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         <h1 class="page_title">CRX Package Format</h1>
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             <li>
               <a href="#H2-0">Package header</a>
               <ol>
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             </li><li>
               <a href="#H2-1">Extension contents</a>
               <ol>
               </ol>
             </li><li>
               <a href="#H2-2">Example</a>
               <ol>
               </ol>
             </li><li>
               <a href="#scripts">Packaging scripts</a>
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                 <li>
                   <a href="#ruby">Ruby</a>
                 </li><li>
                   <a href="#H3-5">Bash</a>
                 </li>
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         <div id="static"><div id="pageData-name" class="pageData">CRX Package Format</div>
 <div id="pageData-showTOC" class="pageData">true</div>
 <p>
 CRX files are ZIP files with a special header and the <code>.crx</code> file
 extension.
 </p>
 <a name="H2-0"></a><h2>Package header</h2>
 <p>
 The header contains the author's public key and the extension's signature.
 The signature is generated from the ZIP file using SHA-1 with the
 author's private key. The header requires a little-endian byte ordering with
 4-byte alignment. The following table describes the fields of
 the <code>.crx</code> header in order:
 </p>
 <table>
   <tbody><tr>
     <th>Field</th><th>Type</th><th>Length</th><th>Value</th><th>Description</th>
   </tr>
   <tr>
     <td><em>magic number</em></td><td>char[]</td><td>32 bits</td><td>Cr24</td>
     <td>
       Chrome requires this constant at the beginning of every <code>.crx</code>
       package.
     </td>
   </tr>
   <tr>
     <td><em>version</em></td><td>unsigned&nbsp;int</td><td>32 bits</td><td>2</td>
     <td>The version of the <code>*.crx</code> file format used (currently 2).</td>
   </tr>
   <tr>
     <td><em>public key length</em></td><td>unsigned&nbsp;int</td><td>32 bits</td>
     <td><i>pubkey.length</i></td>
     <td>
       The length of the RSA public key in <em>bytes</em>.
     </td>
   </tr>
   <tr>
     <td><em>signature length</em></td><td>unsigned&nbsp;int</td><td>32 bits</td>
     <td><i>sig.length</i></td>
     <td>
       The length of the signature in <em>bytes</em>.
     </td>
   </tr>
   <tr>
     <td><em>public key</em></td><td>byte[]</td><td><i>pubkey.length</i></td>
     <td><i>pubkey.contents</i></td>
     <td>
       The contents of the author's RSA public key, formatted as an X509
       SubjectPublicKeyInfo block.
     </td>
   </tr>
   <tr>
     <td><em>signature</em></td><td>byte[]</td><td><i>sig.length</i></td>
     <td><i>sig.contents</i></td>
     <td>
       The signature of the ZIP content using the author's private key. The
       signature is created using the RSA algorithm with the SHA-1 hash function.
     </td>
   </tr>
 </tbody></table>
 <a name="H2-1"></a><h2>Extension contents</h2>
 <p>
 The extension's ZIP file is appended to the <code>*.crx</code> package after the
 header. This should be the same ZIP file that the signature in the header
 was generated from.
 </p>
 <a name="H2-2"></a><h2>Example</h2>
 <p>
 The following is an example hex dump from the beginning of a <code>.crx</code>
 file.
 </p>
 <pre>43 72 32 34   # "Cr24" -- the magic number
 02 00 00 00   # 2 -- the crx format version number
 A2 00 00 00   # 162 -- length of public key in bytes
 80 00 00 00   # 128 -- length of signature in bytes
 ...........   # the contents of the public key
 ...........   # the contents of the signature
 ...........   # the contents of the zip file
 </pre>
 <h2 id="scripts">Packaging scripts</h2>
 <p>
 Members of the community have written the following scripts to package
 <code>.crx</code> files.
 </p>
 <h3 id="ruby">Ruby</h3>
 <blockquote>
 <a href="http://github.com/Constellation/crxmake">github: crxmake</a>
 </blockquote>
 <a name="H3-5"></a><h3>Bash</h3>
 <pre>#!/bin/bash -e
 #
 # Purpose: Pack a Chromium extension directory into crx format
 if test $# -ne 2; then
   echo "Usage: crxmake.sh &lt;extension dir&gt; &lt;pem path&gt;"
   exit 1
 fi
 dir=$1
 key=$2
 name=$(basename "$dir")
 crx="$name.crx"
 pub="$name.pub"
 sig="$name.sig"
 zip="$name.zip"
 trap 'rm -f "$pub" "$sig" "$zip"' EXIT
 # zip up the crx dir
 cwd=$(pwd -P)
 (cd "$dir" &amp;&amp; zip -qr -9 -X "$cwd/$zip" .)
 # signature
 openssl sha1 -sha1 -binary -sign "$key" &lt; "$zip" &gt; "$sig"
 # public key
 openssl rsa -pubout -outform DER &lt; "$key" &gt; "$pub" 2&gt;/dev/null
 byte_swap () {
   # Take "abcdefgh" and return it as "ghefcdab"
   echo "${1:6:2}${1:4:2}${1:2:2}${1:0:2}"
 }
 crmagic_hex="4372 3234" # Cr24
 version_hex="0200 0000" # 2
 pub_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$pub" | awk '{print $5}')))
 sig_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$sig" | awk '{print $5}')))
 (
   echo "$crmagic_hex $version_hex $pub_len_hex $sig_len_hex" | xxd -r -p
   cat "$pub" "$sig" "$zip"
 ) &gt; "$crx"
 echo "Wrote $crx"
 </pre>
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	<div class="g-unit" id="gc-pagecontent">
	<div id="pageTitle">
	<h1 class="page_title">CRX Package Format</h1>
	</div>
	<!-- TABLE OF CONTENTS -->
	<div id="toc">
	<h2>Contents</h2>
	<ol>
	<li>
	<a href="#H2-0">Package header</a>
	<ol>
	</ol>
	</li><li>
	<a href="#H2-1">Extension contents</a>
	<ol>
	</ol>
	</li><li>
	<a href="#H2-2">Example</a>
	<ol>
	</ol>
	</li><li>
	<a href="#scripts">Packaging scripts</a>
	<ol>
	<li>
	<a href="#ruby">Ruby</a>
	</li><li>
	<a href="#H3-5">Bash</a>
	</li>
	</ol>
	</li>
	</ol>
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	<!-- /TABLE OF CONTENTS -->
	<!-- Standard content lead-in for experimental API pages -->
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	<div id="static"><div id="pageData-name" class="pageData">CRX Package Format</div>
	<div id="pageData-showTOC" class="pageData">true</div>
	<p>
	CRX files are ZIP files with a special header and the <code>.crx</code> file
	extension.
	</p>
	<a name="H2-0"></a><h2>Package header</h2>
	<p>
	The header contains the author's public key and the extension's signature.
	The signature is generated from the ZIP file using SHA-1 with the
	author's private key. The header requires a little-endian byte ordering with
	4-byte alignment. The following table describes the fields of
	the <code>.crx</code> header in order:
	</p>
	<table>
	<tbody><tr>
	<th>Field</th><th>Type</th><th>Length</th><th>Value</th><th>Description</th>
	</tr>
	<tr>
	<td><em>magic number</em></td><td>char[]</td><td>32 bits</td><td>Cr24</td>
	<td>
	Chrome requires this constant at the beginning of every <code>.crx</code>
	package.
	</td>
	</tr>
	<tr>
	<td><em>version</em></td><td>unsigned int</td><td>32 bits</td><td>2</td>
	<td>The version of the <code>*.crx</code> file format used (currently 2).</td>
	</tr>
	<tr>
	<td><em>public key length</em></td><td>unsigned int</td><td>32 bits</td>
	<td><i>pubkey.length</i></td>
	<td>
	The length of the RSA public key in <em>bytes</em>.
	</td>
	</tr>
	<tr>
	<td><em>signature length</em></td><td>unsigned int</td><td>32 bits</td>
	<td><i>sig.length</i></td>
	<td>
	The length of the signature in <em>bytes</em>.
	</td>
	</tr>
	<tr>
	<td><em>public key</em></td><td>byte[]</td><td><i>pubkey.length</i></td>
	<td><i>pubkey.contents</i></td>
	<td>
	The contents of the author's RSA public key, formatted as an X509
	SubjectPublicKeyInfo block.
	</td>
	</tr>
	<tr>
	<td><em>signature</em></td><td>byte[]</td><td><i>sig.length</i></td>
	<td><i>sig.contents</i></td>
	<td>
	The signature of the ZIP content using the author's private key. The
	signature is created using the RSA algorithm with the SHA-1 hash function.
	</td>
	</tr>
	</tbody></table>
	<a name="H2-1"></a><h2>Extension contents</h2>
	<p>
	The extension's ZIP file is appended to the <code>*.crx</code> package after the
	header. This should be the same ZIP file that the signature in the header
	was generated from.
	</p>
	<a name="H2-2"></a><h2>Example</h2>
	<p>
	The following is an example hex dump from the beginning of a <code>.crx</code>
	file.
	</p>
	<pre>43 72 32 34 # "Cr24" -- the magic number
	02 00 00 00 # 2 -- the crx format version number
	A2 00 00 00 # 162 -- length of public key in bytes
	80 00 00 00 # 128 -- length of signature in bytes
	........... # the contents of the public key
	........... # the contents of the signature
	........... # the contents of the zip file
	</pre>
	<h2 id="scripts">Packaging scripts</h2>
	<p>
	Members of the community have written the following scripts to package
	<code>.crx</code> files.
	</p>
	<h3 id="ruby">Ruby</h3>
	<blockquote>
	<a href="http://github.com/Constellation/crxmake">github: crxmake</a>
	</blockquote>
	<a name="H3-5"></a><h3>Bash</h3>
	<pre>#!/bin/bash -e
	#
	# Purpose: Pack a Chromium extension directory into crx format
	if test $# -ne 2; then
	echo "Usage: crxmake.sh <extension dir> <pem path>"
	exit 1
	fi
	dir=$1
	key=$2
	name=$(basename "$dir")
	crx="$name.crx"
	pub="$name.pub"
	sig="$name.sig"
	zip="$name.zip"
	trap 'rm -f "$pub" "$sig" "$zip"' EXIT
	# zip up the crx dir
	cwd=$(pwd -P)
	(cd "$dir" && zip -qr -9 -X "$cwd/$zip" .)
	# signature
	openssl sha1 -sha1 -binary -sign "$key" < "$zip" > "$sig"
	# public key
	openssl rsa -pubout -outform DER < "$key" > "$pub" 2>/dev/null
	byte_swap () {
	# Take "abcdefgh" and return it as "ghefcdab"
	echo "${1:6:2}${1:4:2}${1:2:2}${1:0:2}"
	}
	crmagic_hex="4372 3234" # Cr24
	version_hex="0200 0000" # 2
	pub_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$pub" \| awk '{print $5}')))
	sig_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$sig" \| awk '{print $5}')))
	(
	echo "$crmagic_hex $version_hex $pub_len_hex $sig_len_hex" \| xxd -r -p
	cat "$pub" "$sig" "$zip"
	) > "$crx"
	echo "Wrote $crx"
	</pre>
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