/*

 * pgp.c        -- PGP utility functions

 *

 * Copyright (C) 2006-2015 Mikael Berthe <mikael@lilotux.net>

 * Some parts inspired by centericq (impgp.cc)

 *

 * This program 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.

 *

 * This program 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, see <http://www.gnu.org/licenses/>.

 */

#include <config.h>

#ifdef HAVE_GPGME

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <locale.h>

#include <sys/mman.h>

#include <glib.h>

#include "pgp.h"

#include "settings.h"

#include "utils.h"

#include "logprint.h"

#define MIN_GPGME_VERSION "1.1.0"

static struct gpg_struct

{

  int   enabled;

  int   version1;

  char *private_key;

  char *passphrase;

} gpg;

//  gpg_init(priv_key, passphrase)

// Initialize the GPG sub-systems.  This function must be invoked early.

// Note: priv_key & passphrase are optional, they can be set later.

// This function returns 0 if gpgme is available and initialized;

// if not it returns the gpgme error code.

int gpg_init(const char *priv_key, const char *passphrase)

{

  gpgme_error_t err;

  gpgme_ctx_t ctx;

  gpgme_engine_info_t info;

  const char *gpg_path, *gpg_home;

  // Check for version and OpenPGP protocol support.

  if (!gpgme_check_version(MIN_GPGME_VERSION)) {

    scr_LogPrint(LPRINT_LOGNORM,

                 "GPGME initialization error: Bad library version");

    return -1;

  }

  err = gpgme_engine_check_version(GPGME_PROTOCOL_OpenPGP);

  if (err) {

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME initialization error: %s", gpgme_strerror(err));

    return err;

  }

  // Set the locale information.

  gpgme_set_locale(NULL, LC_CTYPE, setlocale(LC_CTYPE, NULL));

  gpgme_set_locale(NULL, LC_MESSAGES, setlocale(LC_MESSAGES, NULL));

  // The path to the gpg binary can be specified in order to force

  // version 1, for example.

  gpg_path = settings_opt_get("gpg_path");

  gpg_home = settings_opt_get("gpg_home");

  if (gpg_path || gpg_home) {

    char *xp_gpg_home = expand_filename(gpg_home);

    err = gpgme_set_engine_info(GPGME_PROTOCOL_OpenPGP, gpg_path, xp_gpg_home);

    g_free(xp_gpg_home);

    if (err) return -1;

  }

  // Store private data.

  gpg_set_private_key(priv_key);

  gpg_set_passphrase(passphrase);

  err = gpgme_new(&ctx);

  if (err) return -1;

  // Check OpenPGP engine version; with version 2+ the agent is mandatory

  // and we do not manage the passphrase.

  gpgme_set_protocol(ctx, GPGME_PROTOCOL_OpenPGP);

  if (err) return -1;

  err = gpgme_get_engine_info(&info);

  if (!err) {

    while (info && info->protocol != gpgme_get_protocol(ctx))

      info = info->next;

    if (info && info->version) {

      if (!strncmp(info->version, "1.", 2))

        gpg.version1 = TRUE;

      scr_log_print(LPRINT_DEBUG, "GPGME: Engine version is '%s'.",

                    info->version);

    }

  }

  gpgme_release(ctx);

  gpg.enabled = 1;

  return 0;

}

//  gpg_is_version1()

// Return TRUE if the GnuPG OpenPGP engine version is 1.x

int gpg_is_version1(void)

{

  return gpg.version1;

}

//  gpg_terminate()

// Destroy data and free memory.

void gpg_terminate(void)

{

  gpg.enabled = 0;

  gpg_set_passphrase(NULL);

  gpg_set_private_key(NULL);

}

//  gpg_set_passphrase(passphrase)

// Set the current passphrase (use NULL to erase it).

void gpg_set_passphrase(const char *passphrase)

{

  // Remove current passphrase

  if (gpg.passphrase) {

    ssize_t len = strlen(gpg.passphrase);

    memset(gpg.passphrase, 0, len);

    munlock(gpg.passphrase, len);

    g_free(gpg.passphrase);

  }

  if (passphrase) {

    gpg.passphrase = g_strdup(passphrase);

    mlock(gpg.passphrase, strlen(gpg.passphrase));

  } else {

    gpg.passphrase = NULL;

  }

}

//  gpg_set_private_key(keyid)

// Set the current private key id (use NULL to unset it).

void gpg_set_private_key(const char *priv_keyid)

{

  g_free(gpg.private_key);

  if (priv_keyid)

    gpg.private_key = g_strdup(priv_keyid);

  else

    gpg.private_key = NULL;

}

//  gpg_get_private_key_id()

// Return the current private key id (static string).

const char *gpg_get_private_key_id(void)

{

  return gpg.private_key;

}

//  strip_header_footer(data)

// Remove PGP header & footer from data.

// Return a new string, or NULL.

// The string must be freed by the caller with g_free() when no longer needed.

static char *strip_header_footer(const char *data)

{

  char *p, *q;

  if (!data)

    return NULL;

  // p: beginning of real data

  // q: end of real data

  // Strip header (to the first empty line)

  p = strstr(data, "\n\n");

  if (!p)

    return g_strdup(data);

  // Strip footer

  // We want to remove the last lines, until the line beginning with a '-'

  p += 2;

  for (q = p ; *q; q++) ;

  // (q is at the end of data now)

  for (q--; q > p && (*q != '\n' || *(q+1) != '-'); q--) ;

  if (q <= p)

    return NULL; // Shouldn't happen...

  return g_strndup(p, q-p);

}

// GCC ignores casts to void, thus we need to hack around that

static inline void ignore(void*x) {}

//  passphrase_cb()

// GPGME passphrase callback function.

static gpgme_error_t passphrase_cb(void *hook, const char *uid_hint,

                       const char *passphrase_info, int prev_was_bad, int fd)

{

  ssize_t len;

  // Abort if we do not have the password.

  if (!gpg.passphrase) {

    ignore((void*)write(fd, "\n", 1)); // We have an error anyway, thus it does

                                       // not matter if we fail again.

    return gpg_error(GPG_ERR_CANCELED);

  }

  // Write the passphrase to the file descriptor.

  len = strlen(gpg.passphrase);

  if (write(fd, gpg.passphrase, len) != len)

    return gpg_error(GPG_ERR_CANCELED);

  if (write(fd, "\n", 1) != 1)

    return gpg_error(GPG_ERR_CANCELED);

  return 0; // Success

}

//  gpg_verify(gpg_data, text, *sigsum)

// Verify that gpg_data is a correct signature for text.

// Return the key id (or fingerprint), and set *sigsum to

// the gpgme signature summary value.

// The returned string must be freed with g_free() after use.

char *gpg_verify(const char *gpg_data, const char *text,

                 gpgme_sigsum_t *sigsum)

{

  gpgme_ctx_t ctx;

  gpgme_data_t data_sign, data_text;

  char *data;

  char *verified_key = NULL;

  gpgme_key_t key;

  gpgme_error_t err;

  const char prefix[] = "-----BEGIN PGP SIGNATURE-----\n\n";

  const char suffix[] = "\n-----END PGP SIGNATURE-----\n";

  // Reset the summary.

  *sigsum = 0;

  if (!gpg.enabled)

    return NULL;

  err = gpgme_new(&ctx);

  if (err) {

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME error: %s", gpgme_strerror(err));

    return NULL;

  }

  gpgme_set_protocol(ctx, GPGME_PROTOCOL_OpenPGP);

  // Surround the given data with the prefix & suffix

  data = g_new(char, sizeof(prefix) + sizeof(suffix) + strlen(gpg_data));

  strcpy(data, prefix);

  strcat(data, gpg_data);

  strcat(data, suffix);

  err = gpgme_data_new_from_mem(&data_sign, data, strlen(data), 0);

  if (!err) {

    err = gpgme_data_new_from_mem(&data_text, text, strlen(text), 0);

    if (!err) {

      err = gpgme_op_verify(ctx, data_sign, data_text, 0);

      if (!err) {

        gpgme_verify_result_t vr = gpgme_op_verify_result(ctx);

        if (vr && vr->signatures) {

            gpgme_signature_t s = NULL;

            // check all signatures and stop if the first could be verified

            for (s = vr->signatures; s && !verified_key; s = s->next) {

                // Found the fingerprint.  Let's try to get the key id.

                if (NULL != s->fpr) {

                    if (!gpgme_get_key(ctx, s->fpr, &key, 0)) {

                        if (key) {

                            verified_key = g_strdup(key->subkeys->keyid);

                            gpgme_key_release(key);

                        }

                    }

                }

                *sigsum = s->summary;

                // For some reason summary could be 0 when status is 0 too,

                // which means the signature is valid...

                if ((!*sigsum) && (!s->status))

                    *sigsum = GPGME_SIGSUM_GREEN;

            }

        }

      }

      gpgme_data_release(data_text);

    }

    gpgme_data_release(data_sign);

  }

  if (err)

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME verification error: %s", gpgme_strerror(err));

  gpgme_release(ctx);

  g_free(data);

  return verified_key;

}

//  gpg_sign(gpg_data)

// Return a signature of gpg_data (or NULL).

// The returned string must be freed with g_free() after use.

char *gpg_sign(const char *gpg_data)

{

  gpgme_ctx_t ctx;

  gpgme_data_t in, out;

  char *signed_data = NULL;

  size_t nread;

  gpgme_key_t key;

  gpgme_error_t err;

  if (!gpg.enabled || !gpg.private_key)

    return NULL;

  err = gpgme_new(&ctx);

  if (err) {

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME error: %s", gpgme_strerror(err));

    return NULL;

  }

  gpgme_set_protocol(ctx, GPGME_PROTOCOL_OpenPGP);

  gpgme_set_textmode(ctx, 0);

  gpgme_set_armor(ctx, 1);

  if (gpg.version1) {

    // GPG_AGENT_INFO isn't used by GnuPG version 2+

    char *p = getenv("GPG_AGENT_INFO");

    if (!(p && strchr(p, ':')))

      gpgme_set_passphrase_cb(ctx, passphrase_cb, 0);

  }

  err = gpgme_get_key(ctx, gpg.private_key, &key, 1);

  if (err || !key) {

    scr_LogPrint(LPRINT_LOGNORM, "GPGME error: private key not found");

    gpgme_release(ctx);

    return NULL;

  }

  gpgme_signers_clear(ctx);

  gpgme_signers_add(ctx, key);

  gpgme_key_release(key);

  err = gpgme_data_new_from_mem(&in, gpg_data, strlen(gpg_data), 0);

  if (!err) {

    err = gpgme_data_new(&out);

    if (!err) {

      err = gpgme_op_sign(ctx, in, out, GPGME_SIG_MODE_DETACH);

      if (err) {

        gpgme_data_release(out);

      } else {

        signed_data = gpgme_data_release_and_get_mem(out, &nread);

        if (signed_data) {

          // We need to add a trailing NULL

          char *dd = g_strndup(signed_data, nread);

          free(signed_data);

          signed_data = strip_header_footer(dd);

          g_free(dd);

        }

      }

    }

    gpgme_data_release(in);

  }

  if (err && err != GPG_ERR_CANCELED)

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME signature error: %s", gpgme_strerror(err));

  gpgme_release(ctx);

  return signed_data;

}

//  gpg_decrypt(gpg_data)

// Return decrypted gpg_data (or NULL).

// The returned string must be freed with g_free() after use.

char *gpg_decrypt(const char *gpg_data)

{

  gpgme_ctx_t ctx;

  gpgme_data_t in, out;

  char *data;

  char *decrypted_data = NULL;

  size_t nread;

  gpgme_error_t err;

  const char prefix[] = "-----BEGIN PGP MESSAGE-----\n\n";

  const char suffix[] = "\n-----END PGP MESSAGE-----\n";

  if (!gpg.enabled)

    return NULL;

  err = gpgme_new(&ctx);

  if (err) {

    scr_LogPrint(LPRINT_LOGNORM|LPRINT_NOTUTF8,

                 "GPGME error: %s", gpgme_strerror(err));

    return NULL;

  }

  gpgme_set_protocol(ctx, GPGME_PROTOCOL_OpenPGP);

  if (gpg.version1) {

    // GPG_AGENT_INFO isn't used by GnuPG version 2+

    char *p = getenv("GPG_AGENT_INFO");

    if (!(p && strchr(p, ':')))

      gpgme_set_passphrase_cb(ctx, passphrase_cb, 0);