HTTPS, Forward Secrecy vs. Compatibility

When talking SSL and HTTPS nowadays, the talk often goes about “Forward Secrecy” (aka. FS). Now, as Wikipedia perfectly explains what that is, there are basically two requirements that tend to conflict very often in politics, technology and every day life: Security and Compatibility. While it may be best from a security standpoint not to use a car for transportation, it’s quite an incompatible choice in many regions of the world. Same goes for SSL and encryption standards.

There are a lot of internet users today and many are using outdated technology. Based on the target group of your web service, you need to take these people into consideration, even if it means that most bleeding-edge and probably more secure standards cannot be used. It’s totally up to you what decision to take. For my personal site, i opted to force people using modern browsers and operating systems. If you run an online shop and care more about revenue than security or education of your visitors, the opposite decision may be fine for you.

While this is targeted to server administrators, there are quite a few ways for users to prefer more secure connections, for example by re-configuring their browser. For example, check out these german or english guides on how to remove RC4 usage from Firefox.

The provided configuration examples have been tested and implemented with Apache 2.4 and most current openssl - most Linux distributions won’t offer this yet so you may need a fallback to Apache 2.2 (and not use TLS1.2), switch to nginx or install packages from a different distribution flavour. OCSP stapling is also only available with Apache 2.3 or later. When working with any kind of SSL setting, please note that your users and your systems security depends on much more than just a potentially secure SSL link.

I am referring to some popular SSL testing services, however i think they’re not entirely accurate and a “80/100” rating does not mean that your server is insecure. Still, they are a good pointer and great for auditing the current configuration.

The first configuration mitigates the BEAST attack by not using TLS 1.0 as well as CRIME and BREACH by disabling SSL compression and it does not offer potentially broken RC4 ciphers. Note that since TLS 1.0 and 1.1 are disabled with this configuration, it will definitely cause compatibility issues. TLS 1.0 is the “gold standard” (read: legacy stuff everybody implemented) and almost every SSL enabled site uses it. SSLv2 and SSLv3 are definitely dead and should be avoided. TLS 1.2 is not as common yet, just the most recent browser versions do support it. Keep in mind that such settings will also keep some website crawlers from indexing your site and providing a less optimal SEO rating.

SSLEngine On
SSLCertificateFile /etc/ssl/certs/your.crt
SSLCertificateKeyFile /etc/ssl/private/your.key
SSLHonorCipherOrder On
SSLCompression off
SSLProtocol +TLSv1.2

OCSP stapling needs to be configured outside of the “VirtualHost” scope. Note that the OCSP responder is usually provided by your CA. This is most likely not the case if you’re using self-signed certificates. The Strict-Transport-Security (HSTS) header signals, that the server only wants to talk via TLS/SSL and is used to avoid man-in-the-middle attacks on SSL.

Header add Strict-Transport-Security "max-age=15768000"
SSLUseStapling on
SSLStaplingCache shmcb:/var/run/ocsp(128000)

These settings will give you a Grade A 100-90-90 rating over at or, however be assure that it’s not the most compatible setting. Connecting is possible with current versions of Chrome, Internet Explorer, Firefox and Safari.

The second configuration is more compatible to legacy browsers. However, it does not mitigate the BEAST attack since we have to stick with TLS 1.0 and 1.1 for compatibility reasons.

Not offering RSA+3DES as cipher did essentially kill off Internet Explorer on Windows XP so this cipher gets added in this configuration. Note that the order of ciphers is relevant to define their priority. Putting a potentially weak cipher first is not a good idea since it may lure browsers to a lower security level than they could provide.

SSLProtocol +TLSv1 +TLSv1.1 +TLSv1.2

This will still give you a Grade A 95-90-90 rating and will work with all browsers. FS is used for every browser except Internet Explorer. Keep in mind that this configuration will not mitigate the BEAST attack on web servers.

Overall, there is no “perfect” SSL configuration for Apache. Especially the lack of TLS 1.2 implementations legacy clients is quite a PITA when aiming to offer secure connections. Compared to the default Apache mod_ssl configuration, even the “more compatible” SSL configuration discussed here is a step forward in security for clients that run current operating systems and browsers.

Fun with legacy XEN and LVM
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