gnupg/agent/command.c

/* command.c - gpg-agent command handler
 *	Copyright (C) 2001, 2002 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

/* FIXME: we should not use the default assuan buffering but setup
   some buffering in secure mempory to protect session keys etc. */

#include <config.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>

#include "agent.h"
#include "../assuan/assuan.h"

/* maximum allowed size of the inquired ciphertext */
#define MAXLEN_CIPHERTEXT 4096
/* maximum allowed size of the key parameters */
#define MAXLEN_KEYPARAM 1024

#define set_error(e,t) assuan_set_error (ctx, ASSUAN_ ## e, (t))


#if MAX_DIGEST_LEN < 20
#error MAX_DIGEST_LEN shorter than keygrip
#endif

/* Data used to associate an Assuan context with local server data */
struct server_local_s {
  ASSUAN_CONTEXT assuan_ctx;
  int message_fd;
};





static void
reset_notify (ASSUAN_CONTEXT ctx)
{
  CTRL ctrl = assuan_get_pointer (ctx);

  memset (ctrl->keygrip, 0, 20);
  ctrl->have_keygrip = 0;
  ctrl->digest.valuelen = 0;
}

/* SIGKEY <hexstring_with_keygrip>
   SETKEY <hexstring_with_keygrip>
  
   Set the  key used for a sign or decrypt operation */
static int
cmd_sigkey (ASSUAN_CONTEXT ctx, char *line)
{
  int n;
  char *p;
  CTRL ctrl = assuan_get_pointer (ctx);
  unsigned char *buf;

  /* parse the hash value */
  for (p=line,n=0; hexdigitp (p); p++, n++)
    ;
  if (*p)
    return set_error (Parameter_Error, "invalid hexstring");
  if ((n&1))
    return set_error (Parameter_Error, "odd number of digits");
  n /= 2;
  if (n != 20)
    return set_error (Parameter_Error, "invalid length of keygrip");

  buf = ctrl->keygrip;
  for (p=line, n=0; n < 20; p += 2, n++)
    buf[n] = xtoi_2 (p);
  ctrl->have_keygrip = 1;
  return 0;
}

/* SETHASH <algonumber> <hexstring> 

  The client can use this command to tell the server about the data
  (which usually is a hash) to be signed. */
static int
cmd_sethash (ASSUAN_CONTEXT ctx, char *line)
{
  int n;
  char *p;
  CTRL ctrl = assuan_get_pointer (ctx);
  unsigned char *buf;
  char *endp;
  int algo;

  /* parse the algo number and check it */
  algo = (int)strtoul (line, &endp, 10);
  for (line = endp; *line == ' ' || *line == '\t'; line++)
    ;
  if (!algo || gcry_md_test_algo (algo))
    return set_error (Unsupported_Algorithm, NULL);
  ctrl->digest.algo = algo;

  /* parse the hash value */
  for (p=line,n=0; hexdigitp (p); p++, n++)
    ;
  if (*p)
    return set_error (Parameter_Error, "invalid hexstring");
  if ((n&1))
    return set_error (Parameter_Error, "odd number of digits");
  n /= 2;
  if (n != 16 && n != 20 && n != 24 && n != 32)
    return set_error (Parameter_Error, "unsupported length of hash");
  if (n > MAX_DIGEST_LEN)
    return set_error (Parameter_Error, "hash value to long");

  buf = ctrl->digest.value;
  ctrl->digest.valuelen = n;
  for (p=line, n=0; n < ctrl->digest.valuelen; p += 2, n++)
    buf[n] = xtoi_2 (p);
  for (; n < ctrl->digest.valuelen; n++)
    buf[n] = 0;
  return 0;
}


/* PKSIGN <options>

   Perform the actual sign operation. Neither input nor output are
   sensitive to eavesdropping */
static int
cmd_pksign (ASSUAN_CONTEXT ctx, char *line)
{
  int rc;
  CTRL ctrl = assuan_get_pointer (ctx);

  rc = agent_pksign (ctrl, assuan_get_data_fp (ctx));
  return map_to_assuan_status (rc);
}

/* PKDECRYPT <options>

   Perform the actual decrypt operation.  Input is not 
   sensitive to eavesdropping */
static int
cmd_pkdecrypt (ASSUAN_CONTEXT ctx, char *line)
{
  int rc;
  CTRL ctrl = assuan_get_pointer (ctx);
  char *value;
  size_t valuelen;

  /* First inquire the data to decrypt */
  rc = assuan_inquire (ctx, "CIPHERTEXT",
                       &value, &valuelen, MAXLEN_CIPHERTEXT);
  if (rc)
    return rc;

  rc = agent_pkdecrypt (ctrl, value, valuelen, assuan_get_data_fp (ctx));
  xfree (value);
  return map_to_assuan_status (rc);
}


/* GENKEY

   Generate a new key, store the secret part and return the public
   part.  Here is an example transaction:

   C: GENKEY
   S: INQUIRE KEYPARM
   C: D (genkey (rsa (nbits  1024)))
   C: END
   S: D (public-key
   S: D   (rsa (n 326487324683264) (e 10001)))
   S  OK key created
*/

static int
cmd_genkey (ASSUAN_CONTEXT ctx, char *line)
{
  CTRL ctrl = assuan_get_pointer (ctx);
  int rc;
  char *value;
  size_t valuelen;

  /* First inquire the parameters */
  rc = assuan_inquire (ctx, "KEYPARAM", &value, &valuelen, MAXLEN_KEYPARAM);
  if (rc)
    return rc;

  rc = agent_genkey (ctrl, value, valuelen, assuan_get_data_fp (ctx));
  xfree (value);
  return map_to_assuan_status (rc);
}


/* GET_PASSPHRASE <cache_id> [<error_message> <prompt> <description>]

   This function is usually used to ask for a passphrase to be used
   for conventional encryption, but may aslo be used by programs which
   need specal handling of passphrases.  This command uses a syntax
   which helps clients to use the agent with minimum effort.  The
   agent either returns with an error or with a OK followed by the hex
   encoded passphrase.  Note that the length of the strings is
   implicitly limited by the maximum length of a command.
*/

static int
cmd_get_passphrase (ASSUAN_CONTEXT ctx, char *line)
{
  int rc;
  char *response;
  char *desc, *prompt, *errtext;

  /* FIXME: Parse that stuff */
  desc = "We need a passphrase";
  prompt = NULL;
  errtext = "try again";

  rc = agent_get_passphrase (&response, desc, prompt, errtext);
  if (!rc)
    {
      rc = assuan_set_okay_line (ctx, response);
      xfree (response);
    }

  return map_to_assuan_status (rc);
}


/* CLEAR_PASSPHRASE <cache_id>

   may be used to invalidate the cache entry for a passphrase.  The
   function returns with OK even when ther eis no cached passphrase.
*/

static int
cmd_clear_passphrase (ASSUAN_CONTEXT ctx, char *line)
{
  int rc;

  /* fixme: no caching yet. so return with OK */
  rc = 0;

  return map_to_assuan_status (rc);
}



/* Tell the assuan library about our commands */
static int
register_commands (ASSUAN_CONTEXT ctx)
{
  static struct {
    const char *name;
    int cmd_id;
    int (*handler)(ASSUAN_CONTEXT, char *line);
  } table[] = {
    { "SIGKEY",     0,  cmd_sigkey },
    { "SETKEY",     0,  cmd_sigkey },
    { "SETHASH",    0,  cmd_sethash },
    { "PKSIGN",     0,  cmd_pksign },
    { "PKDECRYPT",  0,  cmd_pkdecrypt },
    { "GENKEY",     0,  cmd_genkey },
    { "GET_PASSPHRASE",0, cmd_get_passphrase },
    { "CLEAR_PASSPHRASE",0, cmd_clear_passphrase },
    { "",     ASSUAN_CMD_INPUT, NULL }, 
    { "",     ASSUAN_CMD_OUTPUT, NULL }, 
    { NULL }
  };
  int i, j, rc;

  for (i=j=0; table[i].name; i++)
    {
      rc = assuan_register_command (ctx,
                                    table[i].cmd_id? table[i].cmd_id
                                                   : (ASSUAN_CMD_USER + j++),
                                    table[i].name, table[i].handler);
      if (rc)
        return rc;
    } 
  assuan_register_reset_notify (ctx, reset_notify);
  return 0;
}


/* Startup the server */
void
start_command_handler (void)
{
  int rc;
  int filedes[2];
  ASSUAN_CONTEXT ctx;
  struct server_control_s ctrl;

  memset (&ctrl, 0, sizeof ctrl);

  /* For now we use a simple pipe based server so that we can work
     from scripts.  We will later add options to run as a daemon and
     wait for requests on a Unix domain socket */
  filedes[0] = 0;
  filedes[1] = 1;
  rc = assuan_init_pipe_server (&ctx, filedes);
  if (rc)
    {
      log_error ("failed to initialize the server: %s\n",
                 assuan_strerror(rc));
      agent_exit (2);
    }
  rc = register_commands (ctx);
  if (rc)
    {
      log_error ("failed to the register commands with Assuan: %s\n",
                 assuan_strerror(rc));
      agent_exit (2);
    }

  assuan_set_pointer (ctx, &ctrl);
  ctrl.server_local = xcalloc (1, sizeof *ctrl.server_local);
  ctrl.server_local->assuan_ctx = ctx;
  ctrl.server_local->message_fd = -1;

  for (;;)
    {
      rc = assuan_accept (ctx);
      if (rc == -1)
        {
          break;
        }
      else if (rc)
        {
          log_info ("Assuan accept problem: %s\n", assuan_strerror (rc));
          break;
        }
      
      rc = assuan_process (ctx);
      if (rc)
        {
          log_info ("Assuan processing failed: %s\n", assuan_strerror (rc));
          continue;
        }
    }


  assuan_deinit_pipe_server (ctx);
}