Category Archives: controls

Thoughts on Wulim

One of the exciting developments at CCC last month was a talk discussing the copy protection features in the Wulim tablet produced by the Pyongyang Information Center. This post is an attempt to reconcile the features they describe with my experience with devices around Pyongyang and provide some additional context of the environment the device exists within.

Threat Model

As mentioned in the talk, the Wulim tablet, and most of the devices available in Pyongyang for that matter, do a good job of defending against the primary threat model anticipated: of casual dissemination of subversive material. To that end, transfer of content between devices is strictly regulated, with watermarking to track how material has been transferred, a screenshot-based verification systems for visual inspection, and technical limitations on the ability to run externally created Applications.

One of the interesting points of note is that the Wulim, and the earlier pyongyang phone from PIC implement much of their security through a system application and kernel process named ‘Red Flag’, which shares an icon and name with the protection system on the Red Star desktop system. While the code is most likely entirely different (I haven’t actually compared), the interesting point is that these implementations come from two separate labs and entities, indicating that there is potentially coordination or joint compliance with a common set of security requirements.

System Security

The Wulim was difficult for the CCC presenters to gain access to. While there were bugs allowing them to view the file system, there was no easy way to casually circumvent the security systems in place. This indicates a general success of the threat model the system was designed to protect against and shows a significant increase in technical proficiency from the 2013/2014 devices. In the initial generations of android-based hardware, most devices had an enabled recovery mode, and the security could generally be breached without more than a computer. The alternative start-up mode found at CCC indicates that the labs are still not deeply familiar with all of the intricacies of Android, and there remain quirks in its operation that they haven’t anticipated. This will likely continue, with a pattern of an attack surface area that continues to shrink as exploits are discovered and make their way back to pyongyang.

The ‘crown jewel’ for this system, it should be noted, is an exploit that the CCC presenters did not claim to have found: the ability to create applications which can be installed on the device without modification. One of the first and most effective security mechanisms employed by the wulim and previous generations of PIC android systems is the requirement that applications be signed with a lab-issued key. While it might be possible that either the security check of applications, or information about the private key might be recovered from a device, this code has likely been checked quite well, and I expect such a major lapse in security to be unlikely.

The presence of this security means that I cannot install an Application on your tablet from an SD card, computer, or via bluetooth transfer if it has not already been pre-approved. This key is potentially shared between KCC and PIC, because the stores offering to install after-market applications around pyongyang have a single list, and are willing to try adding them to systems produced by either lab.


The Wulim is a 2015-2016 model, and evidences a feeling of confidence from the labs that they’ve got the software security at a reasonably appropriate level of security, and are more comfortable opening back up appropriate levels of connectivity between devices. 2013 and 2014 models of tablets and phones were quite limited in connectivity, with bluetooth as a ‘high-end’ option only available on the flag-ship models, and wifi connectivity removed completely. In contrast, the Wulim has models with both bluetooth and wifi, as well as the capability for PPPOE based connectivity to intranet services broader than a single network.

This connectivity extends in two additional ways of note:

  • First, there continue to be rumors of mobile data services being tested for broader availability within the country, and the Gateway mechanism in the wulim presents yet another clue towards how this will manifest down the road. While the wulim tablet does not have 3G connectivity, the same software stack has been seen on phones (for instance the pyongyang phone series with the most recent generation ‘2610’ released in 2015).
  • Second, the same basic android system is being used for wider installations, and is on display in the science and technology exhibition center. In that context, a custom deployment of tablets with modified software have been installed in both tablet and desktop configuration (desktop through USB peripheral keyboards and mice), and are connected through a LAN-local wifi network for searching the library resources on-site.


The screenshot ‘trace viewer’ mentioned in the CCC talk is really just a file-system viewer of images taken by the same red flag security tool integrated into the system. The notable points here are that screen shots are taken at regular interval on images not in a predefined white-list, so even if new signed applications are created, there will be an alternative system were their presence can be detected even if they’ve been uninstalled by the user prior to inspection. It’s worth noting that it is more effective against the transmission of images and videos containing subversive content then against applications. Applications in android will likely be able to take advantage of screen-security APIs to prevent themselves from appearing in the list. Or, more to the point, once external code is running, the system age is typically 2-3 years behind current android and one of several root methods can be used to escalate privileges and disable the security measures on the device.

While the CCC talk indicates that images and videos can only be viewed on the device they have been created on, this was not what I observed. It was relatively common for citizens to transfer content between devices, including road-maps and pictures of family and friends. The watermarking may be able to indicate lineage, but these sorts of transfer were not restricted or prevented.


Very little underlying data was released from the CCC talk, although they indicate the intention to release some applications and data available on the tablet they have access to. This is unfortunate. The talk, and the general environment has already signaled to Pyongyang that devices are available externally, and much of their reaction to this reality has already occurred. In particular, devices are no longer sold to foreigners within the country regularly, as they were in 2013/14 – with a couple exceptions where a limited software release (without the protections imposed on locals) and on older hardware can be obtained.

The only remaining risk then is the fear of retribution against the individual who brought the device out of the country. The CCC presenters were worried that the device they have may have a serial number tied to an individual. This has not been my experience, and I believe it is highly unlikely. Cellphones with connectivity do need to be attached to a passport at the point of sale, but tablet, as of spring 2015 continue to be sold without registration. The serial numbers observed by the CCC presenters are version numbers common to the image placed on all of the tablets of that generation released.

Internet Censorship 2016

We have reached the end of 2016, as well as the annual CCC congress in Germany. I had the exciting chance to speak together with Philipp Winter on the shifting landscape of Internet censorship in 2016. The talk followed mostly the same format as last year’s, calling out the continuing normalization and ubiquity of censorship around the world.

I left congress once again energized to work on system infrastructure advancing the Internet community in the face of these existential threats.

Slides from the talk are on this site.
A writeup (in german) is on Netzpolitik blog.

Thoughts on China’s Updated Cyber-security Regulations

On Monday, China ratified an updated cybersecurity legislation that will enter effect next June. The policy regulates a number of aspects of the Chinese Internet: What data companies need to keep on domestic servers, the interaction between companies and the government, and the interaction between companies and Chinese users.

Notably, when considering the impact on the Internet, the law include:

  • Network operators are expected to record network security incidents and store logs for at least 6 months (Article 21)
    Note that the punishment for refusing to keep logs is a fine up to 10,000usd to the operator, and of up to 5,000usd to the responsible person.
  • Services must require real-identity information for network access, telecom service, domain registration, blogging, or IM (Article 24)
    The punishment for failing to require identity is up to 100,000usd and suspension of operations.
  • Network operators must provide support to the government for national security and crime investigations (Article 28)
  • If a service discovers prohibited user generated content they must remove it, save logs, and report to the government (Article 47)
    The punishment for this is up to 100,000usd and closing down the website

The concerns from foreign companies seem to center around a couple things: The first is that there’s a fairly vague classification of ‘critical infrastructure’, which includes power, water and other infrastructure elements explicitly, but also refers to services needed for public welfare and national security. Any such service gets additional monitoring requirements, and needs to keep all data on the mainland. Companies are worried they could be classified as a critical service, and that there aren’t clear guidelines about how to avoid or limit their risk of becoming subject to those additional regulations.

The other main concern seems to be around the fairly ambiguous regulation of supporting national security investigations by the government. There’s a concern that there aren’t really any limits in place for how much the government can request from services, which could include requiring them to include back doors, or perform significant technical analysis without compensation.

My impression is that these regulations aren’t much of a surprise within China, and they are unlikely to cause much in the way of change from how smaller companies and individuals experience Internet management already.


I’m excited to present Satellite, a network measurement project I’ve been working on over the last couple years, at USENIX ATC next month.

Satellite takes a look at understanding shared CDN behaviors and automatically detecting censorship by regularly querying open DNS resolvers around the world.

For example, we can watch the trends in censorship in Iran using only a single, external machine.

The data for satellite is posted publicly each week, and will shortly be merged into the OONI data set to help provide better baselines for what behavior should be occurring.