path: root/gpg2ssh.c

#include "gnutls-helpers.h"

#include <gnutls/openpgp.h>
#include <gnutls/x509.h>

/* for waitpid() */
#include <sys/types.h>
#include <sys/wait.h>

/* 
   Author: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
   Date: Tue, 08 Apr 2008
   License: GPL v3 or later

   monkeysphere public key translator: execute this with an GPG
   certificate (public key(s) + userid(s)) on stdin.  It currently
   only works with RSA keys.

   It will spit out a version of the first key capable of being used
   for authentication on stdout.  The output format should be suitable
   for appending a known_hosts file.

   Requirements: I've only built this so far with GnuTLS v2.3.4 --
   version 2.2.0 does not contain the appropriate pieces.

 */

int main(int argc, char* argv[]) {
  gnutls_datum_t data;
  int ret;
  gnutls_openpgp_crt_t openpgp_crt;
  gnutls_openpgp_keyid_t keyid;
  printable_keyid p_keyid;
  unsigned int keyidx;
  unsigned int usage, bits;
  gnutls_pk_algorithm_t algo;

  gnutls_datum_t m, e, p, q, g, y;
  gnutls_datum_t algolabel;

  char output_data[10240];
  char userid[10240];
  size_t uidsz = sizeof(userid);

  const gnutls_datum_t* all[5];
  int pipefd;
  pid_t child_pid;
  char* const args[] = {"/usr/bin/base64", "--wrap=0", NULL};
  const char* algoname;
  int mpicount;

  init_gnutls();
  
  init_datum(&data);

  init_datum(&m);
  init_datum(&e);
  init_datum(&p);
  init_datum(&q);
  init_datum(&g);
  init_datum(&y);

  init_datum(&algolabel);

  init_keyid(keyid);

  /* slurp in the private key from stdin */
  if (ret = set_datum_fd(&data, 0), ret) {
    err("didn't read file descriptor 0\n");
    return 1;
  }


  if (ret = gnutls_openpgp_crt_init(&openpgp_crt), ret) {
    err("Failed to initialize OpenPGP certificate (error: %d)\n", ret);
    return 1;
  }

  /* format could be either: GNUTLS_OPENPGP_FMT_RAW,
     GNUTLS_OPENPGP_FMT_BASE64; if MONKEYSPHERE_RAW is set, use RAW,
     otherwise, use BASE64: */

  /* FIXME: we should be auto-detecting the input format, and
     translating it as needed. */

  if (getenv("MONKEYSPHERE_RAW")) {
    err("assuming RAW formatted certificate\n");
    if (ret = gnutls_openpgp_crt_import(openpgp_crt, &data, GNUTLS_OPENPGP_FMT_RAW), ret) {
      err("failed to import the OpenPGP certificate in RAW format (error: %d)\n", ret);
      return ret;
    }
  } else {
    err("assuming BASE64 formatted certificate\n");
    if (ret = gnutls_openpgp_crt_import (openpgp_crt, &data, GNUTLS_OPENPGP_FMT_BASE64), ret) {
      err("failed to import the OpenPGP certificate in BASE64 format (error: %d)\n", ret);
      return ret;
    }
  }

  if (gnutls_openpgp_crt_get_revoked_status(openpgp_crt)) {
    err("the primary key was revoked!\n");
    return 1;
  }

  /* FIXME: We're currently looking at the primary key or maybe the
     first authentication-capable subkey.  

     Instead, we should be iterating through the primary key and all
     subkeys: for each one with the authentication usage flag set of a
     algorithm we can handle, we should output matching UserIDs and
     the SSH version of the key. */
     

  if (ret = gnutls_openpgp_crt_get_key_usage(openpgp_crt, &usage), ret) {
    err("failed to get the usage flags for the primary key (error: %d)\n", ret);
    return ret;
  }
  if (usage & GNUTLS_KEY_KEY_AGREEMENT) {
    err("the primary key can be used for authentication\n");

    algo = gnutls_openpgp_crt_get_pk_algorithm(openpgp_crt, &bits);
    if (algo < 0) {
      err("failed to get the algorithm of the OpenPGP public key (error: %d)\n", algo);
      return algo;
    } else if (algo == GNUTLS_PK_RSA) {
      
      err("OpenPGP RSA certificate, with %d bits\n", bits);
      ret = gnutls_openpgp_crt_get_pk_rsa_raw(openpgp_crt, &m, &e);
      if (GNUTLS_E_SUCCESS != ret) {
    err ("failed to export RSA key parameters (error: %d)\n", ret);
    return 1;
      }
    } else if (algo == GNUTLS_PK_DSA) {
      err("OpenPGP DSA Key, with %d bits\n", bits);
      ret = gnutls_openpgp_crt_get_pk_dsa_raw(openpgp_crt, &p, &q, &g, &y);
      if (GNUTLS_E_SUCCESS != ret) {
    err ("failed to export DSA key parameters (error: %d)\n", ret);
    return 1;
      }
    } else {
      err("OpenPGP Key was not RSA or DSA -- can't deal! (actual algorithm was: %d)\n", algo);
      return 1;
    }
    
  } else {
    err("primary key is only good for: 0x%08x.  Trying subkeys...\n", usage);
    
    if (ret = gnutls_openpgp_crt_get_auth_subkey(openpgp_crt, keyid), ret) {
      err("failed to find a subkey capable of authentication (error: %d)\n", ret);
      return ret;
    }
    make_keyid_printable(p_keyid, keyid);
    err("found authentication subkey %.16s\n", p_keyid);

    ret = gnutls_openpgp_crt_get_subkey_idx(openpgp_crt, keyid);
    if (ret < 0) {
      err("could not get the index of subkey %.16s (error: %d)\n", ret);
      return ret;
    }
    keyidx = ret;

    if (gnutls_openpgp_crt_get_subkey_revoked_status(openpgp_crt, keyidx)) {
      err("The authentication subkey was revoked!\n");
      return 1;
    }

    if (ret = gnutls_openpgp_crt_get_subkey_usage(openpgp_crt, keyidx, &usage), ret) {
      err("could not figure out usage of subkey %.16s (error: %d)\n", p_keyid, ret);
      return ret;
    }
    if ((usage & GNUTLS_KEY_KEY_AGREEMENT) == 0) {
      err("could not find a subkey with authentication privileges.\n");
      return 1;
    }

    /* switch, based on the algorithm in question, to extract the MPI
       components: */

    algo = gnutls_openpgp_crt_get_subkey_pk_algorithm(openpgp_crt, keyidx, &bits);
    if (algo < 0) {
      err("failed to get the algorithm of the authentication subkey (error: %d)\n", algo);
      return algo;
    } else if (algo == GNUTLS_PK_RSA) {
      
      err("OpenPGP RSA subkey, with %d bits\n", bits);
      ret = gnutls_openpgp_crt_get_subkey_pk_rsa_raw(openpgp_crt, keyidx, &m, &e);
      if (GNUTLS_E_SUCCESS != ret) {
    err ("failed to export RSA subkey parameters (error: %d)\n", ret);
    return 1;
      }
    } else if (algo == GNUTLS_PK_DSA) {
      err("OpenPGP DSA subkey, with %d bits\n", bits);
      ret = gnutls_openpgp_crt_get_subkey_pk_dsa_raw(openpgp_crt, keyidx, &p, &q, &g, &y);
      if (GNUTLS_E_SUCCESS != ret) {
    err ("failed to export DSA subkey parameters (error: %d)\n", ret);
    return 1;
      }
    } else {
      err("OpenPGP subkey was not RSA or DSA -- can't deal! (actual algorithm was: %d)\n", algo);
      return 1;
    }
  } 

  /* make sure userid is NULL-terminated */
  userid[sizeof(userid) - 1] = 0;
  uidsz--;

  /* FIXME: we're just choosing the first UserID from the certificate:
     instead, we should be selecting every User ID that is adequately
     signed and matches the spec, and aggregating them with commas for
     known_hosts output */

  if (ret = gnutls_openpgp_crt_get_name(openpgp_crt, 0, userid, &uidsz), ret) {
    err("Failed to fetch the first UserID (error: %d)\n", ret);
    return ret;
  }

  if (ret = validate_ssh_host_userid(userid), ret) {
    err("bad userid: not a valid ssh host.\n");
    return ret;
  }

  /* remove ssh:// from the beginning of userid */
  memmove(userid, userid + strlen("ssh://"), 1 + strlen(userid) - strlen("ssh://"));
  

  /* now we have algo, and the various MPI data are set.  Can we
     export them cleanly? */

  /* for the moment, we'll just dump the info raw, and pipe it
     externally through coreutils' /usr/bin/base64 */

  if (algo == GNUTLS_PK_RSA) {
    algoname = "ssh-rsa";
    mpicount = 3;

    all[0] = &algolabel;
    all[1] = &e;
    all[2] = &m;
  } else if (algo == GNUTLS_PK_DSA) {
    algoname = "ssh-dss";
    mpicount = 5;

    all[0] = &algolabel;
    all[1] = &p;
    all[2] = &q;
    all[3] = &g;
    all[4] = &y;
  } else {
    err("no idea what this algorithm is: %d\n", algo);
    return 1;
  }

  if (ret = datum_from_string(&algolabel, algoname), ret) {
    err("couldn't label string (error: %d)\n", ret);
    return ret;
  }

  snprintf(output_data, sizeof(output_data), "%s %s ", userid, algoname);

  write(1, output_data, strlen(output_data));

  pipefd = create_writing_pipe(&child_pid, args[0], args);
  if (pipefd < 0) {
    err("failed to create a writing pipe (returned %d)\n", pipefd);
    return pipefd;
  }
    
  if (0 != write_data_fd_with_length(pipefd, all, mpicount)) {
    err("was not able to write out RSA key data\n");
    return 1;
  }
  close(pipefd);
  if (child_pid != waitpid(child_pid, NULL, 0)) {
    err("could not wait for child process to return for some reason.\n");
    return 1;
  }

  write(1, "\n", 1);



  gnutls_openpgp_crt_deinit(openpgp_crt);
  gnutls_global_deinit();
  return 0;
}