auth.c

/*
 * auth.c - Authentication with SSH protocols
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2003-2013 by Aris Adamantiadis <aris@0xbadc0de.be>
 * Copyright (c) 2008-2013 Andreas Schneider <asn@cryptomilk.org>
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <stdio.h>
#include <string.h>

#ifndef _WIN32
#include <netinet/in.h>
#include <arpa/inet.h>
#endif

#include "libssh/priv.h"
#include "libssh/crypto.h"
#include "libssh/ssh2.h"
#include "libssh/buffer.h"
#include "libssh/agent.h"
#include "libssh/misc.h"
#include "libssh/packet.h"
#include "libssh/session.h"
#include "libssh/keys.h"
#include "libssh/auth.h"
#include "libssh/pki.h"
#include "libssh/gssapi.h"
#include "libssh/legacy.h"

/**
 * @defgroup libssh_auth The SSH authentication functions
 * @ingroup libssh
 *
 * Functions to authenticate with a server.
 *
 * @{
 */

/**
 * @internal
 *
 * @brief Ask for access to the ssh-userauth service.
 *
 * @param[in] session   The SSH session handle.
 *
 * @returns SSH_OK on success, SSH_ERROR on error.
 * @returns SSH_AGAIN on nonblocking mode, if calling that function
 * again is necessary
 */
static int ssh_userauth_request_service(ssh_session session)
{
    int rc;

    rc = ssh_service_request(session, "ssh-userauth");
    if ((rc != SSH_OK) && (rc != SSH_AGAIN)) {
        SSH_LOG(SSH_LOG_WARN,
                "Failed to request \"ssh-userauth\" service");
    }

    return rc;
}

static int ssh_auth_response_termination(void *user)
{
    ssh_session session = (ssh_session)user;
    switch (session->auth.state) {
        case SSH_AUTH_STATE_NONE:
        case SSH_AUTH_STATE_KBDINT_SENT:
        case SSH_AUTH_STATE_GSSAPI_REQUEST_SENT:
        case SSH_AUTH_STATE_GSSAPI_TOKEN:
        case SSH_AUTH_STATE_GSSAPI_MIC_SENT:
        case SSH_AUTH_STATE_PUBKEY_AUTH_SENT:
        case SSH_AUTH_STATE_PUBKEY_OFFER_SENT:
        case SSH_AUTH_STATE_PASSWORD_AUTH_SENT:
        case SSH_AUTH_STATE_AUTH_NONE_SENT:
            return 0;
        default:
            return 1;
    }
}

static const char *ssh_auth_get_current_method(ssh_session session)
{
    const char *method = "unknown";

    switch (session->auth.current_method) {
    case SSH_AUTH_METHOD_NONE:
        method = "none";
        break;
    case SSH_AUTH_METHOD_PASSWORD:
        method = "password";
        break;
    case SSH_AUTH_METHOD_PUBLICKEY:
        method = "publickey";
        break;
    case SSH_AUTH_METHOD_HOSTBASED:
        method = "hostbased";
        break;
    case SSH_AUTH_METHOD_INTERACTIVE:
        method = "keyboard interactive";
        break;
    case SSH_AUTH_METHOD_GSSAPI_MIC:
        method = "gssapi";
        break;
    default:
        break;
    }

    return method;
}

/**
 * @internal
 * @brief Wait for a response of an authentication function.
 *
 * @param[in] session   The SSH session.
 *
 * @returns SSH_AUTH_SUCCESS Authentication success, or pubkey accepted
 *          SSH_AUTH_PARTIAL Authentication succeeded but another mean
 *                           of authentication is needed.
 *          SSH_AUTH_INFO    Data for keyboard-interactive
 *          SSH_AUTH_AGAIN   In nonblocking mode, call has to be made again
 *          SSH_AUTH_ERROR   Error during the process.
 */
static int ssh_userauth_get_response(ssh_session session)
{
    int rc = SSH_AUTH_ERROR;

    rc = ssh_handle_packets_termination(session, SSH_TIMEOUT_USER,
        ssh_auth_response_termination, session);
    if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }
    if (!ssh_auth_response_termination(session)) {
        return SSH_AUTH_AGAIN;
    }

    switch(session->auth.state) {
        case SSH_AUTH_STATE_ERROR:
            rc = SSH_AUTH_ERROR;
            break;
        case SSH_AUTH_STATE_FAILED:
            rc = SSH_AUTH_DENIED;
            break;
        case SSH_AUTH_STATE_INFO:
            rc = SSH_AUTH_INFO;
            break;
        case SSH_AUTH_STATE_PARTIAL:
            rc = SSH_AUTH_PARTIAL;
            break;
        case SSH_AUTH_STATE_PK_OK:
        case SSH_AUTH_STATE_SUCCESS:
            rc = SSH_AUTH_SUCCESS;
            break;
        case SSH_AUTH_STATE_KBDINT_SENT:
        case SSH_AUTH_STATE_GSSAPI_REQUEST_SENT:
        case SSH_AUTH_STATE_GSSAPI_TOKEN:
        case SSH_AUTH_STATE_GSSAPI_MIC_SENT:
        case SSH_AUTH_STATE_PUBKEY_OFFER_SENT:
        case SSH_AUTH_STATE_PUBKEY_AUTH_SENT:
        case SSH_AUTH_STATE_PASSWORD_AUTH_SENT:
        case SSH_AUTH_STATE_AUTH_NONE_SENT:
        case SSH_AUTH_STATE_NONE:
            /* not reached */
            rc = SSH_AUTH_ERROR;
            break;
    }

    return rc;
}

/**
 * @internal
 *
 * @brief Handles a SSH_USERAUTH_BANNER packet.
 *
 * This banner should be shown to user prior to authentication
 */
SSH_PACKET_CALLBACK(ssh_packet_userauth_banner) {
    ssh_string banner;
    (void)type;
    (void)user;

    banner = ssh_buffer_get_ssh_string(packet);
    if (banner == NULL) {
        SSH_LOG(SSH_LOG_WARN,
                "Invalid SSH_USERAUTH_BANNER packet");
    } else {
        SSH_LOG(SSH_LOG_DEBUG,
                "Received SSH_USERAUTH_BANNER packet");
        if (session->banner != NULL)
            SSH_STRING_FREE(session->banner);
        session->banner = banner;
    }

    return SSH_PACKET_USED;
}

/**
 * @internal
 *
 * @brief Handles a SSH_USERAUTH_FAILURE packet.
 *
 * This handles the complete or partial authentication failure.
 */
SSH_PACKET_CALLBACK(ssh_packet_userauth_failure) {
    const char *current_method = ssh_auth_get_current_method(session);
    char *auth_methods = NULL;
    uint8_t partial = 0;
    int rc;
    (void) type;
    (void) user;

    rc = ssh_buffer_unpack(packet, "sb", &auth_methods, &partial);
    if (rc != SSH_OK) {
        ssh_set_error(session, SSH_FATAL,
                      "Invalid SSH_MSG_USERAUTH_FAILURE message");
        session->auth.state = SSH_AUTH_STATE_ERROR;
        goto end;
    }

    if (partial) {
        session->auth.state = SSH_AUTH_STATE_PARTIAL;
        SSH_LOG(SSH_LOG_INFO,
                "Partial success for '%s'. Authentication that can continue: %s",
                current_method,
                auth_methods);
    } else {
        session->auth.state = SSH_AUTH_STATE_FAILED;
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "Access denied for '%s'. Authentication that can continue: %s",
                      current_method,
                      auth_methods);
        SSH_LOG(SSH_LOG_INFO,
                "%s",
                ssh_get_error(session));

    }
    session->auth.supported_methods = 0;
    if (strstr(auth_methods, "password") != NULL) {
        session->auth.supported_methods |= SSH_AUTH_METHOD_PASSWORD;
    }
    if (strstr(auth_methods, "keyboard-interactive") != NULL) {
        session->auth.supported_methods |= SSH_AUTH_METHOD_INTERACTIVE;
    }
    if (strstr(auth_methods, "publickey") != NULL) {
        session->auth.supported_methods |= SSH_AUTH_METHOD_PUBLICKEY;
    }
    if (strstr(auth_methods, "hostbased") != NULL) {
        session->auth.supported_methods |= SSH_AUTH_METHOD_HOSTBASED;
    }
    if (strstr(auth_methods, "gssapi-with-mic") != NULL) {
        session->auth.supported_methods |= SSH_AUTH_METHOD_GSSAPI_MIC;
    }

end:
    session->auth.current_method = SSH_AUTH_METHOD_UNKNOWN;
    SAFE_FREE(auth_methods);

    return SSH_PACKET_USED;
}

/**
 * @internal
 *
 * @brief Handles a SSH_USERAUTH_SUCCESS packet.
 *
 * It is also used to communicate the new to the upper levels.
 */
SSH_PACKET_CALLBACK(ssh_packet_userauth_success)
{
  struct ssh_crypto_struct *crypto = NULL;

  (void)packet;
  (void)type;
  (void)user;

  SSH_LOG(SSH_LOG_DEBUG, "Authentication successful");
  SSH_LOG(SSH_LOG_TRACE, "Received SSH_USERAUTH_SUCCESS");

  session->auth.state = SSH_AUTH_STATE_SUCCESS;
  session->session_state = SSH_SESSION_STATE_AUTHENTICATED;
  session->flags |= SSH_SESSION_FLAG_AUTHENTICATED;

  crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_OUT);
  if (crypto != NULL && crypto->delayed_compress_out) {
      SSH_LOG(SSH_LOG_DEBUG, "Enabling delayed compression OUT");
      crypto->do_compress_out = 1;
  }

  crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_IN);
  if (crypto != NULL && crypto->delayed_compress_in) {
      SSH_LOG(SSH_LOG_DEBUG, "Enabling delayed compression IN");
      crypto->do_compress_in = 1;
  }

    /* Reset errors by previous authentication methods. */
    ssh_reset_error(session);
    session->auth.current_method = SSH_AUTH_METHOD_UNKNOWN;
  return SSH_PACKET_USED;
}

/**
 * @internal
 *
 * @brief Handles a SSH_USERAUTH_PK_OK or SSH_USERAUTH_INFO_REQUEST packet.
 *
 * Since the two types of packets share the same code, additional work is done
 * to understand if we are in a public key or keyboard-interactive context.
 */
SSH_PACKET_CALLBACK(ssh_packet_userauth_pk_ok) {
    int rc;

    SSH_LOG(SSH_LOG_TRACE,
            "Received SSH_USERAUTH_PK_OK/INFO_REQUEST/GSSAPI_RESPONSE");

    if (session->auth.state == SSH_AUTH_STATE_KBDINT_SENT) {
        /* Assuming we are in keyboard-interactive context */
        SSH_LOG(SSH_LOG_TRACE,
                "keyboard-interactive context, "
                "assuming SSH_USERAUTH_INFO_REQUEST");
        rc = ssh_packet_userauth_info_request(session,type,packet,user);
#ifdef WITH_GSSAPI
    } else if (session->auth.state == SSH_AUTH_STATE_GSSAPI_REQUEST_SENT) {
        rc = ssh_packet_userauth_gssapi_response(session, type, packet, user);
#endif
    } else if (session->auth.state == SSH_AUTH_STATE_PUBKEY_OFFER_SENT) {
        session->auth.state = SSH_AUTH_STATE_PK_OK;
        SSH_LOG(SSH_LOG_TRACE, "Assuming SSH_USERAUTH_PK_OK");
        rc = SSH_PACKET_USED;
    } else {
        session->auth.state = SSH_AUTH_STATE_ERROR;
        SSH_LOG(SSH_LOG_TRACE, "SSH_USERAUTH_PK_OK received in wrong state");
        rc = SSH_PACKET_USED;
    }

    return rc;
}

/**
 * @brief Get available authentication methods from the server.
 *
 * This requires the function ssh_userauth_none() to be called before the
 * methods are available. The server MAY return a list of methods that may
 * continue.
 *
 * @param[in] session   The SSH session.
 *
 * @param[in] username  Deprecated, set to NULL.
 *
 * @returns             A bitfield of the following values:
 *                      - SSH_AUTH_METHOD_PASSWORD
 *                      - SSH_AUTH_METHOD_PUBLICKEY
 *                      - SSH_AUTH_METHOD_HOSTBASED
 *                      - SSH_AUTH_METHOD_INTERACTIVE
 *
 * @warning Other reserved flags may appear in future versions.
 * @see ssh_userauth_none()
 */
int ssh_userauth_list(ssh_session session, const char *username)
{
    (void) username; /* unused */

    if (session == NULL) {
        return 0;
    }

    return session->auth.supported_methods;
}

/**
 * @brief Try to authenticate through the "none" method.
 *
 * @param[in] session   The ssh session to use.
 *
 * @param[in] username    The username, this SHOULD be NULL.
 *
 * @returns SSH_AUTH_ERROR:   A serious error happened.\n
 *          SSH_AUTH_DENIED:  Authentication failed: use another method\n
 *          SSH_AUTH_PARTIAL: You've been partially authenticated, you still
 *                            have to use another method\n
 *          SSH_AUTH_SUCCESS: Authentication success\n
 *          SSH_AUTH_AGAIN:   In nonblocking mode, you've got to call this again
 *                            later.
 *
 * @note Most server implementations do not permit changing the username during
 * authentication. The username should only be set with ssh_options_set() only
 * before you connect to the server.
 */
int ssh_userauth_none(ssh_session session, const char *username)
{
    int rc;

    switch (session->pending_call_state) {
        case SSH_PENDING_CALL_NONE:
            break;
        case SSH_PENDING_CALL_AUTH_NONE:
            goto pending;
        default:
            ssh_set_error(session, SSH_FATAL,
                          "Wrong state (%d) during pending SSH call",
                          session->pending_call_state);
            return SSH_AUTH_ERROR;
    }

    rc = ssh_userauth_request_service(session);
    if (rc == SSH_AGAIN) {
        return SSH_AUTH_AGAIN;
    } else if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

    /* request */
    rc = ssh_buffer_pack(session->out_buffer, "bsss",
            SSH2_MSG_USERAUTH_REQUEST,
            username ? username : session->opts.username,
            "ssh-connection",
            "none"
            );
    if (rc < 0) {
        goto fail;
    }

    session->auth.current_method = SSH_AUTH_METHOD_NONE;
    session->auth.state = SSH_AUTH_STATE_AUTH_NONE_SENT;
    session->pending_call_state = SSH_PENDING_CALL_AUTH_NONE;
    rc = ssh_packet_send(session);
    if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

pending:
    rc = ssh_userauth_get_response(session);
    if (rc != SSH_AUTH_AGAIN) {
        session->pending_call_state = SSH_PENDING_CALL_NONE;
    }

    return rc;
fail:
    ssh_set_error_oom(session);
    ssh_buffer_reinit(session->out_buffer);

    return SSH_AUTH_ERROR;
}

/**
 * @brief Try to authenticate with the given public key.
 *
 * To avoid unnecessary processing and user interaction, the following method
 * is provided for querying whether authentication using the 'pubkey' would
 * be possible.
 *
 * @param[in] session     The SSH session.
 *
 * @param[in] username    The username, this SHOULD be NULL.
 *
 * @param[in] pubkey      The public key to try.
 *
 * @return  SSH_AUTH_ERROR:   A serious error happened.\n
 *          SSH_AUTH_DENIED:  The server doesn't accept that public key as an
 *                            authentication token. Try another key or another
 *                            method.\n
 *          SSH_AUTH_PARTIAL: You've been partially authenticated, you still
 *                            have to use another method.\n
 *          SSH_AUTH_SUCCESS: The public key is accepted, you want now to use
 *                            ssh_userauth_publickey().\n
 *          SSH_AUTH_AGAIN:   In nonblocking mode, you've got to call this again
 *                            later.
 *
 * @note Most server implementations do not permit changing the username during
 * authentication. The username should only be set with ssh_options_set() only
 * before you connect to the server.
 */
int ssh_userauth_try_publickey(ssh_session session,
                               const char *username,
                               const ssh_key pubkey)
{
    ssh_string pubkey_s = NULL;
    const char *sig_type_c = NULL;
    bool allowed;
    int rc;

    if (session == NULL) {
        return SSH_AUTH_ERROR;
    }

    if (pubkey == NULL || !ssh_key_is_public(pubkey)) {
        ssh_set_error(session, SSH_FATAL, "Invalid pubkey");
        return SSH_AUTH_ERROR;
    }

    switch(session->pending_call_state) {
        case SSH_PENDING_CALL_NONE:
            break;
        case SSH_PENDING_CALL_AUTH_OFFER_PUBKEY:
            goto pending;
        default:
            ssh_set_error(session,
                          SSH_FATAL,
                          "Wrong state (%d) during pending SSH call",
                          session->pending_call_state);
            return SSH_AUTH_ERROR;
    }

    /* Check if the given public key algorithm is allowed */
    sig_type_c = ssh_key_get_signature_algorithm(session, pubkey->type);
    if (sig_type_c == NULL) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "Invalid key type (unknown)");
        return SSH_AUTH_DENIED;
    }
    rc = ssh_key_algorithm_allowed(session, sig_type_c);
    if (!rc) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The key algorithm '%s' is not allowed to be used by"
                      " PUBLICKEY_ACCEPTED_TYPES configuration option",
                      sig_type_c);
        return SSH_AUTH_DENIED;
    }
    allowed = ssh_key_size_allowed(session, pubkey);
    if (!allowed) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The '%s' key type of size %d is not allowed by "
                      "RSA_MIN_SIZE", sig_type_c, ssh_key_size(pubkey));
        return SSH_AUTH_DENIED;
    }

    rc = ssh_userauth_request_service(session);
    if (rc == SSH_AGAIN) {
        return SSH_AUTH_AGAIN;
    } else if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

    /* public key */
    rc = ssh_pki_export_pubkey_blob(pubkey, &pubkey_s);
    if (rc < 0) {
        goto fail;
    }

    /* request */
    rc = ssh_buffer_pack(session->out_buffer, "bsssbsS",
            SSH2_MSG_USERAUTH_REQUEST,
            username ? username : session->opts.username,
            "ssh-connection",
            "publickey",
            0, /* private key ? */
            sig_type_c, /* algo */
            pubkey_s /* public key */
            );
    if (rc < 0) {
        goto fail;
    }

    SSH_STRING_FREE(pubkey_s);

    session->auth.current_method = SSH_AUTH_METHOD_PUBLICKEY;
    session->auth.state = SSH_AUTH_STATE_PUBKEY_OFFER_SENT;
    session->pending_call_state = SSH_PENDING_CALL_AUTH_OFFER_PUBKEY;
    rc = ssh_packet_send(session);
    if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

pending:
    rc = ssh_userauth_get_response(session);
    if (rc != SSH_AUTH_AGAIN) {
        session->pending_call_state = SSH_PENDING_CALL_NONE;
    }

    return rc;
fail:
    SSH_STRING_FREE(pubkey_s);
    ssh_set_error_oom(session);
    ssh_buffer_reinit(session->out_buffer);

    return SSH_AUTH_ERROR;
}

/**
 * @brief Authenticate with public/private key or certificate.
 *
 * @param[in] session     The SSH session.
 *
 * @param[in] username    The username, this SHOULD be NULL.
 *
 * @param[in] privkey     The private key for authentication.
 *
 * @return  SSH_AUTH_ERROR:   A serious error happened.\n
 *          SSH_AUTH_DENIED:  The server doesn't accept that public key as an
 *                            authentication token. Try another key or another
 *                            method.\n
 *          SSH_AUTH_PARTIAL: You've been partially authenticated, you still
 *                            have to use another method.\n
 *          SSH_AUTH_SUCCESS: The public key is accepted.\n
 *          SSH_AUTH_AGAIN:   In nonblocking mode, you've got to call this again
 *                            later.
 *
 * @note Most server implementations do not permit changing the username during
 * authentication. The username should only be set with ssh_options_set() only
 * before you connect to the server.
 */
int ssh_userauth_publickey(ssh_session session,
                           const char *username,
                           const ssh_key privkey)
{
    ssh_string str = NULL;
    bool allowed;
    int rc;
    const char *sig_type_c = NULL;
    enum ssh_keytypes_e key_type;
    enum ssh_digest_e hash_type;

    if (session == NULL) {
        return SSH_AUTH_ERROR;
    }

    if (privkey == NULL || !ssh_key_is_private(privkey)) {
        ssh_set_error(session, SSH_FATAL, "Invalid private key");
        return SSH_AUTH_ERROR;
    }

    switch(session->pending_call_state) {
        case SSH_PENDING_CALL_NONE:
            break;
        case SSH_PENDING_CALL_AUTH_PUBKEY:
            goto pending;
        default:
            ssh_set_error(session,
                          SSH_FATAL,
                          "Bad call during pending SSH call in ssh_userauth_try_publickey");
            return SSH_AUTH_ERROR;
    }

    /* Cert auth requires presenting the cert type name (*-cert@openssh.com) */
    key_type = privkey->cert != NULL ? privkey->cert_type : privkey->type;

    /* Check if the given public key algorithm is allowed */
    sig_type_c = ssh_key_get_signature_algorithm(session, key_type);
    if (sig_type_c == NULL) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "Invalid key type (unknown)");
        return SSH_AUTH_DENIED;
    }
    rc = ssh_key_algorithm_allowed(session, sig_type_c);
    if (!rc) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The key algorithm '%s' is not allowed to be used by"
                      " PUBLICKEY_ACCEPTED_TYPES configuration option",
                      sig_type_c);
        return SSH_AUTH_DENIED;
    }
    allowed = ssh_key_size_allowed(session, privkey);
    if (!allowed) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The '%s' key type of size %d is not allowed by "
                      "RSA_MIN_SIZE", sig_type_c, ssh_key_size(privkey));
        return SSH_AUTH_DENIED;
    }

    rc = ssh_userauth_request_service(session);
    if (rc == SSH_AGAIN) {
        return SSH_AUTH_AGAIN;
    } else if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

    /* get public key or cert */
    rc = ssh_pki_export_pubkey_blob(privkey, &str);
    if (rc < 0) {
        goto fail;
    }

    /* request */
    rc = ssh_buffer_pack(session->out_buffer, "bsssbsS",
            SSH2_MSG_USERAUTH_REQUEST,
            username ? username : session->opts.username,
            "ssh-connection",
            "publickey",
            1, /* private key */
            sig_type_c, /* algo */
            str /* public key or cert */
            );
    if (rc < 0) {
        goto fail;
    }
    SSH_STRING_FREE(str);

    /* Get the hash type to be used in the signature based on the key type */
    hash_type = ssh_key_type_to_hash(session, privkey->type);

    /* sign the buffer with the private key */
    str = ssh_pki_do_sign(session, session->out_buffer, privkey, hash_type);
    if (str == NULL) {
        goto fail;
    }

    rc = ssh_buffer_add_ssh_string(session->out_buffer, str);
    SSH_STRING_FREE(str);
    str = NULL;
    if (rc < 0) {
        goto fail;
    }

    session->auth.current_method = SSH_AUTH_METHOD_PUBLICKEY;
    session->auth.state = SSH_AUTH_STATE_PUBKEY_AUTH_SENT;
    session->pending_call_state = SSH_PENDING_CALL_AUTH_PUBKEY;
    rc = ssh_packet_send(session);
    if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

pending:
    rc = ssh_userauth_get_response(session);
    if (rc != SSH_AUTH_AGAIN) {
        session->pending_call_state = SSH_PENDING_CALL_NONE;
    }

    return rc;
fail:
    SSH_STRING_FREE(str);
    ssh_set_error_oom(session);
    ssh_buffer_reinit(session->out_buffer);

    return SSH_AUTH_ERROR;
}

static int ssh_userauth_agent_publickey(ssh_session session,
                                        const char *username,
                                        ssh_key pubkey)
{
    ssh_string pubkey_s = NULL;
    ssh_string sig_blob = NULL;
    const char *sig_type_c = NULL;
    bool allowed;
    int rc;

    switch(session->pending_call_state) {
        case SSH_PENDING_CALL_NONE:
            break;
        case SSH_PENDING_CALL_AUTH_AGENT:
            goto pending;
        default:
            ssh_set_error(session,
                          SSH_FATAL,
                          "Bad call during pending SSH call in ssh_userauth_try_publickey");
            return SSH_ERROR;
    }

    rc = ssh_userauth_request_service(session);
    if (rc == SSH_AGAIN) {
        return SSH_AUTH_AGAIN;
    } else if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

    /* public key */
    rc = ssh_pki_export_pubkey_blob(pubkey, &pubkey_s);
    if (rc < 0) {
        goto fail;
    }

    /* Check if the given public key algorithm is allowed */
    sig_type_c = ssh_key_get_signature_algorithm(session, pubkey->type);
    if (sig_type_c == NULL) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "Invalid key type (unknown)");
        SSH_STRING_FREE(pubkey_s);
        return SSH_AUTH_DENIED;
    }
    rc = ssh_key_algorithm_allowed(session, sig_type_c);
    if (!rc) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The key algorithm '%s' is not allowed to be used by"
                      " PUBLICKEY_ACCEPTED_TYPES configuration option",
                      sig_type_c);
        SSH_STRING_FREE(pubkey_s);
        return SSH_AUTH_DENIED;
    }
    allowed = ssh_key_size_allowed(session, pubkey);
    if (!allowed) {
        ssh_set_error(session, SSH_REQUEST_DENIED,
                      "The '%s' key type of size %d is not allowed by "
                      "RSA_MIN_SIZE", sig_type_c, ssh_key_size(pubkey));
        SSH_STRING_FREE(pubkey_s);
        return SSH_AUTH_DENIED;
    }

    /* request */
    rc = ssh_buffer_pack(session->out_buffer, "bsssbsS",
            SSH2_MSG_USERAUTH_REQUEST,
            username ? username : session->opts.username,
            "ssh-connection",
            "publickey",
            1, /* private key */
            sig_type_c, /* algo */
            pubkey_s /* public key */
            );
    SSH_STRING_FREE(pubkey_s);
    if (rc < 0) {
        goto fail;
    }

    /* sign the buffer with the private key */
    sig_blob = ssh_pki_do_sign_agent(session, session->out_buffer, pubkey);
    if (sig_blob == NULL) {
        goto fail;
    }

    rc = ssh_buffer_add_ssh_string(session->out_buffer, sig_blob);
    SSH_STRING_FREE(sig_blob);
    if (rc < 0) {
        goto fail;
    }

    session->auth.current_method = SSH_AUTH_METHOD_PUBLICKEY;
    session->auth.state = SSH_AUTH_STATE_PUBKEY_AUTH_SENT;
    session->pending_call_state = SSH_PENDING_CALL_AUTH_AGENT;
    rc = ssh_packet_send(session);
    if (rc == SSH_ERROR) {
        return SSH_AUTH_ERROR;
    }

pending:
    rc = ssh_userauth_get_response(session);
    if (rc != SSH_AUTH_AGAIN) {
        session->pending_call_state = SSH_PENDING_CALL_NONE;
    }

    return rc;
fail:
    ssh_set_error_oom(session);
    ssh_buffer_reinit(session->out_buffer);
    SSH_STRING_FREE(pubkey_s);

    return SSH_AUTH_ERROR;
}

enum ssh_agent_state_e {
    SSH_AGENT_STATE_NONE = 0,
    SSH_AGENT_STATE_PUBKEY,
    SSH_AGENT_STATE_AUTH
};

struct ssh_agent_state_struct {
    enum ssh_agent_state_e state;
    ssh_key pubkey;
    char *comment;
};

/* Internal function */
void ssh_agent_state_free(void *data)
{
    struct ssh_agent_state_struct *state = data;

    if (state) {
        SSH_STRING_FREE_CHAR(state->comment);
        ssh_key_free(state->pubkey);
        free (state);
    }
}

/**
 * @brief Try to do public key authentication with ssh agent.
 *
 * @param[in]  session  The ssh session to use.
 *
 * @param[in]  username The username, this SHOULD be NULL.
 *
 * @return  SSH_AUTH_ERROR:   A serious error happened.\n
 *          SSH_AUTH_DENIED:  The server doesn't accept that public key as an
 *                            authentication token. Try another key or another
 *                            method.\n
 *          SSH_AUTH_PARTIAL: You've been partially authenticated, you still
 *                            have to use another method.\n
 *          SSH_AUTH_SUCCESS: The public key is accepted, you want now to use
 *                            ssh_userauth_publickey().\n
 *          SSH_AUTH_AGAIN:   In nonblocking mode, you've got to call this again
 *                            later.
 *
 * @note Most server implementations do not permit changing the username during
 * authentication. The username should only be set with ssh_options_set() only
 * before you connect to the server.
 */
int ssh_userauth_agent(ssh_session session,
                       const char *username)
{
    int rc = SSH_AUTH_ERROR;
    struct ssh_agent_state_struct *state;

    if (session == NULL) {
        return SSH_AUTH_ERROR;
    }

    if (!ssh_agent_is_running(session)) {
        return SSH_AUTH_DENIED;
    }

    if (!session->agent_state) {
        session->agent_state = malloc(sizeof(struct ssh_agent_state_struct));
        if (!session->agent_state) {
            ssh_set_error_oom(session);
            return SSH_AUTH_ERROR;
        }
        ZERO_STRUCTP(session->agent_state);
        session->agent_state->state=SSH_AGENT_STATE_NONE;
    }

    state = session->agent_state;
    if (state->pubkey == NULL) {
        state->pubkey = ssh_agent_get_first_ident(session, &state->comment);
    }

    if (state->pubkey == NULL) {
        return SSH_AUTH_DENIED;
    }

    while (state->pubkey != NULL) {
        if (state->state == SSH_AGENT_STATE_NONE) {
            SSH_LOG(SSH_LOG_DEBUG,
                    "Trying identity %s", state->comment);
        }
        if (state->state == SSH_AGENT_STATE_NONE ||
                state->state == SSH_AGENT_STATE_PUBKEY) {
            rc = ssh_userauth_try_publickey(session, username, state->pubkey);
            if (rc == SSH_AUTH_ERROR) {
                ssh_agent_state_free (state);
                session->agent_state = NULL;
                return rc;
            } else if (rc == SSH_AUTH_AGAIN) {
                state->state = SSH_AGENT_STATE_PUBKEY;
                return rc;
            } else if (rc != SSH_AUTH_SUCCESS) {
                SSH_LOG(SSH_LOG_DEBUG,
                        "Public key of %s refused by server", state->comment);
                SSH_STRING_FREE_CHAR(state->comment);
                state->comment = NULL;
                ssh_key_free(state->pubkey);
                state->pubkey = ssh_agent_get_next_ident(session, &state->comment);
                state->state = SSH_AGENT_STATE_NONE;
                continue;
            }

            SSH_LOG(SSH_LOG_DEBUG,
                    "Public key of %s accepted by server", state->comment);
            state->state = SSH_AGENT_STATE_AUTH;
        }
        if (state->state == SSH_AGENT_STATE_AUTH) {
            rc = ssh_userauth_agent_publickey(session, username, state->pubkey);
            if (rc == SSH_AUTH_AGAIN)
                return rc;
            SSH_STRING_FREE_CHAR(state->comment);
            state->comment = NULL;
            if (rc == SSH_AUTH_ERROR || rc == SSH_AUTH_PARTIAL) {
                ssh_agent_state_free (session->agent_state);
                session->agent_state = NULL;
                return rc;
            } else if (rc != SSH_AUTH_SUCCESS) {
                SSH_LOG(SSH_LOG_INFO,
                        "Server accepted public key but refused the signature");
                ssh_key_free(state->pubkey);
                state->pubkey = ssh_agent_get_next_ident(session, &state->comment);
                state->state = SSH_AGENT_STATE_NONE;
                continue;
            }
            ssh_agent_state_free (session->agent_state);
            session->agent_state = NULL;
            return SSH_AUTH_SUCCESS;
        }
    }

    ssh_agent_state_free (session->agent_state);
    session->agent_state = NULL;
    return rc;
}

enum ssh_auth_auto_state_e {
    SSH_AUTH_AUTO_STATE_NONE = 0,
    SSH_AUTH_AUTO_STATE_PUBKEY,
    SSH_AUTH_AUTO_STATE_KEY_IMPORTED,
    SSH_AUTH_AUTO_STATE_PUBKEY_ACCEPTED