Description:

How to use: drag and drop files into the executable icon. You will be asked for a password. The program will then create encrypted files with the ".gpg" extension (it will not delete the original files for you).

If you drop files with the ".gpg" extension, the files will be un-encrypted back.

Installation: use "PAR" (or Perl2EXE/PerlApp) to make an executable file, and copy it to the pen drive. You will need to copy the "gpg" executable to the same directory.

I've tested it with perlapp, in Windows XP and NT.

#!/usr/bin/perl -w
# Copyright (c) 2005 Flavio S. Glock.  All rights reserved.
# This program is free software; you can redistribute it 
# and/or modify it under the same terms as Perl itself.

use strict;
use Tk;

{
    my $gpg = $0;
    $gpg =~ s/[a-z0-9.]+$/gpg.exe/i;
    exit unless @ARGV;
    my $main = MainWindow->new;
    $main->Label(-text => 'Passphrase')->pack;
    my $pass = $main->Entry(-width => 12,
                            -show => '*');
    $pass->pack;
    $main->Button(-text => 'Go',
                  -command => sub {
                           do_encrypt($pass, $gpg, @ARGV);
                           $main->destroy;
                         }
                 )->pack;

    $main->Button(-text => 'Cancel',
                  -command => [$main => 'destroy']
                 )->pack;
    MainLoop;
}

sub do_encrypt {
    my ($pass, $gpg, @files) = @_;
    my @cmd;
    for ( @files )
    {
        if ( $_ =~ /(.*)\.gpg$/i )
        {
            @cmd = ($gpg,
                '--decrypt',
                '--passphrase-fd 0',
                '-o', '"' . $1 . '"',
                '--batch', '--no-tty',
                '"' . $_ . '"',
                );
        }
        else
        {
            @cmd = ($gpg,
                '--symmetric',
                '--passphrase-fd 0',
                '-o', '"' . $_ . '.gpg"',
                '--batch', '--no-tty',
                '"' . $_ . '"',
                );
        }
        open( FILE, '|-', "@cmd" );
        print FILE $pass->get, "\n";
        close( FILE );
    }
}