You can send the 16 bit crc as 00 00 and the client will accept it just fine.
I do it in the chat channels and in my partially implemented login server.
As for the crypto key, it is not sent from server->client. It is static and in eqmain.dll. Everytime you log in on live you send the same chunk of data for the same user/pass. Supposedly it is 3des with some transpositions. Just need the key and what transpositions they do.
