files, id, next);
					TAILQ_INSERT_TAIL(preferred, id, next);
					id->agent_fd = agent_fd;
					found = 1;
					break;
				}
			}
			if (!found && !options.identities_only) {
				id = xcalloc(1, sizeof(*id));
				/* XXX "steals" key/comment from idlist */
				id->key = idlist->keys[j];
				id->filename = idlist->comments[j];
				idlist->keys[j] = NULL;
				idlist->comments[j] = NULL;
				id->agent_fd = agent_fd;
				TAILQ_INSERT_TAIL(&agent, id, next);
			}
		}
		ssh_free_identitylist(idlist);
		/* append remaining agent keys */
		TAILQ_CONCAT(preferred, &agent, next);
		authctxt->agent_fd = agent_fd;
	}
	/* Prefer PKCS11 keys that are explicitly listed */
	TAILQ_FOREACH_SAFE(id, &files, next, tmp) {
		if (id->key == NULL || (id->key->flags & SSHKEY_FLAG_EXT) == 0)
			continue;
		found = 0;
		TAILQ_FOREACH(id2, &files, next) {
			if (id2->key == NULL ||
			    (id2->key->flags & SSHKEY_FLAG_EXT) != 0)
				continue;
			if (sshkey_equal(id->key, id2->key)) {
				TAILQ_REMOVE(&files, id, next);
				TAILQ_INSERT_TAIL(preferred, id, next);
				found = 1;
				break;
			}
		}
		/* If IdentitiesOnly set and key not found then don't use it */
		if (!found && options.identities_only) {
			TAILQ_REMOVE(&files, id, next);
			freezero(id, sizeof(*id));
		}
	}
	/* append remaining keys from the config file */
	TAILQ_CONCAT(preferred, &files, next);
	/* finally, filter by PubkeyAcceptedAlgorithms */
	TAILQ_FOREACH_SAFE(id, preferred, next, id2) {
		if (id->key != NULL && !key_type_allowed_by_config(id->key)) {
			debug("Skipping %s key %s - "
			    "corresponding algo not in PubkeyAcceptedAlgorithms",
			    sshkey_ssh_name(id->key), id->filename);
			TAILQ_REMOVE(preferred, id, next);
			sshkey_free(id->key);
			free(id->filename);
			memset(id, 0, sizeof(*id));
			continue;
		}
	}
	/* List the keys we plan on using */
	TAILQ_FOREACH_SAFE(id, preferred, next, id2) {
		ident = format_identity(id);
		debug("Will attempt key: %s", ident);
		free(ident);
	}
	debug2_f("done");
}

static void
pubkey_cleanup(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	Identity *id;

	if (authctxt->agent_fd != -1) {
		ssh_close_authentication_socket(authctxt->agent_fd);
		authctxt->agent_fd = -1;
	}
	for (id = TAILQ_FIRST(&authctxt->keys); id;
	    id = TAILQ_FIRST(&authctxt->keys)) {
		TAILQ_REMOVE(&authctxt->keys, id, next);
		sshkey_free(id->key);
		free(id->filename);
		free(id);
	}
}

static void
pubkey_reset(Authctxt *authctxt)
{
	Identity *id;

	TAILQ_FOREACH(id, &authctxt->keys, next)
		id->tried = 0;
}

static int
try_identity(struct ssh *ssh, Identity *id)
{
	if (!id->key)
		return (0);
	if (sshkey_type_plain(id->key->type) == KEY_RSA &&
	    (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
		debug("Skipped %s key %s for RSA/MD5 server",
		    sshkey_type(id->key), id->filename);
		return (0);
	}
	return 1;
}

static int
userauth_pubkey(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	Identity *id;
	int sent = 0;
	char *ident;

	while ((id = TAILQ_FIRST(&authctxt->keys))) {
		if (id->tried++)
			return (0);
		/* move key to the end of the queue */
		TAILQ_REMOVE(&authctxt->keys, id, next);
		TAILQ_INSERT_TAIL(&authctxt->keys, id, next);
		/*
		 * send a test message if we have the public key. for
		 * encrypted keys we cannot do this and have to load the
		 * private key instead
		 */
		if (id->key != NULL) {
			if (try_identity(ssh, id)) {
				ident = format_identity(id);
				debug("Offering public key: %s", ident);
				free(ident);
				sent = send_pubkey_test(ssh, id);
			}
		} else {
			debug("Trying private key: %s", id->filename);
			id->key = load_identity_file(id);
			if (id->key != NULL) {
				if (try_identity(ssh, id)) {
					id->isprivate = 1;
					sent = sign_and_send_pubkey(ssh, id);
				}
				sshkey_free(id->key);
				id->key = NULL;
				id->isprivate = 0;
			}
		}
		if (sent)
			return (sent);
	}
	return (0);
}

/*
 * Send userauth request message specifying keyboard-interactive method.
 */
static int
userauth_kbdint(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	int r;

	if (authctxt->attempt_kbdint++ >= options.number_of_password_prompts)
		return 0;
	/* disable if no SSH2_MSG_USERAUTH_INFO_REQUEST has been seen */
	if (authctxt->attempt_kbdint > 1 && !authctxt->info_req_seen) {
		debug3("userauth_kbdint: disable: no info_req_seen");
		ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST, NULL);
		return 0;
	}

	debug2("userauth_kbdint");
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, "")) != 0 ||		/* lang */
	    (r = sshpkt_put_cstring(ssh, options.kbd_interactive_devices ?
	    options.kbd_interactive_devices : "")) != 0 ||
	    (r = sshpkt_send(ssh)) != 0)
		fatal_fr(r, "send packet");

	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST, &input_userauth_info_req);
	return 1;
}

/*
 * parse INFO_REQUEST, prompt user and send INFO_RESPONSE
 */
static int
input_userauth_info_req(int type, u_int32_t seq, struct ssh *ssh)
{
	Authctxt *authctxt = ssh->authctxt;
	char *name = NULL, *inst = NULL, *lang = NULL, *prompt = NULL;
	char *display_prompt = NULL, *response = NULL;
	u_char echo = 0;
	u_int num_prompts, i;
	int r;

	debug2_f("entering");

	if (authctxt == NULL)
		fatal_f("no authentication context");

	authctxt->info_req_seen = 1;

	if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &inst, NULL)) != 0 ||
	    (r = sshpkt_get_cstring(ssh, &lang, NULL)) != 0)
		goto out;
	if (strlen(name) > 0)
		logit("%s", name);
	if (strlen(inst) > 0)
		logit("%s", inst);

	if ((r = sshpkt_get_u32(ssh, &num_prompts)) != 0)
		goto out;
	/*
	 * Begin to build info response packet based on prompts requested.
	 * We commit to providing the correct number of responses, so if
	 * further on we run into a problem that prevents this, we have to
	 * be sure and clean this up and send a correct error response.
	 */
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE)) != 0 ||
	    (r = sshpkt_put_u32(ssh, num_prompts)) != 0)
		goto out;

	debug2_f("num_prompts %d", num_prompts);
	for (i = 0; i < num_prompts; i++) {
		if ((r = sshpkt_get_cstring(ssh, &prompt, NULL)) != 0 ||
		    (r = sshpkt_get_u8(ssh, &echo)) != 0)
			goto out;
		if (asmprintf(&display_prompt, INT_MAX, NULL, "(%s@%s) %s",
		    authctxt->server_user, options.host_key_alias ?
		    options.host_key_alias : authctxt->host, prompt) == -1)
			fatal_f("asmprintf failed");
		response = read_passphrase(display_prompt, echo ? RP_ECHO : 0);
		if ((r = sshpkt_put_cstring(ssh, response)) != 0)
			goto out;
		freezero(response, strlen(response));
		free(prompt);
		free(display_prompt);
		display_prompt = response = prompt = NULL;
	}
	/* done with parsing incoming message. */
	if ((r = sshpkt_get_end(ssh)) != 0 ||
	    (r = sshpkt_add_padding(ssh, 64)) != 0)
		goto out;
	r = sshpkt_send(ssh);
 out:
	if (response)
		freezero(response, strlen(response));
	free(prompt);
	free(display_prompt);
	free(name);
	free(inst);
	free(lang);
	return r;
}

static int
ssh_keysign(struct ssh *ssh, struct sshkey *key, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen)
{
	struct sshbuf *b;
	struct stat st;
	pid_t pid;
	int r, to[2], from[2], status;
	int sock = ssh_packet_get_connection_in(ssh);
	u_char rversion = 0, version = 2;
	void (*osigchld)(int);

	*sigp = NULL;
	*lenp = 0;

	if (stat(_PATH_SSH_KEY_SIGN, &st) == -1) {
		error_f("not installed: %s", strerror(errno));
		return -1;
	}
	if (fflush(stdout) != 0) {
		error_f("fflush: %s", strerror(errno));
		return -1;
	}
	if (pipe(to) == -1) {
		error_f("pipe: %s", strerror(errno));
		return -1;
	}
	if (pipe(from) == -1) {
		error_f("pipe: %s", strerror(errno));
		return -1;
	}
	if ((pid = fork()) == -1) {
		error_f("fork: %s", strerror(errno));
		return -1;
	}
	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
	if (pid == 0) {
		close(from[0]);
		if (dup2(from[1], STDOUT_FILENO) == -1)
			fatal_f("dup2: %s", strerror(errno));
		close(to[1]);
		if (dup2(to[0], STDIN_FILENO) == -1)
			fatal_f("dup2: %s", strerror(errno));
		close(from[1]);
		close(to[0]);

		if (dup2(sock, STDERR_FILENO + 1) == -1)
			fatal_f("dup2: %s", strerror(errno));
		sock = STDERR_FILENO + 1;
		fcntl(sock, F_SETFD, 0);	/* keep the socket on exec */
		closefrom(sock + 1);

		debug3_f("[child] pid=%ld, exec %s",
		    (long)getpid(), _PATH_SSH_KEY_SIGN);
		execl(_PATH_SSH_KEY_SIGN, _PATH_SSH_KEY_SIGN, (char *)NULL);
		fatal_f("exec(%s): %s", _PATH_SSH_KEY_SIGN,
		    strerror(errno));
	}
	close(from[1]);
	close(to[0]);
	sock = STDERR_FILENO + 1;

	if ((b = sshbuf_new()) == NULL)
		fatal_f("sshbuf_new failed");
	/* send # of sock, data to be signed */
	if ((r = sshbuf_put_u32(b, sock)) != 0 ||
	    (r = sshbuf_put_string(b, data, datalen)) != 0)
		fatal_fr(r, "buffer error");
	if (ssh_msg_send(to[1], version, b) == -1)
		fatal_f("couldn't send request");
	sshbuf_reset(b);
	r = ssh_msg_recv(from[0], b);
	close(from[0]);
	close(to[1]);
	if (r < 0) {
		error_f("no reply");
		goto fail;
	}

	errno = 0;
	while (waitpid(pid, &status, 0) == -1) {
		if (errno != EINTR) {
			error_f("waitpid %ld: %s", (long)pid, strerror(errno));
			goto fail;
		}
	}
	if (!WIFEXITED(status)) {
		error_f("exited abnormally");
		goto fail;
	}
	if (WEXITSTATUS(status) != 0) {
		error_f("exited with status %d", WEXITSTATUS(status));
		goto fail;
	}
	if ((r = sshbuf_get_u8(b, &rversion)) != 0) {
		error_fr(r, "buffer error");
		goto fail;
	}
	if (rversion != version) {
		error_f("bad version");
		goto fail;
	}
	if ((r = sshbuf_get_string(b, sigp, lenp)) != 0) {
		error_fr(r, "buffer error");
 fail:
		ssh_signal(SIGCHLD, osigchld);
		sshbuf_free(b);
		return -1;
	}
	ssh_signal(SIGCHLD, osigchld);
	sshbuf_free(b);

	return 0;
}

static int
userauth_hostbased(struct ssh *ssh)
{
	Authctxt *authctxt = (Authctxt *)ssh->authctxt;
	struct sshkey *private = NULL;
	struct sshbuf *b = NULL;
	u_char *sig = NULL, *keyblob = NULL;
	char *fp = NULL, *chost = NULL, *lname = NULL;
	size_t siglen = 0, keylen = 0;
	int i, r, success = 0;

	if (authctxt->ktypes == NULL) {
		authctxt->oktypes = xstrdup(options.hostbased_accepted_algos);
		authctxt->ktypes = authctxt->oktypes;
	}

	/*
	 * Work through each listed type pattern in HostbasedAcceptedAlgorithms,
	 * trying each hostkey that matches the type in turn.
	 */
	for (;;) {
		if (authctxt->active_ktype == NULL)
			authctxt->active_ktype = strsep(&authctxt->ktypes, ",");
		if (authctxt->active_ktype == NULL ||
		    *authctxt->active_ktype == '\0')
			break;
		debug3_f("trying key type %s", authctxt->active_ktype);

		/* check for a useful key */
		private = NULL;
		for (i = 0; i < authctxt->sensitive->nkeys; i++) {
			if (authctxt->sensitive->keys[i] == NULL ||
			    authctxt->sensitive->keys[i]->type == KEY_UNSPEC)
				continue;
			if (!sshkey_match_keyname_to_sigalgs(
			    sshkey_ssh_name(authctxt->sensitive->keys[i]),
			    authctxt->active_ktype))
				continue;
			/* we take and free the key */
			private = authctxt->sensitive->keys[i];
			authctxt->sensitive->keys[i] = NULL;
			break;
		}
		/* Found one */
		if (private != NULL)
			break;
		/* No more keys of this type; advance */
		authctxt->active_ktype = NULL;
	}
	if (private == NULL) {
		free(authctxt->oktypes);
		authctxt->oktypes = authctxt->ktypes = NULL;
		authctxt->active_ktype = NULL;
		debug("No more client hostkeys for hostbased authentication.");
		goto out;
	}

	if ((fp = sshkey_fingerprint(private, options.fingerprint_hash,
	    SSH_FP_DEFAULT)) == NULL) {
		error_f("sshkey_fingerprint failed");
		goto out;
	}
	debug_f("trying hostkey %s %s using sigalg %s",
	    sshkey_ssh_name(private), fp, authctxt->active_ktype);

	/* figure out a name for the client host */
	lname = get_local_name(ssh_packet_get_connection_in(ssh));
	if (lname == NULL) {
		error_f("cannot get local ipaddr/name");
		goto out;
	}

	/* XXX sshbuf_put_stringf? */
	xasprintf(&chost, "%s.", lname);
	debug2_f("chost %s", chost);

	/* construct data */
	if ((b = sshbuf_new()) == NULL) {
		error_f("sshbuf_new failed");
		goto out;
	}
	if ((r = sshkey_to_blob(private, &keyblob, &keylen)) != 0) {
		error_fr(r, "sshkey_to_blob");
		goto out;
	}
	if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->server_user)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->method->name)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->active_ktype)) != 0 ||
	    (r = sshbuf_put_string(b, keyblob, keylen)) != 0 ||
	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
	    (r = sshbuf_put_cstring(b, authctxt->local_user)) != 0) {
		error_fr(r, "buffer error");
		goto out;
	}

#ifdef DEBUG_PK
	sshbuf_dump(b, stderr);
#endif
	if ((r = ssh_keysign(ssh, private, &sig, &siglen,
	    sshbuf_ptr(b), sshbuf_len(b))) != 0) {
		error("sign using hostkey %s %s failed",
		    sshkey_ssh_name(private), fp);
		goto out;
	}
	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->active_ktype)) != 0 ||
	    (r = sshpkt_put_string(ssh, keyblob, keylen)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, chost)) != 0 ||
	    (r = sshpkt_put_cstring(ssh, authctxt->local_user)) != 0 ||
	    (r = sshpkt_put_string(ssh, sig, siglen)) != 0 ||
	    (r = sshpkt_send(ssh)) != 0) {
		error_fr(r, "packet error");
		goto out;
	}
	success = 1;

 out:
	if (sig != NULL)
		freezero(sig, siglen);
	free(keyblob);
	free(lname);
	free(fp);
	free(chost);
	sshkey_free(private);
	sshbuf_free(b);

	return success;
}

/* find auth method */

/*
 * given auth method name, if configurable options permit this method fill
 * in auth_ident field and return true, otherwise return false.
 */
static int
authmethod_is_enabled(Authmethod *method)
{
	if (method == NULL)
		return 0;
	/* return false if options indicate this method is disabled */
	if  (method->enabled == NULL || *method->enabled == 0)
		return 0;
	/* return false if batch mode is enabled but method needs interactive mode */
	if  (method->batch_flag != NULL && *method->batch_flag != 0)
		return 0;
	return 1;
}

static Authmethod *
authmethod_lookup(const char *name)
{
	Authmethod *method = NULL;
	if (name != NULL)
		for (method = authmethods; method->name != NULL; method++)
			if (strcmp(name, method->name) == 0)
				return method;
	debug2("Unrecognized authentication method name: %s", name ? name : "NULL");
	return NULL;
}

/* XXX internal state */
static Authmethod *current = NULL;
static char *supported = NULL;
static char *preferred = NULL;

/*
 * Given the authentication method list sent by the server, return the
 * next method we should try.  If the server initially sends a nil list,
 * use a built-in default list.
 */
static Authmethod *
authmethod_get(char *authlist)
{
	char *name = NULL;
	u_int next;

	/* Use a suitable default if we're passed a nil list.  */
	if (authlist == NULL || strlen(authlist) == 0)
		authlist = options.preferred_authentications;

	if (supported == NULL || strcmp(authlist, supported) != 0) {
		debug3("start over, passed a different list %s", authlist);
		free(supported);
		supported = xstrdup(authlist);
		preferred = options.preferred_authentications;
		debug3("preferred %s", preferred);
		current = NULL;
	} else if (current != NULL && authmethod_is_enabled(current))
		return current;

	for (;;) {
		if ((name = match_list(preferred, supported, &next)) == NULL) {
			debug("No more authentication methods to try.");
			current = NULL;
			return NULL;
		}
		preferred += next;
		debug3("authmethod_lookup %s", name);
		debug3("remaining preferred: %s", preferred);
		if ((current = authmethod_lookup(name)) != NULL &&
		    authmethod_is_enabled(current)) {
			debug3("authmethod_is_enabled %s", name);
			debug("Next authentication method: %s", name);
			free(name);
			return current;
		}
		free(name);
	}
}

static char *
authmethods_get(void)
{
	Authmethod *method = NULL;
	struct sshbuf *b;
	char *list;
	int r;

	if ((b = sshbuf_new()) == NULL)
		fatal_f("sshbuf_new failed");
	for (method = authmethods; method->name != NULL; method++) {
		if (authmethod_is_enabled(method)) {
			if ((r = sshbuf_putf(b, "%s%s",
			    sshbuf_len(b) ? "," : "", method->name)) != 0)
				fatal_fr(r, "buffer error");
		}
	}
	if ((list = sshbuf_dup_string(b)) == NULL)
		fatal_f("sshbuf_dup_string failed");
	sshbuf_free(b);
	return list;
}