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Francois Marier: Ideal OpenSSL configuration for Apache and nginx

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:

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.
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Abusing HTTP Status Codes to Expose Private Information

When you visit my website, I can automatically and silently determine if you’re logged into Facebook, Twitter, GMail and Digg. There are almost certainly thousands of other sites with this issue too, but I picked a few vulnerable well known ones to get your attention. You may not care that I can tell you’re logged into GMail, but would you care if I could tell you’re logged into one or more porn or warez sites? Perhaps http://oppressive-regime.example.org/ would like to collect a list of their users who are logged into http://controversial-website.example.com/?

Ignoring the privacy implications for a second, as a website developer, you might like to know if your visitors are logged into GMail; you could use that information to automatically fill the email fields in your forms with “@gmail.com”… Perhaps you might want to make your Facebook “like” buttons more prominent if you can tell your visitor is logged into Facebook at the moment? Here’s how I achieve this:

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