php-doc-en/security/hiding.xml

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  <chapter xml:id="security.hiding" xmlns="http://docbook.org/ns/docbook">
   <title>Hiding PHP</title>
   <para>
    In general, security by obscurity is one of the weakest forms of security.
    But in some cases, every little bit of extra security is desirable.
   </para>
   <para>
    A few simple techniques can help to hide PHP, possibly slowing
    down an attacker who is attempting to discover weaknesses in your
    system. By setting expose_php to <literal>off</literal> in your 
    &php.ini; file, you reduce the amount of information available to them.
   </para>
   <para>
    Another tactic is to configure web servers such as apache to
    parse different filetypes through PHP, either with an &htaccess;
    directive, or in the apache configuration file itself. You can
    then use misleading file extensions:
    <example>
     <title>Hiding PHP as another language</title>
     <programlisting role="apache-conf">
<![CDATA[
# Make PHP code look like other code types
AddType application/x-httpd-php .asp .py .pl
]]>
     </programlisting>
    </example>
    Or obscure it completely:
    <example>
     <title>Using unknown types for PHP extensions</title>
     <programlisting role="apache-conf">
<![CDATA[
# Make PHP code look like unknown types
AddType application/x-httpd-php .bop .foo .133t
]]>
     </programlisting>
    </example>
    Or hide it as HTML code, which has a slight performance hit because
    all HTML will be parsed through the PHP engine:
    <example>
     <title>Using HTML types for PHP extensions</title>
     <programlisting role="apache-conf">
<![CDATA[
# Make all PHP code look like HTML
AddType application/x-httpd-php .htm .html
]]>
     </programlisting>
    </example>
    For this to work effectively, you must rename your PHP files with
    the above extensions. While it is a form of security through
    obscurity, it's a minor preventative measure with few drawbacks.
   </para>
  </chapter>


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