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282 lines
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282 lines
13 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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This file is generated from xml source: DO NOT EDIT
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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-->
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<title>SSL/TLS Strong Encryption: How-To - Apache HTTP Server</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body id="manual-page"><div id="page-header">
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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>
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<p class="apache">Apache HTTP Server Version 2.1</p>
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<img alt="" src="../images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.1</a> > <a href="./">SSL/TLS</a></div><div id="page-content"><div id="preamble"><h1>SSL/TLS Strong Encryption: How-To</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/ssl/ssl_howto.html" title="English"> en </a></p>
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</div>
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<blockquote>
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<p>The solution of this problem is trivial
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and is left as an exercise for the reader.</p>
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<p class="cite">-- <cite>Standard textbook cookie</cite></p>
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</blockquote>
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<p>How to solve particular security constraints for an SSL-aware
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webserver is not always obvious because of the coherences between SSL,
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HTTP and Apache's way of processing requests. This chapter gives
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instructions on how to solve such typical situations. Treat is as a first
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step to find out the final solution, but always try to understand the
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stuff before you use it. Nothing is worse than using a security solution
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without knowing its restrictions and coherences.</p>
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</div>
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<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#ciphersuites">Cipher Suites and Enforced Strong Security</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#accesscontrol">Client Authentication and Access Control</a></li>
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</ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="ciphersuites" id="ciphersuites">Cipher Suites and Enforced Strong Security</a></h2>
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<ul>
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<li><a href="#realssl">SSLv2 only server</a></li>
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<li><a href="#onlystrong">strong encryption only server</a></li>
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<li><a href="#upgradeenc">server gated cryptography</a></li>
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<li><a href="#strongurl">stronger per-directory requirements</a></li>
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</ul>
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<h3><a name="realssl" id="realssl">How can I create a real SSLv2-only server?</a></h3>
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<p>The following creates an SSL server which speaks only the SSLv2 protocol and
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its ciphers.</p>
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<div class="example"><h3>httpd.conf</h3><p><code>
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SSLProtocol -all +SSLv2<br />
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SSLCipherSuite SSLv2:+HIGH:+MEDIUM:+LOW:+EXP<br />
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</code></p></div>
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<h3><a name="onlystrong" id="onlystrong">How can I create an SSL server which accepts strong encryption
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only?</a></h3>
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<p>The following enables only the seven strongest ciphers:</p>
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<div class="example"><h3>httpd.conf</h3><p><code>
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SSLProtocol all<br />
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SSLCipherSuite HIGH:MEDIUM<br />
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</code></p></div>
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<h3><a name="upgradeenc" id="upgradeenc">How can I create an SSL server which accepts strong encryption
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only, but allows export browsers to upgrade to stronger encryption?</a></h3>
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<p>This facility is called Server Gated Cryptography (SGC) and details
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you can find in the <code>README.GlobalID</code> document in the
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mod_ssl distribution. In short: The server has a Global ID server
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certificate, signed by a special CA certificate from Verisign which
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enables strong encryption in export browsers. This works as following:
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The browser connects with an export cipher, the server sends its Global
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ID certificate, the browser verifies it and subsequently upgrades the
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cipher suite before any HTTP communication takes place. The question
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now is: How can we allow this upgrade, but enforce strong encryption.
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Or in other words: Browser either have to initially connect with
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strong encryption or have to upgrade to strong encryption, but are
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not allowed to keep the export ciphers. The following does the trick:</p>
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<div class="example"><h3>httpd.conf</h3><p><code>
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# allow all ciphers for the initial handshake,<br />
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# so export browsers can upgrade via SGC facility<br />
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SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br />
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<br />
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<Directory /usr/local/apache2/htdocs><br />
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# but finally deny all browsers which haven't upgraded<br />
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SSLRequire %{SSL_CIPHER_USEKEYSIZE} >= 128<br />
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</Directory>
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</code></p></div>
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<h3><a name="strongurl" id="strongurl">How can I create an SSL server which accepts all types of ciphers
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in general, but requires a strong ciphers for access to a particular
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URL?</a></h3>
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<p>Obviously you cannot just use a server-wide <code class="directive"><a href="../mod/mod_ssl.html#sslciphersuite">SSLCipherSuite</a></code> which restricts the
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ciphers to the strong variants. But mod_ssl allows you to reconfigure
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the cipher suite in per-directory context and automatically forces
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a renegotiation of the SSL parameters to meet the new configuration.
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So, the solution is:</p>
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<div class="example"><p><code>
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# be liberal in general<br />
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SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br />
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<br />
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<Location /strong/area><br />
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# but https://hostname/strong/area/ and below<br />
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# requires strong ciphers<br />
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SSLCipherSuite HIGH:MEDIUM<br />
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</Location>
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</code></p></div>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="accesscontrol" id="accesscontrol">Client Authentication and Access Control</a></h2>
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<ul>
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<li><a href="#allclients">simple certificate-based client authentication</a></li>
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<li><a href="#arbitraryclients">selective certificate-based client authentication</a></li>
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<li><a href="#certauthenticate">particular certificate-based client authentication</a></li>
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<li><a href="#intranet">intranet vs. internet authentication</a></li>
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</ul>
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<h3><a name="allclients" id="allclients">How can I authenticate clients based on certificates when I know
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all my clients?</a></h3>
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<p>When you know your user community (i.e. a closed user group
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situation), as it's the case for instance in an Intranet, you can
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use plain certificate authentication. All you have to do is to
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create client certificates signed by your own CA certificate
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<code>ca.crt</code> and then verify the clients against this
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certificate.</p>
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<div class="example"><h3>httpd.conf</h3><p><code>
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# require a client certificate which has to be directly<br />
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# signed by our CA certificate in ca.crt<br />
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SSLVerifyClient require<br />
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SSLVerifyDepth 1<br />
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SSLCACertificateFile conf/ssl.crt/ca.crt
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</code></p></div>
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<h3><a name="arbitraryclients" id="arbitraryclients">How can I authenticate my clients for a particular URL based on
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certificates but still allow arbitrary clients to access the remaining
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parts of the server?</a></h3>
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<p>For this we again use the per-directory reconfiguration feature
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of <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code>:</p>
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<div class="example"><h3>httpd.conf</h3><p><code>
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SSLVerifyClient none<br />
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SSLCACertificateFile conf/ssl.crt/ca.crt<br />
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<br />
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<Location /secure/area><br />
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SSLVerifyClient require<br />
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SSLVerifyDepth 1<br />
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</Location><br />
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</code></p></div>
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<h3><a name="certauthenticate" id="certauthenticate">How can I authenticate only particular clients for a some URLs based
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on certificates but still allow arbitrary clients to access the remaining
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parts of the server?</a></h3>
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<p>The key is to check for various ingredients of the client certificate.
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Usually this means to check the whole or part of the Distinguished
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Name (DN) of the Subject. For this two methods exists: The <code class="module"><a href="../mod/mod_auth_basic.html">mod_auth_basic</a></code> based variant and the <code class="directive"><a href="../mod/mod_ssl.html#sslrequire">SSLRequire</a></code> variant. The first method is
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good when the clients are of totally different type, i.e. when their
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DNs have no common fields (usually the organisation, etc.). In this
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case you've to establish a password database containing <em>all</em>
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clients. The second method is better when your clients are all part of
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a common hierarchy which is encoded into the DN. Then you can match
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them more easily.</p>
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<p>The first method:</p>
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<div class="example"><h3>httpd.conf</h3><pre>
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SSLVerifyClient none
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<Directory /usr/local/apache2/htdocs/secure/area>
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SSLVerifyClient require
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SSLVerifyDepth 5
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SSLCACertificateFile conf/ssl.crt/ca.crt
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SSLCACertificatePath conf/ssl.crt
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SSLOptions +FakeBasicAuth
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SSLRequireSSL
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AuthName "Snake Oil Authentication"
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AuthType Basic
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AuthBasicProvider file
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AuthUserFile /usr/local/apache2/conf/httpd.passwd
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require valid-user
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</Directory></pre></div>
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<div class="example"><h3>httpd.passwd</h3><pre>
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/C=DE/L=Munich/O=Snake Oil, Ltd./OU=Staff/CN=Foo:xxj31ZMTZzkVA
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/C=US/L=S.F./O=Snake Oil, Ltd./OU=CA/CN=Bar:xxj31ZMTZzkVA
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/C=US/L=L.A./O=Snake Oil, Ltd./OU=Dev/CN=Quux:xxj31ZMTZzkVA</pre></div>
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<p>The second method:</p>
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<div class="example"><h3>httpd.conf</h3><pre>
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SSLVerifyClient none
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<Directory /usr/local/apache2/htdocs/secure/area>
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SSLVerifyClient require
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SSLVerifyDepth 5
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SSLCACertificateFile conf/ssl.crt/ca.crt
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SSLCACertificatePath conf/ssl.crt
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SSLOptions +FakeBasicAuth
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SSLRequireSSL
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SSLRequire %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd." \
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and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"}
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</Directory></pre></div>
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<h3><a name="intranet" id="intranet">How can I require HTTPS with strong ciphers and either basic
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authentication or client certificates for access to a subarea on the
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Intranet website for clients coming from the Internet but still allow
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plain HTTP access for clients on the Intranet?</a></h3>
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<p>Let us assume the Intranet can be distinguished through the IP
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network 192.160.1.0/24 and the subarea on the Intranet website has
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the URL <code>/subarea</code>. Then configure the following outside
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your HTTPS virtual host (so it applies to both HTTPS and HTTP):</p>
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<div class="example"><h3>httpd.conf</h3><pre>
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SSLCACertificateFile conf/ssl.crt/company-ca.crt
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<Directory /usr/local/apache2/htdocs>
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# Outside the subarea only Intranet access is granted
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Order deny,allow
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Deny from all
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Allow from 192.168.1.0/24
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</Directory>
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<Directory /usr/local/apache2/htdocs/subarea>
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# Inside the subarea any Intranet access is allowed
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# but from the Internet only HTTPS + Strong-Cipher + Password
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# or the alternative HTTPS + Strong-Cipher + Client-Certificate
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# If HTTPS is used, make sure a strong cipher is used.
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# Additionally allow client certs as alternative to basic auth.
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SSLVerifyClient optional
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SSLVerifyDepth 1
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SSLOptions +FakeBasicAuth +StrictRequire
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SSLRequire %{SSL_CIPHER_USEKEYSIZE} >= 128
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# Force clients from the Internet to use HTTPS
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RewriteEngine on
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RewriteCond %{REMOTE_ADDR} !^192\.168\.1\.[0-9]+$
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RewriteCond %{HTTPS} !=on
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RewriteRule .* - [F]
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# Allow Network Access and/or Basic Auth
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Satisfy any
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# Network Access Control
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Order deny,allow
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Deny from all
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Allow 192.168.1.0/24
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# HTTP Basic Authentication
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AuthType basic
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AuthName "Protected Intranet Area"
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AuthBasicProvider file
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AuthUserFile conf/protected.passwd
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Require valid-user
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</Directory></pre></div>
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</div></div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/ssl/ssl_howto.html" title="English"> en </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 1999-2004 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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<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></div>
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</body></html> |