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<h2> ZIP Obfuscation </h2> Using obfuscations like XOR.
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<!--border--> <date> 15. July 2002 </date>
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<h3> The EXT/IO calls </h3>
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You really should read the section about the
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<a href="zzip-extio.html">EXT/IO feature</a> of the zziplib since the
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obfuscation routines are built on top of it. In order to use obfuscation,
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you will generally need to use all the three additional argument that
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can be passsed to _open_ext_io functions. For the XOR-example, only one
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IO-handler is modified being the read()-call that will simply xor each
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data byte upon read with a specific value. It two advantages - doing an
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xor twice does yield the same data, so as a developer you do not have
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to wonder about the encryption/decryption pair, and it is a stateless
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obfuscation that does not need to know about the current position
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within the zip-datafile or zippedfile-datatream.
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The examples provided just use a simple routine for xoring data that
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is defined in all the three of the example programs: <pre>
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static int xor_value = 0x55;
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static zzip_ssize_t xor_read (int f, void* p, zzip_size_t l)
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zzip_size_t r = read(f, p, l);
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zzip_size_t i; char* q = p;
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for (x=0; x < r; x++) q[x] ^= xor_value;
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and place this routine into the io-handlers after initializing
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zzip_init_io (&xor_handlers, 0); xor_handlers.read = &xor_read;
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<h3> The examples </h3>
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There are three example programs. The first one is
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<a href="zzxorcopy.c">zzxorcopy.c</a> which actually is not a zziplib
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based program. It just opens a file via stdio, loops through all data bytes
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it can read thereby xor'ing it, and writes it out to the output file. A
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call like <code><nobr>"zzxorcopy file.zip file.dat"</nobr></code> will
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create an obfuscated dat-file from a zip-file that has been possibly
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create with the normal infozip tools or any other archive program to
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generate a zip-file. The output dat-file is not recognized by normal
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zip-enabled apps - the filemagic is obfuscated too. This output
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dat-file however is subject to the other two example programs.
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The <a href="zzxordir.c">zzxordir.c</a> program will open such an obfuscated
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zip file and decode the central directory of that zip. Everything is
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still there in just the way it can be shown with the normal unzip
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programs and routines. And the <a href="zzxorcat.c">zzxorcat.c</a> program
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can extract data from this obfuscated zip - and print it un-obfuscated
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to the screen. These example programs can help you jumpstart with
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your own set of obfuscator routines, possibly more complex ones.
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By the way, just compare those with their non-xor counterparts that
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you can find in <a href="zzdir.c">zzdir.c</a> and
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<a href="zzxorcat.c">zzxorcat.c</a>. Notice that the difference is
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in the setup part until the _open_ call after which one can just
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use the normal zzip_ routines on that obfuscated file. This is
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great for developing since you can start of with the magic-wrappers
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working on real-files then slowly turning to pack-files that hold
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most of the data and finally ending with a zip-only and obfuscated
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dat-file for your project.
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<h3> Some rationale </h3>
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Some people might ask why not adding standard zip-encryption. Well,
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first of all the standard zip-encryption has not been strong enough
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for modern computers, and there are hacker tools that even a
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half-literate computer-user can use to crack the password of a
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zip-archive. Furthermore, adding real encryption is a heavy weight
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that many people do not need, see the last argument for seeing the
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standard one is useless anyway, and adding a non-standard one
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should not be the case of the standard zziplib either, ye know.
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On the other hand, obfuscation is a means to fear off half-literates
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just as well - there are no premade tools for the obfuscation you
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can invent from the xor examples. And a hacker that can de-obfuscate
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such a dat-file is able to dissassemble your program as well thereby
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going to see your decryption routine <em>and</em> the decryption key.
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Although there is a difference, it just ranges on about times and
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exprience, not magnitudes. Remember the old saying: you can irritate
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some people for some time but not irritate all people for all the time.
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As for encryption of artwork and AI scripts in games and applications,
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just keep in mind that the final recipient has the decryption key on
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his system anyway, just obfuscated. So each such encryption is nothing
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more than just a clever form of obfuscation, nothing mathemetical strong.
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Some other people might ask why to obfuscate anyway. Well, the reason
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is theft. Even people who write opensource free software generally
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like to get some reward for what they do, some fame or atleast some
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sweet dream to have helped the world go a bit easier in the future.
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As for program text this is quite natural for the programmers who
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pick up some code from somewhere else - it happens that most of them
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have gone through some formation and they know how hard it is to get
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even some lines of code out of your brain. This is not the case for
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some artwork and AI parameters, people do not have much respect for
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those - they just pick it up, put it under their umbrella, and
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that's it - they even claim they could have done that themselves,
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and in most cases it is that they never have been really trying to
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do it and think of it as being comparable to that action-art they've
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Just be sure that there is nothing wrong with obfuscating
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things for a binary distribution of your program even for the
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opensource case - the program text itself is an obfuscation in its
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source form when being compiled into cpu instructions. Still, the
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interested people can get hold of the source code since you provide
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it somewhere and actually the original programmers like to hear
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from literate people who could help with modifying the project. The
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same is true for you artwork and AI scripts, the interested people
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can still see them in the opensource project material, but only
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those will look who dare to, not just the halfwit next door.
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Well, you do not need to that on the other hand - ID software has
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shown that it can be very helpful since people will start to
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write new maps and new bots, pack them and publish them. An open
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data format is a form of attraction for people who can use a
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graphics program and an editor but who do not know how to program.
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And if you use obfuscation within an opensource program, it is
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surely enought to just use the xor-format presented here, so that
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it easy for third people to get involved if they want to, they
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just have to rewrite their new datapacks with zzxorcopy, and
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As for the non-opensource projects, be aware that there are
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some ways to even staticlink the zziplib into your project, so
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you can even hide that you used zip tools to create your dat files.
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This is well enough for anyone to do - as soon as a hacker will
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get to the point to notice you used a zip format, he would have
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had found any other deobfusation or decryption routine as well.
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If you are frightened, just encrypt the executable with tools
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you bought from somewhere else. On the other hand, should there
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be problems or bugs, you have an easier time to find them when
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they could be caused by your dat entries, and it is again easy
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to send a fixup file to your clients, since the command line
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tools are just a breeze compared with some other anti-hacking
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tools you'll find on the market.
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Well, hope this is enough rationale to tell you that I do not
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see a need to implement anything more than obfuscation within
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zziplib - if you need real encryption, use real encryption
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software and its fileformat that supports it, not zip files.
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<p align="right"><small><small><small>
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<a href="staticlink.txt">staticlink.txt</a>
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</small></small></small></p>
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