1decrypt(3)            User Contributed Perl Documentation           decrypt(3)
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NAME

6       Filter::decrypt - template for a decrypt source filter
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SYNOPSIS

9           use Filter::decrypt ;
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DESCRIPTION

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

20       It is important to note that a decryption filter can never provide
21       complete security against attack. At some point the parser within Perl
22       needs to be able to scan the original decrypted source. That means that
23       at some stage fragments of the source will exist in a memory buffer.
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25       Also, with the introduction of the Perl Compiler backend modules, and
26       the B::Deparse module in particular, using a Source Filter to hide
27       source code is becoming an increasingly futile exercise.
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29       The best you can hope to achieve by decrypting your Perl source using a
30       source filter is to make it unavailable to the casual user.
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32       Given that proviso, there are a number of things you can do to make
33       life more difficult for the prospective cracker.
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35       1.   Strip the Perl binary to remove all symbols.
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37       2.   Build the decrypt extension using static linking. If the extension
38            is provided as a dynamic module, there is nothing to stop someone
39            from linking it at run time with a modified Perl binary.
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41       3.   Do not build Perl with "-DDEBUGGING". If you do then your source
42            can be retrieved with the "-DP" command line option.
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44            The sample filter contains logic to detect the "DEBUGGING" option.
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46       4.   Do not build Perl with C debugging support enabled.
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48       5.   Do not implement the decryption filter as a sub-process (like the
49            cpp source filter). It is possible to peek into the pipe that
50            connects to the sub-process.
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52       6.   Check that the Perl Compiler isn't being used.
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54            There is code in the BOOT: section of decrypt.xs that shows how to
55            detect the presence of the Compiler. Make sure you include it in
56            your module.
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58            Assuming you haven't taken any steps to spot when the compiler is
59            in use and you have an encrypted Perl script called "myscript.pl",
60            you can get access the source code inside it using the perl
61            Compiler backend, like this
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63                perl -MO=Deparse myscript.pl
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65            Note that even if you have included the BOOT: test, it is still
66            possible to use the Deparse module to get the source code for
67            individual subroutines.
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69       7.   Do not use the decrypt filter as-is. The algorithm used in this
70            filter has been purposefully left simple.
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72       If you feel that the source filtering mechanism is not secure enough
73       you could try using the unexec/undump method. See the Perl FAQ for
74       further details.
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AUTHOR

77       Paul Marquess
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DATE

80       19th December 1995
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84perl v5.26.3                      2017-11-15                        decrypt(3)