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                    <h1 class="navbar-item">Encryption tool</h1>
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                    <h2><a href="index.html">Documentation</a></h2><div class="category"><h3>Classes</h3><ul><li><a href="Feistel.html">Feistel</a></li><li><a href="SessionManager.html">SessionManager</a></li></ul><h3>Components</h3><ul><li><a href="App.html">App</a></li><li><a href="Footer.html">Footer</a></li><li><a href="Header.html">Header</a></li><li><a href="Login.html">Login</a></li><li><a href="Main.html">Main</a></li><li><a href="MainLayout.html">MainLayout</a></li><li><a href="Selector.html">Selector</a></li><li><a href="TextArea.html">TextArea</a></li></ul><h3>Global</h3><ul><li><a href="global.html#openNotification">openNotification</a></li></ul></div><div class="category"><h2>Constants</h2><h3>Global</h3><ul><li><a href="global.html#BITWISE_FUNCTIONS">BITWISE_FUNCTIONS</a></li></ul></div><div class="category"><h2>Utils</h2><h3>Global</h3><ul><li><a href="global.html#base64ToUTF16">base64ToUTF16</a></li><li><a href="global.html#binaryToText">binaryToText</a></li><li><a href="global.html#decimalToBinary">decimalToBinary</a></li><li><a href="global.html#enableTabulatorInTextArea">enableTabulatorInTextArea</a></li><li><a href="global.html#from8BitBinaryToUnicode">from8BitBinaryToUnicode</a></li><li><a href="global.html#generateKey">generateKey</a></li><li><a href="global.html#getBitWiseFunc">getBitWiseFunc</a></li><li><a href="global.html#textToBinary">textToBinary</a></li><li><a href="global.html#textToUnicodeDecimalArray">textToUnicodeDecimalArray</a></li><li><a href="global.html#unicodeTo8BitBinary">unicodeTo8BitBinary</a></li><li><a href="global.html#UTF16ToBase64">UTF16ToBase64</a></li></ul></div>
                
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    <h3> </h3>


    <section>
        <article><h1>Cipher</h1>
<p><em>This is an ecnryption tool that implements Feistel Cipher and allows to encrypt and decrypt any text string - inluding all languages characters, symbols and emojis.</em></p>
<h3>Links</h3>
<h4><strong><a href="https://www.cipher.ovh/">Demo</a></strong></h4>
<h4><strong><a href="https://www.cipher.ovh/docs">Documentation</a></strong></h4>
<h3>Motivation</h3>
<p>This tool was created for the recruitment process and as a portfolio. As well to to learn and improve programming skills.</p>
<h3>Password</h3>
<blockquote>
<p><strong>Password</strong> : <em>admin</em></p>
</blockquote>
<p>As mentioned above, this tool was created for the recruitment process which required logging in, thus the password is made public.</p>
<h2>Feistel Cipher implementation</h2>
<p>You can read how Feistel Cipher works on <a href="https://en.wikipedia.org/wiki/Feistel_cipher">Wikipedia</a></p>
<p>Diagram below shows basic usage:</p>
<p><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Feistel_cipher_diagram_en.svg/410px-Feistel_cipher_diagram_en.svg.png" alt="enter image description here"></p>
<h3>Algorithm assumptions:</h3>
<ul>
<li>Encrypting function F defined as one of:
<ul>
<li>xor</li>
<li>or</li>
<li>and</li>
<li>signed right shift</li>
</ul>
</li>
<li>Round-dependant key (sub-key) creation function:
<ol>
<li>Define master key as hashed user provided key (string) with sh256 hash function truncated to 64bit hash</li>
<li>Round subkey is defined as sha256 of <em>master key</em> + <em>round number</em> + <em>round number to the power of 37</em> truncated to 64bit hash</li>
</ol>
</li>
<li>Every character is represented in 16bit format</li>
<li>Every block size has size of 128bit</li>
<li>Key size is 64bit</li>
<li>Padding character is defined as Unicode End of Text (\u0003)</li>
<li>In order to provide user friendly encrypted text, result of algorithm is converted to Base64 on input and output.</li>
</ul>
<h3>Algorithm steps:</h3>
<h5>Encryption</h5>
<ol>
<li>Divide input string into 128bit blocks
<ul>
<li>Due to asumptions every single block has 8 characters (block size 128bit / char size 16bit)</li>
<li>Last block is filled with padding character when necessary - less than 8 characters</li>
</ul>
</li>
<li>Every block is processed separately</li>
<li>Each block input text is converted to binary represantation</li>
<li>Core Feistel Cipher alhorithm is executed
<ul>
<li>Binary input is split into two equal pieces</li>
<li>In each round right halft of the block goes through unchanged and becomes new left</li>
<li>Left half is XOR-ed with output of encryption function F that takes right side and round key as parameters - result of that becomes new left</li>
<li>Once the last round is completed - right side is swapped with left.</li>
</ul>
</li>
<li>Concatenate results from each block converted back to UTF16 string as final cipher</li>
</ol>
<h5>Decryption</h5>
<ol>
<li>Same as encryption process but order of applied keys is reversed.</li>
<li>Possible padding characters (\u0003) are removed from final text.</li>
</ol>
<h3>Tests</h3>
<p>Cipher app includes unit tests created with <a href="https://jestjs.io/">JEST.js</a></p>
<h3>Documentation</h3>
<p>Documentation created with <a href="https://jsdoc.app/">JSDoc</a></p>
<p>Available at <strong><a href="https://www.cipher.ovh/docs/">cipher.ovh/docs</a></strong></p>
<h3>Available Scripts</h3>
<pre class="prettyprint source"><code>npm run start - Runs the app in the development mode
npm run test - Runs all tests
npm run build - Builds the app for production to the build folder
npm run docs - Generates docs in docs folder
</code></pre>
<hr>
<p>© May 2021 Patryk Bura</p></article>
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