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gerrit-public.fairphone.software / platform / external / ImageMagick / eed6cb663d33342848fce694ad45fe2db637547f / . / www / cipher.html
blob: 98853fab576b87a0f8666fffb1566200d9e1b400 [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">
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]4<html version="-//W3C//DTD XHTML 1.1//EN"
5 xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
6 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
7 xsi:schemaLocation="http://www.w3.org/1999/xhtml
8 http://www.w3.org/MarkUp/SCHEMA/xhtml11.xsd">
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]9<head>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]10 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
cristy1efc1ab2011-08-01 14:47:02 +0000[diff] [blame]11 <meta name="google-site-verification" content="MxsMq6bdLOx0KSuz1MY6yG9ZTIJ7_7DVRfl5NCAT5Yg"/>
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]12 <title>ImageMagick: Encipher or Decipher an Image</title>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]13 <meta http-equiv="Content-Language" content="en-US"/>
14 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
15 <meta http-equiv="Reply-to" content="magick-users@imagemagick.org"/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]16 <meta name="Application-name" content="ImageMagick"/>
cristye6e84152011-06-06 14:16:49 +0000[diff] [blame]17 <meta name="Description" content="Use ImageMagick to convert, edit, or compose bitmap images in a variety of formats. In addition resize, rotate, shear, distort and transform images automagically."/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]18 <meta name="Application-url" content="http://www.imagemagick.org"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]19 <meta name="Generator" content="PHP"/>
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]20 <meta name="Keywords" content="encipher, or, decipher, an, image, ImageMagick, PerlMagick, image processing, OpenMP, software development library, image, photo, software, Magick++, MagickWand"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]21 <meta name="Rating" content="GENERAL"/>
22 <meta name="Robots" content="INDEX, FOLLOW"/>
23 <meta name="Generator" content="ImageMagick Studio LLC"/>
24 <meta name="Author" content="ImageMagick Studio LLC"/>
25 <meta name="Revisit-after" content="2 DAYS"/>
26 <meta name="Resource-type" content="document"/>
cristy1454be72011-12-19 01:52:48 +0000[diff] [blame]27 <meta name="Copyright" content="Copyright (c) 1999-2012 ImageMagick Studio LLC"/>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]28 <meta name="Distribution" content="Global"/>
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]29 <link rel="icon" href="../images/wand.png"/>
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]30 <link rel="shortcut icon" href="../images/wand.ico" type="images/x-icon"/>
cristy29c5c992011-06-25 13:58:49 +0000[diff] [blame]31 <link rel="canonical" href="http://www.imagemagick.org" />
cristy3c98a4f2010-08-13 20:09:41 +0000[diff] [blame]32 <link rel="meta" type="application/rdf+xml" title="ICI" href="http://imagemagick.org/ici.rdf"/>
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]33 <!-- Add jQuery library -->
34 <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7/jquery.min.js"></script>
35
36 <!-- Optionaly include easing and/or mousewheel plugins -->
37 <script type="text/javascript" src="http://www.imagemagick.org/fancybox/jquery.easing-1.3.pack.js"></script>
38 <script type="text/javascript" src="http://www.imagemagick.org/fancybox/jquery.mousewheel-3.0.6.pack.js"></script>
39
40 <!-- Add fancyBox -->
41 <link rel="stylesheet" href="http://www.imagemagick.org/fancybox/jquery.fancybox.css?v=2.0.3" type="text/css" media="screen" />
42 <script type="text/javascript" src="http://www.imagemagick.org/fancybox/jquery.fancybox.pack.js?v=2.0.3"></script>
43
44 <!-- Optionaly include button and/or thumbnail helpers -->
45 <link rel="stylesheet" href="http://www.imagemagick.org/fancybox/helpers/jquery.fancybox-buttons.css?v=2.0.3" type="text/css" media="screen" />
46 <script type="text/javascript" src="http://www.imagemagick.org/fancybox/helpers/jquery.fancybox-buttons.js?v=2.0.3"></script>
47
48 <link rel="stylesheet" href="http://www.imagemagick.org/fancybox/helpers/jquery.fancybox-thumbs.css?v=2.0.3" type="text/css" media="screen" />
49 <script type="text/javascript" src="http://www.imagemagick.org/fancybox/helpers/jquery.fancybox-thumbs.js?v=2.0.3"></script>
50 <script type="text/javascript">
51 $(document).ready(function() {
52 $(".fancybox").fancybox();
53 });
54 </script>
55 <!-- ImageMagick style -->
cristy7a40ba82011-01-08 20:31:18 +0000[diff] [blame]56 <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]57 <style type="text/css" media="all">
58 @import url("../www/magick.css");
59 </style>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]60</head>
61
62<body id="www-imagemagick-org">
63<div class="titlebar">
cristyb52981c2011-03-19 17:09:31 +0000[diff] [blame]64<div style="margin: 17px auto; float: left;">
65 <script type="text/javascript">
66 <!--
67 google_ad_client = "pub-3129977114552745";
68 google_ad_slot = "5439289906";
69 google_ad_width = 728;
70 google_ad_height = 90;
71 //-->
72 </script>
73 <script type="text/javascript"
74 src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
75 </script>
76</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]77<a href="http://www.imagemagick.org/discourse-server/">
cristyaf8d6652011-02-04 21:57:45 +0000[diff] [blame]78 <img src="../images/logo.jpg"
79 alt="ImageMagick Logo"
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]80 style="width: 123px; height: 118px; border: 0px; float: right;" /></a>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]81<a href="../index.html">
cristyaf8d6652011-02-04 21:57:45 +0000[diff] [blame]82 <img src="../images/sprite.jpg"
83 alt="ImageMagick Sprite"
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]84 style="width: 114px; height: 118px; border: 0px; float: right;" /></a>
85</div>
86
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]87<div class="westbar">
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]88
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]89<div class="menu">
cristy83a272e2010-05-07 20:40:35 +0000[diff] [blame]90 <a title="About ImageMagick" href="../index.html">About ImageMagick</a>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]91</div>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]92<div class="menu">
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94</div>
95<div class="sub">
96 <a title="Binary Release: Unix" href="../www/binary-releases.html#unix">Unix</a>
97</div>
98<div class="sub">
99 <a title="Binary Release: MacOS X" href="../www/binary-releases.html#macosx">Mac OS X</a>
100</div>
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106</div>
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108<div class="menu">
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114<div class="sub">
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117<div class="sub">
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120<div class="menu">
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145<div class="menu">
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224</div>
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cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]226
cristyce69bb02010-07-27 19:49:46 +0000[diff] [blame]227<div class="eastbar">
cristy29c5c992011-06-25 13:58:49 +0000[diff] [blame]228 <div class="g-plusone" data-size="standard" data-count="false"></div>
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]229 <script type="text/javascript">
230 window.___gcfg = {
231 lang: 'en-US'
232 };
233
234 (function() {
235 var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
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cristy29c5c992011-06-25 13:58:49 +0000[diff] [blame]240</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]241
242<div class="main">
243
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]244<h1>Enciphering and Deciphering Images</h1>
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]245<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]246
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]247<div class="doc-section">
248
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]249<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]250
251<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>
252
253</div>
254
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]255<h2><a id="encipher"></a>Encipher an Image</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]256<div class="doc-section">
257
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]258<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]259
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]260<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert rose.jpg -encipher passphrase.txt rose.png</span></p>
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]261<p>Here we encipher an image using another image as the passphrase:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]262
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]263<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert rose.jpg -encipher smiley.gif rose.png</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]264</div>
265
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]266<h2><a id="decipher"></a>Decipher an Image</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]267<div class="doc-section">
268
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]269<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]270
cristyeed6cb62012-01-28 19:38:34 +0000[diff] [blame^]271<p class='crt'><span class="crtprompt"> $ </span><span class='crtin'>convert rose.png -decipher passphrase.txt rose.jpg</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]272</div>
273
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]274<h2><a id="caveats"></a>Encipher and Decipher Caveats</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]275<div class="doc-section">
276
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]277<p>Some formats do not support enciphered pixels-- the JPEG or GIF format, for
278example. To ensure your image format is supported, encipher a test image and
279verify you can restore its original content <em>before</em> you encipher any
280additional images in that format.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]281
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]282<p>The image format also should be 8-bit and RGB (TrueColor). As such you may
283like to include the options "-depth 8 -type TrueColor" before the output
284filename. </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]285
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]286<p>The passphrase can be any combinations of letters and symbols. It should
287be a minimum of 12 character combinations to help ensure your image remains
288private. Also make sure your passphrase file permissions prevent others from
289reading it otherwise unintended users may be able to view the original image
290content.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]291
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]292<p>You can only restore the original image content if you know your
293passphrase. If you lose or forget it, your original image content is lost
294forever.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]295
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]296<p>ImageMagick only scrambles the image pixels. The image metadata remains
297untouched and readable by anyone with access to the image file.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]298
cristyd0bda5e2010-09-21 16:22:45 +0000[diff] [blame]299<p>ImageMagick uses the <a
300href="http://en.wikipedia.org/wiki/Advanced_Encryption_Standard">AES</a>
301cipher in cipher feedback mode. We use the passphrase to derive the cipher
302key and the required nonce.</p>
303
304<p>Currently only ImageMagick can restore your enciphered image content. We
305use a standard cipher and mode so other vendors are encouraged to support
306enciphered image content.</p>
307
308<p>Some small practical examples of image enciphering can be found in IM
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]309Examples <a href="http://www.imagemagick.org/Usage/transform/#encipher"
310>Encrypting Image Data</a>. </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]311
cristybebec402010-04-23 19:19:08 +0000[diff] [blame]312</div>
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