Problem: In a private block chain network, how does setting up a new node authenticate itself into the network. Is there anything which prevents one node from getting to the network and download data from other nodes.

I have seen the json file which contains a private and public key which is a config file for the node. I believe this is used for securing the data transmission between the nodes. however, this does not possible seems to have any correlation to authenticate of the node to the network.

i am a newbie to block chain so any help would be greatly appreciated. I am working on developing a startup around block chain