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

<name>mod_ssl</name>
<description>Strong cryptography using the Secure Sockets
Layer (SSL) and Transport Layer Security (TLS) protocols</description>
<status>Extension</status>
<sourcefile>mod_ssl.c</sourcefile>
<identifier>ssl_module</identifier>

<summary>
<p>This module provides SSL v3 and TLS v1.x support for the Apache
HTTP Server. SSL v2 is no longer supported.</p>

<p>This module relies on <a href="http://www.openssl.org/">OpenSSL</a>
to provide the cryptography engine.</p>

<p>Further details, discussion, and examples are provided in the
<a href="../ssl/">SSL documentation</a>.</p>
</summary>

<section id="envvars"><title>Environment Variables</title>

<p>This module can be configured to provide several items of SSL information
as additional environment variables to the SSI and CGI namespace. This
information is not provided by default for performance reasons. (See
<directive>SSLOptions</directive> StdEnvVars, below.) The generated variables
are listed in the table below. For backward compatibility the information can
be made available under different names, too. Look in the <a
href="../ssl/ssl_compat.html">Compatibility</a> chapter for details on the
compatibility variables.</p>

<table border="1">
<columnspec><column width=".3"/><column width=".2"/><column width=".5"/>
</columnspec>
<tr>
 <th><a name="table3">Variable Name:</a></th>
 <th>Value Type:</th>
 <th>Description:</th>
</tr>
<tr><td><code>HTTPS</code></td>                         <td>flag</td>      <td>HTTPS is being used.</td></tr>
<tr><td><code>SSL_PROTOCOL</code></td>                  <td>string</td>    <td>The SSL protocol version (SSLv3, TLSv1, TLSv1.1, TLSv1.2)</td></tr>
<tr><td><code>SSL_SESSION_ID</code></td>                <td>string</td>    <td>The hex-encoded SSL session id</td></tr>
<tr><td><code>SSL_SESSION_RESUMED</code></td>           <td>string</td>    <td>Initial or Resumed SSL Session.  Note: multiple requests may be served over the same (Initial or Resumed) SSL session if HTTP KeepAlive is in use</td></tr>
<tr><td><code>SSL_SECURE_RENEG</code></td>              <td>string</td>    <td><code>true</code> if secure renegotiation is supported, else <code>false</code></td></tr>
<tr><td><code>SSL_CIPHER</code></td>                    <td>string</td>    <td>The cipher specification name</td></tr>
<tr><td><code>SSL_CIPHER_EXPORT</code></td>             <td>string</td>    <td><code>true</code> if cipher is an export cipher</td></tr>
<tr><td><code>SSL_CIPHER_USEKEYSIZE</code></td>         <td>number</td>    <td>Number of cipher bits (actually used)</td></tr>
<tr><td><code>SSL_CIPHER_ALGKEYSIZE</code></td>         <td>number</td>    <td>Number of cipher bits (possible)</td></tr>
<tr><td><code>SSL_COMPRESS_METHOD</code></td>           <td>string</td>    <td>SSL compression method negotiated</td></tr>
<tr><td><code>SSL_VERSION_INTERFACE</code></td>         <td>string</td>    <td>The mod_ssl program version</td></tr>
<tr><td><code>SSL_VERSION_LIBRARY</code></td>           <td>string</td>    <td>The OpenSSL program version</td></tr>
<tr><td><code>SSL_CLIENT_M_VERSION</code></td>          <td>string</td>    <td>The version of the client certificate</td></tr>
<tr><td><code>SSL_CLIENT_M_SERIAL</code></td>           <td>string</td>    <td>The serial of the client certificate</td></tr>
<tr><td><code>SSL_CLIENT_S_DN</code></td>               <td>string</td>    <td>Subject DN in client's certificate</td></tr>
<tr><td><code>SSL_CLIENT_S_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of client's Subject DN</td></tr>
<tr><td><code>SSL_CLIENT_SAN_Email_</code><em>n</em></td> <td>string</td>  <td>Client certificate's subjectAltName extension entries of type rfc822Name</td></tr>
<tr><td><code>SSL_CLIENT_SAN_DNS_</code><em>n</em></td> <td>string</td>    <td>Client certificate's subjectAltName extension entries of type dNSName</td></tr>
<tr><td><code>SSL_CLIENT_SAN_OTHER_msUPN_</code><em>n</em></td> <td>string</td>    <td>Client certificate's subjectAltName extension entries of type otherName, Microsoft User Principal Name form (OID 1.3.6.1.4.1.311.20.2.3)</td></tr>
<tr><td><code>SSL_CLIENT_I_DN</code></td>               <td>string</td>    <td>Issuer DN of client's certificate</td></tr>
<tr><td><code>SSL_CLIENT_I_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of client's Issuer DN</td></tr>
<tr><td><code>SSL_CLIENT_V_START</code></td>            <td>string</td>    <td>Validity of client's certificate (start time)</td></tr>
<tr><td><code>SSL_CLIENT_V_END</code></td>              <td>string</td>    <td>Validity of client's certificate (end time)</td></tr>
<tr><td><code>SSL_CLIENT_V_REMAIN</code></td>           <td>string</td>    <td>Number of days until client's certificate expires</td></tr>
<tr><td><code>SSL_CLIENT_A_SIG</code></td>              <td>string</td>    <td>Algorithm used for the signature of client's certificate</td></tr>
<tr><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><td><code>SSL_CLIENT_CERT</code></td>               <td>string</td>    <td>PEM-encoded client certificate</td></tr>
<tr><td><code>SSL_CLIENT_CERT_CHAIN_</code><em>n</em></td> <td>string</td>    <td>PEM-encoded certificates in client certificate chain</td></tr>
<tr><td><code>SSL_CLIENT_CERT_RFC4523_CEA</code></td>   <td>string</td>    <td>Serial number and issuer of the certificate. The format matches that of the CertificateExactAssertion in RFC4523</td></tr>
<tr><td><code>SSL_CLIENT_VERIFY</code></td>             <td>string</td>    <td><code>NONE</code>, <code>SUCCESS</code>, <code>GENEROUS</code> or <code>FAILED:</code><em>reason</em></td></tr>
<tr><td><code>SSL_SERVER_M_VERSION</code></td>          <td>string</td>    <td>The version of the server certificate</td></tr>
<tr><td><code>SSL_SERVER_M_SERIAL</code></td>           <td>string</td>    <td>The serial of the server certificate</td></tr>
<tr><td><code>SSL_SERVER_S_DN</code></td>               <td>string</td>    <td>Subject DN in server's certificate</td></tr>
<tr><td><code>SSL_SERVER_SAN_Email_</code><em>n</em></td> <td>string</td>  <td>Server certificate's subjectAltName extension entries of type rfc822Name</td></tr>
<tr><td><code>SSL_SERVER_SAN_DNS_</code><em>n</em></td> <td>string</td>    <td>Server certificate's subjectAltName extension entries of type dNSName</td></tr>
<tr><td><code>SSL_SERVER_SAN_OTHER_dnsSRV_</code><em>n</em></td> <td>string</td>    <td>Server certificate's subjectAltName extension entries of type otherName, SRVName form (OID 1.3.6.1.5.5.7.8.7, RFC 4985)</td></tr>
<tr><td><code>SSL_SERVER_S_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of server's Subject DN</td></tr>
<tr><td><code>SSL_SERVER_I_DN</code></td>               <td>string</td>    <td>Issuer DN of server's certificate</td></tr>
<tr><td><code>SSL_SERVER_I_DN_</code><em>x509</em></td> <td>string</td>    <td>Component of server's Issuer DN</td></tr>
<tr><td><code>SSL_SERVER_V_START</code></td>            <td>string</td>    <td>Validity of server's certificate (start time)</td></tr>
<tr><td><code>SSL_SERVER_V_END</code></td>              <td>string</td>    <td>Validity of server's certificate (end time)</td></tr>
<tr><td><code>SSL_SERVER_A_SIG</code></td>              <td>string</td>    <td>Algorithm used for the signature of server's certificate</td></tr>
<tr><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><td><code>SSL_SERVER_CERT</code></td>               <td>string</td>    <td>PEM-encoded server certificate</td></tr>
<tr><td><code>SSL_SRP_USER</code></td>                  <td>string</td>    <td>SRP username</td></tr>
<tr><td><code>SSL_SRP_USERINFO</code></td>              <td>string</td>    <td>SRP user info</td></tr>
<tr><td><code>SSL_TLS_SNI</code></td>                   <td>string</td>    <td>Contents of the SNI TLS extension (if supplied with ClientHello)</td></tr>
</table>

<p><em>x509</em> specifies a component of an X.509 DN; one of
<code>C,ST,L,O,OU,CN,T,I,G,S,D,UID,Email</code>.  In httpd 2.2.0 and
later, <em>x509</em> may also include a numeric <code>_n</code>
suffix.  If the DN in question contains multiple attributes of the
same name, this suffix is used as a zero-based index to select a
particular attribute.  For example, where the server certificate
subject DN included two OU attributes, <code>SSL_SERVER_S_DN_OU_0</code>
and
<code>SSL_SERVER_S_DN_OU_1</code> could be used to reference each.  A
variable name without a <code>_n</code> suffix is equivalent to that
name with a <code>_0</code> suffix; the first (or only) attribute.
When the environment table is populated using
the <code>StdEnvVars</code> option of
the <directive module="mod_ssl">SSLOptions</directive> directive, the
first (or only) attribute of any DN is added only under a non-suffixed
name; i.e. no <code>_0</code> suffixed entries are added.</p>

<p>In httpd 2.4.32 and later, an optional <em>_RAW</em> suffix may be
added to <em>x509</em> in a DN component, to suppress conversion of
the attribute value to UTF-8. This must be placed after the index
suffix (if any). For example, <code>SSL_SERVER_S_DN_OU_RAW</code> or
<code>SSL_SERVER_S_DN_OU_0_RAW</code> could be used.</p>

<p>The format of the <em>*_DN</em> variables has changed in Apache HTTPD
2.3.11. See the <code>LegacyDNStringFormat</code> option for
<directive module="mod_ssl">SSLOptions</directive> for details.</p>

<p><code>SSL_CLIENT_V_REMAIN</code> is only available in version 2.1
and later.</p>

<p>A number of additional environment variables can also be used
in <directive>SSLRequire</directive> expressions, or in custom log
formats:</p>

<note><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
THE_REQUEST            SERVER_NAME           TIME_MIN
REQUEST_FILENAME       SERVER_PORT           TIME_SEC
REQUEST_METHOD         SERVER_PROTOCOL       TIME_WDAY
REQUEST_SCHEME         REMOTE_ADDR           TIME
REQUEST_URI            REMOTE_USER</pre></note>

<p>In these contexts, two special formats can also be used:</p>

<dl>
  <dt><code>ENV:<em>variablename</em></code></dt>
  <dd>This will expand to the standard environment
  variable <em>variablename</em>.</dd>

  <dt><code>HTTP:<em>headername</em></code></dt>
  <dd>This will expand to the value of the request header with name
  <em>headername</em>.</dd>
</dl>

</section>

<section id="logformats"><title>Custom Log Formats</title>

<p>When <module>mod_ssl</module> 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
<module>mod_log_config</module>. 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 the above table.</p>
<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/ssl_compat.html">Compatibility</a> chapter.</p>
<example><title>Example</title>
<highlight language="config">
CustomLog "logs/ssl_request_log" "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
</highlight>
</example>
<p>These formats even work without setting the <code>StdEnvVars</code>
option of the <directive module="mod_ssl">SSLOptions</directive>
directive.</p>
</section>

<section id="notes"><title>Request Notes</title>

<p><module>mod_ssl</module> sets "notes" for the request which can be
used in logging with the <code>%{<em>name</em>}n</code> format
string in <module>mod_log_config</module>.</p>

<p>The notes supported are as follows:</p>

<dl>
  <dt><code>ssl-access-forbidden</code></dt>
  <dd>This note is set to the value <code>1</code> if access was
  denied due to an <directive>SSLRequire</directive>
  or <directive>SSLRequireSSL</directive> directive.</dd>

  <dt><code>ssl-secure-reneg</code></dt>
  <dd>If <module>mod_ssl</module> is built against a version of
  OpenSSL which supports the secure renegotiation extension, this note
  is set to the value <code>1</code> if SSL is in used for the current
  connection, and the client also supports the secure renegotiation
  extension.  If the client does not support the secure renegotiation
  extension, the note is set to the value <code>0</code>.
  If <module>mod_ssl</module> is not built against a version of
  OpenSSL which supports secure renegotiation, or if SSL is not in use
  for the current connection, the note is not set.</dd>
</dl>

</section>

<section id="expressionparser"><title>Expression Parser Extension</title>

<p>When <module>mod_ssl</module> is built into Apache or at least
loaded (under DSO situation) any <a name="envvars">variables</a>
provided by <module>mod_ssl</module> can be used in expressions
for the <a href="../expr.html">ap_expr Expression Parser</a>.
The variables can be referenced using the syntax
``<code>%{</code><em>varname</em><code>}</code>''. Starting
with version 2.4.18 one can also use the
<module>mod_rewrite</module> style syntax
``<code>%{SSL:</code><em>varname</em><code>}</code>'' or
the function style syntax
``<code>ssl(</code><em>varname</em><code>)</code>''.</p>
<example><title>Example (using <module>mod_headers</module>)</title>
<highlight language="config">
Header set X-SSL-PROTOCOL "expr=%{SSL_PROTOCOL}"
Header set X-SSL-CIPHER "expr=%{SSL:SSL_CIPHER}"
</highlight>
</example>
<p>This feature even works without setting the <code>StdEnvVars</code>
option of the <directive module="mod_ssl">SSLOptions</directive>
directive.</p>
</section>

<section id="authzproviders"><title>Authorization providers for use with Require</title>

  <p><module>mod_ssl</module> provides a few authentication providers for use
  with <module>mod_authz_core</module>'s
  <directive module="mod_authz_core">Require</directive> directive.</p>

  <section id="reqssl"><title>Require ssl</title>

    <p>The <code>ssl</code> provider denies access if a connection is not
       encrypted with SSL. This is similar to the
       <directive>SSLRequireSSL</directive> directive.</p>

    <highlight language="config">
      Require ssl
    </highlight>

  </section>

  <section id="reqverifyclient"><title>Require ssl-verify-client</title>

    <p>The <code>ssl</code> provider allows access if the user is
       authenticated with a valid client certificate. This is only
       useful if <code>SSLVerifyClient optional</code> is in effect.</p>

    <p>The following example grants access if the user is authenticated
       either with a client certificate or by username and password.</p>

    <highlight language="config">
Require ssl-verify-client
Require valid-user
    </highlight>

  </section>

</section>

<directivesynopsis>
<name>SSLPassPhraseDialog</name>
<description>Type of pass phrase dialog for encrypted private
keys</description>
<syntax>SSLPassPhraseDialog <em>type</em></syntax>
<default>SSLPassPhraseDialog builtin</default>
<contextlist><context>server config</context></contextlist>

<usage>
<p>
When Apache starts up it has to read the various Certificate (see
<directive module="mod_ssl">SSLCertificateFile</directive>) and
Private Key (see <directive
module="mod_ssl">SSLCertificateKeyFile</directive>) 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>:</p>
<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>
    <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>

<li><code>|/path/to/program [args...]</code>

   <p>This mode allows an external program to be used which acts as a
   pipe to a particular input device; the program is sent the standard
   prompt text used for the <code>builtin</code> mode on
   <code>stdin</code>, and is expected to write password strings on
   <code>stdout</code>.  If several passwords are needed (or an
   incorrect password is entered), additional prompt text will be
   written subsequent to the first password being returned, and more
   passwords must then be written back.</p></li>

<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>'', ``<code>DSA</code>'', ``<code>ECC</code>'' or an
    integer index starting at 3 if more than three keys are configured), which
    indicate for which server and algorithm it has to print the corresponding
    Pass Phrase to <code>stdout</code>. In versions 2.4.8 (unreleased)
    and 2.4.9, it is called with one argument, a string of the
    form ``<code>servername:portnumber:index</code>'' (with <code>index</code>
    being a zero-based integer number), which indicate the server, TCP port
    and certificate number.  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>
    <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>
    <p>
    The reuse-algorithm above is used here, too. In other words: The external
    program is called only once per unique Pass Phrase.</p></li>
</ul>
<example><title>Example</title>
<highlight language="config">
SSLPassPhraseDialog "exec:/usr/local/apache/sbin/pp-filter"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLRandomSeed</name>
<description>Pseudo Random Number Generator (PRNG) seeding
source</description>
<syntax>SSLRandomSeed <em>context</em> <em>source</em>
[<em>bytes</em>]</syntax>
<contextlist><context>server config</context></contextlist>

<usage>
<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>
<p>
The following <em>source</em> variants are available:</p>
<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 a randomly
    chosen 128 bytes extract of the stack.
    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>
<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
    derivatives like FreeBSD and Linux).</p>
    <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></li>

<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>
<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.</p></li>
</ul>
<example><title>Example</title>
<highlight language="config">
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
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSessionCache</name>
<description>Type of the global/inter-process SSL Session
Cache</description>
<syntax>SSLSessionCache <em>type</em></syntax>
<default>SSLSessionCache none</default>
<contextlist><context>server config</context></contextlist>

<usage>
<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 unnecessary session handshakes.</p>
<p>
The following five storage <em>type</em>s are currently supported:</p>
<ul>
<li><code>none</code>

    <p>This disables the global/inter-process Session Cache.  This
    will incur a noticeable speed penalty and may cause problems if
    using certain browsers, particularly if client certificates are
    enabled.  This setting is not recommended.</p></li>

<li><code>nonenotnull</code>

    <p>This disables any global/inter-process Session Cache.  However
    it does force OpenSSL to send a non-null session ID to
    accommodate buggy clients that require one.</p></li>

<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. This session cache may suffer reliability issues under
    high load. To use this, ensure that
    <module>mod_socache_dbm</module> is loaded.</p></li>

<li><code>shmcb:/path/to/datafile</code>[<code>(</code><em>size</em><code>)</code>]

    <p>This makes use of a high-performance cyclic buffer
    (approx. <em>size</em> 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 is the recommended session cache. To use this,
    ensure that <module>mod_socache_shmcb</module> is loaded.</p></li>

<li><code>dc:UNIX:/path/to/socket</code>

    <p>This makes use of the <a
    href="http://distcache.sourceforge.net/">distcache</a> distributed session
    caching libraries.  The argument should specify the location of
    the server or proxy to be used using the distcache address syntax;
    for example, <code>UNIX:/path/to/socket</code> specifies a UNIX
    domain socket (typically a local dc_client proxy);
    <code>IP:server.example.com:9001</code> specifies an IP
    address. To use this, ensure that
    <module>mod_socache_dc</module> is loaded.</p></li>

</ul>

<example><title>Examples</title>
<highlight language="config">
SSLSessionCache "dbm:/usr/local/apache/logs/ssl_gcache_data"
SSLSessionCache "shmcb:/usr/local/apache/logs/ssl_gcache_data(512000)"
</highlight>
</example>

<p>The <code>ssl-cache</code> mutex is used to serialize access to
the session cache to prevent corruption.  This mutex can be configured
using the <directive module="core">Mutex</directive> directive.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSessionCacheTimeout</name>
<description>Number of seconds before an SSL session expires
in the Session Cache</description>
<syntax>SSLSessionCacheTimeout <em>seconds</em></syntax>
<default>SSLSessionCacheTimeout 300</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Applies also to RFC 5077 TLS session resumption in Apache 2.4.10 and later</compatibility>

<usage>
<p>
This directive sets the timeout in seconds for the information stored in the
global/inter-process SSL Session Cache, the OpenSSL internal memory cache and
for sessions resumed by TLS session resumption (RFC 5077).
It can be set as low as 15 for testing, but should be set to higher
values like 300 in real life.</p>
<example><title>Example</title>
<highlight language="config">
SSLSessionCacheTimeout 600
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLEngine</name>
<description>SSL Engine Operation Switch</description>
<syntax>SSLEngine on|off|optional</syntax>
<default>SSLEngine off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>
This directive toggles the usage of the SSL/TLS Protocol Engine. This
is should be used inside a <directive module="core"
type="section">VirtualHost</directive> section to enable SSL/TLS for a
that virtual host. By default the SSL/TLS Protocol Engine is
disabled for both the main server and all configured virtual hosts.</p>
<example><title>Example</title>
<highlight language="config">
&lt;VirtualHost _default_:443&gt;
SSLEngine on
#...
&lt;/VirtualHost&gt;
</highlight>
</example>
<p>In Apache 2.1 and later, <directive>SSLEngine</directive> can be set to
<code>optional</code>. This enables support for
<a href="http://www.ietf.org/rfc/rfc2817.txt">RFC 2817</a>, Upgrading to TLS
Within HTTP/1.1. At this time no web browsers support RFC 2817.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLFIPS</name>
<description>SSL FIPS mode Switch</description>
<syntax>SSLFIPS on|off</syntax>
<default>SSLFIPS off</default>
<contextlist><context>server config</context></contextlist>

<usage>
<p>
This directive toggles the usage of the SSL library FIPS_mode flag.
It must be set in the global server context and cannot be configured
with conflicting settings (SSLFIPS on followed by SSLFIPS off or
similar).  The mode applies to all SSL library operations.
</p>
<p>
If httpd was compiled against an SSL library which did not support
the FIPS_mode flag, <code>SSLFIPS on</code> will fail.  Refer to the
FIPS 140-2 Security Policy document of the SSL provider library for
specific requirements to use mod_ssl in a FIPS 140-2 approved mode
of operation; note that mod_ssl itself is not validated, but may be
described as using FIPS 140-2 validated cryptographic module, when
all components are assembled and operated under the guidelines imposed
by the applicable Security Policy.
</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProtocol</name>
<description>Configure usable SSL/TLS protocol versions</description>
<syntax>SSLProtocol [+|-]<em>protocol</em> ...</syntax>
<default>SSLProtocol all -SSLv3 (up to 2.4.16: all)</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>
This directive can be used to control which versions of the SSL/TLS protocol
will be accepted in new connections.</p>
<p>
The available (case-insensitive) <em>protocol</em>s are:</p>
<ul>
<li><code>SSLv3</code>
    <p>
    This is the Secure Sockets Layer (SSL) protocol, version 3.0, from
    the Netscape Corporation.
    It is the successor to SSLv2 and the predecessor to TLSv1, but is
    deprecated in <a href="http://www.ietf.org/rfc/rfc7568.txt">RFC 7568</a>.</p></li>

<li><code>TLSv1</code>
    <p>
    This is the Transport Layer Security (TLS) protocol, version 1.0.
    It is the successor to SSLv3 and is defined in
    <a href="http://www.ietf.org/rfc/rfc2246.txt">RFC 2246</a>.
    It is supported by nearly every client.</p></li>

<li><code>TLSv1.1</code> (when using OpenSSL 1.0.1 and later)
    <p>
    A revision of the TLS 1.0 protocol, as defined in
    <a href="http://www.ietf.org/rfc/rfc4346.txt">RFC 4346</a>.</p></li>

<li><code>TLSv1.2</code> (when using OpenSSL 1.0.1 and later)
    <p>
    A revision of the TLS 1.1 protocol, as defined in
    <a href="http://www.ietf.org/rfc/rfc5246.txt">RFC 5246</a>.</p></li>

<li><code>TLSv1.3</code> (when using OpenSSL 1.1.1 and later)
    <p>
    A new version of the TLS protocol, as defined in
    <a href="http://www.ietf.org/rfc/rfc8446.txt">RFC 8446</a>.</p></li>

<li><code>all</code>
    <p>
    This is a shortcut for ``<code>+SSLv3 +TLSv1</code>'' or
    - when using OpenSSL 1.0.1 and later -
    ``<code>+SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2</code>'', respectively
    (except for OpenSSL versions compiled with the ``no-ssl3'' configuration
    option, where <code>all</code> does not include <code>+SSLv3</code>).</p></li>
</ul>
<example><title>Example</title>
<highlight language="config">
SSLProtocol TLSv1
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCipherSuite</name>
<description>Cipher Suite available for negotiation in SSL
handshake</description>
<syntax>SSLCipherSuite [<em>protocol</em>] <em>cipher-spec</em></syntax>
<default>SSLCipherSuite DEFAULT (depends on OpenSSL version)</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
<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. The optional 
protocol specifier can configure the Cipher Suite for a specific SSL version.
Possible values include "SSL" for all SSL Protocols up to and including TLSv1.2.
</p>
<p>
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 renegotiation with the
reconfigured Cipher Suite after the HTTP request was read but before the HTTP
response is sent.</p>
<p>
If the SSL library supports TLSv1.3 (OpenSSL 1.1.1 and later), the protocol 
specifier "TLSv1.3" can be used to configure the cipher suites for that protocol.
Since TLSv1.3 does not offer renegotiations, specifying ciphers for it in
a directory context is not allowed.</p>
<p>
For a list of TLSv1.3 cipher names, see 
<a href="https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ciphersuites.html">the OpenSSL
documentation</a>.</p>
<p>
An SSL cipher specification in <em>cipher-spec</em> is composed of 4 major
attributes plus a few extra minor ones:</p>
<ul>
<li><em>Key Exchange Algorithm</em>:<br />
    RSA, Diffie-Hellman, Elliptic Curve Diffie-Hellman, Secure Remote Password
</li>
<li><em>Authentication Algorithm</em>:<br />
    RSA, Diffie-Hellman, DSS, ECDSA, or none.
</li>
<li><em>Cipher/Encryption Algorithm</em>:<br />
    AES, DES, Triple-DES, RC4, RC2, IDEA, etc.
</li>
<li><em>MAC Digest Algorithm</em>:<br />
    MD5, SHA or SHA1, SHA256, SHA384.
</li>
</ul>
<p>An SSL cipher can also be an export cipher. SSLv2 ciphers are no longer
supported. 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>). The actually available ciphers and aliases depends on the used
openssl version. Newer openssl versions may include additional ciphers.</p>

<table border="1">
<columnspec><column width=".5"/><column width=".5"/></columnspec>
<tr><th><a name="table1">Tag</a></th> <th>Description</th></tr>
<tr><td colspan="2"><em>Key Exchange Algorithm:</em></td></tr>
<tr><td><code>kRSA</code></td>   <td>RSA key exchange</td></tr>
<tr><td><code>kDHr</code></td>   <td>Diffie-Hellman key exchange with RSA key</td></tr>
<tr><td><code>kDHd</code></td>   <td>Diffie-Hellman key exchange with DSA key</td></tr>
<tr><td><code>kEDH</code></td>   <td>Ephemeral (temp.key) Diffie-Hellman key exchange (no cert)</td>   </tr>
<tr><td><code>kSRP</code></td>   <td>Secure Remote Password (SRP) key exchange</td></tr>
<tr><td colspan="2"><em>Authentication Algorithm:</em></td></tr>
<tr><td><code>aNULL</code></td>  <td>No authentication</td></tr>
<tr><td><code>aRSA</code></td>   <td>RSA authentication</td></tr>
<tr><td><code>aDSS</code></td>   <td>DSS authentication</td> </tr>
<tr><td><code>aDH</code></td>    <td>Diffie-Hellman authentication</td></tr>
<tr><td colspan="2"><em>Cipher Encoding Algorithm:</em></td></tr>
<tr><td><code>eNULL</code></td>  <td>No encryption</td>         </tr>
<tr><td><code>NULL</code></td>   <td>alias for eNULL</td>         </tr>
<tr><td><code>AES</code></td>    <td>AES encryption</td>        </tr>
<tr><td><code>DES</code></td>    <td>DES encryption</td>        </tr>
<tr><td><code>3DES</code></td>   <td>Triple-DES encryption</td> </tr>
<tr><td><code>RC4</code></td>    <td>RC4 encryption</td>       </tr>
<tr><td><code>RC2</code></td>    <td>RC2 encryption</td>       </tr>
<tr><td><code>IDEA</code></td>   <td>IDEA encryption</td>       </tr>
<tr><td colspan="2"><em>MAC Digest Algorithm</em>:</td></tr>
<tr><td><code>MD5</code></td>    <td>MD5 hash function</td></tr>
<tr><td><code>SHA1</code></td>   <td>SHA1 hash function</td></tr>
<tr><td><code>SHA</code></td>    <td>alias for SHA1</td> </tr>
<tr><td><code>SHA256</code></td> <td>SHA256 hash function</td> </tr>
<tr><td><code>SHA384</code></td> <td>SHA384 hash function</td> </tr>
<tr><td colspan="2"><em>Aliases:</em></td></tr>
<tr><td><code>SSLv3</code></td>  <td>all SSL version 3.0 ciphers</td> </tr>
<tr><td><code>TLSv1</code></td>  <td>all TLS version 1.0 ciphers</td> </tr>
<tr><td><code>EXP</code></td>    <td>all export ciphers</td>  </tr>
<tr><td><code>EXPORT40</code></td> <td>all 40-bit export ciphers only</td>  </tr>
<tr><td><code>EXPORT56</code></td> <td>all 56-bit export ciphers only</td>  </tr>
<tr><td><code>LOW</code></td>    <td>all low strength ciphers (no export, single DES)</td></tr>
<tr><td><code>MEDIUM</code></td> <td>all ciphers with 128 bit encryption</td> </tr>
<tr><td><code>HIGH</code></td>   <td>all ciphers using Triple-DES</td>     </tr>
<tr><td><code>RSA</code></td>    <td>all ciphers using RSA key exchange</td> </tr>
<tr><td><code>DH</code></td>     <td>all ciphers using Diffie-Hellman key exchange</td> </tr>
<tr><td><code>EDH</code></td>    <td>all ciphers using Ephemeral Diffie-Hellman key exchange</td> </tr>
<tr><td><code>ECDH</code></td>   <td>Elliptic Curve Diffie-Hellman key exchange</td>   </tr>
<tr><td><code>ADH</code></td>    <td>all ciphers using Anonymous Diffie-Hellman key exchange</td> </tr>
<tr><td><code>AECDH</code></td>    <td>all ciphers using Anonymous Elliptic Curve Diffie-Hellman key exchange</td> </tr>
<tr><td><code>SRP</code></td>    <td>all ciphers using Secure Remote Password (SRP) key exchange</td> </tr>
<tr><td><code>DSS</code></td>    <td>all ciphers using DSS authentication</td> </tr>
<tr><td><code>ECDSA</code></td>    <td>all ciphers using ECDSA authentication</td> </tr>
<tr><td><code>aNULL</code></td>   <td>all ciphers using no authentication</td> </tr>
</table>
<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>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:</p>
<ul>
<li>none: add cipher to list</li>
<li><code>+</code>: move matching ciphers to the current location in list</li>
<li><code>-</code>: remove cipher from list (can be added later again)</li>
<li><code>!</code>: kill cipher from list completely (can <strong>not</strong> be added later again)</li>
</ul>

<note>
<title><code>aNULL</code>, <code>eNULL</code> and <code>EXP</code>
ciphers are always disabled</title>
<p>Beginning with version 2.4.7, null and export-grade
ciphers are always disabled, as mod_ssl unconditionally adds
<code>!aNULL:!eNULL:!EXP</code> to any cipher string at initialization.</p>
</note>

<p>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
depends on the version of the OpenSSL libraries used. Let's suppose it is
``<code>RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5</code>'' which
means the following: Put <code>RC4-SHA</code> and <code>AES128-SHA</code> at
the beginning. We do this, because these ciphers offer a good compromise
between speed and security. Next, include high and medium security ciphers.
Finally, remove all ciphers which do not authenticate, i.e. for SSL the
Anonymous Diffie-Hellman ciphers, as well as all ciphers which use
<code>MD5</code> as hash algorithm, because it has been proven insufficient.</p>
<example>
<pre>
$ openssl ciphers -v 'RC4-SHA:AES128-SHA:HIGH:MEDIUM:!aNULL:!MD5'
RC4-SHA                 SSLv3 Kx=RSA      Au=RSA  Enc=RC4(128)  Mac=SHA1
AES128-SHA              SSLv3 Kx=RSA      Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
...                     ...               ...     ...           ...
SEED-SHA                SSLv3 Kx=RSA      Au=RSA  Enc=SEED(128) Mac=SHA1
PSK-RC4-SHA             SSLv3 Kx=PSK      Au=PSK  Enc=RC4(128)  Mac=SHA1
KRB5-RC4-SHA            SSLv3 Kx=KRB5     Au=KRB5 Enc=RC4(128)  Mac=SHA1
</pre>
</example>
<p>The complete list of particular RSA &amp; DH ciphers for SSL is given in <a
href="#table2">Table 2</a>.</p>
<example><title>Example</title>
<highlight language="config">
SSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW
</highlight>
</example>
<table border="1">
<columnspec><column width=".3"/><column width=".1"/><column width=".13"/>
<column width=".1"/><column width=".13"/><column width=".1"/>
<column width=".13"/></columnspec>
<tr><th><a name="table2">Cipher-Tag</a></th> <th>Protocol</th> <th>Key Ex.</th> <th>Auth.</th> <th>Enc.</th> <th>MAC</th> <th>Type</th> </tr>
<tr><td colspan="7"><em>RSA Ciphers:</em></td></tr>
<tr><td><code>DES-CBC3-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>3DES(168)</td> <td>SHA1</td> <td></td> </tr>
<tr><td><code>IDEA-CBC-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>IDEA(128)</td> <td>SHA1</td> <td></td> </tr>
<tr><td><code>RC4-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>RC4(128)</td> <td>SHA1</td> <td></td> </tr>
<tr><td><code>RC4-MD5</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>RC4(128)</td> <td>MD5</td> <td></td> </tr>
<tr><td><code>DES-CBC-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>DES(56)</td> <td>SHA1</td> <td></td> </tr>
<tr><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><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><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><td><code>NULL-SHA</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>None</td> <td>SHA1</td> <td></td> </tr>
<tr><td><code>NULL-MD5</code></td> <td>SSLv3</td> <td>RSA</td> <td>RSA</td> <td>None</td> <td>MD5</td> <td></td> </tr>
<tr><td colspan="7"><em>Diffie-Hellman Ciphers:</em></td></tr>
<tr><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></td> </tr>
<tr><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></td> </tr>
<tr><td><code>ADH-RC4-MD5</code></td> <td>SSLv3</td> <td>DH</td> <td>None</td> <td>RC4(128)</td> <td>MD5</td> <td></td> </tr>
<tr><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></td> </tr>
<tr><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></td> </tr>
<tr><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></td> </tr>
<tr><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></td> </tr>
<tr><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><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><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><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>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCertificateFile</name>
<description>Server PEM-encoded X.509 certificate data file</description>
<syntax>SSLCertificateFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>
This directive points to a file with certificate data in PEM format.
At a minimum, the file must include an end-entity (leaf) certificate.
The directive can be used multiple times (referencing different filenames)
to support multiple algorithms for server authentication - typically
RSA, DSA, and ECC. The number of supported algorithms depends on the
OpenSSL version being used for mod_ssl: with version 1.0.0 or later,
<code>openssl list-public-key-algorithms</code> will output a list
of supported algorithms, see also the note below about limitations
of OpenSSL versions prior to 1.0.2 and the ways to work around them.
</p>

<p>
The files may also include intermediate CA certificates, sorted from
leaf to root. This is supported with version 2.4.8 and later,
and obsoletes <directive module="mod_ssl">SSLCertificateChainFile</directive>.
When running with OpenSSL 1.0.2 or later, this allows
to configure the intermediate CA chain on a per-certificate basis.
</p>

<p>
Custom DH parameters and an EC curve name for ephemeral keys,
can also be added to end of the first file configured using
<directive module="mod_ssl">SSLCertificateFile</directive>.
This is supported in version 2.4.7 or later.
Such parameters can be generated using the commands
<code>openssl dhparam</code> and <code>openssl ecparam</code>.
The parameters can be added as-is to the end of the first
certificate file. Only the first file can be used for custom
parameters, as they are applied independently of the authentication
algorithm type.
</p>

<p>
Finally the end-entity certificate's private key can also be
added to the certificate file instead of using a separate
<directive module="mod_ssl">SSLCertificateKeyFile</directive>
directive. This practice is highly discouraged. If it is used,
the certificate files using such an embedded key must be configured
after the certificates using a separate key file. If the private
key is encrypted, the pass phrase dialog is forced at startup time.
</p>

<note>
<title>DH parameter interoperability with primes > 1024 bit</title>
<p>
Beginning with version 2.4.7, mod_ssl makes use of
standardized DH parameters with prime lengths of 2048, 3072 and 4096 bits
and with additional prime lengths of 6144 and 8192 bits beginning with
version 2.4.10
(from <a href="http://www.ietf.org/rfc/rfc3526.txt">RFC 3526</a>), and hands
them out to clients based on the length of the certificate's RSA/DSA key.
With Java-based clients in particular (Java 7 or earlier), this may lead
to handshake failures - see this
<a href="../ssl/ssl_faq.html#javadh">FAQ answer</a> for working around
such issues.
</p>
</note>

<note>
<title>Default DH parameters when using multiple certificates and OpenSSL
versions prior to 1.0.2</title>
<p>
When using multiple certificates to support different authentication algorithms
(like RSA, DSA, but mainly ECC) and OpenSSL prior to 1.0.2, it is recommended
to either use custom DH parameters (preferably) by adding them to the
first certificate file (as described above), or to order the
<directive>SSLCertificateFile</directive> directives such that RSA/DSA
certificates are placed <strong>after</strong> the ECC one.
</p>
<p>
This is due to a limitation in older versions of OpenSSL which don't let the
Apache HTTP Server determine the currently selected certificate at handshake
time (when the DH parameters must be sent to the peer) but instead always
provide the last configured certificate. Consequently, the server may select
default DH parameters based on the length of the wrong certificate's key (ECC
keys are much smaller than RSA/DSA ones and their length is not relevant for
selecting DH primes).
</p>
<p>
Since custom DH parameters always take precedence over the default ones, this
issue can be avoided by creating and configuring them (as described above),
thus using a custom/suitable length.
</p>
</note>

<example><title>Example</title>
<highlight language="config">
SSLCertificateFile "/usr/local/apache2/conf/ssl.crt/server.crt"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCertificateKeyFile</name>
<description>Server PEM-encoded private key file</description>
<syntax>SSLCertificateKeyFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>
This directive points to the PEM-encoded private key file for the
server. If the contained private key is encrypted, the pass phrase
dialog is forced at startup time.</p>

<p>
The directive can be used multiple times (referencing different filenames)
to support multiple algorithms for server authentication. For each
<directive module="mod_ssl">SSLCertificateKeyFile</directive>
directive, there must be a matching <directive>SSLCertificateFile</directive>
directive.</p>

<p>
The private key may also be combined with the certificate in the file given by
<directive module="mod_ssl">SSLCertificateFile</directive>, but this practice
is highly discouraged. If it is used, the certificate files using such
an embedded key must be configured after the certificates using a separate
key file.</p>

<example><title>Example</title>
<highlight language="config">
SSLCertificateKeyFile "/usr/local/apache2/conf/ssl.key/server.key"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCertificateChainFile</name>
<description>File of PEM-encoded Server CA Certificates</description>
<syntax>SSLCertificateChainFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<note><title>SSLCertificateChainFile is deprecated</title>
<p><code>SSLCertificateChainFile</code> became obsolete with version 2.4.8,
when <directive module="mod_ssl">SSLCertificateFile</directive>
was extended to also load intermediate CA certificates from the server
certificate file.</p>
</note>

<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 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>
<p>
This should be used alternatively and/or additionally to <directive
module="mod_ssl">SSLCACertificatePath</directive> 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 <directive
module="mod_ssl">SSLCACertificatePath</directive> 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.</p>
<p>
But be careful: Providing the certificate chain works only if you are using a
<em>single</em> RSA <em>or</em> DSA based server certificate. If you are
using a coupled RSA+DSA certificate pair, this will work only if actually both
certificates use the <em>same</em> certificate chain. Else the browsers will be
confused in this situation.</p>
<example><title>Example</title>
<highlight language="config">
SSLCertificateChainFile "/usr/local/apache2/conf/ssl.crt/ca.crt"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCACertificatePath</name>
<description>Directory of PEM-encoded CA Certificates for
Client Auth</description>
<syntax>SSLCACertificatePath <em>directory-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<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>
<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
<em>hash-value</em><code>.N</code>. And you should always make sure this directory
contains the appropriate symbolic links.</p>
<example><title>Example</title>
<highlight language="config">
SSLCACertificatePath "/usr/local/apache2/conf/ssl.crt/"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCACertificateFile</name>
<description>File of concatenated PEM-encoded CA Certificates
for Client Auth</description>
<syntax>SSLCACertificateFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<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
<directive module="mod_ssl">SSLCACertificatePath</directive>.</p>
<example><title>Example</title>
<highlight language="config">
SSLCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-client.crt"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCADNRequestFile</name>
<description>File of concatenated PEM-encoded CA Certificates
for defining acceptable CA names</description>
<syntax>SSLCADNRequestFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>When a client certificate is requested by mod_ssl, a list of
<em>acceptable Certificate Authority names</em> is sent to the client
in the SSL handshake.  These CA names can be used by the client to
select an appropriate client certificate out of those it has
available.</p>

<p>If neither of the directives <directive
module="mod_ssl">SSLCADNRequestPath</directive> or <directive
module="mod_ssl">SSLCADNRequestFile</directive> are given, then the
set of acceptable CA names sent to the client is the names of all the
CA certificates given by the <directive
module="mod_ssl">SSLCACertificateFile</directive> and <directive
module="mod_ssl">SSLCACertificatePath</directive> directives; in other
words, the names of the CAs which will actually be used to verify the
client certificate.</p>

<p>In some circumstances, it is useful to be able to send a set of
acceptable CA names which differs from the actual CAs used to verify
the client certificate - for example, if the client certificates are
signed by intermediate CAs.  In such cases, <directive
module="mod_ssl">SSLCADNRequestPath</directive> and/or <directive
module="mod_ssl">SSLCADNRequestFile</directive> can be used; the
acceptable CA names are then taken from the complete set of
certificates in the directory and/or file specified by this pair of
directives.</p>

<p><directive module="mod_ssl">SSLCADNRequestFile</directive> must
specify an <em>all-in-one</em> file containing a concatenation of
PEM-encoded CA certificates.</p>

<example><title>Example</title>
<highlight language="config">
SSLCADNRequestFile "/usr/local/apache2/conf/ca-names.crt"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCADNRequestPath</name>
<description>Directory of PEM-encoded CA Certificates for
defining acceptable CA names</description>
<syntax>SSLCADNRequestPath <em>directory-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>

<p>This optional directive can be used to specify the set of
<em>acceptable CA names</em> which will be sent to the client when a
client certificate is requested.  See the <directive
module="mod_ssl">SSLCADNRequestFile</directive> directive for more
details.</p>

<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
<em>hash-value</em><code>.N</code>. And you should always make sure
this directory contains the appropriate symbolic links.</p>
<example><title>Example</title>
<highlight language="config">
SSLCADNRequestPath "/usr/local/apache2/conf/ca-names.crt/"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCARevocationPath</name>
<description>Directory of PEM-encoded CA CRLs for
Client Auth</description>
<syntax>SSLCARevocationPath <em>directory-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<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>
<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
<em>hash-value</em><code>.rN</code>. And you should always make sure this directory
contains the appropriate symbolic links.</p>
<example><title>Example</title>
<highlight language="config">
SSLCARevocationPath "/usr/local/apache2/conf/ssl.crl/"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCARevocationFile</name>
<description>File of concatenated PEM-encoded CA CRLs for
Client Auth</description>
<syntax>SSLCARevocationFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<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 <directive
module="mod_ssl">SSLCARevocationPath</directive>.</p>
<example><title>Example</title>
<highlight language="config">
SSLCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-client.crl"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCARevocationCheck</name>
<description>Enable CRL-based revocation checking</description>
<syntax>SSLCARevocationCheck chain|leaf|none <em>flag</em>s</syntax>
<default>SSLCARevocationCheck none</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Optional <em>flag</em>s available in httpd 2.4.21 or
later</compatibility>

<usage>
<p>
Enables certificate revocation list (CRL) checking. At least one of
<directive module="mod_ssl">SSLCARevocationFile</directive>
or <directive module="mod_ssl">SSLCARevocationPath</directive> must be
configured. When set to <code>chain</code> (recommended setting),
CRL checks are applied to all certificates in the chain, while setting it to
<code>leaf</code> limits the checks to the end-entity cert.
</p>
<p>The available <em>flag</em>s are:</p>
<ul>
<li><code>no_crl_for_cert_ok</code>
    <p>
    Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when
    no CRL(s) for the checked certificate(s) were found in any of the locations
    configured with <directive module="mod_ssl">SSLCARevocationFile</directive>
    or <directive module="mod_ssl">SSLCARevocationPath</directive>.
    </p>
    <p>
    With the introduction of <directive>SSLCARevocationFile</directive>,
    the behavior has been changed: by default with <code>chain</code> or
    <code>leaf</code>, CRLs <strong>must</strong> be present for the
    validation to succeed - otherwise it will fail with an
    <code>"unable to get certificate CRL"</code> error.
    </p>
    <p>
    The <em>flag</em> <code>no_crl_for_cert_ok</code> allows to restore
    previous behaviour.
    </p>
</li>
</ul>
<example><title>Example</title>
<highlight language="config">
SSLCARevocationCheck chain
</highlight>
</example>
<example><title>Compatibility with versions 2.2</title>
<highlight language="config">
SSLCARevocationCheck chain no_crl_for_cert_ok
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLVerifyClient</name>
<description>Type of Client Certificate verification</description>
<syntax>SSLVerifyClient <em>level</em></syntax>
<default>SSLVerifyClient none</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
<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 renegotiation with the
reconfigured client verification level after the HTTP request was read but
before the HTTP response is sent.</p>
<p>
The following levels are available for <em>level</em>:</p>
<ul>
<li><strong>none</strong>:
     no client Certificate is required at all</li>
<li><strong>optional</strong>:
     the client <em>may</em> present a valid Certificate</li>
<li><strong>require</strong>:
     the client <em>has to</em> present a valid Certificate</li>
<li><strong>optional_no_ca</strong>:
     the client may present a valid Certificate<br />
     but it need not to be (successfully) verifiable. This option
     cannot be relied upon for client authentication.  </li>
</ul>
<example><title>Example</title>
<highlight language="config">
SSLVerifyClient require
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLVerifyDepth</name>
<description>Maximum depth of CA Certificates in Client
Certificate verification</description>
<syntax>SSLVerifyDepth <em>number</em></syntax>
<default>SSLVerifyDepth 1</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
<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 renegotiation with the reconfigured client verification depth after the
HTTP request was read but before the HTTP response is sent.</p>
<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
<directive module="mod_ssl">SSLCACertificatePath</directive>), etc.</p>
<example><title>Example</title>
<highlight language="config">
SSLVerifyDepth 10
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSRPVerifierFile</name>
<description>Path to SRP verifier file</description>
<syntax>SSLSRPVerifierFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or
later</compatibility>

<usage>
<p>
This directive enables TLS-SRP and sets the path to the OpenSSL SRP (Secure
Remote Password) verifier file containing TLS-SRP usernames, verifiers, salts,
and group parameters.</p>
<example><title>Example</title>
SSLSRPVerifierFile "/path/to/file.srpv"
</example>
<p>
The verifier file can be created with the <code>openssl</code> command line
utility:</p>
<example><title>Creating the SRP verifier file</title>
openssl srp -srpvfile passwd.srpv -userinfo "some info" -add username
</example>
<p> The value given with the optional <code>-userinfo</code> parameter is
avalable in the <code>SSL_SRP_USERINFO</code> request environment variable.</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSRPUnknownUserSeed</name>
<description>SRP unknown user seed</description>
<syntax>SSLSRPUnknownUserSeed <em>secret-string</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.4 and later, if using OpenSSL 1.0.1 or
later</compatibility>

<usage>
<p>
This directive sets the seed used to fake SRP user parameters for unknown
users, to avoid leaking whether a given user exists. Specify a secret
string. If this directive is not used, then Apache will return the
UNKNOWN_PSK_IDENTITY alert to clients who specify an unknown username.
</p>
<example><title>Example</title>
SSLSRPUnknownUserSeed "secret"
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOptions</name>
<description>Configure various SSL engine run-time options</description>
<syntax>SSLOptions [+|-]<em>option</em> ...</syntax>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
<context>.htaccess</context></contextlist>
<override>Options</override>

<usage>
<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>
<p>
The available <em>option</em>s are:</p>
<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>
<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><em>n</em> (with <em>n</em> = 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>
<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>

    <p>Note that the <directive module="mod_auth_basic">AuthBasicFake</directive>
    directive within <module>mod_auth_basic</module> can be used as a more
    general mechanism for faking basic authentication, giving control over the
    structure of both the username and password.</p>
</li>
<li><code>StrictRequire</code>
    <p>
    This <em>forces</em> 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
    <code>Satisfy</code> 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>
<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 <em>every</em> per-directory reconfiguration of
    SSL parameters causes a <em>full</em> 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 may not be what the user expects, so enable this on a
    per-directory basis only, please.</p>
</li>
<li><code>LegacyDNStringFormat</code>
    <p>
    This option influences how values of the
    <code>SSL_{CLIENT,SERVER}_{I,S}_DN</code> variables are formatted. Since
    version 2.3.11, Apache HTTPD uses a RFC 2253 compatible format by
    default. This uses commas as delimiters between the attributes, allows the
    use of non-ASCII characters (which are converted to UTF8), escapes
    various special characters with backslashes, and sorts the attributes
    with the "C" attribute last.</p>

    <p>If <code>LegacyDNStringFormat</code> is set, the old format will be
    used which sorts the "C" attribute first, uses slashes as separators, and
    does not handle non-ASCII and special characters in any consistent way.
    </p>
</li>
</ul>
<example><title>Example</title>
<highlight language="config">
SSLOptions +FakeBasicAuth -StrictRequire
&lt;Files ~ "\.(cgi|shtml)$"&gt;
    SSLOptions +StdEnvVars -ExportCertData
&lt;/Files&gt;
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLRequireSSL</name>
<description>Deny access when SSL is not used for the
HTTP request</description>
<syntax>SSLRequireSSL</syntax>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
<p><!-- XXX: I think the syntax is wrong -->
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><title>Example</title>
<highlight language="config">
SSLRequireSSL
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLRequire</name>
<description>Allow access only when an arbitrarily complex
boolean expression is true</description>
<syntax>SSLRequire <em>expression</em></syntax>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>

<note><title>SSLRequire is deprecated</title>
<p><code>SSLRequire</code> is deprecated and should in general be replaced
by <a href="mod_authz_core.html#reqexpr">Require expr</a>. The so called
<a href="../expr.html">ap_expr</a> syntax of <code>Require expr</code> is
a superset of the syntax of <code>SSLRequire</code>, with the following
exception:</p>

<p>In <code>SSLRequire</code>, the comparison operators <code>&lt;</code>,
<code>&lt;=</code>, ... are completely equivalent to the operators
<code>lt</code>, <code>le</code>, ... and work in a somewhat peculiar way that
first compares the length of two strings and then the lexical order.
On the other hand, <a href="../expr.html">ap_expr</a> has two sets of
comparison operators: The operators <code>&lt;</code>,
<code>&lt;=</code>, ... do lexical string comparison, while the operators
<code>-lt</code>, <code>-le</code>, ... do integer comparison.
For the latter, there are also aliases without the leading dashes:
<code>lt</code>, <code>le</code>, ...
</p>

</note>

<p>
This directive specifies a general access requirement which has to be
fulfilled in order to allow access. It is a very powerful directive because the
requirement specification is an arbitrarily complex boolean expression
containing any number of access checks.</p>
<p>
The <em>expression</em> must match the following syntax (given as a BNF
grammar notation):</p>
<blockquote>
<pre>
expr     ::= "<strong>true</strong>" | "<strong>false</strong>"
           | "<strong>!</strong>" expr
           | expr "<strong>&amp;&amp;</strong>" expr
           | expr "<strong>||</strong>" expr
           | "<strong>(</strong>" expr "<strong>)</strong>"
           | comp

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

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

word     ::= digit
           | cstring
           | variable
           | function

digit    ::= [0-9]+
cstring  ::= "..."
variable ::= "<strong>%{</strong>" varname "<strong>}</strong>"
function ::= funcname "<strong>(</strong>" funcargs "<strong>)</strong>"
</pre>
</blockquote>
<p>For <code>varname</code> any of the variables described in <a
href="#envvars">Environment Variables</a> can be used.  For
<code>funcname</code> the available functions are listed in
the <a href="../expr.html#functions">ap_expr documentation</a>.</p>

<p>The <em>expression</em> is parsed into an internal machine
representation when the configuration is loaded, and then evaluated 
during request processing.  In .htaccess context, the <em>expression</em> is 
both parsed and executed each time the .htaccess file is encountered during 
request processing.</p>

<example><title>Example</title>
<highlight language="config">
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} -ge 1 and %{TIME_WDAY} -le 5          \
            and %{TIME_HOUR} -ge 8 and %{TIME_HOUR} -le 20       ) \
           or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/
</highlight>
</example>

<p>The <code>PeerExtList(<em>object-ID</em>)</code> function expects
to find zero or more instances of the X.509 certificate extension
identified by the given <em>object ID</em> (OID) in the client certificate.
The expression evaluates to true if the left-hand side string matches
exactly against the value of an extension identified with this OID.
(If multiple extensions with the same OID are present, at least one
extension must match).</p>

<example><title>Example</title>
<highlight language="config">
SSLRequire "foobar" in PeerExtList("1.2.3.4.5.6")
</highlight>
</example>

<note><title>Notes on the PeerExtList function</title>

<ul>

<li><p>The object ID can be specified either as a descriptive
name recognized by the SSL library, such as <code>"nsComment"</code>,
or as a numeric OID, such as <code>"1.2.3.4.5.6"</code>.</p></li>

<li><p>Expressions with types known to the SSL library are rendered to
a string before comparison.  For an extension with a type not
recognized by the SSL library, mod_ssl will parse the value if it is
one of the primitive ASN.1 types UTF8String, IA5String, VisibleString,
or BMPString.  For an extension of one of these types, the string
value will be converted to UTF-8 if necessary, then compared against
the left-hand-side expression.</p></li>

</ul>
</note>

</usage>
<seealso><a href="../env.html">Environment Variables in Apache HTTP Server</a>,
for additional examples.
</seealso>
<seealso><a href="mod_authz_core.html#reqexpr">Require expr</a></seealso>
<seealso><a href="../expr.html">Generic expression syntax in Apache HTTP Server</a>
</seealso>
</directivesynopsis>

<directivesynopsis>
<name>SSLRenegBufferSize</name>
<description>Set the size for the SSL renegotiation buffer</description>
<syntax>SSLRenegBufferSize <var>bytes</var></syntax>
<default>SSLRenegBufferSize 131072</default>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>

<p>If an SSL renegotiation is required in per-location context, for
example, any use of <directive
module="mod_ssl">SSLVerifyClient</directive> in a Directory or
Location block, then <module>mod_ssl</module> must buffer any HTTP
request body into memory until the new SSL handshake can be performed.
This directive can be used to set the amount of memory that will be
used for this buffer. </p>

<note type="warning"><p>
Note that in many configurations, the client sending the request body
will be untrusted so a denial of service attack by consumption of
memory must be considered when changing this configuration setting.
</p></note>

<example><title>Example</title>
<highlight language="config">
SSLRenegBufferSize 262144
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStrictSNIVHostCheck</name>
<description>Whether to allow non-SNI clients to access a name-based virtual
host.
</description>
<syntax>SSLStrictSNIVHostCheck on|off</syntax>
<default>SSLStrictSNIVHostCheck off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in Apache 2.2.12 and later</compatibility>

<usage>
<p>
This directive sets whether a non-SNI client is allowed to access a name-based
virtual host. If set to <code>on</code> in the default name-based virtual
host, clients that are SNI unaware will not be allowed to access <em>any</em>
virtual host, belonging to this particular IP / port combination.
If set to <code>on</code> in any other virtual host, SNI unaware clients
are not allowed to access this particular virtual host.
</p>

<note type="warning"><p>
This option is only available if httpd was compiled against an SNI capable
version of OpenSSL.
</p></note>

<example><title>Example</title>
<highlight language="config">
SSLStrictSNIVHostCheck on
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyMachineCertificatePath</name>
<description>Directory of PEM-encoded client certificates and keys to be used by the proxy</description>
<syntax>SSLProxyMachineCertificatePath <em>directory</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the directory where you keep the certificates and
keys used for authentication of the proxy server to remote servers.
</p>
<p>The files in this directory must be PEM-encoded and are accessed through
hash filenames. Additionally, you must create symbolic links named
<code><em>hash-value</em>.N</code>. And you should always make sure this
directory contains the appropriate symbolic links.</p>
<note type="warning">
<p>Currently there is no support for encrypted private keys</p>
</note>
<example><title>Example</title>
<highlight language="config">
SSLProxyMachineCertificatePath "/usr/local/apache2/conf/proxy.crt/"
</highlight>
</example>
</usage>
</directivesynopsis>


<directivesynopsis>
<name>SSLProxyMachineCertificateFile</name>
<description>File of concatenated PEM-encoded client certificates and keys to be used by the proxy</description>
<syntax>SSLProxyMachineCertificateFile <em>filename</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the all-in-one file where you keep the certificates and
keys used for authentication of the proxy server to remote servers.
</p>
<p>
This referenced file is simply the concatenation of the various PEM-encoded
certificate files, in order of preference. Use this directive alternatively
or additionally to <code>SSLProxyMachineCertificatePath</code>.
</p>
<note type="warning">
<p>Currently there is no support for encrypted private keys</p>
</note>
<example><title>Example</title>
<highlight language="config">
SSLProxyMachineCertificateFile "/usr/local/apache2/conf/ssl.crt/proxy.pem"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyMachineCertificateChainFile</name>
<description>File of concatenated PEM-encoded CA certificates to be used by the proxy for choosing a certificate</description>
<syntax>SSLProxyMachineCertificateChainFile <em>filename</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the all-in-one file where you keep the certificate chain
for all of the client certs in use. This directive will be needed if the
remote server presents a list of CA certificates that are not direct signers
of one of the configured client certificates.
</p>
<p>
This referenced file is simply the concatenation of the various PEM-encoded
certificate files. Upon startup, each client certificate configured will
be examined and a chain of trust will be constructed.
</p>
<note type="warning"><title>Security warning</title>
<p>If this directive is enabled, all of the certificates in the file will be
trusted as if they were also in <directive module="mod_ssl">
SSLProxyCACertificateFile</directive>.</p>
</note>
<example><title>Example</title>
<highlight language="config">
SSLProxyMachineCertificateChainFile "/usr/local/apache2/conf/ssl.crt/proxyCA.pem"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyVerify</name>
<description>Type of remote server Certificate verification</description>
<syntax>SSLProxyVerify <em>level</em></syntax>
<default>SSLProxyVerify none</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>

<p>When a proxy is configured to forward requests to a remote SSL
server, this directive can be used to configure certificate
verification of the remote server. </p>
<p>
The following levels are available for <em>level</em>:</p>
<ul>
<li><strong>none</strong>:
     no remote server Certificate is required at all</li>
<li><strong>optional</strong>:
     the remote server <em>may</em> present a valid Certificate</li>
<li><strong>require</strong>:
     the remote server <em>has to</em> present a valid Certificate</li>
<li><strong>optional_no_ca</strong>:
     the remote server may present a valid Certificate<br />
     but it need not to be (successfully) verifiable.</li>
</ul>
<p>In practice only levels <strong>none</strong> and
<strong>require</strong> are really interesting, because level
<strong>optional</strong> doesn't work with all servers 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><title>Example</title>
<highlight language="config">
SSLProxyVerify require
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyVerifyDepth</name>
<description>Maximum depth of CA Certificates in Remote Server
Certificate verification</description>
<syntax>SSLProxyVerifyDepth <em>number</em></syntax>
<default>SSLProxyVerifyDepth 1</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets how deeply mod_ssl should verify before deciding that the
remote server does not have a valid certificate. </p>
<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 remote server certificate. A depth of 0 means that self-signed
remote server certificates are accepted only, the default depth of 1 means
the remote server 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
<directive module="mod_ssl">SSLProxyCACertificatePath</directive>), etc.</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyVerifyDepth 10
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCheckPeerExpire</name>
<description>Whether to check if remote server certificate is expired
</description>
<syntax>SSLProxyCheckPeerExpire on|off</syntax>
<default>SSLProxyCheckPeerExpire on</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets whether it is checked if the remote server certificate
is expired or not. If the check fails a 502 status code (Bad Gateway) is
sent.
</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCheckPeerExpire on
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCheckPeerCN</name>
<description>Whether to check the remote server certificate's CN field
</description>
<syntax>SSLProxyCheckPeerCN on|off</syntax>
<default>SSLProxyCheckPeerCN on</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets whether the remote server certificate's CN field is
compared against the hostname of the request URL. If both are not equal
a 502 status code (Bad Gateway) is sent. <code>SSLProxyCheckPeerCN</code> is
superseded by <directive module="mod_ssl">SSLProxyCheckPeerName</directive>
in release 2.4.5 and later. 
</p>
<p>
In all releases 2.4.5 through 2.4.20, setting
<code>SSLProxyCheckPeerName off</code> was sufficient to enable this behavior
(as the <code>SSLProxyCheckPeerCN</code> default was <code>on</code>.) In 
these releases, both directives must be set to <code>off</code> to completely
avoid remote server certificate name validation. Many users reported this
to be very confusing.
</p>
<p>
As of release 2.4.21, all configurations which enable either one of the
<code>SSLProxyCheckPeerName</code> or <code>SSLProxyCheckPeerCN</code> options
will use the new <directive module="mod_ssl">SSLProxyCheckPeerName</directive>
behavior, and all configurations which disable either one of the 
<code>SSLProxyCheckPeerName</code> or <code>SSLProxyCheckPeerCN</code> options
will suppress all remote server certificate name validation. Only the following
configuration will trigger the legacy certificate CN comparison in 2.4.21 and
later releases;
</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCheckPeerCN on
SSLProxyCheckPeerName off
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCheckPeerName</name>
<description>Configure host name checking for remote server certificates
</description>
<syntax>SSLProxyCheckPeerName on|off</syntax>
<default>SSLProxyCheckPeerName on</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>
<compatibility>Apache HTTP Server 2.4.5 and later</compatibility>

<usage>
<p>
This directive configures host name checking for server certificates when 
mod_ssl is acting as an SSL client. The check will succeed if the host name 
from the request URI matches one of the CN attribute(s) of the certificate's 
subject, or matches the subjectAltName extension. If the check fails, the SSL 
request is aborted and a 502 status code (Bad Gateway) is returned.
</p>
<p>
Wildcard matching is supported for specific cases: an subjectAltName entry
of type dNSName, or CN attributes starting with <code>*.</code> will match
with any host name of the same number of name elements and the same suffix.
E.g. <code>*.example.org</code> will match <code>foo.example.org</code>,
but will not match <code>foo.bar.example.org</code>, because the number of
elements in the respective host names differs.
</p>
<p>
This feature was introduced in 2.4.5 and superseded the behavior of the 
<directive module="mod_ssl">SSLProxyCheckPeerCN</directive> directive, which 
only tested the exact value in the first CN attribute against the host name.
However, many users were confused by the behavior of using these directives
individually, so the mutual behavior of <code>SSLProxyCheckPeerName</code> 
and <code>SSLProxyCheckPeerCN</code> directives were improved in release 
2.4.21. See the <directive module="mod_ssl">SSLProxyCheckPeerCN</directive> 
directive description for the original behavior and details of these 
improvements.
</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyEngine</name>
<description>SSL Proxy Engine Operation Switch</description>
<syntax>SSLProxyEngine on|off</syntax>
<default>SSLProxyEngine off</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive toggles the usage of the SSL/TLS Protocol Engine for proxy. This
is usually used inside a <directive module="core"
type="section">VirtualHost</directive> section to enable SSL/TLS for proxy
usage in a particular virtual host. By default the SSL/TLS Protocol Engine is
disabled for proxy both for the main server and all configured virtual hosts.</p>

<p>Note that the <directive>SSLProxyEngine</directive> directive should not, in
general, be included in a virtual host that will be acting as a
forward proxy (using <directive module="mod_proxy" type="section">Proxy</directive>
or <directive module="mod_proxy">ProxyRequests</directive> directives).
<directive>SSLProxyEngine</directive> is not required to enable a forward proxy
server to proxy SSL/TLS requests.</p>

<example><title>Example</title>
<highlight language="config">
&lt;VirtualHost _default_:443&gt;
    SSLProxyEngine on
    #...
&lt;/VirtualHost&gt;
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyProtocol</name>
<description>Configure usable SSL protocol flavors for proxy usage</description>
<syntax>SSLProxyProtocol [+|-]<em>protocol</em> ...</syntax>
<default>SSLProxyProtocol all -SSLv3 (up to 2.4.16: all)</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<!-- XXX Why does this have an override and not .htaccess context? -->
<p>
This directive can be used to control the SSL protocol flavors mod_ssl should
use when establishing its server environment for proxy . It will only connect
to servers using one of the provided protocols.</p>
<p>Please refer to <directive module="mod_ssl">SSLProtocol</directive>
for additional information.
</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCipherSuite</name>
<description>Cipher Suite available for negotiation in SSL
proxy handshake</description>
<syntax>SSLProxyCipherSuite [<em>protocol</em>] <em>cipher-spec</em></syntax>
<default>SSLProxyCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+EXP</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>Equivalent to <directive module="mod_ssl">SSLCipherSuite</directive>, but
for the proxy connection.
Please refer to <directive module="mod_ssl">SSLCipherSuite</directive>
for additional information.</p>
</usage>

</directivesynopsis>
<directivesynopsis>
<name>SSLProxyCACertificatePath</name>
<description>Directory of PEM-encoded CA Certificates for
Remote Server Auth</description>
<syntax>SSLProxyCACertificatePath <em>directory-path</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the directory where you keep the Certificates of
Certification Authorities (CAs) whose remote servers you deal with. These are used to
verify the remote server certificate on Remote Server Authentication.</p>
<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
<em>hash-value</em><code>.N</code>. And you should always make sure this directory
contains the appropriate symbolic links.</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCACertificatePath "/usr/local/apache2/conf/ssl.crt/"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCACertificateFile</name>
<description>File of concatenated PEM-encoded CA Certificates
for Remote Server Auth</description>
<syntax>SSLProxyCACertificateFile <em>file-path</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the <em>all-in-one</em> file where you can assemble the
Certificates of Certification Authorities (CA) whose <em>remote servers</em> you deal
with. These are used for Remote Server 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
<directive module="mod_ssl">SSLProxyCACertificatePath</directive>.</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCACertificateFile "/usr/local/apache2/conf/ssl.crt/ca-bundle-remote-server.crt"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCARevocationPath</name>
<description>Directory of PEM-encoded CA CRLs for
Remote Server Auth</description>
<syntax>SSLProxyCARevocationPath <em>directory-path</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
This directive sets the directory where you keep the Certificate Revocation
Lists (CRL) of Certification Authorities (CAs) whose remote servers you deal with.
These are used to revoke the remote server certificate on Remote Server Authentication.</p>
<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
<em>hash-value</em><code>.rN</code>. And you should always make sure this directory
contains the appropriate symbolic links.</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCARevocationPath "/usr/local/apache2/conf/ssl.crl/"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCARevocationFile</name>
<description>File of concatenated PEM-encoded CA CRLs for
Remote Server Auth</description>
<syntax>SSLProxyCARevocationFile <em>file-path</em></syntax>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<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>remote servers</em> you deal with. These are used
for Remote Server 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 <directive
module="mod_ssl">SSLProxyCARevocationPath</directive>.</p>
<example><title>Example</title>
<highlight language="config">
SSLProxyCARevocationFile "/usr/local/apache2/conf/ssl.crl/ca-bundle-remote-server.crl"
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLProxyCARevocationCheck</name>
<description>Enable CRL-based revocation checking for Remote Server Auth</description>
<syntax>SSLProxyCARevocationCheck chain|leaf|none</syntax>
<default>SSLProxyCARevocationCheck none</default>
<contextlist><context>server config</context> <context>virtual host</context>
<context>proxy section</context></contextlist>

<usage>
<p>
Enables certificate revocation list (CRL) checking for the
<em>remote servers</em> you deal with. At least one of
<directive module="mod_ssl">SSLProxyCARevocationFile</directive>
or <directive module="mod_ssl">SSLProxyCARevocationPath</directive> must be
configured. When set to <code>chain</code> (recommended setting),
CRL checks are applied to all certificates in the chain, while setting it to
<code>leaf</code> limits the checks to the end-entity cert.
</p>
<note>
<title>When set to <code>chain</code> or <code>leaf</code>,
CRLs <em>must</em> be available for successful validation</title>
<p>
Prior to version 2.3.15, CRL checking in mod_ssl also succeeded when
no CRL(s) were found in any of the locations configured with
<directive module="mod_ssl">SSLProxyCARevocationFile</directive>
or <directive module="mod_ssl">SSLProxyCARevocationPath</directive>.
With the introduction of this directive, the behavior has been changed:
when checking is enabled, CRLs <em>must</em> be present for the validation
to succeed - otherwise it will fail with an
<code>"unable to get certificate CRL"</code> error.
</p>
</note>
<example><title>Example</title>
<highlight language="config">
SSLProxyCARevocationCheck chain
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLUserName</name>
<description>Variable name to determine user name</description>
<syntax>SSLUserName <em>varname</em></syntax>
<contextlist><context>server config</context>
<context>directory</context>
<context>.htaccess</context></contextlist>
<override>AuthConfig</override>

<usage>
<p>
This directive sets the "user" field in the Apache request object.
This is used by lower modules to identify the user with a character
string. In particular, this may cause the environment variable
<code>REMOTE_USER</code> to be set.  The <em>varname</em> can be
any of the <a href="#envvars">SSL environment variables</a>.</p>

<p>Note that this directive has no effect if the
<code>FakeBasicAuth</code> option is used (see <a
href="#ssloptions">SSLOptions</a>).</p>

<example><title>Example</title>
<highlight language="config">
SSLUserName SSL_CLIENT_S_DN_CN
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLHonorCipherOrder</name>
<description>Option to prefer the server's cipher preference order</description>
<syntax>SSLHonorCipherOrder on|off</syntax>
<default>SSLHonorCipherOrder off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>When choosing a cipher during an SSLv3 or TLSv1 handshake, normally
the client's preference is used.  If this directive is enabled, the
server's preference will be used instead.</p>
<example><title>Example</title>
<highlight language="config">
SSLHonorCipherOrder on
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCryptoDevice</name>
<description>Enable use of a cryptographic hardware accelerator</description>
<syntax>SSLCryptoDevice <em>engine</em></syntax>
<default>SSLCryptoDevice builtin</default>
<contextlist><context>server config</context></contextlist>

<usage>
<p>
This directive enables use of a cryptographic hardware accelerator
board to offload some of the SSL processing overhead.  This directive
can only be used if the SSL toolkit is built with "engine" support;
OpenSSL 0.9.7 and later releases have "engine" support by default, the
separate "-engine" releases of OpenSSL 0.9.6 must be used.</p>

<p>To discover which engine names are supported, run the command
&quot;<code>openssl engine</code>&quot;.</p>

<example><title>Example</title>
<highlight language="config">
# For a Broadcom accelerator:
SSLCryptoDevice ubsec
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPEnable</name>
<description>Enable OCSP validation of the client certificate chain</description>
<syntax>SSLOCSPEnable on|leaf|off</syntax>
<default>SSLOCSPEnable off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Mode <em>leaf</em> available in httpd 2.4.34 and later</compatibility>

<usage>
<p>This option enables OCSP validation of the client certificate
chain.  If this option is enabled, certificates in the client's
certificate chain will be validated against an OCSP responder after
normal verification (including CRL checks) have taken place. In 
mode 'leaf', only the client certificate itself will be validated.</p>

<p>The OCSP responder used is either extracted from the certificate
itself, or derived by configuration; see the
<directive module="mod_ssl">SSLOCSPDefaultResponder</directive> and
<directive module="mod_ssl">SSLOCSPOverrideResponder</directive>
directives.</p>

<example><title>Example</title>
<highlight language="config">
SSLVerifyClient on
SSLOCSPEnable on
SSLOCSPDefaultResponder "http://responder.example.com:8888/responder"
SSLOCSPOverrideResponder on
</highlight>
</example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPDefaultResponder</name>
<description>Set the default responder URI for OCSP validation</description>
<syntax>SSLOCSDefaultResponder <em>uri</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>This option sets the default OCSP responder to use.  If <directive
module="mod_ssl">SSLOCSPOverrideResponder</directive> is not enabled,
the URI given will be used only if no responder URI is specified in
the certificate being verified.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPOverrideResponder</name>
<description>Force use of the default responder URI for OCSP validation</description>
<syntax>SSLOCSPOverrideResponder on|off</syntax>
<default>SSLOCSPOverrideResponder off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>This option forces the configured default OCSP responder to be used
during OCSP certificate validation, regardless of whether the
certificate being validated references an OCSP responder.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPResponseTimeSkew</name>
<description>Maximum allowable time skew for OCSP response validation</description>
<syntax>SSLOCSPResponseTimeSkew <em>seconds</em></syntax>
<default>SSLOCSPResponseTimeSkew 300</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>This option sets the maximum allowable time skew for OCSP responses
(when checking their <code>thisUpdate</code> and <code>nextUpdate</code> fields).</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPResponseMaxAge</name>
<description>Maximum allowable age for OCSP responses</description>
<syntax>SSLOCSPResponseMaxAge <em>seconds</em></syntax>
<default>SSLOCSPResponseMaxAge -1</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>This option sets the maximum allowable age ("freshness") for OCSP responses.
The default value (<code>-1</code>) does not enforce a maximum age,
which means that OCSP responses are considered valid as long as their
<code>nextUpdate</code> field is in the future.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPResponderTimeout</name>
<description>Timeout for OCSP queries</description>
<syntax>SSLOCSPResponderTimeout <em>seconds</em></syntax>
<default>SSLOCSPResponderTimeout 10</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>

<usage>
<p>This option sets the timeout for queries to OCSP responders, when
<directive module="mod_ssl">SSLOCSPEnable</directive> is turned on.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPUseRequestNonce</name>
<description>Use a nonce within OCSP queries</description>
<syntax>SSLOCSPUseRequestNonce on|off</syntax>
<default>SSLOCSPUseRequestNonce on</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.10 and later</compatibility>

<usage>
<p>This option determines whether queries to OCSP responders should contain
a nonce or not. By default, a query nonce is always used and checked against
the response's one. When the responder does not use nonces (e.g. Microsoft OCSP
Responder), this option should be turned <code>off</code>.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPNoverify</name>
<description>skip the OCSP responder certificates verification</description>
<syntax>SSLOCSPNoverify <em>On/Off</em></syntax>
<default>SSLOCSPNoverify Off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.26 and later, if using OpenSSL 0.9.7 or later</compatibility>
<usage>
<p>Skip the OCSP responder certificates verification, mostly useful when
testing an OCSP server.</p>
</usage>
</directivesynopsis>


<directivesynopsis>
<name>SSLOCSPResponderCertificateFile</name>
<description>Set of trusted PEM encoded OCSP responder certificates</description>
<syntax>SSLOCSPResponderCertificateFile <em>file</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.26 and later, if using OpenSSL 0.9.7 or later</compatibility>
<usage>
<p>This supplies a list of trusted OCSP responder certificates to be used
during OCSP responder certificate validation. The supplied certificates are
implicitly trusted without any further validation. This is typically used
where the OCSP responder certificate is self signed or omitted from the OCSP
response.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOCSPProxyURL</name>
<description>Proxy URL to use for OCSP requests</description>
<syntax>SSLOCSPProxyURL <em>url</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.19 and later</compatibility>

<usage>
<p>This option allows to set the URL of a HTTP proxy that should be used for
all queries to OCSP responders.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLInsecureRenegotiation</name>
<description>Option to enable support for insecure renegotiation</description>
<syntax>SSLInsecureRenegotiation on|off</syntax>
<default>SSLInsecureRenegotiation off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.2.15 and later, if using OpenSSL 0.9.8m or later</compatibility>

<usage>
<p>As originally specified, all versions of the SSL and TLS protocols
(up to and including TLS/1.2) were vulnerable to a Man-in-the-Middle
attack
(<a href="http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2009-3555">CVE-2009-3555</a>)
during a renegotiation.  This vulnerability allowed an attacker to
"prefix" a chosen plaintext to the HTTP request as seen by the web
server.  A protocol extension was developed which fixed this
vulnerability if supported by both client and server.</p>

<p>If <module>mod_ssl</module> is linked against OpenSSL version 0.9.8m
or later, by default renegotiation is only supported with
clients supporting the new protocol extension.  If this directive is
enabled, renegotiation will be allowed with old (unpatched) clients,
albeit insecurely.</p>

<note type="warning"><title>Security warning</title>
<p>If this directive is enabled, SSL connections will be vulnerable to
the Man-in-the-Middle prefix attack as described
in <a href="http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2009-3555">CVE-2009-3555</a>.</p>
</note>

<example><title>Example</title>
<highlight language="config">
SSLInsecureRenegotiation on
</highlight>
</example>

<p>The <code>SSL_SECURE_RENEG</code> environment variable can be used
from an SSI or CGI script to determine whether secure renegotiation is
supported for a given SSL connection.</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLUseStapling</name>
<description>Enable stapling of OCSP responses in the TLS handshake</description>
<syntax>SSLUseStapling on|off</syntax>
<default>SSLUseStapling off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>This option enables OCSP stapling, as defined by the "Certificate
Status Request" TLS extension specified in RFC 6066. If enabled (and
requested by the client), mod_ssl will include an OCSP response
for its own certificate in the TLS handshake. Configuring an
<directive module="mod_ssl">SSLStaplingCache</directive> is a
prerequisite for enabling OCSP stapling.</p>

<p>OCSP stapling relieves the client of querying the OCSP responder
on its own, but it should be noted that with the RFC 6066 specification,
the server's <code>CertificateStatus</code> reply may only include an
OCSP response for a single cert. For server certificates with intermediate
CA certificates in their chain (the typical case nowadays),
stapling in its current implementation therefore only partially achieves the
stated goal of "saving roundtrips and resources" - see also
<a href="http://www.ietf.org/rfc/rfc6961.txt">RFC 6961</a>
(TLS Multiple Certificate Status Extension).
</p>

<p>When OCSP stapling is enabled, the <code>ssl-stapling</code> mutex is used
to control access to the OCSP stapling cache in order to prevent corruption,
and the <code>sss-stapling-refresh</code> mutex is used to control refreshes
of OCSP responses.  These mutexes can be configured using the
<directive module="core">Mutex</directive> directive.
</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingCache</name>
<description>Configures the OCSP stapling cache</description>
<syntax>SSLStaplingCache <em>type</em></syntax>
<contextlist><context>server config</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>Configures the cache used to store OCSP responses which get included
in the TLS handshake if <directive module="mod_ssl">SSLUseStapling</directive>
is enabled. Configuration of a cache is mandatory for OCSP stapling.
With the exception of <code>none</code> and <code>nonenotnull</code>,
the same storage types are supported as with
<directive module="mod_ssl">SSLSessionCache</directive>.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingResponseTimeSkew</name>
<description>Maximum allowable time skew for OCSP stapling response validation</description>
<syntax>SSLStaplingResponseTimeSkew <em>seconds</em></syntax>
<default>SSLStaplingResponseTimeSkew 300</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>This option sets the maximum allowable time skew when mod_ssl checks the
<code>thisUpdate</code> and <code>nextUpdate</code> fields of OCSP responses
which get included in the TLS handshake (OCSP stapling). Only applicable
if <directive module="mod_ssl">SSLUseStapling</directive> is turned on.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingResponderTimeout</name>
<description>Timeout for OCSP stapling queries</description>
<syntax>SSLStaplingResponderTimeout <em>seconds</em></syntax>
<default>SSLStaplingResponderTimeout 10</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>This option sets the timeout for queries to OCSP responders when
<directive module="mod_ssl">SSLUseStapling</directive> is enabled
and mod_ssl is querying a responder for OCSP stapling purposes.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingResponseMaxAge</name>
<description>Maximum allowable age for OCSP stapling responses</description>
<syntax>SSLStaplingResponseMaxAge <em>seconds</em></syntax>
<default>SSLStaplingResponseMaxAge -1</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>This option sets the maximum allowable age ("freshness") when
considering OCSP responses for stapling purposes, i.e. when
<directive module="mod_ssl">SSLUseStapling</directive> is turned on.
The default value (<code>-1</code>) does not enforce a maximum age,
which means that OCSP responses are considered valid as long as their
<code>nextUpdate</code> field is in the future.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingStandardCacheTimeout</name>
<description>Number of seconds before expiring responses in the OCSP stapling cache</description>
<syntax>SSLStaplingStandardCacheTimeout <em>seconds</em></syntax>
<default>SSLStaplingStandardCacheTimeout 3600</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>Sets the timeout in seconds before responses in the OCSP stapling cache
(configured through <directive module="mod_ssl">SSLStaplingCache</directive>)
will expire. This directive applies to <em>valid</em> responses, while
<directive module="mod_ssl">SSLStaplingErrorCacheTimeout</directive> is
used for controlling the timeout for invalid/unavailable responses.
</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingReturnResponderErrors</name>
<description>Pass stapling related OCSP errors on to client</description>
<syntax>SSLStaplingReturnResponderErrors on|off</syntax>
<default>SSLStaplingReturnResponderErrors on</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>When enabled, mod_ssl will pass responses from unsuccessful
stapling related OCSP queries (such as responses with an overall status
other than "successful", responses with a certificate status other than
"good", expired responses etc.) on to the client.
If set to <code>off</code>, only responses indicating a certificate status
of "good" will be included in the TLS handshake.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingFakeTryLater</name>
<description>Synthesize "tryLater" responses for failed OCSP stapling queries</description>
<syntax>SSLStaplingFakeTryLater on|off</syntax>
<default>SSLStaplingFakeTryLater on</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>When enabled and a query to an OCSP responder for stapling
purposes fails, mod_ssl will synthesize a "tryLater" response for the
client. Only effective if <directive
module="mod_ssl">SSLStaplingReturnResponderErrors</directive>
is also enabled.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingErrorCacheTimeout</name>
<description>Number of seconds before expiring invalid responses in the OCSP stapling cache</description>
<syntax>SSLStaplingErrorCacheTimeout <em>seconds</em></syntax>
<default>SSLStaplingErrorCacheTimeout 600</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>Sets the timeout in seconds before <em>invalid</em> responses
in the OCSP stapling cache (configured through <directive
module="mod_ssl">SSLStaplingCache</directive>) will expire.
To set the cache timeout for valid responses, see
<directive module="mod_ssl">SSLStaplingStandardCacheTimeout</directive>.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLStaplingForceURL</name>
<description>Override the OCSP responder URI specified in the certificate's AIA extension</description>
<syntax>SSLStaplingForceURL <em>uri</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>This directive overrides the URI of an OCSP responder as obtained from
the authorityInfoAccess (AIA) extension of the certificate.
One potential use is when a proxy is used for retrieving OCSP queries.</p>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSessionTicketKeyFile</name>
<description>Persistent encryption/decryption key for TLS session tickets</description>
<syntax>SSLSessionTicketKeyFile <em>file-path</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.0 and later, if using OpenSSL 0.9.8h or later</compatibility>

<usage>
<p>Optionally configures a secret key for encrypting and decrypting
TLS session tickets, as defined in
<a href="http://www.ietf.org/rfc/rfc5077.txt">RFC 5077</a>.
Primarily suitable for clustered environments where TLS sessions information
should be shared between multiple nodes. For single-instance httpd setups,
it is recommended to <em>not</em> configure a ticket key file, but to
rely on (random) keys generated by mod_ssl at startup, instead.</p>
<p>The ticket key file must contain 48 bytes of random data,
preferrably created from a high-entropy source. On a Unix-based system,
a ticket key file can be created as follows:</p>

<example>
dd if=/dev/random of=/path/to/file.tkey bs=1 count=48
</example>

<p>Ticket keys should be rotated (replaced) on a frequent basis,
as this is the only way to invalidate an existing session ticket -
OpenSSL currently doesn't allow to specify a limit for ticket lifetimes.
A new ticket key only gets used after restarting the web server.
All existing session tickets become invalid after a restart.</p>

<note type="warning">
<p>The ticket key file contains sensitive keying material and should
be protected with file permissions similar to those used for
<directive module="mod_ssl">SSLCertificateKeyFile</directive>.</p>
</note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLCompression</name>
<description>Enable compression on the SSL level</description>
<syntax>SSLCompression on|off</syntax>
<default>SSLCompression off</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.3 and later, if using OpenSSL 0.9.8 or later;
virtual host scope available if using OpenSSL 1.0.0 or later.
The default used to be <code>on</code> in version 2.4.3.</compatibility>

<usage>
<p>This directive allows to enable compression on the SSL level.</p>
<note type="warning">
<p>Enabling compression causes security issues in most setups (the so called
CRIME attack).</p>
</note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLSessionTickets</name>
<description>Enable or disable use of TLS session tickets</description>
<syntax>SSLSessionTickets on|off</syntax>
<default>SSLSessionTickets on</default>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.11 and later, if using OpenSSL 0.9.8f
or later.</compatibility>

<usage>
<p>This directive allows to enable or disable the use of TLS session tickets
(RFC 5077).</p>
<note type="warning">
<p>TLS session tickets are enabled by default. Using them without restarting
the web server with an appropriate frequency (e.g. daily) compromises perfect
forward secrecy.</p>
</note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>SSLOpenSSLConfCmd</name>
<description>Configure OpenSSL parameters through its <em>SSL_CONF</em> API</description>
<syntax>SSLOpenSSLConfCmd <em>command-name</em> <em>command-value</em></syntax>
<contextlist><context>server config</context>
<context>virtual host</context></contextlist>
<compatibility>Available in httpd 2.4.8 and later, if using OpenSSL 1.0.2 or later</compatibility>

<usage>
<p>This directive exposes OpenSSL's <em>SSL_CONF</em> API to mod_ssl,
allowing a flexible configuration of OpenSSL parameters without the need
of implementing additional <module>mod_ssl</module> directives when new
features are added to OpenSSL.</p>

<p>The set of available <directive>SSLOpenSSLConfCmd</directive> commands
depends on the OpenSSL version being used for <module>mod_ssl</module>
(at least version 1.0.2 is required). For a list of supported command
names, see the section <em>Supported configuration file commands</em> in the
<a href="http://www.openssl.org/docs/man1.0.2/ssl/SSL_CONF_cmd.html#SUPPORTED-CONFIGURATION-FILE-COMMANDS">SSL_CONF_cmd(3)</a> manual page for OpenSSL.</p>

<p>Some of the <directive>SSLOpenSSLConfCmd</directive> commands can be used
as an alternative to existing directives (such as
<directive module="mod_ssl">SSLCipherSuite</directive> or
<directive module="mod_ssl">SSLProtocol</directive>),
though it should be noted that the syntax / allowable values for the parameters
may sometimes differ.</p>

<example><title>Examples</title>
<highlight language="config">
SSLOpenSSLConfCmd Options -SessionTicket,ServerPreference
SSLOpenSSLConfCmd ECDHParameters brainpoolP256r1
SSLOpenSSLConfCmd ServerInfoFile "/usr/local/apache2/conf/server-info.pem"
SSLOpenSSLConfCmd Protocol "-ALL, TLSv1.2"
SSLOpenSSLConfCmd SignatureAlgorithms RSA+SHA384:ECDSA+SHA256
</highlight>
</example>
</usage>
</directivesynopsis>

</modulesynopsis>
