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<h1>The International Obfuscated C Code Contest</h1>
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<h2>2014/birken - Best use of port 1701</h2>
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<h3>Klingon web server</h3>
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<h2 id="authors">Authors:</h2>
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<ul>
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<li>Name: <a href="../../authors.html#Alexander_Prishchepov">Alexander Prishchepov</a><br>
|
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Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)
|
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<br><br></li>
|
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<li>Name: <a href="../../authors.html#Michael_Birken">Michael Birken</a><br>
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Location: <a href="../../location.html#US">US</a> - <em>United States of America</em> (<em>United States</em>)</li>
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<!-- BEFORE: 1st line of markdown file: 2014/birken/README.md -->
|
||
<h2 id="to-build">To build:</h2>
|
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<pre><code> make</code></pre>
|
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<p>There is alternate code that lets you redefine the port to bind to, in case
|
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there is a firewall issue, and also lets you redefine the timing constant,
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<code>STARDATE</code>. See <a href="#alternate-code">Alternate code</a> below.</p>
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<h2 id="to-use">To use:</h2>
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<pre><code> ./prog < some_secret_or_something
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./prog http://host[:port]</code></pre>
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<h2 id="try">Try:</h2>
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<pre><code> ./prog < README.md</code></pre>
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<p>or maybe:</p>
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<pre><code> echo "IOCCC 2014!" | ./prog</code></pre>
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<p>Next, try in another terminal, as the above one is running:</p>
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<pre><code> ./prog http://127.0.0.1:1701</code></pre>
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<p>What happens if you specify instead of a regular file something like
|
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<code>/dev/null</code> ?</p>
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||
<p>But there’s more! Try opening in a browser the same address and then see what
|
||
happens. This is explained by the authors when explaining their inspiration.</p>
|
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<h2 id="alternate-code">Alternate code:</h2>
|
||
<p>This version allows you to redefine the port to bind to, should 1701 be a
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problem for some reason, and it also allows you to change the timing as
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described by the author. See <a href="#configuration">configuration</a> below.</p>
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<h3 id="alternate-build">Alternate build:</h3>
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<p>To specify the port to say, 31337, try:</p>
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<pre><code> make clobber PORT=31337 alt</code></pre>
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<p>To change the timing constant, <code>STARDATE</code>, try:</p>
|
||
<pre><code> make clobber TIME=5000000 alt</code></pre>
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<p>You can combine them both of course.</p>
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<h3 id="alternate-use">Alternate use:</h3>
|
||
<p>Use <code>prog.alt</code> as you would <code>prog</code> above. Remember that ports < 1024 are
|
||
privileged ports that unprivileged users cannot use.</p>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>Port 1701? Well this is not the l2f registered TCP/1701 protocol.
|
||
Sniff the traffic to/from that port. You will see HTTP client
|
||
and server traffic. The HTML content you may see is static and
|
||
immutable. Nothing funny with the HTTP status codes. Even the
|
||
timestamp cookie, once set, remains static throughout the
|
||
session. The data appears to not be transmitted within the
|
||
binary content communicated between client and server.</p>
|
||
<p>So how does this program do it? A trek though the cloak of
|
||
obfuscation awaits the reader of the source!</p>
|
||
<h2 id="authors-remarks">Authors’ remarks:</h2>
|
||
<h3 id="abstract">Abstract</h3>
|
||
<p>When launched in web server mode, this application appears to deliver nothing
|
||
more than a static HTML page. But, in actuality, it allows covert file
|
||
transfer over the Internet. This is demonstrated by starting the application as
|
||
a client-side downloader. The hidden transmitted data cannot be reconstructed
|
||
or even detected from the binary content of the traffic between the client and
|
||
the server.</p>
|
||
<h2 id="to-use-web-server">To use web server</h2>
|
||
<pre><code> ./prog < secret_file_to_be_downloaded</code></pre>
|
||
<p>Try using the program’s source code as the secret file:</p>
|
||
<pre><code> ./prog < prog.c</code></pre>
|
||
<h2 id="to-use-client-side-downloader">To use client-side downloader</h2>
|
||
<pre><code> ./prog http://host[:port]</code></pre>
|
||
<p>The optional port defaults to 1701. If the web server instance is started on
|
||
the same box, try:</p>
|
||
<pre><code> ./prog http://127.0.0.1:1701</code></pre>
|
||
<p>It will incrementally display the contents of the hidden file at a rate of
|
||
approximately 1 baud.</p>
|
||
<p>The client-side downloader will automatically terminate if the web server is
|
||
bounced.</p>
|
||
<h3 id="html-content">HTML content</h3>
|
||
<p>Plug the URL into a browser to view a static HTML page containing ASCII artwork.</p>
|
||
<h3 id="exploration">Exploration</h3>
|
||
<p>Studying the network traffic will reveal that the HTML content is static and
|
||
immutable, the HTTP request and response fields do not contain anything
|
||
remarkable, HTTP status and error codes are not exploited, no unusual or
|
||
deprecated features of HTTP are used, and while the cookie is based on a
|
||
timestamp, its value also remains unchanged throughout the session. As
|
||
mentioned in the abstract, the data is not transmitted within the binary content
|
||
communicated between the client and the server. A full explanation of the
|
||
protocol appears below, but feel free to explore before reading further.</p>
|
||
<h3 id="inspiration">Inspiration</h3>
|
||
<p>The inspiration for this program comes from <a href="https://memory-alpha.fandom.com/wiki/Star_Trek_VI:_The_Undiscovered_Country">Star Trek VI: The Undiscovered
|
||
Country</a>,
|
||
specifically the final confrontation between the
|
||
<a href="https://memory-alpha.fandom.com/wiki/USS_Enterprise_(NCC-1701)">Enterprise</a> and
|
||
the enhanced prototype <a href="https://memory-alpha.fandom.com/wiki/Klingon_Bird-of-Prey">Klingon Bird of
|
||
Prey</a>. The definitive
|
||
feature of the prototype was its ability to fire while cloaked. But, perhaps
|
||
even more impressive was its ability to keep an open communication channel with
|
||
the Enterprise throughout the battle, enabling the antagonist
|
||
<a href="https://memory-alpha.fandom.com/wiki/Chang_(General)">Chang</a> to taunt <a href="https://memory-alpha.fandom.com/wiki/James_T._Kirk">Captain
|
||
Kirk</a> with
|
||
<a href="https://en.wikipedia.org/wiki/William_Shakespeare">Shakespearian</a> quotes while
|
||
he slowly pelted his ship with torpedoes. Normally, cloaked vessels must
|
||
maintain silent running to avoid detection.</p>
|
||
<p>The battle is commemorated in the form of ASCII artwork depicting the ships
|
||
faced head-to-head in the page delivered by the web server. Plus, the program
|
||
source code is formatted in the shape of a Klingon Bird of Prey. The code
|
||
itself includes a number of Star Trek references: the registry number of the
|
||
Enterprise (NCC-1701) is defined as a constant; variable names spell out Cpt.
|
||
James T. Kirk and <a href="https://memory-alpha.fandom.com/wiki/Odo">Odo</a> (the <a href="https://memory-alpha.fandom.com/wiki/Star_Trek:_Deep_Space_Nine">Deep
|
||
Space 9</a>
|
||
character was played by René Auberjonois who also appeared as <a href="https://memory-alpha.fandom.com/wiki/West">Colonel
|
||
West</a> in <a href="https://memory-alpha.fandom.com/wiki/Star_Trek_VI:_The_Undiscovered_Country">Star Trek
|
||
VI</a> movie);
|
||
the <code>STARDATE</code> constant makes timing configurable; and, the constant <code>k</code> stands
|
||
for <a href="https://memory-alpha.fandom.com/wiki/Khan_Noonien_Singh">Khan</a> (in the
|
||
final engagement in <a href="https://memory-alpha.fandom.com/wiki/Star_Trek_II:_The_Wrath_of_Khan">Star Trek II: The Wrath of
|
||
Khan</a>, the
|
||
damaged Enterprise managed to disable the USS
|
||
<a href="https://memory-alpha.fandom.com/wiki/USS_Reliant_(NCC-1864)%20ship">Reliant</a>’s shield
|
||
generator by accessing its prefix code: 16309).</p>
|
||
<h3 id="secondary-size-limit">Secondary size limit</h3>
|
||
<p>As obligated by a program that employs 23rd century cloaking technology, when
|
||
the source is fed as input to <a href="https://github.com/ioccc-src/winner/blob/master/2014/iocccsize.c">IOCCC size tool version
|
||
2014-09-23-v19</a>, and the <code>-i</code> command line option is used, the
|
||
value printed is 0.</p>
|
||
<h3 id="transmission-protocol-revealed">Transmission protocol revealed</h3>
|
||
<p>The client-side downloader relies on the response time of the web server rather
|
||
than the binary content of the response. The server transmits 1 nibble at a
|
||
time by counting to the nibble value via a sequence of rapid responses
|
||
terminated by a long response. For instance, the value 5 would be transmitted
|
||
by making a series of requests that result in 5 near instantaneous responses
|
||
followed by a half-second delayed response. The long delay is skipped in the
|
||
case of 15, the maximal nibble value. With the aid of an ASCII table, it is
|
||
actually possible to read the nibbles by repeatedly pressing the refresh button
|
||
within a browser and observing the page refresh delay.</p>
|
||
<p>Nibble Count Coding (file transfer protocol NCC-1701) is faster than
|
||
transmitting each individual bit as a short or long delay because it sends each
|
||
byte with 2 long delays whereas communicating individual bits requires 8 long
|
||
delays in the worst case scenario. In fact, Nibble Count Coding is faster than
|
||
applying Huffman Coding since that is designed to produce compact codes under
|
||
the assumption that the bit value does not affect transmission time.</p>
|
||
<p>The server relies on the cookie to identify each client uniquely, enabling it to
|
||
transfer the sequence independently to each client.</p>
|
||
<h3 id="configuration">Configuration</h3>
|
||
<p>As with all network communication, accurate transmission of data relies on the
|
||
nature of hardware revealed through statistics and timeouts set accordingly.
|
||
The long delay is arbitrarily set to <code>0.5</code> seconds. This is microsecond tunable
|
||
via the <code>STARDATE</code> constant defined at the top of the source code. Increase the
|
||
value in the event of transmission errors. Decrease the value to download
|
||
faster and less reliably.</p>
|
||
<p>The NCC constant is the web server port number.</p>
|
||
<h3 id="obfuscations">Obfuscations</h3>
|
||
<ul>
|
||
<li>The ASCII artwork is compressed using run-length encoding.</li>
|
||
<li>One long string stores a series of strings concatenated together and
|
||
referenced via pointers.</li>
|
||
<li>The long string is shift encrypted.</li>
|
||
<li>Short and meaningless identifiers are used throughout.</li>
|
||
<li>Reversed array indexing was applied immoderately.</li>
|
||
<li>Minus is used in place of not-equals.</li>
|
||
<li><code>O</code> and <code>l</code> were selected for their resemblance to <code>0</code> and <code>1</code> respectively.</li>
|
||
<li>Standard constants and ASCII characters were replaced with their respective
|
||
numerical values.</li>
|
||
</ul>
|
||
<h3 id="compiler-warnings">Compiler warnings</h3>
|
||
<p>For space considerations, the following include statements were dropped
|
||
resulting in compiler warnings:</p>
|
||
<pre><code> #include <asm/byteorder.h>
|
||
#include <ctype.h>
|
||
#include <netinet/in.h>
|
||
#include <stdlib.h>
|
||
#include <string.h>
|
||
#include <sys/select.h>
|
||
#include <sys/socket.h>
|
||
#include <sys/types.h>
|
||
#include <sys/unistd.h></code></pre>
|
||
<p>It may be necessary to restore some of these under certain environments.</p>
|
||
<!--
|
||
|
||
Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
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||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
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<div id="inventory">
|
||
<h1 id="inventory-for-2014birken">Inventory for 2014/birken</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/prog.c">prog.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/prog.alt.c">prog.alt.c</a> - alternate source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/prog.orig.c">prog.orig.c</a> - original source code</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2014_birken.tar.bz2">2014_birken.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2014/birken/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
|
||
</ul>
|
||
<hr style="width:10%;text-align:left;margin-left:0">
|
||
<h4>
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Jump to: <a href="#">top</a>
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</h4>
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</div>
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<!--
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|
||
Copyright © 1984-2025 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
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|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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||
For more information, see:
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|
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https://creativecommons.org/licenses/by-sa/4.0/
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-->
|
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<div class="footer">
|
||
|
||
<div id="copyright"><h3>Copyright © 1984-2025 by Landon Curt Noll:
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||
<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">Some Rights Reserved</a></h3>
|
||
<p>
|
||
This work is <b>licensed by Landon Curt Noll</b> under
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||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
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target="_blank"
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rel="license noopener noreferrer"
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style="display:inline-block;">CC BY-SA 4.0</a></b>.
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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src="../../png/cc.png"
|
||
alt="cc inside circle symbol">
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
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src="../../png/by.png"
|
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alt="person inside circle symbol">
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<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
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src="../../png/sa.png"
|
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alt="arrow looping back on itself inside circle symbol"><br>
|
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You should <b>carefully review</b> the
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<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en"
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target="_blank"
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rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
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before using the licensed material.<br>
|
||
You may wish to review the
|
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<b><a href="../../license.html"
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||
target="_blank"
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rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
|
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of <b>CC BY-SA 4.0</b>.<br>
|
||
</p>
|
||
</div>
|
||
|
||
<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2014%2Fbirken%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
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<a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a><br>
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