Hanno's blog

I recently switched my personal web page and my blog to deliver content exclusively encrypted via HTTPS. I want to take this opportunity to give some facts about enabling TLS encryption by default and problems you may face.

First of all the non-problems: Enabling HTTPS by default is almost never a significant performance problem. If people tell me that they can not possibly enable HTTPS due to performance reasons the first thing I ask is if they believe this or if they have real benchmark data showing this. If you don't believe me on that, I can quote Adam Langley from Google here: "In January this year (2010), Gmail switched to using HTTPS for everything by default. Previously it had been introduced as an option, but now all of our users use HTTPS to secure their email between their browsers and Google, all the time. In order to do this we had to deploy no additional machines and no special hardware. On our production frontend machines, SSL/TLS accounts for less than 1% of the CPU load, less than 10KB of memory per connection and less than 2% of network overhead."

Enabling HTTPS may cause a number of compatibility issues you may not instantly think about. First of all, we know that IPs in the IPv4 space are limited and expensive these days, so many people probably can't afford having a distinct IP for their web page. The solution to that is a TLS extension called SNI (Server Name Indication) which allows to have different certificates for different domain names on the same IP. It works in all major browsers and has been working for quite some time. The only major browser you'll face these days that doesn't support SNI is the Android 2.x browser.

There are some subtle issues with SNI. One is that browsers have fallback modes if they cannot connect via TLS and that may lead to a connection downgrade to SSLv3. And that ancient protocol doesn't support extensions and thus no SNI. So you may have irregular certificate errors if you are on a bad connection. A solution to that on the server side is to just disable SSLv3. It will make SNI much more reliable.

I don't really have a clear picture how many browsers will fail with SNI. There are probably a number of embedded devices out there like smart TVs with browsers or things alike that have problems. If you have any experiences feel free to post them in the comments.

The first issue I only noticed after I switched to HTTPS: I had an application called RSS Graffiti set up to automatically post all articles I write to a facebook fan page. After changing to HTTPS only it silently stopped working. Re-adding my feed didn't work. I now found a similar service called dlvr.it that I now use to post my RSS feed to facebook. I can only assume that this is a glimpse of a much bigger problem: There are probably tons of applications and online services out there not prepared for an encrypted Internet. If we want more people to deploy encryption by default we need to find these issues, document them and hopefully put enough pressure on their developers to fix them.

Another yet unfixed issue is the Yandex Bot. Yandex is a search engine and although you may never have heard of it it's probably one of the few companies in this area that can claim to be a serious competitor to Google. The reason you may not know it is that it's mostly operating in Russian language. Depending on who your page visitors are this may matter more or less.

The Yandex Bot speaks SSL but according to the Qualys SSL test it only supports the ancient SSLv3. So you have a choice between three possibilities: Don't enable HTTPS by default, enable HTTPS with a shitty configuration supporting ancient technology that will cause trouble for SNI or enable HTTPS with a sane configuration and get no traffic from the leading Russian search engine. None of them sounds very good to me.

Another issue is third party content. For security reasons today's browsers block all active HTTP content (CSS, JavaScript etc.) on HTTPS webpages. This isn't much of a problem for me, but it's a problem for webpages that rely on advertising because from what I hear most advertisement providers don't support HTTPS yet (Google being a laudable exception here). This is the main reason you won't see many news webpages enforcing HTTPS. However, I still have passive third party HTTP content on my blog. That's why you'll probably see a yellow warning sign in front of the URL in some browsers.

A big problem with web security in the past was that it was impossible to have https-hosts with more than one certificate per IP. This is due to the protocol design of https, which needs to establish an ssl-connection with the certificate before the hostname is transferred.

There is a solution though, called Server Name Indication (SNI) and part of TLS. Strange enough, client compatibility isn't that much of a problem. Firefox, Opera and IE already support it in their current versions, konqueror will with kde4, I've no information when it'll hit safari. Oh, and I haven't testet w3m, lynx, links and wget yet, but if you want, feel free to add your experiences to the comments :-)

The problem was that until some weeks ago, openssl didn't support SNI, apachen mod_ssl didn't, lighttpd didn't. Only GnuTLS, but mod_gnutls is considered unstable by it's authors. With OpenSSL 0.9.8f, TLS Extensions and with them SNI landet in openssl, apache still needs patches.

We've now implemented SNI on schokokeks.org, which you can test:
https://www.schokokeks.org/
https://www.hboeck.de/
https://www.fabian-fingerle.de/

If your browser supports SNI, you should see different certificates, all on the same IP. All certs are cacert-signed, they also have a Wiki page from the VhostTaskForce for SNI and alternative solutions.