diff --git a/cookie.md b/cookie.md index 9a25248..0a6939e 100644 --- a/cookie.md +++ b/cookie.md @@ -1,17 +1,17 @@ What is the cookie ================== -The cookie is used to prevent address spoffing, without the firewall having to remember the ip-address of the clients. +The cookie is used to prevent address spoofing, 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. +It works on the same principle that authenticators do. This method forces 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. +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. ClientIp, ServerIp, ClientPort and ServerPort are in network order. ``` -cookie_seed = sha512(random_seed << 4 | (time & ~3)) -cookie = siphash24(cookie_seed >> ((time & 3) * 16), ClientIp + ServerIp + ClientPort + ServerPort) +cookie_seed = sha512(random_seed << 32 | (unix_time & 0xffffffff)) +cookie = siphash24(cookie_seed >> ((time & 3) * 128), Concat(ClientIp, ServerIp, ClientPort, ServerPort)) ``` What is the `Random-Seed` @@ -50,7 +50,7 @@ Format of `COMMAND_GET_COOKIE` | RESERVERD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ``` -* All fields are encoded in lower encodian, unless otherwise specified. +* All fields are encoded in big endian, unless otherwise specified. * `PacketId` is always `101`. * `ClientId` is always `0`. * `Type + Flags` is always `0x88`.