iodine/doc/proto_00000403.txt

Detailed specification of protocol in version 00000403
======================================================

CMC = 2 byte Cache Miss Counter, increased every time it is used

Version:
Client sends:
	First byte v or V
	Rest encoded with base32:
	4 bytes big endian protocol version
	CMC
Server replies:
	4 chars:
		VACK (version ok), followed by login challenge
		VNAK (version differs), followed by server protocol version
		VFUL (server has no free slots), followed by max users
	4 byte value: means login challenge/server protocol version/max users
	1 byte userid of the new user, or any byte if not VACK
	
Login:
Client sends:
	First byte l or L
	Rest encoded with base32:
	1 byte userid
	16 bytes MD5 hash of: (first 32 bytes of password) xor (8 repetitions of login challenge)
	CMC
Server replies:
	LNAK means not accepted
	x.x.x.x-y.y.y.y-mtu means accepted (server ip, client ip, mtu)

Case check:
Client sends: 
	First byte z or Z
	Lots of data that should not be decoded
Server replies:
	The requested domain copied raw

Switch codec:
Client sends:
	First byte s or S
	One byte ASCII digit, meaning userid
	One byte ASCII digit, with value 5 or 6, representing number of bits per byte in encoding
Server sends:
	Name of codec if accepted. After this all upstream data packets must be encoded with the new codec.
	BADCODEC if not accepted. Client must then revert to Base32

Data:
Data header:
	 321 0 
	+---+-+
	|UUU|L|
	+---+-+

UUU = Userid
L = Last fragment in packet flag

First 4 bits coded as hex in ASCII. 
Followed by data encoded with the chosen codec.

Ping:
Command = 0x04, User = userid
Client sends:
	Only a CMC

The server responses to Ping and Data packets is a DNS NULL type response:
If server has nothing to send, data length is 0 bytes.
If server has a packet to send, data length is set and the data is a full raw
unencoded ip packet, prefixed with 32 bits tun data.