iodine/doc/proto_00000403.txt

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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
5 bits coded as Base32 char, meaning userid
5 bits coded as Base32 char, with value 5 or 6, representing number of raw
bits per encoded byte
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:
Upstream data header:
3210 432 10 43 210 4321 0
+----+---+--+--+---+----+-+
|UUUU|SSS|FF|FF|DDD|GGGG|L|
+----+---+--+--+---+----+-+
Downstream data header:
7 654 3210 765 4321 0
+-+---+----+---+----+-+
|C|SSS|FFFF|DDD|GGGG|L|
+-+---+----+---+----+-+
UUUU = Userid
L = Last fragment in packet flag
SS = Upstream packet sequence number
FFFF = Upstream fragment number
DDD = Downstream packet sequence number
GGGG = Downstream fragment number
C = Compression enabled for downstream packet
Upstream data packet starts with 1 byte ASCII hex coded user byte, then 3 bytes
Base32 encoded header, then comes the payload data, encoded with chosen codec.
Downstream data starts with 2 byte header. Then payload data, which may be
compressed.
Ping:
Client sends:
First byte p or P
Rest encoded with Base32:
1 byte with 4 bits userid
1 byte with:
3 bits downstream seqno
4 bits downstream fragment
CMC
The server response 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 something to send, it will send a downstream data packet,
prefixed with 2 bytes header as shown above.