[apache] / docs / manual / ssl / ssl_reference.wml

#use "ssl_template.inc" title="Reference" tag=ref num=3 

<page_prev name="Introduction"  url="ssl_intro.html">
<page_next name="Compatibility" url="ssl_compat.html">

#use wml::std::toc style=nbsp
#use wml::std::grid

<quotation width=150 author="Unknown">
``Try to understand everything,
but believe nothing!''
</quotation>

<p>
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<big T>his chapter provides a reference to all configuration directives and
additional user visible features mod_ssl provides. It's intended as the
official resource when you want to know how a particilar mod_ssl functionality
is actually configured or activated.  Each directive is documented similar to
the way standard Apache directives are documented in the official Apache
documentation set, i.e. for each directive especially the syntax, default and
context where applicable is given. 

<p>
Notice that there are three major classes of directives which are used by
mod_ssl: First <em>Global Directives</em> (i.e. directives with context
``server config''), which can occur inside the server config files but only
outside of any sectioning commands like &lt;VirtualHost&gt;.  Second
<em>Per-Server Directives</em> (i.e. those with context ``server config,
virtual host''), which can occur inside the server config files both outside
(for the main/default server) and inside &lt;VirtualHost&gt; sections.  

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<font face="Arial,Helvetica" color="#ccccff">
<b>Table Of Contents</b>
</font>
</td>
</tr>
<tr>
<td>
<font face="Arial,Helvetica" size="-1">
<toc>
</font>
</td>
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</div>

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<p>
And third <em>Per-Directory Directives</em> (i.e. those with context ``server
config, virtual host, directory, .htaccess''), which can pretty much occur
everywhere.  Especially both inside the server config files and the
per-directory <code>.htaccess</code> files.  The three classes are subsets of
each other, i.e. directives from the per-directory class can also be used in
the per-server and global context, and directives from the per-server class
can also be used the in the global context.

<p>
Additional directives and environment variables provided by mod_ssl (via
on-the-fly mapping) for backward compatiblity to other Apache SSL solutions
are documented in the <a href="ssl_compat.html">Compatibility</a> chapter.


<h1>Configuration Directives</h1>

The most visible and error-prone things of mod_ssl are its configuration
directives. So we document them in great detail here to assist you in setting
up the best possible configuration of your SSL-aware webserver.


<!-- SSLPassPhraseDialog -------------------------------------------->

<p>
<br>
<a name="SSLPassPhraseDialog"></a>
<h2>SSLPassPhraseDialog</h2>

<p>
<directive
    name="SSLPassPhraseDialog"
    description="Type of pass phrase dialog for encrypted private keys"
    syntax="<code>SSLPassPhraseDialog</code> <em>type</em>"
    default="<code>SSLPassPhraseDialog builtin</code>"
    context="server config"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
When Apache starts up it has to read the various Certificate (see <a
href="#SSLCertificateFile">SSLCertificateFile</a>) and Private Key (see <a
href="#SSLCertificateKeyFile">SSLCertificateKeyFile</a>) files of the
SSL-enabled virtual servers. Because for security reasons the Private Key
files are usually encrypted, mod_ssl needs to query the administrator for a
Pass Phrase in order to decrypt those files. This query can be done in two ways
which can be configured by <em>type</em>:

<ul>
<li><code>builtin</code>
    <p>
    This is the default where an interactive terminal dialog occurs at startup
    time just before Apache detaches from the terminal. Here the administrator
    has to manually enter the Pass Phrase for each encrypted Private Key file.
    Because a lot of SSL-enabled virtual hosts can be configured, the
    following reuse-scheme is used to minimize the dialog: When a Private Key
    file is encrypted, all known Pass Phrases (at the beginning there are
    none, of course) are tried. If one of those known Pass Phrases succeeds no
    dialog pops up for this particular Private Key file.  If none succeeded,
    another Pass Phrase is queried on the terminal and remembered for the next
    round (where it perhaps can be reused). 
    <p> 
    This scheme allows mod_ssl to be maximally flexible (because for N encrypted
    Private Key files you <em>can</em> use N different Pass Phrases - but then
    you have to enter all of them, of course) while minimizing the terminal
    dialog (i.e. when you use a single Pass Phrase for all N Private Key files
    this Pass Phrase is queried only once).
<p>
<li><code>exec:/path/to/program</code>
    <p>
    Here an external program is configured which is called at startup for each
    encrypted Private Key file. It is called with two arguments (the first is
    of the form ``<code>servername:portnumber</code>'', the second is either
    ``<code>RSA</code>'' or ``<code>DSA</code>''), which indicate for which
    server and algorithm it has to print the corresponding Pass Phrase to
    <code>stdout</code>.  The intent is that this external program first runs
    security checks to make sure that the system is not compromised by an
    attacker, and only when these checks were passed successfully it provides
    the Pass Phrase. 
    <p>
    Both these security checks, and the way the Pass Phrase is determined, can
    be as complex as you like. Mod_ssl just defines the interface: an
    executable program which provides the Pass Phrase on <code>stdout</code>.
    Nothing more or less! So, if you're really paranoid about security, here
    is your interface. Anything else has to be left as an exercise to the
    administrator, because local security requirements are so different.
    <p>
    The reuse-algorithm above is used here, too. In other words: The external
    program is called only once per unique Pass Phrase.
</ul>

<p>
Example:
<blockquote>
<pre>
SSLPassPhraseDialog exec:/usr/local/apache/sbin/pp-filter
</pre>
</blockquote>


<!-- SSLMutex ------------------------------------------------------->

<p>
<br>
<a name="SSLMutex"></a>
<h2>SSLMutex</h2>

<p>
<directive
    name="SSLMutex"
    description="Semaphore for internal mutual exclusion of operations"
    syntax="<code>SSLMutex</code> <em>type</em>"
    default="<code>SSLMutex none</code>"
    context="server config"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
This configures the SSL engine's semaphore (aka. lock) which is used for mutual
exclusion of operations which have to be done in a synchronized way between the
pre-forked Apache server processes. This directive can only be used in the
global server context because it's only useful to have one global mutex.

<p>
The following Mutex <em>types</em> are available:

<ul>
<li><code>none</code>
    <p>
    This is the default where no Mutex is used at all. Use it at your own
    risk. But because currently the Mutex is mainly used for synchronizing
    write access to the SSL Session Cache you can live without it as long
    as you accept a sometimes garbled Session Cache. So it's not recommended
    to leave this the default. Instead configure a real Mutex.
<p>
<li><code>file:/path/to/mutex</code>
    <p>
    This is the portable and (under Unix) always provided Mutex variant where
    a physical (lock-)file is used as the Mutex. Always use a local disk
    filesystem for <code>/path/to/mutex</code> and never a file residing on a
    NFS- or AFS-filesystem. Note: Internally, the Process ID (PID) of the
    Apache parent process is automatically appended to
    <code>/path/to/mutex</code> to make it unique, so you don't have to worry
    about conflicts yourself. Notice that this type of mutex is not available
    under the Win32 environment. There you <i>have</i> to use the semaphore
    mutex.
<p>
<li><code>sem</code>
    <p>
    This is the most elegant but also most non-portable Mutex variant where a
    SysV IPC Semaphore (under Unix) and a Windows Mutex (under Win32) is used
    when possible. It is only available when the underlying platform
    supports it.
</ul>

<p>
Example:
<blockquote>
<pre>
SSLMutex file:/usr/local/apache/logs/ssl_mutex
</pre>
</blockquote>


<!-- SSLRandomSeed -------------------------------------------------->

<p>
<br>
<a name="SSLRandomSeed"></a>
<h2>SSLRandomSeed</h2>

<p>
<directive
    name="SSLRandomSeed"
    description="Pseudo Random Number Generator (PRNG) seeding source"
    syntax="<code>SSLRandomSeed</code> <em>context</em> <em>source</em> [<em>bytes</em>]"
    default="<em>none</em>"
    context="server config"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.2"
>

<p>
This configures one or more sources for seeding the Pseudo Random Number
Generator (PRNG) in OpenSSL at startup time (<em>context</em> is
<code>startup</code>) and/or just before a new SSL connection is established
(<em>context</em> is <code>connect</code>).  This directive can only be used
in the global server context because the PRNG is a global facility.

<p>
The following <em>source</em> variants are available:

<ul>
<li><code>builtin</code>
    <p> This is the always available builtin seeding source.  Its usage
    consumes minimum CPU cycles under runtime and hence can be always used
    without drawbacks. The source used for seeding the PRNG contains of the
    current time, the current process id and (when applicable) a randomly
    choosen 1KB extract of the inter-process scoreboard structure of Apache.
    The drawback is that this is not really a strong source and at startup
    time (where the scoreboard is still not available) this source just
    produces a few bytes of entropy. So you should always, at least for the
    startup, use an additional seeding source.
<p>
<li><code>file:/path/to/source</code>
    <p>
    This variant uses an external file <code>/path/to/source</code> as the
    source for seeding the PRNG. When <em>bytes</em> is specified, only the
    first <em>bytes</em> number of bytes of the file form the entropy (and
    <em>bytes</em> is given to <code>/path/to/source</code> as the first
    argument). When <em>bytes</em> is not specified the whole file forms the
    entropy (and <code>0</code> is given to <code>/path/to/source</code> as
    the first argument). Use this especially at startup time, for instance
    with an available <code>/dev/random</code> and/or
    <code>/dev/urandom</code> devices (which usually exist on modern Unix
    derivates like FreeBSD and Linux).
    <p>
    <em>But be careful</em>: Usually <code>/dev/random</code> provides only as
    much entropy data as it actually has, i.e. when you request 512 bytes of
    entropy, but the device currently has only 100 bytes available two things
    can happen: On some platforms you receive only the 100 bytes while on
    other platforms the read blocks until enough bytes are available (which
    can take a long time). Here using an existing <code>/dev/urandom</code> is
    better, because it never blocks and actually gives the amount of requested
    data. The drawback is just that the quality of the received data may not
    be the best. 
    <p>
    On some platforms like FreeBSD one can even control how the entropy is
    actually generated, i.e. by which system interrupts. More details one can
    find under <i>rndcontrol(8)</i> on those platforms.  Alternatively, when
    your system lacks such a random device, you can use tool
    like <a href="http://www.lothar.com/tech/crypto/">EGD</a>
    (Entropy Gathering Daemon) and run its client program with the
    <code>exec:/path/to/program/</code> variant (see below) or use
    <code>egd:/path/to/egd-socket</code> (see below).
<p>
<li><code>exec:/path/to/program</code>
    <p>
    This variant uses an external executable <code>/path/to/program</code> as
    the source for seeding the PRNG. When <em>bytes</em> is specified, only the
    first <em>bytes</em> number of bytes of its <code>stdout</code> contents
    form the entropy. When <em>bytes</em> is not specified, the entirety of
    the data produced on <code>stdout</code> form the entropy. Use this only
    at startup time when you need a very strong seeding with the help of an
    external program (for instance as in the example above with the
    <code>truerand</code> utility you can find in the mod_ssl distribution
    which is based on the AT&amp;T <em>truerand</em> library). Using this in
    the connection context slows down the server too dramatically, of course.
    So usually you should avoid using external programs in that context.
<p>
<li><code>egd:/path/to/egd-socket</code> (Unix only)
    <p>
    This variant uses the Unix domain socket of the
    external Entropy Gathering Daemon (EGD) (see <a
    href="http://www.lothar.com/tech/crypto/">http://www.lothar.com/tech
    /crypto/</a>) to seed the PRNG. Use this if no random device exists
    on your platform.
</ul>

<p>
Example:
<blockquote>
<pre>
SSLRandomSeed startup builtin
SSLRandomSeed startup file:/dev/random
SSLRandomSeed startup file:/dev/urandom 1024
SSLRandomSeed startup exec:/usr/local/bin/truerand 16
SSLRandomSeed connect builtin
SSLRandomSeed connect file:/dev/random
SSLRandomSeed connect file:/dev/urandom 1024
</pre>
</blockquote>


<!-- SSLSessionCache ------------------------------------------------>

<p>
<br>
<a name="SSLSessionCache"></a>
<h2>SSLSessionCache</h2>

<directive
    name="SSLSessionCache"
    description="Type of the global/inter-process SSL Session Cache"
    syntax="<code>SSLSessionCache</code> <em>type</em>"
    default="<code>SSLSessionCache none</code>"
    context="server config"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
This configures the storage type of the global/inter-process SSL Session
Cache. This cache is an optional facility which speeds up parallel request
processing. For requests to the same server process (via HTTP keep-alive),
OpenSSL already caches the SSL session information locally. But because modern
clients request inlined images and other data via parallel requests (usually
up to four parallel requests are common) those requests are served by
<em>different</em> pre-forked server processes. Here an inter-process cache
helps to avoid unneccessary session handshakes.

<p>
The following two storage <em>type</em>s are currently supported:

<ul>
<li><code>none</code>
    <p>
    This is the default and just disables the global/inter-process Session
    Cache. There is no drawback in functionality, but a noticeable speed
    penalty can be observed.
<p>
<li><code>dbm:/path/to/datafile</code>
    <p>
    This makes use of a DBM hashfile on the local disk to synchronize the
    local OpenSSL memory caches of the server processes. The slight increase
    in I/O on the server results in a visible request speedup for your
    clients, so this type of storage is generally recommended.
<p>
<li><code>shm:/path/to/datafile</code>[<code>(</code><i>size</i><code>)</code>]
    <p>
    This makes use of a high-performance hash table (approx. <i>size</i> bytes
    in size) inside a shared memory segment in RAM (established via
    <code>/path/to/datafile</code>) to synchronize the local OpenSSL memory
    caches of the server processes.  This storage type is not available on all
    platforms. See the mod_ssl <code>INSTALL</code> document for details on
    how to build Apache+EAPI with shared memory support.
</ul>

<p>
Examples:
<blockquote>
<pre>
SSLSessionCache dbm:/usr/local/apache/logs/ssl_gcache_data
SSLSessionCache shm:/usr/local/apache/logs/ssl_gcache_data(512000)
</pre>
</blockquote>


<!-- SSLSessionCacheTimeout ----------------------------------------->

<p>
<br>
<a name="SSLSessionCacheTimeout"></a>
<h2>SSLSessionCacheTimeout</h2>

<directive
    name="SSLSessionCacheTimeout"
    description="Number of seconds before an SSL session expires in the Session Cache"
    syntax="<code>SSLSessionCacheTimeout</code> <em>seconds</em>"
    default="<code>SSLSessionCacheTimeout 300</code>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.0"
>

<p>
This directive sets the timeout in seconds for the information stored in the
global/inter-process SSL Session Cache and the OpenSSL internal memory cache.
It can be set as low as 15 for testing, but should be set to higher
values like 300 in real life.

<p>
Example:
<blockquote>
<pre>
SSLSessionCacheTimeout 600
</pre>
</blockquote>


<!-- SSLEngine ------------------------------------------------------>

<p>
<br>
<a name="SSLEngine"></a>
<h2>SSLEngine</h2>

<directive
    name="SSLEngine"
    description="SSL Engine Operation Switch"
    syntax="<code>SSLEngine</code> <em>on|off</em>"
    default="<code>SSLEngine off</code>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
This directive toggles the usage of the SSL/TLS Protocol Engine. This is
usually used inside a &lt;VirtualHost&gt; section to enable SSL/TLS for a
particular virtual host. By default the SSL/TLS Protocol Engine is disabled
for both the main server and all configured virtual hosts. 

<p>
Example:
<blockquote>
<pre>
&lt;VirtualHost _default_:443&gt;
SSLEngine on
...
&lt;/VirtualHost&gt;
</pre>
</blockquote>


<!-- SSLProtocol ---------------------------------------------------->

<p>
<br>
<a name="SSLProtocol"></a>
<h2>SSLProtocol</h2>

<directive
    name="SSLProtocol"
    description="Configure usable SSL protocol flavors"
    syntax="<code>SSLProtocol</code> [+-]<em>protocol</em> ..."
    default="<code>SSLProtocol all</code>"
    context="server config, virtual host"
    override="Options"
    compat="mod_ssl 2.2"
>

<p>
This directive can be used to control the SSL protocol flavors mod_ssl should
use when establishing its server environment.  Clients then can only connect
with one of the provided protocols.

<p>
The available (case-insensitive) <em>protocol</em>s are:

<ul>
<li><code>SSLv2</code>
    <p>
    This is the Secure Sockets Layer (SSL) protocol, version 2.0. It is the
    original SSL protocol as designed by Netscape Corporation.
<p>
<li><code>SSLv3</code>
    <p>
    This is the Secure Sockets Layer (SSL) protocol, version 3.0.  It is the
    successor to SSLv2 and the currently (as of February 1999) de-facto
    standardized SSL protocol from Netscape Corporation. It's supported by
    almost all popular browsers.
<p>
<li><code>TLSv1</code>
    <p>
    This is the Transport Layer Security (TLS) protocol, version 1.0.  It is the
    successor to SSLv3 and currently (as of February 1999) still under
    construction by the Internet Engineering Task Force (IETF).  It's still
    not supported by all popular browsers.
<p>
<li><code>All</code>
    <p>
    This is a shortcut for ``<code>+SSLv2 +SSLv3 +TLSv1</code>'' and a
    convinient way for enabling all protocols except one when used in
    combination with the minus sign on a protocol as the example above shows.
</ul>

<p>
Example:
<blockquote>
<pre>
\#   enable SSLv3 and TLSv1, but not SSLv2
SSLProtocol all -SSLv2
</pre>
</blockquote>


<!-- SSLCipherSuite ------------------------------------------------->

<p>
<br>
<a name="SSLCipherSuite"></a>
<h2>SSLCipherSuite</h2>

<directive
    name="SSLCipherSuite"
    description="Cipher Suite available for negotiation in SSL handshake"
    syntax="<code>SSLCipherSuite</code> <em>cipher-spec</em>"
    default="<code>SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP</code>"
    context="server config, virtual host, directory, .htaccess"
    override="AuthConfig"
    compat="mod_ssl 2.1"
>

<p>
This complex directive uses a colon-separated <em>cipher-spec</em> string
consisting of OpenSSL cipher specifications to configure the Cipher Suite the
client is permitted to negotiate in the SSL handshake phase. Notice that this
directive can be used both in per-server and per-directory context. In
per-server context it applies to the standard SSL handshake when a connection
is established. In per-directory context it forces a SSL renegotation with the
reconfigured Cipher Suite after the HTTP request was read but before the HTTP
response is sent.

<p>
An SSL cipher specification in <em>cipher-spec</em> is composed of 4 major
attributes plus a few extra minor ones:

<ul>
<li><em>Key Exchange Algorithm</em>:<br>
    RSA or Diffie-Hellman variants.
<p>
<li><em>Authentication Algorithm</em>:<br>
    RSA, Diffie-Hellman, DSS or none.
<p>
<li><em>Cipher/Encryption Algorithm</em>:<br>
    DES, Triple-DES, RC4, RC2, IDEA or none.
<p>
<li><em>MAC Digest Algorithm</em>:<br>
    MD5, SHA or SHA1.
</ul>

An SSL cipher can also be an export cipher and is either a SSLv2 or SSLv3/TLSv1
cipher (here TLSv1 is equivalent to SSLv3). To specify which ciphers to use,
one can either specify all the Ciphers, one at a time, or use aliases to
specify the preference and order for the ciphers (see <a href="#table1">Table
1</a>).  

<p>
<float name="table1" caption="Table 1: OpenSSL Cipher Specification Tags">
<table border="0" cellspacing="0" cellpadding="2" width=598>
<tr id=D><td><b>Tag</b></td> <td><b>Description</b></td>

<tr id=H><td colspan=2><em>Key Exchange Algorithm:</em></td></tr>
<tr id=D><td><code>kRSA</code></td>   <td>RSA key exchange</td></tr>
<tr id=H><td><code>kDHr</code></td>   <td>Diffie-Hellman key exchange with RSA key</td></tr>
<tr id=D><td><code>kDHd</code></td>   <td>Diffie-Hellman key exchange with DSA key</td></tr>
<tr id=H><td><code>kEDH</code></td>   <td>Ephemeral (temp.key) Diffie-Hellman key exchange (no cert)</td>   </tr>

<tr id=H><td colspan=2><em>Authentication Algorithm:</em></td></tr>
<tr id=D><td><code>aNULL</code></td>  <td>No authentication</td></tr>
<tr id=H><td><code>aRSA</code></td>   <td>RSA authentication</td></tr>
<tr id=D><td><code>aDSS</code></td>   <td>DSS authentication</td> </tr>
<tr id=H><td><code>aDH</code></td>    <td>Diffie-Hellman authentication</td></tr>

<tr id=D><td colspan=2><em>Cipher Encoding Algorithm:</em></td></tr></tr>
<tr id=H><td><code>eNULL</code></td>  <td>No encoding</td>         </tr>
<tr id=D><td><code>DES</code></td>    <td>DES encoding</td>        </tr>
<tr id=H><td><code>3DES</code></td>   <td>Triple-DES encoding</td> </tr>
<tr id=D><td><code>RC4</code></td>    <td>RC4 encoding</td>       </tr>
<tr id=H><td><code>RC2</code></td>    <td>RC2 encoding</td>       </tr>
<tr id=D><td><code>IDEA</code></td>   <td>IDEA encoding</td>       </tr>

<tr id=H><td colspan=2><em>MAC Digest Algorithm</em>:</td></tr>
<tr id=D><td><code>MD5</code></td>    <td>MD5 hash function</td></tr>
<tr id=H><td><code>SHA1</code></td>   <td>SHA1 hash function</td></tr>
<tr id=D><td><code>SHA</code></td>    <td>SHA hash function</td> </tr>

<tr id=H><td colspan=2><em>Aliases:</em></td></tr>
<tr id=D><td><code>SSLv2</code></td>  <td>all SSL version 2.0 ciphers</td></tr>
<tr id=H><td><code>SSLv3</code></td>  <td>all SSL version 3.0 ciphers</td> </tr>
<tr id=D><td><code>TLSv1</code></td>  <td>all TLS version 1.0 ciphers</td> </tr>
<tr id=H><td><code>EXP</code></td>    <td>all export ciphers</td>  </tr>
<tr id=D><td><code>EXPORT40</code></td> <td>all 40-bit export ciphers only</td>  </tr>
<tr id=H><td><code>EXPORT56</code></td> <td>all 56-bit export ciphers only</td>  </tr>
<tr id=D><td><code>LOW</code></td>    <td>all low strength ciphers (no export, single DES)</td></tr>
<tr id=H><td><code>MEDIUM</code></td> <td>all ciphers with 128 bit encryption</td> </tr>
<tr id=D><td><code>HIGH</code></td>   <td>all ciphers using Triple-DES</td>     </tr>
<tr id=H><td><code>RSA</code></td>    <td>all ciphers using RSA key exchange</td> </tr>
<tr id=D><td><code>DH</code></td>     <td>all ciphers using Diffie-Hellman key exchange</td> </tr>
<tr id=H><td><code>EDH</code></td>    <td>all ciphers using Ephemeral Diffie-Hellman key exchange</td> </tr>
<tr id=D><td><code>ADH</code></td>    <td>all ciphers using Anonymous Diffie-Hellman key exchange</td> </tr>
<tr id=H><td><code>DSS</code></td>    <td>all ciphers using DSS authentication</td> </tr>
<tr id=D><td><code>NULL</code></td>   <td>all ciphers using no encryption</td> </tr>

</table>
</float>

<p>
Now where this becomes interesting is that these can be put together
to specify the order and ciphers you wish to use. To speed this up
there are also aliases (<code>SSLv2, SSLv3, TLSv1, EXP, LOW, MEDIUM,
HIGH</code>) for certain groups of ciphers. These tags can be joined
together with prefixes to form the <em>cipher-spec</em>. Available
prefixes are:

<ul>
<li>none: add cipher to list
<li><code>+</code>: add ciphers to list and pull them to current location in list
<li><code>-</code>: remove cipher from list (can be added later again)
<li><code>!</code>: kill cipher from list completely (can <b>not</b> be added later again)
</ul>

A simpler way to look at all of this is to use the ``<code>openssl ciphers
-v</code>'' command which provides a nice way to successively create the
correct <em>cipher-spec</em> string.  The default <em>cipher-spec</em> string
is ``<code>ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP</code>'' which
means the following: first, remove from consideration any ciphers that do not
authenticate, i.e. for SSL only the Anonymous Diffie-Hellman ciphers. Next,
use ciphers using RC4 and RSA. Next include the high, medium and then the low
security ciphers. Finally <em>pull</em> all SSLv2 and export ciphers to the
end of the list.

<blockquote>
<pre>
$ openssl ciphers -v 'ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP'
NULL-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=None      Mac=SHA1
NULL-MD5                SSLv3 Kx=RSA      Au=RSA  Enc=None      Mac=MD5 
EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
...                     ...               ...     ...           ...
EXP-RC4-MD5             SSLv3 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export
EXP-RC2-CBC-MD5         SSLv2 Kx=RSA(512) Au=RSA  Enc=RC2(40)   Mac=MD5  export
EXP-RC4-MD5             SSLv2 Kx=RSA(512) Au=RSA  Enc=RC4(40)   Mac=MD5  export
</pre>
</blockquote>

The complete list of particular RSA &amp; DH ciphers for SSL is given in <a
href="#table2">Table 2</a>.

<p>
Example:
<blockquote>
<pre>
#   allow only strongest RSA ciphers
SSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW
</pre>
</blockquote>

<p>
<float name="table2" caption="Table 2: Particular SSL Ciphers">
<table border="0" cellspacing="0" cellpadding="2" width=598>
<tr id=D><td><b>Cipher-Tag</b></td> <td><b>Protocol</b></td> <td><b>Key Ex.</b></td> <td><b>Auth.</b></td> <td><b>Enc.</b></td> <td><b>MAC</b></td> <td><b>Type</b></td> </tr>

<tr id=H><td colspan=7><em>RSA Ciphers:</em></td></tr>
<tr id=D><td><code>DES-CBC3-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>3DES(168)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>DES-CBC3-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>3DES(168)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=D><td><code>IDEA-CBC-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>IDEA(128)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>RC4-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>RC4(128)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=D><td><code>RC4-MD5</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>RC4(128)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=H><td><code>IDEA-CBC-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>IDEA(128)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=D><td><code>RC2-CBC-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>RC2(128)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=H><td><code>RC4-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>RC4(128)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=D><td><code>DES-CBC-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>DES(56)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>RC4-64-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>RC4(64)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=D><td><code>DES-CBC-MD5</code></td> <td>SSLv2</td> <td>RSA</td> <td>RSA</td> <td>DES(56)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=H><td><code>EXP-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>RSA(512)</td> <td>RSA</td> <td>DES(40)</td> <td>SHA1</td> <td> export</td> </tr>
<tr id=D><td><code>EXP-RC2-CBC-MD5</code></td> <td>SSLv3</td> <td>RSA(512)</td> <td>RSA</td> <td>RC2(40)</td> <td>MD5</td> <td>  export</td> </tr>
<tr id=H><td><code>EXP-RC4-MD5</code></td> <td>SSLv3</td> <td>RSA(512)</td> <td>RSA</td> <td>RC4(40)</td> <td>MD5</td> <td>  export</td> </tr>
<tr id=D><td><code>EXP-RC2-CBC-MD5</code></td> <td>SSLv2</td> <td>RSA(512)</td> <td>RSA</td> <td>RC2(40)</td> <td>MD5</td> <td>  export</td> </tr>
<tr id=H><td><code>EXP-RC4-MD5</code></td> <td>SSLv2</td> <td>RSA(512)</td> <td>RSA</td> <td>RC4(40)</td> <td>MD5</td> <td>  export</td> </tr>
<tr id=D><td><code>NULL-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>None</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>NULL-MD5</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>None</td> <td>MD5</td> <td>&nbsp; </td> </tr>

<tr id=D><td colspan=7><em>Diffie-Hellman Ciphers:</em></td></tr>
<tr id=H><td><code>ADH-DES-CBC3-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>None</td> <td>3DES(168)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=D><td><code>ADH-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>None</td> <td>DES(56)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>ADH-RC4-MD5</code></td> <td>SSLv3</td> <td>DH</td> <td>None</td> <td>RC4(128)</td> <td>MD5</td> <td>&nbsp; </td> </tr>
<tr id=D><td><code>EDH-RSA-DES-CBC3-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>RSA</td> <td>3DES(168)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>EDH-DSS-DES-CBC3-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>DSS</td> <td>3DES(168)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=D><td><code>EDH-RSA-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>RSA</td> <td>DES(56)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=H><td><code>EDH-DSS-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH</td> <td>DSS</td> <td>DES(56)</td> <td>SHA1</td> <td>&nbsp;</td> </tr>
<tr id=D><td><code>EXP-EDH-RSA-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH(512)</td> <td>RSA</td> <td>DES(40)</td> <td>SHA1</td> <td> export</td> </tr>
<tr id=H><td><code>EXP-EDH-DSS-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH(512)</td> <td>DSS</td> <td>DES(40)</td> <td>SHA1</td> <td> export</td> </tr>
<tr id=D><td><code>EXP-ADH-DES-CBC-SHA</code></td> <td>SSLv3</td> <td>DH(512)</td> <td>None</td> <td>DES(40)</td> <td>SHA1</td> <td> export</td> </tr>
<tr id=H><td><code>EXP-ADH-RC4-MD5</code></td> <td>SSLv3</td> <td>DH(512)</td> <td>None</td> <td>RC4(40)</td> <td>MD5</td> <td>  export</td> </tr>
</table>
</float>


<!-- SSLCertificateFile --------------------------------------------->

<p>
<br>
<a name="SSLCertificateFile"></a>
<h2>SSLCertificateFile</h2>

<directive
    name="SSLCertificateFile"
    description="Server PEM-encoded X.509 Certificate file"
    syntax="<code>SSLCertificateFile</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.0"
>

<p>
This directive points to the PEM-encoded Certificate file for the server and
optionally also to the corresponding RSA or DSA Private Key file for it
(contained in the same file). If the contained Private Key is encrypted the
Pass Phrase dialog is forced at startup time. This directive can be used up to
two times (referencing different filenames) when both a RSA and a DSA based
server certificate is used in parallel.

<p>
Example:
<blockquote>
<pre>
SSLCertificateFile /usr/local/apache/conf/ssl.crt/server.crt
</pre>
</blockquote>


<!-- SSLCertificateKeyFile ------------------------------------------>

<p>
<br>
<a name="SSLCertificateKeyFile"></a>
<h2>SSLCertificateKeyFile</h2>

<directive
    name="SSLCertificateKeyFile"
    description="Server PEM-encoded Private Key file"
    syntax="<code>SSLCertificateKeyFile</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.0"
>

<p>
This directive points to the PEM-encoded Private Key file for the server. If
the Private Key is not combined with the Certificate in the
<code>SSLCertificateFile</code>, use this additional directive to point to the
file with the stand-alone Private Key.  When <code>SSLCertificateFile</code>
is used and the file contains both the Certificate and the Private Key this
directive need not be used.  But we strongly discourage this practice.
Instead we recommend you to separate the Certificate and the Private Key.  If
the contained Private Key is encrypted, the Pass Phrase dialog is forced at
startup time.  This directive can be used up to two times (referencing
different filenames) when both a RSA and a DSA based private key is used in
parallel.

<p>
Example:
<blockquote>
<pre>
SSLCertificateKeyFile /usr/local/apache/conf/ssl.key/server.key
</pre>
</blockquote>


<!-- SSLCertificateChainFile ---------------------------------------->

<p>
<br>
<a name="SSLCertificateChainFile"></a>
<h2>SSLCertificateChainFile</h2>

<directive
    name="SSLCertificateChainFile"
    description="File of PEM-encoded Server CA Certificates"
    syntax="<code>SSLCertificateChainFile</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.3.6"
>

<p>
This directive sets the optional <em>all-in-one</em> file where you can
assemble the certificates of Certification Authorities (CA) which form the
certificate chain of the server certificate. This starts with the issuing CA
certificate of of the server certificate and can range up to the root CA
certificate. Such a file is simply the concatenation of the various
PEM-encoded CA Certificate files, usually in certificate chain order. 

<p>
This should be used alternatively and/or additionally to <a
href="#SSLCACertificatePath">SSLCACertificatePath</a> for explicitly
constructing the server certificate chain which is sent to the browser in
addition to the server certificate. It is especially useful to avoid conflicts
with CA certificates when using client authentication. Because although
placing a CA certificate of the server certificate chain into <a
href="#SSLCACertificatePath">SSLCACertificatePath</a> has the same effect for
the certificate chain construction, it has the side-effect that client
certificates issued by this same CA certificate are also accepted on client
authentication. That's usually not one expect.

<p>
But be careful: Providing the certificate chain works only if you are using a
<i>single</i> (either RSA <i>or</i> DSA) based server certificate. If you are
using a coupled RSA+DSA certificate pair, this will work only if actually both
certificates use the <i>same</i> certificate chain.  Else the browsers will be
confused in this situation.

<p>
Example:
<blockquote>
<pre>
SSLCertificateChainFile /usr/local/apache/conf/ssl.crt/ca.crt
</pre>
</blockquote>


<!-- SSLCACertificatePath ------------------------------------------->

<p>
<br>
<a name="SSLCACertificatePath"></a>
<h2>SSLCACertificatePath</h2>

<directive
    name="SSLCACertificatePath"
    description="Directory of PEM-encoded CA Certificates for Client Auth."
    syntax="<code>SSLCACertificatePath</code> <em>directory</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.0"
>

<p>
This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose clients you deal with. These are used to
verify the client certificate on Client Authentication.

<p>
The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
<i>hash-value</i><tt>.N</tt>.  And you should always make sure this directory
contains the appropriate symbolic links. Use the <code>Makefile</code> which
comes with mod_ssl to accomplish this task.

<p>
Example:
<blockquote>
<pre>
SSLCACertificatePath /usr/local/apache/conf/ssl.crt/
</pre>
</blockquote>


<!-- SSLCACertificateFile ------------------------------------------->

<p>
<br>
<a name="SSLCACertificateFile"></a>
<h2>SSLCACertificateFile</h2>

<directive
    name="SSLCACertificateFile"
    description="File of concatenated PEM-encoded CA Certificates for Client Auth."
    syntax="<code>SSLCACertificateFile</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.0"
>

<p>
This directive sets the <em>all-in-one</em> file where you can assemble the
Certificates of Certification Authorities (CA) whose <em>clients</em> you deal
with.  These are used for Client Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to <a
href="#SSLCACertificatePath">SSLCACertificatePath</a>.

<p>
Example:
<blockquote>
<pre>
SSLCACertificateFile /usr/local/apache/conf/ssl.crt/ca-bundle-client.crt
</pre>
</blockquote>


<!-- SSLCARevocationPath -------------------------------------------->

<p>
<br>
<a name="SSLCARevocationPath"></a>
<h2>SSLCARevocationPath</h2>

<directive
    name="SSLCARevocationPath"
    description="Directory of PEM-encoded CA CRLs for Client Auth."
    syntax="<code>SSLCARevocationPath</code> <em>directory</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.3"
>

<p>
This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose clients you deal with.
These are used to revoke the client certificate on Client Authentication.

<p>
The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
<i>hash-value</i><tt>.rN</tt>.  And you should always make sure this directory
contains the appropriate symbolic links. Use the <code>Makefile</code> which
comes with mod_ssl to accomplish this task.

<p>
Example:
<blockquote>
<pre>
SSLCARevocationPath /usr/local/apache/conf/ssl.crl/
</pre>
</blockquote>


<!-- SSLCARevocationFile -------------------------------------------->

<p>
<br>
<a name="SSLCARevocationFile"></a>
<h2>SSLCARevocationFile</h2>

<directive
    name="SSLCARevocationFile"
    description="File of concatenated PEM-encoded CA CRLs for Client Auth."
    syntax="<code>SSLCARevocationFile</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.3"
>

<p>
This directive sets the <em>all-in-one</em> file where you can assemble the
Certificate Revocation Lists (CRL) of Certification Authorities (CA) whose
<em>clients</em> you deal with.  These are used for Client Authentication.
Such a file is simply the concatenation of the various PEM-encoded CRL
files, in order of preference. This can be used alternatively and/or
additionally to <a href="#SSLCARevocationPath">SSLCARevocationPath</a>.

<p>
Example:
<blockquote>
<pre>
SSLCARevocationFile /usr/local/apache/conf/ssl.crl/ca-bundle-client.crl
</pre>
</blockquote>


<!-- SSLVerifyClient ------------------------------------------------->

<p>
<br>
<a name="SSLVerifyClient"></a>
<h2>SSLVerifyClient</h2>

<directive
    name="SSLVerifyClient"
    description="Type of Client Certificate verification"
    syntax="<code>SSLVerifyClient</code> <em>level</em>"
    default="<code>SSLVerifyClient none</code>"
    context="server config, virtual host, directory, .htaccess"
    override="AuthConfig"
    compat="mod_ssl 2.0"
>

<p>
This directive sets the Certificate verification level for the Client
Authentication.  Notice that this directive can be used both in per-server and
per-directory context. In per-server context it applies to the client
authentication process used in the standard SSL handshake when a connection is
established. In per-directory context it forces a SSL renegotation with the
reconfigured client verification level after the HTTP request was read but
before the HTTP response is sent.

<p>
The following levels are available for <em>level</em>:

<ul>
<li><strong>none</strong>:
     no client Certificate is required at all
<li><strong>optional</strong>:
     the client <em>may</em> present a valid Certificate
<li><strong>require</strong>:
     the client <em>has to</em> present a valid Certificate
<li><strong>optional_no_ca</strong>:
     the client may present a valid Certificate<br> 
     but it need not to be (successfully) verifiable.
</ul>

In practice only levels <strong>none</strong> and <strong>require</strong> are
really interesting, because level <strong>optional</strong> doesn't work with
all browsers and level <strong>optional_no_ca</strong> is actually against the
idea of authentication (but can be used to establish SSL test pages, etc.)

<p>
Example:
<blockquote>
<pre>
SSLVerifyClient require
</pre>
</blockquote>


<!-- SSLVerifyDepth ------------------------------------------------->

<p>
<br>
<a name="SSLVerifyDepth"></a>
<h2>SSLVerifyDepth</h2>

<directive
    name="SSLVerifyDepth"
    description="Maximum depth of CA Certificates in Client Certificate verification"
    syntax="<code>SSLVerifyDepth</code> <em>number</em>"
    default="<code>SSLVerifyDepth 1</code>"
    context="server config, virtual host, directory, .htaccess"
    override="AuthConfig"
    compat="mod_ssl 2.0"
>

<p> 
This directive sets how deeply mod_ssl should verify before deciding that the
clients don't have a valid certificate.  Notice that this directive can be
used both in per-server and per-directory context. In per-server context it
applies to the client authentication process used in the standard SSL
handshake when a connection is established. In per-directory context it forces
a SSL renegotation with the reconfigured client verification depth after the
HTTP request was read but before the HTTP response is sent.

<p>
The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the client certificate. A depth of 0 means that self-signed client
certificates are accepted only, the default depth of 1 means the client
certificate can be self-signed or has to be signed by a CA which is directly
known to the server (i.e. the CA's certificate is under
<code>SSLCACertificatePath</code>), etc.

<p>
Example:
<blockquote>
<pre>
SSLVerifyDepth 10
</pre>
</blockquote>


<!-- SSLLog --------------------------------------------------------->

<p>
<br>
<a name="SSLLog"></a>
<h2>SSLLog</h2>

<directive
    name="SSLLog"
    description="Where to write the dedicated SSL engine logfile"
    syntax="<code>SSLLog</code> <em>filename</em>"
    default="<em>None</em>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
This directive sets the name of the dedicated SSL protocol engine logfile.
Error type messages are additionally duplicated to the general Apache error
log file (directive <code>ErrorLog</code>). Put this somewhere where it cannot
be used for symlink attacks on a real server (i.e. somewhere where only root
can write). If the <em>filename</em> does not begin with a slash
('<code>/</code>') then it is assumed to be relative to the <em>Server
Root</em>.  If <em>filename</em> begins with a bar ('<code>|</code>') then the
following string is assumed to be a path to an executable program to which a
reliable pipe can be established. The directive should occur only once per
virtual server config.  

<p>
Example:
<blockquote>
<pre>
SSLLog /usr/local/apache/logs/ssl_engine_log
</pre>
</blockquote>


<!-- SSLLogLevel ---------------------------------------------------->

<p>
<br>
<a name="SSLLogLevel"></a>
<h2>SSLLogLevel</h2>

<directive
    name="SSLLogLevel"
    description="Logging level for the dedicated SSL engine logfile"
    syntax="<code>SSLLogLevel</code> <em>level</em>"
    default="<code>SSLLogLevel none</code>"
    context="server config, virtual host"
    override="<em>Not applicable</em>"
    compat="mod_ssl 2.1"
>

<p>
This directive sets the verbosity degree of the dedicated SSL protocol engine
logfile. The <em>level</em> is one of the following (in ascending order where
higher levels include lower levels):

<ul>
<li><code>none</code><br>
    no dedicated SSL logging is done, but messages of level
    ``<code>error</code>'' are still written to the general Apache error
    logfile.
<p>
<li><code>error</code><br>
    log messages of error type only, i.e. messages which show fatal situations
    (processing is stopped).  Those messages are also duplicated to the
    general Apache error logfile.
<p>
<li><code>warn</code><br>
    log also warning messages, i.e. messages which show non-fatal problems
    (processing is continued).
<p>
<li><code>info</code><br>
    log also informational messages, i.e.  messages which show major
    processing steps.
<p>
<li><code>trace</code><br>
    log also trace messages, i.e.  messages which show minor processing steps.
<p>
<li><code>debug</code><br>
    log also debugging messages, i.e.  messages which show development and
    low-level I/O information.
</ul>

<p>
Example:
<blockquote>
<pre>
SSLLogLevel warn
</pre>
</blockquote>


<!-- SSLOptions ----------------------------------------------------->

<p>
<br>
<a name="SSLOptions"></a>
<h2>SSLOptions</h2>

<directive
    name="SSLOptions"
    description="Configure various SSL engine run-time options"
    syntax="<code>SSLOptions</code> [+-]<em>option</em> ..."
    default="<em>None</em>"
    context="server config, virtual host, directory, .htaccess"
    override="Options"
    compat="mod_ssl 2.1"
>

<p>
This directive can be used to control various run-time options on a
per-directory basis.  Normally, if multiple <code>SSLOptions</code> could
apply to a directory, then the most specific one is taken completely; the
options are not merged. However if <em>all</em> the options on the
<code>SSLOptions</code> directive are preceded by a plus (<code>+</code>) or
minus (<code>-</code>) symbol, the options are merged. Any options preceded by
a <code>+</code> are added to the options currently in force, and any options
preceded by a <code>-</code> are removed from the options currently in force.

<p>
The available <em>option</em>s are:

<ul>
<li><code>StdEnvVars</code>
    <p>
    When this option is enabled, the standard set of SSL related CGI/SSI
    environment variables are created. This per default is disabled for
    performance reasons, because the information extraction step is a
    rather expensive operation. So one usually enables this option for
    CGI and SSI requests only.
<p>
<li><code>CompatEnvVars</code>
    <p>
    When this option is enabled, additional CGI/SSI environment variables are
    created for backward compatibility to other Apache SSL solutions.  Look in
    the <a href="ssl_compat.html">Compatibility</a> chapter for details 
    on the particular variables generated.
<p>
<li><code>ExportCertData</code>
    <p>
    When this option is enabled, additional CGI/SSI environment variables are
    created: <code>SSL_SERVER_CERT</code>, <code>SSL_CLIENT_CERT</code> and
    <code>SSL_CLIENT_CERT_CHAIN</code><i>n</i> (with <i>n</i> = 0,1,2,..).
    These contain the PEM-encoded X.509 Certificates of server and client for
    the current HTTPS connection and can be used by CGI scripts for deeper
    Certificate checking. Additionally all other certificates of the client
    certificate chain are provided, too.  This bloats up the environment a
    little bit which is why you have to use this option to enable it on
    demand.
<p>
<li><code>FakeBasicAuth</code>
    <p>
    When this option is enabled, the Subject Distinguished Name (DN) of the
    Client X509 Certificate is translated into a HTTP Basic Authorization
    username.  This means that the standard Apache authentication methods can
    be used for access control. The user name is just the Subject of the
    Client's X509 Certificate (can be determined by running OpenSSL's
    <code>openssl x509</code> command: <code>openssl x509 -noout -subject -in
    </code><em>certificate</em><code>.crt</code>).  Note that no password is
    obtained from the user. Every entry in the user file needs this password:
    ``<code>xxj31ZMTZzkVA</code>'', which is the DES-encrypted version of the
    word `<code>password</code>''. Those who live under MD5-based encryption
    (for instance under FreeBSD or BSD/OS, etc.) should use the following MD5
    hash of the same word: ``<code>$1$OXLyS...$Owx8s2/m9/gfkcRVXzgoE/</code>''.
<p>
<li><code>StrictRequire</code>
    <p>
    This <i>forces</i> forbidden access when <code>SSLRequireSSL</code> or
    <code>SSLRequire</code> successfully decided that access should be
    forbidden. Usually the default is that in the case where a ``<code>Satisfy
    any</code>'' directive is used, and other access restrictions are passed,
    denial of access due to <code>SSLRequireSSL</code> or
    <code>SSLRequire</code> is overridden (because that's how the Apache
    <tt>Satisfy</tt> mechanism should work.) But for strict access restriction
    you can use <code>SSLRequireSSL</code> and/or <code>SSLRequire</code> in
    combination with an ``<code>SSLOptions +StrictRequire</code>''. Then an
    additional ``<code>Satisfy Any</code>'' has no chance once mod_ssl has
    decided to deny access.
<p>
<li><code>OptRenegotiate</code>
    <p>
    This enables optimized SSL connection renegotiation handling when SSL
    directives are used in per-directory context. By default a strict
    scheme is enabled where <i>every</i> per-directory reconfiguration of
    SSL parameters causes a <i>full</i> SSL renegotiation handshake. When this
    option is used mod_ssl tries to avoid unnecessary handshakes by doing more
    granular (but still safe) parameter checks. Nevertheless these granular
    checks sometimes maybe not what the user expects, so enable this on a
    per-directory basis only, please.
</ul>

<p>
Example:
<blockquote>
<pre>
SSLOptions +FakeBasicAuth -StrictRequire
&lt;Files ~ "\.(cgi|shtml)$"&gt;
    SSLOptions +StdEnvVars +CompatEnvVars -ExportCertData
&lt;Files&gt;
</pre>
</blockquote>


<!-- SSLRequireSSL -------------------------------------------------->

<p>
<br>
<a name="SSLRequireSSL"></a>
<h2>SSLRequireSSL</h2>

<directive
    name="SSLRequireSSL"
    description="Deny access when SSL is not used for the HTTP request"
    syntax="<code>SSLRequireSSL</code>"
    default="<em>None</em>"
    context="directory, .htaccess"
    override="AuthConfig"
    compat="mod_ssl 2.0"
>

<p>
This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for
the current connection.  This is very handy inside the SSL-enabled virtual
host or directories for defending against configuration errors that expose
stuff that should be protected. When this directive is present all requests
are denied which are not using SSL.

<p>
Example:
<blockquote>
<pre>
SSLRequireSSL
</pre>
</blockquote>


<!-- SSLRequire ----------------------------------------------------->

<p>
<br>
<a name="SSLRequire"></a>
<h2>SSLRequire</h2>

<directive
    name="SSLRequire"
    description="Allow access only when an arbitrarily complex boolean expression is true"
    syntax="<code>SSLRequire</code> <em>expression</em>"
    default="<em>None</em>"
    context="directory, .htaccess"
    override="AuthConfig"
    compat="mod_ssl 2.1"
>

<p>
This directive specifies a general access requirement which has to be
fulfilled in order to allow access. It's a very powerful directive because the
requirement specification is an arbitrarily complex boolean expression
containing any number of access checks.

<p>
The <em>expression</em> must match the following syntax (given as a BNF
grammar notation):

<blockquote>
<pre>
expr     ::= "<b>true</b>" | "<b>false</b>" 
           | "<b>!</b>" expr
           | expr "<b>&&</b>" expr
           | expr "<b>||</b>" expr
           | "<b>(</b>" expr "<b>)</b>"
           | comp

comp     ::= word "<b>==</b>" word | word "<b>eq</b>" word
           | word "<b>!=</b>" word | word "<b>ne</b>" word
           | word "<b>&lt;</b>"  word | word "<b>lt</b>" word
           | word "<b>&lt;=</b>" word | word "<b>le</b>" word
           | word "<b>&gt;</b>"  word | word "<b>gt</b>" word
           | word "<b>&gt;=</b>" word | word "<b>ge</b>" word
           | word "<b>in</b>" "<b>{</b>" wordlist "<b>}</b>"
           | word "<b>=~</b>" regex
           | word "<b>!~</b>" regex

wordlist ::= word 
           | wordlist "<b>,</b>" word

word     ::= digit
           | cstring
           | variable
           | function

digit    ::= [0-9]+
cstring  ::= "..."
variable ::= "<b>%{</b>" varname "<b>}</b>" 
function ::= funcname "<b>(</b>" funcargs "<b>)</b>"
</pre>
</blockquote>

while for <code>varname</code> any variable from <a href="#table3">Table 3</a>
can be used.  Finally for <code>funcname</code> the following functions
are available:

<ul>
<li><code>file(</code><em>filename</em><code>)</code>
    <p>
    This function takes one string argument and expands to the contents of the
    file. This is especially useful for matching this contents against a
    regular expression, etc.
</ul>

Notice that <em>expression</em> is first parsed into an internal machine
representation and then evaluated in a second step. Actually, in Global and
Per-Server Class context <em>expression</em> is parsed at startup time and
at runtime only the machine representation is executed. For Per-Directory
context this is different: here <em>expression</em> has to be parsed and
immediately executed for every request.

<p>
Example:
<blockquote>
<pre>
SSLRequire (    %{SSL_CIPHER} !~ m/^(EXP|NULL)-/ \\
            and %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd." \\
            and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"} \\
            and %{TIME_WDAY} >= 1 and %{TIME_WDAY} <= 5 \\
            and %{TIME_HOUR} >= 8 and %{TIME_HOUR} <= 20       ) \\
           or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/
</pre>
</blockquote>

<float name="table3" caption="Table 3: Available Variables for SSLRequire">
<table><tr><td>
<em>Standard CGI/1.0 and Apache variables:</em>
<pre>
HTTP_USER_AGENT        PATH_INFO             AUTH_TYPE       
HTTP_REFERER           QUERY_STRING          SERVER_SOFTWARE  
HTTP_COOKIE            REMOTE_HOST           API_VERSION      
HTTP_FORWARDED         REMOTE_IDENT          TIME_YEAR       
HTTP_HOST              IS_SUBREQ             TIME_MON        
HTTP_PROXY_CONNECTION  DOCUMENT_ROOT         TIME_DAY        
HTTP_ACCEPT            SERVER_ADMIN          TIME_HOUR       
HTTP:headername        SERVER_NAME           TIME_MIN        
THE_REQUEST            SERVER_PORT           TIME_SEC        
REQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAY       
REQUEST_SCHEME         REMOTE_ADDR           TIME            
REQUEST_URI            REMOTE_USER           ENV:<b>variablename</b>
REQUEST_FILENAME
</pre> 

<em>SSL-related variables:</em>
<pre>
HTTPS                  SSL_CLIENT_M_VERSION   SSL_SERVER_M_VERSION
                       SSL_CLIENT_M_SERIAL    SSL_SERVER_M_SERIAL 
SSL_PROTOCOL           SSL_CLIENT_V_START     SSL_SERVER_V_START  
SSL_SESSION_ID         SSL_CLIENT_V_END       SSL_SERVER_V_END    
SSL_CIPHER             SSL_CLIENT_S_DN        SSL_SERVER_S_DN     
SSL_CIPHER_EXPORT      SSL_CLIENT_S_DN_C      SSL_SERVER_S_DN_C   
SSL_CIPHER_ALGKEYSIZE  SSL_CLIENT_S_DN_ST     SSL_SERVER_S_DN_ST  
SSL_CIPHER_USEKEYSIZE  SSL_CLIENT_S_DN_L      SSL_SERVER_S_DN_L   
SSL_VERSION_LIBRARY    SSL_CLIENT_S_DN_O      SSL_SERVER_S_DN_O   
SSL_VERSION_INTERFACE  SSL_CLIENT_S_DN_OU     SSL_SERVER_S_DN_OU  
                       SSL_CLIENT_S_DN_CN     SSL_SERVER_S_DN_CN  
                       SSL_CLIENT_S_DN_T      SSL_SERVER_S_DN_T  
                       SSL_CLIENT_S_DN_I      SSL_SERVER_S_DN_I  
                       SSL_CLIENT_S_DN_G      SSL_SERVER_S_DN_G  
                       SSL_CLIENT_S_DN_S      SSL_SERVER_S_DN_S  
                       SSL_CLIENT_S_DN_D      SSL_SERVER_S_DN_D  
                       SSL_CLIENT_S_DN_UID    SSL_SERVER_S_DN_UID  
                       SSL_CLIENT_S_DN_Email  SSL_SERVER_S_DN_Email
                       SSL_CLIENT_I_DN        SSL_SERVER_I_DN       
                       SSL_CLIENT_I_DN_C      SSL_SERVER_I_DN_C    
                       SSL_CLIENT_I_DN_ST     SSL_SERVER_I_DN_ST   
                       SSL_CLIENT_I_DN_L      SSL_SERVER_I_DN_L    
                       SSL_CLIENT_I_DN_O      SSL_SERVER_I_DN_O    
                       SSL_CLIENT_I_DN_OU     SSL_SERVER_I_DN_OU   
                       SSL_CLIENT_I_DN_CN     SSL_SERVER_I_DN_CN   
                       SSL_CLIENT_I_DN_T      SSL_SERVER_I_DN_T  
                       SSL_CLIENT_I_DN_I      SSL_SERVER_I_DN_I  
                       SSL_CLIENT_I_DN_G      SSL_SERVER_I_DN_G  
                       SSL_CLIENT_I_DN_S      SSL_SERVER_I_DN_S  
                       SSL_CLIENT_I_DN_D      SSL_SERVER_I_DN_D  
                       SSL_CLIENT_I_DN_UID    SSL_SERVER_I_DN_UID  
                       SSL_CLIENT_I_DN_Email  SSL_SERVER_I_DN_Email
                       SSL_CLIENT_A_SIG       SSL_SERVER_A_SIG    
                       SSL_CLIENT_A_KEY       SSL_SERVER_A_KEY    
                       SSL_CLIENT_CERT        SSL_SERVER_CERT    
                       SSL_CLIENT_CERT_CHAIN<b>n</b>
                       SSL_CLIENT_VERIFY
</pre>
</td></tr></table>
</float>

<br>
<br>
<p>
<h1>Additional Features</h1>

<h2>Environment Variables</h2>

This module provides a lot of SSL information as additional environment
variables to the SSI and CGI namespace. The generated variables are listed in
<a href="#table4">Table 4</a>. For backward compatibility the information can
be made available under different names, too.  Look in the <a
href="ssl_compat.html">Compatibility</a> chapter for details on the
compatibility variables.

<p>
<float name="table4" caption="Table 4: SSI/CGI Environment Variables">
<table border="0" cellspacing="0" cellpadding="2" width=598>
<tr id=H>
 <td><b>Variable Name:</b></td> 
 <td><b>Value Type:</b></td> 
 <td><b>Description:</b></td>
</tr>
<tr id=D><td><code>HTTPS</code></td>                         <td>flag</td>      <td>HTTPS is being used.</td></tr>
<tr id=H><td><code>SSL_PROTOCOL</code></td>                  <td>string</td>    <td>The SSL protocol version (SSLv2, SSLv3, TLSv1)</td></tr>
<tr id=H><td><code>SSL_SESSION_ID</code></td>                <td>string</td>    <td>The hex-encoded SSL session id</td></tr>
<tr id=D><td><code>SSL_CIPHER</code></td>                    <td>string</td>    <td>The cipher specification name</td></tr>
<tr id=D><td><code>SSL_CIPHER_EXPORT</code></td>             <td>string</td>    <td><code>true</code> if cipher is an export cipher</td></tr>
<tr id=H><td><code>SSL_CIPHER_USEKEYSIZE</code></td>         <td>number</td>    <td>Number of cipher bits (actually used)</td></tr>
<tr id=D><td><code>SSL_CIPHER_ALGKEYSIZE</code></td>         <td>number</td>    <td>Number of cipher bits (possible)</td></tr>
<tr id=H><td><code>SSL_VERSION_INTERFACE</code></td>         <td>string</td>    <td>The mod_ssl program version</td></tr>
<tr id=D><td><code>SSL_VERSION_LIBRARY</code></td>           <td>string</td>    <td>The OpenSSL program version</td></tr>
<tr id=H><td><code>SSL_CLIENT_M_VERSION</code></td>          <td>string</td>    <td>The version of the client certificate</td></tr>
<tr id=D><td><code>SSL_CLIENT_M_SERIAL</code></td>           <td>string</td>    <td>The serial of the client certificate</td></tr>
<tr id=H><td><code>SSL_CLIENT_S_DN</code></td>               <td>string</td>    <td>Subject DN in client's certificate</td></tr>
<tr id=D><td><code>SSL_CLIENT_S_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of client's Subject DN</td></tr>
<tr id=H><td><code>SSL_CLIENT_I_DN</code></td>               <td>string</td>    <td>Issuer DN of client's certificate</td></tr>
<tr id=D><td><code>SSL_CLIENT_I_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of client's Issuer DN</td></tr>
<tr id=H><td><code>SSL_CLIENT_V_START</code></td>            <td>string</td>    <td>Validity of client's certificate (start time)</td></tr>
<tr id=D><td><code>SSL_CLIENT_V_END</code></td>              <td>string</td>    <td>Validity of client's certificate (end time)</td></tr>
<tr id=H><td><code>SSL_CLIENT_A_SIG</code></td>              <td>string</td>    <td>Algorithm used for the signature of client's certificate</td></tr>
<tr id=D><td><code>SSL_CLIENT_A_KEY</code></td>              <td>string</td>    <td>Algorithm used for the public key of client's certificate</td></tr>
<tr id=H><td><code>SSL_CLIENT_CERT</code></td>               <td>string</td>    <td>PEM-encoded client certificate</td></tr>
<tr id=D><td><code>SSL_CLIENT_CERT_CHAIN</code><i>n</i></td> <td>string</td>    <td>PEM-encoded certificates in client certificate chain</td></tr>
<tr id=H><td><code>SSL_CLIENT_VERIFY</code></td>             <td>string</td>    <td><tt>NONE</tt>, <tt>SUCCESS</tt>, <tt>GENEROUS</tt> or <tt>FAILED:</tt><i>reason</i></td></tr>
<tr id=D><td><code>SSL_SERVER_M_VERSION</code></td>          <td>string</td>    <td>The version of the server certificate</td></tr>
<tr id=H><td><code>SSL_SERVER_M_SERIAL</code></td>           <td>string</td>    <td>The serial of the server certificate</td></tr>
<tr id=D><td><code>SSL_SERVER_S_DN</code></td>               <td>string</td>    <td>Subject DN in server's certificate</td></tr>
<tr id=H><td><code>SSL_SERVER_S_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of server's Subject DN</td></tr>
<tr id=D><td><code>SSL_SERVER_I_DN</code></td>               <td>string</td>    <td>Issuer DN of server's certificate</td></tr>
<tr id=H><td><code>SSL_SERVER_I_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of server's Issuer DN</td></tr>
<tr id=D><td><code>SSL_SERVER_V_START</code></td>            <td>string</td>    <td>Validity of server's certificate (start time)</td></tr>
<tr id=H><td><code>SSL_SERVER_V_END</code></td>              <td>string</td>    <td>Validity of server's certificate (end time)</td></tr>
<tr id=D><td><code>SSL_SERVER_A_SIG</code></td>              <td>string</td>    <td>Algorithm used for the signature of server's certificate</td></tr>
<tr id=H><td><code>SSL_SERVER_A_KEY</code></td>              <td>string</td>    <td>Algorithm used for the public key of server's certificate</td></tr>
<tr id=D><td><code>SSL_SERVER_CERT</code></td>               <td>string</td>    <td>PEM-encoded server certificate</td></tr>
</table>
[ where <em>x509</em> is a component of a X.509 DN:
  <code>C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email</code> ]
</float>


<p>
<br>
<h2>Custom Log Formats</h2>

When mod_ssl is built into Apache or at least loaded (under DSO situation)
additional functions exist for the <a
href="../mod_log_config.html#formats">Custom Log Format</a> of <a
href="../mod_log_config.html">mod_log_config</a>.  First there is an additional
``<code>%{</code><em>varname</em><code>}x</code>'' eXtension format function
which can be used to expand any variables provided by any module, especially
those provided by mod_ssl which can you find in <a href="#table4">Table 4</a>.

<p>
For backward compatibility there is additionally a special
``<code>%{</code><em>name</em><code>}c</code>'' cryptography format function
provided.  Information about this function is provided in the <a
href="ssl_compat.html">Compatibility</a> chapter.

<p>
Example:
<blockquote>
<pre>
CustomLog logs/ssl_request_log \\
          "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
</pre>
</blockquote>