/* $OpenBSD: sshconnect2.c,v 1.385 2026/04/02 07:48:13 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 <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/queue.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pwd.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <unistd.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 "sshconnect.h"
#include "authfile.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 "hostfile.h"
#include "ssherr.h"
#include "utf8.h"
#include "sk-api.h"

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

/* import */
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 key_type_allowed(struct sshkey *, const char *);

static int
verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh)
{
        int r;

        if ((r = sshkey_check_rsa_length(hostkey,
            options.required_rsa_size)) != 0)
                fatal_r(r, "Bad server host key");
        if (!key_type_allowed(hostkey, options.hostkeyalgorithms)) {
                fatal("Server host key %s not in HostKeyAlgorithms",
                    sshkey_ssh_name(hostkey));
        }
        if (verify_host_key(xxx_host, xxx_hostaddr, hostkey,
            xxx_conn_info) != 0)
                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, hostname);
        }
        /*
         * 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];
        char *all_key, *hkalgs = NULL;
        int r, use_known_hosts_order = 0;

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

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

        /*
         * 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 (use_known_hosts_order)
                hkalgs = order_hostkeyalgs(host, hostaddr, port, cinfo);

        kex_proposal_populate_entries(ssh, myproposal,
            options.kex_algorithms, options.ciphers, options.macs,
            compression_alg_list(options.compression),
            hkalgs ? hkalgs : options.hostkeyalgorithms);

        free(hkalgs);

        /* 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;
        ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
#endif
        ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
        ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
        ssh->kex->kex[KEX_KEM_MLKEM768X25519_SHA256] = kex_gen_client;
        ssh->kex->verify_host_key=&verify_host_key_callback;

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

#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, uint32_t, struct ssh *);
static int input_userauth_success(int, uint32_t, struct ssh *);
static int input_userauth_failure(int, uint32_t, struct ssh *);
static int input_userauth_banner(int, uint32_t, struct ssh *);
static int input_userauth_error(int, uint32_t, struct ssh *);
static int input_userauth_info_req(int, uint32_t, struct ssh *);
static int input_userauth_pk_ok(int, uint32_t, struct ssh *);
static int input_userauth_passwd_changereq(int, uint32_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, uint32_t, struct ssh *);
static int input_gssapi_token(int type, uint32_t, struct ssh *);
static int input_gssapi_error(int, uint32_t, struct ssh *);
static int input_gssapi_errtok(int, uint32_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;
        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, kex_input_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);
#ifdef GSSAPI
        if (authctxt.gss_supported_mechs != NULL) {
                u_int ms;

                gss_release_oid_set(&ms, &authctxt.gss_supported_mechs);
                authctxt.gss_supported_mechs = NULL;
        }
#endif
        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);
        }
}

static int
input_userauth_service_accept(int type, uint32_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);

        /* accept EXT_INFO at any time during userauth */
        ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, ssh->kex->ext_info_s ?
            &kex_input_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;
}

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;
                }
        }
}

static int
input_userauth_error(int type, uint32_t seq, struct ssh *ssh)
{
        fatal_f("bad message during authentication: type %d", type);
        return 0;
}

static int
input_userauth_banner(int type, uint32_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;
}

static int
input_userauth_success(int type, uint32_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 */
        ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, dispatch_protocol_error);
        return 0;
}

#if 0
static int
input_userauth_success_unexpected(int type, uint32_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

static int
input_userauth_failure(int type, uint32_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;
}

static int
input_userauth_pk_ok(int type, uint32_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);
                r = SSH_ERR_INVALID_FORMAT;
                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);
                r = SSH_ERR_INVALID_FORMAT;
                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);
                r = SSH_ERR_INVALID_FORMAT;
                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;
}

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;
}

static int
input_gssapi_response(int type, uint32_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;
}

static int
input_gssapi_token(int type, uint32_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;
}

static int
input_gssapi_errtok(int type, uint32_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;
}

static int
input_gssapi_error(int type, uint32_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
 */
static int
input_userauth_passwd_changereq(int type, uint32_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, addnl;
        size_t len;

        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 ((len = strlen(info)) > 0) {
                addnl = info[len] != '\n';
                fmprintf(stderr, "%s%s", info, addnl ? "\n" : "");
        }
        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 is_agent = 0, 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;
                is_agent = 1;
        } 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;
        }
 retry_pin:
        /* Prompt for touch for non-agent FIDO keys that request UP */
        if (!is_agent && sshkey_is_sk(sign_key) &&
            (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 (!retried && pin == NULL && !is_agent &&
                    sshkey_is_sk(sign_key) &&
                    r == SSH_ERR_KEY_WRONG_PASSPHRASE) {
                        notify_complete(notifier, NULL);
                        notifier = NULL;
                        xasprintf(&prompt, "Enter PIN for %s key %s: ",
                            sshkey_type(sign_key), id->filename);
                        pin = read_passphrase(prompt, 0);
                        retried = 1;
                        goto retry_pin;
                }
                goto out;
        }

        /*
         * PKCS#11 tokens may not support all signature algorithms,
         * so check what we get back.
         */
        if ((id->key->flags & SSHKEY_FLAG_EXT) != 0 &&
            (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 (id->agent_fd == -1 && 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 && (r = sshkey_check_rsa_length(private,
                    options.required_rsa_size)) != 0) {
                        debug_fr(r, "Skipping key %s", 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(struct sshkey *key, const char *allowlist)
{
        if (match_pattern_list(sshkey_ssh_name(key), allowlist, 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", allowlist, 0) == 1)
                        return 1;
                if (match_pattern_list("rsa-sha2-256", allowlist, 0) == 1)
                        return 1;
                break;
        case KEY_RSA_CERT:
                if (match_pattern_list("rsa-sha2-512-cert-v01@openssh.com",
                    allowlist, 0) == 1)
                        return 1;
                if (match_pattern_list("rsa-sha2-256-cert-v01@openssh.com",
                    allowlist, 0) == 1)
                        return 1;
                break;
        }
        return 0;
}

static int
key_type_allowed_by_config(struct sshkey *key)
{
        return key_type_allowed(key, options.pubkey_accepted_algos);
}

/* 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 disallowed, agent_fd = -1, i, r, found;
        size_t j;
        struct ssh_identitylist *idlist;
        char *cp, *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++) {
                        if ((r = sshkey_check_rsa_length(idlist->keys[j],
                            options.required_rsa_size)) != 0) {
                                debug_fr(r, "ignoring %s agent key",
                                    sshkey_ssh_name(idlist->keys[j]));
                                continue;
                        }
                        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) {
                disallowed = 0;
                cp = NULL;
                if (id->key == NULL)
                        continue;
                if (!key_type_allowed_by_config(id->key)) {
                        debug("Skipping %s key %s - corresponding algorithm "
                            "not in PubkeyAcceptedAlgorithms",
                            sshkey_ssh_name(id->key), id->filename);
                        disallowed = 1;
                } else if (ssh->kex->server_sig_algs != NULL &&
                    (cp = key_sig_algorithm(ssh, id->key)) == NULL) {
                        debug("Skipping %s key %s - corresponding algorithm "
                            "not supported by server",
                            sshkey_ssh_name(id->key), id->filename);
                        disallowed = 1;
                }
                free(cp);
                if (!disallowed)
                        continue;
                /* remove key */
                TAILQ_REMOVE(preferred, id, next);
                sshkey_free(id->key);
                free(id->filename);
                freezero(id, sizeof(*id));
        }
        /* 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
userauth_pubkey(struct ssh *ssh)
{
        Authctxt *authctxt = (Authctxt *)ssh->authctxt;
        Identity *id;
        int sent = 0;
        char *ident;
        static int prepared;

        if (!prepared) {
                pubkey_prepare(ssh, authctxt);
                prepared = 1;
        }

        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) {
                        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) {
                                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, uint32_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, addnl;
        size_t len;

        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 ((len = strlen(name)) > 0) {
                addnl = name[len] != '\n';
                fmprintf(stderr, "%s%s", name, addnl ? "\n" : "");
        }
        if ((len = strlen(inst)) > 0) {
                addnl = inst[len] != '\n';
                fmprintf(stderr, "%s%s", inst, addnl ? "\n" : "");
        }

        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;
                if (fcntl(sock, F_SETFD, 0) == -1) /* keep the socket on exec */
                        debug3_f("fcntl F_SETFD: %s", strerror(errno));
                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;
}