docs/manual/ssl/ssl_howto.xml - httpd - Git at Google

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

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

 <summary>
 <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 is 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>
 </summary>

 <section id="ciphersuites">
 <title>Cipher Suites and Enforced Strong Security</title>
 <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>

 <section id="realssl">
 <title>How can I create a real SSLv2-only server?</title>
     <p>The following creates an SSL server which speaks only the SSLv2 protocol and
     its ciphers.</p>

     <example><title>httpd.conf</title>
       SSLProtocol -all +SSLv2<br />
       SSLCipherSuite SSLv2:+HIGH:+MEDIUM:+LOW:+EXP<br />
     </example>
 </section>

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

 <section id="upgradeenc">
 <title>How can I create an SSL server which accepts strong encryption
 only, but allows export browsers to upgrade to stronger encryption?</title>
     <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>
     <example><title>httpd.conf</title>
       # allow all ciphers for the inital handshake,<br />
       # so export browsers can upgrade via SGC facility<br />
       SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL<br />
       <br />
       &lt;Directory /usr/local/apache2/htdocs&gt;<br />
       # but finally deny all browsers which haven't upgraded<br />
       SSLRequire %{SSL_CIPHER_USEKEYSIZE} &gt;= 128<br />
       &lt;/Directory&gt;
     </example>
 </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 you cannot just use a server-wide <directive
     module="mod_ssl">SSLCipherSuite</directive> 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>
     <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:MEDIUM<br />
       &lt;/Location&gt;
     </example>
 </section>
 </section>
 <!-- /ciphersuites -->

 <section id="accesscontrol">
 <title>Client Authentication and Access Control</title>
 <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>

 <section id="allclients">
 <title>How can I authenticate clients based on certificates when I know
 all my clients?</title>
     <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 verifiy 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 authenticate my clients for a particular URL based on
 certificates but still allow arbitrary clients to access the remaining
 parts of the server?</title>
     <p>For this we again use the per-directory reconfiguration feature
     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 authenticate only particular clients for a some URLs based
 on certificates but still allow arbitrary clients to access the remaining
 parts of the server?</title>
     <p>The key is to check for various ingredients of the client certficate.
     Usually this means to check the whole or part of the Distinguished
     Name (DN) of the Subject. For this two methods exists: The <module
     >mod_auth</module> based variant and the <directive
     module="mod_ssl">SSLRequire</directive> 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>
     <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>

     <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>The second method:</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 a subarea on the
 Intranet website for clients coming from the Internet but still allow
 plain HTTP access for clients on the Intranet?</title>
    <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>

     <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 -->

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

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

	<summary>
	<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 is 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>
	</summary>

	<section id="ciphersuites">
	<title>Cipher Suites and Enforced Strong Security</title>
	<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>

	<section id="realssl">
	<title>How can I create a real SSLv2-only server?</title>
	<p>The following creates an SSL server which speaks only the SSLv2 protocol and
	its ciphers.</p>

	<example><title>httpd.conf</title>
	SSLProtocol -all +SSLv2<br />
	SSLCipherSuite SSLv2:+HIGH:+MEDIUM:+LOW:+EXP<br />
	</example>
	</section>

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

	<section id="upgradeenc">
	<title>How can I create an SSL server which accepts strong encryption
	only, but allows export browsers to upgrade to stronger encryption?</title>
	<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>
	<example><title>httpd.conf</title>
	# allow all ciphers for the inital 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>
	</example>
	</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 you cannot just use a server-wide <directive
	module="mod_ssl">SSLCipherSuite</directive> 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>
	<example>
	# 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>
	</example>
	</section>
	</section>
	<!-- /ciphersuites -->

	<section id="accesscontrol">
	<title>Client Authentication and Access Control</title>
	<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>

	<section id="allclients">
	<title>How can I authenticate clients based on certificates when I know
	all my clients?</title>
	<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 verifiy 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 authenticate my clients for a particular URL based on
	certificates but still allow arbitrary clients to access the remaining
	parts of the server?</title>
	<p>For this we again use the per-directory reconfiguration feature
	of <module>mod_ssl</module>:</p>

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

	<section id="certauthenticate">
	<title>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?</title>
	<p>The key is to check for various ingredients of the client certficate.
	Usually this means to check the whole or part of the Distinguished
	Name (DN) of the Subject. For this two methods exists: The <module
	>mod_auth</module> based variant and the <directive
	module="mod_ssl">SSLRequire</directive> 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>
	<example><title>httpd.conf</title><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>
	</example>

	<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>The second method:</p>

	<example><title>httpd.conf</title><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>
	</example>
	</section>

	<section id="intranet">
	<title>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?</title>
	<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>

	<example><title>httpd.conf</title><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>
	</example>
	</section>
	</section>
	<!-- /access control -->

	</manualpage>