Ideal OpenSSL configuration for Apache and nginx

The TLS world is moving fast and this post is now out of date! You might want to look at the SSL configuration recommended by Mozilla.

After recently reading a number of SSL/TLS-related articles, I decided to experiment and look for the ideal OpenSSL configuration for Apache (using mod_ssl since I haven't tried mod_gnutls yet) and nginx.

By "ideal" I mean that this configuration needs to be compatible with most user agents likely to interact with my website as well as being fast and secure.

Here is what I came up with for Apache:

SSLProtocol TLSv1  
SSLHonorCipherOrder On  
SSLCipherSuite RC4-SHA:HIGH:!kEDH

and for nginx:

ssl_protocols  TLSv1;  
ssl_ciphers  RC4-SHA:HIGH:!kEDH;  
ssl_prefer_server_ciphers   on;

Cipher and protocol selection

In terms of choosing a cipher to use, this configuration does three things:

disables all weak ciphers and protocols
disables very slow ciphers that use ephemeral Diffie-Hellman exchanges
gives priority to the RC4 cipher to minimize CPU usage and defend against the BEAST attack

Testing tools

The main tool I used while testing various configurations was the SSL labs online tool. The CipherFox extension for Firefox was also quite useful to quickly identify the selected cipher.

Of course, you'll want to make sure that your configuration works in common browsers, but you should also test with tools like wget, curl and httping. Many of the online monitoring services are based on these.

Other considerations

To increase the performance and security of your connections, you should ensure that the following features are enabled:

SSL session caching with a session store shared between all of your web servers
HSTS headers to let browsers know that they should always visit your site over HTTPS

Note: If you have different SSL-enabled name-based vhosts on the same IP address (using SNI), make sure that their SSL cipher and protocol settings are identical.