r4sas/ts3init_linux_netfilter_module
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Added first version of cookie.md

Browse Source
This commit is contained in:
Maximilian Münchow 2016-10-14 15:20:50 +02:00
parent 98fb883767
commit 4509ac2612
1 changed files with 61 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
cookie.md Normal file
View File

@ -0,0 +1,61 @@
What is the cookie
==================
The cookie is used to prevent address spoffing, without the firewall having to remember the ip-address of the clients.
It does this by forcing the client to send a cookie, it can only get from the server. The cookie is generated from the current time, the source and destination address and port, and a secret that only the server has.
It works on the same principle that authenticators do. And force the client to reply with the same ip/port to the same server ip/port in order to continue.
How is the cookie generated
===========================
The cookie is the hashed `ClientIp`, `ServerIp`, `ClientPort` and `ServerPort` using `siphash24` and a key that is one quarter of a `cookie_seed`. Every second another quarter of the `cookie_seed` is used as key.
The server generates a new `cookie_seed` every 4 seconds, and always keeps 2 `cookie_seeds`. That means a client has atleast 4 seconds, and atmost 8 seconds to reply before the cookie becomes invalid.
```
cookie_seed = sha512(random_seed << 4 | (time & ~3))
cookie = siphash24(cookie_seed >> ((time & 3) * 16), ClientIp + ServerIp + ClientPort + ServerPort)
```
What is the `Random-Seed`
========================
The server keeps a secret called `random-seed`. Should a attacker ever get hold of the `random-seed` a new `random-seed` must be used. Otherwise any protection that the cookie offers would be compromised. Since a cookie is only valid for atmost eight seconds, changing the `random-seed` would at the worst prevent users from logging into a Teamspeak-Server for atmost eight seconds, but the most common case would be no outage what so ever.
How to generate a `Random-Seed`
-------------------------------
```
xxd -l 60 -c 60 -p /dev/urandom > random_seed
```
Format of `COMMAND_GET_COOKIE`
=============================
```
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 'T' | 'S' | '3' | 'I' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 'N' | 'I' | 'T' | '1' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PacketId | ClientId |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type + Flags | Client Version ->
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command | Timestamp ->
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Random Sequence ->
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVERD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVERD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```
* All fields are encoded in lower encodian, unless otherwise specified.
* `PacketId` is always `101`.
* `ClientId` is always `0`.
* `Type + Flags` is always `0x88`.
* `Client Version` is the build number of the client.
* `Command` is always `0`.
* `Timestamp` is the unixtime of the client maschine, encoded in big endian.
* `Random Sequence` is a random value generated by the client.
* Every `RESERVED` field must be zero.