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[apache] / docs / manual / mod / mod_crypto.xml

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<modulesynopsis metafile="mod_crypto.xml.meta">

<name>mod_crypto</name>
<description>Support for symmetrical encryption and decryption</description>
<status>Extension</status>
<sourcefile>mod_crypto.c</sourcefile>
<identifier>crypto_module</identifier>
<compatibility>Available in Apache 2.5 and later</compatibility>

<summary>
    <p>This module provides the ability to <strong>encrypt and decrypt</strong>
    data on the input and output filter stacks.</p>

    <p>Most specifically, it can be used to implement <strong>on-the-fly HLS
    encryption</strong> as described by
    <a href="http://www.ietf.org/id/draft-pantos-http-live-streaming-19.txt">
    draft-pantos-http-live-streaming-19</a>.</p>

    <p>Alternatively, it can be used to deliver secure data over insecure CDN
    to suitable clients.</p>

    <p>The crypto filter may be added to either the input or the
    output filter stacks, as appropriate, using the
    <directive module="core">SetInputFilter</directive>,
    <directive module="core">SetOutputFilter</directive>,
    <directive module="mod_mime">AddOutputFilter</directive> or
    <directive module="mod_filter">AddOutputFilterByType</directive> directives.</p>

</summary>
<seealso><a href="../filter.html">Filters</a></seealso>

<section id="format">
    <title>Stream Format</title>

    <p>The encrypted stream consists of an optional IV block, followed by encrypted
    blocks using the chosen cipher. The final block is padded before being written. The
    size of the blocks is governed by the choice of cipher in use.</p>

    <p>When the IV is specified with the <directive module="mod_crypto">CryptoIV</directive>
    directive, that IV is used, and is not written to or read from the stream.</p>

</section>

<section id="config">
    <title>Keys and IVs</title>

    <p>
        The
        <directive module="mod_crypto">CryptoKey</directive>
        and
        <directive module="mod_crypto">CryptoIV</directive>
        directives expect binary
        values which can be specified in a number of ways as below. The most significant bits of the relevant values
        are used, and if the values are too short, they are padded on the left
        with zero bits.
    </p>

    <dl>
    <dt>file:</dt><dd>Read the value directly from the given file.</dd>
    <dt>hex:</dt><dd>Parse the expression as a hex value, which may contain colon separators.</dd>
    <dt>decimal:</dt><dd>Parse the expression as a decimal value.</dd>
    <dt>base64:</dt><dd>Parse the expression as a base64 value.</dd>
    <dt>none</dt><dd>No value is specified.</dd>
    </dl>

    <p>If the IV is unspecified a random IV will be generated during
        encryption and written
        as the first block. During decryption, the first block will be
        interpreted as the IV.
    </p>

    <p>With the exception of file:, the <directive module="mod_crypto">CryptoKey</directive>
       and <directive module="mod_crypto">CryptoIV</directive> directives allow
       <a href="../expr.html">expression syntax</a> to provide flexibility when setting the values.
       This allows both keys and IVs to be salted with values available to the webserver, such
       as REMOTE_USER, or the URL.
    </p>

</section>

<section id="handler">
    <title>Crypto Key Handler</title>

    <p>For convenience, the <strong>crypto-key</strong> handler can be used to serve the key
    to suitably authorized clients, removing the need to store the key within the directory
    space of the webserver. This also allows the same <a href="../expr.html">expression
    syntax</a> to be used to derive the key for both the clients and the encrypted content.</p>

    <example><title>Crypto Key Handler with a File</title>
      &lt;Location /key&gt;<br />
      <indent>
        SetHandler crypto-key<br />
        CryptoCipher aes128<br />
        CryptoKey file:/path/to/file.key<br />
        AuthType basic<br />
        ...<br />
        </indent>
      &lt;/Location&gt;<br />
    </example>

</section>

<section id="hls">
    <title>HTTP Live Streaming</title>

    <p>The HLS protocol supports encrypted streams using the AES-128 cipher and a
    corresponding key. Access is granted to the stream by sharing the key with
    the HLS client, typically over a secured connection.</p>

    <p>The IV used for encrypting each media segment is specified within
        HLS in one of two ways:</p>

    <ul>
        <li>
            Explicitly specified within an IV attribute inside the EXT-X-KEY
            tag as a <strong>hexadecimal</strong> value.
        </li>
        <li>
            Implicitly specified by interpreting the <strong>decimal</strong>
            value of the EXT-X-MEDIA-SEQUENCE tag.
        </li>
    </ul>

    <p>The media sequence value is usually embedded within the media
        segment filenames, and can be matched by using named regular
        expressions as per the example below.
    </p>

    <example><title>HLS Example - IV from media sequence</title>
      &lt;LocationMatch (?&lt;SEQUENCE&gt;[\d]+)[^\d^/]+$&gt;<br />
      <indent>
        SetOutputFilter ENCRYPT<br />
        CryptoCipher aes128<br />
        CryptoKey file:/path/to/file.key<br />
        CryptoIV decimal:%{env:MATCH_SEQUENCE}<br />
        </indent>
      &lt;/LocationMatch&gt;<br />
    </example>

</section>

<directivesynopsis>
<name>CryptoDriver</name>
<description>Name of the crypto driver to use</description>
<syntax>CryptoDriver name</syntax>
<default>CryptoDriver openssl</default>
<contextlist><context>server config</context>
</contextlist>

<usage>
    <p>The <directive module="mod_crypto">CryptoDriver</directive>
    directive specifies the name of the crypto driver to use. There is usually
    a recommended default driver on each platform. Possible values include
    <strong>openssl</strong>, <strong>commoncrypto</strong> and
    <strong>nss</strong>.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>CryptoCipher</name>
<description>Cipher to be used by the crypto filter</description>
<syntax>CryptoCipher name</syntax>
<default>CryptoCipher aes256</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context>
</contextlist>

<usage>
    <p>The <directive>CryptoCipher</directive> directive allows specification of
    the cipher to be used during encryption or decryption. If not specified, the
    cipher defaults to <code>aes256</code>.</p>

    <p>Possible values depend on the crypto driver in use, and could be one of:</p>

    <ul><li>3des192</li><li>aes128</li><li>aes192</li><li>aes256</li></ul>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>CryptoIV</name>
<description>IV (Initialisation Vector) to be used by the crypto filter</description>
<syntax>CryptoIV value</syntax>
<default>CryptoIV none</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context>
</contextlist>

<usage>
    <p>The <directive>CryptoIV</directive> directive allows the IV (initialisation
    vector) to be specified for the particular URL space. The IV can be read from
    a file, or can be set based on the <a href="../expr.html">expression parser</a>,
    allowing for flexible scenarios for the setting of keys.</p>

    <p>Values can be specified as read from a file, or as a hexadecimal, decimal or
    base64 value based on the following prefixes:</p>

    <ul><li>file:</li><li>hex:</li><li>decimal:</li><li>base64:</li></ul>

    <p>The value 'none' disables setting of the IV. In this case, during encryption
    a random IV will be generated and inserted as the first block, and during
    decryption the first block will interpreted as the IV.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>CryptoKey</name>
<description>Key to be used by the crypto filter</description>
<syntax>CryptoKey value</syntax>
<default>CryptoKey none</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context>
</contextlist>

<usage>
    <p>The <directive>CryptoKey</directive> directive allows the encryption / decryption
    key to be specified for the particular URL space. The key can be read from a file, or
    can be set based on the <a href="../expr.html">expression parser</a>, allowing for
    flexible scenarios for the setting of keys.</p>

    <p>Values can be specified as read from a file, or as a hexadecimal, decimal or
    base64 value based on the following prefixes:</p>

    <ul><li>file:</li><li>hex:</li><li>decimal:</li><li>base64:</li></ul>

    <p>The value 'none' disables the key. An attempt to serve a file through the ENCRYPT
    or DECRYPT filters without a key will cause the request to fail.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>CryptoSize</name>
<description>Maximum size in bytes to buffer by the crypto filter</description>
<syntax>CryptoSize integer</syntax>
<default>CryptoSize 131072</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context>
</contextlist>

<usage>
    <p>The <directive module="mod_crypto">CryptoSize</directive>
    directive specifies the amount of data in bytes that will be
    buffered before being encrypted or decrypted during each request.
    The default is 128 kilobytes.</p>
</usage>
</directivesynopsis>

</modulesynopsis>