If you were to go do a search on the internet for “configuring SSL” you would find a ton of references on configuring your favorite web server to do SSL some of it good and some of it not so good. But what you don’t see a lot of content on is how to deploy it successfully.

What do I mean by successfully? These articles ignore the larger picture, for example:

1. Are there changes to your content you will need to make?
2. What about external content and script references?
3. Are there any SEO considerations?
4. Are there other related considerations?

To some these things may be common-sense but even for those a refresher never hurt so lets go over them again briefly.

Are there changes to your content you will need to make?

Probably, lots of content I encounter explicitly references a protocol serving it (aka href=”http://…” and src=”http://…”) and if that’s the way your content looks then yes you will want to update your content to use relative references, for example

href=”//{hostname}/{uri}”

src=”/{uri}”

This way your content is independent of what protocols are used to transport it, it will also help prevent your users from encountering “mixed content” warnings.

What about external content and script references?

Another scenario that causes mixed content warnings is when sites use of scripts and content hosted on other servers that is explicitly referenced over HTTP. The two most common I encounter are YouTube Embeds and Google Analytics but there are lots of different third-party content and scripts out there and each one you embed will also need to support SSL.

Thankfully I have never encountered one that does not support SSL and in most cases you will just need to make the reference relative (“//”) and let the browser decide what protocol to use to get the reference. In the very rare cases where this does not work a quick email to support at the content/script provider will get you the URL to the SSL version of the content/script.

Though this has always been the case one thing to keep in mind is that the perceived performance and actual security of your site is dependent on the performance and security of the providers you include in it. I strongly recommend you check their performance and SSL configuration and ask them to make any changes necessary to address issues this might identify.

Are there any SEO considerations?

Aren’t there always? So to achieve all of security benefits of SSL you have to deploy SSL across your entire site (this is commonly referred to as Always On SSL). This means that as far as a search engine is concerned there could be two copies of the same content. This is treated as a negative condition in most page ranking schemes, we address this in a few ways:

1. Tell the search engine which content is authoritative (aka which one we want them to index), we do this using:

• Updating <link rel=”canonical”> to point to the HTTPS version.
• Updating the XML Sitemap to refer to the HTTPS version of the content.

Making these two changes ensures the search engine will index the SSL version of the site so the first link the user visits will be your HTTPS version.

These things not only improve the users experience by making them get at the content quicker (instead of relying on a rewrite rule to get them to the HTTPS content) but also help to mitigate MITM attacks that would be possible for organic traffic based on your HTTP urls.

2. Ensure the robots.txt is available over SSL.

3. Redirect all HTTP requests to your site to the HTTPs version using a permanent redirect (a HTTP 301), this will transfer your PageRank to the SSL url.

4. Update the search engine webmaster tools to refer to the HTTPS url instead of the HTTP URL.

Are there other considerations?

There are a few, for one there is performance. There is a myth that SSL is computationally expensive, it’s simply not true (at least today) but that doesn’t mean you don’t need to be concerned with performance.

There are several settings you care about, for example it’s common for websites to use domain sharding means when you’re using SSL is each one of those requests represents a new SSL negotiation and the negotiation is the most costly part of the SSL session. While we can’t eliminate this cost we can ensure that the servers terminating our SSL sessions implement session caching and reuse to reduce the impact of the SSL overhead. We can also try to limit the number of domains we use when sharding so reduce the number of SSL sessions needed to finish rendering a site.

You may also want to look at deploying a forward proxy in front of your web servers where all SSL would be terminated; this can give you performance benefits beyond SSL and can simplify key and SSL management in your environment at the same time.

Then there is the question of cookies, while all sensitive cookies should already be marked “secure” so they won’t get sent over non-secure sessions you should consider marking all cookies as “secure” since the whole site is now supposed to be served over SSL.

Depending on how you have authored your rewrite rules there may be static references to HTTP buried in there, you will want to review your rewites to ensure they are protocol independent (where appropriate) so that you don’t end up forcing users through an unnecessary redirect.

And finally setting the HTTP Strict Transport Security header means browsers will visit you over HTTPS the every time, even if not from search results; this will improve relative perceived performance and help protect from MITM attacks.

Ryan

Resources

1. Choose the Right Certificate, CA Security

2. Deploying SSL – How to get your server configuration right, Ryan Hurst

3. SSL Configuration Checker, X509 Labs

4. SSL Pulse, Trustworthy Internet Movement

5. Bulletproof SSL/TLS and PKI, Ivan Ristic

6. High Performance Browser Networking, Ilya Grigorik

7. How to get the latest stable OpenSSL, Apache and Nginx, Ryan Hurst

8. Always On SSL, OTA

9. Revocation Report, X509 Labs

10. SSL/TLS Deployment Best Practices, Qualys Labs

11. Transport Layer Security, WikiPedia

12. How to botch TLS forward secrecy, AGL

They say the most complicated skill is to be simple; despite SSL and HTTPS having been around for a long time, they still are not as simple as they could be.

One of the reasons for this is that the security industry is constantly learning more about how to design and build secure systems; as a result, the protocols and software used to secure online services need to continuously evolve to keep up with the latest risks.

This situation creates a moving target for server administrators, creating a situation where this year’s “best practice” may not meet next year’s. So how is a web server administrator to keep up with the ever-changing SSL deployment best practices?

There is, of course, a ton of great resources on the web that you can use to follow industry trends and recent security research, but it’s often difficult to distill this information into actionable and interoperable SSL configuration choices.

To help manage this problem there are tools like the X509labs SSL Configuration Checker which look your server’s configuration and makes recommendations on what you should change to address current industry best practices. This tool makes recommendations that are based on current and past security research, trends, and both client and server behavior and capability.

The tool performs over 33 different tests on your server configuration and, based on the results, recommends specific changes you should make to address its findings.

In general, the guidance the tool provides can be categorized as follows:

Support latest versions of TLS protocol

Often organizations are slow to pick up newer versions of their web server and SSL implementations.  This is normally a conscious decision attributed to the old adages of “if it’s not broken don’t fix it.”

The problem is that these older versions are plagued with security issues. In many cases, these organizations pick up security patches, but these patches do not include the more recent (and more secure) versions of the protocols.

It is important that all sites add support for TLS 1.2 as this new version of the protocol offers security improvements over its predecessors and lays the groundwork for addressing future security concerns.

Disable older known insecure versions of the SSL protocol

SSL was defined in 1995 and has evolved significantly since then, SSL 2.0 in particular has been found to have a number of vulnerabilities. Thankfully these issues have been resolved in later version of the protocol.

Unfortunately at least 28% of sites today still support it (based on SSL-pulse data); when I speak to server administrators about why they enable this older version they commonly mention concerns over client interoperability. Thankfully browser statistics show us that TLS 1.0 support is ubiquitous and it is no longer necessary to support the older insecure version of the protocol.

Choose secure and modern cipher suites

This is one of the more confusing parts of configuring SSL; it’s also one of the most important. No matter how strong the cryptographic key material that goes into your certificate, the strength of your SSL is only as secure as the cryptography used to encrypt the session.

You don’t need to be a cryptographer or security researcher to make the right choices though, the X509Labs SSL configuration checker will help you keep on top of current recommendations. Based on current research, the following would be solid choices for you to go with:

Apache

SSLProtocol -ALL +SSLv3 +TLSv1 +TLSv1.1 +TLSv1.2;
SSLCipherSuite "EECDH+ECDSA+AESGCM EECDH+aRSA+AESGCM EECDH+ECDSA+SHA384 EECDH+ECDSA+SHA256 EECDH+aRSA+SHA384 EECDH+aRSA+SHA256 EECDH+aRSA+RC4 EECDH EDH+aRSA RC4 !aNULL !eNULL !LOW !3DES !MD5 !EXP !PSK !SRP !DSS"
SSLHonorCipherOrder on;

Nginx

ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers "EECDH+ECDSA+AESGCM EECDH+aRSA+AESGCM EECDH+ECDSA+SHA384 EECDH+ECDSA+SHA256 EECDH+aRSA+SHA384 EECDH+aRSA+SHA256 EECDH+aRSA+RC4 EECDH EDH+aRSA RC4 !aNULL !eNULL !LOW !3DES !MD5 !EXP !PSK !SRP !DSS";
ssl_prefer_server_ciphers on;

These settings were chosen based on several factors including strength of the cryptography, interoperability and support for forward secrecy whenever it is supported by both the client and the server.

What is forward secrecy? You have forward secrecy when an attacker needs more than the encrypted traffic from your server and its private key to decrypt the traffic.

For you to be able to use the cipher suites that support forward secrecy here you will need to be using a version of OpenSSL and your web server that was built with ECDHE support. If you’re not you can still use these settings you just won’t offer forward secrecy to your users.

Disable insecure options in SSL and HTTP

As a general rule, protocols have options; these options can have unforeseen side-effects.

A great example of this is the option of SSL compression. Compression was added to SSL to improve performance of the protocol but it had a side effect – it enabled attackers to perform cryptanalysis on the cryptographic keys used in SSL. This attack was called CRIME (Compression Ratio Info-leak Made Easy) and, as such, this option is disabled today in secure SSL configurations.

Ensuring your configuration does not enable any such options is key to having a secure SSL configuration.

Enable performance optimizing options in SSL

To truly benefit from deploying SSL you need to apply it to your whole site—not doing so exposes sessions to attacks. The most common reason I hear from organizations as to why they are not deploying SSL across their whole site concerns performance.

This is a legitimate concern, according to Forester Research “The average online shopper expects your pages to load in two seconds or less, down from four seconds in 2006; after three seconds, up to 40% will abandon your site”.

And while it is true that an improperly configured web server will perform notably different than a properly configured one, it’s not difficult to configure your servers so that performance is not a major concern.

Ryan

Resources

1. Getting the Most Out of SSL Part 1: Choose the Right Certificate, CA Security
2. SSL Configuration Checker, CA Security
3. SSL Pulse, Trustworthy Internet Movement
4. Bulletproof SSL/TLS and PKI, Ivan Ristic
5. High Performance Browser Networking, Ilya Grigorik
6. How to get the latest stable OpenSSL, Apache and Nginx, Ryan Hurst
7. Always On SSL, OTA
8. Revocation Report, X509 Labs
9. Transport Layer Security, WikiPedia
10. Perfect forward secrecy , Wikipedia
11. SSL Labs: Deploying Forward Secrecy, Qualys
12. Intercepted today, decrypted tomorrow, Netcraft
13. How to Build Your Own OpenSSL, Ryan Hurst
14. Deploying forward secrecy on RedHat, Centos or Fedora based systems, Ryan Hurst