Talking at PETCon2018 in Hamburg, Germany and OpenPGP Email Summit in Brussels, Belgium

Just like last year, I managed to be invited to the Privacy Enhancing Technologies Conference to talk about GNOME. First, Simone Fischer-Huebner from Karlstadt University talked about her projects which are on the edge of security, cryptography, and usability, which I find a fascinating area to be in. She presented outcomes of her Prismacloud project which also involves fancy youtube videos…

I got to talk about how I believe GNOME is in a good position make a safe and secure operating system. I presented some case studies and reported on the challenges that I see. For example, Simone mentioned in her talk that certain users don’t trust a software if it is too simple. Security stuff must be hard, right?! So how do measure the success of your security solution? Obviously you can test with users, but certain things are just very hard to get users for. For example, testing GNOME Keysign requires a user not only with a set up MUA but also with a configured GnuPG. This is not easy to come by. The discussions were fruitful and I got sent a few references that might be useful in determining a way forward.

OpenPGP Email Summit

I also attended the OpenPGP Email Summit in Brussels a few weeks ago. It’s been a tiny event graciously hosted by a local company. Others have written reports, too, which are highly interesting to read.

It’s been an intense weekend with lots of chatting, thinking, and discussing. The sessions were organised in a bar-camp style manner. That is, someone proposed what to discuss about and the interested parties then came together. My interest was in visual security indication, as triggered by this story. Unfortunately, I was lured away by another interesting session about keyserver and GDPR compliance which ran in parallel.

For the plenary session, Holger Krekel reported on the current state of Delta.Chat. If you haven’t tried it yet, give it a go. It’s trying to provide an instant messaging interface with an email transport. I’ve used this for a while now and my experience is mixed. I still get to occasional email I cannot decrypt and interop with my other MUA listening on the very same mailbox is hit and miss. Sometimes, the other MUA snatches the email before Delta.chat sees it, I think. Otherwise, I like the idea very much. Oh, and of course, it implements Autocrypt, so your clients automatically encrypt the messages.

Continuing the previous talk, Azul went on to talk about countermitm, an attempt to overcome Autocrypt 1.0‘s weaknesses. This is important work. Because without the vision of how to go from Autocrypt Level 1 to Level 2, you may very well question to usefulness. As of now, Emails are encrypted along their way (well. Assuming MTA-STS) and if you care about not storing plain text messages in your mailbox, you could encrypt them already now. Defending against active attackers is hard so having sort of a plan is great. Anyway, countermitm defines “verified groups” which involves a protocol to be run via Email. I think I’ve mentioned earlier that I still think that it’s a bit a sad that we don’t have the necessary interfaces to run protocols over Email. Outlook, I think, can do simple stuff like voting for of many options or retracting an email. I would want my key exchange to be automated further, i.e. when GNOME Keysign sends the encrypted signature, I would want the recipient to decrypt it and send it back.

Phil Zimmermann, the father of PGP, mentioned a few issues he sees with the spec, although he also said that it’s been a while that he was deeply into this matter. He wanted the spec to be more modern and more aggressively pushing for today’s cryptography rather than for the crypto of the past. And in fact, he wants the crypto of tomorrow. Now. He said that we know that big agencies are storing message today for later analyses. And we currently have no good way of having what people call “perfect forward secrecy” so a future key compromise makes the messages of today readable. He wants post quantum crypto to defeat the prying eyes. I wonder whether anybody has implemented pq-schemes for GnuPG, or any other OpenPGP implementation, yet.

My takeaways are: The keyserver network needs a replacement. Currently, it is used for initial key discovery, key updates, and revocations. I think we can solve some of these problems better if we separate them. For example, revocations are pretty much a fire and forget thing whereas other key updates are not necessarily interesting in twenty years from now. Many approaches for making initial key discovery work have been proposed. WKD, Autocrypt, DANE, Keybase, etc. Eventually one of these approaches wins the race. If not, we can still resort back to a (plain) list of Email addresses and their key ids. That’s as good or bad as the current situation. For updates, the situation is maybe not as bad. But we might still want to investigate how to prevent equivocation.

Another big thing was deprecating cruft in the spec to move a bit faster in terms of cryptography and to allow implementers to get a compliant program running (more) quickly. Smaller topics were the use of PQ safe algorithm and exploitation of backwards incompatible changes to the spec, i.e. v5 keys with full fingerprints. Interestingly enough, a trimmed down spec had already been developed here.

Speaking at FIfFKon 18 in Berlin, Germany

I was invited to be a panellist at this year’s FIfFKon in Berlin, Germany. While I said hi to the people at All Systems Go!, my main objective in Berlin was to attend the annual conference of the FIfF, the association for people in computing caring about peace and social responsibility.

The most interesting talk for me was held by Rainer Mühlhoff on the incapacitation if the user. The claim, very broadly speaking, is that providing a usable interface prevents your users from learning how to operate the machine properly. Or in other words: Making an interface for dumb people will attract dumb people and not make them smarter. Of course, he was more elaborate than that.

He presented Android P which nudges the user into a certain behaviour. In Android, you get to see for how long you have used an app and encourages you to stop. Likewise, Google nudges you into providing your phone number for account recovery. The design of that dialogue makes it hard to hit the button to proceed without providing the number. Those nudges do not prevent a choice to be made, they just make it more likely that the user makes one particular choice. The techniques are borrowed from public policy making and commercial settings. So the users are being an instrument themselves rather than a sovereign entity.

Half way through his talk he made a bit of a switch to “sealed interfaces” and presented the user interface of a vacuum cleaner. In the beginning, the nozzle had a “bristly” or “flat” setting, depending on whether you wanted to use it on a carpet or a flat surface. Nowadays, the pictogram does not show the nozzle any more, but rather the surface you want to operate on. Similarly, microwave ovens do not show the two levers for wattage and time any more, but rather full recipes like pizza, curry, or fish.
The user is prevented from understanding the device in its mechanical details and use it as an instrument based on what it does. Instead the interaction is centred on the end purpose rather than using the device as a tool to achieve this end. The commercialisation of products numbs people down in their thinking. We are going from “Don’t make me think” to “Can you do the thinking for me” as, he said, we can see with the newer Android interfaces which tries to know already what you intend to do.

Eventually, you adapt the technology to the human rather than adapting the human to the technology. And while this is correct, he says, and it has gotten us very far, it is wrong from a social theory point of view. Mainly because it suggests that it’s a one-way process whereas it really is an interdependency. Because the interaction with technology forms habits and coins how the user experiences the machine. Imagine, he said, to get a 2018 smartphone in 1995. Back in the day, you probably could not have made sense out of it. The industrial user experience design is a product of numbing users down.

A highly interesting talk that got me thinking a little whether we ought to teach the user the inner workings of software systems.

The panel I was invited for had the topic “More privacy for smart phones – will the GDPR get us a new break through?” and we were discussing with a corporate representative and other people working in data protection. I was there in my capacity as a Free Software representative and as someone who was working on privacy enhancing technologies. I used my opportunities to praise Free Software and claim that many problems we were discussion would not exist if we consequently used Free Software. The audience was quite engaged and asked a lot of questions. Including the ever popular point of *having* to use WhatsApp, Signal, or any of those proprietary products, because of the network effect and they demanded more regulation. I cautioned that call for various reasons and mentioned that the freedom to choose the software to run has not yet fully been exploited. Afterwards, some projects presented themselves. It was an interesting mix of academic and actual project work. The list is on the conference page.

Talking at OSDNConf in Kyiv, Ukraine

I was fortunate enough to be invited to Kyiv to keynote (video) the local Open Source Developer Network conference. Actually, I had two presentations. The opening keynote was on building a more secure operating system with fewer active security measures. I presented a few case studies why I believe that GNOME is well positioned to deliver a nice and secure user experience. The second talk was on PrivacyScore and how I believe that it makes the world a little bit better by making security and privacy properties of Web sites transparent.

The audience was super engaged which made it very nice to be on stage. The questions, also in the hallway track, were surprisingly technical. In fact, most of the conference was around Kernel stuff. At least in the English speaking track. There is certainly a lot of potential for Free Software communities. I hope we can recruit these excellent people for writing Free Software.

Lennart eventually talked about CAsync and how you can use that to ship your images. I’m especially interested in the cryptography involved to defend against certain attacks. We also talked about how to protect the integrity of the files on the offline disk, e.g. when your machine is off and some can access the (encrypted) drive. Currently, LUKS does not use authenticated encryption which makes it possible that an attacker can flip some bits in the disk image you read.

Canonical’s Christian Brauner talked about mounting in user namespaces which, historically, seemed to have been a contentious topic. I found that interesting, because I think we currently have a problem: Filesystem drivers are not meant for dealing with maliciously crafted images. Let that sink for a moment. Your kernel cannot deal with arbitrary data on the pen drive you’ve found on the street and are now inserting into your system. So yeah, I think we should work on allowing for insertion of random images without having to risk a crash of the system. One approach might be libguestfs, but launching a full VM every time might be a bit too much. Also you might somehow want to promote drives as being trusted enough to get the benefit of higher bandwidth and lower latency. So yeah, so much work left to be done. ouf.

Then, Tycho Andersen talked about forwarding syscalls to userspace. Pretty exciting and potentially related to the disk image problem mentioned above. His opening example was the loading of a kernel module from within a container. This is scary, of course, and you shouldn’t be able to do it. But you may very well want that if you have to deal with (proprietary) legacy code like Cisco, his employer, does. Eventually, they provide a special seccomp filter which forwards all the syscall details back to userspace.

As I’ve already mentioned, the conference was highly technical and kernel focussed. That’s very good, because I could have enlightening discussions which hopefully get me forward in solving a few of my problems. Another one of those I was able to discuss with Jakob on the days around the conference which involves the capabilities of USB keyboards. Eventually, you wouldn’t want your machine to be hijacked by a malicious security device like the Yubikey. I have some idea there involving modifying the USB descriptor to remove the capabilities of sending funny keys. Stay tuned.

Anyway, we’ve visited the city and the country before and after the event and it’s certainly worth a visit. I was especially surprised by the coffee that was readily available in high quality and large quantities.

GNOME Keysign 0.9.9

tl;dr: We have a new Keysign release with support for exchanging keys via the Internet.

I am very proud to announce this version of GNOME Keysign, because it marks an important step towards a famous “1.0”. In fact, it might be just that. But given the potentially complicated new dependencies, I thought it’d be nice to make sort of an rc release.

The main feature is a transport via the Internet. In fact, the code has been lurking around since last summer thanks to Ludovico’s great work. I felt it needed some massaging and more gentle introduction to the code base before finally enabling it.

For the transport we use Magic Wormhole, an amazing package for transferring files securely. If you don’t know it yet, give it a try. It is a very convenient tool for sending files across the Internet. They have a rendezvous server so that it works in NATted environments, too. Great.

You may wonder why we need an Internet transport, given that we have local network and Bluetooth already. And the question is good, because initially I didn’t think that we’d expose ourselves to the Internet. Simply because the attack surface is just so much larger and also because I think that it’s so weird to go all the way through the Internet when all we need is to transfer a few bytes between two physically close machines. It doesn’t sound very clever to connect to the Internet when all we need is to bridge 20 centimetres.

Anyway, as it turns out, WiFi access points don’t allow clients to connect to each other :( Then we have Bluetooth, but it’s still a bit awkward to use. My impression is that people are not satisfied with the quality of Bluetooth connections. Also, the Internet is comparatively easy to use, both as a programmer and a user.

Of course, we now also have the option to exchange keys when not being physically close. I do not recommend that, though, because our security assumes the visual channel to be present and, in fact, secure. In other words: Scan the barcode for a secure key signing experience. Be aware that if you transfer the “security code” manually via other means, you may be compromised.

With this change, the UX changes a bit for the non-Internet transports, too. For example, we have a final page now which indicates success or failure. We can use this as a base for accompanying the signing process further, e.g. sign the key again with a non-exportable short-term signature s.t. the user can send an email right away. Or exchange the keys again after the email has been received. Exciting times ahead.

Now, after the wall of text, you may wonder how to get hold of this release. It should show up on Flathub soon.

Talking at GUADEC 2018 in Almería, Spain

I’ve more or less just returned from this year’s GUADEC in Almeria, Spain where I got to talk about assessing and improving the security of our apps. My main point was to make people use ASan, which I think Michael liked ;) Secondarily, I wanted to raise awareness for the security sensitivity of some seemingly minor bugs and how the importance of getting fixes out to the user should outweigh blame shifting games.

I presented a three-staged approach to assess and improve the security of your app: Compilation time, Runtime, and Fuzzing. First, you use some hardening flags to compile your app. Then you can use amazing tools such as ASan or Valgrind. Finally, you can combine this with afl to find bugs in your code. Bonus points if you do that as part of your CI.

I encountered a few problems, when going that route with Flatpak. For example, the libasan.so is not in the Platform image, so you have to use an extension to have it loaded. It’s better than it used to be, though. I tried to compile loads of apps with ASan in the past and I needed to compile a custom GCC. And then mind the circular dependencies, e.g. libmfpr is needed by GCC. If I then compile a libmfpr with ASan, then GCC would stop working, because gcc itself is not linked against ASan. It seems silly to have those annoyances in the stack. And it is. I hope that by making people play around with these technologies a bit more, we can get to a point where we do not have to catch those time consuming bugs.

Panorama in Frigiliana

The organisation around the presentation was a bit confusing as the projector didn’t work for the first ten minutes. And it was a bit unclear who was responsible for making it work. In that room the audio also used to be wonky. I hope it went well alright after all.

GNOME Keysign 0.9.8 released

It’s been a while after my last post. This time, we have many exciting news to share. For one, we have a new release of GNOME Keysign which fixes a few bugs here and there as well as introduces Bluetooth support. That is, you can transfer your key with your buddy via Bluetooth and don’t need a network connection. In fact, it becomes more and more popular for WiFis to block clients talking to each other. A design goal is (or rather: was, see down below) to not require an Internet connection, simply because it opens up a can of worms with potential failures and attacks. Now you can transfer the key even if your WiFi doesn’t let you communicate with the other machine. Of course, both of you need have to have Bluetooth hardware and have it enabled.

The other exciting news is the app being on Flathub. Now it’s easier than ever to install the app. Simply go to Flathub and install it from there. This is a big step towards getting the app into users’ hands. And the sandbox makes the app a bit more trustworthy, I hope.


flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak install flathub org.gnome.Keysign

The future brings cool changes. We have already patches lined up that bring an Internet transport with the app. Yeah, that’s contrary to what I’ve just said a few paragraphs above. And it does cause some issues in the UI, because we do not necessarily want the user to use the Internet if the local transport just works. But that “if” is unfortunately getting bigger and bigger. So I’m happy to have a mix of transports now. I’m wondering what the best way is to expose that information to the user, though. Do we add a button for the potentially privacy invading act of connecting to the Internet? If we do, then why do we not offer buttons for the other transports like Bluetooth or the local network?

Anyway, stay tuned for future updates.

Talking at Cubaconf 2017 in Havanna, Cuba

Few weeks ago I had a talk at Cubaconf 2017 in Havanna, Cuba. It’s certainly been an interesting experience. If only because of Carribean people. But also because of the food and the conditions the country has be run under the last decades.

Before entering Cuba, I needed a tourist visa in form of the turist trajeta. It was bothering me for more than it should have. I thought I’d have to go to the embassy or take a certain airline in order to be able to get hold of one of these cased. It turned out that you can simply buy these tourist cards in the Berlin airport from the TUI counter. Some claimed it was possible to buy at the immigration, but I couldn’t find any tourist visa for sale there, so be warned. Also, I read that you have to prove that you have health insurance, but nobody was interested in mine. That said, I think it’s extremely clever to have one…

Connecting to the Internet is a bit difficult in Cuba. I booked a place which had “Wifi” marked as their features and I naïvely thought that it meant that you by booking the place I also get to connect to the Internet. Turns out that it’s not entirely correct. It’s not entirely wrong either, though. In my case, there was an access point in the apartment in which I rented a room. The owner needs to turn it on first and run a weird managing software on his PC. That software then makes the AP connect to other already existing WiFis and bridges connections. That other WiFi, in turn, does not have direct Internet access, but instead somehow goes through the ISP which requires you to log in. The credentials for logging in can be bought in the ISPs shops. You can buy credentials worth 1 hour of WiFi connection (note that I’m avoiding the term “Internet” here) for 3 USD or so from the dealer around the corner. You can get your fix from the legal dealer cheaper (i.e. the Internet office…), but that will probably involve waiting in queues. I often noticed people gathering somewhere on the street looking into their phones. That’s where some signal was. When talking to the local hacker community, I found out that they were using a small PCB with an ESP8266 which repeats the official WiFi signal. The hope is that someone will connect to their piece of electronics so that the device is authenticated and also connects the other clients associated with the fake hotspot. Quite clever.

The conference was surprisingly well attended. I reckon it’s been around hundred people. I say surprisingly, because from all what I could see the event was weirdly organised. I had close to zero communication with the organisers and it was pure luck for me to show up in time. But other people seemed to be in the know so I guess I fell through the cracks somehow. Coincidentally, you could only install the conference’s app from Google, because they wouldn’t like to offer a plain APK that you can install. I also didn’t really know how long my talks should be and needed to prepare for anything between 15 and 60 minutes.

My first talk was on PrivacyScore.org, a Web scanner for privacy and security issues. As I’ve indicated, the conference was a bit messily organised. The person before me was talking into my slot and then there was no cable to hook my laptop up with the projector. We ended up transferring my presentation to a different machine (via pen drives instead of some fancy distributed local p2p network) in order for me to give my presentation. And then I needed to rush through my content, because we were pressed for going for lunch in time. Gnah. But I think a few people were still able to grasp the concepts and make it useful for them. My argument was that Web pages load much faster if you don’t have to load as many trackers and other external content. Also, these people don’t get updates in time, so they might rather want to visit Web sites which generally seem to care about their security. I was actually approached by a guy running StreetNet, the local DIY Internet. His idea is to run PrivacyScore against their network to see what is going on and to improve some aspects. Exciting.

My other talk was about GNOME and how I believe it makes more secure operating systems. Here, my thinking was that many people don’t have expectations of how their system is supposed to be looking or even working. And being thrown into the current world in which operating systems spy on you could lead to being primed to have low expectations of the security of the system. In the GNOME project, however, we believe that users must have confidence in their computing being safe and sound. To that end, Flatpak was a big thing, of course. People were quite interested. Mostly, because they know everything about Docker. My trick to hook these people is to claim that Docker does it all wrong. Then they ask pesky questions which gives me many opportunities to mention that for some applications squashfs is inferior to, say, OStree, or that you’d probably want to hand out privileges only for a certain time rather than the whole life-time of an app. I was also to make people look at EndlessOS which attempts to solve many problems I think Cubans have.

The first talk of the conference was given by Ismael and I was actually surprised to meet people I know. He talked about his hackerspace in Almería, I think. It was a bit hard to me to understand, because it was in Spanish. He was followed by Valessio Brito who talked about putting a price on Open Source Software. He said he started working on Open Source Software at the age of 16. He wondered how you determine how much software should cost. Or your work on Open Source. His answer was that one of the determining factors was simply personal preference of the work to be performed. As an example he said that if you were vegan and didn’t like animals to be killed, you would likely not accept a job doing exactly that. At least, you’d be inclined to demand a higher price for your time. That’s pretty much all he could advise the audience on what to do. But it may also very be that I did not understand everything because it was half English and half Spanish and I never noticed quickly enough that the English was on.

An interesting talk was given by Christian titled “Free Data and the Infrastructure of the Commons”. He began saying that the early textile industry in Lyon, France made use of “software” in 1802 with (hard wired) wires for the patterns to produce. With the rise of computers, software used to be common good in the early 1960s, he said. Software was a common good and exchanged freely, he said. The sharing of knowledge about software helped to get the industry going, he said. At the end of the 1970s, software got privatised and used to be licensed from the manufacturer which caused the young hacker movement to be felt challenged. Eventually, the Free Software movement formed and hijacked the copyright law in order to preserve the users’ freedoms, he said. He then compared the GPL with the French revolution and basic human rights in that the Free Software movement had a radical position and made the users’ rights explicit. Eventually, Free Software became successful, he said, mainly because software was becoming more successful in general. And, according to him, Free Software used to fill a gap that other software created in the 80s. Eventually, the last bastion to overcome was the desktop, he said, but then the Web happened which changed the landscape. New struggles are software patents, DRM, and privacy of the “bad services”. He, in my point of view rightfully so, said that all the proliferation of free and open source software, has not lead to less proprietary software though. Also, he is missing the original FOSS attitude and enthusiasm. Eventually he said that data is the new software. Data not was not an issue back when software, or Free Software even, started. He said that 99% of the US growth is coming from the data processing ad companies like Google or Facebook. Why does data have so much value, he asked. He said that actually living a human is a lot of work. Now you’re doing that labour for Facebook by entering the data of your human life into their system. That, he said, is where the value in coming from. He made the the point that Software Freedoms are irrelevant for data. He encouraged the hackers to think of information systems, not software. Although he left me wondering a bit how I could actually do that. All in all, a very inspiring talk. I’m happy that there is a (bad) recording online:

I visited probably the only private company in Cuba which doubles as a hackerspace. It’s interesting to see, because in my world, people go and work (on computer stuff) to make enough money to be free to become a singer, an author, or an artist. In Cuba it seems to be the other way around, people work in order to become computer professionals. My feeling is that many Cubans are quite artsy. There is music and dancing everywhere. Maybe it’s just the prospects of a rich life though. The average Cuban seems to make about 30USD a month. That’s surprising given that an hour of bad WiFi costs already 1 USD. A beer costs as much. I was told that everybody has their way to get hold of some more money. Very interesting indeed. Anyway, the people in the hackerspace seemed to be happy to offer their work across the globe. Their customers can be very happy, because these Cubans are a dedicated bunch of people. And they have competitive prices. Even if these specialists make only hundred times as much the average Cuban, they’d still be cheap in the so called developed world.

After having arrived back from Cuba, I went to the Rust Hackfest in Berlin. It was hosted by the nice Kinvolk folks and I enjoyed meeting all the hackers who care about making use of a safer language. I could continue my work on rustifying pixbuf loaders which will hopefully make it much harder to exploit them. Funnily enough, I didn’t manage to write a single line of Rust during the hackfest. But I expected that, because we need to get to code ready to be transformed to Rust first. More precisely, restructure it a bit so that it has explicit error codes instead of magic numbers. And because we’re parsing stuff, there are many magic numbers. While digging through the code, other bugs popped up as well which we needed to eliminate as side challenges. I’m looking much forward to writing an actual line of Rust soon! ;-)

Talking at Kieler LinuxTage 2017 in Kiel, Germany

I was invited to present GNOME at the Kieler LinuxTage in Kiel, Germany.

logo

Compared to other events, it’s a tiny happening with something between fifty and hundred people or so. I was presenting on how I think GNOME pushes the envelope regarding making secure operating systems (slides, videos to follow). I was giving three examples of how GNOME achieves its goal of priding a secure OS without compromising on usability. In fact, I claimed that the most successful security solutions must not involve the user. That sounds a bit counter intuitive to people in the infosec world, because we’re trying to protect the user, surely they must be involved in the process. But we better not do that. This is not to say that we shouldn’t allow the user to change preferences regarding how the solutions behave, but rather that it should work without intervention. My talk was fairly good attended, I think, and we had a great discussion. I tend to like the discussion bit better than the actual presentation, because I see it as an indicator for how much the people care. I couldn’t attend many other presentations, because I would only attend the second day. That’s why I couldn’t meet with Jim :-/

But I did watch Benni talking about hosting a secure Web site (slides). He started his show with mentioning DNS which everybody could read, He introduced DNSSEC. Which, funnily enough, everybody also can read, but he failed to mention that. But at least nobody can manipulate the response. Another issue is that you leak information about your host names with negative responses, because you tell the client that there is nothing between a.example.com and b.example.com. He continued with SSH for deploying your Web site and mentioned SSHFP which is a mechanism for authenticating the host key. The same mechanism exists for Web or Mail servers, he said: DANE, DNS-based Authentication of named entities. It works via TLSA records which encode either the certificate or the used public key. Another DNS-based mechanism is relatively young: CAA. It asserts that a certificate for a host name shall be signed by a certain entity. So you can hopefully prevent a CA that you’ve never heard of creating a certificate for your hosts. All of these mechanisms try to make the key exchange in TLS a bit less shady. TLS ensures a secure channel, i.e. confidentiality, non-repudiation, and integrity. That is considered to be generally useful in the Web context. TLS tends to be a bit of a minefield, because of the version and configuration matrix. He recommended to use at least TLS as of version 1.2, to disable compression due to inherent attacks on typical HTTP traffic (CRIME), and to use “perfect forward secrecy” ciphers for protecting the individual connections after the main key leaked. Within TLS you use x509 certificates for authenticating the parties, most importantly in the Web world, the server side. The certificate shall use a long enough RSA key, he said, The certificate shall not use a CN field to indicate the host name, but rather the SAN field. The signatures should be produced with “at least SHA-256”. He then mentioned OCSP because life happens and keys get lost or stolen. However, with regular OSCP the clients expose the host names they visit, he said. Enter OCSP Stapling. In that case the Web server itself gets the OCSP response and hands it over to the client. Of course, this comes with its own challenges. But it may also happen that CAs issue certificates for a host name which doesn’t expect that new certificate. In that case, Certificate transparency becomes useful. It’s composed of three components, he said. Log servers which logs all created certificates, monitors which pull the logs, and auditors which check the logs for host names. Again, your Browser may want to check whether the given certificate is in the CT logs. This opens the same privacy issue as with OCSP and can be somewhat countered with signed log statements from a few trusted log servers.

In any case, TLS is only useful, he said, if you are actually using it. Assuming you had a secure connection once, you can use the TLS Strict Transport Security header. It tells the browser to use TLS in the future. Of course, if you didn’t have that first connection, you can have your webapp entered in the STS Preloading list which is then baked into major browsers. Another mechanism is HTTP Public Key Pinning which is a HTTP header to tell the client which certificates or CAs shall be accepted. The header value is a simple list of hashed certificates. He mentioned the risk of someone hijacking your Web presence with an injected HPKP header. A TLS connection has eventually been established successfully. Now the HTTP layer gets interesting, he said. The Content Type Options header prevents Internet Explorer from snooping content types which might cause an image to be executed as JavaScript. Many Cross-Site Scripting attacks, he said, originate from being embedded in a frame. To prevent that, you can set the X-Frame-Options header. To activate Cross-Site Scripting protection mechanisms, the X-XSS-Protection header can be set. It’s probably turned off by default for compatibility reasons, he said. If you know where exactly your data is coming from, you can make use of a Content Security Policy which is like SELinux for your browser. It’s a bit of a complicated mechanism though. For protecting your Webapp he mentioned Sub-Resource Integrity which is essentially the hash of what script you expect. This prevents tampering with the foreign script, malicious or not.

I think that was one of the better talks in the schedule with many interesting details to be discovered. I enjoyed it a lot. I did not enjoy their Web sites, though, which are close to being unusable. The interface for submitting talks gives you a flashback to the late 90’s. Anyway, it seems to have worked for many years now and hope they will have many years to come.

Talked at mrmcd 2017 in Darmstadt, Germany

I attended this year’s MRMCD in Darmstadt, Germany. I attended a few times in the past and I think this year’s edition was not as successful as the last ones. The venue changed this year, what probably contributed to some more chaos than usual and hence things not running as smoothly as they did. I assume it will be better next year, when people know how to operate the venue. Although all tickets were sold during the presale phase, it felt smaller than in the last years. In fairness, though, the venue was also bigger this year. The schedule had some interesting talks, but I didn’t really get around to attend many, because I was busy preparing my own shows (yeah, should’ve done that before…).

I had two talks at this conference. The first was on playing the children’s game “battleship” securely (video). That means with cryptography. Lennart and I explained how concepts such as commitment schemes, zero knowledge proofs of knowledge, oblivious transfer, secure multiparty computation and Yao’s protocol can be used to play that game without a trusted third party. The problem, in short, is to a) make sure that the other party’s ships are placed correctly and b) to make sure the other party answers correctly. Of course, if you get hold of the placements of the ships these problems are trivial. But your opponent doesn’t like you to know about the placements. Then a trusted third party would solve that problem trivially. But let’s assume we don’t have such a party. Also, we want to decentralise things, so let’s come up with a solution that involves two players only.

The second problem can be solved with a commitment. A commitment is a statement about a something you’ve chosen but that doesn’t reveal the choice itself nor allows for changing ones mind later. Think of a letter in a closed envelope that you hand over. The receiver doesn’t know what’s written in the letter and the sender cannot change the content anymore. Once the receiver is curious, they can open the envelope. This analogy isn’t the best and I’m sure there’s better real-world concepts to compare to commitment schemes. Anyway, for battleship, you can make the other party commit to the placement of the ships. Then, when the battle starts, you have the other party open the commitment for the field that you’re shooting. You can easily check whether the commitment verifies correctly in order to determine whether you hit a ship or water.

The other problem is the correct placement of the ships, e.g. no ships shall be adjacent, exactly ten ships, exactly one five-field ship, etc. You could easily wait until the end of the game and then check whether everything was placed correctly. But that wouldn’t be (cryptographic) fun. Let’s assume one round of shooting is expensive and you want to make sure to only engage if the other party indeed follows the rules. Now it’s getting a bit crazy, because we need to perform a calculation without learning anything else than “the ships are correctly placed”. That’s a classic zero knowledge problem. And I think it’s best explained with the magic door in a cave.

Even worse, we need to somehow make sure that we cannot change our placement afterwards. There is a brain melting concept of secure multi-party computation which allows you to do exactly that. You can execute a function without knowing what you’re doing. Crazy. I won’t be able to explain how it works in a single blog post and I also don’t intend to, because others are much better in doing that than I could ever be. The gist of the protocol is, that you model your functionality as a Boolean circuit and assign random values to represent “0” or “1” for each wire. You then build the truth table for each gate and replace the values of the table (zeros and ones) with an encryption under both the random value for the first input wire and the random value for the second input wire. The idea now is that the evaluator can only decrypt one value in the truth table given the input keys. There are many more details to care about but eventually you have a series of encrypted, or garbled, gates and you need the relevant keys in order to evaluate it. You can’t tell from the keys you get whether it represents a “0” or a “1”. Hence you can evaluate without knowing the other party’s input.

My other talk was about a probable successor of Return Oriented Programming: Data Oriented Programming (video). In Return Oriented Programming (ROP) and its variants like JOP the aim is to diverge the original control flow in order to make the program execute the attacker’s functionality. This, however, can probably be thwarted by Control Flow Integrity. In its simplest form, it checks on every branch whether it is legit. Think of a database with a list of addresses which are allowed to a list of other addresses. Of course, real-world implementations are more clever. Anyway, let’s assume that we’ll have a hard time exploiting our target with ROP, because we cannot change the CFG of the program. If our attack doesn’t change the CFG, though, we should be safe for anything that detects its modification. That’s the central idea of DOP.

Although I’m not super excited about this year’s edition, I’m looking forward to seeing the next year’s event. I hope it’s going to be a bit more organised; including myself ;-)

Talking at FrOSCon 2017

I attended my first FrOSCon in St. Augusting, Germany. It’s one of the bigger Free Software events in Germany. Supposedly, the Chemnitzer LinuxTage is one of the few events which are bigger than FrOSCon. I thought it’s time for me to attend this event, so I went.

I was scheduled for two talks. One in the very first slot and one in the very last slot. So, to some extent, I was opening and closing the conference ;-) But the official keynote was, to my surprise, performed by Karen. She keynoted the conferences with her “big heart” talk. He told her story about her wanting to find out what software her pacemaker runs. Of course, it was an endless quest with no success. She described herself as a cyborg because of the machinery that is linked up to her body. She researched the security of devices such as pacemakers and found devastating results. In fact, software is deployed in many critical parts with people having no clue how the impact will be if the software is being attacked. She described the honeymoon effect and projected it to the security aspects of deployed software. She described it as a time in which no vulnerabilities are known. But once a vulnerability has been found, the number of known vulnerability increases exponentially. She found a study which shows that Free Software responds better to found vulnerabilities than proprietary systems. She said she went from thinking “Open Source was cool” to “Open Source is essential” because it responds much better in case of security breaches. She cautioned us to be careful with the Internet of Things™, because it will lead to people being connected without the people even knowing. All software has bugs, she said, but with Software Freedom we are able to do something about the situation. It’s been an enjoyable talk and I recommend watching the video.

Another interesting talk was given by Raffa about open data in public transport. Open data, especially in trip planning, can give us better results, he said, because personal preferences can be respected better. But also competition will become tougher if the data is free which might lead to better products. My personal argument in favour of open data is that it would allow offline routing rather than having to connect to the Internet. Some public transportation companies have freed their data, like the companies in Berlin, Ulm, Rhein Neckar, and Rhein Sieg, which is, funnily enough, the local company responsible for the public transport in the area of the event. However, some companies are still hesitant. The reasons are manifold. One is that they don’t want to deal with complaints about wrongly displayed data or simply outdated data that the third party didn’t bother to update. Also abuse is a concern. What would abuse even mean in this context? Well, some companies are afraid that the data is not only being used for trip planning but for finding out how the companies work or what their financial situation is, e.g. by inferring information from the data.

Andreas Schreiber talked about the complications of Open Source in Science. He works at DLR, which is a publicly funded research institute. Software is important to the DLR. 1500 people develop software which costs around 150 Million EUR per year and makes them probably the biggest software house in Germany, he said. As they are producing as releasing software they got in trouble with licensing issues. For example, they released software which was not open source although they thought it was. They also used software themselves which they may not have been entitled to use. Their CIO eventually issued a warning regarding the use and release of Open Source which made the speaker offer workshops and knowledge databases for issues around open source. They created a brochure which they intend to distribute to other institutes, too, because they tend to get more requests for this kind of information from the outside than from the inside of their organisation. I found interesting that the problems, according to the participants of their workshops, are that monetising won’t work, that building a community is hard, and that it costs more time to do “open source” than not which is demotivating. It’s been interesting to learn about issues involved in both consuming and producing open source software.

As I’ve mentioned, I was booked for two events, a talk and a workshop. My workshop was about signing OpenPGP keys. I held a small presentation and ranted, some times a bit unfairly, about the current state of affairs. I showed how people do it as of now and how I think we can do better than that. It’s been the first slot in this conference and the audience was small, albeit larger than expected. We even got to suggest improvements in Gentoo’s packaging, so I consider it a success. My talk (slides) was about how GNOME advances the security of desktop systems. The audience was super engaged and I felt I couldn’t focus so much on other things I only touched upon. But the discussion showed that people do care about a usable desktop. We were talking a lot about dialogues and modal prompts and how they do not contribute to the security of a system. I claimed that they exist because they were cheap for the app developer to do. But we at GNOME, I said, try or at least should try to avoid those as much as possible and we find other ways of enabling the app to capture the user’s intent. I’m surprised that we had such a lively discussion in the very last slot of the conference.

I’m happy to have attended the event and to meet surprisingly many GNOME people! It’s surprisingly close to Frankfurt and Cologne both of which have good connections via plane or train. With around 1800 attendees it’s quite big although the many tracks and rooms make it feel less crowded.