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© 2012-2017 Mike Tigas (@mtigas)
Mozilla Public License 2.0

Onion Browser is a free web browser for iPhone and iPad that encrypts and tunnels web traffic through the Tor network. See the official site for more details and App Store links.

• OnionBrowser: 1.7.5 (20170521.1) - See official release history and changelog.
• Tor.framework: mtigas/tor0.3.0.7-libevent2.1.8-openssl1.0.2k-v2 / 69ca6f1 (May 21 2017)
  • Tor: 0.3.0.7
  • libevent: 2.1.8
  • OpenSSL: 1.0.2k
• iObfs: 26463e2 (Jul 15 2016)
  • obfs4proxy: 0.0.8-dev, upstream 97a875e (Nov 15 2016)
  • golang: 1.7.4 (Dec 01 2016)

The app uses the Tor.framework package to build the Tor, OpenSSL, and libevent dependencies.

Because iOS applications cannot launch subprocesses or otherwise execute other binaries, the tor client is run in-process in a NSThread subclass which executes the tor_main() function (as an external tor executable would) and attempts to safely wrap Tor within the app. (libor.a and libtor.a, intermediate binaries created when compiling Tor, are used to provide Tor.) Side-effects of this method have not yet been fully evaluated. Management of most tor functionality (status checks, reloading tor on connection changes) is handled by accessing the Tor control port in an internal, telnet-like session from the AppDelegate.

The app uses a NSURLProtocol subclass (ProxyURLProtocol), registered to handle HTTP/HTTPS requests. That protocol uses the CKHTTPConnection class which nearly matches the NSURLConnection class, providing wrappers and access to the underlying CFHTTP Core Framework connection bits. This connection class is where SOCKS5 connectivity is enabled. (Because we are using SOCKS5, DNS requests are sent over the Tor network, as well.)

• Read more about Onion Browser and the challenges of implementing Tor clients on iOS in this post on the Tor Project blog.