path: root/docs/manual/ssl/ssl_howto.xml

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<!-- $LastChangedRevision$ -->

<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<manualpage metafile="ssl_howto.xml.meta">
<parentdocument href="./">SSL/TLS</parentdocument>

  <title>SSL/TLS Strong Encryption: How-To</title>

<summary>
<blockquote>
<p>The solution to this problem is trivial
and is left as an exercise for the reader.</p>

<p class="cite">-- <cite>Standard textbook cookie</cite></p>
</blockquote>

<p>How to solve particular security problems for an SSL-aware
webserver is not always obvious because of the interactions between SSL,
HTTP and Apache's way of processing requests. This chapter gives
instructions on how to solve some typical situations. Treat it as a first
step to find out the final solution, but always try to understand the 
stuff before you use it. Nothing is worse than using a security solution
without knowing its restrictions and how it interacts with other systems.</p>
</summary>

<section id="configexample">
<title>Basic Configuration Example</title>

<p>Your SSL configuration will need to contain, at a minumum, the
following directives.</p>

<example>
   Listen 443<br />
   &lt;VirtualHost _default_:443&gt;<br />
   <indent>
        ServerName www.domain.com<br />
        SSLEngine on<br />
        SSLCertificateFile /path/to/www.comain.com.cert<br />
        SSLCertificateKeyFile /path/to/www.domain.com.key<br />
   </indent>
   &lt;/VirtualHost&gt;
</example>

</section>

<section id="ciphersuites">
<title>Cipher Suites and Enforcing Strong Security</title>
<ul>
<li><a href="#onlystrong">How can I create an SSL server which accepts strong encryption only?</a></li>
<li><a href="#strongurl">How can I create an SSL server which accepts all types of ciphers in general, but 
requires a strong cipher for access to a particular URL?</a></li>
</ul>

<section id="onlystrong">
<title>How can I create an SSL server which accepts strong encryption
only?</title>
    <p>The following enables only the strongest ciphers:</p>
    <example><title>httpd.conf</title>
      SSLProtocol all -SSLv2<br />
      SSLCipherSuite HIGH:!ADH:!EXP:!MD5:!NULL<br />
    </example>

    <p>While with the following configuration you enable two ciphers
    which are resonably secure, and fast:</p>

    <example><title>httpd.conf</title>
      SSLProtocol all -SSLv2<br />
      SSLCipherSuite RC4-SHA:AES128-SHA:HIGH:!ADH:!EXP:!MD5:!NULL<br />
      SSLHonorCipherOrder on
    </example>

    <p>This strongly reflects the default value of <directive module="mod_ssl"
    >SSLCipherSuite</directive> and is the recommanded way to configure it.</p>
</section>

<section id="strongurl">
<title>How can I create an SSL server which accepts all types of ciphers
in general, but requires a strong ciphers for access to a particular
URL?</title>
    <p>Obviously, a server-wide <directive
    module="mod_ssl">SSLCipherSuite</directive> which restricts 
    ciphers to the strong variants, isn't the answer here. However, 
    <module>mod_ssl</module> can be reconfigured within <code>Location</code>
    blocks, to give a per-directory solution, and can automatically force
    a renegotiation of the SSL parameters to meet the new configuration.
    This can be done as follows:</p>
    <example>
      # be liberal in general<br />
      SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br />
      <br />
      &lt;Location /strong/area&gt;<br />
      # but https://hostname/strong/area/ and below<br />
      # requires strong ciphers<br />
      SSLCipherSuite HIGH:!ADH:!EXP:!MD5:!NULL<br />
      &lt;/Location&gt;
    </example>
</section>
</section>
<!-- /ciphersuites -->

<section id="accesscontrol">
<title>Client Authentication and Access Control</title>
<ul>
<li><a href="#allclients">How can I force clients to authenticate using certificates?</a></li>
<li><a href="#arbitraryclients">How can I force clients to authenticate using certificates for a 
        particular URL, but still allow arbitrary clients to access the rest of the server?</a></li>
<li><a href="#certauthenticate">How can I allow only clients who have certificates to access a
        particular URL, but allow all clients to access the rest of the server?</a></li>
<li><a href="#intranet">How can I require HTTPS with strong ciphers, and either
basic authentication or client certificates, for access to part of the
Intranet website, for clients coming from the Internet?</a></li>
</ul>

<section id="allclients">
<title>How can I force clients to authenticate using certificates?</title>

    <p>When you know all of your users (eg, as is often the case on a corporate
    Intranet), you can require plain certificate authentication. All you
    need to do is to create client certificates signed by your own CA
    certificate (<code>ca.crt</code>) and then verify the clients against this
    certificate.</p>
    <example><title>httpd.conf</title>
      # require a client certificate which has to be directly<br />
      # signed by our CA certificate in ca.crt<br />
      SSLVerifyClient require<br />
      SSLVerifyDepth 1<br />
      SSLCACertificateFile conf/ssl.crt/ca.crt
    </example>
</section>

<section id="arbitraryclients">
<title>How can I force clients to authenticate using certificates for a
  particular URL, but still allow arbitrary clients to access the rest of the server?</title>

    <p>To force clients to authenticate using certificates for a particular URL,
    you can use the per-directory reconfiguration features of
    <module>mod_ssl</module>:</p>

    <example><title>httpd.conf</title>
    SSLVerifyClient none<br />
    SSLCACertificateFile conf/ssl.crt/ca.crt<br />
    <br />
    &lt;Location /secure/area&gt;<br />
    SSLVerifyClient require<br />
    SSLVerifyDepth 1<br />
    &lt;/Location&gt;<br />
    </example>
</section>

<section id="certauthenticate">
<title>How can I allow only clients who have certificates to access a
  particular URL, but allow all clients to access the rest of the server?</title>

    <p>The key to doing this is checking that part of the client certificate
    matches what you expect. Usually this means checking all or part of the
    Distinguished Name (DN), to see if it contains some known string.
    There are two ways to do this, using either <module>mod_auth_basic</module> or
    <directive module="mod_ssl">SSLRequire</directive>.</p> 
    
    <p>The <module>mod_auth_basic</module> method is generally required when
    the certificates are completely arbitrary, or when their DNs have
    no common fields (usually the organisation, etc.). In this case,
    you should establish a password database containing <em>all</em>
    clients allowed, as follows:</p>
    
    <example><title>httpd.conf</title><pre>
SSLVerifyClient      none
&lt;Directory /usr/local/apache2/htdocs/secure/area&gt;

SSLVerifyClient      require
SSLVerifyDepth       5
SSLCACertificateFile conf/ssl.crt/ca.crt
SSLCACertificatePath conf/ssl.crt
SSLOptions           +FakeBasicAuth
SSLRequireSSL
AuthName             "Snake Oil Authentication"
AuthType             Basic
AuthBasicProvider    file
AuthUserFile         /usr/local/apache2/conf/httpd.passwd
Require              valid-user
&lt;/Directory&gt;</pre>
    </example>
    
    <p>The password used in this example is the DES encrypted string "password".
    See the <directive module="mod_ssl">SSLOptions</directive> docs for more 
    information.</p>
    
    <example><title>httpd.passwd</title><pre>
/C=DE/L=Munich/O=Snake Oil, Ltd./OU=Staff/CN=Foo:xxj31ZMTZzkVA
/C=US/L=S.F./O=Snake Oil, Ltd./OU=CA/CN=Bar:xxj31ZMTZzkVA
/C=US/L=L.A./O=Snake Oil, Ltd./OU=Dev/CN=Quux:xxj31ZMTZzkVA</pre>
    </example>

    <p>When your clients are all part of a common hierarchy, which is encoded
    into the DN, you can match them more easily using <directive module="mod_ssl"
    >SSLRequire</directive>, as follows:</p>


    <example><title>httpd.conf</title><pre>
SSLVerifyClient      none
&lt;Directory /usr/local/apache2/htdocs/secure/area&gt;

  SSLVerifyClient      require
  SSLVerifyDepth       5
  SSLCACertificateFile conf/ssl.crt/ca.crt
  SSLCACertificatePath conf/ssl.crt
  SSLOptions           +FakeBasicAuth
  SSLRequireSSL
  SSLRequire       %{SSL_CLIENT_S_DN_O}  eq "Snake Oil, Ltd." \
               and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"}
&lt;/Directory&gt;</pre>
    </example>
</section>

<section id="intranet">
<title>How can I require HTTPS with strong ciphers, and either basic
authentication or client certificates, for access to part of the
Intranet website, for clients coming from the Internet? I still want to allow
plain HTTP access for clients on the Intranet.</title>
   
   <p>These examples presume that clients on the Intranet have IPs in the range 
   192.168.1.0/24, and that the part of the Intranet website you want to allow
   internet access to is <code>/usr/local/apache2/htdocs/subarea</code>. 
   This configuration should remain outside of your HTTPS virtual host, so
   that it applies to both HTTPS and HTTP.</p>

    <example><title>httpd.conf</title><pre>
SSLCACertificateFile conf/ssl.crt/company-ca.crt

&lt;Directory /usr/local/apache2/htdocs&gt;
#   Outside the subarea only Intranet access is granted
Order                deny,allow
Deny                 from all
Allow                from 192.168.1.0/24
&lt;/Directory&gt;

&lt;Directory /usr/local/apache2/htdocs/subarea&gt;
#   Inside the subarea any Intranet access is allowed
#   but from the Internet only HTTPS + Strong-Cipher + Password
#   or the alternative HTTPS + Strong-Cipher + Client-Certificate

#   If HTTPS is used, make sure a strong cipher is used.
#   Additionally allow client certs as alternative to basic auth.
SSLVerifyClient      optional
SSLVerifyDepth       1
SSLOptions           +FakeBasicAuth +StrictRequire
SSLRequire           %{SSL_CIPHER_USEKEYSIZE} &gt;= 128

#   Force clients from the Internet to use HTTPS
RewriteEngine        on
RewriteCond          %{REMOTE_ADDR} !^192\.168\.1\.[0-9]+$
RewriteCond          %{HTTPS} !=on
RewriteRule          .* - [F]

#   Allow Network Access and/or Basic Auth
Satisfy              any

#   Network Access Control
Order                deny,allow
Deny                 from all
Allow                192.168.1.0/24

#   HTTP Basic Authentication
AuthType             basic
AuthName             "Protected Intranet Area"
AuthBasicProvider    file
AuthUserFile         conf/protected.passwd
Require              valid-user
&lt;/Directory&gt;</pre>
    </example>
</section>
</section>
<!-- /access control -->

<section id="logging">
    <title>Logging</title>

    <p><module>mod_ssl</module> can log extremely verbose debugging information
    to the error log, when its <directive module="core">LogLevel</directive> is
    set to the higher trace levels. On the other hand, on a very busy server,
    level <code>info</code> may already be too much. Remember that you can
    configure the <directive module="core">LogLevel</directive> per module to
    suite your needs.</p>
</section>

</manualpage>