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Landon Curt Noll 09750f8899 release winning entries of IOCCC28 under the year 2024
Congratulations to:

* 2024/anders - Prize in sound coding - layered music generator
* 2024/burton - Prize in pentagrammatology - wordle hard mode solver
* 2024/cable1 - Prize in bot talk - LLM inference engine
* 2024/cable2 - Prize in murky waters - salmon recipe
* 2024/carlini - Prize in perfect timing - Intel 4004 emulation
* 2024/codemeow - Prize in tray planting - bonsai generator
* 2024/endoh1 - Prize in patient pointillism - slow ray tracer in CPP
* 2024/endoh2 - Prize in solid body physics - rotating rigid body simulation
* 2024/ferguson1 - Prize in diabolical logistics - Oregon trail pact with the devil
* 2024/ferguson2 - Prize in yil-tas - Navajo code talker translator
* 2024/howe - Nice accent eh-ward - mini vi
* 2024/kramer - Prize in linguistic arithmetic - natural language numerical calculator
* 2024/kurdyukov1 - Prize in phased periodicity - phase of the Moon
* 2024/kurdyukov2 - Prize in art restoration - JPEG artifact removal
* 2024/kurdyukov3 - Prize in virtual quietus - gaming VM and doom
* 2024/kurdyukov4 - Prize in embiggening - encode without literals
* 2024/maffiodo - Prize in creative interpretation - Jav\*script interpreter
* 2024/mills - Prize in ℤ₃ - Infocom v3 story interpreter
* 2024/stedolan - Best one liner - icon from MD5
* 2024/straadt - Prize in imitative rebooting - OpenRISC CPU and Linux
* 2024/tmarrec - Prize in cyclonic coding - 3D tornado simulation
* 2024/tompng - Prize in quasi bijection - vortex encryptor decryptor
* 2024/weaver - Sur prize - rickroll

Ran `make update` to perform the above.
 	new file:   2024/burton/.entry.json
2025-08-02 14:43:07 -07:00

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<h1>The International Obfuscated C Code Contest</h1>
<h2>2024/tompng - Prize in quasi bijection</h2>
<h3>vortex encryptor decryptor</h3>
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<a class="Left" href="../tmarrec/index.html">&larr; 2024/tmarrec</a>
<a class="Left" href="../index.html">&uarr; 2024 &uarr;</a>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2024/tompng/prog.c">C code</a>
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<h2 id="author">Author:</h2>
<ul>
<li>Name: <a href="../../authors.html#Tompng">tompng</a><br>
Location: <a href="../../location.html#JP">JP</a> - <em>Japan</em></li>
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<h2 id="to-build">To build:</h2>
<pre><code> make all</code></pre>
<h2 id="to-use">To use:</h2>
<h3 id="encryption">Encryption</h3>
<pre><code> prog &lt; file.txt &gt; file.enc.txt</code></pre>
<h3 id="decryption">Decryption</h3>
<pre><code> prog &lt; file.enc.txt &gt; file.txt</code></pre>
<h3 id="command-line-arguments">Command line arguments</h3>
<p>You can also specify SIZE of the text-stirring area and a PASSWORD.</p>
<pre><code> ./prog 30 &lt; input &gt; output
./prog PASSWORD &lt; input &gt; output
./prog 40 PASSWORD &lt; input &gt; output</code></pre>
<p>You need to specify the same SIZE and PASSWORD to decrypt correctly.</p>
<h2 id="try">Try:</h2>
<pre><code> ./try.sh</code></pre>
<h2 id="judges-remarks">Judges’ remarks:</h2>
<p>It is well-known that the Enigma cipher was broken due to the fact that a letter could never map to itself.
Is this algorithm susceptible to a similar cryptanalysis?</p>
<h2 id="authors-remarks">Author’s remarks:</h2>
<h3 id="vortex-encryptordecryptor">Vortex Encryptor/Decryptor</h3>
<p>Secure encryption/decryption is a black box. It’s highly based on difficult mathematics. We just blindly TRUST when using it.</p>
<p>This entry is a visual vortex encryptor/decryptor for a text file.
You can visually see how this program stirs the text to encrypt/decrypt. It’s not a black box at all.</p>
<h3 id="easter-eggs">Easter Eggs</h3>
<h4 id="random-encryptordecryptor">Random Encryptor/Decryptor</h4>
<p>Some might dislike vortex-encryption algorithm. Alternately, there is one more visual text mixing algorithm.</p>
<pre><code> ./prog &lt; prog.c &gt; rand.c</code></pre>
<p>This program <code>rand.c</code> is NOT A VORTEX encryptor/deryptor. You can see the text <code>N O /,T ,A</code> somewhere in the code. It randomly swaps characters instead of stirring with vortex.</p>
<p>To check the randomness, compile it as an executable <code>rand</code> and try <code>./rand &lt; prog.c</code> or <code>./rand &lt; rand.c</code>.
You can find that the encrypted text claims to be really RAND/rand-om.</p>
<h4 id="important-passwords">Important Passwords</h4>
<p>“password” is the 1st most used alphabet password in the world. Wait, what’s the 0th used password? It might be “ioccc” or “IOCCC”.
Let’s encrypt prog.c with these passwords.</p>
<pre><code> ./prog ioccc &lt; prog.c &gt; prog1.enc.c
./prog IOCCC &lt; prog.c &gt; prog2.enc.c</code></pre>
<p>Imagine if you accidentally hit your head hard, forgot the password, lost everything except prog executable and the encrypted prog.c file.
There’s nothing to worry about. Just like important passwords often written on sticky notes, you can find this password in the encrypted text.</p>
<h3 id="internal">Internal</h3>
<h4 id="encryptiondecryption">Encryption/Decryption</h4>
<p>This program internally have forward-text-stir and backward-text-stir operation.
It tries both operation and select the one that makes the output have less entropy.
This is why this program doesn’t need a command line argument such as <code>--encrypt</code> or <code>--decrypt</code>.</p>
<h4 id="seed-and-hash">Seed and Hash</h4>
<p>For security reason, vortex used to encrypt/decrypt varies over input text.
Seed is calculated with vortex-stir-stable hash algorithm. This hash doesn’t change over encryption/decryption.
This is making hard to embed easter eggs into this program.</p>
<h4 id="vortex-stirring-algorithm">Vortex stirring algorithm</h4>
<p>Character should not disappear by vortex stirring operation, so the velocity field of the vortex is required to be no divergence.
Velocity field that has no divergence can be created from a <a href="https://en.wikipedia.org/wiki/Stream_function">stream function</a>.
In this program, stream function which is a scalar field is made of horizontal, vertical and diagonal periodic waves.
With a simple mathematics, this vortex stirring operation can be decomposed into horizontal, vertical, and diagonal array rotation which is a reversible operation.</p>
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