I think Acme::Bleach is ideal for your purposes.

After Compline,
Zaxo

Amplifying on the previous answers: you can't.

However, if you can restrict access to the environment in which your scripts run, you can use some external key to decrypt them. Of course, if an attacker can lay hands on that key, you still lose. Think of it as exactly the same as using Acme::Bleach, only keeping decryption knowledge for everything localised at a single place.

Put the password "<kbd>foobar</kbd>" (without the quotes) in your environment variable <samp>PASSWD</samp> (I told you it was laughably insecure!), and execute this code:

#!/usr/local/bin/perl
use warnings;
use strict;
use Crypt::CBC;
use Crypt::DES;         # give compile-time error if uninstalled
use Digest::MD5 qw/md5/;

my $cr = new Crypt::CBC ({ key => $ENV{PASSWD},
                           cipher => 'DES',
                         });
$cr->start('decrypting');
eval join '', (map {$cr->crypt(unpack 'u',$_)} <DATA>), $cr->finish;
__END__
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[download]

Here's a program to "encrypt". Again, put your password in envariable <samp>PASSWD</samp>.

#!/usr/local/bin/perl
use warnings;
use strict;
use Crypt::CBC;
use Crypt::DES;            # give compile-time error if uninstalled
use Digest::MD5 qw/md5/;

die "$0: Gimme a password in environment variable PASSWD\n"
  unless exists $ENV{PASSWD};
my $cr = new Crypt::CBC ({ key => $ENV{PASSWD},
               cipher => 'DES',
             });
$cr->start('encrypting');

my $hdr =  <<'END_HEADER';
    #!/usr/local/bin/perl
    use warnings;
    use strict;
    use Crypt::CBC;
    use Crypt::DES;        # give compile-time error if uninstalled
    use Digest::MD5 qw/md5/;
    
    my $cr = new Crypt::CBC ({ key => $ENV{PASSWD},
                               cipher => 'DES',
                             });
    $cr->start('decrypting');
    eval join '', (map {$cr->crypt(unpack 'u',$_)} <DATA>), $cr->finis
+h;
    __END__
END_HEADER

$hdr =~ s/^ {4}//mg;
print $hdr;

while (<>) {
  print pack 'u', $cr->crypt($_);
}
print pack 'u', $cr->finish;
[download]

Adding encryption for modules is "left as an exercise for the interested reader" (i.e. I'm too indolent to do something so useless).

Finally, I cannot stress this enough: you get very little security from this sort of thing. If you need security, take a good hard look at what it is you're trying to do. Any encryption (including the superstars like AES, RSA, and any other TLA) is no stronger than the protection of its key. And if you want to run your code, you must provide access to that key.

Or, the module Filter::CBC appears to be a more solid way of doing exactly this. I've not used it, so I cannot comment on its security...

I'm wondering why your 'myscript.cgi' is readable by others. If it's the fact that people can simply type some URL into their browser and download the source then there's a significant security hole on the server and you should really get it fixed by contacting the server administrator, or getting another server.

If you're worried about other people logged into the server being able to see it then set the permissions so only the user it runs as can read it. This works far better when you're running on a machine where each script executes as the user who has it in their cgi-bin, or even better a special account for them to run CGIs as.

If this isn't the case on your server then I'd recommend you get another, more secure, server before playing about with encryption as it's a far better way to guarantee safety.

Now for the bit with disclaimers- I'm really not recommending this cause of action, I'm only putting it here in case you're determined to follow this course. Giving you enough rope to shoot yourself in the foot, or somesuch.

If you're just trying to make the script difficult to read for customers etc. to stop them messing with your carefully-crafted code then look at the Obfuscation section of this very site.. many people write 'Obfuscation engines' to hide the meaning of code. This will help to hide the details, but expect a significant performance hit whilst it's decrypted, and make sure you test the encrypted version exceptionally well since it's quite possible it's broken it.

Longer answer: You can, but it won't hold up. For your program to continue working, the source still has to be there in some form or another. This different form of your code might (emphasis on "might") be harder for a determined person to read, but if they have enough time they can recover the source or at worst an obfuscated version of the source.

--
IndyZ

For example Acme::Bleach has been suggested above by Zaxo but this is trivial to decrypt (although conceptually brilliant). see also unbleach.pl which was not written by TheDamian

cheers

tachyon

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/s