Httpd SSL Configuration

External

• http://httpd.apache.org/docs/2.4/ssl/
• http://wiki.centos.org/HowTos/Https
• http://www.thegeekstuff.com/2012/05/install-apache-2-on-centos-6/

Internal

• httpd Configuration#Subjects
• SSL/TLS
• Let's Encrypt

Overview

In order to protect a web site with SSL, you will need to make sure mod_ssl is available and functional, then create a virtual host that listens on port different from the non-SSL protected sites (usually 443), turn the SSLEngine on for that virtual host, and specify the paths to the certificate and the private key.

Procedure

Obtain Certificate

Obtain a certificate. Options:

• Use a generated self-signed certificate. Note that a Centos installation comes with a local certificate available in /etc/pki/tls/certs/localhost.crt and a private key /etc/pki/tls/private/localhost.key, which can be used for testing. httpd is configured by default to use it. This is how you generate a self-signed certificate.
• Install a valid certificated provided by Let's Encrypt. The procedure is available here, and usually is fully automatic:

Let's Encrypt

• Obtain a commercial certificate signed by a known CA.

Install mod_ssl and openssl

yum -y install mod_ssl
yum -y install openssl

By default, this ends up installing mod_ssl.so in /etc/httpd/modules. It also creates the default SSL configuration file ssl.conf in /etc/httpd/conf.d.

ssl.conf

ssl.conf must be included explicitly, yum installation, while it creates, it does not include it. However, usually the main httpd.conf configuration file contains an "include all conf.d" line:

IncludeOptional conf.d/*.conf

which should take care of ssl.conf inclusion. More about IncludeOptional.

If not present, explicitly add the following Include directive above the virtual host area:

Include conf.d/ssl.conf

ssl.conf contains the configuration of a default secure virtual host, and the custom secure virtual hosts should be added under it. See Secure Virtual Hosts

Listen

Restrict the secure server to listen to a specific, dedicated interface by specifying it in ssl.conf Listen:

Listen 1.2.3.4:443 https

Note that the main configuration file might still contain a Listen directive for port 80. This is fine if your web server still wants to serve unsecured pages, multiple Listen directives for different ports are legal. ⚠️ However, if more than one Listen directives instruct the server to listen on the same port, the server will fail to start. More details about Listen are available here:

Listen directive

Log Location

By default, the SSL logs level and location is different:

ErrorLog logs/ssl_error_log
TransferLog logs/ssl_access_log
LogLevel warn

localhost Key and Certificate

These are self-signed, test certificates.

Secure Virtual Hosts

Add custom secure virtual hosts at the bottom of ssl.conf:

<VirtualHost 1.2.3.4:443>
    ServerName praetorian.novaordis.com
    SSLEngine on
    SSLCertificateFile "/etc/pki/tls/certs/praetorian.novaordis.com.crt"
    SSLCertificateKeyFile "/etc/pki/tls/private/praetorian.novaordis.com.key"
    SSLCertificateChainFile "/etc/pki/tls/certs/praetorian.novaordis.com-godaddy-chain.crt"
    DocumentRoot "/var/www/praetorian.novaordis.com"
</VirtualHost>

GoDaddy certificate installation instructions: https://www.godaddy.com/help/installing-an-ssl-certificate-in-apache-centos-5238

Site Private Key

Place the private key under /etc/pki/tls/private.

Name it <secure-site-FQN>.key. Example: praetorian.novaordis.com.key.

Make it available to apache:apache and only it:

chown apache:apache praetorian.novaordis.com.key
chmod go-rwx praetorian.novaordis.com.key

Site Certificate

Place the certificate file under /etc/pki/tls/certs.

Name it <secure-site-FQN>.crt. Example: praetorian.novaordis.com.crt.

Site Chain/Intermediate Certificate

Most trusted certificates require that you install at least one other intermediate/chain certificate on the server, to link your certificate up to the trusted source. For example, the GoDaddy-issued certificates require that.

Place the intermediate/chain certificate file under /etc/pki/tls/certs.

Name it <secure-site-FQN>-godaddy-chain.crt. Example: praetorian.novaordis.com-godaddy-chain.crt.

Specify the path to the certificate chain under the corresponding secure virtual host as:

SSLCertificateChainFile "/etc/pki/tls/certs/praetorian.novaordis.com-godaddy-chain.crt"

Note that for Apache 2.4.8 and higher you need to use SSLCACertificatePath instead.

Test Certificate

Use all of below. Testing is a good idea, test may reveal weaknesses and vulnerabilities. If everything was installed correctly, the checks should be successful.

• https://casecurity.ssllabs.com
• https://www.sslshopper.com/ssl-checker.html or similar.

Other Details

• Protect against the POODLE Attack.
• Disable support for RC4 Cipher
• Support Forward Secrecy with the reference browsers.

Troubleshooting

"SSLCertificateFile: file '/etc/pki/tls/certs/kb.novaordis.com.crt' does not exist or is empty"

If I get an error message similar to SSLCertificateFile: file '/etc/pki/tls/certs/kb.novaordis.com.crt' does not exist or is empty, and the certificate file exists, is readable and it is a valid certificate, the cause is related to selinux misconfiguration.