#!/usr/bin/perl
#
# Copyright (c) 2017 Gareth Palmer <gareth.palmer3@gmail.com>
# This program is free software, distributed under the terms of
# the GNU General Public License Version 2.

use strict;
use FindBin;
use lib $FindBin::RealBin;
use POSIX qw/EXIT_FAILURE EXIT_SUCCESS strftime/;
use English qw/-no_match_vars/;
use IO::File;
use Crypt::OpenSSL::RSA;
use Crypt::OpenSSL::X509 qw/FORMAT_ASN1 FORMAT_PEM/;
use Convert::ASN1;
use Math::BigInt;
use File::Basename qw/basename/;
use Getopt::Long qw//;
use TLV::Tags qw/:header :digest/;
use TLV::Parser;
use TLV::Builder;

sub parse_sgn {
    my ($sgn_file, $certificate_file);

    $sgn_file         = shift;
    $certificate_file = shift;

    my ($file, $content);

    unless ($file = IO::File->new ($certificate_file, '<:raw')) {
	die 'Unable to read ' . $certificate_file . ': ' . $OS_ERROR;
    }

    $content = do {local $INPUT_RECORD_SEPARATOR; $file->getline};
    $file->close;

    my $x509 = Crypt::OpenSSL::X509->new_from_string ($content, FORMAT_PEM);
    die 'Unable to load certificate' unless ($x509);

    unless ($file = IO::File->new ($sgn_file, '<:raw')) {
	die 'Unable to read ' . $sgn_file . ': ' . $OS_ERROR;
    }

    $content = do {local $INPUT_RECORD_SEPARATOR; $file->getline};
    $file->close;

    my $parser = TLV::Parser->new ($content);

    # Header
    die 'Not a version tag: ' . $parser->tag if ($parser->next_tag != HEADER_VERSION);
    die 'Wrong version length: ' . $parser->length if ($parser->next_length != 2);

    my $version = join ('.', unpack ('CC', $parser->next_value));

    die 'Not a header_length tag: ' . $parser->tag if ($parser->next_tag != HEADER_LENGTH);
    die 'Wrong header_length length: ' . $parser->length if ($parser->next_length != 2);

    my $header_length = unpack ('S>', $parser->next_value);

    print 'Version:                  ', $version, "\n",
	  'Header Length:            ', $header_length, ' bytes', "\n";

    my ($header_digest_algorithm, $header_signature_index, $header_signature_length);

    while ($parser->index < $header_length) {
	$parser->next_tag;
	next if ($parser->tag == HEADER_PADDING);
	$parser->next_length;

	if ($parser->tag == HEADER_SIGNER_ID) {
	    my $signer_id = $parser->length;

	    print 'Signer ID:                ', $signer_id, "\n";
	} elsif ($parser->tag == HEADER_SIGNER_NAME) {
	    my $signer_name = unpack ('Z*', $parser->next_value);

	    print 'Signer Name:              ', $signer_name, "\n";
	} elsif ($parser->tag == HEADER_SERIAL_NUMBER) {
	    my $serial_number = uc unpack ('H*', $parser->next_value);

	    print 'Serial Number:            ', join (':', $serial_number =~ m/(..)/g), "\n";
	} elsif ($parser->tag == HEADER_CA_NAME) {
	    my $ca_name = unpack ('Z*', $parser->next_value);

	    print 'CA Name:                  ', $ca_name, "\n";
	} elsif ($parser->tag == HEADER_SIGNATURE_INFO) {
	    my $signature_info = $parser->length;

	    print 'Signature Info:           ', $signature_info, "\n";
	} elsif ($parser->tag == HEADER_DIGEST_ALGORITHM) {
	    die 'Invalid digest_algorithm length: ' . $parser->length if ($parser->length != 1);

	    my $digest_algorithm = unpack ('C', $parser->next_value);

	    $header_digest_algorithm = $digest_algorithm;

	    print 'Digest Algorithm:         ';

	    if ($digest_algorithm == DIGEST_SHA1) {
		print 'SHA1';
	    } elsif ($digest_algorithm == DIGEST_SHA256) {
		print 'SHA256';
	    }

	    print "\n";
	} elsif ($parser->tag == HEADER_SIGNATURE_ALGORITHM_INFO) {
	    my $signature_algorithm_info = $parser->length;

	    print 'Signature Algorithm Info: ', $signature_algorithm_info, "\n";
	} elsif ($parser->tag == HEADER_SIGNATURE_ALGORITHM) {
	    die 'Invalid signature_algorithm length: ' . $parser->length if ($parser->length != 1);

	    my $signature_algorithm = unpack ('C', $parser->next_value);

	    print 'Signature Algorithm:      ', $signature_algorithm, "\n";
	} elsif ($parser->tag == HEADER_SIGNATURE_MODULUS) {
	    die 'Invalid signature_modulus length: ' . $parser->length if ($parser->length != 1);

	    my $signature_modulus = unpack ('C', $parser->next_value);

	    print 'Signature Modulus:        ', $signature_modulus, "\n";
	} elsif ($parser->tag == HEADER_SIGNATURE) {
	    my $signature = $parser->next_value;

	    # The removal index for the signature
	    $header_signature_index  = $parser->index - $parser->length - 3;
	    $header_signature_length = $parser->length + 3;

	    print 'Signature:                ', length ($signature), ' bytes', "\n";
	} elsif ($parser->tag == HEADER_FILENAME) {
	    my $filename = unpack ('Z*', $parser->next_value);

	    print 'Filename:                 ', $filename, "\n";
	} elsif ($parser->tag == HEADER_TIMESTAMP) {
	    die 'Invalid timestamp length: ' . $parser->length if ($parser->length != 4);

	    my $timestamp = unpack ('L>', $parser->next_value);

	    print 'Timestamp:                ', strftime ('%a, %d %b %Y %H:%M:%S %z', localtime $timestamp), "\n";
	} else {
	    die 'Unknown tag: ' . $parser->tag . ' at index: ' . ($parser->index - 3);
	}
    }

    print "\n";

    die 'No header digest algorithm' unless ($header_digest_algorithm);
    die 'No header signature' unless ($header_signature_index);

    my $rsa = Crypt::OpenSSL::RSA->new_public_key ($x509->pubkey);
    die 'Unable to parse RSA public key' unless ($rsa);

    if ($header_digest_algorithm == DIGEST_SHA1) {
	$rsa->use_sha1_hash;
    } elsif ($header_digest_algorithm == DIGEST_SHA256) {
	$rsa->use_sha256_hash;
    } else {
	die 'Unknown header_digest_algorithm: ' . $header_digest_algorithm;
    }

    $content = $parser->content;
    my $signature = substr ($content, $header_signature_index + 3, $header_signature_length - 3);

    # Remove the signature block
    substr ($content, $header_signature_index, $header_signature_length, '');

    if ($rsa->verify ($content, $signature)) {
	print 'Valid signature', "\n";
    } else {
	print 'Invalid signature', "\n";
    }
}

sub build_sgn {
    my ($content_file, $certificate_file, $digest_algorithm, $filename);

    $content_file     = shift;
    $certificate_file = shift;
    $digest_algorithm = shift;
    $filename         = shift;

    my ($file, $content);

    unless ($file = IO::File->new ($certificate_file, '<:raw')) {
	die 'Unable to read ' . $certificate_file . ': ' . $OS_ERROR;
    }

    $content = do {local $INPUT_RECORD_SEPARATOR; $file->getline};
    $file->close;

    my $x509 = Crypt::OpenSSL::X509->new_from_string ($content, FORMAT_PEM);
    die 'Unable to load header certificate' unless ($x509);

    my $rsa = Crypt::OpenSSL::RSA->new_private_key ($content);
    die 'Unable to load header private key' unless ($rsa);

    if ($digest_algorithm eq 'SHA1') {
	$rsa->use_sha1_hash;
    } elsif ($digest_algorithm eq 'SHA256') {
	$rsa->use_sha256_hash;
    } else {
	die 'Unknown digest_algorithm: ' . $digest_algorithm;
    }

    my $builder = TLV::Builder->new;
    my $header_signature_index;

    do {
	# Header
	$builder->next_tag (HEADER_VERSION);
	$builder->next_length (2);
	$builder->next_value (pack ('CC', 1, 2));

	$builder->next_tag (HEADER_LENGTH);
	$builder->next_length (2);
	$builder->next_value (pack ('S>', 0));

	(my $signer_name = $x509->subject) =~ s/, /;/g;
	(my $ca_name = $x509->issuer) =~ s/, /;/g;
	my $serial_number = pack ('H*', $x509->serial);

	# Combined TLV length for signer_name, serial_number and ca_name
	my $signer_id = 3 + length ($signer_name) + 1 + 3 + length ($serial_number) + 3 + length ($ca_name) + 1;

	$builder->next_tag (HEADER_SIGNER_ID);
	$builder->next_length ($signer_id);

	$builder->next_tag (HEADER_SIGNER_NAME);
	$builder->next_length (length ($signer_name) + 1);
	$builder->next_value (pack ('Z*', $signer_name));

	$builder->next_tag (HEADER_SERIAL_NUMBER);
	$builder->next_length (length $serial_number);
	$builder->next_value ($serial_number);

	$builder->next_tag (HEADER_CA_NAME);
	$builder->next_length (length ($ca_name) + 1);
	$builder->next_value (pack ('Z*', $ca_name));

	$builder->next_tag (HEADER_SIGNATURE_INFO);
	$builder->next_length (15); # Unknown

	$builder->next_tag (HEADER_DIGEST_ALGORITHM);
	$builder->next_length (1);
	$builder->next_value (pack ('C', do {
	    if ($digest_algorithm eq 'SHA1') {
		DIGEST_SHA1;
	    } elsif ($digest_algorithm eq 'SHA256') {
		DIGEST_SHA256;
	    } else {
		die 'Unknown digest algorithm: ' . $digest_algorithm;
	    }
	}));

	$builder->next_tag (HEADER_SIGNATURE_ALGORITHM_INFO);
	$builder->next_length (8); # Unknown

	$builder->next_tag (HEADER_SIGNATURE_ALGORITHM);
	$builder->next_length (1);
	$builder->next_value (pack ('C', 0)); # Unknown

	my $signature_modulus;

	if ($rsa->size == 64) {
	    $signature_modulus = 0;
	} elsif ($rsa->size == 128) {
	    $signature_modulus = 1;
	} elsif ($rsa->size == 256) {
	    $signature_modulus = 2;
	} elsif ($rsa->size == 512) {
	    $signature_modulus = 3;
	} else {
	    die 'Unsupported RSA key size: ' . $rsa->size;
	}

	$builder->next_tag (HEADER_SIGNATURE_MODULUS);
	$builder->next_length (1);
	$builder->next_value (pack ('C', $signature_modulus));

	# The insertion index of the signature
	$header_signature_index = $builder->index;

	$builder->next_tag (HEADER_FILENAME);
	$builder->next_length (length ($filename) + 1);
	$builder->next_value (pack ('Z*', $filename));

	$builder->next_tag (HEADER_TIMESTAMP);
	$builder->next_length (4);
	$builder->next_value (pack ('L>', time));

	# Header must be padded to 32-bit boundary
	while (($builder->index + 3 + $rsa->size) % 4) {
	    $builder->next_tag (HEADER_PADDING);
	}

	# Signed content includes the length of the signature block
	$builder->length (8, $builder->index + 3 + $rsa->size);
    };

    unless ($file = IO::File->new ($content_file, '<:raw')) {
	die 'Unable to read ' . $content_file . ': ' . $OS_ERROR;
    }

    $content = do {local $INPUT_RECORD_SEPARATOR; $file->getline};
    $file->close;

    $builder->next_value ($content);

    $content = $builder->content;
    die 'Unable to sign content' unless (my $signature = $rsa->sign ($content));

    # Insert signature into content
    substr ($content, $header_signature_index, 0, pack ('CS>a*', HEADER_SIGNATURE, $rsa->size, $signature));

    my $sgn_file = $content_file . '.sgn';

    unless ($file = IO::File->new ($sgn_file, '>:raw')) {
	die 'Unable to write ' . $sgn_file . ': ' . $OS_ERROR;
    }

    $file->print ($content);
    $file->close;

    print 'Built ', $sgn_file, "\n";
}

eval {
    my ($mode, $content_file, $sgn_file, $certificate_file, $digest_algorithm, $filename, $show_help);

    my $getopt = Getopt::Long::Parser->new;

    $getopt->configure (qw/no_ignore_case/);

    unless ($getopt->getoptions ('p|parse'         => sub {shift; $mode = 'parse'},
				 'b|build'         => sub {shift; $mode = 'build'},
				 'c|certificate=s' => sub {shift; $certificate_file = shift},
				 'd|digest=s'      => sub {shift; $digest_algorithm = uc shift},
				 'F|filename=s'    => sub {shift; $filename  = shift},
				 'h|help'          => sub {shift; $show_help = shift})) {
	die 'Error parsing options';
    }

    if ($show_help) {
	print 'Usage: ', basename ($PROGRAM_NAME), ' <FILE> [OPTIONS]', "\n",
	      'Parse or build a .sgn file', "\n",
	      "\n",
	      '  -p --parse                 parse a .sgn file', "\n",
	      '  -b --build                 build a .sgn file', "\n",
	      '  -c --certificate <file>    certificate to use for verifying or signing', "\n",
	      '  -d --digest <name>         signature digest (sha1, sha256)', "\n",
	      '  -F --filename <name>       header filename in built .sgn file (optional)', "\n",
	      '  -h --help                  print this help and exit', "\n",
	      "\n";

	return;
    }

    die 'No verifying/signing certificate file specified' unless (length $certificate_file);

    if ($mode eq 'parse') {
	die 'No .sgn file specified' unless (length ($sgn_file = shift));

	parse_sgn ($sgn_file, $certificate_file);
    } elsif ($mode eq 'build') {
	die 'No file specified' unless (length ($content_file = shift));

	$digest_algorithm = 'SHA1' unless (length $digest_algorithm);
	$filename = basename ($content_file) . '.sgn' unless (length $filename);

	build_sgn ($content_file, $certificate_file, $digest_algorithm, $filename);
    } else {
	die 'No mode specified';
    }
};

if (length $EVAL_ERROR) {
    $EVAL_ERROR =~ s/ at \S+ line \d+\.//;
    warn $EVAL_ERROR;

    exit EXIT_FAILURE;
}

exit EXIT_SUCCESS;