From 4509ac26123ec4fa48f41f220b47e1b4edec87b2 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Maximilian=20M=C3=BCnchow?= Date: Fri, 14 Oct 2016 15:20:50 +0200 Subject: [PATCH] Added first version of cookie.md --- cookie.md | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 cookie.md diff --git a/cookie.md b/cookie.md new file mode 100644 index 0000000..9a25248 --- /dev/null +++ b/cookie.md @@ -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.