udp-tunnel-sketch
=================
General goals:
* posix-like api
* strong cryptography, following the ideas of curvecp -- skipping client auth
* resistance to replay attacks
* resistance to DDOS attacks, no allocations on server-side connections
* unencrypted data is just four bytes for protocol \0r#{version}#{proto}
* fast-enough to handle hundreds of connections
* trust on first use
Design:
there should be a worker thread that polls an underlying unix socket, and feeds messages into a queue only accessible by that thread, those messages are doled out to the calling thread by calls to accept, select, send, connect, send and recv.
the worker thread polls the parent fd, and fills in buffers independent of calls to recv, and writes to the socket pair: https://www.gnu.org/software/libc/manual/html_node/Socket-Pairs.html
sockets should only be changed from the main thread
inspiration: https://github.com/nanomsg/nanomsg/blob/master/src/core/global.c
there should be useful global statistics reporting
connections are identified by connection public key to facilitate server and client roaming. These keys are generated on a connection on connection basis.
requirements:
nacl or sodium or tweetnacl (included)
basic posix
pthreads
Protocol:
client server
----------------------------------------
HELLO
byte version
32 bytes connection public key
random padding
----------------------------------------
COOKIE
byte version
32 bytes long term public key
(Connection Public key
Secret Key encrypted with server's minute key)
encrypted with server public key and
client's public key
random padding
-----------------------------------------
INIT
byte version
32 bytes connection public key
nonce
encrypted cookie
encrypted message
-----------------------------------------
DATA
byte version
32 bytes connection public key
nonce
encrypted message
-----------------------------------------
DATA
byte version
32 bytes connection public key
nonce
message
message format encrypted
crypto_box_BOXZEROBYTES
uint32_t seq
uint32_t ack
time_t timestamp
time_t delay
size_t size < max_packet_size (1088 bytes)
data
the resending algorithm follows tcp vegas