path: root/src/keytrans/pem2openpgp

#!/usr/bin/perl -w -T

# pem2openpgp: take a PEM-encoded RSA private-key on standard input, a
# User ID as the first argument, and generate an OpenPGP secret key
# and certificate from it.

# WARNING: the secret key material *will* appear on stdout (albeit in
# OpenPGP form) -- if you redirect stdout to a file, make sure the
# permissions on that file are appropriately locked down!

# Usage:

# pem2openpgp 'ssh://'$(hostname -f) < /etc/ssh/ssh_host_rsa_key | gpg --import

# Authors:
#  Jameson Rollins <jrollins@finestructure.net>
#  Daniel Kahn Gillmor <dkg@fifthhorseman.net>

# Started on: 2009-01-07 02:01:19-0500

# License: GPL v3 or later (we may need to adjust this given that this
# connects to OpenSSL via perl)

use strict;
use warnings;
use Crypt::OpenSSL::RSA;
use Crypt::OpenSSL::Bignum;
use Crypt::OpenSSL::Bignum::CTX;
use Digest::SHA1;
use MIME::Base64;

## make sure all length() and substr() calls use bytes only:
use bytes;

my $uid = shift;

# FIXME: fail if there is no given user ID; or should we default to
# hostname_long() from Sys::Hostname::Long ?


my $old_format_packet_lengths = { one => 0,
                  two => 1,
                  four => 2,
                  indeterminate => 3,
};

# see RFC 4880 section 9.1 (ignoring deprecated algorithms for now)
my $asym_algos = { rsa => 1,
           elgamal => 16,
           dsa => 17,
           };

# see RFC 4880 section 9.2
my $ciphers = { plaintext => 0,
        idea => 1,
        tripledes => 2,
        cast5 => 3,
        blowfish => 4,
        aes128 => 7,
        aes192 => 8,
        aes256 => 9,
        twofish => 10,
          };

# see RFC 4880 section 9.3
my $zips = { uncompressed => 0,
         zip => 1,
         zlib => 2,
         bzip2 => 3,
       };

# see RFC 4880 section 9.4
my $digests = { md5 => 1,
        sha1 => 2,
        ripemd160 => 3,
        sha256 => 8,
        sha384 => 9,
        sha512 => 10,
        sha224 => 11,
          };

# see RFC 4880 section 5.2.3.21
my $usage_flags = { certify => 0x01,
            sign => 0x02,
            encrypt_comms => 0x04,
            encrypt_storage => 0x08,
            encrypt => 0x0c, ## both comms and storage
            split => 0x10, # the private key is split via secret sharing
            authenticate => 0x20,
            shared => 0x80, # more than one person holds the entire private key
          };

# see RFC 4880 section 4.3
my $packet_types = { pubkey_enc_session => 1,
             sig => 2,
             symkey_enc_session => 3,
             onepass_sig => 4,
             seckey => 5,
             pubkey => 6,
             sec_subkey => 7,
             compressed_data => 8,
             symenc_data => 9,
             marker => 10,
             literal => 11,
             trust => 12,
             uid => 13,
             pub_subkey => 14,
             uat => 17,
             symenc_w_integrity => 18,
             mdc => 19,
           };

# see RFC 4880 section 5.2.1
my $sig_types = { binary_doc => 0x00,
          text_doc => 0x01,
          standalone => 0x02,
          generic_certification => 0x10,
          persona_certification => 0x11,
          casual_certification => 0x12,
          positive_certification => 0x13,
          subkey_binding => 0x18,
          primary_key_binding => 0x19,
          key_signature => 0x1f,
          key_revocation => 0x20,
          subkey_revocation => 0x28,
          certification_revocation => 0x30,
          timestamp => 0x40,
          thirdparty => 0x50,
        };


# see RFC 4880 section 5.2.3.1
my $subpacket_types = { sig_creation_time => 2,
            sig_expiration_time => 3,
            exportable => 4,
            trust_sig => 5,
            regex => 6,
            revocable => 7,
            key_expiration_time => 9,
            preferred_cipher => 11,
            revocation_key => 12,
            issuer => 16,
            notation => 20,
            preferred_digest => 21,
            preferred_compression => 22,
            keyserver_prefs => 23,
            preferred_keyserver => 24,
            primary_uid => 25,
            policy_uri => 26,
            usage_flags => 27,
            signers_uid => 28,
            revocation_reason => 29,
            features => 30,
            signature_target => 31,
            embedded_signature => 32,
               };

# bitstring (see RFC 4880 section 5.2.3.24)
my $features = { mdc => 0x01
           };

# bitstring (see RFC 4880 5.2.3.17)
my $keyserver_prefs = { nomodify => 0x80
              };

###### end lookup tables ######

# FIXME: if we want to be able to interpret openpgp data as well as
# produce it, we need to produce key/value-swapped lookup tables as well.


########### Math/Utility Functions ##############


# see the bottom of page 43 of RFC 4880
sub simple_checksum {
  my $bytes = shift;

  return unpack("%32W*",$bytes) % 65536;
}

# calculate the multiplicative inverse of a mod b this is euclid's
# extended algorithm.  For more information see:
# http://en.wikipedia.org/wiki/Extended_Euclidean_algorithm the
# arguments here should be Crypt::OpenSSL::Bignum objects.  $a should
# be the larger of the two values, and the two values should be
# coprime.

sub modular_multi_inverse {
  my $a = shift;
  my $b = shift;


  my $origdivisor = $b->copy();

  my $ctx = Crypt::OpenSSL::Bignum::CTX->new();
  my $x = Crypt::OpenSSL::Bignum->zero();
  my $y = Crypt::OpenSSL::Bignum->one();
  my $lastx = Crypt::OpenSSL::Bignum->one();
  my $lasty = Crypt::OpenSSL::Bignum->zero();

  my $finalquotient;
  my $finalremainder;

  while (! $b->is_zero()) {
    my ($quotient, $remainder) = $a->div($b, $ctx);

    $a = $b;
    $b = $remainder;

    my $temp = $x;
    $x = $lastx->sub($quotient->mul($x, $ctx));
    $lastx = $temp;

    $temp = $y;
    $y = $lasty->sub($quotient->mul($y, $ctx));
    $lasty = $temp;
  }

  if (!$a->is_one()) {
    die "did this math wrong.\n";
  }

  # let's make sure that we return a positive value because RFC 4880,
  # section 3.2 only allows unsigned values:

  ($finalquotient, $finalremainder) = $lastx->add($origdivisor)->div($origdivisor, $ctx);

  return $finalremainder;
}


############ OpenPGP formatting functions ############

# make an old-style packet out of the given packet type and body.
# old-style  (see RFC 4880 section 4.2)
sub make_packet {
  my $type = shift;
  my $body = shift;
  my $options = shift;

  my $len = length($body);
  my $pseudolen = $len;

  # if the caller wants to use at least N octets of packet length,
  # pretend that we're using that many.
  if (defined $options && defined $options->{'packet_length'}) {
      $pseudolen = 2**($options->{'packet_length'} * 8) - 1;
  }
  if ($pseudolen < $len) {
      $pseudolen = $len;
  }

  my $lenbytes;
  my $lencode;

  if ($pseudolen < 2**8) {
    $lenbytes = $old_format_packet_lengths->{one};
    $lencode = 'C';
  } elsif ($pseudolen < 2**16) {
    $lenbytes = $old_format_packet_lengths->{two};
    $lencode = 'n';
  } elsif ($pseudolen < 2**31) {
    ## not testing against full 32 bits because i don't want to deal
    ## with potential overflow.
    $lenbytes = $old_format_packet_lengths->{four};
    $lencode = 'N';
  } else {
    ## what the hell do we do here?
    $lenbytes = $old_format_packet_lengths->{indeterminate};
    $lencode = '';
  }

  return pack('C'.$lencode, 0x80 + ($type * 4) + $lenbytes, $len).
    $body;
}


# takes a Crypt::OpenSSL::Bignum, returns it formatted as OpenPGP MPI
# (RFC 4880 section 3.2)
sub mpi_pack {
  my $num = shift;

  my $val = $num->to_bin();
  my $mpilen = length($val)*8;

# this is a kludgy way to get the number of significant bits in the
# first byte:
  my $bitsinfirstbyte = length(sprintf("%b", ord($val)));

  $mpilen -= (8 - $bitsinfirstbyte);

  return pack('n', $mpilen).$val;
}

# FIXME: genericize these to accept either RSA or DSA keys:
sub make_rsa_pub_key_body {
  my $key = shift;
  my $timestamp = shift;

  my ($n, $e) = $key->get_key_parameters();

  return
    pack('CN', 4, $timestamp).
      pack('C', $asym_algos->{rsa}).
    mpi_pack($n).
      mpi_pack($e);
}

sub make_rsa_sec_key_body {
  my $key = shift;
  my $timestamp = shift;

  # we're not using $a and $b, but we need them to get to $c.
  my ($n, $e, $d, $p, $q) = $key->get_key_parameters();

  my $c3 = modular_multi_inverse($p, $q);

  my $secret_material = mpi_pack($d).
    mpi_pack($p).
      mpi_pack($q).
    mpi_pack($c3);

  # according to Crypt::OpenSSL::RSA, the closest value we can get out
  # of get_key_parameters is 1/q mod p; but according to sec 5.5.3 of
  # RFC 4880, we're actually looking for u, the multiplicative inverse
  # of p, mod q.  This is why we're calculating the value directly
  # with modular_multi_inverse.

  return
    pack('CN', 4, $timestamp).
      pack('C', $asym_algos->{rsa}).
    mpi_pack($n).
      mpi_pack($e).
        pack('C', 0). # seckey material is not encrypted -- see RFC 4880 sec 5.5.3
          $secret_material.
        pack('n', simple_checksum($secret_material));
}

# expects an RSA key (public or private) and a timestamp
sub fingerprint {
  my $key = shift;
  my $timestamp = shift;

  my $rsabody = make_rsa_pub_key_body($key, $timestamp);

  return Digest::SHA1::sha1(pack('Cn', 0x99, length($rsabody)).$rsabody);
}

# we're just not dealing with newline business right now.  slurp in
# the whole file.
undef $/;
my $buf = <STDIN>;


my $rsa = Crypt::OpenSSL::RSA->new_private_key($buf);

$rsa->use_sha1_hash();

# see page 22 of RFC 4880 for why i think this is the right padding
# choice to use:
$rsa->use_pkcs1_padding();

if (! $rsa->check_key()) {
  die "key does not check";
}

my $version = pack('C', 4);
# strong assertion of identity:
my $sigtype = pack('C', $sig_types->{positive_certification});
# RSA
my $pubkey_algo = pack('C', $asym_algos->{rsa});
# SHA1
my $hash_algo = pack('C', $digests->{sha1});

# FIXME: i'm worried about generating a bazillion new OpenPGP
# certificates from the same key, which could easily happen if you run
# this script more than once against the same key (because the
# timestamps will differ).  How can we prevent this?

# this environment variable (if set) overrides the current time, to
# be able to create a standard key?  If we read the key from a file
# instead of stdin, should we use the creation time on the file?
my $timestamp = 0;
if (defined $ENV{PEM2OPENPGP_TIMESTAMP}) {
  $timestamp = ($ENV{PEM2OPENPGP_TIMESTAMP} + 0);
} else {
  $timestamp = time();
}

my $creation_time_packet = pack('CCN', 5, $subpacket_types->{sig_creation_time}, $timestamp);


my $flags = 0;
if (! defined $ENV{PEM2OPENPGP_USAGE_FLAGS}) {
  $flags = $usage_flags->{certify};
} else {
  my @ff = split(",", $ENV{PEM2OPENPGP_USAGE_FLAGS});
  foreach my $f (@ff) {
    if (! defined $usage_flags->{$f}) {
      die "No such flag $f";
    }
    $flags |= $usage_flags->{$f};
  }
}

my $usage_packet = pack('CCC', 2, $subpacket_types->{usage_flags}, $flags);


# how should we determine how far off to set the expiration date?
# default is no expiration.  Specify the timestamp in seconds from the
# key creation.
my $expiration_packet = '';
if (defined $ENV{PEM2OPENPGP_EXPIRATION}) {
  my $expires_in = $ENV{PEM2OPENPGP_EXPIRATION} + 0;
  $expiration_packet = pack('CCN', 5, $subpacket_types->{key_expiration_time}, $expires_in);
}


# prefer AES-256, AES-192, AES-128, CAST5, 3DES:
my $pref_sym_algos = pack('CCCCCCC', 6, $subpacket_types->{preferred_cipher},
              $ciphers->{aes256},
              $ciphers->{aes192},
              $ciphers->{aes128},
              $ciphers->{cast5},
              $ciphers->{tripledes}
             );

# prefer SHA-1, SHA-256, RIPE-MD/160
my $pref_hash_algos = pack('CCCCC', 4, $subpacket_types->{preferred_digest},
               $digests->{sha1},
               $digests->{sha256},
               $digests->{ripemd160}
              );

# prefer ZLIB, BZip2, ZIP
my $pref_zip_algos = pack('CCCCC', 4, $subpacket_types->{preferred_compression},
              $zips->{zlib},
              $zips->{bzip2},
              $zips->{zip}
             );

# we support the MDC feature:
my $feature_subpacket = pack('CCC', 2, $subpacket_types->{features},
                 $features->{mdc});

# keyserver preference: only owner modify (???):
my $keyserver_pref = pack('CCC', 2, $subpacket_types->{keyserver_prefs},
              $keyserver_prefs->{nomodify});

my $subpackets_to_be_hashed =
  $creation_time_packet.
  $usage_packet.
  $expiration_packet.
  $pref_sym_algos.
  $pref_hash_algos.
  $pref_zip_algos.
  $feature_subpacket.
  $keyserver_pref;

my $subpacket_octets = pack('n', length($subpackets_to_be_hashed));

my $sig_data_to_be_hashed =
  $version.
  $sigtype.
  $pubkey_algo.
  $hash_algo.
  $subpacket_octets.
  $subpackets_to_be_hashed;

my $pubkey = make_rsa_pub_key_body($rsa, $timestamp);
my $seckey = make_rsa_sec_key_body($rsa, $timestamp);

# this is for signing.  it needs to be an old-style header with a
# 2-packet octet count.

my $key_data = make_packet($packet_types->{pubkey}, $pubkey, {'packet_length'=>2});

# take the last 8 bytes of the fingerprint as the keyid:
my $keyid = substr(fingerprint($rsa, $timestamp), 20 - 8, 8);

# the v4 signature trailer is:

# version number, literal 0xff, and then a 4-byte count of the
# signature data itself.
my $trailer = pack('CCN', 4, 0xff, length($sig_data_to_be_hashed));

my $uid_data =
  pack('CN', 0xb4, length($uid)).
  $uid;

my $datatosign =
  $key_data.
  $uid_data.
  $sig_data_to_be_hashed.
  $trailer;

my $data_hash = Digest::SHA1::sha1_hex($datatosign);

my $issuer_packet = pack('CCa8', 9, $subpacket_types->{issuer}, $keyid);

my $sig = Crypt::OpenSSL::Bignum->new_from_bin($rsa->sign($datatosign));

my $sig_body =
  $sig_data_to_be_hashed.
  pack('n', length($issuer_packet)).
  $issuer_packet.
  pack('n', hex(substr($data_hash, 0, 4))).
  mpi_pack($sig);

print
  make_packet($packet_types->{seckey}, $seckey).
  make_packet($packet_types->{uid}, $uid).
  make_packet($packet_types->{sig}, $sig_body);