libssh first steps

Here I describe some first steps for using libssh on an old setup (WinXP with Visual Studio 2008). I think steps for other platforms are more or less similar.

OpenSSL:
Win32OpenSSL-1_0_2m.exe from http://slproweb.com/products/Win32OpenSSL.html
-> Install it.

zlib123dll.zip from http://www.winimage.com/zLibDll/
zlibwapi.dll renamed to zlib1.dll
-> I placed it into my working directory.

libssh-0.7.2-msvc.zip from https://red.libssh.org/projects/libssh/files
-> files placed into c:\Programme\Microsoft Visual Studio 9.0\VC in my case

Now everything is ready for running a simple example. It is a client that executes a command on a ssh server (a Kali box here):

 
#include <libssh/libssh.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>

int verify_knownhost(ssh_session session)
{
  int state, hlen;
  unsigned char *hash = NULL;
  char *hexa;
  char buf[10];
  state = ssh_is_server_known(session);
  hlen = ssh_get_pubkey_hash(session, &hash);
  if (hlen < 0)
    return -1;
  switch (state)
  {
    case SSH_SERVER_KNOWN_OK:
      break; /* ok */
    case SSH_SERVER_KNOWN_CHANGED:
      fprintf(stderr, "Host key for server changed: it is now:\n");
      ssh_print_hexa("Public key hash", hash, hlen);
      fprintf(stderr, "For security reasons, connection will be stopped\n");
      free(hash);
      return -1;
    case SSH_SERVER_FOUND_OTHER:
      fprintf(stderr, "The host key for this server was not found but an other"
        "type of key exists.\n");
      fprintf(stderr, "An attacker might change the default server key to"
        "confuse your client into thinking the key does not exist\n");
      free(hash);
      return -1;
    case SSH_SERVER_FILE_NOT_FOUND:
      fprintf(stderr, "Could not find known host file.\n");
      fprintf(stderr, "If you accept the host key here, the file will be"
       "automatically created.\n");
      /* fallback to SSH_SERVER_NOT_KNOWN behavior */
    case SSH_SERVER_NOT_KNOWN:
      hexa = ssh_get_hexa(hash, hlen);
      fprintf(stderr,"The server is unknown. Do you trust the host key?\n");
      fprintf(stderr, "Public key hash: %s\n", hexa);
      free(hexa);
      if (fgets(buf, sizeof(buf), stdin) == NULL)
      {
        free(hash);
        return -1;
      }
      if (strncmp(buf, "yes", 3) != 0)
      {
        free(hash);
        return -1;
      }
      if (ssh_write_knownhost(session) < 0)
      {
        fprintf(stderr, "Error %s\n", strerror(errno));
        free(hash);
        return -1;
      }
      break;
    case SSH_SERVER_ERROR:
      fprintf(stderr, "Error %s", ssh_get_error(session));
      free(hash);
      return -1;
  }
  free(hash);
  return 0;
}

int show_remote_processes(ssh_session session)
{
  ssh_channel channel;
  int rc;
  char buffer[256];
  int nbytes;
  channel = ssh_channel_new(session);
  if (channel == NULL)
    return SSH_ERROR;
  rc = ssh_channel_open_session(channel);
  if (rc != SSH_OK)
  {
    ssh_channel_free(channel);
    return rc;
  }
  rc = ssh_channel_request_exec(channel, "ps aux");
  if (rc != SSH_OK)
  {
    ssh_channel_close(channel);
    ssh_channel_free(channel);
    return rc;
  }
  nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
  while (nbytes > 0)
  {
    if (write(1, buffer, nbytes) != (unsigned int) nbytes)
    {
      ssh_channel_close(channel);
      ssh_channel_free(channel);
      return SSH_ERROR;
    }
    nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
  }

  if (nbytes < 0)
  {
    ssh_channel_close(channel);
    ssh_channel_free(channel);
    return SSH_ERROR;
  }
  ssh_channel_send_eof(channel);
  ssh_channel_close(channel);
  ssh_channel_free(channel);
  return SSH_OK;
}

int main()
{
  ssh_session my_ssh_session;
  int rc;
  char *password;
  // Open session and set options
  my_ssh_session = ssh_new();
  if (my_ssh_session == NULL)
    exit(-1);
  ssh_options_set(my_ssh_session, SSH_OPTIONS_HOST, "192.168.153.149");
  ssh_options_set(my_ssh_session, SSH_OPTIONS_USER, "root");
  // Connect to server
  rc = ssh_connect(my_ssh_session);
  if (rc != SSH_OK)
  {
    fprintf(stderr, "Error connecting to localhost: %s\n",
            ssh_get_error(my_ssh_session));
    ssh_free(my_ssh_session);
    exit(-1);
  }
  // Verify the server's identity
  // For the source code of verify_knowhost(), check previous example
  if (verify_knownhost(my_ssh_session) < 0)
  {
    ssh_disconnect(my_ssh_session);
    ssh_free(my_ssh_session);
    exit(-1);
  }
  // Authenticate ourselves
  // Give password here
  password = ""; //getpass("Password: ");
  rc = ssh_userauth_password(my_ssh_session, NULL, password);
  if (rc != SSH_AUTH_SUCCESS)
  {
    fprintf(stderr, "Error authenticating with password: %s\n",
            ssh_get_error(my_ssh_session));
    ssh_disconnect(my_ssh_session);
    ssh_free(my_ssh_session);
    exit(-1);
  }
  show_remote_processes(my_ssh_session);
  ssh_disconnect(my_ssh_session);
  ssh_free(my_ssh_session);
}

Compile with:

cl test.c /link ssh.lib

Output:

E:\>test
USER        PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root          1  0.0  0.3 139204  6352 ?        Ss   Oct23   0:33 /sbin/init
root          2  0.0  0.0      0     0 ?        S    Oct23   0:00 [kthreadd]
root          3  0.0  0.0      0     0 ?        S    Oct23   0:01 [ksoftirqd/0]
root          5  0.0  0.0      0     0 ?        S<   Oct23   0:00 [kworker/0:0H]

root          7  0.0  0.0      0     0 ?        S    Oct23   0:19 [rcu_sched]
root          8  0.0  0.0      0     0 ?        S    Oct23   0:00 [rcu_bh]
root          9  0.0  0.0      0     0 ?        S    Oct23   0:01 [migration/0]
root         10  0.0  0.0      0     0 ?        S<   Oct23   0:00 [lru-add-drain]
...

The code comes from the tutorial:
http://api.libssh.org/master/libssh_tutorial.html