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| #use "ssl_template.inc" title="HowTo" tag=howto num=5 |
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| <page_prev name="Compatibility" url="ssl_compat.html"> |
| <page_next name="F.A.Q. List" url="ssl_faq.html"> |
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| #use wml::std::toc style=nbsp |
| |
| <quotation width=200 author="Standard textbook cookie"> |
| ``The solution of this problem is trivial |
| and is left as an exercise for the reader.'' |
| </quotation> |
| |
| <p> |
| <table cellspacing=0 cellpadding=0 border=0> |
| <tr valign=bottom> |
| <td> |
| |
| <big H>ow 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. |
| |
| </td> |
| <td> |
| |
| </td> |
| <td> |
| |
| <div align=right> |
| <table cellspacing=0 cellpadding=5 border=0 bgcolor="#ccccff" width=300> |
| <tr> |
| <td bgcolor="#333399"> |
| <font face="Arial,Helvetica" color="#ccccff"> |
| <b>Table Of Contents</b> |
| </font> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <font face="Arial,Helvetica" size=-1> |
| <toc> |
| </font> |
| </td> |
| </tr> |
| </table> |
| </div> |
| |
| </td> |
| </tr> |
| </table> |
| |
| # container tag for layouting a question |
| <define-tag howto endtag=required> |
| <preserve ref> |
| <preserve toc> |
| <set-var %attributes> |
| <p> |
| <li><toc_h3 alt="<get-var toc>"></toc_h3> |
| <a name="<get-var ref>"></a> |
| <strong id="howto">%body</strong>\ |
| |
| [<a href="http://www.modssl.org/docs/2.8/ssl_howto.html#<get-var ref>"><b>L</b></a>] |
| <p> |
| <restore toc> |
| <restore ref> |
| </define-tag> |
| |
| <define-tag config endtag=required> |
| <preserve file> |
| <set-var %attributes> |
| <ifeq "<get-var file>" "" <set-var file="httpd.conf">> |
| <box header="<font face="Arial,Helvetica" color="#999999"><get-var file></font>" |
| bdwidth=1 bdcolor="#cccccc" bgcolor="#ffffff" fgcolor="#000000"> |
| <pre> |
| %body |
| </pre> |
| </box>\ |
| <restore file> |
| </define-tag> |
| |
| <h2>Cipher Suites and Enforced Strong Security</h2> |
| |
| <ul> |
| |
| <howto ref="cipher-sslv2" toc="SSLv2 only server"> |
| How can I create a real SSLv2-only server? |
| </howto> |
| |
| The following creates an SSL server which speaks only the SSLv2 protocol and |
| its ciphers. |
| |
| <p> |
| <config> |
| SSLProtocol -all +SSLv2 |
| SSLCipherSuite SSLv2:+HIGH:+MEDIUM:+LOW:+EXP |
| </config> |
| |
| <howto ref="cipher-strong" toc="strong encryption only server"> |
| How can I create an SSL server which accepts strong encryption only? |
| </howto> |
| |
| The following enables only the seven strongest ciphers: |
| |
| <p> |
| <config> |
| SSLProtocol all |
| SSLCipherSuite HIGH:MEDIUM |
| </config> |
| |
| <howto ref="cipher-sgc" toc="server gated cryptography"> |
| How can I create an SSL server which accepts strong encryption only, |
| but allows export browsers to upgrade to stronger encryption? |
| </howto> |
| |
| 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> |
| <config> |
| \# allow all ciphers for the inital handshake, |
| \# so export browsers can upgrade via SGC facility |
| SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL |
| <Directory /usr/local/apache/htdocs> |
| \# but finally deny all browsers which haven't upgraded |
| SSLRequire %{SSL_CIPHER_USEKEYSIZE} >= 128 |
| </Directory> |
| </config> |
| |
| <howto ref="cipher-perdir" toc="stronger per-directory requirements"> |
| 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? |
| </howto> |
| |
| Obviously you cannot just use a server-wide <code>SSLCipherSuite</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> |
| <config> |
| \# be liberal in general |
| SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL |
| <Location /strong/area> |
| \# but https://hostname/strong/area/ and below requires strong ciphers |
| SSLCipherSuite HIGH:MEDIUM |
| </Location> |
| </config> |
| |
| </ul> |
| |
| <h2>Client Authentication and Access Control</h2> |
| |
| <ul> |
| |
| <howto ref="auth-simple" toc="simple certificate-based client authentication"> |
| How can I authenticate clients based on certificates when I know all my |
| clients? |
| </howto> |
| |
| 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> |
| <config> |
| \# require a client certificate which has to be directly |
| \# signed by our CA certificate in ca.crt |
| SSLVerifyClient require |
| SSLVerifyDepth 1 |
| SSLCACertificateFile conf/ssl.crt/ca.crt |
| </config> |
| |
| <howto ref="auth-selective" toc="selective certificate-based client authentication"> |
| 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? |
| </howto> |
| |
| For this we again use the per-directory reconfiguration feature of mod_ssl: |
| |
| <p> |
| <config> |
| SSLVerifyClient none |
| SSLCACertificateFile conf/ssl.crt/ca.crt |
| <Location /secure/area> |
| SSLVerifyClient require |
| SSLVerifyDepth 1 |
| </Location> |
| </config> |
| |
| <howto ref="auth-particular" toc="particular certificate-based client authentication"> |
| 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? |
| </howto> |
| |
| 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 <code>mod_auth</code> based variant |
| and the <code>SSLRequire</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> |
| The first method: |
| |
| <p> |
| <config file="/usr/local/apache/conf/httpd.conf"> |
| SSLVerifyClient none |
| <Directory /usr/local/apache/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 |
| AuthUserFile /usr/local/apache/conf/httpd.passwd |
| require valid-user |
| </Directory> |
| </config> |
| |
| <p> |
| <config file="/usr/local/apache/conf/httpd.passwd"> |
| /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 |
| </config> |
| |
| <p> |
| The second method: |
| |
| <p> |
| <config> |
| SSLVerifyClient none |
| <Directory /usr/local/apache/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> |
| </config> |
| |
| <howto ref="auth-intranet" toc="intranet vs. internet authentication"> 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? |
| </howto> |
| |
| 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 |
| <tt>/subarea</tt>. Then configure the following outside your HTTPS virtual |
| host (so it applies to both HTTPS and HTTP): |
| |
| <p> |
| <config> |
| SSLCACertificateFile conf/ssl.crt/company-ca.crt |
| |
| <Directory /usr/local/apache/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/apache/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" |
| AuthUserFile conf/protected.passwd |
| Require valid-user |
| </Directory> |
| </config> |
| |
| </ul> |
| |