Month: April 2014

Throughout the recent months (and particularly: weeks), people have asked me how to properly secure their SSL/TLS communication, particularly on web servers. At the same time I’ve started to look for good literature on SSL/TLS. I noticed that many of the “guides” on how to do a good SSL/TLS setup are actually cargo cult. Cargo cult is a really dangerous thing for two reasons: First of all, security is never a one-size-fits-all solution. Your setup needs to work in your environment, taking into account possible limitation imposed by hardware or software in your infrastructure. And secondly, some of those guides are outdated, e.g. they do neglect the clear need for Perfect Forward Secrecy, or use now-insecure ciphers. At the worst case, they are simply wrong. So I won’t be providing yet another soon-outdated tutorial that leaves you non-the-wiser. Instead, I’ll share my collection of free and for-pay documents, books and resources on the topic which I found particularly useful in the hope that they may help you in gaining some insight.

Introduction to SSL/TLS

If you’re unfamiliar with SSL/TLS, you definitely should take half an hour to read the Crypto primer, and bookmark SSL/TLS Strong Encryption: An Introduction for reference.

Crypto Primer: How does SSL work? sums up the functionality of SSL/TLS
SSL/TLS Strong Encryption: An Introduction is less of an introduction than a very elaborate glossary of SSL/TLS and crypto terminology

Deploying SSL/TLS

So you want to get your hands dirty? Check your server setup with Qualys SSL Labs’ server test. Make sure you fix the most important issues. You should at least be able to get an “A-” grading. If you find yourself in trouble (and are the administrator of an Apache or nginx setup), you should read the OpenSSL cookbook. Professional system administrators should have Bulletproof SSL/TLS and PKI on the shelf/eBook reader.¹⁾

If you find yourself with too little time on your hands, you can skip through to Mozilla’s awesome config tool which will help you with setting up your SSL vhost for Apache, nginx and HAproxy. However, some background may still be needed. You will find it on Mozillla’s Cipher recommendation page and the OpenSSL cookbook.

Qualys SSL Labs is a web site that can analyze the quality of a given SSL/TLS setup (HTTP only) using a nice rating scheme ²⁾ and providing hints on how to easily improve your setup.
Bulletproof SSL/TLS and PKI — Subtitled The Complete Guide to Securely Using SSL/TLS and PKI in Infrastructure Deployment and Web Application Development, this book is still work in progress (and is constantly updated, also according to readers feedback). Its author, Ivan Ristić, is also the guy behind ssllabs.com). Purchasers will receive updates to the eBook once finished. You can also purchase a hard copy
OpenSSL Cookbook — Extended excerpt from Bulletproof SSL/TLS and PKI. Suitable to secure your web server. Free download (requires registration).
Mozilla’s SSL Configuration Generator provides sane boiler plate configurations for your Apache/Nginx/HAproxy setups.
Up-to-date cipher suite recommendation from Mozilla with detailed explanation on why it was chosen. (Thanks to Tom Brossman).
Efficiently picking PFS-compatible cipher suites for IIS (using PowerShell).

The SSL, the TLS and the Ugly

If you are a dedicated IT professional, you should not miss the next section. Although it’s not crucial for those wishing to “simply secure their server”, it provides those who are responsible for data security with a clear understanding of the numerous theoretical and practical limitations of SSL/TLS.

SSL: Paved with Good Intentions: Presentation on history and weaknesses of SSL/TLS by Richard Moore, CTO at Westpoint Ltd and the maintainer of the Qt SSL/TLS stack.
Adam Langley (Google Chrome) on the risks of Revocation Checks
20 years of SSL/TLS Research Dissertation providing an excellent background on the pitfalls, attacks and risks of SSL/TLS. Suitable for non-scholars (and highly recommended). You may skip the math.
The case for OCSP-Must-Staple: Great commentary on what is needed for SSL/TLS beyond OCSP Stapling to have good support for certificate revocation.
Analyzing Forged SSL Certiﬁcates in the Wild – Paper analyzing forged certificates for Facebook, highlighting scenarios where forged certificates can be encountered.

Tools and Utilities for Debugging SSL/TLS

Sometimes you need to debug errors during the SSL handshake. While a bit primitive, OpenSSL’s s_client tool is the weapon of choice. When it comes to monitoring SSL/TLS encrypted communications, use mitmproxy or Charles. They need to be added as proxies, but can also intercept PFS connections, due to their active MITM position.

Server Config Generator for Apache, nginx and HA proxies
sslyze – a command line script to check SSL/TLS on servers (Python)
cipherscan – command line client to check effectively supported cipher suites (Bash)
openssl s_client is a command line tool that provides details on the handshake phase and establishes a secure connection. Use it to debug problems with certificate chaining, OCSP stapling, etc.
Wireshark packet analyzer (and why it will not help you if you’re using PFS)
mitmproxy suite — command line tools to analyze encrypted traffic (Python-based, Free)
Charles Web Debugging Proxy (Java, Commercial)

This list is not exhaustive and if you have more suggestions, please go ahead and post them in the comments. I’ll be happy to add them. Finally, just like with system administration in general, you’re never “done” with security. SSL/TLS is a swiftly moving target, and you need to be aware of what is going on. If you are an IT professional, subscribe to security mailing lists and the announcement lists of your vendor. Finally, while I’m aiming to update this page, there’s never a guarantee of up-to-dateness for this list either.

Update (22.04.2014): Don’t miss the discussion on this article over at Hacker News.

Article History

21.04.2014 – Initial version
21.04.2014 – Added “The Case for OCSP-Must-Staple”, Mozilla Cipher suite recommendation
22.04.2014 – Updated to add sslyze and cipherscan, added HN link, fixed typos
02.05.2014 – Add “Analyzing Forged SSL Certificate” paper
19.12.2014 – Add Mozilla SSL Generator, updated text on book availability

1) I do realize that I am courting Ivan a lot in this section and that relying on only an a single external web service that can go away any day is not a good thing. At the same time I think that the handshake simulation and the simple rating process are priceless, as such assessment cannot be trivially done by people whom’s life does not revolve around crypto and security 24/7. At the same time, I’m happy for any pointers towards other, user friendly tools.

2) While blindly following the rating can easily lead to the establishment of cargo cult, ssllabs.com is continuously updated to only give those a good grading that follow the best pactices. Again: Avoid Cargo Cult, make sure you have a good idea of what you are doing.

Now that ownCloud 1.6.0 beta1 is out, it’s time to explain the story behind it:

This release was developed under the promise that it would improve performance ¹⁾, and we have made tremendous improvements: Using a new Qt-based propagator implementation, we can now perform multiple simultaneous up- and downloads. We still provide the old propagator for certain situation where it’s more suitable, such as for situations where bandwidth limitation is needed.

Furthermore, the sync journal access code has been significantly optimized. It paid tribute to most of the high CPU load during the mandatory interval checks. CPU usage should be much lower now, and the client should be usable with more files at the same time.

Windows users should also find update times improved as the time spent in file stat operations has been reduced. Mac OS X users will enjoy the benefits of a much improved file watcher. To be able to use the more efficient API, 1.6 drops support for Mac OS Snow Leopard (10.6) and now requires Mac OS 10.7 or better.

At the same time, production releases are now using Qt 5 rather than Qt 4 on Windows and Mac OS X²⁾. This fixes a lot of visual bugs in Mac OS X, especially for Mavericks users, and allows us to profit from improvements in the SSL handling, especially on the Mac.

We also implemented an item that was on many peoples wish list: a concise sync log. Next to the database, the sync folder now holds a hidden file called .owncloudsync.log. It will store all sync processes in a minimal CSV file. Contrary to previous logging facilities, it always logs and only collects information relevant to the actual sync algorithm decisions.

Because this tour was not as colorful as the previous one, let’s close this blog post with a feature contributed by Denis Dzyubenko: The settings dialog on Mac OS X now has a native look & feel:

<a href="https://www.youtube.com/watch?v=jnsfbLl-s80">Watch on Youtube</a>

Get ownCloud Client 1.6.0 beta1 now and provide feedback!

¹⁾ Now that while the client is multi-threaded, you may find that the transfer time still doesn’t improve as much as you would expect. This is due locking issues on the server which prevent efficient parallel transfers. This has been improved in 1.7, and could potentilly improved even further by implementing support for X-Sendfile/X-Accel-Redirect in SabreDAV, the DAV framework used by ownCloud server.

²⁾ We can’t do the switch even on modern Linux distributions mostly due of the poor support for modern and divergent Systray/Notification area support in Qt5: Even in Qt 4 we could only use it because Canonical had patched their Qt to make QSystemTrayIcon work with Unity, which they have not ported to Qt 5 yet. Gnome 3 also hides away traditional Systray icons way to well, not to speak of Plasma. Any leads would be helpful.

PS: Martin’s blog on the subject indicates that Qt 5.3 might solve the problem.