This document is intended to be a quick guide to generating and installing an SSL certificate on an Apache web server with the mod_ssl module. While this is not an overly difficult process, it does involve running several long commands with numerous options. This document should be all that you need to walk you through the process of generating the certificate and installing it in your web server.
This section will serve as a very brief introduction to SSL, the Secure Socket Layer. Cryptography is a very extensive topic which literally fills volumes of texts. The following is an extremely simplified view of how SSL is implemented and what part the certificate plays in the entire process. There may be some small inaccuracies in an effort to present the information in the easiest possible format.
Normal web traffic is sent unencrypted over the Internet. That is, anyone with access to the right tools can snoop all of that traffic. Obviously, this can lead to problems, especially where security and privacy is necessary, such as in credit card data and bank transactions. The Secure Socket Layer is used to encrypt the data stream between the web server and the web client (the browser).
SSL makes use of what is known as asymmetric cryptography, commonly referred to as public key cryptography (PKI). With public key cryptography, two keys are created, one public, one private. Anything encrypted with either key can only be decrypted with its corresponding key. Thus if a message or data stream were encrypted with the server's private key, it can be decrypted only using its corresponding public key, ensuring that the data only could have come from the server.
If SSL utilizes public key cryptography to encrypt the data stream traveling over the Internet, why is a certificate necessary? The technical answer to that question is that a certificate is not really necessary--the data is secure and cannot easily be decrypted by a third party. However, certificates do serve a crucial role in the communication process. The certificate, signed by a trusted Certificate Authority (CA), ensures that the certificate holder is really who he claims to be. Without a trusted signed certificate, your data may be encrypted, however, the party you are communicating with may not be whom you think. Without certificates, impersonation attacks would be much more common.
The openssl toolkit is used to generate an RSA Private Key and CSR (Certificate Signing Request). It can also be used to generate self-signed certificates which can be used for testing purposes or internal usage. The utility used to do all of these tasks is known simply as openssl. It should be installed in the /usr/local/ssl/bin directory. You may want to add this directory to your PATH, or copy or link the openssl utility to a directory that is already in your PATH so that you do not have to type the full path to the executable. The examples below will assume that openssl is in a location that is accessible to you without using the full path to the command.
The first step is to create your RSA Private Key. This key is a 1024 bit RSA key which is encrypted using Triple-DES and stored in a PEM format so that it is readable as ASCII text. We will use several files as random seed enhancers which will help to make the key more secure. Text files that have been compressed with a utility such as gzip are good choices. The key is generated using the following command, where file1:file2:etc represents the random compressed files.
The command will prompt you for a pass-phrase and then store the key in the file server.key. It is critical that the pass-phrase be secure and not forgotten. If either the key is lost, or the pass-phrase is forgotten, the certificate will be useless! It cannot be stressed enough how important the private key is to the certificate. If the private key and pass-phrase are compromised, the certificate will have to be revoked, costing you the price of the certificate all over again if you have paid an authority for the certificate. It may be a wise idea to back this file up to secure media, such as tape or diskette.
Once the private key is generated a Certificate Signing Request can be generated. The CSR is then used in one of two ways. Ideally, the CSR will be sent to a Certificate Authority, such as Thawte or Verisign who will verify the identity of the requestor and issue a signed certificate. The second option is to self-sign the CSR, which will be demonstrated in the next section.
What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank.
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Domain.com, Inc.
At this point you will need to generate a self-signed certificate because you either don't plan on having your certificate signed by a CA, or you wish to test your new SSL implementation while the CA is signing your certificate. In my experience dealing with Thawte, it can take up to a week or more before receiving your signed certificate. The time it takes to receive the certificate will vary based on how quickly they receive your required documentation. This temporary certificate will generate an error in the client browser to the effect that the signing certificate authority is unknown and not trusted.
When Apache with mod_ssl is installed, it creates several directories in the Apache config directory. The location of this directory will differ depending on how Apache was compiled. If using my instructions on compiling Apache, the config directory is /usr/local/apache/etc. The directories mod_ssl creates include ssl.crt, ssl.csr, and ssl.key. These are good locations to store server certificates, CSRs, and private keys, respectively. If there will be multiple SSL enabled hosts on one server, it may be good practice to name the files with the fully qualified domain name of the SSL enabled host.
This will create an SSL virtualhost named www.domain.com, which is accessed via port 443 (the standard port for https) on the default IP address of the web server. It is possible to add as many additional virtualhosts as there are IP addresses that the web server listens to. Simply add additional virtualhost blocks inside of the <IfDefine SSL> and </IfDefine> tags. Due to the nature of the SSL encryption of the HTTP traffic, it is NOT possible to have name-based (HTTP1.1) SSL virtual hosts. To create a new SSL virtualhost on a different IP address, simply replace _default_ with the IP address of the virtualhost.
After adding the virtualhost to the ssl.conf file, Apache must be killed and restarted in order for it to recognize the new virtualhost. Unfortunately, this is one of the rare instances where a simple HUP signal will not work. After restarting the server, depending on whether the encrypted or unencrypted key was used, Apache will prompt you for the pass-phrase(s) of the SSL virtualhost(s). Enter the pass-phrase(s) and the web server will start.
Now, point your favorite browser to the new virtualhost you just created, remembering to use https:// instead of http://, and you should be greeted with a warning dialog if you are using the self-signed certificate. Acknowledge the dialog and the page will continue to load, protected by SSL. The status bar of your browser should be graced by the 'lock' icon, which signifies the page is protected via SSL. This is all there is to it!