Remove hint.html and index.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta name="GENERATOR" content="mkd2html 2.2.0">
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<meta http-equiv="Content-Type"
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content="text/html; charset=utf-8"> <link rel="stylesheet"
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type="text/css"
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href="../hint.css">
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<title>Most in need of transparency</title>
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</head>
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<body>
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<h1>Most in need of transparency</h1>
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<p>Don Yang<br>
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<a href="http://uguu.org/">http://uguu.org/</a></p>
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<h2>Judges' comments:</h2>
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<h3>To use:</h3>
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<pre><code>make
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./prog sample_input.txt a b c d
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cat a
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cat b
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cat c
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cat d
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cat a b c d | ./prog
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</code></pre>
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<h3>Try:</h3>
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<pre><code>./prog prog.c a b c d e
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cat a
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cat b
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cat c
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cat d
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cat e
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cat a b c d e | ./prog
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cat a b c d e | ./prog | diff - prog.c
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</code></pre>
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<h3>Selected Judges Remarks:</h3>
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<p>Do you understand how this program works?
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You may have to go over and over the output again.</p>
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<h2>Author’s comments:</h2>
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<h1>Summary</h1>
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<p>Scramble/unscramble to single file:</p>
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<pre><code>./prog original.txt > scrambled.txt
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./prog < scrambled.txt > unscrambled.txt
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</code></pre>
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<p>Scramble/unscramble to multiple files:</p>
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<pre><code>./prog input.txt output1.txt output2.txt ...
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cat output1.txt output2.txt ... | ./prog > unscrambled.txt
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</code></pre>
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<p>Re-scramble:</p>
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<pre><code>./prog original.txt | ./prog - > scrambled1.txt
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./prog original.txt | ./prog - | ./prog - > scrambled2.txt
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./prog original.txt | ./prog - | ./prog - | ... > scrambled3.txt
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</code></pre>
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<p>Scramble slowly:</p>
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<pre><code>./prog input.txt | ruby prog.c
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</code></pre>
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<p>Input must be in UTF-8 encoding.</p>
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<h1>Details</h1>
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<p>This is a text scrambling utility. To scramble text, specify input
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file name as the first argument:</p>
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<pre><code>./prog input.txt > output.txt
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</code></pre>
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<p>If original input file was small enough to fit in your terminal, you
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can simply use <code>cat</code> to unscramble the output text.</p>
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<pre><code>cat output.txt
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</code></pre>
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<p>It might seem like nothing was scrambled, but you can try passing the
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output through <code>strings(1)</code> and see that most of the original strings
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are gone. What happened is that the original text has been shuffled
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with ANSI cursor positioning codes inserted such that characters are
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printed in random order. This effect is more visible if there is a
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delay after each character is printed. For convenience, an utility is
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included in the source to output characters slowly:</p>
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<pre><code>./prog input.txt | ruby prog.c
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</code></pre>
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<p>Scrambling order is deterministic, but you can reshuffle the output by
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piping it through the same utility again, by specifying <code>-</code> as the
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first argument:</p>
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<pre><code>./prog input.txt | ./prog - | ./prog - | ...
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</code></pre>
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<p>You can also split the input to multiple files, each getting a subset
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of the original input characters:</p>
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<pre><code>./prog input.txt output1.txt output2.txt ...
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cat output1.txt output2.txt ... > unscrambled.txt
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</code></pre>
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<p>You can only unscramble files with <code>cat</code> if the input fits in a single
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terminal screen. If you don’t know what will be the terminal size of
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the recipient, note that <code>prog.c</code> will fit in a 80x25 terminal, so a
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good guideline is to pick files that have fewer rows and columns than
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<code>prog.c</code>.</p>
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<p>For files that are larger than your terminal window, <code>cat</code> will not be
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sufficient for unscrambling because any scrolling causes the character
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positions to be misaligned. But fear not, this utility also includes
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unscrambling functionality. If no argument is specified, input will
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be read through stdin and unscrambled to stdout:</p>
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<pre><code>./prog < scrambled.txt > unscrambled.txt
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</code></pre>
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<p>Where this is useful is that if you scramble the input to multiple
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files and unscramble each output files individually, those output
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files can be printed on transparencies and distributed separately.</p>
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<pre><code>./prog input.txt output1.txt output2.txt output3.txt
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./prog < output1.txt > layer1.txt
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./prog < output2.txt > layer2.txt
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./prog < output3.txt > layer3.txt
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</code></pre>
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<p>In other words, this is a utility for facilitating
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<a href="https://en.wikipedia.org/wiki/Visual_cryptography">visual cryptography</a>.</p>
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<p>This utility can also be used just for removing trailing whitespaces
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and expanding tabs to 8 spaces.</p>
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<pre><code>./prog input.txt | ./prog
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</code></pre>
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<h1>Features</h1>
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<h2>UTF-8 support</h2>
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<p>A simple text scrambling utility might not have required a screenful
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of code, but this particular one natively supports UTF-8.
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Specifically: individual UTF-8 byte sequences will not be split into
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broken ones, and the utility is aware of full-width versus half-width
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differences such that cursor is positioned correctly for most CJK
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input. <code>sample_input.txt</code> demonstrates this feature with a mix of
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Basic Latin and Japanese characters.</p>
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<p>Output cursor positions will most definitely be wrong for inputs
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containing combining characters and right-to-left text, but it should
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be possible to unscramble those text back to the original using this
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same utility, since the utility is self-consistent in how cursor
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positions are handled.</p>
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<h2>Error handling</h2>
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<p>If any file can not be opened for reading or writing, an error is
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printed to stderr, and the utility will exit with nonzero status.</p>
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<p>If there isn’t enough memory, the utility will likely crash.</p>
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<p>If input contains CR-LF end of line sequences, those CRs are silently
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dropped. In fact, most control codes are silently ignored except line
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feeds (preserved) and tabs (expanded to 8 spaces).</p>
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<h2>Compatibility</h2>
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<p>Verified to work and compiles without warnings on these environments:</p>
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<ul>
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<li> gcc 7.3.0 on Linux</li>
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<li> gcc 7.4.0 on Cygwin</li>
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<li> clang 4.0.1-10 on Linux</li>
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<li> clang 5.0.1 on Cygwin</li>
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<li> gcc 4.8.4 on Linux</li>
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</ul>
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<h2>Full version</h2>
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<p>I tried really hard to make <code>prog.c</code> fit in a 80x25 terminal without
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wrapping. If I were not constrained by space, I would have made an
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ASCII art out of it. <code>violet.c</code> is that program, and also comes with
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the minor benefit of supporting lines longer than a million columns
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depending on <code>sizeof(int)</code>.</p>
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<p>Violet is named after “Violet Evergarden”, the character who is highly
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skilled in writing letters.</p>
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<hr />
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<TABLE><TR>
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<TD><a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/"><img alt="Creative Commons License" style="border-width:0" src="/png/by-sa-3.0-88x31.png" /></a></TD>
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<TD><P>© Copyright 1984-2019,
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<A HREF="/judges.html">Leo Broukhis, Simon Cooper, Landon Curt Noll</A>
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- All rights reserved<BR>
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This work is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by-sa/3.0/">Creative Commons Attribution-ShareAlike 3.0 Unported License</a>.</P></TD>
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<TD> <!--<a href="https://validator.w3.org/check?uri=referer"><img src="https://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional" height="31" width="88"></a>--></TD>
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</TR></TABLE>
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</body>
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</html>
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