Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / ImageMagick / 7a40ba8d8dae1086103297305d7cd8825ea59fa9 / . / www / cipher.html
blob: 86a01b52ff9c3f86fe633c3cc2efaa29ed4b7db8 [file] [log] [blame]
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
3 "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
4<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" dir="ltr">
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]5<head>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]6 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
7 <meta name="verify-v1" content="g222frIIxcQTrvDR3NBRUSKP3AnMNoqxOkIniCEkV7U="/>
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]8 <title>ImageMagick: Encipher or Decipher an Image</title>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]9 <meta http-equiv="Content-Language" content="en-US"/>
10 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
11 <meta http-equiv="Reply-to" content="magick-users@imagemagick.org"/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]12 <meta name="Application-name" content="ImageMagick"/>
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]13 <meta name="Description" content="ImageMagick is a software suite to create, edit, compose, or convert bitmap images in a variety of formats. Use ImageMagick to scale, rotate, shear, distort and transform images."/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]14 <meta name="Application-url" content="http://www.imagemagick.org"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]15 <meta name="Generator" content="PHP"/>
16 <meta name="Keywords" content="encipher, or, decipher, an, image, ImageMagick, ImageMagic, MagickCore, MagickWand, PerlMagick, Magick++, RMagick, PythonMagick, JMagick, TclMagick, Image, Magick, Magic, Wand, ImageMagickObject, Swiss, Army, Knife, Image, Processing"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]17 <meta name="Rating" content="GENERAL"/>
18 <meta name="Robots" content="INDEX, FOLLOW"/>
19 <meta name="Generator" content="ImageMagick Studio LLC"/>
20 <meta name="Author" content="ImageMagick Studio LLC"/>
21 <meta name="Revisit-after" content="2 DAYS"/>
22 <meta name="Resource-type" content="document"/>
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]23 <meta name="Copyright" content="Copyright (c) 1999-2011 ImageMagick Studio LLC"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]24 <meta name="Distribution" content="Global"/>
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]25 <link rel="icon" href="../images/wand.png"/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]26 <link rel="shortcut icon" href="../images/wand.ico" type="images/x-icon"/>
27 <link rel="meta" type="application/rdf+xml" title="ICI" href="http://imagemagick.org/ici.rdf"/>
cristy7a40ba82011-01-08 20:31:18 +0000[diff] [blame^]28 <link rel="stylesheet" href="http://www.google.com/cse/style/look/default.css" type="text/css" />
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]29 <style type="text/css" media="all">
30 @import url("../www/magick.css");
31 </style>
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]32 <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js"></script>
cristy361f4662010-12-31 23:02:52 +0000[diff] [blame]33 <script type="text/javascript" src="../fancybox/jquery.fancybox-1.3.4.pack.js"></script>
34 <link rel="stylesheet" type="text/css" href="../fancybox/jquery.fancybox-1.3.4.css" media="screen" />
35 <script type="text/javascript">
36 $(document).ready(function() {
37 $("a[href$=.jpg],a[href$=.png],a[href$=.gif]").fancybox({
38 'transitionIn' : 'elastic',
39 'transitionOut' : 'elastic',
40 'overlayShow' : false,
41 'opacity' : true
42 });
43 });
44 </script>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]45</head>
46
47<body id="www-imagemagick-org">
48<div class="titlebar">
49<a href="../index.html">
50 <img src="../images/script.png" alt="[ImageMagick]"
51 style="width: 350px; height: 60px; margin: 28px auto; float: left;" /></a>
52<a href="http://www.networkredux.com">
53 <img src="../images/networkredux.png" alt="[sponsor]"
54 style="margin: 45px auto; border: 0px; float: left;" /></a>
55<a href="http://www.imagemagick.org/discourse-server/">
56 <img src="../images/logo.jpg" alt=""
57 style="width: 114px; height: 118px; border: 0px; float: right;" /></a>
58<a href="../index.html">
59 <img src="../images/sprite.jpg" alt=""
60 style="width: 114px; height: 118px; border: 0px; float: right;" /></a>
61</div>
62
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]63<div class="westbar">
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]64
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]65<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]66 <a title="About ImageMagick" href="../index.html">About ImageMagick</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]67</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]68<div class="sep"></div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]69<div class="menu">
cristybb503372010-05-27 20:51:26 +0000[diff] [blame]70 <a title="Binary Releases" href="../www/binary-releases.html">Binary Releases</a>
71</div>
72<div class="sub">
73 <a title="Binary Release: Unix" href="../www/binary-releases.html#unix">Unix</a>
74</div>
75<div class="sub">
76 <a title="Binary Release: MacOS X" href="../www/binary-releases.html#macosx">Mac OS X</a>
77</div>
78<div class="sub">
79 <a title="Binary Release: Windows" href="../www/binary-releases.html#windows">Windows</a>
80</div>
81<div class="sep"></div>
82<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]83 <a title="Command-line Tools" href="../www/command-line-tools.html">Command-line Tools</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]84</div>
85<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]86 <a title="Command-line Tools: Processing" href="../www/command-line-processing.html">Processing</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]87</div>
88<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]89 <a title="Command-line Tools: Options" href="../www/command-line-options.html">Options</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]90</div>
91<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]92 <a title="Command-line Tools: Usage" href="http://www.imagemagick.org/Usage/">Usage</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]93</div>
94<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]95 <a title="Program Interfaces" href="../www/api.html">Program Interfaces</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]96</div>
97<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]98 <a title="Program Interface: MagickWand" href="../www/magick-wand.html">MagickWand</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]99</div>
100<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]101 <a title="Program Interface: MagickCore" href="../www/magick-core.html">MagickCore</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]102</div>
103<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]104 <a title="Program Interface: PerlMagick" href="../www/perl-magick.html">PerlMagick</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]105</div>
106<div class="sub">
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]107 <a title="Program Interface: Magick++" href="../www/magick++.html">Magick++</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]108</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]109<div class="sep"></div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]110<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]111 <a title="Install from Source" href="../www/install-source.html">Install from Source</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]112</div>
113<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]114 <a title="Install from Source: Unix" href="../www/install-source.html#unix">Unix</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]115</div>
116<div class="sub">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]117 <a title="Install from Source: Windows" href="../www/install-source.html#windows">Windows</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]118 </div>
119<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]120 <a title="Resources" href="../www/resources.html">Resources</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]121</div>
cristybb503372010-05-27 20:51:26 +0000[diff] [blame]122<div class="menu">
123 <a title="Architecture" href="../www/architecture.html">Architecture</a>
124</div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]125<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]126 <a title="Download" href="../www/download.html">Download</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]127</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]128<div class="sep"></div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]129<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]130 <a title="Search" href="http://www.imagemagick.org/script/search.php">Search</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]131</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]132<div class="sep"></div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]133<div class="menu">
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]134 <a title="Site Map" href="../www/sitemap.html">Site Map</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]135</div>
136<div class="sub">
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]137 <a title="Site Map: Links" href="../www/links.html">Links</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]138</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]139<div class="sep"></div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]140<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]141 <a title="Sponsors" href="../www/sponsors.html">Sponsors:</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]142
143<div class="sponsbox">
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]144<div class="sponsor">
145 <a title="Sponsor: Web Hosting" href="http://www.bodhost.com/hosting.html">Web Hosting</a><!-- 201104010090 -->
cristy7d52cd62010-10-01 17:26:59 +0000[diff] [blame]146</div>
147<div class="sponsor">
148 <a title="Sponsor: Druckerei" href="http://print24.com/de/">Druckerei</a><!-- 201110010720 -->
cristy73fd1cd2010-09-12 19:14:25 +0000[diff] [blame]149</div>
150<div class="sponsor">
cristyc5baf4f2010-08-31 15:05:33 +0000[diff] [blame]151 <a title="Sponsor: Image Converter" href="http://www.batchphoto.com">Image Converter</a><!-- 201103010900 Bits Coffee-->
152</div>
153<div class="sponsor">
cristy851dbce2010-08-06 21:40:00 +0000[diff] [blame]154 <a title="Sponsor: Flyer drucken" href="http://www.online-druck.biz">Flyer drucken</a><!-- 201109010900 Floeter-->
155</div>
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]156<div class="sponsor">
cristy7a40ba82011-01-08 20:31:18 +0000[diff] [blame^]157 <a title="Sponsor: Free Catalogs" href="http://www.who-sells-it.com/">Free Catalogs</a><!-- 20120801000600 -->
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]158</div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]159</div>
160</div>
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]161</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]162
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]163<div class="eastbar">
164 <script type="text/javascript">
165 <!--
166 google_ad_client = "pub-3129977114552745";
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]167 google_ad_slot = "0574824969";
168 google_ad_width = 160;
169 google_ad_height = 600;
170 //-->
171 </script>
172 <script type="text/javascript"
173 src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
174 </script>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]175</div>
176
177<div class="main">
178
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]179<h1>Enciphering and Deciphering Images</h2>
180<p class="navigation-index">[<a href="#encipher">Encipher an Image</a> &bull; <a href="#decipher">Decipher an Image</a> &bull; <a href="#caveats">Encipher and Decipher Caveats</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]181
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]182<div class="doc-section">
183
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]184<p>Most images, by design, are made to be viewed often and by many people. Web images, for example, may be viewed hundreds of times a day by a multitude of web 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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]185
186<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>
187
188</div>
189
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]190<h2><a id="encipher"></a>Encipher an Image</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]191<div class="doc-section">
192
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]193<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]194
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]195<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert rose.jpg -encipher passphrase.txt rose.png</span></p>
196<p>Here we encipher an image using another image as the passphrase:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]197
198<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert rose.jpg -encipher smiley.gif rose.png</span></p>
199</div>
200
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]201<h2><a id="decipher"></a>Decipher an Image</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]202<div class="doc-section">
203
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]204<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>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]205
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]206<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert rose.png -decipher passphrase.txt rose.jpg</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]207</div>
208
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]209<h2><a id="caveats"></a>Encipher and Decipher Caveats</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]210<div class="doc-section">
211
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]212<p>Some formats do not support enciphered pixels-- the JPEG or GIF format, for
213example. To ensure your image format is supported, encipher a test image and
214verify you can restore its original content <em>before</em> you encipher any
215additional images in that format.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]216
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]217<p>The image format also should be 8-bit and RGB (TrueColor). As such you may
218like to include the options "-depth 8 -type TrueColor" before the output
219filename. </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]220
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]221<p>The passphrase can be any combinations of letters and symbols. It should
222be a minimum of 12 character combinations to help ensure your image remains
223private. Also make sure your passphrase file permissions prevent others from
224reading it otherwise unintended users may be able to view the original image
225content.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]226
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]227<p>You can only restore the original image content if you know your
228passphrase. If you lose or forget it, your original image content is lost
229forever.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]230
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]231<p>ImageMagick only scrambles the image pixels. The image metadata remains
232untouched and readable by anyone with access to the image file.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]233
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]234<p>ImageMagick uses the <a
235href="http://en.wikipedia.org/wiki/Advanced_Encryption_Standard">AES</a>
236cipher in cipher feedback mode. We use the passphrase to derive the cipher
237key and the required nonce.</p>
238
239<p>Currently only ImageMagick can restore your enciphered image content. We
240use a standard cipher and mode so other vendors are encouraged to support
241enciphered image content.</p>
242
243<p>Some small practical examples of image enciphering can be found in IM
244Examples <A HREF="http://www.imagemagick.org/Usage/transform/#encipher"
245>Encrypting Image Data</A>. </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]246
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]247</div>
248
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]249</div>
250
251<div id="linkbar">
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]252 <span id="linkbar-west">&nbsp;</span>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]253 <span id="linkbar-center">
254 <a href="http://www.imagemagick.org/discourse-server/">Discourse Server</a> &bull;
cristya8902942010-07-30 00:49:52 +0000[diff] [blame]255 <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">Studio</a>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]256 </span>
257 <span id="linkbar-east">&nbsp;</span>
258 </div>
259 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]260 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]261 <span id="footer-east"> <a href="http://www.imagemagick.org/script/contact.php">Contact the Wizards</a></span>
262 </div>
263 <div style="clear: both; margin: 0; width: 100%; "></div>
cristya8902942010-07-30 00:49:52 +0000[diff] [blame]264 <script type="text/javascript">
265 var _gaq = _gaq || [];
266 _gaq.push(['_setAccount', 'UA-17690367-1']);
267 _gaq.push(['_trackPageview']);
268
269 (function() {
270 var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
271 ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
272 var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
273 })();
274 </script>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]275</body>
276</html>