#!/usr/bin/perl
# cryptoa - revised 9/8/07
# kurt theis <ktheis@landfall.net>
# use rc4 as stream generator to en/decrypt file
# works on both *unix and Windows NT varients (XP, etc)

#make sure there are no inconsistancies between versions/op sys etc.
$digest = substr((crypt("cryptoa",12)),2);
if ($digest ne "4WIS3iP/du2") {
	die "Incompatable version of Perl - bad crypt()\n";
}

$ARGCOUNT = $#ARGV + 1;
if ($ARGCOUNT == 0) { usage(); } # show usage and exit
if ($ARGV[0] eq "?") { usage(); } # show usage and exit

# get file name to work on
$filename = $ARGV[0];

# open the files
open(INFILE, $filename) || die "Error opening file $filename - $! \n";
open(OUTFILE, ">_$filename") || die "Error opening file $filename - $! \n";
binmode(INFILE);
binmode(OUTFILE);

# get a password
use Term::ReadKey;
print "Password: ";
ReadMode('noecho');
$pword = ReadLine(0);
if ($ENV{"OS"} ne "Windows_NT") {
	system("stty sane");	# do this for *nix boxes
}
chomp($pword);
$password = substr((crypt($pword,12)),2);	# remove salt

# set up initial key structure based on password
init_rc4();


while (<INFILE>) {
	$line = $_;
	chop($line);
	$length = length($line);
	$count = 0;
	while ($count <= $length) {
		$char = substr($_,($count++),1);
		$enchar = $char ^ (chr rc4());
		print OUTFILE $enchar;
	}
	if (eof(INFILE) == 1) { last; }
}

# clean up
close(INFILE);
close(OUTFILE);

# rename original file to newly created
if ($ENV{"OS"} eq "Windows_NT") {
	# windows command
	$cmd = "move _$filename $filename";
	system($cmd) ==0 || die "Error changing file $filename - $! \n";
} else {
	# unix command
	$cmd = "mv _$filename $filename";
	system($cmd) == 0 || die "Error changing file $filename - $! \n";
}

# fini
print "\nDone.\n";
exit;



# ---------------- Subroutines Here ------------------

sub usage {

	print "\nUsage: cryptoa [filename]\n";
	exit;
}

sub rc4 {

	$i = ($i+1) % 256;
	$j = ($j + $s[$i]) % 256;
	my $temp = $s[$i];
	$s[$i] = $s[$j];
	$s[$j] = $temp;
	$t = ($s[$i] + $s[$j]) % 256;
	# print "\nin rc4() i=$i   j=$j val=$s[$t]";
	return $s[$t];
}

sub init_rc4 {

	for ($n=0; $n<256; $n++) {
		$s[$n] = $n;
	}
	$j = 0;
	my $len = length($password);
	for ($n=0; $n<256; $n++) {
		$k[$n] = ord(substr($password,($n % $len),1));
	}
	for ($i=0; $i<256; $i++) {
		$j = ($j + $s[$i] + $k[$i]) % 256;
		my $temp = $s[$i];
		$s[$i] = $s[$j];
		$s[$j] = $temp;
	}
	$i = 1;
	$j = 1;
}