1 package Filter::decrypt ;
7 use vars qw(@ISA $VERSION);
11 bootstrap Filter::decrypt ;
17 Filter::decrypt - template for a decrypt source filter
25 This is a sample decrypting source filter.
27 Although this is a fully functional source filter and it does implement
28 a I<very> simple decrypt algorithm, it is I<not> intended to be used as
29 it is supplied. Consider it to be a template which you can combine with
30 a proper decryption algorithm to develop your own decryption filter.
34 It is important to note that a decryption filter can I<never> provide
35 complete security against attack. At some point the parser within Perl
36 needs to be able to scan the original decrypted source. That means that
37 at some stage fragments of the source will exist in a memory buffer.
39 Also, with the introduction of the Perl Compiler backend modules, and
40 the B::Deparse module in particular, using a Source Filter to hide source
41 code is becoming an increasingly futile exercise.
43 The best you can hope to achieve by decrypting your Perl source using a
44 source filter is to make it unavailable to the casual user.
46 Given that proviso, there are a number of things you can do to make
47 life more difficult for the prospective cracker.
53 Strip the Perl binary to remove all symbols.
57 Build the decrypt extension using static linking. If the extension is
58 provided as a dynamic module, there is nothing to stop someone from
59 linking it at run time with a modified Perl binary.
63 Do not build Perl with C<-DDEBUGGING>. If you do then your source can
64 be retrieved with the C<-Dp> command line option.
66 The sample filter contains logic to detect the C<DEBUGGING> option.
70 Do not build Perl with C debugging support enabled.
74 Do not implement the decryption filter as a sub-process (like the cpp
75 source filter). It is possible to peek into the pipe that connects to
80 Check that the Perl Compiler isn't being used.
82 There is code in the BOOT: section of decrypt.xs that shows how to detect
83 the presence of the Compiler. Make sure you include it in your module.
85 Assuming you haven't taken any steps to spot when the compiler is in
86 use and you have an encrypted Perl script called "myscript.pl", you can
87 get access the source code inside it using the perl Compiler backend,
90 perl -MO=Deparse myscript.pl
92 Note that even if you have included the BOOT: test, it is still
93 possible to use the Deparse module to get the source code for individual
98 Do not use the decrypt filter as-is. The algorithm used in this filter
99 has been purposefully left simple.
103 If you feel that the source filtering mechanism is not secure enough
104 you could try using the unexec/undump method. See the Perl FAQ for