+# 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);
+}
+
+
+my $rsa;
+if (defined $ENV{PEM2OPENPGP_NEWKEY}) {
+ $rsa = Crypt::OpenSSL::RSA->generate_key($ENV{PEM2OPENPGP_NEWKEY});
+} else {
+ # we're just not dealing with newline business right now. slurp in
+ # the whole file.
+ undef $/;
+ $rsa = Crypt::OpenSSL::RSA->new_private_key(<STDIN>);
+}