# What should an identifer in the client-server model?

I am fairly new to cryptography and I am trying to understand this picture here. I have some questions regarding this picture.

1. What should be an identifer for a side? For example, in the picture, it says that A sends an identifer with a nonce to B. Should I just set a fix alias for each side, something like String ID_A = "ID_A"?
2. Would AES make sense here, or would RSA be better?

Again, I apologize if these questions do not make much sense, but I am new and trying to grasp the idea.

EDIT: I have updated some further details.

• Yes. I have now updated with some further details. Thank you! – thehollow May 11 at 16:06

The notation $$E(PR_a,K_s)$$ is syntactically incorrect. You don't encrypt using the private key in an asymmetric encryption scheme.