#!/usr/local/bin/perl

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

#
# smime.pl - frontend for S/MIME message generation and parsing
#

use Getopt::Std;

@boundarychars = ( "0" .. "9", "A" .. "F" );

# path to cmsutil
$cmsutilpath = "cmsutil";

#
# Thanks to Gisle Aas <gisle@aas.no> for the base64 functions
# originally taken from MIME-Base64-2.11 at www.cpan.org
#
sub encode_base64($)
{
    my $res = "";
    pos($_[0]) = 0;                          # ensure start at the beginning
    while ($_[0] =~ /(.{1,45})/gs) {
	$res .= substr(pack('u', $1), 1);    # get rid of length byte after packing
	chop($res);
    }
    $res =~ tr|` -_|AA-Za-z0-9+/|;
    # fix padding at the end
    my $padding = (3 - length($_[0]) % 3) % 3;
    $res =~ s/.{$padding}$/'=' x $padding/e if $padding;
    # break encoded string into lines of no more than 76 characters each
    $res =~ s/(.{1,76})/$1\n/g;
    $res;
}

sub decode_base64($)
{
    local($^W) = 0; # unpack("u",...) gives bogus warning in 5.00[123]

    my $str = shift;
    my $res = "";

    $str =~ tr|A-Za-z0-9+=/||cd;            # remove non-base64 chars
    if (length($str) % 4) {
	require Carp;
	Carp::carp("Length of base64 data not a multiple of 4")
    }
    $str =~ s/=+$//;                        # remove padding
    $str =~ tr|A-Za-z0-9+/| -_|;            # convert to uuencoded format
    while ($str =~ /(.{1,60})/gs) {
	my $len = chr(32 + length($1)*3/4); # compute length byte
	$res .= unpack("u", $len . $1 );    # uudecode
    }
    $res;
}

#
# parse headers into a hash
#
# %headers = parseheaders($headertext);
#
sub parseheaders($)
{
    my ($headerdata) = @_;
    my $hdr;
    my %hdrhash;
    my $hdrname;
    my $hdrvalue;
    my @hdrvalues;
    my $subhdrname;
    my $subhdrvalue;

    # the expression in split() correctly handles continuation lines
    foreach $hdr (split(/\n(?=\S)/, $headerdata)) {
	$hdr =~ s/\r*\n\s+/ /g;	# collapse continuation lines
	($hdrname, $hdrvalue) = $hdr =~ m/^(\S+):\s+(.*)$/;

	# ignore non-headers (or should we die horribly?)
	next unless (defined($hdrname));
	$hdrname =~ tr/A-Z/a-z/;			# lowercase the header name
	@hdrvalues = split(/\s*;\s*/, $hdrvalue);	# split header values (XXXX quoting)

	# there is guaranteed to be at least one value
	$hdrvalue = shift @hdrvalues;
	if ($hdrvalue =~ /^\s*\"(.*)\"\s*$/) {		# strip quotes if there
	    $hdrvalue = $1;
	}

	$hdrhash{$hdrname}{MAIN} = $hdrvalue;
	# print "XXX $hdrname = $hdrvalue\n";

	# deal with additional name-value pairs
	foreach $hdrvalue (@hdrvalues) {
	    ($subhdrname, $subhdrvalue) = $hdrvalue =~ m/^(\S+)\s*=\s*(.*)$/;
	    # ignore non-name-value pairs (or should we die?)
	    next unless (defined($subhdrname));
	    $subhdrname =~ tr/A-Z/a-z/;
	    if ($subhdrvalue =~ /^\s*\"(.*)\"\s*$/) {	# strip quotes if there
		$subhdrvalue = $1;
	    }
	    $hdrhash{$hdrname}{$subhdrname} = $subhdrvalue;
	}

    }
    return %hdrhash;
}

#
# encryptentity($entity, $options) - encrypt an S/MIME entity,
#                                    creating a new application/pkcs7-smime entity
#
# entity  - string containing entire S/MIME entity to encrypt
# options - options for cmsutil
#
# this will generate and return a new application/pkcs7-smime entity containing
# the enveloped input entity.
#
sub encryptentity($$)
{
    my ($entity, $cmsutiloptions) = @_;
    my $out = "";
    my $boundary;

    $tmpencfile = "/tmp/encryptentity.$$";

    #
    # generate a random boundary string
    #
    $boundary = "------------ms" . join("", @boundarychars[map{rand @boundarychars }( 1 .. 24 )]);

    #
    # tell cmsutil to generate a enveloped CMS message using our data
    #
    open(CMS, "|$cmsutilpath -E $cmsutiloptions -o $tmpencfile") or die "ERROR: cannot pipe to cmsutil";
    print CMS $entity;
    unless (close(CMS)) {
	print STDERR "ERROR: encryption failed.\n";
	unlink($tmpsigfile);
	exit 1;
    }

    $out  = "Content-Type: application/pkcs7-mime; smime-type=enveloped-data; name=smime.p7m\n";
    $out .= "Content-Transfer-Encoding: base64\n";
    $out .= "Content-Disposition: attachment; filename=smime.p7m\n";
    $out .= "\n";			# end of entity header

    open (ENC, $tmpencfile) or die "ERROR: cannot find newly generated encrypted content";
    local($/) = undef;			# slurp whole file
    $out .= encode_base64(<ENC>), "\n";	# entity body is base64-encoded CMS message
    close(ENC);

    unlink($tmpencfile);

    $out;
}

#
# signentity($entity, $options) - sign an S/MIME entity
#
# entity  - string containing entire S/MIME entity to sign
# options - options for cmsutil
#
# this will generate and return a new multipart/signed entity consisting
# of the canonicalized original content, plus a signature block.
#
sub signentity($$)
{
    my ($entity, $cmsutiloptions) = @_;
    my $out = "";
    my $boundary;

    $tmpsigfile = "/tmp/signentity.$$";

    #
    # generate a random boundary string
    #
    $boundary = "------------ms" . join("", @boundarychars[map{rand @boundarychars }( 1 .. 24 )]);

    #
    # tell cmsutil to generate a signed CMS message using the canonicalized data
    # The signedData has detached content (-T) and includes a signing time attribute (-G)
    #
    # if we do not provide a password on the command line, here's where we would be asked for it
    #
    open(CMS, "|$cmsutilpath -S -T -G $cmsutiloptions -o $tmpsigfile") or die "ERROR: cannot pipe to cmsutil";
    print CMS $entity;
    unless (close(CMS)) {
	print STDERR "ERROR: signature generation failed.\n";
	unlink($tmpsigfile);
	exit 1;
    }

    open (SIG, $tmpsigfile) or die "ERROR: cannot find newly generated signature";

    #
    # construct a new multipart/signed MIME entity consisting of the original content and
    # the signature
    #
    # (we assume that cmsutil generates a SHA256 digest)
    $out .= "Content-Type: multipart/signed; protocol=\"application/pkcs7-signature\"; micalg=sha256; boundary=\"${boundary}\"\n";
    $out .= "\n";		# end of entity header
    $out .= "This is a cryptographically signed message in MIME format.\n"; # explanatory comment
    $out .= "\n--${boundary}\n";
    $out .= $entity;
    $out .= "\n--${boundary}\n";
    $out .= "Content-Type: application/pkcs7-signature; name=smime.p7s\n";
    $out .= "Content-Transfer-Encoding: base64\n";
    $out .= "Content-Disposition: attachment; filename=smime.p7s\n";
    $out .= "Content-Description: S/MIME Cryptographic Signature\n";
    $out .= "\n";		# end of signature subentity header

    local($/) = undef;		# slurp whole file
    $out .= encode_base64(<SIG>);	# append base64-encoded signature
    $out .= "\n--${boundary}--\n";

    close(SIG);
    unlink($tmpsigfile);

    $out;
}

sub usage {
    print STDERR "usage: smime [options]\n";
    print STDERR " options:\n";
    print STDERR " -S nick             generate signed message, use certificate named \"nick\"\n";
    print STDERR "  -p passwd          use \"passwd\" as security module password\n";
    print STDERR " -E rec1[,rec2...]   generate encrypted message for recipients\n";
    print STDERR " -D                  decode a S/MIME message\n";
    print STDERR "  -p passwd          use \"passwd\" as security module password\n";
    print STDERR "                     (required for decrypting only)\n";
    print STDERR " -C pathname         set pathname of \"cmsutil\"\n";
    print STDERR " -d directory        set directory containing certificate db\n";
    print STDERR "                     (default: ~/.netscape)\n";
    print STDERR "\nWith -S or -E, smime will take a regular RFC822 message or MIME entity\n";
    print STDERR "on stdin and generate a signed or encrypted S/MIME message with the same\n";
    print STDERR "headers and content from it. The output can be used as input to a MTA.\n";
    print STDERR "-D causes smime to strip off all S/MIME layers if possible and output\n";
    print STDERR "the \"inner\" message.\n";
}

#
# start of main procedures
#

#
# process command line options
#
unless (getopts('S:E:p:d:C:D')) {
    usage();
    exit 1;
}

unless (defined($opt_S) or defined($opt_E) or defined($opt_D)) {
    print STDERR "ERROR: -S and/or -E, or -D must be specified.\n";
    usage();
    exit 1;
}

$signopts = "";
$encryptopts = "";
$decodeopts = "";

# pass -d option along
if (defined($opt_d)) {
    $signopts .= "-d \"$opt_d\" ";
    $encryptopts .= "-d \"$opt_d\" ";
    $decodeopts .= "-d \"$opt_d\" ";
}

if (defined($opt_S)) {
    $signopts .= "-N \"$opt_S\" ";
}

if (defined($opt_p)) {
    $signopts .= "-p \"$opt_p\" ";
    $decodeopts .= "-p \"$opt_p\" ";
}

if (defined($opt_E)) {
    @recipients = split(",", $opt_E);
    $encryptopts .= "-r ";
    $encryptopts .= join (" -r ", @recipients);
}

if (defined($opt_C)) {
    $cmsutilpath = $opt_C;
}

#
# split headers into mime entity headers and RFC822 headers
# The RFC822 headers are preserved and stay on the outer layer of the message
#
$rfc822headers = "";
$mimeheaders = "";
$mimebody = "";
$skippedheaders = "";
while (<STDIN>) {
    last if (/^$/);
    if (/^content-\S+: /i) {
	$lastref = \$mimeheaders;
    } elsif (/^mime-version: /i) {
	$lastref = \$skippedheaders;			# skip it
    } elsif (/^\s/) {
	;
    } else {
	$lastref = \$rfc822headers;
    }
    $$lastref .= $_;
}

#
# if there are no MIME entity headers, generate some default ones
#
if ($mimeheaders eq "") {
    $mimeheaders .= "Content-Type: text/plain; charset=us-ascii\n";
    $mimeheaders .= "Content-Transfer-Encoding: 7bit\n";
}

#
# slurp in the entity body
#
$saveRS = $/;
$/ = undef;
$mimebody = <STDIN>;
$/ = $saveRS;
chomp($mimebody);

if (defined $opt_D) {
    #
    # decode
    #
    # possible options would be:
    # - strip off only one layer
    # - strip off outer signature (if present)
    # - just print information about the structure of the message
    # - strip n layers, then dump DER of CMS message

    $layercounter = 1;

    while (1) {
	%hdrhash = parseheaders($mimeheaders);
	unless (exists($hdrhash{"content-type"}{MAIN})) {
	    print STDERR "ERROR: no content type header found in MIME entity\n";
	    last;	# no content-type - we're done
	}

	$contenttype = $hdrhash{"content-type"}{MAIN};
	if ($contenttype eq "application/pkcs7-mime") {
	    #
	    # opaque-signed or enveloped message
	    #
	    unless (exists($hdrhash{"content-type"}{"smime-type"})) {
		print STDERR "ERROR: no smime-type attribute in application/pkcs7-smime entity.\n";
		last;
	    }
	    $smimetype = $hdrhash{"content-type"}{"smime-type"};
	    if ($smimetype eq "signed-data" or $smimetype eq "enveloped-data") {
		# it's verification or decryption time!

		# can handle only base64 encoding for now
		# all other encodings are treated as binary (8bit)
		if ($hdrhash{"content-transfer-encoding"}{MAIN} eq "base64") {
		    $mimebody = decode_base64($mimebody);
		}

		# if we need to dump the DER, we would do it right here

		# now write the DER
		$tmpderfile = "/tmp/der.$$";
		open(TMP, ">$tmpderfile") or die "ERROR: cannot write signature data to temporary file";
		print TMP $mimebody;
		unless (close(TMP)) {
		    print STDERR "ERROR: writing signature data to temporary file.\n";
		    unlink($tmpderfile);
		    exit 1;
		}

		$mimeheaders = "";
		open(TMP, "$cmsutilpath -D $decodeopts -h $layercounter -i $tmpderfile |") or die "ERROR: cannot open pipe to cmsutil";
		$layercounter++;
		while (<TMP>) {
		    last if (/^\r?$/);			# empty lines mark end of header
		    if (/^SMIME: /) {			# add all SMIME info to the rfc822 hdrs
			$lastref = \$rfc822headers;
		    } elsif (/^\s/) {
			;				# continuation lines go to the last dest
		    } else {
			$lastref = \$mimeheaders;	# all other headers are mime headers
		    }
		    $$lastref .= $_;
		}
		# slurp in rest of the data to $mimebody
		$saveRS = $/; $/ = undef; $mimebody = <TMP>; $/ = $saveRS;
		close(TMP);

		unlink($tmpderfile);

	    } else {
		print STDERR "ERROR: unknown smime-type \"$smimetype\" in application/pkcs7-smime entity.\n";
		last;
	    }
	} elsif ($contenttype eq "multipart/signed") {
	    #
	    # clear signed message
	    #
	    unless (exists($hdrhash{"content-type"}{"protocol"})) {
		print STDERR "ERROR: content type has no protocol attribute in multipart/signed entity.\n";
		last;
	    }
	    if ($hdrhash{"content-type"}{"protocol"} ne "application/pkcs7-signature") {
		# we cannot handle this guy
		print STDERR "ERROR: unknown protocol \"", $hdrhash{"content-type"}{"protocol"},
			"\" in multipart/signed entity.\n";
		last;
	    }
	    unless (exists($hdrhash{"content-type"}{"boundary"})) {
		print STDERR "ERROR: no boundary attribute in multipart/signed entity.\n";
		last;
	    }
	    $boundary = $hdrhash{"content-type"}{"boundary"};

	    # split $mimebody along \n--$boundary\n - gets you four parts
	    # first (0), any comments the sending agent might have put in
	    # second (1), the message itself
	    # third (2), the signature as a mime entity
	    # fourth (3), trailing data (there shouldn't be any)

	    @multiparts = split(/\r?\n--$boundary(?:--)?\r?\n/, $mimebody);

	    #
	    # parse the signature headers
	    ($submimeheaders, $submimebody) = split(/^$/m, $multiparts[2]);
	    %sighdrhash = parseheaders($submimeheaders);
	    unless (exists($sighdrhash{"content-type"}{MAIN})) {
		print STDERR "ERROR: signature entity has no content type.\n";
		last;
	    }
	    if ($sighdrhash{"content-type"}{MAIN} ne "application/pkcs7-signature") {
		# we cannot handle this guy
		print STDERR "ERROR: unknown content type \"", $sighdrhash{"content-type"}{MAIN},
			"\" in signature entity.\n";
		last;
	    }
	    if ($sighdrhash{"content-transfer-encoding"}{MAIN} eq "base64") {
		$submimebody = decode_base64($submimebody);
	    }

	    # we would dump the DER at this point

	    $tmpsigfile = "/tmp/sig.$$";
	    open(TMP, ">$tmpsigfile") or die "ERROR: cannot write signature data to temporary file";
	    print TMP $submimebody;
	    unless (close(TMP)) {
		print STDERR "ERROR: writing signature data to temporary file.\n";
		unlink($tmpsigfile);
		exit 1;
	    }

	    $tmpmsgfile = "/tmp/msg.$$";
	    open(TMP, ">$tmpmsgfile") or die "ERROR: cannot write message data to temporary file";
	    print TMP $multiparts[1];
	    unless (close(TMP)) {
		print STDERR "ERROR: writing message data to temporary file.\n";
		unlink($tmpsigfile);
		unlink($tmpmsgfile);
		exit 1;
	    }

	    $mimeheaders = "";
	    open(TMP, "$cmsutilpath -D $decodeopts -h $layercounter -c $tmpmsgfile -i $tmpsigfile |") or die "ERROR: cannot open pipe to cmsutil";
	    $layercounter++;
	    while (<TMP>) {
		last if (/^\r?$/);
		if (/^SMIME: /) {
		    $lastref = \$rfc822headers;
		} elsif (/^\s/) {
		    ;
		} else {
		    $lastref = \$mimeheaders;
		}
		$$lastref .= $_;
	    }
	    $saveRS = $/; $/ = undef; $mimebody = <TMP>; $/ = $saveRS;
	    close(TMP);
	    unlink($tmpsigfile);
	    unlink($tmpmsgfile);

	} else {

	    # not a content type we know - we're done
	    last;

	}
    }

    # so now we have the S/MIME parsing information in rfc822headers
    # and the first mime entity we could not handle in mimeheaders and mimebody.
    # dump 'em out and we're done.
    print $rfc822headers;
    print $mimeheaders . "\n" . $mimebody;

} else {

    #
    # encode (which is much easier than decode)
    #

    $mimeentity = $mimeheaders . "\n" . $mimebody;

    #
    # canonicalize inner entity (rudimentary yet)
    # convert single LFs to CRLF
    # if no Content-Transfer-Encoding header present:
    #  if 8 bit chars present, use Content-Transfer-Encoding: quoted-printable
    #  otherwise, use Content-Transfer-Encoding: 7bit
    #
    $mimeentity =~ s/\r*\n/\r\n/mg;

    #
    # now do the wrapping
    # we sign first, then encrypt because that's what Communicator needs
    #
    if (defined($opt_S)) {
	$mimeentity = signentity($mimeentity, $signopts);
    }

    if (defined($opt_E)) {
	$mimeentity = encryptentity($mimeentity, $encryptopts);	
    }

    #
    # XXX sign again to do triple wrapping (RFC2634)
    #

    #
    # now write out the RFC822 headers
    # followed by the final $mimeentity
    #
    print $rfc822headers;
    print "MIME-Version: 1.0 (NSS SMIME - http://www.mozilla.org/projects/security)\n";	# set up the flag
    print $mimeentity;
}

exit 0;