Add a ssh_config HostbasedKeyType option to control which

host public key types are tried during hostbased authentication.

This may be used to prevent too many keys being sent to the server,
and blowing past its MaxAuthTries limit.

bz#2211 based on patch by Iain Morgan; ok markus@

7 files changed, 245 insertions, 120 deletions

diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index 5b330e19f76..45027a3cc60 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.229 2015/01/26 03:04:45 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.230 2015/01/30 11:43:14 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -145,7 +145,7 @@ typedef enum {
 	oCanonicalDomains, oCanonicalizeHostname, oCanonicalizeMaxDots,
 	oCanonicalizeFallbackLocal, oCanonicalizePermittedCNAMEs,
 	oStreamLocalBindMask, oStreamLocalBindUnlink, oRevokedHostKeys,
-	oFingerprintHash, oUpdateHostkeys,
+	oFingerprintHash, oUpdateHostkeys, oHostbasedKeyTypes,
 	oIgnoredUnknownOption, oDeprecated, oUnsupported
 } OpCodes;
 
@@ -263,6 +263,7 @@ static struct {
 	{ "revokedhostkeys", oRevokedHostKeys },
 	{ "fingerprinthash", oFingerprintHash },
 	{ "updatehostkeys", oUpdateHostkeys },
+	{ "hostbasedkeytypes", oHostbasedKeyTypes },
 	{ "ignoreunknown", oIgnoreUnknown },
 
 	{ NULL, oBadOption }
@@ -1469,6 +1470,19 @@ parse_int:
 		intptr = &options->update_hostkeys;
 		goto parse_flag;
 
+	case oHostbasedKeyTypes:
+		charptr = &options->hostbased_key_types;
+		arg = strdelim(&s);
+		if (!arg || *arg == '\0')
+			fatal("%.200s line %d: Missing argument.",
+			    filename, linenum);
+		if (!sshkey_names_valid2(arg, 1))
+			fatal("%s line %d: Bad key types '%s'.",
+				filename, linenum, arg ? arg : "<NONE>");
+		if (*activep && *charptr == NULL)
+			*charptr = xstrdup(arg);
+		break;
+
 	case oDeprecated:
 		debug("%s line %d: Deprecated option \"%s\"",
 		    filename, linenum, keyword);
@@ -1648,6 +1662,7 @@ initialize_options(Options * options)
 	options->revoked_host_keys = NULL;
 	options->fingerprint_hash = -1;
 	options->update_hostkeys = -1;
+	options->hostbased_key_types = NULL;
 }
 
 /*
@@ -1827,6 +1842,8 @@ fill_default_options(Options * options)
 		options->fingerprint_hash = SSH_FP_HASH_DEFAULT;
 	if (options->update_hostkeys == -1)
 		options->update_hostkeys = 1;
+	if (options->hostbased_key_types == NULL)
+		options->hostbased_key_types = xstrdup("*");
 
 #define CLEAR_ON_NONE(v) \
 	do { \
@@ -2267,6 +2284,7 @@ dump_client_config(Options *o, const char *host)
 	dump_cfg_string(oControlPath, o->control_path);
 	dump_cfg_string(oHostKeyAlgorithms, o->hostkeyalgorithms ? o->hostkeyalgorithms : KEX_DEFAULT_PK_ALG);
 	dump_cfg_string(oHostKeyAlias, o->host_key_alias);
+	dump_cfg_string(oHostbasedKeyTypes, o->hostbased_key_types);
 	dump_cfg_string(oKbdInteractiveDevices, o->kbd_interactive_devices);
 	dump_cfg_string(oKexAlgorithms, o->kex_algorithms ? o->kex_algorithms : KEX_CLIENT_KEX);
 	dump_cfg_string(oLocalCommand, o->local_command);
@@ -2275,9 +2293,10 @@ dump_client_config(Options *o, const char *host)
 	dump_cfg_string(oPKCS11Provider, o->pkcs11_provider);
 	dump_cfg_string(oPreferredAuthentications, o->preferred_authentications);
 	dump_cfg_string(oProxyCommand, o->proxy_command);
-	dump_cfg_string(oXAuthLocation, o->xauth_location);
 	dump_cfg_string(oRevokedHostKeys, o->revoked_host_keys);
+	dump_cfg_string(oXAuthLocation, o->xauth_location);
 
+	/* Forwards */
 	dump_cfg_forwards(oDynamicForward, o->num_local_forwards, o->local_forwards);
 	dump_cfg_forwards(oLocalForward, o->num_local_forwards, o->local_forwards);
 	dump_cfg_forwards(oRemoteForward, o->num_remote_forwards, o->remote_forwards);
diff --git a/usr.bin/ssh/readconf.h b/usr.bin/ssh/readconf.h
index 7a8ae17c058..701b9c6965e 100644
--- a/usr.bin/ssh/readconf.h
+++ b/usr.bin/ssh/readconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.107 2015/01/26 03:04:45 djm Exp $ */
+/* $OpenBSD: readconf.h,v 1.108 2015/01/30 11:43:14 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -150,6 +150,8 @@ typedef struct {
 
 	int	 update_hostkeys;
 
+	char	*hostbased_key_types;
+
 	char	*ignored_unknown; /* Pattern list of unknown tokens to ignore */
 }       Options;
 
diff --git a/usr.bin/ssh/scp.1 b/usr.bin/ssh/scp.1
index b80ad8bfcfd..0e84780e0e5 100644
--- a/usr.bin/ssh/scp.1
+++ b/usr.bin/ssh/scp.1
@@ -8,9 +8,9 @@
 .\"
 .\" Created: Sun May  7 00:14:37 1995 ylo
 .\"
-.\" $OpenBSD: scp.1,v 1.65 2015/01/26 13:55:29 jmc Exp $
+.\" $OpenBSD: scp.1,v 1.66 2015/01/30 11:43:14 djm Exp $
 .\"
-.Dd $Mdocdate: January 26 2015 $
+.Dd $Mdocdate: January 30 2015 $
 .Dt SCP 1
 .Os
 .Sh NAME
@@ -150,6 +150,7 @@ For full details of the options listed below, and their possible values, see
 .It HashKnownHosts
 .It Host
 .It HostbasedAuthentication
+.It HostbasedKeyTypes
 .It HostKeyAlgorithms
 .It HostKeyAlias
 .It HostName
diff --git a/usr.bin/ssh/sftp.1 b/usr.bin/ssh/sftp.1
index 9eed155f7b7..214f0118c0b 100644
--- a/usr.bin/ssh/sftp.1
+++ b/usr.bin/ssh/sftp.1
@@ -1,4 +1,4 @@
-.\" $OpenBSD: sftp.1,v 1.100 2015/01/26 12:16:36 djm Exp $
+.\" $OpenBSD: sftp.1,v 1.101 2015/01/30 11:43:14 djm Exp $
 .\"
 .\" Copyright (c) 2001 Damien Miller.  All rights reserved.
 .\"
@@ -22,7 +22,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: January 26 2015 $
+.Dd $Mdocdate: January 30 2015 $
 .Dt SFTP 1
 .Os
 .Sh NAME
@@ -215,6 +215,7 @@ For full details of the options listed below, and their possible values, see
 .It HashKnownHosts
 .It Host
 .It HostbasedAuthentication
+.It HostbasedKeyTypes
 .It HostKeyAlgorithms
 .It HostKeyAlias
 .It HostName
diff --git a/usr.bin/ssh/ssh.1 b/usr.bin/ssh/ssh.1
index 7e734abf022..56492120193 100644
--- a/usr.bin/ssh/ssh.1
+++ b/usr.bin/ssh/ssh.1
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh.1,v 1.354 2015/01/26 12:16:36 djm Exp $
-.Dd $Mdocdate: January 26 2015 $
+.\" $OpenBSD: ssh.1,v 1.355 2015/01/30 11:43:14 djm Exp $
+.Dd $Mdocdate: January 30 2015 $
 .Dt SSH 1
 .Os
 .Sh NAME
@@ -445,6 +445,7 @@ For full details of the options listed below, and their possible values, see
 .It HashKnownHosts
 .It Host
 .It HostbasedAuthentication
+.It HostbasedKeyTypes
 .It HostKeyAlgorithms
 .It HostKeyAlias
 .It HostName
diff --git a/usr.bin/ssh/ssh_config.5 b/usr.bin/ssh/ssh_config.5
index 9c0b357955a..95b7bf6e4f6 100644
--- a/usr.bin/ssh/ssh_config.5
+++ b/usr.bin/ssh/ssh_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.201 2015/01/26 12:16:36 djm Exp $
-.Dd $Mdocdate: January 26 2015 $
+.\" $OpenBSD: ssh_config.5,v 1.202 2015/01/30 11:43:14 djm Exp $
+.Dd $Mdocdate: January 30 2015 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -777,6 +777,17 @@ The default is
 This option applies to protocol version 2 only and
 is similar to
 .Cm RhostsRSAAuthentication .
+.It Cm HostbasedKeyTypes
+Specifies the key types that will be used for hostbased authentication
+as a comma-separated pattern list.
+The default
+.Dq *
+will allow all key types.
+The
+.Fl Q
+option of
+.Xr ssh 1
+may be used to list supported key types.
 .It Cm HostKeyAlgorithms
 Specifies the protocol version 2 host key algorithms
 that the client wants to use in order of preference.
diff --git a/usr.bin/ssh/sshconnect2.c b/usr.bin/ssh/sshconnect2.c
index 12515fdf986..9af29559d9a 100644
--- a/usr.bin/ssh/sshconnect2.c
+++ b/usr.bin/ssh/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.222 2015/01/28 22:36:00 djm Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.223 2015/01/30 11:43:14 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -267,6 +267,8 @@ struct cauthctxt {
 	int agent_fd;
 	/* hostbased */
 	Sensitive *sensitive;
+	char *oktypes, *ktypes;
+	const char *active_ktype;
 	/* kbd-interactive */
 	int info_req_seen;
 	/* generic */
@@ -395,6 +397,7 @@ ssh_userauth2(const char *local_user, const char *server_user, char *host,
 	authctxt.authlist = NULL;
 	authctxt.methoddata = NULL;
 	authctxt.sensitive = sensitive;
+	authctxt.active_ktype = authctxt.oktypes = authctxt.ktypes = NULL;
 	authctxt.info_req_seen = 0;
 	authctxt.agent_fd = -1;
 	if (authctxt.method == NULL)
@@ -1446,78 +1449,116 @@ input_userauth_info_req(int type, u_int32_t seq, void *ctxt)
 }
 
 static int
-ssh_keysign(Key *key, u_char **sigp, u_int *lenp,
-    u_char *data, u_int datalen)
+ssh_keysign(struct sshkey *key, u_char **sigp, size_t *lenp,
+    const u_char *data, size_t datalen)
 {
-	Buffer b;
+	struct sshbuf *b;
 	struct stat st;
 	pid_t pid;
-	int to[2], from[2], status, version = 2;
+	int i, r, to[2], from[2], status, sock = packet_get_connection_in();
+	u_char rversion = 0, version = 2;
+	void (*osigchld)(int);
 
-	debug2("ssh_keysign called");
+	*sigp = NULL;
+	*lenp = 0;
 
 	if (stat(_PATH_SSH_KEY_SIGN, &st) < 0) {
-		error("ssh_keysign: not installed: %s", strerror(errno));
+		error("%s: not installed: %s", __func__, strerror(errno));
+		return -1;
+	}
+	if (fflush(stdout) != 0) {
+		error("%s: fflush: %s", __func__, strerror(errno));
 		return -1;
 	}
-	if (fflush(stdout) != 0)
-		error("ssh_keysign: fflush: %s", strerror(errno));
 	if (pipe(to) < 0) {
-		error("ssh_keysign: pipe: %s", strerror(errno));
+		error("%s: pipe: %s", __func__, strerror(errno));
 		return -1;
 	}
 	if (pipe(from) < 0) {
-		error("ssh_keysign: pipe: %s", strerror(errno));
+		error("%s: pipe: %s", __func__, strerror(errno));
 		return -1;
 	}
 	if ((pid = fork()) < 0) {
-		error("ssh_keysign: fork: %s", strerror(errno));
+		error("%s: fork: %s", __func__, strerror(errno));
 		return -1;
 	}
+	osigchld = signal(SIGCHLD, SIG_DFL);
 	if (pid == 0) {
 		/* keep the socket on exec */
-		fcntl(packet_get_connection_in(), F_SETFD, 0);
+		fcntl(sock, F_SETFD, 0);
 		permanently_drop_suid(getuid());
 		close(from[0]);
 		if (dup2(from[1], STDOUT_FILENO) < 0)
-			fatal("ssh_keysign: dup2: %s", strerror(errno));
+			fatal("%s: dup2: %s", __func__, strerror(errno));
 		close(to[1]);
 		if (dup2(to[0], STDIN_FILENO) < 0)
-			fatal("ssh_keysign: dup2: %s", strerror(errno));
+			fatal("%s: dup2: %s", __func__, strerror(errno));
 		close(from[1]);
 		close(to[0]);
+		/* Close everything but stdio and the socket */
+		for (i = STDERR_FILENO + 1; i < sock; i++)
+			close(i);
+		closefrom(sock + 1);
+		debug3("%s: [child] pid=%ld, exec %s",
+		    __func__, (long)getpid(), _PATH_SSH_KEY_SIGN);
 		execl(_PATH_SSH_KEY_SIGN, _PATH_SSH_KEY_SIGN, (char *) 0);
-		fatal("ssh_keysign: exec(%s): %s", _PATH_SSH_KEY_SIGN,
+		fatal("%s: exec(%s): %s", __func__, _PATH_SSH_KEY_SIGN,
 		    strerror(errno));
 	}
 	close(from[1]);
 	close(to[0]);
 
-	buffer_init(&b);
-	buffer_put_int(&b, packet_get_connection_in()); /* send # of socket */
-	buffer_put_string(&b, data, datalen);
-	if (ssh_msg_send(to[1], version, &b) == -1)
-		fatal("ssh_keysign: couldn't send request");
-
-	if (ssh_msg_recv(from[0], &b) < 0) {
-		error("ssh_keysign: no reply");
-		buffer_free(&b);
-		return -1;
-	}
+	if ((b = sshbuf_new()) == NULL)
+		fatal("%s: sshbuf_new failed", __func__);
+	/* send # of sock, data to be signed */
+	if ((r = sshbuf_put_u32(b, sock) != 0) ||
+	    (r = sshbuf_put_string(b, data, datalen)) != 0)
+		fatal("%s: buffer error: %s", __func__, ssh_err(r));
+	if (ssh_msg_send(to[1], version, b) == -1)
+		fatal("%s: couldn't send request", __func__);
+	sshbuf_reset(b);
+	r = ssh_msg_recv(from[0], b);
 	close(from[0]);
 	close(to[1]);
+	if (r < 0) {
+		error("%s: no reply", __func__);
+		goto fail;
+	}
 
-	while (waitpid(pid, &status, 0) < 0)
-		if (errno != EINTR)
-			break;
-
-	if (buffer_get_char(&b) != version) {
-		error("ssh_keysign: bad version");
-		buffer_free(&b);
+	errno = 0;
+	while (waitpid(pid, &status, 0) < 0) {
+		if (errno != EINTR) {
+			error("%s: waitpid %ld: %s",
+			    __func__, (long)pid, strerror(errno));
+			goto fail;
+		}
+	}
+	if (!WIFEXITED(status)) {
+		error("%s: exited abnormally", __func__);
+		goto fail;
+	}
+	if (WEXITSTATUS(status) != 0) {
+		error("%s: exited with status %d",
+		    __func__, WEXITSTATUS(status));
+		goto fail;
+	}
+	if ((r = sshbuf_get_u8(b, &rversion)) != 0) {
+		error("%s: buffer error: %s", __func__, ssh_err(r));
+		goto fail;
+	}
+	if (rversion != version) {
+		error("%s: bad version", __func__);
+		goto fail;
+	}
+	if ((r = sshbuf_get_string(b, sigp, lenp)) != 0) {
+		error("%s: buffer error: %s", __func__, ssh_err(r));
+ fail:
+		signal(SIGCHLD, osigchld);
+		sshbuf_free(b);
 		return -1;
 	}
-	*sigp = buffer_get_string(&b, lenp);
-	buffer_free(&b);
+	signal(SIGCHLD, osigchld);
+	sshbuf_free(b);
 
 	return 0;
 }
@@ -1525,100 +1566,149 @@ ssh_keysign(Key *key, u_char **sigp, u_int *lenp,
 int
 userauth_hostbased(Authctxt *authctxt)
 {
-	Key *private = NULL;
-	Sensitive *sensitive = authctxt->sensitive;
-	Buffer b;
-	u_char *signature, *blob;
-	char *chost, *pkalg, *p;
+	struct ssh *ssh = active_state;
+	struct sshkey *private = NULL;
+	struct sshbuf *b = NULL;
 	const char *service;
-	u_int blen, slen;
-	int ok, i, found = 0;
-
-	/* XXX provide some way to allow user to specify key types attempted */
+	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_key_types);
+		authctxt->ktypes = authctxt->oktypes;
+	}
 
-	/* check for a useful key */
-	for (i = 0; i < sensitive->nkeys; i++) {
-		private = sensitive->keys[i];
-		if (private && private->type != KEY_RSA1) {
-			found = 1;
+	/*
+	 * Work through each listed type pattern in HostbasedKeyTypes,
+	 * 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("%s: trying key type %s", __func__,
+		    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_RSA1 ||
+			    authctxt->sensitive->keys[i]->type == KEY_UNSPEC)
+				continue;
+			if (match_pattern_list(
+			    sshkey_ssh_name(authctxt->sensitive->keys[i]),
+			    authctxt->active_ktype,
+			    strlen(authctxt->active_ktype), 0) != 1)
+				continue;
 			/* we take and free the key */
-			sensitive->keys[i] = NULL;
+			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 (!found) {
+	if (private == NULL) {
+		free(authctxt->oktypes);
+		authctxt->oktypes = authctxt->ktypes = NULL;
+		authctxt->active_ktype = NULL;
 		debug("No more client hostkeys for hostbased authentication.");
-		return 0;
+		goto out;
 	}
 
-	debug("%s: trying hostkey type %s", __func__, key_type(private));
-
-	if (key_to_blob(private, &blob, &blen) == 0) {
-		key_free(private);
-		return 0;
+	if ((fp = sshkey_fingerprint(private, options.fingerprint_hash,
+	    SSH_FP_DEFAULT)) == NULL) {
+		error("%s: sshkey_fingerprint failed", __func__);
+		goto out;
 	}
+	debug("%s: trying hostkey %s %s",
+	    __func__, sshkey_ssh_name(private), fp);
 
 	/* figure out a name for the client host */
-	p = get_local_name(packet_get_connection_in());
-	if (p == NULL) {
-		error("userauth_hostbased: cannot get local ipaddr/name");
-		key_free(private);
-		free(blob);
-		return 0;
+	if ((lname = get_local_name(packet_get_connection_in())) == NULL) {
+		error("%s: cannot get local ipaddr/name", __func__);
+		goto out;
 	}
-	xasprintf(&chost, "%s.", p);
-	debug2("userauth_hostbased: chost %s", chost);
-	free(p);
+
+	/* XXX sshbuf_put_stringf? */
+	xasprintf(&chost, "%s.", lname);
+	debug2("%s: chost %s", __func__, chost);
 
 	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 	    authctxt->service;
-	pkalg = xstrdup(key_ssh_name(private));
-	buffer_init(&b);
+
 	/* construct data */
-	buffer_put_string(&b, session_id2, session_id2_len);
-	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
-	buffer_put_cstring(&b, authctxt->server_user);
-	buffer_put_cstring(&b, service);
-	buffer_put_cstring(&b, authctxt->method->name);
-	buffer_put_cstring(&b, pkalg);
-	buffer_put_string(&b, blob, blen);
-	buffer_put_cstring(&b, chost);
-	buffer_put_cstring(&b, authctxt->local_user);
+	if ((b = sshbuf_new()) == NULL) {
+		error("%s: sshbuf_new failed", __func__);
+		goto out;
+	}
+	if ((r = sshkey_to_blob(private, &keyblob, &keylen)) != 0) {
+		error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
+		goto out;
+	}
+	if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 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, service)) != 0 ||
+	    (r = sshbuf_put_cstring(b, authctxt->method->name)) != 0 ||
+	    (r = sshbuf_put_cstring(b, key_ssh_name(private))) != 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("%s: buffer error: %s", __func__, ssh_err(r));
+		goto out;
+	}
+
 #ifdef DEBUG_PK
-	buffer_dump(&b);
+	sshbuf_dump(b, stderr);
 #endif
-	if (sensitive->external_keysign)
-		ok = ssh_keysign(private, &signature, &slen,
-		    buffer_ptr(&b), buffer_len(&b));
-	else
-		ok = key_sign(private, &signature, &slen,
-		    buffer_ptr(&b), buffer_len(&b));
-	key_free(private);
-	buffer_free(&b);
-	if (ok != 0) {
-		error("key_sign failed");
-		free(chost);
-		free(pkalg);
-		free(blob);
-		return 0;
+	if (authctxt->sensitive->external_keysign)
+		r = ssh_keysign(private, &sig, &siglen,
+		    sshbuf_ptr(b), sshbuf_len(b));
+	else if ((r = sshkey_sign(private, &sig, &siglen,
+	    sshbuf_ptr(b), sshbuf_len(b), datafellows)) != 0)
+		debug("%s: sshkey_sign: %s", __func__, ssh_err(r));
+	if (r != 0) {
+		error("sign using hostkey %s %s failed",
+		    sshkey_ssh_name(private), fp);
+		goto out;
 	}
-	packet_start(SSH2_MSG_USERAUTH_REQUEST);
-	packet_put_cstring(authctxt->server_user);
-	packet_put_cstring(authctxt->service);
-	packet_put_cstring(authctxt->method->name);
-	packet_put_cstring(pkalg);
-	packet_put_string(blob, blen);
-	packet_put_cstring(chost);
-	packet_put_cstring(authctxt->local_user);
-	packet_put_string(signature, slen);
-	explicit_bzero(signature, slen);
-	free(signature);
+	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, key_ssh_name(private))) != 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("%s: packet error: %s", __func__, ssh_err(r));
+		goto out;
+	}
+	success = 1;
+
+ out:
+	if (sig != NULL) {
+		explicit_bzero(sig, siglen);
+		free(sig);
+	}
+	free(keyblob);
+	free(lname);
+	free(fp);
 	free(chost);
-	free(pkalg);
-	free(blob);
+	sshkey_free(private);
+	sshbuf_free(b);
 
-	packet_send();
-	return 1;
+	return success;
 }
 
 /* find auth method */