chrome/common/extensions/docs/templates/articles/crx.html

   1 <h1>CRX Package Format</h1>
   2
   3
   4 <p>
   5 CRX files are ZIP files with a special header and the <code>.crx</code> file
   6 extension.
   7 </p>
   8
   9 <h2 id="package_header">Package header</h2>
  10
  11 <p>
  12 The header contains the author's public key and the extension's signature.
  13 The signature is generated from the ZIP file using SHA-1 with the
  14 author's private key. The header requires a little-endian byte ordering with
  15 4-byte alignment. The following table describes the fields of
  16 the <code>.crx</code> header in order:
  17 </p>
  18
  19 <table class="simple">
  20   <tr>
  21     <th>Field</th><th>Type</th><th>Length</th><th>Value</th><th>Description</th>
  22   </tr>
  23   <tr>
  24     <td><em>magic number</em></td><td>char[]</td><td>32 bits</td><td>Cr24</td>
  25     <td>
  26       Chrome requires this constant at the beginning of every <code>.crx</code>
  27       package.
  28     </td>
  29   </tr>
  30   <tr>
  31     <td><em>version</em></td><td>unsigned&nbsp;int</td><td>32 bits</td><td>2</td>
  32     <td>The version of the <code>*.crx</code> file format used (currently 2).</td>
  33   </tr>
  34   <tr>
  35     <td><em>public key length</em></td><td>unsigned&nbsp;int</td><td>32 bits</td>
  36     <td><i>pubkey.length</i></td>
  37     <td>
  38       The length of the RSA public key in <em>bytes</em>.
  39     </td>
  40   </tr>
  41   <tr>
  42     <td><em>signature length</em></td><td>unsigned&nbsp;int</td><td>32 bits</td>
  43     <td><i>sig.length</i></td>
  44     <td>
  45       The length of the signature in <em>bytes</em>.
  46     </td>
  47   </tr>
  48   <tr>
  49     <td><em>public key</em></td><td>byte[]</td><td><i>pubkey.length</i></i></td>
  50     <td><i>pubkey.contents</i></td>
  51     <td>
  52       The contents of the author's RSA public key, formatted as an X509
  53       SubjectPublicKeyInfo block.
  54     </td>
  55   </tr>
  56   <tr>
  57     <td><em>signature</em></td><td>byte[]</td><td><i>sig.length</i></td>
  58     <td><i>sig.contents</i></td>
  59     <td>
  60       The signature of the ZIP content using the author's private key. The
  61       signature is created using the RSA algorithm with the SHA-1 hash function.
  62     </td>
  63   </tr>
  64 </table>
  65
  66 <h2 id="extensions_contents">Extension contents</h2>
  67
  68 <p>
  69 The extension's ZIP file is appended to the <code>*.crx</code> package after the
  70 header. This should be the same ZIP file that the signature in the header
  71 was generated from.
  72 </p>
  73
  74 <h2 id="example">Example</h2>
  75
  76 <p>
  77 The following is an example hex dump from the beginning of a <code>.crx</code>
  78 file.
  79 </p>
  80
  81 <pre>
  82 43 72 32 34   # "Cr24" -- the magic number
  83 02 00 00 00   # 2 -- the crx format version number
  84 A2 00 00 00   # 162 -- length of public key in bytes
  85 80 00 00 00   # 128 -- length of signature in bytes
  86 ...........   # the contents of the public key
  87 ...........   # the contents of the signature
  88 ...........   # the contents of the zip file
  89
  90 </pre>
  91
  92 <h2 id="scripts">Packaging scripts</h2>
  93 <p>
  94 Members of the community have written the following scripts to package
  95 <code>.crx</code> files.
  96 </p>
  97
  98 <h3 id="ruby">Ruby</h3>
  99 <blockquote>
 100 <a href="http://github.com/Constellation/crxmake">github: crxmake</a>
 101 </blockquote>
 102
 103 <h3 id="bash">Bash</h3>
 104 <pre>
 105 #!/bin/bash -e
 106 #
 107 # Purpose: Pack a Chromium extension directory into crx format
 108
 109 if test $# -ne 2; then
 110   echo "Usage: crxmake.sh &lt;extension dir&gt; &lt;pem path&gt;"
 111   exit 1
 112 fi
 113
 114 dir=$1
 115 key=$2
 116 name=$(basename "$dir")
 117 crx="$name.crx"
 118 pub="$name.pub"
 119 sig="$name.sig"
 120 zip="$name.zip"
 121 trap 'rm -f "$pub" "$sig" "$zip"' EXIT
 122
 123 # zip up the crx dir
 124 cwd=$(pwd -P)
 125 (cd "$dir" && zip -qr -9 -X "$cwd/$zip" .)
 126
 127 # signature
 128 openssl sha1 -sha1 -binary -sign "$key" < "$zip" > "$sig"
 129
 130 # public key
 131 openssl rsa -pubout -outform DER < "$key" > "$pub" 2>/dev/null
 132
 133 byte_swap () {
 134   # Take "abcdefgh" and return it as "ghefcdab"
 135   echo "${1:6:2}${1:4:2}${1:2:2}${1:0:2}"
 136 }
 137
 138 crmagic_hex="4372 3234" # Cr24
 139 version_hex="0200 0000" # 2
 140 pub_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$pub" | awk '{print $5}')))
 141 sig_len_hex=$(byte_swap $(printf '%08x\n' $(ls -l "$sig" | awk '{print $5}')))
 142 (
 143   echo "$crmagic_hex $version_hex $pub_len_hex $sig_len_hex" | xxd -r -p
 144   cat "$pub" "$sig" "$zip"
 145 ) > "$crx"
 146 echo "Wrote $crx"
 147 </pre>