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The obfourscator (obfs4proxy)
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Yawning Angel 94d3fe9a08 Change the TYPE_PRNG_SEED length to 24. 
This matches what the code actually sends.  It's shorter than the
ScrambleSuit PRNG seed, but that's because the SipHash-2-4 based
Hash_DRBG has 24 bytes of internal state (key + initial output).
 		10 years ago
common Change all the arguments to use base16 from base64. 10 years ago
doc Change the TYPE_PRNG_SEED length to 24. 10 years ago
obfs4proxy Add a ChangeLog and dump the version when invoked with "-v". 10 years ago
transports Display a more useful error on JSON Unmarshall failure. 10 years ago
.gitignore Move to a unified client/server binary, and fix bugs. 10 years ago
ChangeLog Add a ChangeLog and dump the version when invoked with "-v". 10 years ago
LICENSE Document dependencies, add LICENSE (No functional changes). 10 years ago
README.md Massive cleanup/code reorg. 10 years ago

README.md

obfs4 - The obfourscator

Yawning Angel (yawning at torproject dot org)

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).

As an added bonus, obfs4proxy also supports acting as an obfs2/3 client and bridge to ease the transition to the new protocol.

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.

Thanks

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