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Web images, for example, may be viewed hundreds of times a day by a multitude of vistors. However, in some cases, you may want to keep a particular image private so that only you or perhaps a select group of your friends or web visitors can view it. ImageMagick permits you to scramble your images such that unless someone knows your passphrase, they will be unable to view the original content.</p> 87 88 <p>You could use an <a href="http://www.wizards-toolkit.org/www/encipher.html">enciphering</a> utility to scramble your image but they typically scramble the entire file making it unrecognizable as an image format. With ImageMagick, only the pixels are scrambled. The scrambled image continues to be recognized as an image and will even display in your web page. However, the content appears as gibberish, nothing like the original content.</p> 89 90 <h2><a class="anchor" id="encipher"></a>Encipher an Image</h2> 91 92 <p>Use the <a href="../www/command-line-options.html#encipher">-encipher</a> option to scramble your image so that it is unrecognizable. The option requires a filename that contains your passphrase. In this example we scramble an image and save it in the PNG format:</p> 93 94 <pre class="highlight"><code>convert rose.jpg -encipher passphrase.txt rose.png 95 </code></pre> 96 97 <p>Here we encipher an image using another image as the passphrase:</p> 98 99 <pre class="highlight"><code>convert rose.jpg -encipher smiley.gif rose.png 100 </code></pre> 101 102 <h2><a class="anchor" id="decipher"></a>Decipher an Image</h2> 103 104 <p>Use the <a href="../www/command-line-options.html#decipher">-decipher</a> option to unscramble your image so that it is recognizable once again. The option requires a filename that contains your passphrase. In this example we unscramble an image and save it in the JPEG format:</p> 105 106 <pre class="highlight"><code>convert rose.png -decipher passphrase.txt rose.jpg 107 </code></pre> 108 109 <h2><a class="anchor" id="caveats"></a>Encipher and Decipher Caveats</h2> 110 111 <p>Some formats do not support enciphered pixels-- the JPEG or GIF format, for 112 example. To ensure your image format is supported, encipher a test image and 113 verify you can restore its original content <var>before</var> you encipher any 114 additional images in that format.</p> 115 116 <p>The image format may only support 8-bit and RGB (TrueColor). As such you may 117 like to include the options "-depth 8 -type TrueColor" before the output 118 filename.</p> 119 120 <p>The passphrase can be any combinations of letters and symbols. It should 121 be a minimum of 12 character combinations to help ensure your image remains 122 private. Also make sure your passphrase file permissions prevent others from 123 reading it otherwise unintended users may be able to view the original image 124 content.</p> 125 126 <p>You can only restore the original image content if you know your 127 passphrase. If you lose or forget it, your original image content is lost 128 forever.</p> 129 130 <p>ImageMagick only scrambles the image pixels. The image metadata remains 131 untouched and readable by anyone with access to the image file.</p> 132 133 <p>ImageMagick uses the <a 134 href="http://en.wikipedia.org/wiki/Advanced_Encryption_Standard">AES</a> 135 cipher in Counter mode. We use the the first half of your passphrase to derive the nonce. The second half is the cipher key. When used correctly, AES-CTR provides a high level of confidentiality. To avoid information leaks, you must use a fresh passphrase for each image your encrypt.</p> 136 137 <p>Currently only ImageMagick can restore your enciphered image content. We 138 use a standard cipher and mode so other vendors could support enciphered image content.</p> 139 140 <p>Some small practical examples of image enciphering can be found in IM 141 Examples <a href="../Usage/transform/#encipher" 142 >Encrypting Image Data</a>. </p> 143 144 </div> 145 </div> 146 </main><!-- /.container --> 147 <footer class="magick-footer"> 148 <p><a href="../www/security-policy.html">Security</a> 149 <a href="../www/architecture.html">Architecture</a> 150 <a href="../www/links.html">Related</a> 151 <a href="../www/sitemap.html">Sitemap</a> 152 153 <a href="cipher.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 154 155 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> 156 <a href="../www/support.html">Donate</a> 157 <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a> 158 <br/> 159 <small> 1999-2019 ImageMagick Studio LLC</small></p> 160 </footer> 161 162 <!-- Javascript assets --> 163 <script src="assets/magick.js" crossorigin="anonymous"></script> 164 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.3.1/jquery.min.js"><\/script>')</script> 165 </body> 166 </html> 167
