Encrypt / Decrypt packets ( 3.3.5a client )

[gngn]

Hi there,.
After almost 10 years since the first day I found my self interested working on a wow emu server, I finally decided to start developing one for 3.3.5a client on my free times mostly for learning and taking some challenges .
so far I was able to successfully pass the authentication challenge, proof and sending the realm list packet to the client.. therefore I think the task of authentication server development seems to be done.. but I have issue connecting to my world server,.. it keeps showing the connected message to the client when trying to connect to a realm.
so here are my questions:

A : How this encrypt and decrypt HMACSHA1 codes are getting calculated from the session key?
I know there are hard-coded keys which I require to use when creating these hash codes, but whatever method I try they never look like what I receive when I log to a trinity core world server for example.

B : Can someone explain me the very first packets which client sends and receives when connecting to a realm?
I see couple of packets without any data.. are these packets important? are these just ping/pong?
and what can be the packet which causes the client to close the connected message when connecting to a realm?

BTW: I'm coding in NodeJs ( JavaScript )
Thanks in advance.