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The obfourscator (obfs4proxy)
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Yawning Angel e77ddddf4d Add support for IAT obfuscation (disabled by default). 
When enabled, inter-packet delay will be randomized between 0 and 10
ms in 100 usec intervals.  As experiences from ScrambleSuit (and back
of the envelope math based on how networks work) show, this is
extremely expensive and artificially limits the throughput of the link.

When enabled, bulk transfer throughput will be limited to an average of
278 KiB/s.
 		11 years ago
doc Change the maximm handshake length to 8192 bytes. 11 years ago
framing Change the MSS to 1448 bytes, because timestamps are a thing. 11 years ago
ntor Change the handshake wire format. 11 years ago
obfs4proxy Add support for IAT obfuscation (disabled by default). 11 years ago
.gitignore Move to a unified client/server binary, and fix bugs. 11 years ago
README.md Update README (No functional changes). 11 years ago
handshake_ntor.go Change the maximm handshake length to 8192 bytes. 11 years ago
handshake_ntor_test.go Change the maximm handshake length to 8192 bytes. 11 years ago
obfs4.go Add support for IAT obfuscation (disabled by default). 11 years ago
packet.go Add support for IAT obfuscation (disabled by default). 11 years ago
replay_filter.go Change the maximm handshake length to 8192 bytes. 11 years ago
replay_filter_test.go Add replay detection to handshakes. 11 years ago
utils.go Add vim modelines to some files (No functional changes). 11 years ago
weighted_dist.go Change the server failure close delay/discard length to be consistent. 11 years ago

README.md

obfs4 - The obfourscator

Yawning Angel (yawning at torproject dot org)

WARNING

This is pre-alpha. Don't expect any security or wire protocol stability yet. If you want to use something like this, you should currently probably be looking at ScrambleSuit.

What?

This is a look-like nothing obfuscation protocol that incorporates ideas and concepts from Philipp Winter's ScrambleSuit protocol. The obfs naming was chosen primarily because it was shorter, in terms of protocol ancestery obfs4 is much closer to ScrambleSuit than obfs2/obfs3.

The notable differences between ScrambleSuit and obfs4:

  • The handshake always does a full key exchange (no such thing as a Session Ticket Handshake).
  • The handshake uses the Tor Project's ntor handshake with public keys obfuscated via the Elligator 2 mapping.
  • The link layer encryption uses NaCl secret boxes (Poly1305/XSalsa20).

Why not extend ScrambleSuit?

It's my protocol and I'll obfuscate if I want to.

Since a lot of the changes are to the handshaking process, it didn't make sense to extend ScrambleSuit as writing a server implementation that supported both handshake variants without being obscenely slow is non-trivial.

TODO

  • Code cleanups.
  • Write more unit tests.
  • Optimize further.

WON'T DO

  • I do not care that much about standalone mode. Patches MAY be accepted, especially if they are clean and are useful to Tor users.
  • Yes, I use a bunch of code from the borg^w^wGoogle. If that bothers you feel free to write your own implementation.
  • I do not care about older versions of the go runtime.

Thanks

  • David Fifield for goptlib.
  • Adam Langley for his Elligator implementation.
  • Philipp Winter for the ScrambleSuit protocol which provided much of the design.