Greetings from Berlin, Leif and I have been working on ways to deploy, use and sync data with Tahoe on Tails. Tails[0] is a live CD based on Debian GNU/Linux that is supported by the Tor Project. It is intended to lose state after every shutdown, unless a user configures it to keep certain bits of information in a so-called Persistent container. This is usually a LUKS encrypted partition on the same bootable medium that contains Tails.
To start - we worked through bootstrapping Tahoe on a Tails system - the Tahoe package in Debian and thus available in Tails as of the Tails 0.19 release is 1.9.2-1. This is a bit older than we'd like, so we bootstrapped from source with only a few Debian packages from the packaging system. Here is the git repo for the script that we used to bootstrap Tahoe-LAFS on Tails 0.19: https://github.com/leif/tahoe-tails-utils The following ticket covers the overall issues of actually trying to bootstrap Tahoe safely on any network at all: https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2055 The issues outlined in the above ticket should cover Tor users, though likely it equally applies to a VPN user, an i2p user and really, anyone barebacking with the internet. Once this bootstrapping process was completed, we connected the Tails machine to a Tahoe-LAFS grid that is Tor aware. The introducer runs as a Tor hidden service. Each of the Storage Nodes also presents their respective addresses as Tor hidden services through the previously mentioned introducer. We found that the open browser command uses the system browser included with Tails. We weren't thrilled about the main browser being used for local system daemon or system service related activities. I dislike that it talks to the loopback interface, while other content it loads may go over the Tor network or even try to do other things with stored data in the browser or on the file system. This ticket is an example of why total browser isolation is a good idea: https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1942 We prefer that at least this browser data should be isolated from any other web browsing I might perform with this machine. We wrote a quick little hack to use a different profile - we added a wrapper called `tahoe-browser` written in bash and stuffed it into /usr/local/bin/tahoe-browser. We then set BROWSER in the environment to point to it: export BROWSER="/usr/local/bin/tahoe-browser" This allows me to use `tahoe webopen grid-news/Latest/index.html` in a completely separate browser profile. Hooray. What is grid-news? A useful news service on our local Tor grid - any url would have the same issues as noted. Is this useful? Should we generalize this and add it to Tahoe? It would be easy enough to extend src/allmydata/scripts/tahoe_webopen.py to do this job with the addition of another small class. No such tahoe-browser program would be required - though it surely wouldn't hurt to keep them completely separated. An interesting trick would be to put that browser profile itself inside of a user's Tahoe grid. It would provide some on-the-go anti-forensics and keep all Tahoe related url data, bookmarks and so on inside of the grid itself. Leif isn't so hot on this idea because of Tahoe's Magic Folders idea isn't implemented. Abstractly, I like the idea but I'm not sure if it is practical. As it stands, we've now managed to bootstrap Tahoe on Tails - so it is basically possible to do all grid related activity over Tor. We don't have to worry about exit nodes as we're using Tor Hidden Services for all of the services. Though generally, I'm not really worried about Tor Exit nodes in the context of Tahoe-LAFS. In an ideal world, we'd use the Tails persistence feature to store a user's Tahoe's introducer furl and a few other important bits. This could then in turn be used to store all of the other Tails persistance data - things like web browser history, .{ssh,gnupg,pidgin,etc}, and/or even added Debian packages. To do this, we need to add persistence support for Tahoe related configuration in Tails and we need to ensure that Tahoe ships as part of Tails. Here are a few bugs related to this in the Tails bug tracker: https://labs.riseup.net/code/issues/5514 https://labs.riseup.net/code/issues/5804 Adding '/home/amnesia/.tahoe' to the Tails persistence seems to be possible from an existing Tails system. We've filed a bug to add this discuss adding Tahoe as a default option in the persistence configuration dialog: https://labs.riseup.net/code/issues/6227 There are a few interesting improvements that came up for discussion during this process. One such idea relates to changing the way that the Storage Nodes publish data to introducers. Wouldn't it be nice if we could reduce the authority of the introducer even more? With a little bit of effort, we could ensure that an attacker who learns about the introducer is only able to learn the number of Storage Servers but not any other information. For an all Tor Hidden Service grid with such an introducer, an attacker who takes the introducer will learn very little beyond a rough count of the total Storage Nodes connecting to that introducer. The clients are all protected by Tor and the Storage Nodes are similarly protected by Tor. The Storage Nodes would stay not only geographically anonymous as provided by Tor but it wouldn't be possible to learn their .onion names and even begin to have any way to connect with them at all. To do this, we'd need to encrypt the furls shared by the introducer in some way. This requires that clients share a symmetric key or publish a public key or something similar. Thus the introducer could even be shared by a few groups who do not trust each other. If we merge the multi-introducer patch, heavily used by the i2p folks, we could really do interesting things along these lines. These ideas obviously require a design that is beyond the scope of this email. Additionally, we thought it useful to extend Tahoe to be aware of a grid that uses Tor Stealth Hidden Services[1][2]. This essentially adds a layer of authentication between a client and a server at the Tor layer. Thus even if an attacker were to learn of a Storage Nodes's .onion, without the corresponding shared secret - no one will be able to connect to the Storage node or even elicit a reply from that server. This is a bit tricky in the sense that the Storage Node will make outbound connections to the introducer - so Tahoe Storage Node client side exploitation is probably a concern. However, if an introducer were stolen, the Storage Node's .onion would not be useful to the attacker without the Tor Hidden Service authorization keys. Those keys should only be available on the Tahoe client's Tor client, and the Tor Hidden Service Storage Server's Tor client and not on the introducer. We of course want to ensure that Tails has the newest version of Tahoe - though there is some debate about using Tahoe-LAFS or Leif's Truckee Tahoe-LAFS branch. Any thoughts on this topic would be appreciated. What else should we be thinking about? All the best, Jacob [0] https://tails.boum.org/ [1] https://www.torproject.org/docs/tor-hidden-service.html.en [2] https://www.torproject.org/docs/hidden-services.html.en _______________________________________________ tails-dev mailing list tails-dev@boum.org https://mailman.boum.org/listinfo/tails-dev
