Efficient Chat Streams

I'm attempting to create an application which will work as a chat app. I'm currently contemplating the best way to do this and I'm thinking of going with a server sent event package such as the following. Every conversation would have an id, and the message would be emitted under the id. For instance

stream.emit(1512, "Hello") would send the message and

stream.on(1512, function(message){console.log(message)}) would print the message. Only the chat members would have the chatId.

I was initially thinking of using websockets but I thought that not every user should be receiving data, as chats were private and I didn't want to configure authentication within websockets.

Back to server sent events:

I have a few questions on the topic.

1. Are they efficient and, if not, what would be a more efficient solution
2. Is the method of sending chat through a randomized, hashed, id (such as 309ECC489C12D6EB4CC40F50C902F2B4D) secure?
3. Would you recommend a different method for sending chat? This is to be implemented as a mobile application where individual users can chat privately with oneanother so, again, security is pretty important.

Thanks.