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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> 98 99<p>You could use an <a href="https://github.com/ImageMagick/WizardsToolkit">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> 100 101<h2><a class="anchor" id="encipher"></a>Encipher an Image</h2> 102 103<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> 104 105<pre class="highlight"><code>magick rose.jpg -encipher passphrase.txt rose.png 106</code></pre> 107 108<p>Here we encipher an image using another image as the passphrase:</p> 109 110<pre class="highlight"><code>magick rose.jpg -encipher smiley.gif rose.png 111</code></pre> 112 113<h2><a class="anchor" id="decipher"></a>Decipher an Image</h2> 114 115<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> 116 117<pre class="highlight"><code>magick rose.png -decipher passphrase.txt rose.jpg 118</code></pre> 119 120<h2><a class="anchor" id="caveats"></a>Encipher and Decipher Caveats</h2> 121 122<p>Some formats do not support enciphered pixels-- the JPEG or GIF format, for 123example. To ensure your image format is supported, encipher a test image and 124verify you can restore its original content <var>before</var> you encipher any 125additional images in that format.</p> 126 127<p>The image format may only support 8-bit and RGB (TrueColor). As such you may 128like to include the options "-depth 8 -type TrueColor" before the output 129filename.</p> 130 131<p>The passphrase can be any combinations of letters and symbols. It should 132be a minimum of 12 character combinations to help ensure your image remains 133private. Also make sure your passphrase file permissions prevent others from 134reading it otherwise unintended users may be able to view the original image 135content.</p> 136 137<p>You can only restore the original image content if you know your 138passphrase. If you lose or forget it, your original image content is lost 139forever.</p> 140 141<p>ImageMagick only scrambles the image pixels. The image metadata remains 142untouched and readable by anyone with access to the image file.</p> 143 144<p>ImageMagick uses the <a 145href="http://en.wikipedia.org/wiki/Advanced_Encryption_Standard">AES</a> 146cipher in Counter mode. We use 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> 147 148<p>Currently only ImageMagick can restore your enciphered image content. We 149use a standard cipher and mode so other vendors could support enciphered image content.</p> 150 151<p>Some small practical examples of image enciphering can be found in IM 152Examples <a href="https://legacy.imagemagick.org/Usage/transform/#encipher" 153>Encrypting Image Data</a>. </p> 154 155</div> 156 </div> 157 </main><!-- /.container --> 158 <footer class="magick-footer"> 159 <div class="container-fluid"> 160 <a href="../www/security-policy.html">Security</a> • 161 <a href="../www/news.html">News</a> 162 163 <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> 164 165 <a href="../www/links.html">Related</a> • 166 <a href="../www/sitemap.html">Sitemap</a> 167 <br/> 168 <a href="../www/support.html">Sponsor</a> • 169 <a href="../www/cite.html">Cite</a> • 170 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 171 <a href="../www/https://imagemagick.org/script/contact.php">Contact Us</a> 172 <br/> 173 <a href="https://github.com/imagemagick/imagemagick" target="_blank" rel="noopener" aria-label="GitHub"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 499.36" width="2%" height="2%" role="img" focusable="false"><title>GitHub</title><path fill="currentColor" fill-rule="evenodd" d="M256 0C114.64 0 0 114.61 0 256c0 113.09 73.34 209 175.08 242.9 12.8 2.35 17.47-5.56 17.47-12.34 0-6.08-.22-22.18-.35-43.54-71.2 15.49-86.2-34.34-86.2-34.34-11.64-29.57-28.42-37.45-28.42-37.45-23.27-15.84 1.73-15.55 1.73-15.55 25.69 1.81 39.21 26.38 39.21 26.38 22.84 39.12 59.92 27.82 74.5 21.27 2.33-16.54 8.94-27.82 16.25-34.22-56.84-6.43-116.6-28.43-116.6-126.49 0-27.95 10-50.8 26.35-68.69-2.63-6.48-11.42-32.5 2.51-67.75 0 0 21.49-6.88 70.4 26.24a242.65 242.65 0 0 1 128.18 0c48.87-33.13 70.33-26.24 70.33-26.24 14 35.25 5.18 61.27 2.55 67.75 16.41 17.9 26.31 40.75 26.31 68.69 0 98.35-59.85 120-116.88 126.32 9.19 7.9 17.38 23.53 17.38 47.41 0 34.22-.31 61.83-.31 70.23 0 6.85 4.61 14.81 17.6 12.31C438.72 464.97 512 369.08 512 256.02 512 114.62 397.37 0 256 0z"/></svg></a> • 174 <a href="https://twitter.com/imagemagick" target="_blank" rel="noopener" aria-label="Twitter"><svg xmlns="http://www.w3.org/2000/svg" class="navbar-nav-svg" viewBox="0 0 512 416.32" width="2%" height="2%" role="img" focusable="false"><title>Twitter</title><path fill="currentColor" d="M160.83 416.32c193.2 0 298.92-160.22 298.92-298.92 0-4.51 0-9-.2-13.52A214 214 0 0 0 512 49.38a212.93 212.93 0 0 1-60.44 16.6 105.7 105.7 0 0 0 46.3-58.19 209 209 0 0 1-66.79 25.37 105.09 105.09 0 0 0-181.73 71.91 116.12 116.12 0 0 0 2.66 24c-87.28-4.3-164.73-46.3-216.56-109.82A105.48 105.48 0 0 0 68 159.6a106.27 106.27 0 0 1-47.53-13.11v1.43a105.28 105.28 0 0 0 84.21 103.06 105.67 105.67 0 0 1-47.33 1.84 105.06 105.06 0 0 0 98.14 72.94A210.72 210.72 0 0 1 25 370.84a202.17 202.17 0 0 1-25-1.43 298.85 298.85 0 0 0 160.83 46.92"/></svg></a> 175 <br/> 176 <small>© 1999-2021 ImageMagick Studio LLC</small> 177 </div> 178 </footer> 179 180 <!-- Javascript assets --> 181 <script src="assets/magick.js" ></script> 182 </body> 183</html> 184<!-- Magick Cache 13th February 2021 11:37 -->
