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<?xml version="1.0" encoding="ISO-8859-1"?>
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<title>SSL/TLS Strong Encryption: How-To - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.3</p>
<img alt="" src="../images/feather.gif" /></div>
<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">SSL/TLS</a></div><div id="page-content"><div id="preamble"><h1>SSL/TLS Strong Encryption: How-To</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/ssl/ssl_howto.html" title="English"> en </a> |
<a href="../fr/ssl/ssl_howto.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
</div>
<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>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#configexample">Basic Configuration Example</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#ciphersuites">Cipher Suites and Enforcing Strong Security</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#accesscontrol">Client Authentication and Access Control</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#logging">Logging</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="configexample" id="configexample">Basic Configuration Example</a></h2>
<p>Your SSL configuration will need to contain, at a minumum, the
following directives.</p>
<div class="example"><p><code>
Listen 443<br />
<VirtualHost _default_:443><br />
<span class="indent">
ServerName www.example.com<br />
SSLEngine on<br />
SSLCertificateFile /path/to/www.example.com.cert<br />
SSLCertificateKeyFile /path/to/www.example.com.key<br />
</span>
</VirtualHost>
</code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="ciphersuites" id="ciphersuites">Cipher Suites and Enforcing Strong Security</a></h2>
<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>
<h3><a name="onlystrong" id="onlystrong">How can I create an SSL server which accepts strong encryption
only?</a></h3>
<p>The following enables only the strongest ciphers:</p>
<div class="example"><h3>httpd.conf</h3><p><code>
SSLProtocol all -SSLv2<br />
SSLCipherSuite HIGH:!ADH:!EXP:!MD5:!NULL<br />
</code></p></div>
<p>While with the following configuration you enable two ciphers
which are resonably secure, and fast:</p>
<div class="example"><h3>httpd.conf</h3><p><code>
SSLProtocol all -SSLv2<br />
SSLCipherSuite RC4-SHA:AES128-SHA:HIGH:!ADH:!EXP:!MD5:!NULL<br />
SSLHonorCipherOrder on
</code></p></div>
<p>This strongly reflects the default value of <code class="directive"><a href="../mod/mod_ssl.html#sslciphersuite">SSLCipherSuite</a></code> and is the recommanded way to configure it.</p>
<h3><a name="strongurl" id="strongurl">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?</a></h3>
<p>Obviously, a server-wide <code class="directive"><a href="../mod/mod_ssl.html#sslciphersuite">SSLCipherSuite</a></code> which restricts
ciphers to the strong variants, isn't the answer here. However,
<code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> 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>
<div class="example"><p><code>
# be liberal in general<br />
SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br />
<br />
<Location /strong/area><br />
# but https://hostname/strong/area/ and below<br />
# requires strong ciphers<br />
SSLCipherSuite HIGH:!ADH:!EXP:!MD5:!NULL<br />
</Location>
</code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="accesscontrol" id="accesscontrol">Client Authentication and Access Control</a></h2>
<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>
<h3><a name="allclients" id="allclients">How can I force clients to authenticate using certificates?</a></h3>
<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>
<div class="example"><h3>httpd.conf</h3><p><code>
# 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
</code></p></div>
<h3><a name="arbitraryclients" id="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></h3>
<p>To force clients to authenticate using certificates for a particular URL,
you can use the per-directory reconfiguration features of
<code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code>:</p>
<div class="example"><h3>httpd.conf</h3><p><code>
SSLVerifyClient none<br />
SSLCACertificateFile conf/ssl.crt/ca.crt<br />
<br />
<Location /secure/area><br />
SSLVerifyClient require<br />
SSLVerifyDepth 1<br />
</Location><br />
</code></p></div>
<h3><a name="certauthenticate" id="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></h3>
<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 <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code> or
<code class="directive"><a href="../mod/mod_ssl.html#sslrequire">SSLRequire</a></code>.</p>
<p>The <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code> 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>
<div class="example"><h3>httpd.conf</h3><pre>
SSLVerifyClient none
<Directory /usr/local/apache2/htdocs/secure/area>
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
</Directory></pre></div>
<p>The password used in this example is the DES encrypted string "password".
See the <code class="directive"><a href="../mod/mod_ssl.html#ssloptions">SSLOptions</a></code> docs for more
information.</p>
<div class="example"><h3>httpd.passwd</h3><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></div>
<p>When your clients are all part of a common hierarchy, which is encoded
into the DN, you can match them more easily using <code class="directive"><a href="../mod/mod_ssl.html#sslrequire">SSLRequire</a></code>, as follows:</p>
<div class="example"><h3>httpd.conf</h3><pre>
SSLVerifyClient none
<Directory /usr/local/apache2/htdocs/secure/area>
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"}
</Directory></pre></div>
<h3><a name="intranet" id="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? I still want to allow
plain HTTP access for clients on the Intranet.</a></h3>
<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>
<div class="example"><h3>httpd.conf</h3><pre>
SSLCACertificateFile conf/ssl.crt/company-ca.crt
<Directory /usr/local/apache2/htdocs>
# Outside the subarea only Intranet access is granted
Order deny,allow
Deny from all
Allow from 192.168.1.0/24
</Directory>
<Directory /usr/local/apache2/htdocs/subarea>
# 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} >= 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
</Directory></pre></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="logging" id="logging">Logging</a></h2>
<p><code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> can log extremely verbose debugging information
to the error log, when its <code class="directive"><a href="../mod/core.html#loglevel">LogLevel</a></code> 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 <code class="directive"><a href="../mod/core.html#loglevel">LogLevel</a></code> per module to
suite your needs.</p>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/ssl/ssl_howto.html" title="English"> en </a> |
<a href="../fr/ssl/ssl_howto.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
</div><div id="footer">
<p class="apache">Copyright 2011 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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