#!/usr/bin/perl -w
use Fcntl qw(:seek);
use constant READ_LENGTH => 2 ** 13;
sub pad($$) {
  my @c1 = unpack("W*", shift);
  my @c2 = unpack("W*", shift);
  pack("W*", map { ($c1[$_] & ~$c2[$_]) | (~$c1[$_] & $c2[$_]); } (0 .. $#c1))
}
for my $f (@ARGV) {
  eval {
    die $! unless -e $f;

    unless (-e "$f.pad") { # generate one-time pad
      die $! unless -f $f and -r _;

      my $n = (stat $f)[7] or die $!;
      open PAD, ">", "$f.pad" or die $!;
      open RND, "<", "/dev/urandom" or die $!;
      while ($n) {
	my $buf;
	my $c = read(RND, $buf, READ_LENGTH > $n ? $n : READ_LENGTH);
	if ($c) {
	  $n -= $c;
	  print PAD $buf;
	}
	elsif (defined($c)) { next; }
	else { die $! }
      }
      close PAD or die $!;
      close RND or die $!;
    }

    die $! unless -f "$f.pad";
    if ((stat "$f.pad")[7] == (stat $f)[7]) { # encrypt/decrypt
      open PAD, "<", "$f.pad" or die $!;
      open DATA, "+<", $f or die $!;
      my ($n, $buf, $pad);
      while ($n = read(DATA, $buf, READ_LENGTH)) {
 	seek(DATA, -$n, SEEK_CUR) or die $!;
	while (length $pad < length $buf) {
	  defined(read(PAD, $pad, READ_LENGTH, length $pad)) or die $!;
	}
	my $padded = pad($buf, substr($pad, 0, length $buf, ""));
	print DATA $padded or die $!;
      }
      warn "read error: $!\n" if $n < 0;
      close DATA or die $!;
      close PAD or die $!;
    } else {
      warn "data / pad size mismatch.  delete pad.\n";
      die $!;
    }
  };
  warn "error processing file '$f': $@" if $@;
}