I would like to thank all the developers who have worked on this project. Creating Qubes OS has been a great challenge, especially for such a small team as ours, but ultimately, I'm very glad with the final outcome – it really is a stable and reasonably secure desktop OS. In fact I cannot think of any more secure alternative...
I use the term “reasonably secure”, because when it comes to defensive security it's difficult to use definite statements (“secure”, “unbreakable”, etc), unless one can formally prove the whole design and implementation to be 100% secure.
Unfortunately, contrary to common belief, there are no general purpose, desktop OSes, that would be formally proven to be secure. At the very best, there are some parts that are formally verified, such as some microkernels, but not whole OSes. And what good is saying that our microkernel is formally verified, if we continue to use a bloated and buggy X server as our GUI subsystem? After all, a GUI subsystem has access to all the user inputs and output, thus it is as much security sensitive, as is the the microkernel! Or power management subsystem, or filesystem server, or trusted boot scheme, or ... a dozens of other elements, which just cannot be forgotten if one wants to talk about a truly secure OS. As said before, I know of no general-purpose desktop OS that would be formally proven, and thus that could be called “secure”. You can also read more about challenges with formal verification microkernels in this article, and especially in this comment from the seL4 project leader.
In Qubes OS we took a practical approach and we have tried to focus on all those sensitive parts of the OS, and to make them reasonably secure. And, of course, in the first place, we tried to minimize the amount of those trusted parts, in which Qubes really stands out, I think.
So, we believe Qubes OS represents a reasonably secure OS. In fact I'm not aware of any other solution currently on the market that would come close when it comes to secure desktop environment. But then again, I'm biased, of course ;)
I wouldn't call Qubes OS “safe”, however, at least not at this stage. By “safe” I mean a product that is “safe to use”, which also implies “easy to use”, “not requiring special skills”, and thus harmless in the hands of an inexperienced user. I think that Apple iOS is a good example of such a “safe” OS – it automatically puts each application into its own sandbox, essentially not relaying on the user to make any security decisions. However, the isolation that each such sandbox provides is far from being secure, as various practical attacks have proven, and which is mostly a result of exposing too fat APIs to each sandbox, as I understand. In Qubes OS, it's the user that is responsible for making all the security decisions – how to partition her digital life into security domains, what network and other permissions each domain might have, whether to open a given document in a Disposable VM, etc. This provides for great flexibility for more advanced users, but the price to pay is that Qubes OS requires some skills and thinking to actually make the user's data more secure.
Generally Qubes OS is an advanced tool for implementing Security by Isolation approach on your desktop, using domains implemented as lightweight Xen VMs. It tries to marry two contradictory goals: how to make the isolation between domains as strong as possible, mainly due to clever architecture that minimizes the amount of trusted code, and how to make this isolation as seamless and easy as possible. Again, how the user is going to take advantage of this isolation is totally left up to the user. I realize this might be a tricky part for some users and some usage scenarios, yet, on the other hand, this seems to be the most flexible and powerful approach we could provide.
Thus people should realize that by mere fact of using Qubes OS they won't become automatically more secure – it's how they are going to use it might make them significantly more secure. A hypothetical exploit for your favourite web browser would work against Firefox running inside one of the Qubes VMs just as well as it worked for the same browser running on normal Linux. The difference that Qubes makes, is that this attacked browser might be just your for-personal-use-only browser which is isolated from your for-work-use-only-browser, and for-banking-use-only-browser.
Finally, even though Qubes has been created by a reasonably skilled team of people, it should not be considered bug free. In fact, over the last 3 years we already found 3 serious bugs/attacks affecting Qubes OS – one of them in the very code we created, and two other in Intel hardware. Again, we tried as much as possible to limit the amount of code that is security sensitive in the first place, yet we are just humans ;) So, I'm very curious to see others' attempts to break Qubes – I think it might make for a very interesting research. A good starting point for such research might be this page. And I know there are individuals out there who apparently only been waiting for Qubes 1.0 to come out, to get some glory (yet, it's not clear to me why to attack qemu, which is not part of the TCB in Qubes, but I guess great minds have their own mysteries ;)
In other words, please enjoy Qubes OS 1.0, hopefully it could make your digital life safer!
Please send all the technical questions regarding Qubes to the qubes-devel mailing list. Do not send them to me directly, nor post them in this blog's comments.