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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 2.1</p> |
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| <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-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> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="../en/ssl/ssl_howto.html" title="English"> en </a></p> |
| </div> |
| |
| <blockquote> |
| <p>The solution of 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 constraints for an SSL-aware |
| webserver is not always obvious because of the coherences between SSL, |
| HTTP and Apache's way of processing requests. This chapter gives |
| instructions on how to solve such 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 coherences.</p> |
| </div> |
| <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#ciphersuites">Cipher Suites and Enforced Strong Security</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#accesscontrol">Client Authentication and Access Control</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="ciphersuites" id="ciphersuites">Cipher Suites and Enforced Strong Security</a></h2> |
| |
| <ul> |
| <li><a href="#realssl">SSLv2 only server</a></li> |
| <li><a href="#onlystrong">strong encryption only server</a></li> |
| <li><a href="#upgradeenc">server gated cryptography</a></li> |
| <li><a href="#strongurl">stronger per-directory requirements</a></li> |
| </ul> |
| |
| <h3><a name="realssl" id="realssl">How can I create a real SSLv2-only server?</a></h3> |
| |
| <p>The following creates an SSL server which speaks only the SSLv2 protocol and |
| its ciphers.</p> |
| |
| <div class="example"><h3>httpd.conf</h3><p><code> |
| SSLProtocol -all +SSLv2<br /> |
| SSLCipherSuite SSLv2:+HIGH:+MEDIUM:+LOW:+EXP<br /> |
| </code></p></div> |
| |
| |
| <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 seven strongest ciphers:</p> |
| <div class="example"><h3>httpd.conf</h3><p><code> |
| SSLProtocol all<br /> |
| SSLCipherSuite HIGH:MEDIUM<br /> |
| </code></p></div> |
| |
| |
| <h3><a name="upgradeenc" id="upgradeenc">How can I create an SSL server which accepts strong encryption |
| only, but allows export browsers to upgrade to stronger encryption?</a></h3> |
| |
| <p>This facility is called Server Gated Cryptography (SGC) and details |
| you can find in the <code>README.GlobalID</code> document in the |
| mod_ssl distribution. In short: The server has a Global ID server |
| certificate, signed by a special CA certificate from Verisign which |
| enables strong encryption in export browsers. This works as following: |
| The browser connects with an export cipher, the server sends its Global |
| ID certificate, the browser verifies it and subsequently upgrades the |
| cipher suite before any HTTP communication takes place. The question |
| now is: How can we allow this upgrade, but enforce strong encryption. |
| Or in other words: Browser either have to initially connect with |
| strong encryption or have to upgrade to strong encryption, but are |
| not allowed to keep the export ciphers. The following does the trick:</p> |
| <div class="example"><h3>httpd.conf</h3><p><code> |
| # allow all ciphers for the initial handshake,<br /> |
| # so export browsers can upgrade via SGC facility<br /> |
| SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br /> |
| <br /> |
| <Directory /usr/local/apache2/htdocs><br /> |
| # but finally deny all browsers which haven't upgraded<br /> |
| SSLRequire %{SSL_CIPHER_USEKEYSIZE} >= 128<br /> |
| </Directory> |
| </code></p></div> |
| |
| |
| <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 you cannot just use a server-wide <code class="directive"><a href="../mod/mod_ssl.html#sslciphersuite">SSLCipherSuite</a></code> which restricts the |
| ciphers to the strong variants. But mod_ssl allows you to reconfigure |
| the cipher suite in per-directory context and automatically forces |
| a renegotiation of the SSL parameters to meet the new configuration. |
| So, the solution is:</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:MEDIUM<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">simple certificate-based client authentication</a></li> |
| <li><a href="#arbitraryclients">selective certificate-based client authentication</a></li> |
| <li><a href="#certauthenticate">particular certificate-based client authentication</a></li> |
| <li><a href="#intranet">intranet vs. internet authentication</a></li> |
| </ul> |
| |
| <h3><a name="allclients" id="allclients">How can I authenticate clients based on certificates when I know |
| all my clients?</a></h3> |
| |
| <p>When you know your user community (i.e. a closed user group |
| situation), as it's the case for instance in an Intranet, you can |
| use plain certificate authentication. All you have 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 authenticate my clients for a particular URL based on |
| certificates but still allow arbitrary clients to access the remaining |
| parts of the server?</a></h3> |
| |
| <p>For this we again use the per-directory reconfiguration feature |
| 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 authenticate only particular clients for a some URLs based |
| on certificates but still allow arbitrary clients to access the remaining |
| parts of the server?</a></h3> |
| |
| <p>The key is to check for various ingredients of the client certificate. |
| Usually this means to check the whole or part of the Distinguished |
| 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 |
| good when the clients are of totally different type, i.e. when their |
| DNs have no common fields (usually the organisation, etc.). In this |
| case you've to establish a password database containing <em>all</em> |
| clients. The second method is better when your clients are all part of |
| a common hierarchy which is encoded into the DN. Then you can match |
| them more easily.</p> |
| |
| <p>The first method:</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> |
| |
| <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>The second method:</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 a subarea on the |
| Intranet website for clients coming from the Internet but still allow |
| plain HTTP access for clients on the Intranet?</a></h3> |
| |
| <p>Let us assume the Intranet can be distinguished through the IP |
| network 192.160.1.0/24 and the subarea on the Intranet website has |
| the URL <code>/subarea</code>. Then configure the following outside |
| your HTTPS virtual host (so 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> |
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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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| <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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