GateKeeper

GateKeeper Authentication
GateKeeper authentication was designed specifically for clients who connected to MSN Chat.

GateKeeper
GateKeeper is a simple HMAC-MD5 based authentication algorithm. The header consists of a signature, 2 unknown bytes, a GateKeeper version, and a sequence.

Here's an example of a client sending an initial authentication request for version three.

Signature: Version: Sequence:

GateKeeperPassport
GateKeeperPassport was an extension of GateKeeper, allowing those with a .net Passport (now known as a Microsoft Account) to authenticate to the chat network with an 8 byte unique ID.

The authentication was completed exactly as per GateKeeper, but an additional subsequent authentication request was sent by the server that just contained  and the client would send the PassportTicket and PassportProfile cookies to complete the GateKeeperPassport authentication.