GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  FILTER::DECRYPT (3)

.ds Aq ’

NAME

Filter::decrypt - template for a decrypt source filter

CONTENTS

SYNOPSIS



    use Filter::decrypt ;



DESCRIPTION

This is a sample decrypting source filter.

Although this is a fully functional source filter and it does implement a very simple decrypt algorithm, it is not intended to be used as it is supplied. Consider it to be a template which you can combine with a proper decryption algorithm to develop your own decryption filter.

WARNING

It is important to note that a decryption filter can never provide complete security against attack. At some point the parser within Perl needs to be able to scan the original decrypted source. That means that at some stage fragments of the source will exist in a memory buffer.

Also, with the introduction of the Perl Compiler backend modules, and the B::Deparse module in particular, using a Source Filter to hide source code is becoming an increasingly futile exercise.

The best you can hope to achieve by decrypting your Perl source using a source filter is to make it unavailable to the casual user.

Given that proviso, there are a number of things you can do to make life more difficult for the prospective cracker.
1. Strip the Perl binary to remove all symbols.
2. Build the decrypt extension using static linking. If the extension is provided as a dynamic module, there is nothing to stop someone from linking it at run time with a modified Perl binary.
3. Do not build Perl with -DDEBUGGING. If you do then your source can be retrieved with the -Dp command line option.

The sample filter contains logic to detect the DEBUGGING option.

4. Do not build Perl with C debugging support enabled.
5. Do not implement the decryption filter as a sub-process (like the cpp source filter). It is possible to peek into the pipe that connects to the sub-process.
6. Check that the Perl Compiler isn’t being used.

There is code in the BOOT: section of decrypt.xs that shows how to detect the presence of the Compiler. Make sure you include it in your module.

Assuming you haven’t taken any steps to spot when the compiler is in use and you have an encrypted Perl script called myscript.pl, you can get access the source code inside it using the perl Compiler backend, like this



    perl -MO=Deparse myscript.pl



Note that even if you have included the BOOT: test, it is still possible to use the Deparse module to get the source code for individual subroutines.

7. Do not use the decrypt filter as-is. The algorithm used in this filter has been purposefully left simple.
If you feel that the source filtering mechanism is not secure enough you could try using the unexec/undump method. See the Perl FAQ for further details.

AUTHOR

Paul Marquess

DATE

19th December 1995
Search for    or go to Top of page |  Section 3 |  Main Index


perl v5.20.3 DECRYPT (3) 2015-07-26

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.