Setting up SSL for Apache HTTPD

Introduction

I recently had a need to setup a private directory on my web server that could only be accessed by a handful of selected people. The content also needed to be encrypted in transit. This mini-HOWTO details how I did this on a CentOS 5.3/Apache 2.2.3 server using mod_ssl and OpenSSL (0.9.8e and higher). Here are the goals of this small project:

• Require HIGH or MEDIUM level SSL/TLS encryption at the transport (TCP) layer
• Browser must use SSLv3 or TLSv1, not SSLv2
• Require username/password authentication for some subdirectories
• Learn about TLS certificates
• Be a mini-CA (Certificate Authority)
• Use a non-standard port to keep most of the port-scanning riffraff away
• Create client certificates, and require them for specific directories

The key to this whole system is the SSL/TLS protocol. SSL stands for Secure Sockets Layer, and it was developed by Netscape to enable secure transactions over the Web. It operates between the TCP layer and the HTTP application layer. TLSv1 is the IETF standard implementation, based on SSLv3. TLS stands for Transport Layer Security.

Assumptions/Prerequisites

First and foremost, this document assumes that you are using some flavor of Linux, Apache 2.2.x, (with mod_ssl) and that you have OpenSSL installed. These particular instructions were generated using CentOS 5.3. You should also check out the excellent documentation at [httpd.Apache.Org]. Other assumptions:

• This will be used over the Internet
• Your DNS configuration is correct (hostname=FQDN, PTR records O.K., etc.)
• Your firewall is setup to allow connections on the chosen https:// port
• You have a second machine with Mozilla or another modern browser for testing purposes
• In these examples, my FQDN and hostname is: d3xt3r01.tk

Most client tests were performed with the Mozilla web browser. Mozilla is the "reference platform".

Step 1: Setup your own CA (Certificate Authority)

In order to run a secure (SSL/TLS encrypted) web server, you have to have a private key and a certificate for the server. For a commercial web site, you will probably want to purchase a certificate signed by a well-known root CA. For Intranet or special-purpose uses like this, you can be your own CA. This is done with the OpenSSL tools.

Here, we will make a private CA key and a private CA X.509 certificate. We will also make a directory for the certs and keys:

 [root]# mkdir /root/CA
 [root]# chmod 0770 /root/CA
 [root]# cd /root/CA
 [root]# openssl genrsa -des3 -out my-ca.key 2048
 Generating RSA private key, 2048 bit long modulus
 ..........................................................................+++
 ............+++
 e is 65537 (0x10001)
 Enter pass phrase for my-ca.key:
 Verifying - Enter pass phrase for my-ca.key:
 
 [root]# openssl req -new -x509 -days 3650 -key my-ca.key -out my-ca.crt
 Enter pass phrase for my-ca.key:
 You are about to be asked to enter information that will be incorporated
 into your certificate request.
 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
 For some fields there will be a default value,
 If you enter '.', the field will be left blank.
 -----
 Country Name (2 letter code) [GB]:RO
 State or Province Name (full name) [Berkshire]:Dolj
 Locality Name (eg, city) [Newbury]:Craiova
 Organization Name (eg, company) [My Company Ltd]:d3xt3r01.tk
 Organizational Unit Name (eg, section) []:IT
 Common Name (eg, your name or your server's hostname) []:d3xt3r01.tk
 Email Address []:dexter@d3xt3r01.tk
 [root]# openssl x509 -in my-ca.crt -text -noout

Notes: The first OpenSSL command makes the key. The second command makes the X.509 certificate with a 10-year lifetime. The third command lets you view the completed certificate. Make sure that you keep the password in a safe place, you will need this every time you sign another certificate! You will probably also want to make backups of the cert and key and lock them in a safe place.

Step 2: Make a key and a certificate for the web server

Now, we have to make an X.509 certificate and corresponding private key for the web server. Rather than creating a certificate directly, we will create a key and a certificate request, then "sign" the certificate request with the CA key we made in Step 1. You can make keys for multiple web servers this way. One thing to note is that SSL/TLS private keys for web servers need to be either 512 or 1024 bits. Any other key size may be incompatible with certain browsers.

 [root]# openssl genrsa -des3 -out mars-server.key 1024
 Generating RSA private key, 1024 bit long modulus
 ..................++++++
 .................++++++
 e is 65537 (0x10001)
 Enter pass phrase for mars-server.key:
 Verifying - Enter pass phrase for mars-server.key:
 [root]# openssl req -new -key mars-server.key -out mars-server.csr
 Enter pass phrase for mars-server.key:
 You are about to be asked to enter information that will be incorporated
 into your certificate request.
 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
 For some fields there will be a default value,
 If you enter '.', the field will be left blank.
 -----
 Country Name (2 letter code) [GB]:TW
 State or Province Name (full name) [Berkshire]:Taipei County
 Locality Name (eg, city) [Newbury]:Nankang
 Organization Name (eg, company) [My Company Ltd]:d3xt3r01.tk
 Organizational Unit Name (eg, section) []:Web Services
 Common Name (eg, your name or your server's hostname) []:d3xt3r01.tk <=== This must be the real  FQDN of your server!!!
 Email Address []:hostmaster@d3xt3r01.tk
 Please enter the following 'extra' attributes
 to be sent with your certificate request
 A challenge password []:
 An optional company name []:
[root]# openssl x509 -req -in mars-server.csr -out mars-server.crt -sha1 -CA my-ca.crt -CAkey my-ca.key -CAcreateserial -days 3650
 Signature ok
 subject=/C=TW/ST=Taipei County/L=Nankang/O=d3xt3r01.tk/OU=Web Services/CN=d3xt3r01.tk/Email=hostmaster@d3xt3r01.tk
 Getting CA Private Key
 Enter pass phrase for my-ca.key:
 [root]# openssl x509 -in mars-server.crt -text -noout

Make sure that your server name is the same as the FQDN that your clients will use when connecting to your site. Also, let's get in the habit of protecting our keys with appropriate permissions:

 [root]# chmod 0400 *.key

Now, we need to move the new keys and certs into the proper directories in the /etc/httpd hierarchy:

 [root]# mkdir /etc/httpd/CA
 [root]# cp mars-server.crt /etc/httpd/CA
 [root]# cp mars-server.key /etc/httpd/CA
 [root]# cp my-ca.crt /etc/httpd/CA

Step 3: Create directories and files for the secure web service

I do not want the secure branch of my webserver directory tree to be part of my "insecure" branch that serves unencrypted files. My normal web root directory is /var/www/html . The document root for the secure web server will be located at /var/www/SSL .

 [root]# mkdir /var/www/SSL
 [root]# chmod 0775 /var/www/SSL
 [root]# cd /var/www/SSL
 [root]# mkdir Passneeded
 [root]# mkdir Certneeded
 [root]# mkdir PassAndCert

For testing purposes, I added a very simple test SSL index file into /var/www/SSL . Save it as index.html . Copy some JPEG files and text files into each directory, so that there will be something to look at/retrieve in each directory.

Step 4: Configure the Apache web server

On a default CentOS 5.3 install, there are two config files that concern us: httpd.conf and ssl.conf. All of our changes will be made in the /etc/httpd/conf.d/ssl.conf file. It is not necessary to modify the httpd.conf file to accomplish our goals on a stock CentOS 5.3 server. Here are the changes/additions to ssl.conf :

 # Here, I am allowing only "high" and "medium" security key lengths.
 SSLCipherSuite HIGH:MEDIUM
 # Here I am allowing SSLv3 and TLSv1, I am NOT allowing the old SSLv2.
 SSLProtocol all -SSLv2
 #   Server Certificate:
 SSLCertificateFile /etc/httpd/CA/mars-server.crt
 #   Server Private Key:
 SSLCertificateKeyFile /etc/httpd/CA/mars-server.key
 #   Server Certificate Chain:
 SSLCertificateChainFile /etc/httpd/CA/my-ca.crt
 #   Certificate Authority (CA):
 SSLCACertificateFile /etc/httpd/CA/my-ca.crt
 # This is needed so that you can use auto-indexing for some directories in the 
 # /var/www/SSL directory branch.  This can be handy if you would like to have 
 # a list of sensitive files for people to download.
 <Directory "/var/www/SSL">
         Options Indexes
         AllowOverride None
         Allow from from all
         Order allow,deny
 </Directory>

Step 5: Start the web server and test

Run the following commands to start the the Apache web server:

 [root]# /etc/init.d/httpd start
 Starting httpd: Apache/2.2.3 mod_ssl/2.2.3 (Pass Phrase Dialog)
 Some of your private key files are encrypted for security reasons.
 In order to read them you have to provide the pass phrases.
 
 Server d3xt3r01.tk:443 (RSA)
 Enter pass phrase:
 Ok: Pass Phrase Dialog successful.                       [  OK  ]

Note that you will have to enter the password for your server key in order to start the server. You will also have to do this during boot if you have httpd configured to start automatically.

Make sure that the web server is now listening on the SSL/TLS port, TCP port 443:

 [root]# netstat -plantu | grep -i httpd
 Active Internet connections (servers and established)
 Proto Recv-Q Send-Q Local Address           Foreign Address         State
 tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN
 tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN

In order to test that your SSL/TLS web server is running, you will now need to connect to it with a browser. The URL you use should be https://yourservername.com. You will probably get a warning prompt about the Certificate Authority (CA) being unknown. You can view the certificate properties, which will look familiar because you created the cert yourself. You can save the cert in your browser, or import the my-ca.crt file into your browser as a new CA. How you do this will depend on which browser you are using. I had no problems doing this with Mozilla.

Creating Client Certificates for Authentication

Now, let's say that we want a stronger method of authenticating clients, one that is not as susceptible to password guessing and shoulder-surfing. What can we do? We can create an SSL/TLS client certificate. The certificate has to be digitally signed by a CA that the server trusts, the user has to have the client loaded in his browser, and the user has to know a pass phrase to use it. The certificate itself uses strong, public-key cryptography. We can make such a certificate with our OpenSSL toolkit.

A note on certificate formats: The server and CA certs that we have been using up to now are encoded in PEM format, which uses ASCII characters. For some reason, the industry-standard client certs used in web browsers are encoded in the PKCS#12 format, which cannot be viewed as simple text. It is a binary file. We will now create a client cert by following these steps:

• Create a new private key and certificate request
• Sign the certificate request, thereby creating the client certificate
• Generate the PKCS#12 cert file
• View information about the PKCS#12 cert
• Import the PKCS#12 client cert into your browser
• Test!

 [root]# cd /root/CA
 [root]# openssl genrsa -des3 -out dex-c.key 1024
 Generating RSA private key, 1024 bit long modulus
 ..++++++
 ........................................................................++++++
 e is 65537 (0x10001)
 Enter PEM pass phrase:
 Verifying password - Enter PEM pass phrase:
 [root]# openssl req -new -key dex-c.key -out dex-c.csr
 Using configuration from /usr/share/ssl/openssl.cnf
 Enter PEM pass phrase:
 You are about to be asked to enter information that will be incorporated
 into your certificate request.
 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
 For some fields there will be a default value,
 If you enter '.', the field will be left blank.
 -----
 Country Name (2 letter code) [GB]:RO
 State or Province Name (full name) [Berkshire]:Dolj
 Locality Name (eg, city) [Newbury]:Craiova
 Organization Name (eg, company) [My Company Ltd]:d3xt3r01.tk
 Organizational Unit Name (eg, section) []:IT
 Common Name (eg, your name or your server's hostname) []:d3xt3r01.tk
 Email Address []:dexter@d3xt3r01.tk
 Please enter the following 'extra' attributes
 to be sent with your certificate request
 A challenge password []:
 An optional company name []:
 [root]# openssl x509 -req -in dex-c.csr -out dex-c.crt -sha1 -CA my-ca.crt -CAkey my-ca.key -CAcreateserial -days 3650
 [root]# openssl pkcs12 -export -in dex-c.crt -inkey dex-c.key -name "dex Emery Cert" -out dex-c.p12
 [root]# openssl pkcs12 -in dex-c.p12 -clcerts -nokeys -info

Note: The "export password" is all the end-user needs to know. This is what you will be asked for when installing the certificate in a browser.

Now move the dex-c.p12 file to your client machine and import it into your web browser. This is usually done your browser's "Preferences" section under "Privacy and Security", "Certificates", "Manage Certificates". You may be asked to input a Software Security Device Master Password. DO NOT FORGET this password! You will also be asked for the client certificate's export password.

Configure Apache to require client certificates for a specific directory

In order to require client certificates for the /var/www/SSL/Certneeded directory, you will need to add the following lines to the /etc/httpd/conf.d/ssl.conf configuration file:

 <Directory /var/www/SSL/Certneeded>
 	SSLVerifyClient require
 	SSLVerifyDepth 1
 </Directory>

Now, restart Apache with /etc/init.d/httpd restart. You can now connect from your client machine browser to the secure webserver at https://yoursevername.com:444. You should now be able to click on the "Client Certificate Required" link and view the files in that directory.

If you connect from a different browser that does not have the certificate installed, you will not be able to enter the directory at all. When you look in your /var/www/httpd/ssl_error_log file, you will see this error:

 [01:02:41] [error] Re-negotiation handshake failed: Not accepted by client!?
 [01:02:41] [error] SSL handshake failed (server d3xt3r01.tk:444, client 192.168.1.191)
 [01:02:41] [error] SSL Library Error: 336105671 error:140890C7:lib(20):func(137):reason(199)

Configure Apache to require client certificates AND username/password for a specific directory

If you are super paranoid, you may want to require a client certificate AND username/password. This is totally up to you, and it is easy to do.

For this simple example, we will use the .htpasswd file and usernames/passwords that have already been created earlier. This will force clients to have a certificate and a valid username/password pair in order to access the /var/www/SSL/PassAndCert. All we have to do is add the following section to the /etc/httpd/conf.d/ssl.conf configuration file:

 <Directory "/var/www/SSL/PassAndCert">
 	SSLVerifyClient require
 	SSLVerifyDepth 1
 	AuthType Basic
 	AuthName "Restricted Area"
 	AuthUserFile /etc/httpd/.htpasswd
 	Require valid-user
 </Directory>

Now, restart Apache with /etc/init.d/httpd restart. Connect from your client machine browser to the secure webserver. When you click the link for the "Client Cert AND Password Required" directory, you should be prompted for a username and password. You should then be able to view the directory contents. If you delete your client certificate from the browser, you will be unable to access either directory that requires client certificates.

Web Server Key Password

You have probably noticed by now that every time you restart Apache or boot your server, you are forced to enter the password for the server key. This is a security measure, but it can be inconvenient. If you would like to make an insecure server key that will allow Apache to start automatically at boot time, then there is a way to do this. In my case, I don't run an e-commerce site and I'm not worried about someone else creating a fake d3xt3r01.tk secure web site. It is more likely that a power outage will occur that will cause my server to reboot while I am not around, so I want it to boot without requiring a password. The choice is yours...

Here is how you do it:

 [root]# cd /etc/httpd/conf/ssl.key
 [root]# cp mars-server.key mars-server.key.org
 [root]# openssl rsa -in mars-server.key.org -out mars-server.key
 [root]# chmod 0400 mars-server*

Now, you should be able to restart Apache or boot your server without having to input the password. This may also be a very good time to copy all the keys and certificates that you made to floppy or CD. You can imagine what a pain it would be if you lost all of your keys and certs due to a disk failure. You may even want to make paper copies of the PEM encoded certificates and keys, which use ASCII text. Lock them in a secure place, along with any passwords.

Conclusion/Final Comments

As you can see, setting up a secure web server for some specific function is not that difficult. All the tools are included with a standard GNU/Linux distribution. OpenSSL is a fantastic Open Source toolkit that can be used in a number of applications. You can use it to run files through different hashing functions, handle S/MIME encrypted mail, or encrypt & decrypt files.

In order to use Apache as a high-volume e-commerce server with SSL/TLS, you will probably need to do more configuration and hardware tuning. You may need to buy and configure a hardware crypto accelerator card. You will almost certainly want to purchase a "real" server certificate signed by Entrust, Thawte, or one of the other root-level CAs.

In any event, you now have a good feel for all the pieces, parts, and protocols that make it work!