Building a Secure RedHat Apache Server HOWTO: Configuring your Apache Server

4. Configuring your Apache Server

The Apache server must be configured with supplementary API modules in order to support SSL. There are many SSL software packages available. My examples are based on Apache configured with ModSSL and OpenSSL. There are countless mailing lists and newsgroups available to support these products. You may find these instructions helpful for some commercial SSL software packages that are based on the Apache web server.

A few things to keep in mind: You can have multiple virtual hosts on the same server. You can have numerous name-based virtual hosts on the same IP address. You can also have numerous name-based virtual hosts and one (1) secure virtual host on the same IP. But - you cannot have multiple secure virtual hosts on the same IP. The question that so many ask: Why? The answer is: SSL works below the application layer. Name based hosts are not defined until the application layer.

Specifically, you cannot have multiple secure virtual hosts on the same SOCKET (IP address + port). By default, a secure host will use port 443. You can change configure your virtual host to use a different port number with the same IP, thus creating another socket. There are many disadvantages to this approach. The most obvious disadvantage is that if you are not using the default port, your URL must also contain the port number to access the secure site.

Example:

Site using default port - www.something.com - would be accessed as https://www.something.com
A site using port 8888 would be accessed as https://www.something.com:8888

Another disadvantage is that if you introduce more ports, you will be providing more opportunities for port sniffing hackers. Last, if you select a port that is used by something else, you will create conflict problem.

4.1 Define a Secure Virtual Host

Setting up virtual hosts is fairly straightforward. I will go through the basics of setting up a secure virtual host.

In these examples, I use the .crt and .key file extensions. That is my personal way of avoiding confusion with the various files. With Apache, you can use any extension you choose - or no extension at all.

All of your secure virtual hosts should be contained within <IfDefine SSL> and </IfDefine SSL>, usually located towards the end of the httpd.conf file.

An example of a secure virtual host:


<VirtualHost 172.18.116.42:443>
DocumentRoot /etc/httpd/htdocs
ServerName www.somewhere.com
ServerAdmin [email protected]
ErrorLog /etc/httpd/logs/error_log
TransferLog /etc/httpd/logs/access_log
SSLEngine on
SSLCertificateFile /etc/httpd/conf/ssl.crt/server.crt
SSLCertificateKeyFile /etc/httpd/conf/ssl.key/server.key
SSLCACertificateFile /etc/httpd/conf/ssl.crt/ca-bundle.crt
<Files ~ "\.(cgi|shtml)$">
      SSLOptions +StdEnvVars
</Files>
<Directory "/etc/httpd/cgi-bin">
      SSLOptions +StdEnvVars
</Directory>
SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown
CustomLog /etc/httpd/logs/ssl_request_log \
          "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
</VirtualHost>

The directives that are the most important for SSL are the SSLEngine on, SSLCertificateFile, SSLCertificateKeyFile, and in many cases SSLCACertificateFile directives.

SSL Engine

"SSLEngine on" - this is ModSSL's command to start SSL.

SSLCertificateFile

SSLCertificateFile Tells Apache where to find the certificate file and what it is named. The example above shows "server.crt" as the certificate file name. This is the default that is added when you configure ModSSL with Apache. I personally don't recommend using the default names. Save yourself some frustration and name your certificates as servername.crt (domainname.crt). You may also decide to use an alternative directory than the default /etc/httpd/conf/ssl.crt or /usr/local/apache/conf/ssl.crt. Just remember to make the necessary changes to the path.

SSLCertificateKeyFile

SSLCertificateKeyFile tells Apache the name of the private key and where to find it. The directory defined here should have read/write permissions for root only. No one else should have access to this directory.

SSLCACertificateFile

The SSLCACertificateFile directive tells Apache where to find the Intermediate (root) certificate. This directive may or may not be necessary depending on the CA that you are using. This certificate is essentially a ring of trust.

Intermediate Certificate - A Certificate Authority obtains a certificate in much the same way as you. This is known as an intermediate certificate. It basically says that the holder of the intermediate certificate is whom they say they are and is authorized to issue certificates to customers. Web browsers have a list of "trusted" certificate authorities that is updated with each release. If a Certificate authority is fairly new, its intermediate certificate may not be in the browser's list of trusted CA's. Combine this with the fact that most people don't update their browsers very often; it could take years before a CA is recognized as trusted automatically. The solution is to install the intermediate certificate on the server using the SSLCACertificateFile directive. Usually, a "trusted" CA issues the intermediate certificate. If it is not, then you may need to use the SSLCertificateChainFile directive, although this is unlikely.

4.2 Certificate Examples

Server Certificate File

Contents of the Certificate File


Certificate:
   Data:
     Version: 3 (0x2)
     Serial Number: 1516 (0x5ec)
     Signature Algorithm: md5WithRSAEncryption
     Issuer: C=US, O=Equifax Secure Inc, CN=Equifax Secure E-Business CA
     Validity
       Not Before: Jul 12 15:21:01 2000 GMT
       Not After : Jun  2 22:42:34 2001 GMT
     Subject: C=us, ST=ga, L=atlanta, O=Equifax, OU=Rick, CN=172.18.116.44/[email protected]
     Subject Public Key Info:
       Public Key Algorithm: rsaEncryption
       RSA Public Key: (1024 bit)
           Modulus (1024 bit):
             00:c8:eb:93:26:97:ca:00:ce:4c:e4:f3:fd:43:31:
             cd:53:ed:b4:8a:ad:93:84:dc:7a:48:39:b5:28:57:
             03:7f:a9:ac:3e:58:6a:7a:e3:52:3e:1e:52:58:a2:
             6f:23:ad:bb:84:d8:88:ed:6d:a5:da:08:6b:c8:6c:
             a5:4c:34:67:d8:46:1c:ca:20:50:b0:e8:54:7f:ca:
             5e:ef:09:ff:6e:8d:a6:2b:02:f5:54:0f:c2:d0:45:
             12:ad:66:e7:8b:dd:68:be:64:a4:9b:69:bd:a4:1a:
             5e:ef:09:ff:6e:8d:a6:2b:02:f5:54:0f:c2:d0:45:
             12:ad:66:e7:8b:dd:68:be:64:a4:9b:69:bd:a4:1a:
             5a:2f:3b:6e:73:84:d8:d6:17:bd:12:39:34:fa:3d:
             d8:a9:e8:59:3c:c2:61:c5:b3
           Exponent: 65537 (0x10001)
     X509v3 extensions:
       X509v3 Key Usage: critical
          Digital Signature, Non Repudiation, Key Encipherment, Data Encipherment
       Netscape Cert Type:
          SSL Server
       X509v3 Authority Key Identifier:
          keyid:5B:E0:A8:75:1C:78:02:47:71:AB:CE:27:32:E7:24:88:42:28:48:56
   Signature Algorithm: md5WithRSAEncryption
     87:53:74:e9:e1:a6:10:56:8c:fa:63:0e:7b:72:ff:76:4b:79:
     0e:49:2a:58:ed:71:7a:bf:77:61:fa:e8:74:04:37:8c:d3:6a:
     9a:3d:80:76:7a:c3:64:30:e7:1b:40:25:4e:2a:81:8b:e5:ac:
     76:a4:38:67:cc:3f:93:43:e1:1d:c3:8d:ba:ed:cc:d7:aa:a4:
     ab:d3:84:77:7c:8f:26:f6:dd:ba:3b:6a:99:81:e1:9e:7e:0f:
     ca:a6:ff:c0:c3:59:6e:dc:a6:03:23:bf:8f:24:ff:15:ad:ac:
     0d:85:fc:38:bf:d1:24:2d:1a:d3:72:55:12:95:5f:65:f0:60:
     df:b1

Private Key File

Contents of the Private Key


read RSA key
Enter PEM pass phrase:
Private-Key: (1024 bit)
modulus:
    00:c8:eb:93:26:97:ca:00:ce:4c:e4:f3:fd:43:31:
    cd:53:ed:b4:8a:ad:93:84:dc:7a:48:39:b5:28:57:
    03:7f:a9:ac:3e:58:6a:7a:e3:52:3e:1e:52:58:a2:
    6f:23:ad:bb:84:d8:88:ed:6d:a5:da:08:6b:c8:6c:
    a5:4c:34:67:d8:46:1c:ca:20:50:b0:e8:54:7f:ca:
    5e:ef:09:ff:6e:8d:a6:2b:02:f5:54:0f:c2:d0:45:
    12:ad:66:e7:8b:dd:68:be:64:a4:9b:69:bd:a4:1a:
    5a:2f:3b:6e:73:84:d8:d6:17:bd:12:39:34:fa:3d:
    d8:a9:e8:59:3c:c2:61:c5:b3
publicExponent: 65537 (0x10001)
privateExponent:
    00:b6:57:7d:3b:58:24:1e:a9:1b:85:e9:9c:9e:5f:
    d3:3d:69:0c:21:93:37:bf:2b:2c:da:e1:6c:74:48:
    cb:c7:0f:60:5f:50:74:8a:44:45:be:54:5c:5d:4e:
    45:58:f6:f1:a8:b5:af:46:f2:ec:c2:bc:43:bd:28:
    44:b7:ad:13:d3:ca:de:59:24:e8:fa:f8:e5:5f:45:
    38:2c:a0:a3:de:98:13:d8:80:38:e1:47:53:4c:ea:
    e4:66:c3:82:93:89:c3:90:83:44:e1:13:4f:74:76:
    e2:c0:89:97:77:5f:33:d8:7d:27:21:52:55:c2:d7:
    dc:01:f9:bc:21:8d:a3:f5:c1
prime1:
    00:e3:2d:6b:5e:05:6b:e1:46:e6:ab:ae:f3:8b:d0:
    5f:94:5c:6f:f5:47:46:1d:4e:66:d3:7e:98:18:e0:
    2c:0d:08:ca:b7:29:72:af:53:62:30:ec:be:26:1f:
    cc:5a:ed:65:62:65:70:1e:18:19:61:e3:77:00:a7:
    3a:9e:4e:12:93
prime2:
    00:e2:69:56:78:e8:39:ff:17:db:cc:39:d7:7f:70:
    41:dc:c5:59:43:16:c1:84:4c:ae:e7:5d:8a:c5:4b:
    da:88:8e:03:99:7c:88:f2:8a:13:31:57:44:e0:b5:
    c8:0a:60:b0:05:de:f6:9e:f2:00:ec:37:21:8d:3b:
    dc:8e:c9:d4:61
exponent1:
    1a:ad:6a:be:4f:c4:ab:5f:b8:16:d1:24:a8:76:7f:
    c2:dc:58:09:65:a5:46:2b:be:c7:77:46:45:25:8e:
    06:b9:d1:94:50:b9:b6:fd:03:ba:db:12:39:47:e2:
    a7:8a:d9:2d:04:dc:75:ac:3e:ce:cf:f7:59:8c:49:
    c5:ed:45:21
exponent2:
    2d:4e:fd:32:06:ef:0c:40:7f:08:d8:8e:6a:7f:51:
    7e:d7:b3:6c:3c:92:8f:62:35:22:31:d3:02:76:92:
    8d:ff:35:73:32:bb:c9:25:9e:7f:a2:42:33:61:cd:
    5d:5e:49:fb:72:ca:11:b6:c6:3e:7f:2d:e4:b0:95:
    0b:b2:12:21
coefficient:
    50:52:09:22:cb:fb:b2:b8:58:85:ab:1d:82:b9:6e:
    d0:f6:dc:e8:ce:a6:5d:a1:ff:c8:4d:3b:2b:1c:19:
    64:f0:c4:4a:bc:b2:1d:2b:2d:09:59:83:a3:9a:89:
    f8:db:2c:2c:8a:bd:fd:a3:16:51:76:aa:ce:ea:85:
    6b:1c:9f:f7

4.3 Restart the Web Server

The script to restart the webserver may be located in /usr/local/sbin, /usr/sbin, (where the script is called httpd) or /usr/local/apache/bin (where the script is called apachectl). If you are not running the server with SSL enabled, you will need to stop and start the server. You may also write your own customized scripts to start, restart, and stop your server. As long as it starts the SSL engine, you should be OK.

The commands are:


httpd stop
httpd startssl
httpd restart


apachectl stop
apachectl startssl
apachectl restart

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