Tor at the Heart: Orbot and Orfox

During the month of December, we're highlighting other organizations and projects that rely on Tor, build on Tor, or are accomplishing their missions better because Tor exists. Check out our blog each day to learn about our fellow travelers. And please support the Tor Project! We're at the heart of Internet freedom.
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Orbot and Orfox

Orbot is an app for Android that contains the core Tor service and provides connectivity to the Tor network for any app to utilize. Local HTTP and SOCKS proxies are enabled for any proxy-capable app, such as Twitter or Lightning Browser, to use. Orbot also provides an "Apps VPN" feature that redirects traffic from selected apps or the entire device through the Tor network. Finally, Orbot provides an API that allows any developer to build Tor support directly into their app, as demonstrated by apps like Facebook, DuckDuckGo and F-Droid.

Orfox is a web browser for Android that enables mobile phone users to have secure communications through the Tor network. Coupled with the Orbot app, Orfox users can have encryption and anonymity on the Internet. In addition, Orfox comes with NoScript and HTTPS Everywhere preinstalled, and a number of security settings are preselected to enhance your protection against malicious websites.

Orfox is built from the same source code as Tor Browser (which is built upon Firefox), but with a few minor modifications to the privacy enhancing features to make them compatible with Firefox for Android and the Android operating system. The Orfox repository is a fork of the Tor Browser repository, with the necessary modification and Android-specific code as patches on top of the Tor Browser work. Beyond the core Tor Browser components, Orfox also routes all Android-specific code through the Orbot Tor proxy and is otherwise hardened to protect against data and privacy leaks.

Both Orbot and Orfox are produced in partnership with Guardian Project (https://guardianproject.info), a collective of software developers, designers and activists with a focus and expertise on security and privacy solutions for mobile devices.

All of the project, source code and app install links for Orbot and Orfox are available here: https://guardianproject.info/apps/orbot/ and here: https://guardianproject.info/apps/orfox/. You can also jump right to the Tor Project's apps on Google Play here:

And if you are already using Orfox - please update your app! Here is information on a release the team just put out that contains an important security update to Firefox.

Mission Improbable: Hardening Android for Security And Privacy

Updates: See the Changes section for a list of changes since initial posting.

After a long wait, the Tor project is happy to announce a refresh of our Tor-enabled Android phone prototype.

This prototype is meant to show a possible direction for Tor on mobile. While I use it myself for my personal communications, it has some rough edges, and installation and update will require familiarity with Linux.

The prototype is also meant to show that it is still possible to replace and modify your mobile phone's operating system while retaining verified boot security - though only just barely. The Android ecosystem is moving very fast, and in this rapid development, we are concerned that the freedom of users to use, study, share, and improve the operating system software on their phones is being threatened. If we lose these freedoms on mobile, we may never get them back. This is especially troubling as mobile access to the Internet becomes the primary form of Internet usage worldwide.

Quick Recap

We are trying to demonstrate that it is possible to build a phone that respects user choice and freedom, vastly reduces vulnerability surface, and sets a direction for the ecosystem with respect to how to meet the needs of high-security users. Obviously this is a large task. Just as with our earlier prototype, we are relying on suggestions and support from the wider community.

Help from the Community

When we released our first prototype, the Android community exceeded our wildest expectations with respect to their excitement and contributions. The comments on our initial blog post were filled with helpful suggestions.

Soon after that post went up, Cédric Jeanneret took my Droidwall scripts and adapted them into the very nice OrWall, which is exactly how we think a Tor-enabled phone should work in general. Users should have full control over what information applications can access on their phones, including Internet access, and have control over how that Internet access happens. OrWall provides the networking component of this access control. It allows the user to choose which apps route through Tor, which route through non-Tor, and which can't access the Internet at all. It also has an option to let a specific Voice over IP app, like Signal, bypass Tor for the UDP voice data channel, while still sending call setup information over Tor.

At around the time that our blog post went up, the Copperhead project began producing hardened builds of Android. The hardening features make it more difficult to exploit Android vulnerabilities, and also provides WiFi MAC address randomization, so that it is no longer trivial to track devices using this information.

Copperhead is also the only Android ROM that supports verified boot, which prevents exploits from modifying the boot, system, recovery, and vendor device partitions. Coppherhead has also extended this protection by preventing system applications from being overridden by Google Play Store apps, or from writing bytecode to writable partitions (where it could be modified and infected). This makes Copperhead an excellent choice for our base system.

The Copperhead Tor Phone Prototype

Upon the foundation of Copperhead, Orbot, Orwall, F-Droid, and other community contributions, we have built an installation process that installs a new Copperhead phone with Orbot, OrWall, SuperUser, Google Play, and MyAppList with a list of recommended apps from F-Droid.

We require SuperUser and OrWall instead of using the VPN APIs because the Android VPN APIs are still not as reliable as a firewall in terms of preventing leaks. Without a firewall-based solution, the VPN can leak at boot, or if Orbot is killed or crashes. Additionally, DNS leaks outside of Tor still occur with the VPN APIs on some systems.

We provide Google Play primarily because Signal still requires it, but also because some users probably also want apps from the Play Store. You do not need a Google account to use Signal, but then you need to download the Signal android package and sideload it manually (via adb install).

The need to install these components to the system partition means that we must re-sign the Copperhead image and updates if we want to keep the ability to have system integrity from Verified Boot.

Thankfully, the Nexus Devices supported by Copperhead allow the use of user-generated keys. The installation process simply takes a Copperhead image, installs our additional apps, and signs it with the new keys.

Systemic Threats to Software Freedom

Unfortunately, not only is Copperhead the only Android rebuild that supports Verified Boot, but the Google Nexus/Pixel hardware is the only Android hardware that allows the user to install their own keys to retain both the ability to modify the device, as well as have the filesystem security provided by verified boot.

This, combined with Google's increasing hostility towards Android as a fully Open Source platform, as well as the difficulty for external entities to keep up with Android's surprise release and opaque development processes, means that the ability for end-users to use, study, share, and improve the Android system are all in great jeopardy.

This all means that the Android platform is effectively moving to a "Look but don't touch" Shared Source model that Microsoft tried in the early 2000s. However, instead of being explicit about this, Google appears to be doing it surreptitiously. It is a very deeply disturbing trend.

It is unfortunate that Google seems to see locking down Android as the only solution to the fragmentation and resulting insecurity of the Android platform. We believe that more transparent development and release processes, along with deals for longer device firmware support from SoC vendors, would go a long way to ensuring that it is easier for good OEM players to stay up to date. Simply moving more components to Google Play, even though it will keep those components up to date, does not solve the systemic problem that there are still no OEM incentives to update the base system. Users of old AOSP base systems will always be vulnerable to library, daemon, and operating system issues. Simply giving them slightly more up to date apps is a bandaid that both reduces freedom and does not solve the root security problems. Moreover, as more components and apps are moved to closed source versions, Google is reducing its ability to resist the demand that backdoors be introduced. It is much harder to backdoor an open source component (especially with reproducible builds and binary transparency) than a closed source one.

If Google Play is to be used as a source of leverage to solve this problem, a far better approach would be to use it as a pressure point to mandate that OEMs keep their base system updated. If they fail to do so, their users will begin to lose Google Play functionality, with proper warning that notifies them that their vendor is not honoring their support agreement. In a more extreme version, the Android SDK itself could have compiled code that degrades app functionality or disables apps entirely when the base system becomes outdated.

Another option would be to change the license of AOSP itself to require that any parties that distribute binaries of the base system must provide updates to all devices for some minimum period of time. That would create a legal avenue for class-action lawsuits or other legal action against OEMs that make "fire and forget" devices that leave their users vulnerable, and endanger the Internet itself.

While extreme, both of these options would be preferable to completely giving up on free and open computing for the future of the Internet. Google should be competing on overall Google account integration experience, security, app selection, and media store features. They should use their competitive position to encourage/enforce good OEM behavior, not to create barriers and bandaids that end up enabling yet more fragmentation due to out of date (and insecure) devices.

It is for this reason that we believe that projects like Copperhead are incredibly important to support. Once we lose these freedoms on mobile, we may never get them back. It is especially troubling to imagine a future where mobile access to the Internet is the primary form of Internet usage, and for that usage, all users are forced to choose between having either security or freedom.

Hardware Choice

The hardware for this prototype is the Google Nexus 6P. While we would prefer to support lower end models for low income demographics, only the Nexus and Pixel lines support Verified Boot with user-controlled keys. We are not aware of any other models that allow this, but we would love to hear if there are any that do.

In theory, installation should work for any of the devices supported by Copperhead, but updating the device will require the addition of an updater-script and an adaptation of the releasetools.py for that device, to convert the radio and bootloader images to the OTA update format.

If you are not allergic to buying hardware online, we highly recommend that you order them from the Copperhead store. The devices are shipped with tamper-evident security tape, for what it's worth. Otherwise, if you're lucky, you might still be able to find a 6P at your local electronics retail store. Please consider donating to Copperhead anyway. The project is doing everything right, and could use your support.

Hopefully, we can add support for the newer Pixel devices as soon as AOSP (and Copperhead) supports them, too.


Before you dive in, remember that this is a prototype, and you will need to be familiar with Linux.

With the proper prerequisites, installation should be as simple as checking out the Mission Improbable git repository, and downloading a Copperhead factory image for your device.

The run_all.sh script should walk you through a series of steps, printing out instructions for unlocking the phone and flashing the system. Please read the instructions in the repository for full installation details.

The very first device boot after installation will take a while, so be patient. During this boot, you should note the fingerprint of your key on the yellow boot splash screen. That fingerprint is what authenticates the use of your key and the rest of the boot process.

Once the system is booted, after you have given Google Play Services the Location and Storage permissions (as per the instructions printed by the script), make sure you set the Date and Time accurately, or Orbot will not be able to connect to the Tor Network.

Then, you can start Orbot, and allow F-Droid, Download Manager, the Copperhead updater, Google Play Services (if you want to use Signal), and any other apps you want to access the network.

NOTE: To keep Orbot up to date, you will have to go into F-Droid Repositories option, and click Guardian Project Official Releases.

Installation: F-Droid apps

Once you have networking and F-Droid working, you can use MyAppList to install apps from F-Droid. Our installation provides a list of useful apps for MyAppList. The MyAppsList app will allow you to select the subset you want, and install those apps in succession by invoking F-Droid. Start this process by clicking on the upward arrow at the bottom right of the screen:

Alternately, you can add links to additional F-Droid packages in the apk url list prior to running the installation, and they will be downloaded and installed during run_all.sh.

NOTE: Do not update OrWall past 1.1.0 via F-Droid until issue 121 is fixed, or networking will break.

Installation: Signal

Signal is one of the most useful communications applications to have on your phone. Unfortunately, despite being open source itself, Signal is not included in F-Droid, for historical reasons. Near as we can tell, most of the issues behind the argument have actually been since resolved. Now that Signal is reproducible, we see no reason why it can't be included in some F-Droid repo, if not the F-Droid repo, so long as it is the same Signal with the same key. It is unfortunate to see so much disagreement over this point, though. Even if Signal won't make the criterion for the official F-Droid repo (or wherever that tirefire of a flamewar is at right now), we wish that at the very least it could meet the criterion for an alternate "Non-Free" repo, much like the Debian project provides. Nothing is preventing the redistribution of the official Signal apk.

For now, if you do not wish to use a Google account with Google Play, it is possible to download the Signal apks from one of the apk mirror sites (such as APK4fun, apkdot.com, or apkplz.com). To ensure that you have the official Signal apk, perform the following:

  1. Download the apk.
  2. Unzip the apk with unzip org.thoughtcrime.securesms.apk
  3. Verify that the signing key is the official key with keytool -printcert -file META-INF/CERT.RSA
  4. You should see a line with SHA256: 29:F3:4E:5F:27:F2:11:B4:24:BC:5B:F9:D6:71:62:C0 EA:FB:A2:DA:35:AF:35:C1:64:16:FC:44:62:76:BA:26
  5. Make sure that fingerprint matches (the space was added for formatting).
  6. Verify that the contents of that APK are properly signed by that cert with: jarsigner -verify org.thoughtcrime.securesms.apk. You should see jar verified printed out.

Then, you can install the Signal APK via adb with adb install org.thoughtcrime.securesms.apk. You can verify you're up to date with the version in the app store with ApkTrack.

For voice calls to work, select Signal as the SIP application in OrWall, and allow SIP access.


Because Verified Boot ensures filesystem integrity at the device block level, and because we modify the root and system filesystems, normal over the air updates will not work. The fact that we use different device keys will prevent the official updates from installing at all, but even if they did, they would remove the installation of Google Play, SuperUser, and the OrWall initial firewall script.

When the phone notifies you of an update, you should instead download the latest Copperhead factory image to the mission-improbable working directory, and use update.sh to convert it into a signed update zip that will get sideloaded and installed by the recovery. You need to have the same keys from the installation in the keys subdirectory.

The update.sh script should walk you through this process.

Updates may also reset the system clock, which must be accurate for Orbot to connect to the Tor network. If this happens, you may need to reset the clock manually under Date and Time Settings


I use this prototype for all of my personal communications - Email, Signal, XMPP+OTR, Mumble, offline maps and directions in OSMAnd, taking pictures, and reading news and books. I use Intent Intercept to avoid accidentally clicking on links, and to avoid surprising cross-app launching behavior.

For Internet access, I personally use a secondary phone that acts as a router for this phone while it is in airplane mode. That phone has an app store and I use it for less trusted, non-private applications, and for emergency situations should a bug with the device prevent it from functioning properly. However, it is also possible to use a cheap wifi cell router, or simply use the actual cell capabilities on the phone itself. In that case, you may want to look into CSipSimple, and a VoIP provider, but see the Future Work section about potential snags with using SIP and Signal at the same time.

I also often use Google Voice or SIP numbers instead of the number of my actual phone's SIM card just as a general protection measure. I give people this number instead of the phone number of my actual cell device, to prevent remote baseband exploits and other location tracking attacks from being trivial to pull off from a distance. This is a trade-off, though, as you are trusting the VoIP provider with your voice data, and on top of this, many of them do not support encryption for call signaling or voice data, and fewer still support SMS.

For situations where using the cell network at all is either undesirable or impossible (perhaps because it is disabled due to civil unrest), the mesh network messaging app Rumble shows a lot of promise. It supports both public and encrypted groups in a Twitter-like interface run over either a wifi or bluetooth ad-hoc mesh network. It could use some attention.

Future Work

Like the last post on the topic, this prototype obviously has a lot of unfinished pieces and unpolished corners. We've made a lot of progress as a community on many of the future work items from that last post, but many still remain.

Future work: More Device Support

As mentioned above, installation should work on all devices that Copperhead supports out of the box. However, updates require the addition of an updater-script and an adaptation of the releasetools.py for that device, to convert the radio and bootloader images to the OTA update format.

Future Work: MicroG support

Instead of Google Play Services, it might be nice to provide the Open Source MicroG replacements. This requires some hackery to spoof the Google Play Service Signature field, though. Unfortunately, this method creates a permission that any app can request to spoof signatures for any service. We'd be much happier about this if we could find a way for MicroG to be the only app to be able to spoof permissions, and only for the Google services it was replacing. This may be as simple as hardcoding those app ids in an updated version of one of these patches.

Future Work: Netfilter API (or better VPN APIs)

Back in the WhisperCore days, Moxie wrote a Netfilter module using libiptc that enabled apps to edit iptables rules if they had permissions for it. This would eliminate the need for iptables shell callouts for using OrWall, would be more stable and less leaky than the current VPN APIs, and would eliminate the need to have root access on the device (which is additional vulnerability surface). That API needs to be dusted off and updated for the Copperhead compatibility, and then Orwall would need to be updated to use it, if present.

Alternatively, the VPN API could be used, if there were ways to prevent leaks at boot, DNS leaks, and leaks if the app is killed or crashes. We'd also want the ability to control specific app network access, and allow bypass of UDP for VoIP apps.

Future Work: Fewer Binary Blobs

There are unfortunately quite a few binary blobs extracted from the Copperhead build tree in the repository. They are enumerated in the README. This was done for expedience. Building some of those components outside of the android build tree is fairly difficult. We would happily accept patches for this, or for replacement tools.

Future Work: F-Droid auto-updates, crash reporting, and install count analytics

These requests come from Moxie. Having these would make him much happier about F-Droid Signal installs.

It turns out that F-Droid supports full auto-updates with the Priviledged Extension, which Copperhead is working on including.

Future Work: Build Reproducibility

Copperhead itself is not yet built reproducibly. It's our opinion that this is the AOSP's responsibility, though. If it's not the core team at Google, they should at least fund Copperhead or some other entity to work on it for them. Reproducible builds should be an organizational priority for all software companies. Moreover, in combination with free software, they are an excellent deterrent against backdoors.

In this brave new world, even if we can trust that the NSA won't be ordered to attack American companies to insert backdoors, deteriorating relationships with China and other state actors may mean that their incentives to hold back on such attacks will be greatly reduced. Closed source components can also benefit from reproducible builds, since compromising multiple build systems/build teams is inherently harder than compromising just one.

Future Work: Orbot Stability

Unfortunately, the stability of Orbot itself still leaves a lot to be desired. It is fairly fragile to network disconnects. It often becomes stuck in states that require you to go into the Android Settings for Apps, and then Force Stop Orbot in order for it to be able to reconnect properly. The startup UI is also fragile to network connectivity.

Worse: If you tap the start button either too hard or multiple times while the network is disconnected or while the phone's clock is out of sync, Orbot can become confused and say that it is connected when it is not. Luckily, because the Tor network access security is enforce by Orwall (and the Android kernel), instabilities in Orbot do not risk Tor leaks.

Future Work: Backups and Remote Wipe

Unfortunately, backups are an unsolved problem. In theory, adb backup -all should work, but even the latest adb version from the official Android SDK appears to only backup and restore partial data. Apparently this is due to adb obeying manifest restrictions on apps that request not to be backed up. For the purposes of full device backup, it would be nice to have an adb version that really backed up everything.

Instead, I use the export feature of K-9 Mail, Contacts, and the Calendar Import-Export app to export that data to /sdcard, and then adb pull /sdcard. It would be nice to have an end-to-end encrypted remote backup app, though. Flock had promise, but was unfortunately discontinued.

Similarly, if a phone is lost, it would be nice to have a cryptographically secure remote wipe feature.

Future Work: Baseband Analysis (and Isolation)

Until phones with auditable baseband isolation are available (the Neo900 looks like a promising candidate), the baseband remains a problem on all of these phones. It is unknown if vulnerabilities or backdoors in the baseband can turn on the mic, make silent calls, or access device memory. Using a portable hotspot or secondary insecure phone is one option for now, but it is still unknown if the baseband is fully disabled in airplane mode. In the previous post, commenters recommended wiping the baseband, but on most phones, this seems to also disable GPS.

It would be useful to audit whether airplane mode fully disables the baseband using either OpenBTS, OsmocommBB, or a custom hardware monitoring device.

Future Work: Wifi AP Scanning Prevention

Copperhead may randomize the MAC address, but it is quite likely that it still tries to connect to configured APs, even if they are not there (see these two XDA threads). This can reveal information about your home and work networks, and any other networks you have configured.

There is a Wifi Privacy Police App in F-Droid, and Smarter WiFi may be other options, but we have not yet had time to audit/test either. Any reports would be useful here.

Future Work: Port Tor Browser to Android

The Guardian Project is undertaking a port of Tor Browser to Android as part of their OrFox project. This port is still incomplete, however. The Tor Project is working on obtaining funding to bring it on par with the desktop Tor Browser.

Future Work: Better SIP Support

Right now, it is difficult to use two or more SIP clients in OrWall. You basically have to switch between them in the settings, which is also fragile and error prone. It would be ideal if OrWall allowed multiple SIP apps to be selected.

Additionally, SIP providers and SIP clients have very poor support for TLS and SRTP encryption for call setup and voice data. I could find only two such providers that advertised this support, but I was unable to actually get TLS and SRTP working with CSipSimple or LinPhone for either of them.

Future Work: Installation and full OTA updates without Linux

In order for this to become a real end-user phone, we need to remove the requirement to use Linux in order to install and update it. Unfortunately, this is tricky. Technically, Google Play can't be distributed in a full Android firmware, so we'd have to get special approval for that. Alternatively, we could make the default install use MicroG, as above. In either case, it should just be a matter of taking the official Copperhead builds, modifying them, changing the update URL, and shipping those devices with Google Play/MicroG and the new OTA location. Copperhead or Tor could easily support multiple device install configurations this way without needing to rebuild everything for each one. So legal issues aside, users could easily have their choice of MicroG, Google Play, or neither.

Personally, I think the demand is higher for some level of Google account integration functionality than what MicroG provides, so it would be nice to find some way to make that work. But there are solid reasons for avoiding the use of a Google account (such as Google's mistreatment of Tor users, the unavailability of Google in certain areas of the world due to censorship of Google, and the technical capability of Google Play to send targeted backdoored versions of apps to specific accounts).

Future Work: Better Boot Key Representation/Authentication

The truncated fingerprint is not the best way to present a key to the user. It is both too short for security, and too hard to read. It would be better to use something like the SSH Randomart representation, or some other visual representation that encodes a cryptographically strong version of the key fingerprint, and asks the user to click through it to boot. Though obviously, if this boot process can also be modified, this may be insufficient.

Future Work: Faster GPS Lock

The GPS on these devices is device-only by default, which can mean it is very slow. It would be useful to find out if µg UnifiedNlp can help, and which of its backends are privacy preserving enough to recommend/enable by default.

Future Work: Sensor Management/Removal

As pointed out in great detail in one of the comments below, these devices have a large number of sensors on them that can be used to create side channels, gather information about the environment, and send it back. The original Mission Impossible post went into quite a bit of detail about how to remove the microphone from the device. This time around, I focused on software security. But like the commentor suggested, you can still go down the hardware modding rabbithole if you like. Just search YouTube for teardown nexus 6P, or similar.

Changes Since Initial Posting

Like the last post, this post will likely be updated for a while based on community feedback. Here is the list of those changes so far.

  1. Added information about secondary SIP/VoIP usage in the Usage section and the Future Work sections.
  2. Added a warning not to upgrade OrWall until Issue 121 is fixed.
  3. Describe how we could remove the Linux requirement and have OTA updates, as a Future Work item.
  4. Remind users to check their key fingerprint at installation and boot, and point out in the Future Work section that this UI could be better.
  5. Mention the Neo900 in the Future Work: Baseband Isolation section
  6. Wow, the Signal vs F-Droid issue is a stupid hot mess. Can't we all just get along and share the software? Don't make me sing the RMS song, people... I'll do it...
  7. Added a note that you need the Guardian Project F-Droid repo to update Orbot.
  8. Add a thought to the Systemic Threats to Software Freedom section about using licensing to enforce the update requirement in order to use the AOSP.
  9. Mention ApkTrack for monitoring for Signal updates, and Intent Intercept for avoiding risky clicks.
  10. Mention alternate location providers as Future Work, and that we need to pick a decent backend.
  11. Link to Conversations and some other apps in the usage section. Also add some other links here and there.
  12. Mention that Date and Time must be set correctly for Orbot to connect to the network.
  13. Added a link to Moxie's netfilter code to the Future Work section, should anyone want to try to dust it off and get it working with Orwall.
  14. Use keytool instead of sha256sum to verify the Signal key's fingerprint. The CERT.RSA file is not stable across versions.
  15. The latest Orbot 15.2.0-rc8 still has issues claiming that it is connected when it is not. This is easiest to observe if the system clock is wrong, but it can also happen on network disconnects.
  16. Add a Future Work section for sensor management/removal

Tracking The Impact of the WhatsApp Blockage on Tor

On May 2, 2016, a Brazilian judge ordered cell phone carriers to block access to the messaging service WhatsApp for 72 hours. The order applied to the whole nation of Brazil—100 million WhatsApp users. Worldwide, Internet censorship events happen frequently. They may occur in countries like Brazil or in oppressive regimes like Egypt or Saudi Arabia. We want to understand better what happens during these events.

If we can watch certain data points, we can observe, for instance, whether or not our tools are efficiently circumventing such blockages. The Tor Project has a set of tools that can help us learn these answers. We can not only identify whether a censorship event has happened, but see how it was accomplished by the censor, and observe if people are using our tool to bypass it.

The Open Observatory of Network Interference (OONI) is a Tor project focused on detecting censorship, surveillance, and traffic manipulation on the Internet. For the recent WhatsApp case, OONI published a report showing that the Brazilian mobile carriers blocked WhatsApp’s website through DNS hijacking.

OONI was able to determine this by running two tests on Brazil's network:
DNS-consistency tests
HTTP-request tests

While OONI tests are not currently designed to directly test instant messaging (IM) protocols, OONI did monitor access to the WhatsApp website. This data allows us to analyze the censorship mechanisms used, and to determine if tools like Tor can bypass the block.

In this case, an Android user could download Orbot, a Tor proxy tool for Android, and successfully bypass the censorship with its VPN mode.

As soon as the blockade was announced, we began promoting key tips in Portuguese on social media and elsewhere to instruct Brazilians about how to bypass the WhatsApp blockage on Android with Orbot.

For Orbot statistics, we don't use Google Analytics or other system to track Orbot users, other than what Google Play can show us about installs and uninstalls. Based only on that, Orbot's active install for Brazil on May 1st was at 33,458. On May 2nd it went up to 41,333.

Taking a look at the number of downloads for Orbot in Brazil, we saw a 20% to 30% increase in the rate of downloading on those days.

There was a similar increase on the Tor network, where the average number of daily direct connected users for Brazil, went from ~50,000 to 60,000 in 24 hours.

Our metrics.torproject.org portal, which hosts data visualizations from our network, also caught the circumvention event. The little blue dot represents the fact that something is happening in the region. Is great to see that even for very sudden and short-lived actions (the block was lifted in Brazil after about 24 hours), we were still capable of capturing it in our data. You can read here about how we do it and the precautions we take while collecting such data so we don't affect user privacy.

We know that we are talking about a small number of users in a world of 100 million, in the case of WhatsApp. There is still a lot of work to be done to help people become aware of such tools. However, it is great to see our projects coming together to tell this story.

Our experience with the WhatsApp blockage in Brazil demonstrates the potential these efforts have to provide us with information about censorship events and to help us build circumvention mechanisms against them.

We are working hard on new features for these tools; for instance, we want to deploy more mobile network tests for OONI and better visualizations of our data so that others can easily explore and learn from them, and we continue to improve user experience on our apps. Keep an eye on this blog as we develop this work!

GetTor: New Ways to Download Tor Browser

We are pleased to announce the new features available in the GetTor, a service that provides alternative ways to download Tor Browser, aimed for people who live in places with high levels of censorship (e.g. when www.torproject.org is blocked) or people who just don't want to expose the fact that they are downloading Tor Browser. This work adds important new download options and capabilities and includes improvements to the current code, deployment of new channels and providers, and some brand new features such as the GetTor API. We would also like to give special thanks to Nima Fatemi, who was in charge of the non-coding parts of this project (from funding to technical management).

Update note: we now have the gettor@torproject.org account for the XMPP channel. However, we will have the get_tor@riseup.net account enabled for a couple of more weeks just in case you are still using it.

Landing page

A GetTor landing page has been created to offer information in one place (statistics, guides, etc.). If you are interested in what is going on with GetTor, following the landing page is highly recommended.

New Distribution Channels

In the past, GetTor has distributed packages by sending the bundles -- and then, later, just links -- via email. Now there are two more ways to interact with GetTor:

  1. Using Twitter: You can send a direct message to @get_tor account (you don't need to follow the @get_tor acount). Send the word help in a direct message to receive information on how to download the Tor Browser.

  2. Using XMPP: You can send a message to gettor@torproject.org using your favorite XMPP client. Simply enter help in an XMPP message to receive information on how to download the Tor Browser.


GitHub is now a provider of Tor Browser (in addition to Dropbox and Google Drive), and the latest version of Tor Browser may be downloaded from our Github page and our Github repository.

Support for Android

Orbot is a free proxy (i.e. an intermediary) app that empowers other apps to use the Internet more securely. Orbot uses Tor to encrypt your Internet traffic and then hides it by sending it through a series of computers around the world. In addition to the download options provided by Guardian Project (Google Play, F-Droid, Direct download), GetTor provides yet another way to download Orbot to your mobile device. To do this, you have to reach one of our distribution channels and specify the android command (See Examples, at the bottom of this blog post). You will then receive instructions to download Orbot's Android Application Package (APK) file from Github, Google Drive or Dropbox. Once you have downloaded the APK file you can use it to install Orbot (similar to .exe files in Windows) and start using it.

Translated Versions of Tor Browser

GetTor provides a small set of translated packages focused on its end users. The available languages are Farsi, Chinese, Turkish, and English (which is the default). If you want to use this feature in the email autoresponder, for example, you send your request to:

    Farsi: gettor+fa@torproject.org
    Chinese: gettor+zh@torproject.org
    Turkish: gettor+tr@torproject.org
    English: gettor@torproject.org

For the Twitter and XMPP channels, you just need to add the language word to the
message (e.g. linux fa will get you links for Tor Browser in Farsi).


There are many volunteers who use their own servers to provide mirrors of Tor Project's website. One or more of these mirrors may be not blocked in places where torproject.org is censored and could help in downloading Tor Browser. With this new release, you can request a list of these mirrors from GetTor by sending an email (or message, in case of Twitter and XMPP) with the word mirrors in the body of the text.


Some basic but effective improvements have been made to collect anonymous data and compile meaningful statistics about GetTor usage, including requests per channel, operating system, and language. Safeguards have been implemented so that all information collected is anonymous, and it is erased on a daily basis -- we just keep the number and types of requests. Reports about this data will soon be available on GetTor's website.


One of GetTor's major new features is its API. In simple terms, an API is a set of rules and specifications that allow applications to communicate with each other (following these rules). This is helpful to developers who want to create new services or applications based on the information provided by the API. In this case, the GetTor API provides the following information:

  1. Links to download Tor Browser by provider, with filters for operating system and language.

  2. Links to download Tor Browser from Tor Project's website, with filters for choosing the release (latest version , etc.), operating system, and language.

  3. List of mirrors of Tor Project's website.

You can find more information on the API documentation.

Invitation to Collaborate

If you are a Tor user, a developer, good at writing content for non-technical users or anything else, we are happy to hear from you! You can use the comments section below, the tor-talk and tor-dev mailing lists, or come talk to us on IRC (#tor-dev on OFTC; our nicknames are ilv, sukhe and mrphs).

How to Ask for Tor Browser--Some Examples

To help you get started, here are a few examples of GetTor requests with different locales (languages) and operating systems:

Example 1 (Email): To get links for downloading Tor Browser in Farsi for Windows, send an email to gettor+fa@torproject.org with the word windows in the body of the message.

Example 2 (Twitter): To get links for downloading Tor Browser in English for OS X, send a Direct Message to @get_tor with the words osx on it (you don't need to follow the account).

Example 3 (XMPP): To get links for downloading Tor Browser in Chinese for Linux, send a message to gettor@torproject.org account with the words linux zh on it.

Example 4 (Email): To get links for downloading Orbot for Android, send an email to gettor@torproject.org with the word android in the body of the message.

Mission Impossible: Hardening Android for Security and Privacy

Updates: See the Changes section for a list of changes since initial posting.

This post has been updated further by the November 2016 Refresh of the same idea

Executive Summary

The future is here, and ahead of schedule. Come join us, the weather's nice.

This blog post describes the installation and configuration of a prototype of a secure, full-featured, Android telecommunications device with full Tor support, individual application firewalling, true cell network baseband isolation, and optional ZRTP encrypted voice and video support. ZRTP does run over UDP which is not yet possible to send over Tor, but we are able to send SIP account login and call setup over Tor independently.

The SIP client we recommend also supports dialing normal telephone numbers if you have a SIP gateway that provides trunking service.

Aside from a handful of binary blobs to manage the device firmware and graphics acceleration, the entire system can be assembled (and recompiled) using only FOSS components. However, as an added bonus, we will describe how to handle the Google Play store as well, to mitigate the two infamous Google Play Backdoors.


Android is the most popular mobile platform in the world, with a wide variety of applications, including many applications that aid in communications security, censorship circumvention, and activist organization. Moreover, the core of the Android platform is Open Source, auditable, and modifiable by anyone.

Unfortunately though, mobile devices in general and Android devices in particular have not been designed with privacy in mind. In fact, they've seemingly been designed with nearly the opposite goal: to make it easy for third parties, telecommunications companies, sophisticated state-sized adversaries, and even random hackers to extract all manner of personal information from the user. This includes the full content of personal communications with business partners and loved ones. Worse still, by default, the user is given very little in the way of control or even informed consent about what information is being collected and how.

This post aims to address this, but we must first admit we stand on the shoulders of giants. Organizations like Cyanogen, F-Droid, the Guardian Project, and many others have done a great deal of work to try to improve this situation by restoring control of Android devices to the user, and to ensure the integrity of our personal communications. However, all of these projects have shortcomings and often leave gaps in what they provide and protect. Even in cases where proper security and privacy features exist, they typically require extensive configuration to use safely, securely, and correctly.

This blog post enumerates and documents these gaps, describes workarounds for serious shortcomings, and provides suggestions for future work.

It is also meant to serve as a HOWTO to walk interested, technically capable people through the end-to-end installation and configuration of a prototype of a secure and private Android device, where access to the network is restricted to an approved list of applications, and all traffic is routed through the Tor network.

It is our hope that this work can be replicated and eventually fully automated, given a good UI, and rolled into a single ROM or ROM addon package for ease of use. Ultimately, there is no reason why this system could not become a full fledged off the shelf product, given proper hardware support and good UI for the more technical bits.

The remainder of this document is divided into the following sections:

  1. Hardware Selection
  2. Installation and Setup
  3. Google Apps Setup
  4. Recommended Software
  5. Device Backup Procedure
  6. Removing the Built-in Microphone
  7. Removing Baseband Remnants
  8. Future Work
  9. Changes Since Initial Posting

Hardware Selection

If you truly wish to secure your mobile device from remote compromise, it is necessary to carefully select your hardware. First and foremost, it is absolutely essential that the carrier's baseband firmware is completely isolated from the rest of the platform. Because your cell phone baseband does not authenticate the network (in part to allow roaming), any random hacker with their own cell network can exploit these backdoors and use them to install malware on your device.

While there are projects underway to determine which handsets actually provide true hardware baseband isolation, at the time of this writing there is very little public information available on this topic. Hence, the only safe option remains a device with no cell network support at all (though cell network connectivity can still be provided by a separate device). For the purposes of this post, the reference device is the WiFi-only version of the 2013 Google Nexus 7 tablet.

For users who wish to retain full mobile access, we recommend obtaining a cell modem device that provides a WiFi access point for data services only. These devices do not have microphones and in some cases do not even have fine-grained GPS units (because they are not able to make emergency calls). They are also available with prepaid plans, for rates around $20-30 USD per month, for about 2GB/month of 4G data. If coverage and reliability is important to you though, you may want to go with a slightly more expensive carrier. In the US, T-Mobile isn't bad, but Verizon is superb.

To increase battery life of your cell connection, you can connect this access point to an external mobile USB battery pack, which typically will provide 36-48 hours of continuous use with a 6000mAh battery.

The total cost of a Wifi-only tablet with cell modem and battery pack is only roughly USD $50 more than the 4G LTE version of the same device.

In this way, you achieve true baseband isolation, with no risk of audio or network surveillance, baseband exploits, or provider backdoors. Effectively, this cell modem is just another untrusted router in a long, long chain of untrustworthy Internet infrastructure.

However, do note though that even if the cell unit does not contain a fine-grained GPS, you still sacrifice location privacy while using it. Over an extended period of time, it will be possible to make inferences about your physical activity, behavior and personal preferences, and your identity, based on cell tower use alone.

Installation and Setup

We will focus on the installation of Cyanogenmod 11 using Team Win Recovery Project, both to give this HOWTO some shelf life, and because Cyanogenmod 11 features full SELinux support (Dear NSA: What happened to you guys? You used to be cool. Well, some of you. Some of the time. Maybe. Or maybe not).

The use of Google Apps and Google Play services is not recommended due to security issues with Google Play. However, we do provide workarounds for mitigating those issues, if Google Play is required for your use case.

Installation and Setup: ROM and Core App Installation

With the 2013 Google Nexus 7 tablet, installation is fairly straight-forward. In fact, it is actually possible to install and use the device before associating it with a Google Account in any way. This is a desirable property, because by default, the otherwise mandatory initial setup process of the stock Google ROM sends your device MAC address directly to Google and links it to your Google account (all without using Tor, of course).

The official Cyanogenmod installation instructions are available online, but with a fresh out of the box device, here are the key steps for installation without activating the default ROM code at all (using Team Win Recovery Project instead of ClockWorkMod).

First, on your desktop/laptop computer (preferably Linux), perform the following:

  1. Download the latest CyanogenMod 11 release (we used cm-11-20140504-SNAPSHOT-M6)
  2. Download the latest Team Win Recovery Project image (we used
  3. Download the F-Droid package (we used 0.66)
  4. Download the Orbot package from F-Droid (we used 13.0.7)
  5. Download the Droidwall package from F-Droid (we used 1.5.7)
  6. Download the Droidwall Firewall Scripts attached to this blogpost
  7. Download the Google Apps for Cyanogenmod 11 (optional)

Because the download integrity for all of these packages is abysmal, here is a signed set of SHA256 hashes I've observed for those packages.

Once you have all of those packages, boot your tablet into fastboot mode by holding the Power button and the Volume Down button during a cold boot. Then, attach it to your desktop/laptop machine with a USB cable and run the following commands from a Linux/UNIX shell:

 apt-get install android-tools-adb android-tools-fastboot
 fastboot devices
 fastboot oem unlock
 fastboot flash recovery openrecovery-twrp-

After the recovery firmware is flashed successfully, use the volume keys to select Recovery and hit the power button to reboot the device (or power it off, and then boot holding Power and Volume Up).

Once Team Win boots, go into Wipe and select Advanced Wipe. Select all checkboxes except for USB-OTG, and slide to wipe. Once the wipe is done, click Format Data. After the format completes, issue these commands from your Linux shell:

 adb server start
 adb push cm-11-20140504-SNAPSHOT-M6-flo.zip /sdcard/
 adb push gapps-kk-20140105-signed.zip /sdcard/ # Optional

After this push process completes, go to the Install menu, and select the Cyanogen zip, and optionally the gapps zip for installation. Then click Reboot, and select System.

After rebooting into your new installation, skip all CyanogenMod and Google setup, disable location reporting, and immediately disable WiFi and turn on Airplane mode.

Then, go into Settings -> About Tablet and scroll to the bottom and click the greyed out Build number 5 times until developer mode is enabled. Then go into Settings -> Developer Options and turn on USB Debugging.

After that, run the following commands from your Linux shell:

 adb install FDroid.apk
 adb install org.torproject.android_86.apk
 adb install com.googlecode.droidwall_157.apk

You will need to approve the ADB connection for the first package, and then they should install normally.

VERY IMPORTANT: Whenever you finish using adb, always remember to disable USB Debugging and restore Root Access to Apps only. While Android 4.2+ ROMs now prompt you to authorize an RSA key fingerprint before allowing a debugging connection (thus mitigating adb exploit tools that bypass screen lock and can install root apps), you still risk additional vulnerability surface by leaving debugging enabled.

Installation and Setup: Initial Configuration

After the base packages are installed, go into the Settings app, and make the following changes:

  1. Wireless & Networks More... =>
    • Temporarily Disable Airplane Mode
    • NFC -> Disable
    • Re-enable Airplane Mode
  2. Location Access -> Off
  3. Security =>
    • PIN screen Lock
    • Allow Unknown Sources (For F-Droid)
  4. Language & Input =>
    • Spell Checker -> Android Spell Checker -> Disable Contact Names
    • Disable Google Voice Typing/Hotword detection
    • Android Keyboard (AOSP) =>
      • Disable AOSP next-word suggestion (do this first!)
      • Auto-correction -> Off
  5. Backup & reset =>
    • Enable Back up my data (just temporarily, for the next step)
    • Uncheck Automatic restore
    • Disable Backup my data
  6. About Tablet -> Cyanogenmod Statistics -> Disable reporting
  7. Developer Options -> Device Hostname -> localhost
  8. SuperUser -> Settings (three dots) -> Notifications -> Notification (not toast)
  9. Privacy -> Privacy Guard =>
    • Enabled by default
    • Settings (three dots) -> Show Built In Apps
    • Enable Privacy Guard for every app with the following exceptions:
      • Calendar
      • Config Updater
      • Google Account Manager (long press)
        • Modify Settings -> Off
        • Wifi Change -> Off
        • Data Change -> Off
      • Google Play Services (long press)
        • Location -> Off
        • Modify Settings -> Off
        • Draw on top -> Off
        • Record Audio -> Off
        • Wifi Change -> Off
      • Google Play Store (long press)
        • Location -> Off
        • Send SMS -> Off
        • Modify Settings -> Off
        • Data change -> Off
      • Google Services Framework (long press)
        • Modify Settings -> Off
        • Wifi Change -> Off
        • Data Change -> Off
      • Trebuchet

Now, it is time to encrypt your tablet. It is important to do this step early, as I have noticed additional apps and configuration tweaks can make this process fail later on.

We will also do this from the shell, in order to set a different password than your screen unlock pin. This is done to mitigate the risk of compromise of this password from shoulder surfers, and to allow the use of a much longer (and non-numeric) password that you would prefer not to type every time you unlock the screen.

To do this, open the Terminal app, and type the following commands:

vdc cryptfs enablecrypto inplace NewMoreSecurePassword

Watch for typos! That command does not ask you to re-type that password for confirmation.

Installation and Setup: Disabling Invasive Apps and Services

Before you configure the Firewall or enable the network, you likely want to disable at least a subset of the following built-in apps and services, by using Settings -> Apps -> All, and then clicking on each app and hitting the Disable button:

  • com.android.smspush
  • com.google.android.voicesearch
  • Face Unlock
  • Google Backup Transport
  • Google Calendar Sync
  • Google One Time Init
  • Google Partner Setup
  • Google Contacts Sync
  • Google Search
  • Hangouts
  • Market Feedback Agent
  • News & Weather
  • One Time Init
  • Picasa Updater
  • Sound Search for Google Play
  • TalkBack

Installation and Setup: Tor and Firewall configuration

Ok, now let's install the firewall and tor support scripts. Go back into Settings -> Developer Options and enable USB Debugging and change Root Access to Apps and ADB. Then, unzip the android-firewall.zip on your laptop, and run the installation script:


That firewall installation provides several key scripts that provide functionality that is currently impossible to achieve with any app (including Orbot):

  1. It installs a userinit script to block all network access during boot.
  2. It disables "Google Captive Portal Detection", which involves connection attempts to Google servers upon Wifi assocation (these requests are made by the Android Settings UID, which should normally be blocked from the network, unless you are first registering for Google Play).
  3. It contains a Droidwall script that configures Tor transproxy rules to send all of your traffic through Tor. These rules include a fix for a Linux kernel Tor transproxy packet leak issue.
  4. The main firewall-torify-all.sh Droidwall script also includes an input firewall, to block all inbound connections to the device. It also fixes a Droidwall permissions vulnerability
  5. It installs an optional script to allow the Browser app to bypass Tor for logging into WiFi captive portals.
  6. It installs an optional script to temporarily allow network adb access when you need it (if you are paranoid about USB exploits, which you should be).
  7. It provides an optional script to allow the UDP activity of LinPhone to bypass Tor, to allow ZRTP-encrypted Voice and Video SIP/VoIP calls. SIP account login/registration and call setup/signaling can be done over TCP, and Linphone's TCP activity is still sent through Tor with this script.

Note that with the exception of the userinit network blocking script, installing these scripts does not activate them. You still need to configure Droidwall to use them.

We use Droidwall instead of Orbot or AFWall+ for five reasons:

  1. Droidwall's app-based firewall and Orbot's transproxy are known to conflict and reset one another.
  2. Droidwall does not randomly drop transproxy rules when switching networks (Orbot has had several of these types of bugs).
  3. Unlike AFWall+, Droidwall is able to auto-launch at "boot" (though still not before the network and Android Services come online and make connections).
  4. AFWall+'s "fix" for this startup data leak problem does not work on Cyanogenmod (hence our userinit script instead).
  5. Aside from the permissions issue fixed by our firewall-torify-all.sh script, AFWall+ provides no additional security fixes over the stock Droidwall.

To make use of the firewall scripts, open up Droidwall and hit the config button (the vertical three dots), go to More -> Set Custom Script. Enter the following:

. /data/local/firewall-torify-all.sh
#. /data/local/firewall-allow-adb.sh
#. /data/local/firewall-allow-linphone-udp.sh
#. /data/local/firewall-allow-nontor-browser.sh

NOTE: You must not make any typos in the above. If you mistype any of those files, things may break. Because the userinit.sh script blocks all network at boot, if you make a typo in the torify script, you will be unable to use the Internet at all!

Also notice that these scripts have been installed into a readonly root directory. Because they are run as root, installing them to a world-writable location like /sdcard/ is extremely unwise.

Later, if you want to enable one of network adb, LinPhone UDP, or captive portal login, go back into this window and remove the leading comment ('#') from the appropriate lines (this is obviously one of the many aspects of this prototype that could benefit from real UI).

Then, configure the apps you want to allow to access the network. Note that the only Android system apps that must access the network are:

  • CM Updater
  • Downloads, Media Storage, Download Manager
  • F-Droid

Orbot's network access is handled via the main firewall-torify-all.sh script. You do not need to enable full network access to Orbot in Droidwall.

The rest of the apps you can enable at your discretion. They will all be routed through Tor automatically.

Once Droidwall is configured, you can click on the Menu (three dots) and click the "Firewall Disabled" button to enable the firewall. Then, you can enable Orbot. Do not grant Orbot superuser access. It still opens the transproxy ports you need without root, and Droidwall is managing installation of the transproxy rules, not Orbot.

You are now ready to enable Wifi and network access on your device. For vulnerability surface reduction, you may want to use the Advanced Options -> Static IP to manually enter an IP address for your device to avoid using dhclient. You do not need a DNS server, and can safely set it to

Google Apps Setup

If you installed the Google Apps zip, you need to do a few things now to set it up, and to further harden your device. If you opted out of Google Apps, you can skip to the next section.

Google Apps Setup: Initializing Google Play

The first time you use Google Play, you will need to enable four apps in Droidwall: "Google Account Manager, Google Play Services...", "Settings, Dev Tools, Fused Location...", "Gmail", and "Google Play" itself.

If you do not have a Google account, your best bet is to find open wifi to create one, as Google will often block accounts created through Tor, even if you use an Android device.

After you log in for the first time, you should be able to disable the "Google Account Manager, Google Play Services...", "Gmail", and the "Settings..." apps in Droidwall, but your authentication tokens in Google Play may expire periodically. If this happens, you should only need to temporarily enable the "Google Account Manager, Google Play Services..." app in Droidwall to obtain new ones.

Google Apps Setup: Mitigating the Google Play Backdoors

If you do choose to use Google Play, you need to be very careful about how you allow it to access the network. In addition to the risks associated with using a proprietary App Store that can send you targeted malware-infected packages based on your Google Account, it has at least two major user experience flaws:

  1. Anyone who is able to gain access to your Google account can silently install root or full permission apps without any user interaction what-so-ever. Once installed, these apps can retroactively clear what little installation notification and UI-based evidence of their existence there was in the first place.
  2. The Android Update Process does not inform the user of changes in permissions of pending update apps that happen to get installed after an Android upgrade.

The first issue can be mitigated by ensuring that Google Play does not have access to the network when not in use, by disabling it in Droidwall. If you do not do this, apps can be installed silently behind your back. Welcome to the Google Experience.

For the second issue, you can install the SecCheck utility, to monitor your apps for changes in permissions during a device upgrade.

Google Apps Setup: Disabling Google Cloud Messaging

If you have installed the Google Apps zip, you have also enabled a feature called Google Cloud Messaging.

The Google Cloud Messaging Service allows apps to register for asynchronous remote push notifications from Google, as well as send outbound messages through Google.

Notification registration and outbound messages are sent via the app's own UID, so using Droidwall to disable network access by an app is enough to prevent outbound data, and notification registration. However, if you ever allow network access to an app, and it does successfully register for notifications, these notifications can be delivered even when the app is once again blocked from accessing the network by Droidwall.

These inbound notifications can be blocked by disabling network access to the "Google Account Manager, Google Play Services, Google Services Framework, Google Contacts Sync" in Droidwall. In fact, the only reason you should ever need to enable network access by this service is if you need to log in to Google Play again if your authentication tokens ever expire.

If you would like to test your ability to control Google Cloud Messaging, there are two apps in the Google Play store than can help with this. GCM Test allows for simple send and receive pings through GCM. Push Notification Tester will allow you to test registration and asynchronous GCM notification.

Recommended Privacy and Auditing Software

Ok, so now that we have locked down our Android device, now for the fun bit: secure communications!

We recommend the following apps from F-Droid:

  1. Xabber
  2. Xabber is a full Java implementation of XMPP, and supports both OTR and Tor. Its UI is a bit more streamlined than Guardian Project's ChatSecure, and it does not make use of any native code components (which are more vulnerable to code execution exploits than pure Java code). Unfortunately, this means it lacks some of ChatSecure's nicer features, such as push-to-talk voice and file transfer.

    Despite better protection against code execution, it does have several insecure default settings. In particular, you want to make the following changes:

    • Notifications -> Message text in Notifications -> Off (notifications can be read by other apps!)
    • Accounts -> Integration into system accounts -> Off
    • Accounts -> Store message history -> Don't Store
    • Security -> Store History -> Off
    • Security -> Check Server Certificate
    • Chat -> Show Typing Notifications -> Off
    • Connection Settings -> Auto-away -> disabled
    • Connection Settings -> Extended away when idle -> Disabled
    • Keep Wifi Awake -> On
    • Prevent sleep Mode -> On
  3. Offline Calendar
  4. Offline Calendar is a hack to allow you to create a fake local Google account that does not sync to Google. This allows you to use the Calendar App without risk of leaking your activities to Google. Note that you must exempt both this app and Calendar from Privacy Guard for it to function properly.

  5. LinPhone
  6. LinPhone is a FOSS SIP client that supports TCP TLS signaling and ZRTP. Note that neither TLS nor ZRTP are enabled by default. You must manually enable them in Settings -> Network -> Transport and Settings -> Network -> Media Encryption.

    ostel.co is a free SIP service run by the Guardian Project that supports only TLS and ZRTP, but does not allow outdialing to normal PSTN telephone numbers. While Bitcoin has many privacy issues of its own, the Bitcoin community maintains a couple lists of "trunking" providers that allow you to obtain a PSTN phone number in exchange for Bitcoin payment.

  7. Plumble

    Plumble is a Mumble client that will route voice traffic over Tor, which is useful if you would like to communicate with someone over voice without revealing your IP to them, or your activity to a local network observer. However, unlike Linphone, voice traffic is not end-to-end encrypted, so the Mumble server can listen to your conversations.

  8. K-9 Mail and APG

    K-9 Mail is a POP/IMAP client that supports TLS and integrates well with APG, which will allow you to send and receive GPG-encrypted mail easily. Before using it, you should be aware of two things: It identifies itself in your mail headers, which opens you up to targeted attacks specifically tailored for K-9 Mail and/or Android, and by default it includes the subject of messages in mail notifications (which is bad, because other apps can read notifications). There is a privacy option to disable subject text in notifications, but there is no option to disable the user agent in the mail headers.

  9. OSMAnd~
  10. A free offline mapping tool. While the UI is a little clunky, it does support voice navigation and driving directions, and is a handy, private alternative to Google Maps.

  11. VLC

    The VLC port in F-Droid is a fully capable media player. It can play mp3s and most video formats in use today. It is a handy, private alternative to Google Music and other closed-source players that often report your activity to third party advertisers. VLC does not need network access to function.

  12. Firefox
  13. We do not yet have a port of Tor Browser for Android (though one is underway -- see the Future Work section). Unless you want to use Google Play to get Chrome, Firefox is your best bet for a web browser that receives regular updates (the built in Browser app does not). HTTPS-Everywhere and NoScript are available, at least.

  14. Bitcoin
  15. Bitcoin might not be the most private currency in the world. In fact, you might even say it's the least private currency in the world. But, it is a neat toy.

  16. Launch App Ops

    The Launch App Ops app is a simple shortcut into the hidden application permissions editor in Android. A similar interface is available through Settings -> Privacy -> Privacy Guard, but a direct shortcut to edit permissions is handy. It also displays some additional system apps that Privacy Guard omits.

  17. Permissions

    The Permissions app gives you a view of all Android permissions, and shows you which apps have requested a given permission. This is particularly useful to disable the record audio permission for apps that you don't want to suddenly decide to listen to you. (Interestingly, the Record Audio permission disable feature was broken in all Android ROMs I tested, aside from Cyanogenmod 11. You can test this yourself by revoking the permission from the Sound Recorder app, and verifying that it cannot record.)

  18. CatLog
  19. In addition to being supercute, CatLog is an excellent Android monitoring and debugging tool. It allows you to monitor and record the full set of Android log events, which can be helpful in diagnosing issues with apps.

  20. OS Monitor
  21. OS Monitor is an excellent Android process and connection monitoring app, that can help you watch for CPU usage and connection attempts by your apps.

  22. Intent Intercept
  23. Intent Intercept allows you to inspect and extract Android Intent content without allowing it to get forwarded to an actual app. This is useful for monitoring how apps attempt to communicate with eachother, though be aware it only covers one of the mechanisms of inter-app communication in Android.

Backing up Your Device Without Google

Now that your device is fully configured and installed, you probably want to know how to back it up without sending all of your private information directly to Google. While the Team Win Recovery Project will back up all of your system settings and apps (even if your device is encrypted), it currently does not back up the contents of your virtualized /sdcard. Remembering to do a couple adb pulls of key directories can save you a lot of heartache should you suffer some kind of data loss or hardware failure (or simply drop your tablet on a bridge while in a rush to catch a train).

The backup.sh script uses adb to pull your Download and Pictures directories from the /sdcard, as well as pulls the entire TWRP backup directory.

Before you use that script, you probably want to delete old TWRP backup folders so as to only pull one backup, to reduce pull time. These live in /sdcard/TWRP/BACKUPS/, which is also known as /storage/emulated/0/TWRP/BACKUPS in the File Manager app.

To use this script over the network without a usb cable, enable both USB Debugging and ADB Over Network in your developer settings. The script does not require you to enable root access from adb, and you should not enable root because it takes quite a while to run a backup, especially if you are using network adb.

Prior to using network adb, you must edit your Droidwall custom scripts to allow it (by removing the '#' in the #. /data/local/firewall-allow-adb.sh line you entered earlier), and then run the following commands from a non-root Linux shell on your desktop/laptop (the ADB Over Network setting will tell you the IP and port):

killall adb
adb connect ip:5555

VERY IMPORTANT: Don't forget to disable USB Debugging, as well as the Droidwall adb exemption when you are done with the backup!

Removing the Built-in Microphone

If you would really like to ensure that your device cannot listen to you even if it is exploited, it turns out it is very straight-forward to remove the built-in microphone in the Nexus 7. There is only one mic on the 2013 model, and it is located just below the volume buttons (the tiny hole).

To remove it, all you need to do is pop off the the back panel (this can be done with your fingernails, or a tiny screwdriver), and then you can shave the microphone right off that circuit board, and reattach the panel. I have done this to one of my devices, and it was subsequently unable to record audio at all, without otherwise affecting functionality.

You can still use apps that require a microphone by plugging in headphone headset that contains a mic built in (these cost around $20 and you can get them from nearly any consumer electronics store). I have also tested this, and was still able to make a Linphone call from a device with the built in microphone removed, but with an external headset. Note that the 2012 Nexus 7 does not support these combination microphone+headphone jacks (and it has a secondary microphone as well). You must have the 2013 model.

The 2013 Nexus 7 Teardown video can give you an idea of what this looks like before you try it. Again you do not need to fully disassemble the device - you only need to remove the back cover.

Pro-Tip: Before you go too crazy and start ripping out the cameras too, remember that you can cover the cameras with a sticker or tape when not in use. I have found that regular old black electrical tape applies seamlessly, is non-obvious to casual onlookers, and is easy to remove without smudging or gunking up the lenses. Better still, it can be removed and reapplied many times without losing its adhesive.

Removing the Remnants of the Baseband

There is one more semi-hardware mod you may want to make, though.

It turns out that the 2013 Wifi Nexus 7 does actually have a partition that contains a cell network baseband firmware on it, located on the filesystem as the block device /dev/block/platform/msm_sdcc.1/by-name/radio. If you run strings on that block device from the shell, you can see that all manner of CDMA and GSM log messages, comments, and symbols are present in that partition.

According to ADB logs, Cyanogenmod 11 actually does try to bring up a cell network radio at boot on my Wifi-only Nexus 7, but fails due to it being disabled. There is also a strong economic incentive for Asus and Google to make it extremely difficult to activate the baseband even if the hardware is otherwise identical for manufacturing reasons, since they sell the WiFi-only version for $100 less. If it were easy to re-enable the baseband, HOWTOs would exist (which they do not seem to, at least not yet), and they would cut into their LTE device sales.

Even so, since we lack public schematics for the Nexus 7 to verify that cell components are actually missing or hardware-disabled, it may be wise to wipe this radio firmware as well, as defense in depth.

To do this, open the Terminal app, and run:

cd /dev/block/platform/msm_sdcc.1/by-name
dd if=/dev/zero of=./radio

I have wiped that partition while the device was running without any issue, or any additional errors from ADB logs.

Note that an anonymous commenter also suggested it is possible to disable the baseband of a cell-enabled device using a series of Android service disable commands, and by wiping that radio block device. I have not tested this on a device other than the WiFI-only Nexus 7, though, so proceed with caution. If you try those steps on a cell-enabled device, you should archive a copy of your radio firmware first by doing something like the following from that dev directory that contains the radio firmware block device.

dd if=./radio of=/sdcard/radio.img

If anything goes wrong, you can restore that image with:

dd if=/sdcard/radio.img of=./radio

Future Work

In addition to streamlining the contents of this post into a single additional Cyanogenmod installation zip or alternative ROM, the following problems remain unsolved.

Future Work: Better Usability

While arguably very secure, this system is obviously nowhere near usable. Here are some potential improvements to the user interface, based on a brainstorming session I had with another interested developer.

First of all, the AFWall+/Droidwall UI should be changed to be a tri-state: It should allow you to send app traffic over Tor, over your normal internet connection, or block it entirely.

Next, during app installation from either F-Droid or Google Play (this is an Intent another addon app can actually listen for), the user should be given the chance to decide if they would like that app's traffic to be routed over Tor, use the normal Internet connection, or be blocked entirely from accessing the network. Currently, the Droidwall default for new apps is "no network", which is a great default, but it would be nice to ask users what they would like to do during actual app installation.

Moreover, users should also be given a chance to edit the app's permissions upon installation as well, should they desire to do so.

The Google Play situation could also be vastly improved, should Google itself still prove unwilling to improve the situation. Google Play could be wrapped in a launcher app that automatically grants it network access prior to launch, and then disables it upon leaving the window.

A similar UI could be added to LinPhone. Because the actual voice and video transport for LinPhone does not use Tor, it is possible for an adversary to learn your SIP ID or phone number, and then call you just for the purposes of learning your IP. Because we handle call setup over Tor, we can prevent LinPhone from performing any UDP activity, or divulging your IP to the calling party prior to user approval of the call. Ideally, we would also want to inform the user of the fact that incoming calls can be used to obtain information about them, at least prior to accepting their first call from an unknown party.

Future Work: Find Hardware with Actual Isolated Basebands

Related to usability, it would be nice if we could have a serious community effort to audit the baseband isolation properties of existing cell phones, so we all don't have to carry around these ridiculous battery packs and sketch-ass wifi bridges. There is no engineering reason why this prototype could not be just as secure if it were a single piece of hardware. We just need to find the right hardware.

A random commenter claimed that the Galaxy Nexus might actually have exactly the type of baseband isolation we want, but the comment was from memory, and based on software reverse engineering efforts that were not publicly documented. We need to do better than this.

Future Work: Bug Bounty Program

If there is sufficient interest in this prototype, and/or if it gets transformed into a usable addon package or ROM, we may consider running a bug bounty program where we accept donations to a dedicated Bitcoin address, and award the contents of that wallet to anyone who discovers a Tor proxy bypass issue or remote code execution vulnerability in any of the network-enabled apps mentioned in this post (except for the Browser app, which does not receive security updates).

Future Work: Port Tor Browser to Android

The Guardian Project is undertaking a port of Tor Browser to Android as part of their OrFox project. This will greatly improve the privacy of your web browsing experience on the Android device over both Firefox and Chrome. We look forward to helping them in any way we can with this effort.

Future Work: WiFi MAC Address Randomization

It is actually possible to randomize the WiFi MAC address on the Google Nexus 7. The closed-source root app Mac Spoofer is able to modify the device MAC address using Qualcomm-specific methods in such a way that the entire Android OS becomes convinced that this is your actual MAC.

However, doing this requires installation of a root-enabled, closed-source application from the Google Play Store, which we believe is extremely unwise on a device you need to be able to trust. Moreover, this app cannot be autorun on boot, and your MAC address will also reset every time you disable the WiFi interface (which is easy to do accidentally). It also supports using only a single, manually entered MAC address.

Hardware-independent techniques (such as a the Terminal command busybox ifconfig wlan0 hw ether <mac>) appear to interfere with the WiFi management system and prevent it from associating. Moreover, they do not cause the Android system to report the new MAC address, either (visible under Settings -> About Tablet -> Status).

Obviously, an Open Source F-Droid app that properly resets (and automatically randomizes) the MAC every time the WiFi interface is brought up is badly needed.

Future Work: Disable Probes for Configured Wifi Networks

The Android OS currently probes for all of your configured WiFi networks while looking for open wifi to connect to. Configured networks should not be probed for explictly unless activity for their BSSID is seen. The xda-developers forum has a limited fix to change scanning behavior, but users report that it does not disable the active probing behavior for any "hidden" networks that you have configured.

Future Work: Recovery ROM Password Protection

An unlocked recovery ROM is a huge vulnerability surface for Android. While disk encryption protects your applications and data, it does not protect many key system binaries and boot programs. With physical access, it is possible to modify these binaries through your recovery ROM.

The ability to set a password for the Team Win recovery ROM in such a way that a simple "fastboot flash recovery" would overwrite would go a long way to improving device security. At least it would become evident to you if your recovery ROM has been replaced, in this case (due to the absence of the password).

It may also be possible to restore your bootloader lock as an alternative, but then you lose the ability to make backups of your system using Team Win.

Future Work: Disk Encryption via TPM or Clever Hacks

Unfortunately, even disk encryption and a secure recovery firmware is not enough to fully defend against an adversary with an extended period of physical access to your device.

Cold Boot Attacks are still very much a reality against any form of disk encryption, and the best way to eliminate them is through hardware-assisted secure key storage, such as through a TPM chip on the device itself.

It may also be possible to mitigate these attacks by placing key material in SRAM memory locations that will be overwritten as part of the ARM boot process. If these physical memory locations are stable (and for ARM systems that use the SoC SRAM to boot, they will be), rebooting the device to extract key material will always end up overwriting it. Similar ARM CPU-based encryption defenses have also been explored in the research literature.

Future Work: Download and Build Process Integrity

Beyond the download integrity issues mentioned above, better build security is also deeply needed by all of these projects. A Gitian descriptor that is capable of building Cyanogenmod and arbitrary F-Droid packages in a reproducible fashion is one way to go about achieving this property.

Future Work: Removing Binary Blobs

If you read the Cyanogenmod build instructions closely, you can see that it requires extracting the binary blobs from some random phone, and shipping them out. This is the case with most ROMs. In fact, only the Replicant Project seems concerned with this practice, but regrettably they do not support any wifi-only devices. This is rather unfortunate, because no matter what they do with the Android OS on existing cell-enabled devices, they will always be stuck with a closed source, backdoored baseband that has direct access to the microphone, if not the RAM and the entire Android OS.

Kudos to them for finding one of the backdoors though, at least.

Changes Since Initial Posting

  1. Updated firewall scripts to fix Droidwall permissions vulnerability.
  2. Updated Applications List to recommend VLC as a free media player.
  3. Mention the Guardian Project's planned Tor Browser port (called OrFox) as Future Work.
  4. Mention disabling configured WiFi network auto-probing as Future Work
  5. Updated the firewall install script (and the android-firewall.zip that contains it) to disable "Captive Portal detection" connections to Google upon WiFi association. These connections are made by the Settings service user, which should normally be blocked unless you are Activating Google Play for the first time.
  6. Updated the Executive Summary section to make it clear that our SIP client can actually also make normal phone calls, too.
  7. Document removing the built-in microphone, for the truly paranoid folk out there.
  8. Document removing the remnants of the baseband, or disabling an existing baseband.
  9. Update SHA256SUM of FDroid.apk for 0.63
  10. Remove multiport usage from firewall-torify-all.sh script (and update android-firewall.zip).
  11. Add pro-tip to the microphone removal section: Don't remove your cameras. Black electrical tape works just fine, and can be removed and reapplied many times without smudges.
  12. Update android-firewall.zip installation and documentation to use /data/local instead of /etc. CM updates will wipe /etc, of course. Woops. If this happened to you while updating to CM-11-M5, download that new android-firewall.zip and run install-firewall.sh again as per the instructions above, and update your Droidwall custom script locations to use /data/local.
  13. Update the Future work section to describe some specific UI improvements.
  14. Update the Future work section to mention that we need to find hardware with actual isolated basebands. Duh. This should have been in there much earlier.
  15. Update the versions for everything
  16. Suggest enabling disk crypto directly from the shell, to avoid SSD leaks of the originally PIN-encrypted device key material.
  17. GMail network access seems to be required for App Store initialization now. Mention this in Google Apps section.
  18. Mention K-9 Mail, APG, and Plumble in the Recommended Apps section.
  19. Update the Firewall instructions to clarify that you need to ensure there are no typos in the scripts, and actually click the Droidwall UI button to enable the Droidwall firewall (otherwise networking will not work at all due to userinit.sh).
  20. Disable NFC in Settings config

July 2010 Progress Report

New releases read more »

  • On July 4th, we released Tor Browser Bundle 1.3.7 for Microsoft Windows. This is a security update for Firefox and Pidgin. The changes are: update to Firefox 3.5.10 and Pidgin Instant Messenger 2.7.1r2 to fix some security issues.
  • On July 6th, we released Tor Browser Bundle 1.0.8 for GNU/Linux distributions. This fixes a number of security issues with included software. The updates include:
    • Update libpng to 1.4.3 (see CVE-2010-1205)
    • Update Firefox to 3.5.10
    • Update HTTPS Everywhere to 0.2.1
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