The same algorithm as ScrambleSuit is used, except:
* SipHash-2-4 in OFB mode is used to create the distribution.
* The system CSPRNG is used when sampling the distribution.
This fixes most of #3, all that remains is generating and sending a
persistent distribution on the server side to the client.
On second thought instead of using log.Panicf(), panic() and do the
logging with recover(). This somewhat centralizes logging in
obfs4proxy, which will be easier to change when I invariably decide to
do logging differently in the future.
This adds preliminary support for data padding by adding another layer
of encapsulation inside each AEAD frame containing a type and length.
For now, data is still sent unpadded, but the infrastructure for
supporting it is mostly there.
Additionally, use log.Panic[f]() instead of panic through out the code
so that some panics are logged.
Write timeouts are obnoxious to handle as the frame encoder state
already is updated to cover the entire payload for the Write() call
that timed out. In theory it is possible to buffer the pending data,
but that causes Write() to voilate the semantics of the interface.
Like ScrambleSuit, a random interval between 1x and 5x of additional
data from the peer is read and immediately discarded before closing.
Additionally, obfs4 will close off invalid connections anywhere between
0 and 60 seconds after it determines that the incoming connection will
never complete the handshake successfully.
* The old and the busted: obfs4-[client,server].
* The new hotness: obfs4client.
* Add obfs4.ServerHandshake() that servers need to call after a
successful return from Accept(). This allows implementations to
move the handshake into a goroutine or whatever.
