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The obfourscator (obfs4proxy)
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Yawning Angel 5abad1571c Use Vose's Alias Method to sample the weighted distribution. 
The weight generation code also was cleaned up (and now can support
generating distributions that look like what ScrambleSuit does as
a compile time change).

Per: http://www.keithschwarz.com/darts-dice-coins/
 		10 years ago
csrand Use Vose's Alias Method to sample the weighted distribution. 10 years ago
doc Change how the length obfsucation mask is derived. 10 years ago
drbg Change how the length obfsucation mask is derived. 10 years ago
framing Change how the length obfsucation mask is derived. 10 years ago
ntor Move utils.go to csrand/csrand.go, and clean up the interface. 10 years ago
obfs4proxy Allow randomly generating node-ids instead of requiring the fingerprint. 10 years ago
.gitignore Move to a unified client/server binary, and fix bugs. 10 years ago
LICENSE Document dependencies, add LICENSE (No functional changes). 10 years ago
README.md Document dependencies, add LICENSE (No functional changes). 10 years ago
handshake_ntor.go Move the server keypair generation to right after Accept(). 10 years ago
handshake_ntor_test.go Move the server keypair generation to right after Accept(). 10 years ago
obfs4.go Change how the length obfsucation mask is derived. 10 years ago
packet.go Change how the length obfsucation mask is derived. 10 years ago
replay_filter.go Move utils.go to csrand/csrand.go, and clean up the interface. 10 years ago
replay_filter_test.go Add replay detection to handshakes. 10 years ago
weighted_dist.go Use Vose's Alias Method to sample the weighted distribution. 10 years ago
weighted_dist_test.go Use Vose's Alias Method to sample the weighted distribution. 10 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.

Dependencies

Build time library dependencies are handled by go get automatically but are listed for clarity.

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.