The Elligator inverse map uses the least significant bits of the private
key, which clamping sets to 0, to choose a random low-order point to add
to the public key, to ensure uniformity of representatives.
The other ways that the private key is used, namely in calls to
curve25519.ScalarMult and curve25519.ScalarBaseMult, do their own
clamping when necessary and are documented to accept a uniformly random
scalar.
Replace agl's Elligator2 implementation with a different one, that fixes
the various distinguishers stemming from bugs in the original
implementation and "The Elligator paper is extremely hard to read".
All releases prior to this commit are trivially distinguishable with
simple math, so upgrading is strongly recommended. The upgrade is fully
backward-compatible with existing implementations, however the
non-upgraded side will emit traffic that is trivially distinguishable
from random.
Special thanks to Loup Vaillant for his body of work on this primitive,
and for motivating me to fix it.
This commit changes the upstream repo location to:
https://gitlab.com/yawning/obfs4.git
Additionally all the non-`main` sub-packages now have an import
comment annotation. As a matter of courtesy, I will continue to
push to both the existing github.com and git.torproject.org repos
for the foreseeable future, though I reserve the right to stop
doing so at any time.
Differences from my goptlib branch:
* Instead of exposing a net.Listener, just expose a Handshake() routine
that takes an existing net.Conn. (#14135 is irrelevant to this socks
server.
* There's an extra routine for sending back sensible errors on Dial
failure instead of "General failure".
* The code is slightly cleaner (IMO).
Gotchas:
* If the goptlib pt.Args datatype or external interface changes,
args.go will need to be updated.
Tested with obfs3 and obfs4, including IPv6.
Unless you have very good reason to do so, there should be no reason to
actually call these ever, since the log messages are only generated if
they will result in output being written to a log file.
This allows obfs4proxy to be used as a ScrambleSuit client that is wire
compatible with the obfs4proxy implementation, including session ticket
support, and length obfuscation.
The current implementation has the following limitations:
* IAT obfuscation is not supported (and is disabled in all other
ScrambleSuit implementations by default).
* The length distribution and probabilites are different from those
generated by obfsproxy and obfsclient due to a different DRBG.
* Server support is missing and is unlikely to be implemented.
The Go developers decided to move the go.crypto repository to
golang.org/x/crypto, and also to transition from hg to git. The tip of
tree code.google.com copy of the code is broken due to the import paths
pointing at the new repository.
While the change here is simple (just update the import location), this
affects packagers as it now expects the updated package. Sorry for the
inconveneince, I blame the Go people.
WARNING: THIS BREAKS BACKWARD COMPATIBILITY.
This is primarily to work around bug #12930. Base16 was chosen over
unpadded Base64 because the go runtime Base64 decoder does not handle
omitting the padding.
May $deity have mercy on anyone who needs to hand-enter an obfs4 bridge
line because I will not.
* Changed obfs4proxy to be more like obfsproxy in terms of design,
including being an easy framework for developing new TCP/IP style
pluggable transports.
* Added support for also acting as an obfs2/obfs3 client or bridge
as a transition measure (and because the code itself is trivial).
* Massively cleaned up the obfs4 and related code to be easier to
read, and more idiomatic Go-like in style.
* To ease deployment, obfs4proxy will now autogenerate the node-id,
curve25519 keypair, and drbg seed if none are specified, and save
them to a JSON file in the pt_state directory (Fixes Tor bug #12605).
Yawning Angel
David Fifield
Philipp Winter
Yawning Angel
Daniel Martí